Plasma-enhanced chemical vapor deposition of SiO2 from a Si(CH3)3Cl precursor and mixtures Ar/O2 as plasma gas

Plasma-enhanced chemical apo deposi ion o SiO2 om aSi„CH3…3Cl p ecu so and mix u es A ÕO2as plasma gas A. Ba anco Ins i u o de Ciencia de Ma e iales de Se illa (CSIC-Uni e sidad de Se illa) and Dp o de Quı ´mica Ino ga ´nica, A da, Ame ´ ico Vespucio s/n, 41092 Se illa, Spain J. Co ino Dp o de Fı ´sica A o ´mica, Molecula y Nuclea , Facul ad de Fı ´sica, Uni e sidad de Se illa, A da. Reina Me cedes s/n, Se illa, Spain F. Yube o Ins i u o de Ciencia de Ma e iales de Se illa (CSIC-Uni e sidad de Se illa) and Dp o de Quı ´mica Ino ga ´nica, A da, Ame ´ ico Vespucio s/n, 41092 Se illa, Spain T. Gi a deau and S. Camelio Labo a oi e de Me ´ allu gie-Physique Ba ˆ SP2M, Bd. Pie e e Ma ie Cu ie, 86962 Fu u oscope Chasseneuil Cedex, F ance C. Cle c Cen e de Spec ome ´ ie Nucle ´ai e e de Spec ome ´ ie de Masse, IN2P3-CNRS, Ba . 104-108, F-91405 O say, F ance A. R. Gonzalez-Elipea) Ins i u o de Ciencia de Ma e iales de Se illa (CSIC-Uni e sidad de Se illa) and Dp o de Quı ´mica Ino ga ´nica, A da. Ame ´ ico Vespucio s/n, 41092 Se illa, Spain 共Recei ed 3 Janua y 2003; accep ed 31 Ma ch 2003; published 16 May 2003兲 Silicon dioxide hin ilms ha e been p epa ed a oom empe a u e by emo e plasma-enhanced chemical apo deposi ion in a downs eam eac o by using Si(CH3)3Cl as a ola ile p ecu so and a mic owa e elec on cyclo on esonance ex e nal sou ce. Expe imen s a e done a cons an p essu e by changing he ela i e amoun o A species Rin he plasma gas. The aim was o ob ain hin ilms wi h low densi y and, he e o e, low e ac i e index. Cha ac e iza ion o he species o he plasma is ca ied ou by op ical emission spec oscopy. The changes o he plasma condi ions a e co ela ed wi h he g owing a e and mic os uc u e o he ilms, he la e de e mined by a omic o ce mic oscopy and in a ed spec oscopy. I is ound ha he g owing a e o he ilms dec eases and hei oughness inc eases as Rinc eases. The op ical p ope ies o SiO2 hin ilms a e analyzed by op ical ellipsome y. A dec ease in he e ac i e index is ound o he ilms g own wi h high alues o R. The possible ou es o ac i a ion o he p ecu so and he o ma ion o he SiO2 hin ilms a e discussed. © 2003 Ame ican Vacuum Socie y. 关DOI: 10.1116/1.1577134兴 I. INTRODUCTION Silicon dioxide hin ilms a e p epa ed by a la ge a ie y o me hods including plasma-enhanced chemical apo deposi ion 共PECVD兲. This echnique is widely used o his pu pose because i pe mi s a low deposi ion empe a u e, high deposi ion a e, e c.1T adi ionally, SiO2 hin ilms ha e been deposi ed om SiH4/O2o SiH4/N2O plasmas.1,2 O he silicon p ecu so s used a e SiCl4,1,3 e a- e hoxysilane 关(TEOS) Si(O(C2H5)4)兴,4hexame hyldisilox- ane 关(HDMSO) O(Si(CH3)3)2兴,5and mo e ecen ly, e am- e hylsilane 关(TMS) Si(CH3)4兴6,7 and clo o ime hylsilane 关(TMSCl) Si(CH3)3Cl兴.8These p ecu so s ha e been u i- lized in pu e o m o mixed wi h oxygen o N2O. The e a e some ad an ages in using o ganosilicon p ecu so s, such as hei sa e handling, he ac ha hey yield a be e s ep co e age, and he possibili y o p epa e ino ganic SiO2as well as polyme ic SiOxCyHz hin ilms, depending on he dilu ion deg ee o he p ecu so in he oxidizing gas.9,10 Mo e ecen ly, he use o TMS o p epa ing SiO2 hin ilms by PECVD has been in oduced