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Author: JDate: 28 Versie: 3.
M.Sc. The Group: TCommitteIng J.W. BReferencPeriod: N
SURFA
anarthanan Saugust 2010 .0
esis University
Transducer Scee: Prof.Dr.irBerenschot, De: Nov. 2009 – au
ACE TE
undaram
y of Twente
cience and Tecr. M. ElwensDr. J. Snoeijer.
ugust 2010
NSION
DI
chnology Grospoek, Dr.ir.
DRIVEN
IMENSI
up L. Abelmann
N FABRI
ONAL M
n, Dr.ir. N.R.
CATION
MICROS
Tas, Dr.ir. J
N OF TH
STRUCT
J.W. van Ho
HREE‐TURES
onschoten,
Surface tension driven fabrication of three‐dimensional microstructures Page 2
TABLE OF CONTENT 1 Introduction.................................................................................................................................................... 3
1.1 motivation ............................................................................................................................................. 3
1.2 Outline of this project ............................................................................................................................ 4
2 Theory ............................................................................................................................................................ 5
2.1 Capillary forces ...................................................................................................................................... 5
2.1.1 Folding with capillary forces .............................................................................................................. 6
2.1.2 Effects of different contact angles .................................................................................................. 12
2.1.3 Varying the structural dimension .................................................................................................... 14
3 Folding templates ......................................................................................................................................... 15
3.1 Method ................................................................................................................................................ 15
3.1.1 Design of the templates .................................................................................................................. 15
3.1.2 Cleanroom processes ...................................................................................................................... 17
3.1.3 Experimental setup ......................................................................................................................... 18
3.2 Results ................................................................................................................................................. 19
3.2.1 First results folding structures with more the 2 flaps. .................................................................... 19
3.2.2 Results of folding of prism ............................................................................................................... 19
4 Folding with different contact angle ............................................................................................................ 22
4.1 method ................................................................................................................................................ 22
4.1.1 white light measurement using lateral scanning interferometry ................................................... 22
4.2 Results ................................................................................................................................................. 24
5 Varying design of the prisms ........................................................................................................................ 25
5.1 Problem definition ............................................................................................................................... 25
5.1.1 Torsion in folding ............................................................................................................................. 25
5.1.2 Folding without symmetry .............................................................................................................. 26
5.1.3 Varying contact area ....................................................................................................................... 28
5.1.4 Lifting objects out of the plane ....................................................................................................... 28
5.2 Results ................................................................................................................................................. 29
5.2.1 Torsion in folding ............................................................................................................................. 30
5.2.2 Folding without symmetry .............................................................................................................. 30
5.2.3 Varying contact area ....................................................................................................................... 32
5.2.4 Lifting objects out of the plane ....................................................................................................... 34
6 Conclusion .................................................................................................................................................... 36
6.1 Recommendation ................................................................................................................................ 37
7 Bibliography ................................................................................................................................................. 38
8 Appendix – process documents ................................................................................................................... 39
Surface te
1 INT
1.1 M
The inven
compute
has more
transistor
single sili
A process
technolog
scale of t
mobile p
same tec
the figure
will be dr
FIGURE 1 S
IN SIZE FRO
In this re
nitride lik
folding m
of water
We all kn
surface te
an silicon
ension driven
TRODUCTI
MOTIVATION
ntion of the t
r. Even more,
e capacity tha
r, but also by
con chip. This
s technology i
gy creates sm
these mechan
hones, which
chnology as co
e. This planar
ramatically inc
SCANNING ELECT
OM 0.5 MM TO 1
eport we will d
ke the ancient
method has to
drops to fold
now the smal
ension of the
n nitride temp
fabrication o
ON
transistor led
everyone can
an a supercom
the invention
s technology is
is Micro Elect
mall mechanic
nical devices.
h react to mo
omputer chip
r disposition o
creased if the
TRON MICROSCO
MM. (1)
discuss a met
t Japanese tec
be as such th
the structure
ll insects that
water. This sa
plate into a str
of three‐dimen
to a revoluti
n have a comp
mputer of the
n of the whole
s now mature
ro Mechanica
cal systems w
These system
vement, or h
s, all the com
of the structu
re was a way
OPE IMAGE OF A
thod to create
chnique called
hat a small str
s. This is beca
t walk on the
ame force can
ructure like a p
nsional micros
on which ma
puter in his po
e 70’s. This a
e process that
e and is being
al Systems, als
which interact
ms are used in
have a compa
mponents lay
ures limits the
to create ME
SPIDER MITE ON
e three dime
d origami. The
ructure can be
ause capillary
e water, this i
n be used to fo
pyramid.
structures
de possible t
ocket nowada
all was possib
t was needed
used to deve
so called MEM
electrically.
n sensors and
ss function. T
planar on the
e possibilities
MS devices th
N A POLYSILICON
nsional struct
e structures a
e folded. The
forces becom
s possible du
old structures
hat almost ev
ays, the conte
ble not only b
to make mill
lop new types
MS. As the na
Figure 1 gives
can also be f
These structu
e surface. Also
of this techn
hat stood up fr
N MEMS GEAR‐T
tures by foldin
re of course o
method we u
me dominant a
e the capillar
s. One single d
very househo
emporary mob
by the inventi
lions of transi
s of technolog
me already im
s an impressi
found in cont
ures are made
o this can bee
nology. The po
rom the surfa
TRAIN. SPIDER M
ng flat pieces
on a micro sca
use is the capi
at smaller scal
ry force also
drop is enoug
Page 3
ld owns a
bile phone
ion of the
stors on a
gies.
mplies this
ion of the
temporary
e with the
en seen in
ossibilities
ace.
MITES RANGE
s of silicon
ale, so the
llary force
es.
called the
h to fold a
Surface tension driven fabrication of three‐dimensional microstructures Page 4
1.2 OUTLINE OF THIS PROJECT
In this project we are going to fold a template made in silicon nitride using standard IC technology and fold this
into three dimensional structures. Folding will be done by using the capillary forces of water drops. At first we
will determine the theoretical forces working on these structures when a drop of water is placed on them, and
assess whether these structures can be made to fold. And if they fold, will these structures stay folded? We will
determine the folding rate and how different surface parameters will influence this rate. The structures and
theoretical model are already created and determined.
The folding of the structures led to new effects which we will investigate experimentally. Effects that posed
new questions were that of the structures stayed folded after folding and that the structures kept folding
seamlessly every single time. We will look at the stiffness of hinges, the geometry, the manner in which we
dispense water and the surface characteristics of the structures. Getting a clear picture of the forces that play
role.
All these experiments will give enough data to give an understanding on the folding of silicon nitride structures.
In addition to all this we will try to lift the logo of the university out of the plane, and try dispense a drop of
water through a channel, instead of dispensing water off hollow fiber used in the experiments
We will discuss the created model of folding in chapter 2. In this chapter the theory behind capillary folding and
how this force can be harnessed for folding structures. The setup and the method how we did these
experiments are elaborated in chapter 3.1. Different experiments are spread out over different chapters and
have sub results. This is the chronological order in which the experiments were done. Results of the Simple
folding experiments can be found in chapter3.2, experiments with variation of the structure parameters can be
found in chapters 4.2 and 5.2. This is followed by an overall conclusion and recommendations.
Surface te
2 TH
2.1 CA
The force
capillarie
regardles
everywhe
water str
that wet
with a for
This all ca
the same
in the flu
their sha
minimiza
FIGURE 2 LI
Every liqu
where th
liquid air
give an a
factor. Th
example
walk on w
inner wal
ension driven
HEORY
APILLARY FO
e we use to
s. When thes
ss of gravity.
ere in their sy
riders to walk
glasses stick t
rce of 10N, so
an be explain
e liquid. Molec
uid as illustrat
pes to minim
tion of the int
IQUID AIR INTER
uid is specific
he liquid react
interface. The
ngle to the sh
hese forces be
of this scaling
water. Or if w
ll of the straw
Air
Liquid
fabrication o
ORCES
fold structure
e tubes are p
This phenom
stem. But the
k on water. Sa
to flat surface
o hold a glass p
ed by the fac
cules on the s
ted in Figure
mize the expos
terface manif
FACE, TOP MOLE
how it reacts
ts to the solid
ese interface
hape of the dr
ecome domin
g is a small in
we would look
w, and if we loo
of three‐dimen
es is the sam
placed in a bat
menon is use
e same force c
ame force is r
es. A drop of w
plate of 1 kg
ct that molecu
surface will ha
2. This is an
sed surface. T
ests in formin
ECULE IS NOT HA
to the solid s
d is called to s
forces depen
roplet on a so
ant when we
nsect that can
k at a straw w
ok at a shorel
nsional micros
me force that
th of water, t
ed by plants
can be witness
responsible fo
water with a
ules in liquids
ave half less m
unfavorable e
The exposed s
ng of droplets.
APPY BECAUSE IT
surfaces. This
solid liquid in
d on the liqui
lid plane. This
scale down, a
n walk on wat
with water we
ine we will no
structures
can be seen
the water will
to get wate
sed as surface
or sticky hair
radius of 1 cm
want to be s
molecules surr
energy state.
surface is also
.
IS NOT SURROU
has a lot to do
terface, and
id. A contact a
s angle relates
and thus beco
ter using surfa
will see that
ot see this effe
in really nar
tend to flow
er with nutri
e tension, this
when coming
m can hold tw
urrounded by
rounding them
This is the re
o called the li
NDED BY SAME K
o with surface
how the liqui
angle measure
s directly to th
ome favorable
ace tension, b
the water sta
ect. As shown
rrow tubes, a
into the tube
ients from th
s phenomena
g out of the s
wo glass plates
y other molec
m than other
eason that flu
iquid air inter
KIND OF MOLEC
e tension. The
d reacts to ai
ement of the
he solid liquid
e In this appli
but an elepha
ands higher a
n in Figure 3.
Page 5
also called
e upwards
he soil to
is used by
shower or
s together
cules from
molecules
uids adjust
rface. This
ULES
e interface
ir is called
liquid will
d interface
cation. An
ant cannot
gainst the
Surface tension driven fabrication of three‐dimensional microstructures Page 6
FIGURE 3 DIFFERENCE BETWEEN WATER IN A TUBE AND LARGE WATER BODIES. THERE IS A CLEAR EFFECT ON THE EDGE OF THE TUBE
BUT THERE NONE ON THE EDGE OF A SHORELINE
When drop is placed on a surface the drop can form a thin film or become a drop. This depends on the surface
and liquid characteristics. This is quantified by the contact angle θc.
