Commercial CVD diamond films

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E L S E V I E R

Di am o n d an d Re l a t ed Mat e r i a l s 7 (1 9 9 8 ) 5 8 5 - 5 8 8

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Com merc ial CV D dia mo nd films material properties and

their related effects on microwave characteristics

C.P. Schaffer a. I .C. Chen a R.L. Sturdivant b A.T. Hunter ~ R.G. W ilson ~

a Hughes Space and Communications Company, E Segundol CA 90245, USA

b Hughes Sensors and Communications Company, El Segundo, CA 90245, USA

Hughes Research Laboratories, Malibu, CA 90265, USA

Received 23 June 1997: accepzed 19 Aug ust 1997

A b s t r a c t

CVD diam ond offers significant advantage s for the rmal managem ent of .~.%h-power electronics in military and commercial

applications. T he use of diam ond in high-power, high-frequency transm itters and digital processors are two of the most promising

applications. The availability and quality of CV D diam ond for such applications are governed by a sma ll num ber of commercial

suppliers. F ree-standing CVD d iamon d films were ob¢ained from three major US m anufacturer s and characterized using Rama n

spectroscopy, SIMS, FEM, and microwave cavity measurements. The correlation among the individual test methods is investigated

with an emphasis on their relationship to the microwave measurements. A linear relationship between Raman FWH M and

microwave dissipation is demonstrated. The primary tbcus of this research is obtaining accurate and comparable data that can be

employed for m aterial selections and quality control in future prod uction applications. Materials wer e obtained from Crystalline

Materials Corp.. Dianaonex, and No rton Diamon d Film. l(~ 1998 Elsevier Science S.A.

Kevwm'ds. Comm ercial CVD diamon d; Microwave ~haracteristics; Applications

I ntroduction

Thriv ing governmen t and consumer marke ts have

recently inspired rap id progress in electronics teclmology

resul t ing in dramatic increases in packaging densi t ies

and ope ra t ing f requencies . Th is demand i s con t inu ing

to d r ive the deve lopment o f advanced packag ing arch i -

tectures and materials [ ] . Increases in packaging densi-

t ies require higher thermal conductivi ty materials ,

whereas increases in opera t ing f requencies demand

reduced microwave loss factors . These condit ions resul t

in a requirement for a material that not only exhibi ts

high thermal conductivi ty , but also acts as an efficient

microwave d ie lec tr i c. CV D d ia mon d may o ffer p ro found

benefi ts to these and many other applicat ions, but i ts

ul t imate success wil l depend s trongly on the abi l i ty of

the electronics industry both to understand the material

and to develop rel iable man 'ufacturing processes .

Therefore, the object ive of th is paper is not only to

make compar i sons among manufac tu rers , bu t a l so to

* Corr espo ndin g author . Fax: + I 310 416 4512:

e-math cpschaf fer (a ccgate .hat .corn

0925-9635 /98/$19.00 ~-~ 1998 Elsevier Science B.V. A ll r ights reserved.

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S 0 9 2 5 - 9 6 3 5 1 9 7 ) 0 0 2 5 5 - 0

validate inclusive characterizat ion techniques and bring

them. in ,o the context of production progra ms.

Characterizat ion was performed with the use of: l ield

emiss ion scann ing microscopy (FEM), secondary ion

mass spec t romet ry (SIMS), Raman spec t roscopy , and

evanescen t -mode microwave cav i ty measuremen ts .

Raman spectroscopy was chosen because i t has been

shown to p rov ide quan t i t a t ive in fo rmat ion on sp a

(g raph i te ) and sp 3 (d iamo nd) bonded carbon [2 ], and

interna l film stress [3]. The prese nce o f electrically

conductive graphite is presumed to increase the micro-

wave dissipation factor. High intrinsic stress in the tiinls

may increase the incidence of f i lm fi 'acture, which may

ultimately relate to the reli~,bility of the electronics

system. S IM S w as chosen bec, use it provides accu rate

and quanti tat ive infori~, ,at ion on the concentrat ion and

depth of impuri t ies n the films. Several elements, such

as H, N aod B, ha~,e been shown to reduce the resistivity

of diam ond fihns, which would increase the microwa ve

dissipat ion. FEM was used to determine the grain s ize

of the fi lms. Larger grained fi lms should exhibi t a lower

microwave diss ipat ion due to fewer grain boundaries ,

which usual ly contain a s ignificant concentrat ion of



86

C.P. Sch affi'r et al. / Dia mom l amt Rek :ted MateriaL~ 7 ¢ 199~') 58 5-5 88

graphite and H. Finally, microwave measurements were

performed using an evanescent-mode resonant cavity to

determine the f i lms' bulk permitt ivity and dissipation

factor a t 14 GH z.

