Upload
ngokhue
View
218
Download
0
Embed Size (px)
Citation preview
EE213 L03A Manufacturing.1 Pingqiang, ShanghaiTech, 2017
EE213Digital Integrated Circuits II
Lecture 03-A: Manufacturing Primer
Prof. Pingqiang Zhou
http://sist.shanghaitech.edu.cn/faculty/zhoupq/Teaching/Spr17/Digital-IC-2.html
Chapte
r 2
Chapte
r 1&
15
EE213 L03A Manufacturing.2 Pingqiang, ShanghaiTech, 2017
More Resources
EE 130/230A @UC Berkeley
EE143 @UC Berkeley
EE213 L03A Manufacturing.3 Pingqiang, ShanghaiTech, 2017
A Brief History
1958: First integrated circuit
Flip-flop using two transistors
Built by Jack Kilby at Texas Instruments
2010
Intel Core i7 mprocessor
- 2.3 billion transistors
64 Gb Flash memory
- > 16 billion transistors
Courtesy Texas Instruments
[Trinh09]
© 2009 IEEE
EE213 L03A Manufacturing.4 Pingqiang, ShanghaiTech, 2017
EEOL and BEOL
http
s://e
n.w
ikip
edia
.org
/wik
i/Fro
nt_
end_
of_
line
http
s://e
n.w
ikip
edia
.org
/wik
i/Back_
end
_of_
line
EE213 L03A Manufacturing.5 Pingqiang, ShanghaiTech, 2017
Outline
A. MOS transistors
B. Fabrication
C. Packaging
EE213 L03A Manufacturing.6 Pingqiang, ShanghaiTech, 2017
EE213 L03A Manufacturing.7 Pingqiang, ShanghaiTech, 2017
Silicon Lattice
Transistors are built on a silicon substrate
Silicon is a Group IV material
Forms crystal lattice with bonds to four neighbors
Si SiSi
Si SiSi
Si SiSi
EE213 L03A Manufacturing.8 Pingqiang, ShanghaiTech, 2017
Dopants
Silicon is a semiconductor
Pure silicon has no free carriers and conducts poorly
Adding dopants increases the conductivity
Group V: extra electron (n-type)
Group III: missing electron, called hole (p-type)
EE213 L03A Manufacturing.9 Pingqiang, ShanghaiTech, 2017
p-n Junctions
A junction between p-type and n-type semiconductor forms a diode.
Current flows only in one direction
EE213 L03A Manufacturing.10 Pingqiang, ShanghaiTech, 2017
Transistor Types
Bipolar transistors
npn or pnp silicon structure
Small current into very thin base layer controls large currents between emitter and collector
Base currents limit integration density
Metal Oxide Semiconductor (MOS) Field Effect Transistors
nMOS and pMOS MOSFETS
Voltage applied to insulated gate controls current between source and drain
Low power allows very high integration
https://en.wikipedia.org/wiki/Transistor
n+
p
GateSource Drain
bulk Si
SiO2
Polysilicon
n+Body
EE213 L03A Manufacturing.11 Pingqiang, ShanghaiTech, 2017
Transistors as Switches
We can view MOS transistors as electrically controlled switches
Voltage at gate controls path from source to drain
g
s
d
g = 0
s
d
g = 1
s
d
g
s
d
s
d
s
d
nMOS
pMOS
OFFON
ONOFF
VDD
A Y
GND
EE213 L03A Manufacturing.12 Pingqiang, ShanghaiTech, 2017
nMOS Transistor
Four terminals: gate, source, drain, body
Gate – oxide – body stack looks like a capacitor
Gate and body are conductors
SiO2 (oxide) is a very good insulator
Called metal – oxide – semiconductor (MOS) capacitor
Even though gate is no longer made of metal*
* Metal gates are returning today!
n+
p
GateSource Drain
bulk Si
SiO2
Polysilicon
n+Body
Polysilicon Aluminum
EE213 L03A Manufacturing.13 Pingqiang, ShanghaiTech, 2017
nMOS Operation
Body is usually tied to ground (0 V)
When the gate is at a low voltage:
P-type body is at low voltage
Source-body and drain-body diodes are OFF
No current flows, transistor is OFF
n+
p
GateSource Drain
bulk Si
SiO2
Polysilicon
n+D
0
S
EE213 L03A Manufacturing.14 Pingqiang, ShanghaiTech, 2017
nMOS Operation Cont.