When a drop tends to become a thin film on a surface we call this fully wetting. When considering water it will
fully wet a SiN surface. This is the material our templates are made of. Other liquids will react differently to this
surface and may form a droplet. In this case the contact angle of the drop with the surface can be measured by
viewing the drop.
2.1.1 FOLDING WITH CAPILLARY FORCES It was proven recently (2) that when a drop of water is put on a thin sheet of polymer, the polymer would
spontaneously wrap. This is due to that the drop will try to minimize the water air interface, the capillary force
will fold the polymer sheet as shown in Figure 4. As you can see in the figure the sheet of plastic is on a
millimeter scale. After folding the water will totally evaporate. As already explained in the previous chapter this
effect should become larger when we scale down to micrometers.
Water between shorelines
Water in a vertically
placed capillary
millimeters
meters
Surface te
FIGURE 4 W
FOLDING O
There wa
solder. Pl
(3). This w
hinges. F
using wat
By using
in Figure
productio
the prod
object as
most righ
same size
ension driven
WRAPPING OF D
ON A MILIMETER
as a demons
lacing solid so
was scaled do
or folding it w
ter.
water on tem
5(a) to (d). T
on by convent
uction proces
s shown in Fig
ht top templat
e, namely 50µ
fabrication o
ROP OF WATER
SCALE.
tration of as
older on the h
own to scale o
would be gre
mplates the TS
The design of
tional lithogra
sses can be f
gure 5(b). The
te results in th
µm.
of three‐dimen
WITH SQUARE A
sembling mil
hinges and me
of 100nm. Pro
at if we could
ST group alrea
the template
aphic process
found in chap
e top center t
he cube as sh
nsional micros
AND TRIANGULA
limeter sized
elting the sold
oblem with th
d combine th
ady folded var
es are shown
es, and there
pter 3.1. Fold
template resu
own in Figure
structures
R SHEETS OF PDM
structures u
der made the
his technique
e scale of the
rious structure
in Figure 5(a
efore it is desi
ing the long
ults in the sha
e 5 (d). The bla
MS (POLYDIMETH
using capillary
e structures st
is that the so
e last techniq
es (4) with the
). These temp
gned in plana
structure res
pe as shown
ack bar in the
HYLSILOXANE ) E
y effects usin
tand up from
older will be l
que and the b
e use of wate
plates are des
ar manner. M
sults in a pris
in Figure 5 (c
ese figures are
Page 7
EXAMPLE OF
ng molten
the plane
eft on the
benefits of
er. As seen
signed for
ore about
m shaped
c) and the
e all of the
Surface te
FIGURE 5 (A
ZOOM IN O
The prism
made. Be
just take
and the v
figure the
thickness
and then
transition
different
shown in
We will m
structure
progressi
model wh
angle tha
circle. Th
the hinge
ension driven
A) DESIGN TEMP
ON THE HINGES (D
m structure is
ecause a prism
the front view
volume of wa
e flaps are be
s. Structures c
opens, or the
ns are shown
angles and t
Figure 9 is sh
make the follo
e is fully wett
ion of folding
here we again
at flaps make
e angle of thi
e, t is the thick
fabrication o
PLATES (B) FOLDE
D)
s specially de
m structure is
w. By doing th
ter on the str
nt slightly. Th
can behave in
e hinges are l
n in figure 8
he water men
hown in Figure
owing assump
ting and the
we need to d
n take the fro
when folding
s piece of this
kness of the h
of three‐dimen
ED PRISM (C) OP
signed to ver
much longer
his simplificat
ructure. A fron
e hinge is dep
two manners
loose enough
and Figure 9
niscus is show
e 5 (b). An arti
tions, the edg
drop covers t
define the follo
ont view of a p
g. The curvatu
s circle is θ. F
inge; if we tak
nsional micros
EN AND FOLDED
rify the two d
than that it is
tion the variab
nt view of the
picted as a th
s, either the h
so that the s
9. In these fig
wn as a thin l
ist impression
ges of the dro
the whole su
owing dimens
prism to simp
ure of the men
Figure 6 shows
ke l0 as a part
structures
D HALF A DODECA
dimensional t
s wide, we can
bles we can d
e template of
inner line, l0 i
hinges are too
structure can
gures the flap
line. The end
n of the folded
oplet is pinned
urface of the
sions as show
plify the mode
niscus on the
s the bending
of a circle the
AEDER (C) FOLDE
heoretical mo
n neglect long
istinguish are
a prism is sh
s the length o
o stiff and the
fold complete
ps are shown
result of the
d prism is show
d down on the
structure. To
wn in Figure 10
el. W is the w
structure can
g of a hinge, w
en R is the rad
ED AND OPENED
odel the grou
gitudinal dime
e the angles o
own in Figure
of the hinge a
e structure fol
ely. These tw
n schematical
folding prog
wn in Figure 7
e edges of the
o form a mod
0. This figure s
width of the fla
n be seen as a
where l0 is the
dius of this cir
Page 8
D CUBE WITH
up already
ension and
f the flaps
e 6, in this
nd t is the
ds al little
o types of
ly making
ression as
7.
e flap. The
del of the
shows the
aps, φ the
a part of a
e length of
rcle.
Surface te
FIGURE 6 B
FIGURE 7 A
ension driven
ENDING A THE H
ARTISTS IMPRESS
R
fabrication o
HINGE, WHERE l0
ION OF A FOLDE
t
l0
of three‐dimen
IS THE LENGTH O
D PRISM
nsional micros
OF THE HINGE, T
structures
THE THICKNESS A
AND φ THE ANGGLE THAT THE HIN
Page 9
NGE MAKES
Surface tension driven fabrication of three‐dimensional microstructures Page 10
figure 8 schematic overview of the front view of a prism while Folding and opening progresses
Figure 9 schematic overview of the front view of a prism while Folding progresses
Surface te
FIGURE 10
THE MENIS
THE MENIS
A droplet
bending t
interface
the bend
results in
written a
Where
volume a
with:
FIGURE 11
If we min
how the
w
ension driven
THE VARIABLES
SCUS AS A PART O
CUS WHEN ENOU
t placed on t
the flaps. The
of the drople
ding stiffness.
a bending en
s
is the
and in our sim
PHASE DIAGRAM
nimize the ene
equilibrium a
w
θ
fabrication o
FOR THE MODEL
OF A CIRCLE THE
UGH WATER IS E
the surface w
e total energy
et. The bendin
E is the Youn
nergy per unit
. If we n
balance betw
mplification th
M OF THE EVOLUT
ergy in resp
angle change
φ w
of three‐dimen
L, w IS THE WIDT
N θ IS THE ANGL
VAPORATED AN
will tend to m
of the system
ng energy of
ng’s modulus
t length as:
normalize this
ween mechan
he surface S a
sin 2
TION OF EQUILIB
ect to resu
depends on t
w
nsional micros
TH OF A FLAP, φ
LE OF THE TIP OF
D THE STRUCTUR
minimize the
m consists of
a curved plat
and υ the Po
. Th
per unit leng
nical bending f
as constant, t
and
BRIUM STATES A
lting in an equ
the stiffness p
w
θ
structures
φ IS THE ANGLE T
F THIS PART. RIGH
RE DID NOT FOLD
liquid air inte
the elastic en
e can be writ
oisson’s ratio.
he surface ene
th:
forces and ca
the relation o
is the norm
S FUNCTION OF V
uilibrium angl
parameter .
φw
THAT THE FLAP T
HT FIGURE SHOW
D COMPLETELY
erface and de
nergy in the h
ten as and
Bending the
ergy of the liq
pillary forces.
of the angles
malized cross s
VOLUME
e of . As w
For a certain
TAKES, WHEN CO
WS THE CONCAV
eform the str
inges and the
d where
flaps over th
uid air interfa
. When taking
and can
section.
we can see in
stiffness of t
Page 11
ONSIDERING.
E SHAPE OF.
ructure by
e liquid‐air
is
he angle φ
ace can be
g the total
be found
Figure 11,
the hinges
Surface tension driven fabrication of three‐dimensional microstructures Page 12
the flaps bend due to evaporation of the droplet to a certain angle and then open again after attaining the
equilibrium angle , this is shown in Figure 11 as the line where . For a certain lesser stiffness the
flaps fold completely into a prism. The in this case is reached when completely folded. This is depicted as
the line . The stiffness is the threshold stiffness value where we get the transition from folding and
opening into folding completely. For angles smaller then 2 3 the flaps will not close completely and will
open again after reaching this angle. At the angle =2 3 the flaps close completely this corresponds
to √3. Reducing any further will result in a not larger than 1.39 rad, leading to a discontinuous
transition in the diagram. This means that the structure will abruptly reopen again.
In Figure 11 we see that for the interface shape transitions from a convex in to a concave shape. On the
transition point the angle of the interface will be zero ( 0), from this we can find . has a minimum for
=2 3 and this results in √3. Note that there is a gap between after that =2 3 . According to
this model after the gap the structure should fold open.
2.1.2 EFFECTS OF DIFFERENT CONTACT ANGLES Previous experiments we used the fully wetting surfaces. This means that the contact angle of the water with
the surface of the structures is pinned down at the edges and the angle that the water makes with the edge is
totally dependent on the volume of water.
For not fully wetting surface the curvature of the meniscus is dependent on the contact angle this is shown in
Figure 12. Looking at this figure one might observe that there is an dependency between θ and θc. This
dependence is clearly illustrated in Figure 13. We can deduce from this figure that α=180o‐90o‐φ‐½ θ and
α=90o‐θc, this results in ½ θ=θc – φ. Substituting this in the energy function formulated in the previous chapter
will result in
. This means that now the energy is not dependent on θ but
dependent on θc.
FIGURE 12 SCHEMATIC OVERVIEW OF THE MODEL AND VARIABLES WHEN THE LIQUID IS NOT FULLY WETTING . θC IS THE CONTACT
ANGLE, W IS THE WIDTH OF A FLAP, φ IS THE ANGLE THAT THE FLAP TAKES, WHEN CONSIDERING THE MENISCUS AS A PART OF A CIRCLE
THEN θ IS THE ANGLE OF THE TIP OF THIS PART. RIGHT FIGURE SHOWS THE CONCAVE SHAPE OF THE MENISCUS WHEN ENOUGH WATER
IS EVAPORATED AND THE STRUCTURE DID NOT FOLD COMPLETELY.