because he ilms deposi ed wi h TMS⫹O2mix u es p oduce be e wa e epellen lay- e s han hin ilms deposi ed by using an e hoxide-like e ame hoxysilane⫹O2.11 O he au ho s ha e also shown ha by using TMS⫹O2, i is possible o deposi hyd opho- bic SiOx hin ilms in a co ona discha ge plasma a a mo- sphe ic p essu e.6In addi ion, since TMS and TMSCl do no con ain oxygen, i is possible o deposi SiC and polyme ic SiCxHy hin ilms12,13 wi hou adding o he plasma CH4o o he hyd oca bons, as has o be done when using SiH4. Howe e , in con as wi h he ample li e a u e exis ing abou he use o SiH4, TEOS, o HDMSO, much less is known abou he use o TMS o TMSCl. In p e ious wo ks, we ha e employed he p ecu so TMSCl o ob ain s oichiome ic SiO2o SiOxCyHz hin ilms in a emo e mic owa e elec on cyclo on esonance 共ECR兲-PECVD eac o wo king in a downs eam con igu a ion.8,14 Mo eo e , we showed ha un- de ou expe imen al con igu a ion, he exis ence o a SiuCl a兲Au ho o whom co espondence should be add essed; elec onic mail: [email p o ec ed] 900 900J. Vac. Sci. Technol. A 21„4…, JulÕAug 2003 0734-2101Õ2003Õ21„4…Õ900Õ6Õ$19.00 ©2003 Ame ican Vacuum Socie y bond in TMSCl makes his p ecu so mo e suscep ible han TMS o chemical a ack by he exci ed species o he plasma.8 The use o SiO2 hin ilms as an an i e lec i e coa ing in, o example, pho o ol aic cells,15 equi es he ab ica ion o low e ac i e index po ous coa ings o his ma e ial. This can be done by inc easing he o al p essu e o he plasma chambe du ing deposi ion. This pa ame e usually a o s he condensa ion p ocesses in he gas phase and, he e o e, leads o an enhancemen o po osi y. Howe e , as a d awback, his p ocedu e usually has de imen al e ec s wi h espec o he mechanical s abili y o he laye s because o he poo adhe- sion be ween he la ge agg ega es o med in he gas phase. The p esen a icle epo s he p epa a ion a oom em- pe a u e o SiO2 hin ilms by using he TMSCl p ecu so and mix u es A /O2as plasma gas in a emo ely coupled PECVD sys em. I has been ound ha , o a cons an wo k- ing p essu e, he oughness, g owing a e, and o he mic o- s uc u al cha ac e is ics o he ilms depend on he a io be- ween he plasma gases and p ecu so . F om his s udy, some clues a e deduced abou he eac ion mechanism o he TM- SCl p ecu so and he deposi ion p ocesses leading o he o ma ion o he SiO2 hin ilm. The dependence o he op- ical p ope ies o he ilms on hei mic os uc u al cha ac- e is ics is also examined and discussed in ela ion wi h he pa ame e s o he deposi ion p ocess. II. EXPERIMENT Silicon dioxide hin ilms ha e been p epa ed a oom empe a u e by a emo e PECVD p ocedu e. Si(CH3)3Cl has been used as ola ile p ecu so o Si. The plasma eac o has a ‘‘downs eam’’ con igu a ion wi h an ex e nal mic owa e ECR sou ce 共SLAN兲ope a ed a 400 W. The sou ce was sepa a ed om he eac o by a me allic g id p e en ing he mic owa e i adia ion o he subs a es. This g id allows easy con ol o he plasma igni ion and he sepa a ion o he deposi ion a ea om he plasma egion. Also, owing o he p esence o he g id, i is expec ed ha mos ac i a ed spe- cies in he deposi ion zone a e neu al, al hough i canno be uled ou ha some elec ons and posi i ely cha ged plasma species a i e a he sample posi ion. The dis ance om he subs a e and g id was 10 cm. Pieces o one side polished Si共100兲wa e s o 3 cm2we e