When the gate is at a high voltage:
Positive charge on gate of MOS capacitor
Negative charge attracted to body
Inverts a channel under gate to n-type
Now current can flow through n-type silicon from source through channel to drain, transistor is ON
n+
p
GateSource Drain
bulk Si
SiO2
Polysilicon
n+D
1
S
ox
Bssub
BfbtC
qNVV
222
+ for P-body,
– for N-body
Modern Semiconductor Devices for Integrated Circuits (C. Hu)
EE213 L03A Manufacturing.15 Pingqiang, ShanghaiTech, 2017
pMOS Transistor
Similar, but doping and voltages reversed
Body tied to high voltage (VDD)
Gate low: transistor ON
Gate high: transistor OFF
Bubble indicates inverted behavior
SiO2
n
GateSource Drain
bulk Si
Polysilicon
p+ p+
EE213 L03A Manufacturing.16 Pingqiang, ShanghaiTech, 2017
Outline
A. MOS transistors
B. Fabrication
C. Packaging
EE213 L03A Manufacturing.17 Pingqiang, ShanghaiTech, 2017
Schematic vs. Layout
VDD VDD
VinVout
M1
M2
M3
M4
Vout2
See http://www.vlsi-expert.com/2014/11/cmos-layout-design.html
n+
p
GateSource Drain
bulk Si
SiO2
Polysilicon
n+D
1
S
EE213 L03A Manufacturing.18 Pingqiang, ShanghaiTech, 2017
CMOS Fabrication: Inverter Cross-section
Typically use p-type substrate for nMOS transistors
Requires n-well for body of pMOS transistors
n+
p substrate
p+
n well
A
YGND VDD
n+ p+
SiO2
n+ diffusion
p+ diffusion
polysilicon
metal1
nMOS transistor pMOS transistor
EE213 L03A Manufacturing.19 Pingqiang, ShanghaiTech, 2017
Well and Substrate Taps
Substrate must be tied to GND and n-well to VDD
Metal to lightly-doped semiconductor forms poor connection called Shottky Diode (https://en.wikipedia.org/wiki/Schottky_diode)
Use heavily doped well and substrate contacts/taps
n+
p substrate
p+
n well
A
YGND V
DD
n+p+
substrate tapwell
tap
n+ p+
EE213 L03A Manufacturing.20 Pingqiang, ShanghaiTech, 2017
The Fabs
Chips are built in huge factories called fabs
Contain clean rooms as large as football fields
Courtesy of International
Business Machines Corporation.
Unauthorized use not permitted.