φ w
w
w
θ
φw
w
w
θ
θc
θc
Surface te
It was alr
fixed con
the maxim
then see
previous
FIGURE 13
FIGURE 14
ension driven
ready proven
ntact angle it
mum point of
how this ma
model the qu
HOW CONTACT A
MAXIMUM EQU
φeq,ma
φ
fabrication o
that folding s
is not necess
f the progress
ximum equili
uestion arises
ANGLE IS RELATE
ILIBRIUM ANGLE
½ θ
θc
w
½ w
ax1
φeq,max2
φeq,max3
of three‐dimen
structures are
ary to perfor
sion lies, the m
brium angle c
whether the e
ED TO θ
ES FOR DIFFEREN
φ
α
nsional micros
e following th
m all the ang
maximum equ
changes for d
experimental
NT CONTACT ANG
structures
e theoretical
gle measurem
uilibrium angle
ifferent conta
results will fo
GLES
model, so to
ents. We nee
e φeq , as show
act angles θc.
ollow this mod
see the effec
ed to determ
wn in figure 1
in Figure 15.
del.
Page 13
ct of the a
ine where
4. We can
As in the
Surface te
FIGURE 15
2.1.3 VExperime
folded. S
fact that
we need
FIGURE 16 G
Another
end up se
effect to
design in
a view on
ension driven
HOW THE MAXIM
VARYING THEents done rev
EM picture sh
structures sta
change the ar
GLUING RESIDU
effect is that
eamless over
the limit by i
such a way t
n the force tha
fabrication o
MUM ANGLE CHA
E STRUCTURA
veal new phe
how that ther
ay folded. To
re over which
IN THE SEAM OF
the structure
nanometers.
ntroducing ne
hat an additio
at play a role
of three‐dimen
ANGES DUE TO T
L DIMENSION
nomena whic
e are some m
get a better i
the flaps are
F A FOLDED CUBE
e fold seamle
This is a huge
ew designs wh
onal torsion fo
in this folding
nsional micros
THE CHANGE OF C
N ch need to b
material on the
dea about th
glued togeth
E
essly every sin
e accuracy tha
hich will test
orce is neede
g mechanism.
structures
CONTACT ANGLE
be examined
e edge of the
e amount of f
er.
ngle time. The
at is created b
different kind
d to fold seam
E
more. The st
fold. This mig
force that is h
e flaps move
y the capillary
ds of distortio
mlessly. This e
ructures that
ght be the ca
holding the fla
over microm
y force. We pu
ons. We will c
extra hurdle w
Page 14
t fold stay
use of the
aps folded
meters and
ushed this
hange the
will give us
Surface tension driven fabrication of three‐dimensional microstructures Page 15
3 FOLDING TEMPLATES
3.1 METHOD
3.1.1 DESIGN OF THE TEMPLATES Now we have explained the theoretical model we need to design and construct the templates to verify the
model. Design of the templates were done in CleWin and are depicted in Figure 17 and Figure 18. There were
different sets of structures with different hinge types. We varied the hinges so that we can experiment with
different stiffness’s. There are two types of hinges, one type is the solid version, this is a hinge made out of
150nm of SiN. The second type of hinge is also made of 150nm SiN but they are not solid, 8 small hinges
connect the flap with a length of 10µm. Both these designs are shown in Figure 18. Also the width of these
hinges are varied. Every single type of hinge will result in a different . The varieties of this set is listed in Table
1.
The of the perforated hinges are proportional to length of the hinges holding the flaps together divided by
the total length of structure. So how bigger the holes in the length, how smaller the factor .
Typeofhinge Hingewidth(µm) Flapwidth(µm) ß
Solid 3 80 5,08
Solid 5 80 3,05
Solid 8 80 1,90
Solid 15 80 1,02
Solid 5 50 4,88
Solid 8 50 3,05
Solid 12 50 0,20
10µmhinges 10 80 0,24
10µmhinges 20 80 0,12
10µmhinges 6 80 0,27
10µmhinges,5µmgap 25 80 0,07 TABLE 1 TYPES OF DIFFERENT HINGES USED FOR DIFFERENT SETS OF STRUCTURES
Surface te
FIGURE 17
PYRAMID
FIGURE 18
ension driven
DIFFERENT STRU
DESIGN PRISM S
fabrication o
UCTURE TEMPLAT
TRUCTURE (A) SO
of three‐dimen
TES, FIRST ONE I
OLID HINGE (B) H
nsional micros
IS A CUBE, THREE
HINGE WITH HOL
structures
E SIDED PYRAMI
LES
D, HALF A DODEECAEDER AND A
Page 16
FOUR SIDED
Surface tension driven fabrication of three‐dimensional microstructures Page 17
3.1.2 CLEANROOM PROCESSES As already discussed the templates are created using contemporary cleanroom processes. The process
document for creating these structures can be found in the appendix. Here we can see that the following takes
place. On a silicon wafer a SiN layer of 1µm is deposited and etched away by plasma etching, leaving grooves
for the hinges on the surface of the Silicon wafer. On top of this another SiN layer is deposited of 100 nm. This
layer is also deposited between the flaps forming the hinge. Everything but the templates are ethed away,
leaving a SiN template on the surface of the silicon wafer. The total structure is then isotropically underetched,
the left over Silicon form the pillar on which the template rest. Simplified step by step overview is given in
Figure 19.
Blank Silicon wafer
Adding SiN layer
Etching away the hinges
Adding SiN layer
Etching away everything but the template
underetching
FIGURE 19 SIMPLIFIED STEP BY STEP OVERVIEW OF THE PROCESS NEEDED TO CREATE TEMPLATES
Surface te
3.1.3 To get th
just abou
created t
couple of
50µm and
big strong
The setup
relation t
probe m
structure
FIGURE 20
Using thi
that take
measured
three tim
were com
the mode
ension driven
EXPERIMENTA
e structure to
ut 300µm in w
that can dispe
f hundreds of
d a larger one
g fiber, to form
p consists furt
to the table. P
akes it possi
e. On the micr
PHOTO OF THE S
s setup we w
es place. We m
d frame by fr
mes the angle,
mpensated fo
el as discussed
fabrication o
AL SETUP o fold, one mu
width, and th
ense small am
f micrometers
e with an inne
m the nozzle.
ther of a tabl
Previously me
ble to move
oscope a ccd
SETUP WITH THE
will add a drop
measured the
rame by hand
, the average
r the viewing
d in the previo
of three‐dimen
ust get a drop
e drop must
mount of wate
s in diameter.
er diameter of
The big fiber
e with a micr
entioned fiber
the fiber m
camera is plac
IMPORTANT CO
p of water on
angles that t
d using a com
was taken of
angle and pl
ous chapter u
nsional micros
p of water on t
not be much
er through a n
To do so we
f 50µm, the b
is then conne
oscope. This
r is fixed on a
icrometers a
ced, the feed
OMPONENTS HIG
the set of str
the flaps make
mputer softwa
f these three
lotted in a gra
sing these exp
structures
the template.
bigger than
nozzle which i
uses hollow
igger one is st
ected to a pum
microscope is
a probe and fe
t a time and
is recorded o
HLIGHTED
ructures and c
e with the ba
are. For every
measuremen
aph. The ques
perimental re
As explained
that. Therefo
s small enoug
fibers, on wit
tronger. The t
mp.
s placed at an
ed by a pump
d maneuver t
n the comput
create a set o
se of the stru
y flap on ever
nts as the actu
stion is wheth
sults.
d before the te
ore the setup
gh to generate
th an outer di
thin fiber is sli
n angle of 60 d
p with demi w
the tip just a
ter.
of movies of t
ucture. The an
ry frame we
ual angle. The
her we can re
Page 18
emplate is
has to be
e drops of
ameter of
id into the
degrees in
water. This
above the
he folding
ngles were
measured
ese angles
econstruct
Surface te
3.2 R
3.2.1 First expe
not repro
remarkab
Some str
Confirmin
other wa
structure
puddle do
their orig
held its fo
If water i
the flaps
bounce b
FIGURE 21 T
3.2.2 Initial fold
heat of th
folded co
movies ta
shown in
flap is me
measurem
structure
We did s
well. This
edges we
ension driven
ESULTS
FIRST RESULTeriments on t
oducible in th
ble.
uctures had s
ng that the fo
y around. Wh
e floated on th
ownward. So
ginal position.
orm even whe
is added to th
will fold dow
back to their o
TRIANGLE PYRAM
RESULTS OF Fding of prisms
he lights mad
ompletely. The
aken showed
Figure 22. Th
easured. The
ments were t
e folded fully.
see some phe
s happened e
ere pulled tog
fabrication o
TS FOLDING ST
these were no
he amount of
stiff hinges du
olding angle w
hen administe
he surface of t
we had down
This last obs
en the water w
he cavity the f
wn as shown
original state.
MID WITH WATE
FOLDING OF P
s was a succe
e the drop ev
e set with the
that the ang
he measureme
measuremen
taken per fla
enomena wort
every time. Th
ether by the c
of three‐dimen
TRUCTURES W
ot that succes
time I took t
ue to design a
would increase
ering an amou
this puddle. W
nward folding
ervation cont
was evaporate
flaps will floa
in Figure 21.