Character ization experiments were l imited to the

following US manufacturers: Crysta ll ine Mater ia ls

C or po r a t i on ( C M C ) , D ia m one x , a nd N or ton D ia m ond

Film. A quanti ty of f ive coupons were procured from

each vendor a s s tand ard the rmal managem ent grade ,

1 in x 1 in x 0.020 in. coupo ns, with a m irror f inish on

at least one side. The f i lms were a ll deep black in color

and were deemed the most appropr ia te grade for the

aforementioned application~. The deposit ion techniques

and pa ramete r s for the indiv idua l manufac ture r s a re

shown in Table 1.

2 Exper imenta l deta i l s

2 1

S e c o n d a r ) '

ion mass spectrometry

SIMS measurements were pe r formed us ing a PHI

6600 quadrupole ins t rument . Da ta were obta ined by

sputter ing the samples with a pr imary ion beam of 02

and Cs in separate analyses and mass analyzing second-

ary sputtered ions to give a mass survey of a ll e lements

in the mater ia l and their re la tive abundances. Th e analy-

sis area was approximately 250 lam:. Data were obtained

both on th e surface and a few microns below the surface.

Some elements were intentionally lef t out of the results

as they could affect the anonymity of the suppliers.

2 2 Ra ma n f fwetroscop v

Raman spec t ra were measured a t ambient condi t ions

in the backseatter ing geometry. The excita tion radiation

of an ~wgon ion laser with a 5145-A line was focused to

a 100-Bm-diameter beam. A power of approximately

0.24 W was measured at the sample. The scattered l ight

was analyzed by a PC-controlled double spectrometer

followed by a standard photomultiplier tube detection

system. Measurements were performed on both a wide

and a narro w energy loss range: f rom 1000 to

2500 cm ~ t at 20.0 cm ~ resolu tion, and from 1300 to

Table I

Summary of manuhlc turer deposi t ion techniques and charac ter is t ics

Parameter CMC

Dia ~lOlleX Norlo n

Techn ique DC arc jet Hot filament DC arc .jet

Tem perat ure ( C ) 800.980 750- 900 8511 1000

Substm tc Moly bdenum Polysi licon Not avai lable

Subs trate 'ize > 5 in. i 2 in. Not available

Met hane (%t < 3 < 5 < 5

Pressure (Tor r) < 100 10 100 <8 0

Reactor power 80 100 kW 3 60 kW Not a va i la b le

1360 cm-~ a t 4 .0 cm - t r e so lu tion . The Ram an l ine

posit ions and widths were determined by f i t t ing the

measured da ta to a Gauss ian l ine shape . A na tura l type

I I s ingle c rys ta l d iamond was measured for compar ison .

The accuracy of the ene rgy loss measurements was

de te rmined to be +0.6 cm-

2 3 E M mi crowave measuremet i t s

Microwave measurements were pe r formed us ing the

Kent ' (evanescen t-mode) me tho d [4] , which is an

a l te ra t ion of the s tandard re sonant cavi ty technique .

The standard technique uses a c losed cylindrical reso-

nant cavi ty , which i s cha rac te r ized wi th and wi thout the

sample inside, with the difference in the measurements

yielding the permitt ivity and dissipation factor of the

sample. The evanescent-mode technique is different in

that i t is insensit ive to the posit ion of the substra te in

the gap be tween waveguide sec t ions , and no in t ima te

contact is required with the sample. The measurement

error was calculated to be less than 2% with a repeatabil-

i ty of _.+0.5%. Mea surem ents w ere taken at amb ient

condition s a t a nomina l f requency of 14 GHz .

3 Results and discussioh

3 1 Fi eM emi ss i on scwmi ng mi croscopy

Field emission micrographs were taken with a Jeol

. ISM-6310F scanning f ie ld emission microscope. The

grain sizes of the groups were visually approximated

and are labttla~ed in Table 2.