EE213 L03A Manufacturing.21 Pingqiang, ShanghaiTech, 2017
Growing the Silicon Ingot
From Smithsonian, 2000
EE213 L03A Manufacturing.22 Pingqiang, ShanghaiTech, 2017
CMOS Process at a Glance
Define active areas
Etch and fill trenches
Implant well regions
Deposit and patternpolysilicon layer
Implant source and drainregions and substrate contacts
Create contact and via windowsDeposit and pattern metal layers
Built (roughly) from the bottom up
1. metal 2
2. metal 1
3. polysilicon
4. source and drain diffusions
5. tubs (aka wells, active areas)
One full photolithographysequence per layer (mask)
n+
p substrate
p+
n well
n+p+ n+ p+
EE213 L03A Manufacturing.23 Pingqiang, ShanghaiTech, 2017
oxidationoptical
mask
process
step
photoresist coatingphotoresist
removal
(ashing)
spin, rinse,
dryacid etch
photoresist
development
stepper
exposure
Photolithographic Process
EE213 L03A Manufacturing.24 Pingqiang, ShanghaiTech, 2017
Patterning - Photolithography
1. Oxidation
2. Photoresist (PR) coating
3. Stepper exposure
4. Photoresist development and bake
5. Acid etchingUnexposed (negative PR)Exposed (positive PR)
6. Spin, rinse, and dry
7. Processing stepIon implantationPlasma etchingMetal deposition
8. Photoresist removal (ashing)
mask
SiO2 PR
UV light
EE213 L03A Manufacturing.25 Pingqiang, ShanghaiTech, 2017
Planarization (CMP): Polishing the Wafers
From Smithsonian, 2000
EE213 L03A Manufacturing.26 Pingqiang, ShanghaiTech, 2017
Photoresist overview
There are two types of photoresist:• Positive: exposed area removed by
developer.• Negative: unexposed area removed
by developer.
Mask
Positive ResistNegative Resist
Photoresist is a liquid mixture that can be spun onto a substrate, exposed and
developed into a pattern for subsequent processing.
Typically consists of 3 components:• Resin - a binder that provides mechanical properties (adhesion, chemical
resistance…).• Sensitizer - photoactive compound.• Solvent – e.g. n-butyl acetate, xylene, keep the resist in a liquid form for spin
coating. Its content determines viscosity and hence resist thickness.
Cr
resist
Photoresist
EE213 L03A Manufacturing.27 Pingqiang, ShanghaiTech, 2017
Photomasking
[Kahng]
EE213 L03A Manufacturing.28 Pingqiang, ShanghaiTech, 2017
Mask Cost vs. Engineering Cost for ASIC
EE213 L03A Manufacturing.29 Pingqiang, ShanghaiTech, 2017
Inverter Mask Set (Top View)
Transistors and wires are defined by masks
Cross-section taken along dashed line
GND VDD
Y
A
substrate tap well tap
nMOS transistor pMOS transistor
EE213 L03A Manufacturing.30 Pingqiang, ShanghaiTech, 2017
Detailed Mask Views
Six masks
n-well
Polysilicon
n+ diffusion
p+ diffusion
Contact
Metal
Metal
Polysilicon
Contact
n+ Diffusion
p+ Diffusion
n well
SiO2
n+ diffusion
p+ diffusion
polysilicon
metal1
GND VDD
Y
A
substrate tap well tap
nMOS transistor pMOS transistor
EE213 L03A Manufacturing.31 Pingqiang, ShanghaiTech, 2017
Fabrication Steps - Converter
Start with blank p-type wafer
Build inverter from the bottom up
First step will be to form the n-well
p substrate
n+
p substrate
p+
n well
A
YGND V
DD
n+p+
substrate tapwell
tap
n+ p+
EE213 L03A Manufacturing.32 Pingqiang, ShanghaiTech, 2017
1. Oxidation
Grow SiO2 on top of Si wafer
900 – 1200 C with H2O or O2 in oxidation furnace
p substrate
SiO2
EE213 L03A Manufacturing.33 Pingqiang, ShanghaiTech, 2017
2. Photoresist
Spin on photoresist
Photoresist is a light-sensitive organic polymer
p substrate
SiO2
Photoresist
EE213 L03A Manufacturing.34 Pingqiang, ShanghaiTech, 2017
3. Lithography
Expose photoresist through n-well mask
Strip off photoresist defined by n-well mask
p substrate
SiO2
Photoresist
EE213 L03A Manufacturing.35 Pingqiang, ShanghaiTech, 2017
4. Etch
Etch oxide with hydrofluoric acid (HF)
Seeps through skin and eats bone; nasty stuff!!!
Only attacks oxide where resist has been exposed
p substrate
SiO2
Photoresist
EE213 L03A Manufacturing.36 Pingqiang, ShanghaiTech, 2017
5. Strip Photoresist
Strip off remaining photoresist
Use mixture of acids called piranah etch
Necessary so resist doesn’t melt in next step
p substrate
SiO2
EE213 L03A Manufacturing.37 Pingqiang, ShanghaiTech, 2017
6. n-well
n-well is formed with diffusion or ion implantation
Diffusion
Place wafer in furnace with arsenic (As) gas
Heat until As atoms diffuse into exposed Si
Ion Implanatation
Blast wafer with beam of As ions
Ions blocked by SiO2, only enter exposed Si
n well
SiO2
EE213 L03A Manufacturing.38 Pingqiang, ShanghaiTech, 2017
7. Strip Oxide
Strip off the remaining oxide using HF
Back to bare wafer with n-well
Subsequent steps involve similar series of steps
p substrate
n well
n+
p substrate
p+
n well
A
YGND V
DD
n+p+
substrate tapwell
tap
n+ p+
SiO2
n+ diffusion
p+ diffusion
polysilicon
metal1
EE213 L03A Manufacturing.39 Pingqiang, ShanghaiTech, 2017
Polysilicon
Deposit very thin layer of gate oxide
< 20 Å (6-7 atomic layers)
Chemical Vapor Deposition (CVD) of silicon layer
Place wafer in furnace with Silane gas (SiH4)
Forms many small crystals called polysilicon
Heavily doped to be good conductor
Thin gate oxide
Polysilicon
p substraten well
EE213 L03A Manufacturing.40 Pingqiang, ShanghaiTech, 2017
Polysilicon Patterning
Use same lithography process to pattern polysilicon
Polysilicon
p substrate
Thin gate oxide
Polysilicon
n well
EE213 L03A Manufacturing.41 Pingqiang, ShanghaiTech, 2017
Self-Aligned Process
Use oxide and masking to expose where n+ dopants should be diffused or implanted
N-diffusion forms nMOS source, drain, and n-well contact
p substraten well
n+
p substrate
p+
n well
A
YGND V
DD
n+p+
substrate tapwell
tap
n+ p+
SiO2
n+ diffusion
p+ diffusion
polysilicon
metal1
EE213 L03A Manufacturing.42 Pingqiang, ShanghaiTech, 2017
N-diffusion
Pattern oxide and form n+ regions
Self-aligned process where gate blocks diffusion
Polysilicon is better than metal for self-aligned gates because it doesn’t melt during later processing
p substraten well
n+ Diffusion
EE213 L03A Manufacturing.43 Pingqiang, ShanghaiTech, 2017
N-diffusion cont.
Historically dopants were diffused
Usually ion implantation today
But regions are still called diffusion
n wellp substrate
n+n+ n+
EE213 L03A Manufacturing.44 Pingqiang, ShanghaiTech, 2017
N-diffusion cont.