ER IN CAVITY, (B)
PRISM ss. It is fairly e
vaporate it wa
e array of 10µ
gle of the flap
ent is done at
ts are compe
p and averag
th mentioning
he meniscus o
capillary force
nsional micros
WITH MORE TH
ssful. Although
to do the exp
and didn’t fold
e when the h
unt of water in
When this pud
. After all the
tradicts the ob
ed. See Figure
t on the surfa
. After all the
THE WATER IN T
easy to place
as clear that t
m hinges fold
ps increased
t both flaps, a
ensated for th
ged. Table 2 i
g, the structu
of water guid
es, and the str
structures
HE 2 FLAPS.h the group h
periment. The
d into the full
hinges are less
nto the cavity
ddle dried up
water had ev
bservation of
e 5d.
ace of the wa
e water is eva
THE CAVITY IS PU
a drop on the
he flaps bend
ded all comple
until they clo
and the angle
e angle of the
is similar to T
ures that folde
ed both edge
ructure folds s
had successful
ere were som
structures bu
s stiff. Folding
below the st
the flaps follo
aporated the
the cube that
ater and when
aporated in th
ULLING THE FLAP
e structure wit
ded and at som
etely. Frame b
osed seamless
of the flaps in
e microscope
Table 1 but w
ed completely
es of the flaps
seamlessly.
lly folded a cu
me phenomen
ut they bende
g action also
ructure the fl
owed the surf
flaps jumped
t was folded.
n the water e
he cavity the
PS OF THE TEMPL
th the setup.
me type of hi
by frame analy
sly. Measurem
n relation to t
. On every fra
we added wh
y, folded seam
s to each oth
Page 19
ube it was
a that are
ed a little.
works the
aps of the
face of the
d back into
This cube
vaporates
flaps will
LATE DOWN
While the
nges even
ysis of the
ments are
the center
ame three
hether the
mlessly as
er. So the
Surface te
FIGURE 22
Other hi
measurem
structure
FIGURE 23
2
4
6
8
10
12
14
16an
gles in degrees
0
5
10
15
20
25
30
35
angles in degrees
ension driven
MEASUREMENT
nges which
ment done o
e behave in wh
MEASUREMENT
0
20
40
60
80
00
20
40
60
0
0
5
0
5
0
5
0
5
20 25 3
fabrication o
OF FULLY FOLDIN
were solid a
n a structure
hich manner.
OF FOLDING AN
20
30 35 40 45
of three‐dimen
NG, TAKEN FROM
nd were nar
e that doesn’t
In this case a
D OPENING, TAK
40
frame
5 50 55 60
frame
nsional micros
M A MOVIE THAT
rrow were to
t fold comple
maximum an
KEN FROM A MO
60
es
65 70 75
es
structures
T PROGRESSED 5
oo stiff for f
etely. The tab
gle of 32 degr
VIE THAT PROGR
80
80 85 90 9
FRAMES PER SEC
fully folding.
le beneath th
rees is achieve
RESSED 5 FRAME
100
95
COND.
Figure 23 s
his figure sho
ed by both fla
ES PER SECOND
angle ri
angle le
angle
angle
Page 20
hows the
ows which
aps.
ght flap
eft flap
rightflap
left flap
Surface tension driven fabrication of three‐dimensional microstructures Page 21
Typeofhinge Hingewidth Flapwidth(µm) ß foldingSolid 3 80 5,08
Solid 5 80 3,05
Solid 8 80 1,90
Solid 15 80 1,02 Fully
Solid 5 50 4,88
Solid 8 50 3,05
Solid 12 50 0,20 Fully
10µmhinges 10 80 0,24 Fully
10µmhinges 20 80 0,12 Fully
10µmhinges 6 80 0,27 Fully
10µmhinges,5µmgap
25 80 0,07 Fully
TABLE 2 FOLDING OF DIFFERENT STRUCTURES
We can convert the measurements done frame by frame, a time progression, in to a measurement done on
variation of the water volume. This is exactly how we setup the theoretical model and these measurements will
give the measurement point for constructing the graph shown in Figure 24.
FIGURE 24 MEASURED PHASE DIAGRAM OF THE EVOLUTION OF EQUILIBRIUM STATES AS FUNCTION OF VOLUME (4)
It is striking that the simplification of the model has so little influence that the actually measured values
correspond almost exactly to the model. Simplifications like totally ignoring a whole dimension do not make
the theoretical model deviate from the measured values.
0 0.5 1 1.5 2 2.50
0.5
1
1.5
2
normalised volume
eq (
rad
)
= 1.8
= 1.5
= 0.07 = 0.8
Surface tension driven fabrication of three‐dimensional microstructures Page 22
4 FOLDING WITH DIFFERENT CONTACT ANGLE
4.1 METHOD
To determine the effects of a defined contact on the folding of the structure we need to use liquids that have a
defined contact angle on SiN. Or we need to change the surface of the SiN so that water has a contact angle on
the this surface. After drafting a list of liquids with different contact angles we came to a conclusion that not all
liquids were appropriate to use in my setup due to safety reasons.
Changing the property of a surface can be done by depositing a layer of Fluor Carbon. Fluor Carbon is
hydrophobic and the thickness of the layer determines the amount of hydrophobeness and thus the contact
angle of the liquid on this surface. A layer of FC can be deposited by using a Reactive Ion Etching chamber (RIE)
(5).
The results of some reference experiments done on an empty silicon en SiN surface are depicted in Figure 25.
We decided to do the folding measurements by putting the samples in the RIE chamber between 0 and 10
minutes.
FIGURE 25 VARYING OF CONTACT ANGLE DUE TO TIME OF FC DEPOSITION
Changing the surface into hydrophobic means that the drop of water coming from the fiber might cling to the
fiber and not want to stick to the surface. To overcome this we have coated the fiber also with FC, this is done
by submersing the fiber into liquid FC. The fiber did not clog by this layer of FC.
4.1.1 WHITE LIGHT MEASUREMENT USING LATERAL SCANNING INTERFEROMETRY To change the contact angle we chose to deposit a FC layer onto the structures. The question rised whether the
flaps on the structure would bend to the extra force asserted by the elasticity of the FC layer. To measure
whether this is the case, whitelight measurements using lateral scanning interferometry were conducted on
the structures. This will give a clear indication of the orientation of the flaps. The interferometer measures the
horizontal distance of the surface.
0
20
40
60
80
100
120
60 30 10
Angle (degrees)
Time (minutes)
Si : Contact angle water
SiN : Contact angle water
Surface te
FIGURE 26
Figure 26
angle of t
not addit
ension driven
INTERFEROMETE
6 shows one o
the flaps of 0
tionally increa
fabrication o
ER MEASUREMEN
of the actual m
.06 degrees. T
ase the angle o
of three‐dimen
NT OF THE FLAPS
measurement
This we concl
of the flaps.
nsional micros
S
t done on the
luded as negl
structures
structures. T
ectable. This
here was an a
means that a
average incre
adding a layer
Page 23
ase of the
of FC will
Surface tension driven fabrication of three‐dimensional microstructures Page 24
4.2 RESULTS
We did the same folding experiments as in the previous experiments, and this time we looked only to the
maximum of each set. We got similar results as shown in Figure 22 and Figure 23, and from these results we
looked at the maximum angle attained. We managed to do this experiment for two different hinge stiffness’s.
The results of the measurement are depicted In Figure 27. The solid line is the theoretical and expected
progression of to variation of the contact angle . The crosses are the measured points.
FIGURE 27 MAXIMUM ANGLE FOR DIFFERENT CONTACT ANGLES (4)
Again it is striking that we get measurements that fit the model despite of the simplifications. We actually
conclude that capillary properties doe follow the model, and thus this process is predictable and useful for
fabrication of three dimensional structures on this scale.
0 0.5 1 1.5 20
0.1
0.2
0.3
0.4
0.5
0.6
c (rad)
max
(ra
d)
Surface te
5 VA
5.1 P
5.1.1 TWe have
hurdles. O
lateral di
shown in
structure
rear whe
folding p
close sea
FIGURE 28 S
ension driven
ARYING DE
ROBLEM DE
TORSION IN Fseen that ev
One of these
rection. In ot
Figure 28 wil
e would close
re the structu
rocess Other
mlessly, and m
STRUCTURE WIT
D1
D2
fabrication o
SIGN OF T
EFINITION
FOLDING very time the
hurdles is to
her words if
l the structur
seamlessly, a
ure was D1 in
scenario for
may open aga
TH DECREASING F
of three‐dimen
THE PRISM
prism fold th
see whether
we design fla
e fold seamle
at the front w
width, the h
this design is
ain.
FLAP WIDTHS
nsional micros
MS
e fold seamle
the capillary
aps of the pris
ssly. This wou
where the wid
inge would b
s that the hin
structures
essly. To put t
forces will ov
sm with decre
uld result in a
dth is D2 the h
e pressed dow
nge would no
this to the tes
vercome the r
easing flap wi
folding like sh
hinges would
wnwards. add
ot give way an
st we have m
rotational for
idth over the
hown in Figur
stretch out a
ding extra stra
nd the struct
Page 25
ade some
rces in the
length as
e 29 if the
and at the
ain on the
ure won’t
Surface te
FIGURE 29
The diffe
not be an
5.1.2 Next set
shown in
And if th
meet hal
same, in t
ension driven
DISTORTION OF
rence betwee
ny influence o
FOLDING WIT
of structures
Figure 30, th
ey do they ca
fway of the o
the second ca
Rear vie
Fro
fabrication o
THE HINGES
en D1 and D2
f other effect
THOUT SYMM
have flaps of
he width D2 is
an fold in two
other flap as s
ase the angles
ew
ont view
of three‐dimen
are not more
s other than t
ETRY different wid
s larger than D
o ways, the e
shown in Figu
s will be differ
nsional micros
e than the hin
the bending a
dth, the left fla
D1. Again we
nds of the fla
ure 31. In the
rent, ɸ1 is not
structures
ge width of 5
and stretching
ap will have a
will test whe
aps meet each
first case bot
t equal to ɸ2.
µm. This is ch
g of hinges.
a smaller widt
ther these fla
ht other, or o
th the angles
hosen so that
th then the rig
aps will fold se
one end of th
of the flaps w
Page 26
there will
ght one as
eamlessly.
e flap will
will be the
Surface te
FIGURE 30 S
FIGURE 32 (
FIGURE 31
ension driven
STRUCTURE WIT
(A) STANDARD 4
POSSIBLE OUTCO
D1 D
fabrication o
TH DIFFERENT FLA
45 ANGLE EDGE (B
Option
OME FOR FOLDIN
D2
of three‐dimen
AP WIDTHS
B) FLEXIBLE EDGE
n 1
NG A STRUCTURE
nsional micros
E
E WITH DIFFEREN
structures
NT FLAP WIDTHS
optiion 2
Page 27
Surface te
5.1.3 VThird typ
structure
the conta
hinge stif
structure
structure
We will c
is varied f
FIGURE 33 S
FIGURE 34 S
5.1.4
d
d
ension driven
VARYING CONpe of structur
es tend to stay
act surface of
ffness and co
es folding and
es together.
create three se
from 20 µm to
STRUCTURE WIT
STRUCTURE WIT
LIFTING OBJE
fabrication o
NTACT AREA res will have
y folded desp
f the flaps and
ontact area co
d opening aga
ets of three d
o the full 390µ
TH VARYING CON
TH VARYING CON
ECTS OUT OF T
d
d
of three‐dimen
a varying co
pite of the ela
d we will vary
ombination w
ain. This will g
different conta
µm.