The g rai , : ; i: ,es were com parab le amo ng all groups:

therelbrc , grain size should not be a signif icant factor

in the mic row ave m easurements .

3 2 Secom kt rv i on mass spec t rome t ry

In Fig. I Fig. 2Fig. 3, an average for th e im purit ies in

each group is shown both on the surface and several

microns below. For the purposes of this paper , only H,

N, and B are discussed in detail . The S IMS results fi 'om

all groups exhibited a high amount of H ( typically

400--4000 ppm), which is com mo n in CV D dia mon d, as

most c rys ta l boundar ie s a re hydrogen- te rmina ted . One

coupon in Group A exhib i ted an abnormal ly h igh

concent ra t ion of H. 28 000p pm. Grou ps A and C

Fable 2

Smnmary of coupon gra in s izes

Grain s ize (Bin) Gro up A Gro up B Gro up C

Nucle ation 5 I0 5 15 5 10

Grow th 10 60 50 100 40-80



C P. Schaffer et al. / Diamo nd and Related Materials 7 (1998) 585 -588 587

I o~oo oo

1ooooo

1

~ lOOO

o,o.

OOl

o o o

o oo

l

E l e m e n t

Fig. I . Group A SIMS analysis of impurity concentrations on the

immediate surface and approximately 5 tum below.

1001m

, o0 /I ~

E l e m e n t

Fig 2. Gro up B SIMS analysis of impurity concentrations on the

immediate surface and approximately 5 tum below.

°'° ~ . . . . . ; . . . . . . . .

/

o~ . . ..

E l e m o n t

Nt Cu

Fig. 3. Gr oup C SIMS analysis of impurity concentrations on the

imm ediate surface an d ap proxim ately 5 tuna below.

exhibi ted the highest average concentrat ions of H at

~5 00 0p pm . The concen t ra t ions o f B and N in a l l

g roups were very low (~ ,460 ppm). Gro up C had no

detectable N.

To otgtain a general indicat ion of the fi lms ' puri ty ,

impur i ty concen t ra t ions fo r .every de tec tab le e lemen t in

each g roup were averaged bo th on the su rface and

benea th . The average d i s regarded the concen t ra t ion o f

H due to i ts abundance in al l of the samples. Group A

reduced fro m 1064 ppm at the surface to 352 ppm below

the su rface . Accord ing ly , g roup B d ropped f rom 837 to

482 ppm, and g roup C d ropped f rom 613 to 63 ppm.

Table 3

Rama n spectra summ ary of all coupon group s including a natural

diamond specimen for comparison

Grou p A Group B Group C Natu ra l

average average average diamond

FW HM 6.6 8.4 5.5 4.7

Posi tion 332.4 1332.7 1332.7 332.4

3 3 Raman spectroscopy

The R am an spec t ra resu lt s (Tab le 3 ) fo r Grou p C

exh ibi ted the na rrowes t average F W H M of 5 .5 cm -~ ,

with a variat ion of 13 . Group A fol lowed with an

average FW H M of 6 .5 cm - t and a var ia t ion o f 22 .

Gro u p B e x h ib i te d a n a v e ra g e F W HM o f 8.5 c m -~ a n d

a var ia t ion o f 16 . The max imum peak sh i f t f rom

1332.3 cm -~ (s tress free dia mo nd) was only 1332.9 for

the poorest sample: therefore, the maximum intrinsic

s t ress was -0 .3 G pa [3 ]. I t is a l so impor tan t to no te

that the 0 .6 cm -~ shift is equivalent to the accuracy o f

t h e R a m a n m e a s u re m e n t s .

Examin ing the b road band R ama n spec t ra (F ig . 4 ) ,

i t i s apparen t tha t g roups A and C have add i t iona l

peaks a t ~20 60 cm-~, which is mos t l ike ly the pho to -

luminescence backg round o f g raph i te and amorp hous

carbon [5 ] . However , the typ ica l Raman g raph i te and

am orph ous car bon peaks at 1581 cm - ~ and 1352 cm -

do not show up.

3 .4 . M i c r o w a v e c a v ii 1 m e a s u r e m e n t s

The variance in the permit t iv i ty and dissipat ion

appear to be related as one would expect due to the

change in bulk resis t iv i ty . Averaged resul ts arc presented

in Table 4 . An increase in diss ipat ion is related to an

increase in dielectric constant . Within the groups, Group

A exhibi ted a variance of 6 in permit t iv i ty mid 385

in diss ipat ion, Gro up B exhibi ted a variance of 2 .6 in

permit t iv i ty and 93 in diss ipat ion, and Grou p C

exhibi ted a varianc e of 1.14 in permit t iv i ty and 22

.

4 S ,,: ....... i

I i

f i

~ 3t //

i

1000 1200 1400 16 00 1800 2000 2200 2400

avenumbercrn I

Fig. 4. Representative R aman spectra of each coupon group including

a natural diamond specimen for comparison.



588 C P. Scha],] t r el aL / Dia mo nd am /R eh tte d MateriaL~ 7 t i 99~V) 585 58~

Table 4

Summary of the dielectric constant and loss tangent at 14 GHz as

measured by an evanescent-mode technique

Parameter Group A Group B Group C

average average average

Dielectric constant 5.716 5,867 5.736

Loss tangent 0.005 0.011 0.001

in diss ipation. G roup C, which had the lowest variance,

also had the lowest diss ipat ion. One coupon in Group

A ( Fig. 5) seemed to have an ab norma lly large variat ion

in permittivity and dissipation. The average dissipation

for Group A was 0.005, whereas this coupon exhibi ted

a diss ipat ion of 0 .01. Examining the SIMS resul ts tbr

that coupo n revealed an extremely high H concentrat ion

of 2 .8 as well as abnorm ally high concentrat ions of

AI, CI, Na, St, Ca, and Fe. These results would lead

one to conclude that the sample had been contam inated,

which was the cause of the excessive dissipation factor.

4 Conclusion

The dependence of the microwave diss ipat ion factor

on the Raman FWHM seems to correlate wel l and

follows a linear tren d (Fig. 5) relating an increase in

Raman FWHM with an increase in microwave loss

factor. Th ere is clearly a distinct sep, 'tration between the

CVD d iamond manutac tu rers and a vary ing amount o f

scat ter wi thin each group. Group A, which exhibi ted

the largest intergroup scatter also had tile highest impu-

rity levels. In general, the scatter within the groups was

I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

,u

i

O mpO • •

i

•

C

u, i i ....

k o |e T INMIIm

aN

~N

QW

m

n •

m , ....

Fig. 5. Raman FWtlM plotted against microwave dissipation factor

at 14 GHz.

dominated by the microwave loss factor as opposed to

the Ram an FW HM . In add i t ion , the resu l ts o f the SIMS

surveys suggest that coupon puri ty and cleanl iness play

a key role in the microwave loss factor and not in the

R a m a n F W H M .

Curren t ly , Raman measurements have been shown to

provide rel iable info rmat ion ab ou t the f ilm s t ress , sp 2

and

sp a

bonded carbon content , loss tangent , and overal l

quality of the films.

In the future, we hope to demonstrate that Raman

FWHM also relates to thermal conduct ivi ty . Due to

these relationships, Raman spectroscopy will l ikely serve

as a key tool with which a single test will allow electron-

ics companies to easi ly screen and monitor many impor-

t an t p roper t ies o f CVD d iam ond th roughout p roduct ion

programs.

5. Future work

Microwave t ransmission l ine measurements (1 MHz

to 50 GH z) are current ly being performed at Georgia

Inst i tute of Technology ut i l izing an advanced NIST

technique. Thermal conduct ivi ty measurements are also

planned pending the resul ts from the lates t NIST

round-robin.

Acknowledgement

The authors would l ike to thank the Defense

Advanced Research Projects Agency, Defense Sciences

Office for funding this research. We would also like to

thank the Naval Research Laboratories for their valu-

able assistance and input.

References

[I]A. Malshe, H. Naseem, W. Brown, L. Schaper, Application of

Diamond Films and Related Materials, 1995, 611.

[2] V. Vorlicek. J. Rosa, M. Vanecek, M. Nesladek, L.M. Stals, Dia-

mond Relat. Mater. 6 11997) 704-707.

[31 L. Bergman, K.F. Turner, P.W. Morrison, R.J. Nemanich, Appli-

cation of Diamond Fihns and Related Materials, 1995, 451.

[41 G. Kent. IEEE Trans. Microwave Theory Techn. 3611988) 1451.

[5] P. Huong, Diamond and Diamond-t , ke Carbon Coatings, 1990.

DI2 D28.

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Commercial CVD diamond films