Strip off oxide to complete patterning step
n wellp substrate
n+n+ n+
n+
p substrate
p+
n well
A
YGND V
DD
n+p+
substrate tapwell
tap
n+ p+
SiO2
n+ diffusion
p+ diffusion
polysilicon
metal1
EE213 L03A Manufacturing.45 Pingqiang, ShanghaiTech, 2017
P-Diffusion
Similar set of steps form p+ diffusion regions for pMOS source and drain and substrate contact
p+ Diffusion
p substraten well
n+n+ n+p+p+p+
EE213 L03A Manufacturing.46 Pingqiang, ShanghaiTech, 2017
Contacts
Now we need to wire together the devices
Cover chip with thick field oxide
Etch oxide where contact cuts are needed
p substrate
Thick field oxide
n well
n+n+ n+p+p+p+
Contact
EE213 L03A Manufacturing.47 Pingqiang, ShanghaiTech, 2017
Metalization
Sputter on aluminum over whole wafer
Pattern to remove excess metal, leaving wires
p substrate
Metal
Thick field oxide
n well
n+n+ n+p+p+p+
Metal
EE213 L03A Manufacturing.48 Pingqiang, ShanghaiTech, 2017
Design Rules
Interface between designer and process engineer
Guidelines for constructing process masks
10
90
Well
Active3
3
Polysilicon
2
2
Different PotentialSame Potential
Metal13
3
2
Contactor Via
Select
2
or6
2Hole
EE213 L03A Manufacturing.49 Pingqiang, ShanghaiTech, 2017
Layout
Minimum dimensions of masks determine transistor size (and hence speed, cost, and power)
Feature size f = distance between source and drain
Set by minimum width of polysilicon
Feature size improves 30% every 3 years or so
Absolute dimensions (micron rules)
Scalable design rules: l parameter
- Express rules in terms of l = f/2
- E.g. l = 0.3 mm in 0.6 mm process
A A’
np-substrate Field
Oxidep+n+
In
Out
GND VDD
(a) Layout
(b) Cross-Section along A-A’
A A’
EE213 L03A Manufacturing.50 Pingqiang, ShanghaiTech, 2017
Simplified Design Rules
Conservative rules to get you started
EE213 L03A Manufacturing.51 Pingqiang, ShanghaiTech, 2017
Why Have Design Rules?
To be able to tolerate some level of fabrication errors such as
• Mask misalignment
• Dust
“Interlayer defects include missing material in the vias between two metal layers or between a metal layer and polysilicon; and extra material between the substrate and metal (or diffusion or polysilicon) or between two separate metal layers. These interlayer defects occur as a result of local contamination, e.g., dust particles.”
Isreal Koren and Zahava Koren, “Defect tolerance in VLSI circuits: Techniques and Yield analysis”, Proc of the IEEE, vol. 86, no. 9, pp. 1819-1836, Sept. 1998.
• Process parameters (e.g., lateral diffusion)
• Rough surfaces
EE213 L03A Manufacturing.52 Pingqiang, ShanghaiTech, 2017
Inverter Layout
Transistor dimensions specified as Width / Length
Minimum size is 4l/2l, sometimes called 1 unit
In f = 0.6 mm process, this is 1.2 mm wide, 0.6 mm long
EE213 L03A Manufacturing.53 Pingqiang, ShanghaiTech, 2017
Summary
MOS transistors are stacks of gate, oxide, silicon
Act as electrically controlled switches
Build logic gates out of switches
Draw masks to specify layout of transistors
Now you know everything necessary to start designing schematics and layout for a simple chip!
EE213 L03A Manufacturing.54 Pingqiang, ShanghaiTech, 2017
Outline
A. MOS transistors
B. Fabrication
C. Packaging
EE213 L03A Manufacturing.55 Pingqiang, ShanghaiTech, 2017
Packaging Requirements
Electrical: Low parasitics
Mechanical: Reliable and robust
Thermal: Efficient heat removal
Economical: Cheap
EE213 L03A Manufacturing.56 Pingqiang, ShanghaiTech, 2017
56
Bonding Techniques – Wire Bonding
Lead Frame
Substrate
Die
Pad
Wire Bonding
EE213 L03A Manufacturing.57 Pingqiang, ShanghaiTech, 2017
Bonding Techniques – Flip-Chip Bonding
Solder bumps
Substrate
Die
Interconnect
layers
EE213 L03A Manufacturing.58 Pingqiang, ShanghaiTech, 2017
58
Package-to-Board Interconnect
(a) Through-Hole Mounting (b) Surface Mount
EE213 L03A Manufacturing.59 Pingqiang, ShanghaiTech, 2017
EE213 L03A Manufacturing.60 Pingqiang, ShanghaiTech, 2017
Next Lecture and Reminders
Next lecture
Advanced MOS fabrication
Reminders
Guest lecture topics will be posted by this Wed.
HW1 will be posted this week.
Set up HSPICE/Layout environment ASAP.
Chapte
r 15