NTACT SURFACE
NTACT SURFACE F
THE PLANE
d
d
nsional micros
ntact surface
astic forces in
y the elasticit
will be on the
give us inform
act angles. Ev
FOLDED
structures
e. Previous ex
the hinges. T
ty of the hing
transition of
mation of the
very set consis
d
d
d
d
xperiments ha
To test this ph
es . We will t
structures al
e quantity of t
sts of twenty v
ave shown th
henomena we
try to determ
ways staying
the forces ke
variations of d
d
d
Page 28
hat folded
e will vary
mine which
folded to
eeping the
d where d
Surface te
Last but n
created s
from the
will be et
This desig
to perfor
etching n
the etcha
underetc
FIGURE 35 S
FIGURE 36 W
5.2 R
ension driven
not least we w
structures wit
plane and we
tched free fro
gn has a smal
rm well. With
not to free the
ant to reach i
hing. This stru
STRUCTURE WIT
WHERE IT CAN G
ESULTS
fabrication o
will try to lift
h the letters o
e will have a m
m the underly
ll hole in the e
hout the hole
e right flap fro
n the center
ucture suppor
TH A LETTER
GO WRONG WITH
of three‐dimen
a structure o
of the univers
micro billboar
ying silicon, an
extension tha
the addition
om the cente
of the arm. I
rts the flaps th
H UNDERETCHING
nsional micros
of the surface
sity on the fla
rd. In the sam
nd thus hang
at is holding t
to the struct
r flap as show
n this figure t
hat lay on top
G
structures
using this fol
ps. When the
e time that th
freely like the
he letter. This
ture which ho
wn in Figure 3
the white sha
p.
lding action. F
e flaps fold the
he flaps are u
e flaps.
s hole is made
olds the lette
36. The hole w
ape is the stru
For this exper
ese letters wi
nder etched t
e for the und
er can cause t
will make it po
ucture that is
Page 29
riment we
ll be lifted
the letters
er etching
the under
ossible for
s left after
Surface tension driven fabrication of three‐dimensional microstructures Page 30
5.2.1 TORSION IN FOLDING Folding experiments confirm seamless folding. This means that the hinges stretch and fold where needed to
facilitate this. We can conclude that the capillary forces are large enough to force the hinges.
5.2.2 FOLDING WITHOUT SYMMETRY Folding with flaps of different widths resulted in some remarkable results. As already stated in the previous
chapter the folding could have gone in two ways. From the measurements of the optical microscope it looked
like that the folding occurs in the manner as depicted as option 2 in Figure 32b. Further experiments revealed
the full extent of the mechanics in this folding.
In the very first measurements we saw that the flaps will take a maximum angle and fold back when the hinges
were stiff enough. This is due the torque on the flaps. We have determined that the capillary effect administers
a force on the flaps, the folding occurs not when the this force is larger than the counter acting elastic force of
the hinges, but when the width of the flaps times the capillary force is larger than the elastic force. This means
a fully folding structure won’t fully fold when the flaps are made less wide. This is shown in Figure 37.
Another way to explain this is by using the model we used in the previous chapter. We have a factor which is
dependant on the width of the flaps w: . This means that when we change the w we change the
folding property of the flap. In this case in such a way that it will not bend through to close.
FIGURE 37 CAPILARY FORCE VS ELASTICITY FORCE, THIS SIMPLIFIED MODEL SHOWS HOW TORQUE IS RELATED TO THE LENGTH OF THE
FLAP.
We have witnessed that a smaller flap takes a maximum angle, while the normal and larger flap keeps folding
and then crashing into the flap with the maximum angle. The larger flap doesn’t have the width to fold
seamlessly over the a flap that would stop the folding. This shown in frames taken from a measurement in
Figure 38. Here you can see that the right flap stays on the same angle while the left flap keeps on folding, in
the end it will collapse and not stay folded.
T=Fcapilary∙L1
L1
L2
T=Felastic∙L2
Central flap
Folding flap
Surface te
FIGURE 38 A
Although
which ap
previous
maximum
FIGURE 39 S
ension driven
ASYMETRIC FOLD
the width dif
pear to fold n
example, und
m angle, this is
SEM PICTURE OF
fabrication o
DING, RIGHT FLA
fference betw
normally (Figu
der a SEM the
s shown in Fig
F ASYMETRIC FOL
of three‐dimen
AP REACHES A MA
ween flaps in t
ure 39), where
it is clear tha
gure 40.
LDED STRUCTUR
nsional micros
AXIMUM ANGLE
his figure is d
e the differen
at the left flap
E
structures
AND STOPS FOL
ramatic, this p
ce in width ar
crashed into
DING
phenomena o
re not that dr
the right flap
occurs also in
ramatic as sho
p that stood st
Page 31
structures
own in the
teady on a
Surface te
FIGURE 40
FLAP.
5.2.3 VThis expe
contact a
stayed fo
solid hing
µm2. Onl
structure
µm2 the l
area of 7
used in th
This mea
Where
µm this i
µm leads
and gives
SEM pict
middle th
ension driven
CRASHING PHEN
VARYING CONeriment consis
area and every
olded for all c
ge resulted in
ly three type
es revealed tha
ast 7 structur
720 µm2 and w
he calculation
n that for the
is an equilibri
s to 4.4∙10‐5 J
s us a measure
ures of folded
he flaps will no
fabrication o
NOMENA, RIGHT
NTACT AREA sted of three
y variation wa
ontact areas.
n all structure
es of structur
at due to the
res open at 68
we assume th
ns.
energy
10 and w
um point, this
J/m2 . This is t
e for the force
d structure w
ot stay closed
of three‐dimen
T FLAP REACHED
sets, with thre
as repeated te
So we can co
es opening fo
res fell in thi
manufacturin
80 µm2. Becau
hat the deviat
with θ = 2/3
s means that
the minimum
es that the glu
with reduced c
.
nsional micros
A MAXIMUM A
ee different h
en times in te
onclude that t
or all contact
is category. R
ng process the
use the majori
tion is due to
12
π ≈2 we get
a structure th
m energy per s
uing substanc
contact area
structures
ANGLE AND THE
hinge types. Ev
n rows. The h
the hinges we
area’s except
Repeating thi
ere is a deviat
ity of the stru
production p
Ub=4∙10‐5 J/m
hat folds seam
square area n
e has to asser
is shown in F
LEFT FLAP CLOSE
very set had t
hinges with ho
eren’t stiff en
t for contact
s experiment
ion. The first t
cture only sta
process we wi
m2. For a conta
mlessly over t
eeded to kee
rt.
Figure 41. For
ED INTO THE ST
twenty variati
oles in them f
nough. The se
area’s larger
t for the ten
three rows op
ay closed with
ill take this va
act area of 72
he whole leng
ep the structu
r any larger h
Page 32
EADY RIGHT
ons of the
folded and
t with the
than 720
n identical
pen at 720
h a contact
alue to be
20 µm x 1
gth of 800
ure folded,
ole in the
Surface te
FIGURE 41
There wa
middle of
need a la
FIGURE 42
We made
Where w
length) .
height wh
The disto
requiring
expressio
the lengt
dimensio
the same
ension driven
FOLDED STRUCT
as an unexpec
f the folded f
rge force.
BENDING IN THE
e an estimatio
w(x) describes
E is the Youn
hen taking the
ortion is appr
g 0 0,
on for
h of the flaps
. We meas
ons we get 602
e of the whole
fabrication o
URE WITH SMAL
cted effect wh
flaps for very
E MIDDLE OF FOL
on by taking u
the deformat
g’s modulus
e crosssection
roximated by
s. Figure 43 sh
sure a maxim
2 N/m for q. T
e width. If yo
of three‐dimen
LLER CONTACT AR
hile doing the
large gaps. A
LDED STRUCTURE
sing the Euler
tion along the
and I is the s
n of a flap, 1 µ
a 4th order p
0,
. Here u is t
hows the w(x)
mum distortio
This model ass
u look carefu
nsional micros
REA
ese experimen
A SiN flap of 8
ES
r‐Bernoulli eq
e x direction o
second mome
µm and b is th
polynomial:
0, 0 0
the distortion
) when the va
on of 2.4µm
sumes that th
lly you might
structures
nts. As shown
0 by 725 µm
uation:
of the flap, q is
ent of area. In
e width of the
0,
n, L is the leng
alues are filled
m from Figure
e whole flap b
see that in F
in Figure 42
is very rigid.
s the distribut
this case
e flap: 80µm.
. Solvi
,
gth of the flap
d in. Now that
e 42. Filling
bends as a wh
igure 42 the b
there is bend
To deform th
ted load (forc
, wher
ing this funct
, we
ps and x the p
t w(x) is know
in the value
hole, and the
bending on th
Page 33
ding in the
his flap we
ce per unit
re h is the
tion when
acquire
osition on
wn we find
es for the
bending is
he edge is
Surface te
larger tha
flaps. We
resulting
510,5 N/
really larg
FIGURE 43 A
1572 N/m
We need
related to
look at th
the flap,
using the
whole len
µm2) we
If we com
constant
seperatio
1572 N/m
5.2.4 As you m
letter wit
images of
Figure 44
underetc
ension driven
an the bendin
e redo the cal
in a q of 419
m Multiplying
ge for such sm
APPROXIMATION
m2. This is a m
to keep into
o the distance
he torque on
510.5 N/m w
e formula for
ngth of 800µm
get 0.83∙107N
mpare this fo
which is bet
on is the rough
m2. This is a m
LIFTING OBJEmight have see
th the same e
f the lifted let
4b shows the
hing through
fabrication o
ng on the hin
culation for t
9N/m. We tak
g this with th
mall device.
