Irol /! 3N 'funqpooi\scls^qd lo alnllsul uPrlrauv

Blia dtv

I f I 8l Xl .ugsnV,112 g1ytratrg g

ploqol(I'l'Y

6 68 0 Z (ru, &-tn qsnqrlo g,tsJNrollas 'c'(

18016 Y) 'alottuung 't3o1o4a14J T' slolnrohlqfing'I I'l&

SUOJIOtr

spooN eJnlnf, puB snlBls luasorduoIlBzlJolJBJBIIJrolcnpuoJluros

sturmTypewritten TextProceedings of a Workshop at NIST, Jan. 30 - Feb 2, 1995, published by AIP 1996

Energy Dispersive X-Ray Reflectivity Characterization ofSemiconductor Heterostructures and Interfaces

E. Chasona), T.M. Mayera), Z. Matutinovic Krsteljb) and J. C. Sturmb)

a) Sandia National Laboraiories, Albuquerque, NM 871854350b) Dept. ofElectdcal Engineering, Princrton U., Princetor\ N.J 08544

En6$/ dispsrsiv€ X-ray refle.tivity is a versatil€ tool for anallzinS thil film strucNr.s. kyer lhicknds,i erfare roughn€ss and crnpositior can be d€terrnined wilh a singl€ aond€structiv€ messurment. Use of€ner8y dispersive d€t€ction enables sp€cta to be a.quned in l€ss than 500 s vith a rolating anode X-Iavgenentd, ssking the study ofkinetics possible.

Multiple advanced devrce structures incorporatethin semiconductor heterolayeB to oblain enhancedperfonnance, e.g,, heterojunction bipolar transislors(HBT'S), enhanced mobility FETS and resolrantrumeling diodes. These skuclues require precisecontrol of lhe layer thickness and interfac! morpholo$/for optimal perrormance. we have d€veloped atechnique using enerry disp€rsive X-ray reflectivityO(RR) to characterize these structures with high deplhsensitivity. The pammeters that can be determined fromthis measurement are layer ihickness, composition andsurface/interface roughness. Layer thickness can bedetermined in the range of 3 - 200 Dm wilh 1 5%r€solution and surface and interface rouglmess can be

determined in the range of 0.t - 3 nm with I 20%resolulion.

W€ have applied the XRR technique tochaiacterize C\rD-grown SiGe/Si hetercslructures [U,enabling us to correlate the layer thickness and interface

roughness with the groMi conditions. We have alsoperform€d real-time measurcments during low'€nel$/ion spurtering of semiconductors [2,3] and SiO2 [4] todetermine the kinetics of surface evolution. Thesemeasurements confirmed the preseDce of a rapidroughening instability and enabled us to quantitativelydelermine the value of ion€nhanced transportpanmeters (dimBivity, viscosity) importafi for sputler-morphology evolution.

PRINCPLES OF X.RAY REFLECTII'ITY

The origin of >(RR is ueated itr a number ofpublications, bolh in ao optical multilayer I5l and a

O 1996 American lnslilule of Physics

5t2

diftaction fonnalism 16l, so only a brief featnent willbe presented here. x-ray reflectivily is defined as theratio of the reflected intetrsity lo the incident intensityand is measued as a imction ofthe scattering vector,

k = 41rlhc E sine (t)

where E is lhe energy of the X-ray and 2€ is thescattering angl€. ln canlrasi \vilh X-tay dillraction, X-ray rcflectivity is performed at small values of k wherelhe refl€ctivity can be inteDreted using the F.esn€lequatrons. The layer is tre3ted as a @ntinuous mediumwith an index of relractioq n, that depnds on theelectron density, pel [7]. The index of rcfraclion for X-mys in matter is less than I so that for s!fiiciendy smallilcident angles total extemal rcflection occurs.

Above the critical lalue for total exlemal rellection(lt), lhe rcflectivity from an ideal inte ace is given bythe Fresnel reflecdvity (RF{k) wilh the atmplolic formtk4.;t4. For an imperfect inlerface. $e reflectivity rsgiven approximately by [6]

R(k) = RFG)I F(dpel/dz)I2 (z)

where F(dpel/dz) is the Fourier transform of the ele.trondensity gradient in the direchon nonnal to the surface ofthe lilm. It is important to note that this equatron refeNto the s?€cutar reflectivity, i.e., wh€re th€ angle ofincidence equals the angle of rcflection. Under ihes€conditions, the scattering vector is orienled normal lothe surface so that the reflectivity is otrly sensitive rcvariations in lhe electron density nonnal to the fiIo

grs

'sluaurarnseaui ahllosu€l,(el-xe^Bradslp l6reua ro, snprEdde lo clreuaqcs Z ah6ll

Aqan ,{g sanp I ^1ol

roJ epsur oq ol poou suoltra[o,ou os loslsuo, sr aldues eql uo urBrq aqt Jo uudpoJaql ttrql sueaul osp elSue paxg oqJ, uauromsenuoE turmp po^our eq ol o^sq lou soop aldur?s eqtlsql s-uaau e.l]ap!au! Jo al8ue Paxg eql sluatuerns?ournlls u! roJ Sulrurrs olSue puolluo^uor .lo o uon oppo rsJodsp ,{8.rcur ol sarelue^pe I8.r5 5s oJP aroql

'uri I lo ropro eql uo sl s,(er-X oqtJo rI6ueleruoisrlm le-ra?l el{l :Zy. S0 x s0 ,{laeurrxo.tddBs! ue.q Ier-x oql lq peleununlll aldurBs eqlIo eare lstol 5ql po6n Aa) 9f - 8lo e8$Bl ,{tiou. aqlm % Z{ ,qouqxordds 'rol.opp oC 6IIl Jo uonnlosol,{8reua ar0 qqelu ol uesoq5 s! uorlnloser &Il8s€ aql'stlls ,{q pougop se 8op I0 O Jo roFo oql uo ,qeodhs! uRoq Suloflno plre 8uro8q eqt lo ocuafue tp reF8uelql 8ep O I pue,O urr $3q 56m o.uepbul turzsf? le adurss oql Bo luoplsul sr urBoq ,{el-X oql

'urqttds ,{rrouo NapI.uI oql ,(q poz{Puuousr e4.ods Fms?eur oql ',{I^p.ouai aIIl ulslqo ol raprouI I bo Su|s1r rol€ e e^t q pauoAuoc q unDaods,{treuo oql pue ,(8rouo qcps le 6! rpou.I eql amseoutol posn $ topelep eC elsF-pllos V elSuB f'rxg e lBoldures .ql uo trlsnoouelFruls e8uldurl epoue or{ e uroUuolaJper SunlqsrNs-ruorg ,{q ponpold saF$uo ,{el_xJoetu?J peorq atll ')Uo r s8{l fi p.m enbpqsol e Nradslp,&t u. oql q VII 0oI 'Ai 0i rs pele].do lopleuetepoue Surlspr e sl 6mos ,(er-X oqJ Z .Jr8g uI u,noqsorB s$eIsdde Eueuladxo oqr .p sprep eqJ,

f, norNtr)lr TvrNsr.ttruxd(x

'ssoq€nor eiEreur a{l sr D ereq,$ (fzt)dxa)olloJ rellB/Y\-orqeo s r^sq ol u.Isl

^lJe$uet sl sseuqtnor eqJ ssoslolu! &sqs toJ ueqr { SuFeeDu!w r ralssJ sassoraop 6! lpager oql 's..elelul qSnolroJ sacqrelq orlt Jo ssouqSno, or$ ,{q Peunuopp sIAFualul popeuor eql q trsrop eqJ ss.u)l5lql la,{el oqlol Euoruodord ,{lasio^q sI suorElllcso oIIlJo pouod oqJ'$qlleur frrgnq oq) pu? ecq:rns oql uo{ Sulralp.suoo $aq oruer5.p4u! urorJ euroc ?rlaeds ,q^Jlcouar

aql ur u \oqs sroJlsulrso sql rueJper8 &lsuap .qlJo ruroJsuerl rounog oql Iq u5 F s! (pI 3g) .lnpru$qql urorJ ((D{u,i(Du) {l! JpeUo.I pozltsuuou aql

'lopBorq .q ff^l Ieodaql 'esrwlp ro q8no, sr ecqrolu! .tll Jr elqa '^rorrslroq III r zpllodp u! {erd oql ueql qpous sl60E}e}uIeqt JI tI 3g ul uaoqs ss saceyelul es.tn r stBed sstl(zpy'odp) Arsuep uorrol. aqlto luolpel8 eqJ, 'urnn.spus u{g oql 'olellsqm aql uee q6q seceirolu aqlte soSusqc pIIe uuoJ:lun st uoplsoduo, ulg ou etoq^ltuelsuo. q (qI 3g) e.eJms ulg aql 01 Fuuou uorpolrpoql ut AFlItp uorpeta aq.L (?I ,g) ererFqns e uoIo,{q uuoJun a6urs eJo slsls-uoc omlsnrs oql I enl8gul ,fie5nsureq.6 u roqs sl &l^rpouor eW pus utlg uI$aql uo.^!6q (Z) bt ul f!.ssor(ke dlqsuopslor aql

'u{g otnJo aueldar0 ut ampruls ooErrlw eql aqord pu soop plle $PJms

'A|^!]r.uer leusa.U Iq pezlleur.tou ]ualpel6,(Isuepuorpap lo uJrorsue.rl .t3lrnol uJo.4 pe lr€P ,(ll^llcoua8(p lseun p€$op Iq peleclpuD secerlalul lB $lead6ulMoqs Arsuep uorl.qa ul lu€lpere (c 1e) u! elnlc lsol bupuodseroc acelrns ol leuJrou,(l!suap uollc€I3(q ap4sqns uo ra,(El snoeuaoouJoq lo Bulslsuocarnpnrls urlrl (e 1Z) 'be ur pesseldxa se /q^l}cagel lel-x pue arnpn4s u.lll ulql uaa^ leq dlqsuotlEta L €ln6!l

(q

o(oa

P3tp

@oE

46qE-(,

oo59. q

(e

O top (Si caplsico)

A bottom (Slc6/sub6trato)

o 1oo 200growth Prsssure (torr)

F'oure 4. D€Dondsnce ol roughn€ss on growth pressurei"i'i.-" isi J"olsie"t and b;(om (sice/Si substrats)iilrr*"i.rn" ip"ari *"re fit to a two-lav€r modelr thei"rcui"G ,nr"niitv rro. the multilay€r model is shownii ir," l""n"a lin; rn the risures' The intensitv of the

"l",ii"ti"r" t the spectra d;creases for the samples

grown at higher Pressures.

Analvsis of these spedra indicate that the decreas€

ln ttre oscittatloo intensity correslonds to increasediornt n"". ut the inlerfacrs. The roughness at theiic-J*u.uur" int"rr"." -d the sice/Si cap interfacc issio"n ,n ngure 'f as a n nclion of growli

pressr'lfe The

i.".""." in-.rrfa"" roughness wili increasitrg gro*lhor"aa*" *^ aat"a*ir. lo be caus€d by lhe prcs'nce of'nrJ.d hvers at the interfaces created b] a lransient in

ire switciing time of the gases in the 8ro$'dr reactor'

fnis ascovetr was usea ro determine groMh condilroos

to produce mole abrupt interfaces.

KINETICS Otr SURFACE ROUGEENING ANI)

SMOOTEING DURING SPUTTERING

We have used lhe in situ measuemcnt capabilitios

of XRR to sNdv the evolution of sudace 'oughnessiu;ns mutlerine of sio2 I4l sufaces These-.rrit"r.os *"i" p".formed in real t'lme whlle theJ""" w". U"ine .prtt.rcd Be windows allo\xtd lhei-rrvs [o enter ana oif rtte sputteriog chamber withmini'dul attenuation of the be3m.

We initiallv bombard fte sudace with healy Xeions with an eoeiry of loo0 ev. The surface roughnessi"

"nown in nsrre's to rise approximately linearly with

ion nu"n"". ifto" un.tics arc much morc rspid th'nttre iiD tetravior tlat is exp€cled if the $putter beam israoaoorlv remouing atons ftom the surface The Xc-rouehened surface is the$ bombarded with light (H or

ieiiom. The change in roughness with time is shol^'nin fis. 6 and indicates that the surface roughnessdecrJses exponentially with ioo fluence wi$ a Iale that

increases wiih ion energy. )(RR sp€clra corr€s?onding

io irr"r.a"ins He tluence are sho*n in Eg ?l theJo..as" i"

-O. sMace roughness is evident by the

decrqsing slope ofOe sp€ctra.thei kinetic studies confirmed the presenc€ of a

ro'rshenine inslabiliry dMing healy ion spultering

-t'_".a u-tft" .r*"n* aependence of the sputter yieldrt rt i"rd" to -o"h .ot" rapid roughening dun a simplesiochrstic rcmoval process. The smmthing by light ions

o,r" aue to ion+nt anc"a \Tscous flow of the oxide'e,ttfrough in principle similrr measurments could beohain; bv se4uences of AFM meas:urements lhes'wo d be verv tli5icult lo obtain The real timecapabiliiy ofth; )GR Provided criticd kineiic dala for

;0.83 o.z

9o.eIe 0.5

€ o.+

e6 r.ooco--a r."

€ o.o

Xe' He'

200 eV

500 eV

1000 eV

12Fluence, 1o16cm- 2

o 0.5 1.0Fluence, 1o16cm -2

F6ure 5 Krn€tics of SiO, surfacs roughening inducedl"'r"*

"*tgv i" +rtterina. Line r€presents fit to modsl

oi sputter-inriuced roughening instability

Fidure 6. Decrease in surface roughness during He

"oitierino ofsior. Surfaces were in(ially roughened by

i" "p-rtt"Ling.

Li;es show lit to exPonential decay due to

ion-enhanced viscous iow.

514

sr9

'orn6u uo P.lBclpur alnsse,d qY\ oretapou relelllnru lerldo ol lu lue$rdei seull peqseo'elEilsqns rs/aers/dB. !s lo burlsrsuo. sernpn,ls-r"rirq ,*olo-olc uroil erpads uux e eln6rl

(uu/r) Iezt

0'a-

g',t-

0'k

9'0-

0'0

9'0

orO

T

axI s.qord reqp ol poEdulor q8!q ,to^ sl 'tr! IFuosqlap oql, (rum 'r'{dv) soldo'solcrur oqord SuruuPcsrc (Ngf;o ,tdocsorilur uorltolo uolssllusue4 leuopcas-ssoJt ${!I oldues 5$ lD uorperJ l[surs s Jo pEls eeIPot.nl ? Jo o sa8srs e luouamsBJru eqJ soop uor,eJJJpuortrote JxI urnncs^ e srlnbl lou seop enbgq'ore6 aougs rurlqprd e rcu ere flustuuoll^ue Sulss:rord se8

tuarqury ssnbFq:ot 3ulssmord Jtqp pue uonEodrpl{lt^r era]alur lou seop,{reurm8 ooosplrul Bl,r,U?lB tqJ'uonsrsdsd eldurDs leosds ou sermbo, pue o^nJlulsep-uou sr onbJuqJol aql ssauqSnu $eJ.ms ss llt^rt pnqqra "q uBa s5r?y5lu! ra,{el pounq 'Sunerpu'd,(g31q ere s,{er-1 eql ostl".og luornarnsltlrl olSurse ur sseuq8no.r pue ,o1stap sseqJfln alns?5ul ol '(l!llqeeQ sl ulD( JO qEue4s lseleel3 aq], S.8sue^peslpp* .ia"rrenp" slr aunru.pp ol senbFrq,al lerp(leusurtg uIIl ror$o ql!{ uE{ oreduoc ol Fgesn q lI

SXNOINIOf,I Uf,HIOEJI,I\ NOSIUVdI{IO) (NV SflII.II(V'M UUX

'/o0t+ Jo leplo eW oo s! &!4Isuas I95!dA lnq 'ssosqSnor

Jo aorSJp oqr ol Paldnoo flSuolp sl /q!$op uon'elo Jo,on*n-.t"p.q1 uu zo o +Jo al nFues ssauqSno's saqdur sl{l 'sooeJ:rns q}oouls loJ ssruqSnoleql Jo % 0z + ,{lorurxordds Jo uonnloso' e qlu\IrIu e - I oJo oSuet oql ut paurut4tp eq ue' sssuqSno'IooeleNr puB o.eIns eql ulu 0oz - t Jo eSuel eql uIo/o9 + ,{p$urxodds Jo uopnloso, e $pr peuruuolop 0que5 sslu{crF re,{el aql r5loureDd qcgo qlll\ pepl'osselolJa e$ JOJ enle^ I uJs4O Ol prsn sl slopu,?.Ied oq}ur soSuErl5 or lu se nb lsstl aql Jo /ql^nlsuas eqJ.

'$r?etU a^rleul4F {q peuruuelap 'q

usc $eput€red aql p ouros ssapn sloIq o rl ue$ erotuSuruIsNor €l.qan.rts e lopou ol Porpsdu{ 'qPioue?sI ll aumol rurug seIent6-lseol .Igeu{_uou e tuFnDourqqo aje ssauq3nu ,JsJ:Ielu! pegnq puE ssouq8nor

soed 'ssoqrqt ,(r$r5p rt,{q ol SulPuodseuorsreieurered :o sanp^ umurdo posr| sl 3u!'llRcsoldlFu tunocce olul so{el lnn l.po$ re{elnl uIBando us ?rDods ,{rl^nrauJ eW Jo sls^Jelre JoJ

(6gel5 roJ posqdslp uooq e^€q se^nlc aIIl Jo saor5z eql)

senusora iuar"J1p re ,..nrort sEdures aoql urorJ erpods

Al^rpoupl elD ^\oqs

e^r 't aIn8g uI dea IS e pu? la{slonrs ? 'aler$qns Is ? lo polslsuoo s nDltlls aqJ l J5lui p,-rno}

"q,to *otttpuoo lelusoluadYo plrE snle.rsddg

r0xor8 or$ Jo s[4op r:qunl O\J ,tq o,{o,3 eCtS Josa:rnFn4sorelaq ozgoFeErlt ol utll{ Posll e^eq 5 \

sruntJnursouxJf,E e'J!s JIo f,lllouc (I c

'sro.(q aql Jo ornlcnJls ewld_ul .ql lnoqe uo[l8ur'IoJnl

ou s.ppord ull{ 't^[ls pus wgD( s" q.ns sonblqtolsqrfeurl qlt,t uospEduroc q son]cnrs por'Iduro'arour roJ ,{llet3edso 'ouruueFp ol llncglp p0ugqops repursJeJ 5ql Jo sseuenbrun eql srleur sn'[ '{,.oqlJe{sE[nur leafdo u? ol IIJ eq ol paeu snds pe'ns?5uretrr

'pns in rrp peuFno 5q po - uec sDnute,ud

terll are enbluq'4 ,ql ol sl5eq re.IP *Uo t#"po,

/trs?J 5ioru aq uer pue Als:uap uorlaele Ptol 'ql

uo '{[uopu:dop s:,{q aIIl jo serv.dord [Eondo e$ '/'neuiosdrll5w r uospeduoo ul 'elqlssod srJl'upl Jo sopnFs;r.rp* i 00s uerp ssol ut P.u'etqo oq uot "!'odstroncepp eirsredsrp xanue Sulm pue n$ u! pe'{oduseq us, onbpq.o) aqJ (SgU) 3upalw.6{ceq proyoqBU

IITAIIISNf,S (INY SISI'IYNY Xf,X

'odurBs

rm uofl e.uacseronu ,{ej'x Iq aoueDy'lu! clqlssodp* oonrp*, poanpa.I orE uorDoFp 5^!$rdslp '{8,.urol so84us^pesrD a{L pornseolD 5q uEa stqeupl lslo os s

ooc ueql ssq uJ ,olereue8 ,{sr-X po6"q-tuoraoqq e uro,lj

peqelqo 5q uec BJl$ds llonelpsl SunMBrlsstut,lg rl{l

9-rnG,

v-.,'"ccp, -2.0

.0.5

-2.5

1234K (1/nm)

Fioure 7. XRR sDectra from SiO, surfaces smoolhenedby-low ensrgy He sputbring lncreasing ion fluence lromai to d). Dashed Lnes represent ft to optrcal multrlayer

development of modelssmoothing.

In sumnury, XRR

of surface roughening and

is a useful in situ probe ofsemiconducto, thin films. It Provides information aboutlayer ihickness, composition and interface roughnesswirh sensilrvity in lhe nanoscale regme lhal is b€coming

ircreasingly important technologically. Simple non_destructiv€ sample preparalron, rclalively mpid dalaacquisidon and compalabrlity wilh depositiongeometries make il suitable for in situ kinetic studi€s ofmorphologl evolution. For complete characteriTation ofthe stluclure, xRR needs to be combined with other in_plane probes.

The authors gmtefully acknowledge usefuldrscussions with Bruce Kellerman. This work wassupported by the U.S. Depaflment of Ener$/ underconrad DE-ACO4-94AL85000.

L Z. Matutinovic-l&stelj, J.C. Sturm dd E. Chdotr' J. Elect.Mater., submitted.2. E. chason, T.M. Mayer, B K. KeUtrman, D.N. Mcltrov dB.K. Keuerman, Phys. Rev. Letl. 72, 3040 (1994)

3. E. clason, T.M. Mayer, A. Payne End D Wu, Appl. Phys'Let 60,2353 (1992).4. T.M. May€r, E. Chason aod A J. Ho*€rd' J. Appl. Phvs 76,

1633 (1994).

5. L.G. Puatt, Phys. Rev. 95, 359 (1954)

6. J. Als-Nielsn i Sttuct\re and Dt ani.s of Swftces,ediled by W Scholmqs afld P. von Blmckentlasa (Sprinstr,Berlin, t986), p. 18l.7. J.H. Underwood and T.w. Barb€e, Appl opt- 20,3027(1981).

516

nist cover.pdfSlide Number 1