placed in he eac o , while he p ecu so was dosed on op o hei su ace h ough a dis- pe sal ing placed 6 cm om he subs a e o ensu e i s ho- mogeneous spa ial dis ibu ion. The base p essu e o he sys- em is lowe han 10⫺6To . A ully de ailed desc ip ion o he expe imen al se up has been p esen ed elsewhe e.8,16 P e- cu so and plasma gases we e dosed by sui able mass low con olle s. Thus, ixed low a es o 10 sccm o he oxygen and 5 sscm o he p ecu so we e used, while he low a e o A was a ied in he ange 0–5 sccm. Pu e oxygen o mix u es A /O2we e supplied o he sou ce. A o al p essu e o ⬃2⫻10⫺2To was main ained cons an ly in he cham- be du ing deposi ion by adjus ing he pumping capaci y o he sys em wi h a h o le al e. We ha e shown p e iously ha his p essu e co esponds o he maximum in he depo- si ion a e when pu e oxygen is used as plasma gas.8The main pa ame e ollowed in his wo k is he a io Rbe ween he A low and he o al low o gases supplied o he eac- ion chambe 共i.e., Ris he mass low o A di ided by he addi ion o he mass lows o A , O2, and TMSCl兲. This ela i e es ima ion o he A added o he plasma gas p o- ides a mo e app op ia e desc ip ion o he p ocess han he me e A /O2 a io. Op ical emission spec oscopy was ca ied ou du ing hin ilm deposi ion. The ligh emi ed by he plasma was col- lec ed by an op ical ibe which was posi ioned 4 cm down- s eam om he sou ce cen e h ough a hole in he SLAN ai cooling ing. The ibe was joined o a monoch oma o Jobin–Y on HR250 wi h a 1200 g oo es/mm g a ing and equipped wi h a R928 Hamama su pho omul iplie . The g ow h a e was measu ed wi h a qua z-c ys al moni- o placed beside he subs a e. The ypical hickness o he s udied samples was abou 500 nm. A omic o ce mic oscopy 共AFM兲images we e ob ained in ai by using a Topome ix Explo e mic oscope wo king in he noncon ac mode. The can ile e 共supplied by Topome- ix兲wi h a sp ing cons an o 42.6 Nm⫺1was oscilla ed a 130 kHz. Ampli ude educ ion was moni o ed while he su - ace is scanned a a ypical a e o one line pe second. The scanne was calib a ed in he X,Y, and Zdi ec ions wi h g a ings p o ided wi h he equipmen . Bo h opog aphic 共cons an o ce兲and di ec signal 共cons an heigh 兲images we e acqui ed. Fou ie ans o m in a ed 共FT-IR兲spec a we e collec ed in ansmission mode a no mal geome y in a Nicole 510 spec ome e o samples deposi ed on Si共100兲wa e s. The hicknesses o he analyzed samples ha e been chosen o a oid he sa u a ion o he in a ed signal, hus enabling he compa ison o he ela i e in ensi y o he bands. Ru he o d backsca e ing spec oscopy 共RBS兲measu e- men s o he ilms we e pe o med in he Ion Accele a o ARAMIS 共O say, F ance兲using 1.5 MeV ␣ pa icles. The ene gy esolu ion o he de ec o used in he RBS measu e- men s was 15 keV. The spec a we e simula ed using he RUMP code. The samples ha e been deposi ed on Si共100兲and channeling was used o imp o e he sensi i i y o he ech- nique o he SiO2 hin ilms. Spec oscopic ellipsome y expe imen s we e pe o med using a SOPRA comme cially a ailable sys em. The mea- su emen s o ellipsome ic pa ame e s we e made wi hin a wa eleng h ange om 0.21 ␮ m o1.2 ␮ m a di e en angles o incidence 共65°, 70°, and 75°兲. These a e he mos sensi i e angles, since hey a e close o he B ews e angle o a silicon subs a e. Fo he s udied ilms, he i s s ep o he analysis p ocedu e consis s o a eg ession using a Cauchy law o simula e he e ac i e index n(␭), he ex inc ion co- e icien k(␭), and he hickness o he laye . In a second s ep, he laye hickness was ixed as de e mined he ein and a poin -by-poin ex ac ion o he complex e ac i e index was pe o med a each wa eleng h. 901 Ba anco e al. : Plasma enhanced chemical apo deposi ion o SiO2901 JVST A - Vacuum, Su aces, and Films III. RESULTS AND DISCUSSION A. Plasma cha ac e iza ion and deposi ion p ocess Op ical emission spec a o he plasma we e eco ded o inc easing alues o R. The spec a o oxygen/a gon plasmas 共wi hou p ecu so 兲a e domina ed by sha p lines due o emission om a omic oxygen o a gon and by se e al mo- lecula bands esul ing om ansi ions be ween low ib a- ional le els o he O2 ⫹species. The addi ion o he p ecu so o he eac o inc eases he emission om he lines o a omic hyd ogen in de imen o hose o oxygen o a gon. Thus, he op ical emission spec a o he A /O2/TMSCl mix u e, apa om he lines due o oxygen and a gon, exhibi s ong emis- sion lines due o H*共lines o he Balme se ies兲and o he exci ed species such as CH*,CO *,CO ⫹,OH *, e c., he la e e y likely coming om he agmen a ion and oxida- ion o he p ecu so molecule. A sys ema ic analysis o he a ia ion in in ensi y o some selec ed lines can be used o unde s and some o he eac ion pa hways o species in he plasma. Figu e 1 shows he a ia ion o he in ensi y o emis- sion lines/bands (A *a 750 nm, O*a 777 nm, H*a 486 nm, OH*a 306.4 nm, CH*a 431.4 nm, and CO*a 507.1 nm兲wi h R. The assignmen s o hese signals ha e been done in ag eemen wi h he Re s. 17 and 18. The plo o Fig. 1 shows a ne inc ease in he in ensi y o he A *line as R inc eases, while he O*emission inc eases only e y sligh ly and he H*emission dec eases. On he o he hand, he emis- sions co esponding o CH*and OH*bands inc ease as R inc eases. The in ensi y o he CO* emains p ac ically con- s an when A is added o he discha ge. As a i s app oxima ion, he in ensi y o H*lines can be aken as a ace o he deg ee o agmen a ion o he p ecu - so molecule in he plasma 共no e, howe e , ha his is no igo ously ue because he elec on densi y and/o empe a- u e may also con ibu e o changes in he in ensi y o he H* emission兲. Figu e 1 clea ly shows ha he yield o his p o- cess dec eases as he A con en in he plasma inc eases. I is also impo an o men ion ha , o a gi en alue o R, he in ensi y o all emission lines inc eases wi h he mic owa e powe . The g ow h a e o he SiO2 hin ilm was also de e mined as a unc ion o R. Figu e 2 shows ha he deposi ion a e o he ilm diminishes almos linea ly wi h R. We would also like o s ess ha no deposi ion was obse ed when only pu e A was used as plasma gas o when TMS was used as a silicon p ecu so molecule ins ead o TMSCl. In he case o TMS, no deposi ion is obse ed ei he when O2o mix u es A /O2a e used as plasma gas,8while o TMSCl, he g ow h a e inc eases o inc easing p ecu so low. B. Thin- ilm cha ac e iza ion The hin- ilm samples p epa ed in his wo k we e ana- lyzed by RBS o de e mine hei composi ion. All o hem had a silicon dioxide s oichiome y 共i.e., O/Si a io equal o 2兲and no aces o Cl o C we e de ec ed. The e o e, he samples, a leas up o he sensi i i y limi o he RBS spec- oscopy 共⭐5 a .% o C and ⭐1 a .% o Cl兲, can be con- side ed as ee om hese elemen s p esen in he TMSCl p ecu so . The mic os uc u e o he deposi ed SiO2 hin ilms was in es iga ed by AFM and FT-IR. Figu e 3 shows as an ex- ample wo AFM images o he su ace o SiO2 hin ilms co esponding o R⫽0关i.e., Fig. 3共a兲兴 and R⫽0.6 关i.e., Fig. 3共b兲兴. These images clea ly show ha he oughness o he ilms inc eases wi h he ela i e concen a ion o A . A mo e quan i a i e e alua ion o he oughness o he ilms is p o- ided by he oo -mean-squa e 共 ms兲su ace oughness al- ues. Figu e 4 shows he a ia ion o he ms su ace ough- ness o SiO2 hin ilms p epa ed wi h inc easing ela i e FIG. 1. In ensi y o he indica ed emission lines exci ed in he plasma eac o as a unc ion o R. FIG. 2. Deposi ion a e o SiO2 hin ilms as a unc ion o R. The line is plo ed o guide he eyes. 902 Ba anco e al. : Plasma enhanced chemical apo deposi ion o SiO2902 J. Vac. Sci. Technol. A, Vol. 21, No. 4, JulÕAug 2003 amoun s o A in he plasma gas. I is ound ha he ms su ace oughness inc eases as he A concen a ion in he plasma inc eases. Figu e 5 shows FT-IR spec a o SiO2samples p epa ed wi h inc easing concen a ions o A . I is impo an o no e ha no signals om o ganic g oups8a e de ec ed in he FT-IR spec a o any o he deposi ed hin ilms, indica ing ha e en i he in es iga ed p ocess is ca ied ou a oom empe a u e, he comple e emo al o o ganic g oups akes place. The di e en peaks and shoulde s in he 400–1500 cm⫺1 egion ha e been a ibu ed o he ib a ional modes o elemen al SiO4 e ahed al o ming he s uc u e o he SiO2 hin ilms.14,19–21 They can be assigned o a ans e sal op i- cal (TO1) ocking mode 共460 cm⫺1兲,aTO 2bending mode 共800 cm⫺1兲, an asymme ic s e ching mode 共 he big band a ⬃1070 cm⫺1兲,aTO 4asymme ic mode 共1170 cm⫺1兲, and i s co esponding longi udinal mode LO4共1200 cm⫺1兲. These wo la e bands gi e ise o he well de ined shoulde a he igh -hand side o he mos in ense band a ⬃1090 cm⫺1. SiuOH and SiuO⫺ ocking 共578 cm⫺1兲and s e ching 共960 cm⫺1兲modes can be also de ec ed in he spec a. The 960 cm⫺1peak inc eases wi h he alue o Rin ag eemen wi h an inc ease o he inco po a ion o OH⫺g oups in he less compac SiO2 hin ilms. The ela i e in ensi y o he shoulde a 1200 cm⫺1共due o he con ibu ion o se e al elemen al bands as has been men ioned he ein兲has some- imes been aken as a measu e o he deg ee o po osi y o he ilms 共see Re . 14 and e e ences he ein and Re . 19兲. Al hough some o he ac o s besides compac ness may con- ibu e o his in ensi y, he esul s ob ained he e show a pa - allel endency o shoulde in ensi y, ms su ace oughness alues and, as i will be shown in he nex subsec ion, de- c ease in he densi y o he ilms. C. Op ical p ope ies The op ical p ope ies o he SiO2 hin ilms p epa ed un- de di e en condi ions we e de e mined by spec oscopic ellipsome y. Figu e 6 shows he e ac i e index n(␭) and he ex inc ion coe icien k(␭) as a unc ion o he wa e- leng h ␭, o hin ilms p epa ed wi h di e en alues o R. The plo shows ha he e ac i e index o he ilms de- c eases as he ela i e amoun o A in he plasma gas in- c eases, o he en i e wa eleng h ange. FIG. 3. AFM images o SiO2 hin ilms p epa ed wi h R⫽0共a兲and 0.6 共b兲. FIG. 4. ms su ace oughness o SiO2 hin ilms as a unc ion o R. The line is plo ed o guide he eyes. FIG. 5. FT-IR spec a o SiO2 hin ilms p epa ed wi h di e en alues o R. 903 Ba anco e al. : Plasma enhanced chemical apo deposi ion o SiO2903 JVST A - Vacuum, Su aces, and Films I is possible o es ima e changes in he densi y ␳ o he SiO2 hin ilms om he a ia ion o hei e ac i e indices. I has been epo ed22,23 ha in he case o SiO2,⌬ ␳ ⫽5 ⫻⌬ngcm⫺3. In he p esen case, a maximum change o 0.023 is ound in he alue o n o p ac ically all o he isible egion. This di e ence in ngi es a maximum di e - ence in densi y ⌬ ␳ ⫽0.11 gcm⫺3, be ween he mos and leas compac SiO2 hin ilms epo ed he e. The less com- pac ilms a e hose p epa ed a high alues o R. This en- dency ag ees wi h he highe deg ee o oughness and po os- i y deduced om he AFM and FT-IR cha ac e iza ion analysis o he samples 共c . Figs. 3–5兲. I is also wo h no ing ha all o he samples we e o ally anspa en 共k alues equal o ze o on he whole spec al ange兲wi h independence o he R alue, and ha no ligh sca e ing was de ec ed in any o he deposi ed ilms, as i would happen i he size o he agg ega es we e la ge enough o sca e isible ligh . The high anspa ency o he hin ilms suppo s he possible use o he less compac hin ilms as an i e lec i e coa ings o pho o ol aic o simila applica ions.15 D. Plasma-enhanced chemical apo deposi ion hin- ilm o ma ion wi h TMSCl and mix u es A ÕO2 The choice o TMSCl as ola ile p ecu so o Si a he han TMS has been imposed, unde ou expe imen al condi- ions, by he ac ha no hin- ilm deposi ion is ound in his la e case ei he by using pu e O2o mix u es O2/A as plasma gas. This esul s con as s wi h hose epo ed by o he au ho s showing he o ma ion o SiO2 hin ilms by using TMS in plasma mic owa e eac o s wi h downs eam con igu a ions.13,24 Jaube eau e al.25 ha e epo ed ha an a e glow A plasma may yield a la ge agmen a ion o he TMS molecule, mainly ia SiuC bond b eaking. This p o- cess p incipally gene a es Si(CH3) agmen s. Radicals o med h ough he dissocia ion o CuH bonds 关i.e., SiCxHy adicals (y⬍3x)] may be also p oduced, hough wi h smalle e iciency. In ou sys em, a p ocess simila o he i s one does no seem o occu because he e is no deposi ion wi h TMS unde any condi ion o wi h TMSCl wi h an A plasma. Howe e , we belie e ha he polyme iza ion o in- e media e adicals o silicon p oduced h ough an al e na i e mechanism could con ibu e o he o ma ion o he ilm 共see nex 兲. The di e en beha io ound in ou expe imen by using TMS o TMSCl p ecu so s8poin s o ha a SiuCl bond in he p ecu so molecule a o s i s decomposi ion by he plasma o p oduce SiO2 hin ilms. The ac ha no chlo ine is de ec ed in he ilms suppo s ha his a om is emo ed du ing he i s s ages o he eac ion mechanism and ha no, o e y ew, agmen s con aining his a om a i e o he g owing ilm su ace. Thus, i is e y likely ha he i s o one o he ini ial s eps in he deposi ion mechanism o he ilms is he a ack o he SiuCl bond by some ac i a ed species o he plasma and/o ee elec ons. Since in ou ex- pe imen al con igu a ion he concen a ion o ee elec ons and ionic species in he deposi ion zone mus be a he small, we assume ha oxygen species a e mos impo an o he ac i a ion o he p ecu so molecule. Thus, such ac i a ion could be w i en schema ically as Si共CHx兲yCl⫹O→Si共CHx兲yO⫹Cl*. Wi h his p ocess, we p opose ha ac i a ed oxygen species in e ene in he ini ial ac i a ion s eps o he p ecu so mol- ecule leading o he emo al o chlo ine and he o ma ion o Si-con aining adicals, ei he in he gas phase o adso bed on he su ace. I has o be men ioned ha he in ensi y o he O*emission line a 777 nm emains p ac ically cons an in- dependen ly o he alue o he pa ame e R, a ea u e ha poin s o a complex na u e o he whole deposi ion p ocess and s esses he need o conside ing o he pa ame e s, like concen a ion and ene gy o ee elec ons, o he adicals, he ole o A , e c., which a e no accessible in ou expe imen . Al hough, we do no ha e enough e idence o p opose a comple e mechanism o accoun o he o ma ion o he SiO2 hin ilms, in line wi h he p e ious esul s by Jaube eau25 and o he au ho s,9,10 i is easonable o assume ha he o ma ion o he oxide ilm om TMSCl is a p ocess ha in ol es he adso p ion on he subs a e o ei he he p ecu so molecule o some eac i e agmen s esul ing om i s ac i a ion and e en ual agmen a ion. On he su - ace, he compe i ion be ween he polyme iza ion o hese agmen s o yield SiOxCyHzpolyme ic chains and he oxi- da ion o e ching o o ganic agmen s o hese ilms leading o he emo al o o ganic componen s will con ol he o - ma ion o SiuO bonds. In ac , p e ious esul s o ou labo- a o y using TMSCl and pu e oxygen plasmas8showed ha i is possible o deposi SiOxCyHz hin ilms when he low o oxygen is lowe han ha o he p ecu so low. In he p esen in es iga ion, he inc ease wi h Ro he in ensi y o he emis- FIG. 6. Re ac i e index nand ex inc ion coe icien k o SiO2 hin ilms deposi ed wi h di e en alues o R. 904 Ba anco e al. : Plasma enhanced chemical apo deposi ion o SiO2904 J. Vac. Sci. Technol. A, Vol. 21, No. 4, JulÕAug 2003 sion lines o OH*and CH*species 共c . Fig. 1兲migh indi- ca e ha he A addi ion a o s he e ching and oxida ion a he su ace o he o ganosilicon agmen s, a p ocess ha has been epo ed p e iously by o he au ho s.25,26,22 Wi hin his phenomenological desc ip ion, i is possible o econcile he high oughness wi h he low g owing a e as well as he SiO2composi ion o he p epa ed hin ilms by assuming ha in e media e siliconelike laye s and/o ag- men s a e being p oduced du ing he deposi ion o he ilms. Then, his polyme ic ma e ial deposi ed on he su ace is u he oxidized by he plasma o yield gases (CO2and H2O) ha would be deso bed whe eas SiCxOyHzlaye s o ag- men s a e being inco po a ed on o he su ace. The elease o ola ile compounds is likely o yield ilms wi h a la ge oughness and po osi y as has been ac ually obse ed he e by AFM and FT-IR cha ac e iza ion. IV. CONCLUSIONS I has been shown ha TMSCl is a sui able p ecu so o he deposi ion o SiO2 hin ilms by PECVD using mix u es A /O2as plasma gas and a mic owa e ECR plasma sys em in a downs eam con igu a ion. Unde hese condi ions, no deposi ion was ound by using TMS, hus indica ing ha he exis ence o a CuCl bond a o s he plasma ac i a ion o he p ecu so molecule. SiO2wi h no aces o Cl was ob- ained in all cases. This suppo s ha Cl is being emo ed du ing he i s s eps o ac i a ion o he p ecu so molecule. I has been ound ha he hin- ilm mic os uc u e and g ow h a e depend on he plasma condi ions. Inc easing he ela i e concen a ion o A in he plasma gas a cons an o al p essu e leads o a dec ease in he g owing a e by a ac o o 0.6 and, unexpec edly, o an inc ease in he ilm oughness and po osi y. As a consequence, he e ac i e in- dex o he ilms can be ailo ed by con olling he ela i e concen a ion o A in he plasma gas. 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