N OF THE DISTOR
uch smalle th
account the t
e over the fla
the right loca
we get a force
energy Ub , w
m and then d
N/m2 for the ad
orce with van
tween 10‐19 a
hness betwee
uch smalle th
ECTS OUT OF T
en on the cov
experimental
tters.
hole we mad
this hole can
of three‐dimen
ge side. This
he amount be
ke the average
he length of t
RTION
han the adhesi
torque that is
ap. So when w
ation of the st
of 36.5 N/m
where ∙eviding by th
dhesive force
der Waals fo
and 1020, and
en to plates an
han the adhesi
THE PLANE er and in Figu
setup as used
e in the desig
also be seen i
nsional micros
is to be expe
ending as it is
e value as go
he structure
ion force, and
asserted on t
we compare t
tructure. If we
at L2. To calcu
∙ . So this g
e minimal su
needed to ke
orce, which is
d h is the sur
nd in our case
ion force, and
ure 44b, this e
d in the whole
gn so that und
in this figure a
structures
ected because
s on the hinge
od estimation
of 720 µm re
d we must con
the structure.
two different
e take the fac
ulate the torq
gets us a F of
rface that nee
eep the flaps t
s given as
rface seperati
e we will assu
d we must con
experiment w
e project we m
deretching wo
as I have high
e on this side
e side of the f
n of the force
esults in a for
nclude that ot
Figure 37 sho
forces on this
tor times t
que we need t
7.5 N/m . W
ed to keep th
together.
(6), wh
ion between
me it 15nm. T
nclude that ot
as a success a
made Scannin
ould free the
lighted it with
the hinges p
flaps, which i
e asserted on
rce of 0.37 N
ther forces pla
ows how mom
s structure w
he force at th
to calculate t
When taking th
he flaps toget
here A is the
to plates. Th
This results in
ther forces pla
as well. After
ng Electron M
arm. The effe
h a white circl
Page 34
ull on the
s 1.67µm,
the flaps:
. Which is
ay a role.
mentum is
we need to
he edge of
he energy
his for the
her(720x1
Hamaker
he surface
a force of
ay a role.
lifting the
Microscope
ect of this
e.
Surface te
FIGURE 44 (
If lifting f
pull the le
FIGURE 45 (
FIGURE 46 T
ension driven
(A) HOLE IN THE
fails the struct
etter to the fl
(A) LIFTING OF LE
TOP VIEW OF LIF
fabrication o
ARM WAS NEED
ture won’t ret
oor of the cav
ETTER FAILED (B)
FTER LETTERS
of three‐dimen
DED FOR ETCHING
turn to its orig
vity, and gluin
) LIFTED LETTER O
nsional micros
G FREE THE ARM
ginal position
ng the letter to
O
structures
M WITH THE LETT
because wate
o the floor. Re
ER (B) LIFTED 'LE
er will come u
esults of this is
ETTER ‘TWENTE’
under the stru
s shown in Fig
Page 35
ucture and
gure 45a.
Surface tension driven fabrication of three‐dimensional microstructures Page 36
6 CONCLUSION In earlier work it was already proven that folding with capillary forces is a easy and predictive way to create
three dimensional micro structures. But these works were with liquids that solidified and were left behind in
the structure. The decision was made to overcome this by using demi water for folding. Which would
evaporate totally and leave nothing behind. A theoretical model was made for predicting the folding behavior
of the structures.
From experiments it was clear that the folding mechanism followed the theoretical model almost to the letter.
Experiments done with variation of the contact angle by changing the surface characteristics of the structures
revealed the folding progression followed the deviations as expected in the theoretical model. Experiments
with varying contact angles revealed that the capillary force is 70 times larger than the force asserted by the
hinges. Making them ideal for folding.
The choice for using water was made because in theory nothing will be left behind in the structures because
the water evaporates. In our experiments it became clear that a residue is left in the seam of the structures.
Further experiments revealed that this residue has an adhesive force of 0.83∙107 N/m2. Which is much larger
than the van der Waals power, which is 1571 N/m2. So we can conclude that other forces play a role in this
adhesion.
We need to determine what this consists of. One might think of a combination of adhesive forces of the
material with for example electrostatic forces. Further experimentation is needed.
Experiment with contact area variation resulted also in an unexpected bending of the flaps. As shown in Figure
42. We estimated the force needed to bend a flap as 0.37 N. Illustrating once again that the capillary forces are
really large.
When the structures fold completely, every single time the flaps of the structure folds seamlessly. To test this
further new structures where created with varying flap widths over the length. Still the flaps folded seamlessly,
meaning that the hinges were stretched out on one end and folded on the other end. Concluding once again
that the capillary forces are really large.
Experiments were done trying to lift added structures to the normal folding structure. It was no problem to lift
this added structure from the plane. We made a micro billboard for “University Twente” and lifted this out of
the plane. This opens new opportunities we could try create more elaborate self‐assembling structures which
work on this principle.
Surface te
6.1 R
There are
the struc
keeping t
together.
any other
der Waal
We have
every sing
nozzle lik
the midd
experime
FIGURE 47 T
FIGURE 48 T
Close up
created h
of water
the drop
channel s
ension driven
ECOMMEND
e still some un
cture from fol
this structure
. Folding expe
r forces keepi
s interaction.
to consider n
gle template
ke that of an i
dle of the str
ents. Figure 48
TEMPLATE OF A
TOPVIEW OF STR
p images mad
have a diamet
on the chann
of water to
so that gravity
fabrication o
DATION
nanswered qu
ding back. W
es from foldin
eriments with
ng these stru
new ways of d
is not a good
nkjet printer.
ructure. For t
8 and Figure 4
CUBE WITH A CH
RUCTURES WITH
e by a SEM s
ter of 34µm. I
nel did not res
get through
y will generate
of three‐dimen
uestions. Like w
We have to an
ng back. It is
hout this subs
cture togethe
elivering wate
method for m
Or delivering
his last solut
49 are SEM ph
HANNEL (TOPVIEW
CHANNELS
how us the ri
nitial experim
sult in the wa
the channel,
e enough pres
nsional micros
what is the su
alyze this sub
probable th
stance need t
er. One can th
er droplets to
mass producti
g water from
tion the grou
hotos showing
W LEFT OPTICAL
idges created
ments by holdi
ater flowing t
a suggestion
ssure to get th
structures
ubstance that
bstance to ge
at more than
o be perform
ink of electro
the structure
on. We could
the bottom o
p has already
g the structure
L MICROSCOPE, S
by this proce
ing this struct
hrough the ch
n would be to
he water thro
is left on the
t a clear idea
n just the glu
med to determ
static forces,
e. Positioning
consider deli
of the structur
y made some
es from differe
SIDE VIEW ELECTR
ess is shown
ture upside do
hannel. The p
o create a co
ugh the chann
seam, which
a of the force
ue is keeping
mine whether
hydrogen bon
a fiber from t
ivering water
re through a c
e samples to
rent angles.
RON MICROSCOP
in Figure 49.
own and putt
pressure is too
olumn of wat
nels.
Page 37
is keeping
s that are
the flaps
there are
nds or van
the top for
through a
channel in
do initial
PE)
The holes
ing a drop
o large for
ter on the
Surface te
FIGURE 49 C
7 BIB1. www.m
2. Capilla
Lionel Do
3. MEMS
4. Elastoc
Ondarçuh
5. Applica
1994, Sen
6. Casimi
L. Klimch
7. MATER
8. Surface
Yeatman
systems,
9. Pierre
Science+B
10. Critica
s.l. : Ame
ension driven
CHANNEL
BLIOGRAP
mems.sandia
ary Origami: S
oppler, Jose´ B
. R.R.A. Syms
capillary fabri
hu, R. G. P. Sa
ations of fluo
nsors and Act
ir and van der
hitskaya, U. M
RIALS ANALYS
e Tension‐Pow
, Victor M. B
2003.
e‐Gille de Ge
Business Med
al Review: Ad
erican Vacuum
fabrication o
HY .gov, Sandia N
Spontaneous
Bico, Benoıˆt
, E.M. Yeatma
ication of thre
anders, J. Sun
orocarbon pol
uators, Vol. 19
r Waals forces
Mohideen and
IS OF FLUORO
wered Self‐Ass
Bright and Ge
nnes, Fançoi
dia, Inc., 2003.
dhesion in surf
m Society, 199
of three‐dimen
National Labo
Wrapping of
Roman, and C
an, V.M. BRig
ee‐dimensiona
daram, M. Elw
lymers in mic
994, pp. 136‐1
s between two
V. M. Mostep
OCARBON FILM
sembly of Mic
orge M. Whit
se Brochard‐
.
face micromec
7. S0734‐211X
nsional micros
oratories SUM
f a Droplet wi
Charles N. Ba
ght, and G.M.
al microstruct
wenspoek, an
cromechanics
140.
o plates or a s
panenko. 200
MS. J. Elders,
crostructures—
tesides. Vol.
‐Wyart. Capil
chanical struc
X(97)02301‐9
structures
MMiT(TM) Tec
ith an Elastic
roud. 156103
Whitesides. 1
tures. J. W. va
nd N. R. Tas. 9
and microma
sphere lens ab
00, PHYSICAL R
H. V. Jansert
—The State‐of
12 No. 4, s.l.
llarity and W
ctures. Mabou
9.
chnologies.
Sheet. Charlo
3, s.l. : Physica
12,4, 2003.
an Honschote
97, 2010, APP
achining. Jans
bove a plate m
REVIEW A.
and M. Elwen
f‐the‐Art. Rich
: Journal of M
Wetting Pheno
udian, Roya a
otte Py, Paul
al Review Lette
en, J. W. Bere
PLIED PHYSICS
sen, H.V., et
made of real m
nspoek.
hard R. A. Sym
Microelectrom
omena. Paris
and Howe, Ro
Page 38
Reverdy,
ers, 2007.
nschot, T.
LETTERS.
al., et al.
metals. G.
ms, Eric M.
mechanical
: Springer
oger T. 15,
Surface tension driven fabrication of three‐dimensional microstructures Page 39
8 APPENDIX – PROCESS DOCUMENTS
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Capillary origami. Approach 3. Silicon nitride structure on a silicon support with flap deviations 1. Introduction 1.1 Design description 1.2 Explanation of typical process steps 1.3 Masks 2. Mask layout (overview) 3. Process outline wafer 4. Specific design parameters 5. Procesparameters 5.1 Wafer selection 5.2 Top wafer processing 5.3 Bottom wafer processing 5.4 Anodic bonding 6. Processdata form
Projec
ProjecAutho
1
1.1 This Hons The are ftheylengttheroverhingrelat
Figure
ctnr. : Number
ct : Project or : J.Sunda
Introduc
Design d
structure is dschoten.
flaps in thesefive differenty tend to foldth. You can e might be torcome this toe on one endtively relaxed
e 1 structure w
D1
D2
r
aram
ction
descriptio
developed o
e structures t type of strud seamlessly. see this in Fiorsion in theoroidal force d of the strucd.
with decreasing
2
on
n the structu
are shaped ductures. One So this strucgure 1 where hinges. Queor will therecture will be
flap widths
Revision
Rev. byFile
ure defined i
differently totype of struccture is madee the width Destion is whete be a seam. Istretched ou
: 01Page
: J.Sundaram:procesdocum
n the proces
o assess diffecture will tese of flaps thaD1 is larger tther these flaIf they wouldut while the
mment approach
s document
rent aspectst torsion. What decrease inhan D2.Wheaps will closed close seamhinge on the
: 2 of 23: 2010‐0
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of J.W. van
s of folding. Then the flapsn width overen these flapse seamlessly lessly then the other end w
3
05‐05
There s fold, the s fold and he will be
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Next type of structures have flaps of different width, the left flap will have a smaller width then the right one as shown in Figure 3, the width D2 is larger than D1. Again we will test whether these flaps will fold seamlessly. And if they do they can fold in two ways, the ends of the flaps meet eacht other, or one end of the flap will meet halfway of the other flap as shown in Figure 4. In the first case both the angles of the flaps will be the same, in the second case the angles will be different, ɸ1 is not equal to ɸ2.
Rear view
Front view
Figure 2 distortion of the hinges
Projec
ProjecAutho
Figure
Thirdthat phenhing
Figure
ctnr. : Number
ct : Project or : J.Sunda
e 3 structure w
d type of strufolded strucnomena we wes to see wh
e 4 possible ou
D1
r
aram
with different fla
uctures will hctures tend towill vary the hat kind of ef
tcome for foldi
D2
ap widths
have a varyino stay foldedcontact surfaffect these va
ing a structure
Revision
Rev. byFile
ng contact sud despite of tace of the flaariables have
with different f
: 01Page
: J.Sundaram:procesdocum
rface. Previohe elastic foaps and we we.
flap widths
mment approach
ous experimerces in the hwill vary the e
: 4 of 23: 2010‐0
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ents have shoinges. To teselasticity of t
3
05‐05
own st this the
Projec
ProjecAutho
Figure
The flapsfoldeedgeoverprop
ctnr. : Number
ct : Project or : J.Sunda
e 5 structure w
edges of thes (Figure 6 a)ed the stay foes as shown ircome unaligperly.
d
d
r
aram
with varying con
e flaps make c. This is beneolded. To tesin Figure 6 b gment and er
d
d
ntact surface
contact realleficial for thest how this pand Figure 7rrors in proce
d
d
d
Revision
Rev. byFile
y well due toe adhesive prroperty varie7. The edges essing. Small
: 01Page
: J.Sundaram:procesdocum
o the 45 degrroperties of tes we devisehave to be aer form facto
d
d
mment approach
rees slope onthese structud a structureat least 5µm ors will not b
d
d
: 5 of 23: 2010‐0
3.doc
n the edges oures. Ones the with flexiblin width duebe produces
3
05‐05
of the hey are e e to
d
d
Projec
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Figure
Figur
ctnr. : Number
ct : Project or : J.Sunda
e 7 structures w
re 6 (a) standard
r
aram
with flexible ed
d 45 angle edge
dges
e (b) flexible ed
Revision
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dge
: 01Page
: J.Sundaram:procesdocum
mment approach
: 6 of 23: 2010‐0
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3
05‐05
Projec
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Last expefold timeand This undethe uwill m
Figure
ctnr. : Number
ct : Project or : J.Sunda
but not leasteriment we cthese letterse that the flapthus hang fre
design has aer etching tounder etchinmake it poss
e 8 structure w
r
aram
t we will try created strucs will be liftedps are undereely like the
a small hole i perform weg not to freeible for the e
with a letter
to lift a strucctures with thd from the pr etched the lflaps.
n the ‘arm’ tell. The additie the right flaetchant to re
Revision
Rev. byFile
cture of the she letters of tplane and weletters will be
hat is holdinion to the strap from the ceach in the ce
: 01Page
: J.Sundaram:procesdocum
surface usingthe universit will have a me etched free
g the letter. ructure whiccenter flap asenter of the a
mment approach
g this folding ty on the flapmicro billboae from the u
This hole is mh holds the ls shown in Fiarm.
: 7 of 23: 2010‐0
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action. For tps. When theard. In the sanderlying sili
made for theetter can cauigure 9. The h
3
05‐05
this e flaps me icon,
e use hole
Projec
ProjecAutho
Figure
1.2 In stsilicoprevsilico As alit is ninter
1.3 Exam ThreFOLDGEOUND
ctnr. : Number
ct : Project or : J.Sunda
e 9 where it can
Explana
ep 20, plasmon wafer. Thvent stiction oon is complet
lready statednecessary torrupted.
Masks
mple:
ee masks are D :M :D:
r
aram
n go wrong wit
ation of typ
ma etching byhis etching teof the free sttely removed
d in the prev make a hole
needed: : Defin: Defin
Defin
th underetching
pical proce
y (SF6, Oxfordechnique doetanding strucd by the plas
ious paragrae in the arm s
nition of foldnition of finanition of spac
Revision
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g
ess steps
d ) is chosen es not affect tctures by adhma underetc
ph, when usso that the u
ding locationsl geometriesce in the silic
: 01Page
: J.Sundaram:procesdocum
as process sthe silicon nihesion due toch under the
ing the strucunder etching
s. s of the structcon to be und
mment approach
tep for the uitride structuo capillary fo folding flaps
cture with theg process wo
tures deretched
: 8 of 23: 2010‐0
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underetchingure. We are aorces, since ths.
e arm and leon’t get
UN GE FO
3
05‐05
g of the able to he
tters,
ND EOM OLD
Projec
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2
Filen
Figupurp
posit
3
Ste
1.
2.
ctnr. : Number
ct : Project or : J.Sunda
Mask lay
name: maske
re above: paple = UND)
tion de
DeOuDe
Process
ep
Substra(#subs0
Cleanin(#cleanEtching(#etch0
r
aram
yout (ove
erCapOr_fluid
rt of the mas
scription
efinition of unutline of the gefinition of fo
s outline
Process
ate selection001)
ng Standard n003) g HF (1%) use028)
erview)
dchannelvJ3.
sk showing s
nderetchinggeometriesolding lines
wafer
description
n ‐ Silicon <10
er made
Revision
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.cif
ome of the s
00> OSP
: 01Page
: J.Sundaram:procesdocum
structures (re
code
UND GEOM FOLD
mment approach
ed = GEOM; g
layer
Cross‐sect
: 9 of 23: 2010‐0
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green = FOLD
inside whi
Inside whiInside blacInside whi
tion after pro
3
05‐05
D;
te / black
te ck te
ocess
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3. LPCVD SiRN ‐ low‐depostion rate (#depo002)
4. Lithography ‐ Olin 907‐17 (#lith057) Lithography ‐ Postbake standard (#lith009) Plasma etching SiN (Etske) (#etch004)
5. Stripping of Olin PR by oxygen plasma Tepla 300E (#lith017) Cleaning Standard (#clean003) Etching HF (1%) user made (#etch028)
6. LPCVD SiRN ‐ low‐depostion rate (#depo002)
7. Lithography ‐ Olin 907‐17 (#lith057) Lithography ‐ Postbake standard (#lith009) Plasma etching SiN (Etske) (#Etch 072)
8. Stripping of Olin PR by oxygen plasma Tepla 300E (#lith017) Cleaning Standard (#clean003)
9. Lithography ‐ Olin 907‐17 (#lith057) Lithography ‐ Postbake standard (#lith009) Etching HF (1%) user made (#etch028) Plasma etching of Silicon ‐ standard (Oxford) (#etch013)
10. Stripping of Olin PR by oxygen plasma Tepla 300E (#lith017)
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Projec
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4
ctnr. : Number
ct : Project or : J.Sunda
Specific
75µ
r
aram
c design
µm
paramet
Revision
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ers
75µm
: 01Page
: J.Sundaram:procesdocum
mment approach
75µm
: 12 of 2: 2010‐0
3.doc
23
05‐05
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5 Process parameters Top wafer: p‐type, <100> oriented, DSP
5.1 Wafer selection (only a top wafer)
Step Process Process parameters Design related parameters and Remarks
1. Substrate selection ‐ Silicon <100> OSP (#subs001)
CR112B / Wafer Storage Cupboard Supplier: Orientation: <100> Diameter: 100mm Thickness: 525µm +/‐ 25µm Polished: Single side Resistivity: 5‐10Ωcm Type: p
silicon wafer
2. Cleaning Standard (#clean003)
CR112B / Wet‐Bench 131 HNO3 (100%) Selectipur: MERCK HNO3 (69%) VLSI: MERCK • Beaker 1: fumic HNO3 (100%), 5min • Beaker 2: fumic HNO3 (100%), 5min • Quick Dump Rinse <0.1µS • Beaker 3: boiling (95°C) HNO3 (69%), 10min • Quick Dump Rinse <0.1µS • Spin drying
wet chemical cleaning of the wafer
3. Etching HF (1%) user made (#etch028)
CR116B / Wet‐Bench 2 HF (1%) VLSI: MERCK 112629.500 • Quick Dump Rinse <0.1µS • Spin drying
4. LPCVD SiRN ‐ low‐depostion rate (#depo002)
CR125C / Tempress LPCVD new system 2007
program: SiRN01/N2 Tube: G3 • Use 5‐8 boat fillers in front and back of the boat to achieve specifications • SiH2Cl2 flow: 77.5 sccm • NH3 flow: 20 sccm
Thickness SiRN: 1000 nm
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• temperature: 820/850/870°C• pressure: 150 mTorr • deposition rate: ± 4 nm/min • Nf: ± 2.18 • Stress (range): 200‐280 Mpa • Boat position 12: 200 MPa (centre of the boat) •Boat position 1: 280 MPa (front of the boat) • Uniformity/wafer: <2% • Uniformity over the boat: (20 wafers): < 8%
5. Lithography ‐ Olin 907‐17 (#lith057)
CR112B / Suss Micro Tech Spinner (Delta 20) Hotplate 120 °C: • Dehydration bake (120°C): 5min HexaMethylDiSilazane (HMDS): • Spin program: 4 (4000rpm, 20sec) Olin 907‐17: • Spin program: 4 (4000rpm, 20sec) Hotplate 95 °C: • Prebake (95°C): 90s CR117B / EVG 620 Electronic Vision Group 620 Mask Aligner: • Hg‐lamp: 12 mW/cm 2 • Exposure Time: 4sec CR112B / Wet‐Bench 11 Hotplate 120°C (CR112B or CR117B): • After Exposure Bake (120°C): 60sec Developer OPD4262: • Time: 30sec in Beaker 1 • Time: 15‐30sec in Beaker 2 • Quick Dump Rinse <0.1µS • Spin drying
Mask FOLD
6. Lithography ‐ Postbake standard (#lith009)
CR112B / Hotplate 120°C • Time: 30min
7. Plasma etching SiN (Etske) (#etch004)
CR102A / Elektrotech PF310/340 Dirty chamber Styros electrode • Electrode temp.: 10°C • CHF3 flow: 25sccm
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• O2 flow: 5sccm • pressure: 10mTorr • power: 75W Etchrate SiN = 50nm/min (for VDC=‐460V) Etchrate SiN = 75 nm/min (for VDC = ‐580V) Etchrate Olin resist = 95nm/min If DC‐Bias < 375V apply chamber clean (#etch003)
8. Stripping of Olin PR by oxygen plasma Tepla 300E (#lith017)
CR102A / Tepla 300EBarrel Etcher (2.45 GHz) Multipurpose sytem • O2 flow: 200sccm (50%) • Power: 500W • Pressure: 1.2 mbar • Time: 10 min for 1‐3 wafers, 400 nm/min • Time: 20 min for 4‐10 wafers • End point detection by visual inspection of the plasma color. • Blue color means still photoresist on the wafer, purple means clean.
9. Cleaning Standard (#clean003)
CR112B / Wet‐Bench 131 HNO3 (100%) Selectipur: MERCK HNO3 (69%) VLSI: MERCK • Beaker 1: fumic HNO3 (100%), 5min • Beaker 2: fumic HNO3 (100%), 5min • Quick Dump Rinse <0.1µS • Beaker 3: boiling (95°C) HNO3 (69%), 10min • Quick Dump Rinse <0.1µS • Spin drying
10. Etching HF (1%) user made (#etch028)
CR116B / Wet‐Bench 2 HF (1%) VLSI: MERCK 112629.500 • Quick Dump Rinse <0.1µS • Spin drying
11. LPCVD SiRN ‐ low‐depostion rate (#depo002)
CR125C / Tempress LPCVD new system 2007
program: SiRN01/N2 Tube: G3 • Use 5‐8 boat fillers in front and back of the boat to achieve specifications • SiH2Cl2 flow: 77.5 sccm • NH3 flow: 20 sccm
200 nm thickness SiRN (to be varied for different wafers) Note: in the first run, the thickness was 100 nm
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• temperature: 820/850/870°C • pressure: 150 mTorr • deposition rate: ± 4 nm/min • Nf: ± 2.18 • Stress (range): 200‐280 Mpa • Boat position 12: 200 MPa (centre of the boat) •Boat position 1: 280 MPa (front of the boat) • Uniformity/wafer: <2% • Uniformity over the boat: (20 wafers): < 8%
12. Lithography ‐ Olin 908‐35 (#lith059)
CR112B / Suss Micro Tech Spinner (Delta 20) Hotplate 120 °C: • Dehydration bake (120°C): 5min HexaMethylDiSilazane (HMDS): • Spin program: 4 (4000rpm, 20sec) Olin 908‐35: • Spin program: 4 (4000rpm, 20sec) Hotplate 95 °C: • Prebake (95°C): 120s CR117B / EVG 620 Electronic Vision Group 620 Mask Aligner: • Hg‐lamp: 12 mW/cm 2 • Exposure Time: 9sec CR112B / Wet‐Bench 11 Hotplate 120°C (CR112B or CR117B): • After Exposure Bake (120°C): 60sec Developer OPD4262: • Time: 30sec in Beaker 1 • Time: 15‐30sec in Beaker 2 • Quick Dump Rinse <0.1µS • Spin drying
13. Lithography ‐ Postbake standard (#lith009)
CR112B / Hotplate 120°C • Time: 30min
14. Plasma etching SiN (Etske) (#Etch 072)
CR102/ Electrotech PF310/340 Application: roughening of SiRN for Pt adhesion remarks: If Silicon surface is exposed to plasma us a short etch time
Mask GEOM
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Sputter directly after etching step Pt layer (maximum delay time 10 min) Dirty chamber Styros electrode • Electrode : 10 °C • SF6: 30 sccm • O2: 5 sccm • pressure: 40 mTorr • Power: 60 Watt • Time: 30 sec
15. Stripping of Olin PR by oxygen plasma Tepla 300E (#lith017)
CR102A / Tepla 300EBarrel Etcher (2.45 GHz) Multipurpose sytem • O2 flow: 200sccm (50%) • Power: 500W • Pressure: 1.2 mbar • Time: 10 min for 1‐3 wafers, 400 nm/min • Time: 20 min for 4‐10 wafers • End point detection by visual inspection of the plasma color. • Blue color means still photoresist on the wafer, purple means clean.
16. Cleaning Standard (#clean003)
CR112B / Wet‐Bench 131HNO3 (100%) Selectipur: MERCK HNO3 (69%) VLSI: MERCK • Beaker 1: fumic HNO3 (100%), 5min • Beaker 2: fumic HNO3 (100%), 5min • Quick Dump Rinse <0.1µS • Beaker 3: boiling (95°C) HNO3 (69%), 10min • Quick Dump Rinse <0.1µS • Spin drying
17. Lithography ‐ Olin 908‐35 (#lith059)
CR112B / Suss Micro Tech Spinner (Delta 20) Hotplate 120 °C: • Dehydration bake (120°C): 5min HexaMethylDiSilazane (HMDS): • Spin program: 4 (4000rpm, 20sec) Olin 908‐35: • Spin program: 4 (4000rpm, 20sec) Hotplate 95 °C: • Prebake (95°C): 120s CR117B / EVG 620 Electronic Vision Group 620 Mask Aligner: • Hg‐lamp: 12 mW/cm 2 • Exposure Time: 9sec
Mask UND
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CR112B / Wet‐Bench 11 Hotplate 120°C (CR112B or CR117B): • After Exposure Bake (120°C): 60sec Developer OPD4262: • Time: 30sec in Beaker 1 • Time: 15‐30sec in Beaker 2 • Quick Dump Rinse <0.1µS • Spin drying
18. Lithography ‐ Postbake standard (#lith009)
CR112B / Hotplate 120°C• Time: 30min
19. Plasma etching of Silicon ‐ release (Oxford) (#etch070)
CR102A / Oxford Plasmalab 100 ICPApplication: release of membranes and cantilever SLE = poly‐silicon • Temp.: 20°C • SF6 flow: 120sccm • CM pressure: 10mTorr • ICP power: 600W • He pressure: 20mbar Cleaning step: Optional • CCP power: 7.5W • VDC: ‐40‐55V • Time: 1min SLE etching: xx min
Etchrate SiRN: 5 nm/min
(Mask UND) Procedure of Isotropic etching step:
take quarter piece. Use scotch tape to mount it on a 4” SiN wafer (thickness SiN ~ 1000nm) etchrate measured: Sample wafer 282 ‐ Right‐bottom t =60 min 48 micron underetch t=140 min 120 micron underetch (RO_01) t=160 min 140 micron underetch (RO_02) , this one is OK, so 140 micron
20. Stripping of Olin PR by oxygen plasma Tepla 300E (#lith017)
CR102A / Tepla 300E Barrel Etcher (2.45 GHz) Multipurpose sytem • O2 flow: 200sccm (50%) • Power: 500W • Pressure: 1.2 mbar • Time: 10 min for 1‐3 wafers, 400
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nm/min • Time: 20 min for 4‐10 wafers • End point detection by visual inspection of the plasma color. • Blue color means still photoresist on the wafer, purple means clean.
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5.2 Wafer processing The actual cooking of the wafer processing can be performed online using the TST Technology website, which can be found on: http://tst‐server1/tst/
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Remarks and results (Erwin): (the required changes in the process document and in the mask have been made) ‐masks: 1) Put names on the masks (names have been added, JvH ) 2) dimension of the hinges to critical for specific designs (changes have been made, JvH ). 3) if we want to do the isotropic etching on waferscale mask 3 should be uniform 4) now 2 times thick nitride etching is it possible to do it in one run? 5) for metal hinges design should be in such a way that there is only metal on places where the
hinges are. Process: Step 11) thickness of the second SiN layer was ~ 100nm: see the note (JvH) in step 11
12) step coverage problem: next time we should use thicker resist (908‐35) because of the large step in the SiN (1 micron) 17) see step 12) use 908‐35 After step 18) is the usual HF etching not necessary because step 19) is started with a 1 min directional etch. (see opticonal cleaning step.) 19) Oxford system is used: see recipe below: #etch 070
Plasma etching of Silicon ‐ release (Oxford) (#etch070)
CR102A / Oxford Plasmalab 100 ICP Application: release of membranes and cantilever SLE = poly‐silicon • Temp.: 20°C • SF6 flow: 120sccm • CM pressure: 10mTorr • ICP power: 600W • He pressure: 20mbar Cleaning step: Optional • CCP power: 7.5W • VDC: ‐40‐55V • Time: 1min SLE etching: xx min
Etchrate SiRN: 5 nm/min
For the isotropic dry etching of single crystalline silicon: Maskmaterial:
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Olin 908/35 Load: only a few % of the silicon is etched away Procedure of Isotropic etching step:
- take quarter piece. Use scotch tape to mount it on a 4” SiN wafer (thickness SiN ~
1000nm) - etchrate measured: Sample wafer 282 ‐ Right‐bottom t =60 min 48 micron underetch
t=140 min 120 micron underetch (RO_01) t=160 min 140 micron underetch (RO_02) , this one is OK, so 140 micron
underetch is needed to free the whole structure
- After 90 min of etching the photoresist is not shiny anymore: temperature problem!
This will cause not a serious problem. After stripping the resist the structures are shiny again, see picture below. When we do this isotropic etching step on waferscale, the temperature will be constant due to good Helium backside contact and this problem will not occur. Another option to avoid this effect when using quarter pieces: use fomblin oil to make a good thermal contact with the dummy wafer.
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SEM images:
Overview of the mask: