Silicon MBE: Recent developments

Surface Science 168 (1986) 483--497 North-Holland, Amsterdam

SILICON MBE: R E C E N T D E V E L O P M E N T S F A R N A U D D ' A V I T A Y A , S D E L A G E and E R O S E N C H E R C N E T - CNS, Chemm du Vleux Chdne, B P 08, 38243 Meylan, France

Recewed 10 June 1985, accepted for publication 28 June 1985

Some examples ol the capablhtles of Sl molecular beam epitaxy are reviewed It is first demonstrated that electron irradiation enhances significantly the antimony doping efficiency The second topic shows how the pre-oxidation of porous sdlcon allows the growth of defect-free sthcon layers Finally, S1/CoSiffSt structures are examined and a method tor determining the presence of pinholes m the slhclde layer Js presented

1. Introduction During the last five years sthcon molecular beam epltaxy (St MBE) has become a very attractive tool for the reahzatlon of high quality epltaxlal layers and new structures and devices which are difficult, If not impossible, to obtain by using more classical techniques like chemical vapor deposition (CVD) In fact, the field of interest of S1 M B E is very large and it extends from hyperfrequency diodes, which need a perfect control of both the doping levels and the abruptness of doping profiles, to very high speed transistors like metal [1] (MBT) or permeable [2] (PBT) base transistors which necessitate the heteroepltaxlal growth of a metal film on top of a silicon substrate A n o t h e r challenge is the realization of monocrystalhne silicon films on insulator by using full epitaxlal structures like Slepl/fluorlde/Sl~ub~trate [3] or Slep~/ porous slhcon/Slsubstrat e [4] However, many difficulties are encountered in S1 M B E First, doping of silicon and especially the antimony doping (n type) is characterized by a low sticking coefficient as well as a low incorporation coefficient of Sb, both depending on the substrate temperature Moreover Sb segregates continuously at the surface during the growth, which involves a low dynamic doping range as well as long transient delays which are incompatible with abrupt profiles Nevertheless, sharp profiles can be obtained if the temperature of the substrate is higher than 700°C but m this case high doping levels cannot be reached ( < 3 × 1017 cm -~) If for lower substrate temperatures high levels

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P Arnaud d'Avuaya et al / Silicon M B E recent developments

have been obtained, the crystalhne quahty is not proper for device use Many techniques have been tried to enhance the incorporation of antimony in sillcon, that is, low-energy ion implantation of dopants [5] or substrate polarization [6] and slhcon ionization [7] and recently electron irradiation [8] The second problem is the use of porous silicon (PS) PS is a crystalline form of slhcon, and is a promising material for silicon on insulator (SOI) application If growth of silicon epltaxlal layers on top of PS is possible, then the opening of windows m the S1 layer followed by oxidation will lead to monocrystalhne silicon islands fully Isolated by SiO. Many tentatlves have been reported previously [9,10] However, the quahty of the overgrown layer is strongly dependent on the method ot preparation of the PS substrate High-temperature cleaning procedures on as-prepared PS samples must be avoided because of the drastic degradation of the PS structure itself Finally, it has been demonstrated recently [1] that monolithic metal base transistors can be achieved by using the full epltaxlal growth of Sl/slllcIde/Si sandwiches However, the transistor characteristics are strongly dependent on the quality of the metal layer and of the Sl overlayer Too high a temperature during epltaxy ( > 650°C) or too thick a slhclde layer gives rise to island lormatlon [11] and consequently unintentional permeable base transistors are obtained In this paper we present a review of some recent developments in S1 MBE That IS, the effect of electron irradiation on the antimony incorporation durIng the epltaxlal growth, the method for obtaining defect-free silicon layers on top of PS substrates and the oxidation procedure which leads to the fabrication of transistors and, finally, the results of SMS transistors as well as the electrical method for testing the presence of pinholes in the metal layer

2. Experimental The system used here IS an ISA R1BER 231)0 apparatus It is composed ot three main vessels namely the load-lock chamber, the analysis chamber and the evaporation vessel The load-lock chamber can receive up to twelve 2" silicon wafers which are mounted on m o l y b d e n u m sample holders by means of graphite rings The analysis vessel is equipped with a low-energy electron dlffractometer ( L E E D ) , an Auger Electron Spectrometer (AES) and a 2 kW electrostatlcally focused electron beam evaporator commonly used for metal deposition Deposition rate is adjusted by means of a quartz monitor The sample can be heated, by the back side, up to 1100°C by using a tantalum radiating resistor which is attached to the manipulator The evaporation vessel is equipped with a magnetically focused 6 kW electron gun evaporator devoted to silicon evaporation It is controlled by a quartz monitor and the power is adjusted to obtain a deposition rate near 2 A./s The rotating

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m a m p u l a t o r has the same heating facfllt~es as the analys~s vessel one Two effusion cells filled with galhum and antimony respectively provide the p- and n-type doping F u r t h e r m o r e a 1 to 2 keV electron gun, the total emission current of which can be varied between 0 and 2 5 m A , can shower the surface during the growth All the vessels are p u m p e d down to 5 × 10 -11 T o r r by means of ionic pumps and t~tamum subhmatlon The operating pressure, in the evaporation vessel, during the $1 growth remains m the 10 9 Torr range The samples used here are 2" slhcon wafers, their doping type and concentration as well as their crystallographic orientation depend on the experiment The wafers are always cleaned before deposition or treatment by using the chemical cleaning method previously described by Ishlzaka et al [12]

3. Results and discussion

3 1 Antimony doptng of stltcon 3 1 1 Wtthout electron trradtatton According to the work of Metzger and Allen [13] the Sb flux vanes from 6 × 101° to 2 × 1013 atoms/cm 2 s for a temperature of the Sb cell (Teen) rangmg from 225 to 300°C If the t e m p e r a t u r e of the substrate during the epltaxy Ts is lower than 700°C (typically 650°C) doping levels between 1015 and 2 × 1019 cm -3 can be achieved However, the crystalhne quahty decreases drastically as the Sb concentration rise above 1017 cm -~ For the highest doping levels ( > 2 × 1019 cm 3) polycrystalhne films are observed This result is clearly demonstrated by the L E E D observation of the epltaxml surface If a clear 7 × 7 superstructure ~s found for the low doping levels, it ~s not the case when antimony concentranons mcrease The L E E D pattern then presents very diffuse spots which disappear for the highest concentrations Correlatively, AES analysis of the epltaxlal surface shows an mcrease of the Sb surface concentration Similar results are found by ex-s~tu Rutherford backscattermg (RBS) measurements It evidences the Sb segrcganon at the surface and the X.,,. value (random/channehng ratio) representatwe of the crystalhne quahty (lower Smm = higher quality), mcreases with the doping concentration The spreading resistance (SR) profiles show very long transient delays Now, if Ts ~s higher than 700°C, typically 750°C. the quahty of the epflayer r e m a m s excellent throughout the Sb flux range A small decrease of the L E E D intensity is observed, which is correlated with the increase of the Sb surface concentration as seen by A E S RBS Xm,n values, which vary from 3 to 4%, are qmte similar to the slllCon bulk values The SR profiles exhibit sharp profiles and carner concentration in the layer is quite uniform Unfortunately, the d o p m g dynamics is dramatically reduced and the m a x i m u m Sb level which has been reached is lower than 3 × 1017 cm -3

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These two results agree perfectly with those ot Metzger and Allen [13], mainly tor the high 7", value If we consider, according to the results ot Barnett and Greene [14], similar segregation ratios rd for low and high T,, but a two order of magnitude difference in incorporation probabilities Sd, a significant change in the shape of the doping profiles must be observed (from smooth to sharp profile)

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3 1 2 Wtth electron lrradtatton When the wafers are showered with electrons during Sb-doped epltaxy, a slgmflcant increase of the doping concentration Is observed Figs 1 and 2 present the Sb concentration versus TS, for a gwen cell temperature (Tc~.), and the Sb concentration versus Tc~H, for a given T,, w~th and without electron irradiation It is observed that the doping concentration increases with the electron density and two order of magnitude enhancement is obtamed for the highest electron flux Correlatwely, very sharp spreadmg resistance (SR) pro-

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files a r e o b t a i n e d

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It must be noticed that with electron

surface coverage, (2) higher Sb c o n c e n t r a t i o n f o r

the same surface coverage, and (3) a linear increase of doping level with the surface coverage are obtained According to the model of ref [14] the decrease of the segregation coefficient with electron irradiation (by a factor of 50) and the linear variation could be explained by an Increase of the surface binding energy and the independence of the desorptlon coefficient on the surface coverage L E E D patterns exhibit well-ordered superstructures other than the 7 x 7 , a ~ x ~ 3 structure which appears for the low doped layers ( < 4 × 10 In cm -3) and a 5 x 5 for the highest doping levels ( 3 x 1019 cm ~) The corresponding surface coverages as determined by A E S and RBS measurements are 0 3 and 1 m o n o l a y e r

The i n t e r p r e t a t i o n o f t h e e n h a n c e m e n t o l Sb d o p i n g by e l e c t r o n i r r a d i a t i o n is not yet clear It has been d e m o n s t r a t e d before that low-energy Implantation of doping species [5] or substrate polarization [6] and ionization of incident silicon atoms [7] increase significantly the d o p a n t incorporation In these cases direct implantation mechanisms or k n o c k - o n effects were always rev o k e d H o w e v e r , m our experiment these mechanisms cannot be considered *i 30

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First, the sample is grounded and surface charge effects cannot be reasonably involved because of the high concentration of free electrons in the silicon at the given 7", Secondly, the ionization efficiency with 1 keV electrons is qmte low and consequently the n u m b e r of Ionized Sb atoms or molecules due to electron impact is not consistent with the doping enhancement observed Cracking of Sb molecules impinged on the surface and enhancement ot surface diffusion remain a possible way of explaining this p h e n o m e n o n and adsorptlon-desorptlon experiments are in progress to solve this problem

3 2 Sthcon epttaxtal layers on porous sthcon substlates Porous silicon (PS) is a "'strange" monocrystalhne form of the silicon It is obtained by anodlsatlon of (100) oriented p+-type silicon wafers in e t h a n o l H F electrolyte In good conditions (current density of 100 m A / c m 2) the anodlsatlon leads to a material quite similar in structure to bulk silicon, as seen by X-ray diffraction The resulting porosity is 52% and the mean pore size 35 [15] The main difficulty is the annealing of PS which is a necessary step for the surface cleaning as well as for the S1 epltaxy If as-prepared PS is heated in vacuum an enlargement of the pores appears, proportional to the annealing t e m p e r a t u r e Epltaxles performed on these samples exhibit very rough surfaces which are not proper for the use m integrated clrcmt (IC) technology [4] Ion b o m b a r d m e n t followed by annealing give the same results [10] The solution we present here ~s the pre-ox~datlon ol PS by chemical or thermal means The chemical pre-oxldatlon consists m the immersion of the as-prepared PS in a HC1 H20~ H~/O (3 1 1) solution for 10 m m The thermal pre-oxldatlon is a low-temperature process (300°C, 1 h m dry oxygen) These two processes give rise to a quite similar thickness (5-10 ,~) and stabilize the PS layer during further heat treatment The difficulty IS then to clean the pre-oxldlzed PS before the SI epltaxy For this purpose we have studied the thermal desorptlon of the oxide, by following the variation of both silicon and oxygen AES peaks during the ultrahigh-vacuum ( U H V ) anneahng Assuming that, for kinetic reasons, the PS surface will be clean before the bulk, the anneahng must be stopped before the complete disappearance ol the oxygen AES peak Experimentally we have found that this c o n d m o n is rcahzed when the ratio silicon/oxygen reaches 7 (3 keV electron primary energy) A simple calculation based on the screening of a SIO2 layer by slhcon atoms shows that th~s ratio corresponds m tact to one or two silicon monolayers on top of SiO~ Epltaxlal silicon layers, 1 /tm thick, grown at T, = 650°C exhibit a strong 2 x I superstructure commonly attributed to clean and well-ordered (100) surfaces The optical observations show pertect mlrror-hke surtaccs and no details appear on plane-wew SEM mJcrographs SEM cross sections show SI~p,/PS and SI,ub,tratJPS abrupt interfaces and untrans-

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formed PS structure On these layers test structures have been processed The complete process has been described previously [4] The most important step is the oxidation of the PS under layer A good oxide quality is obtained with a two-step oxidation The first one consists in a low-temperature oxidation (850°C) for a long time ( > 5 h) This operation allows the oxygen to diffuse laterally in the PS structure under the SI epltaxlal layer The second one corresponds to the denslflcatlon of the SIO2, which has been formed m the first step, at 1090°C (1 h) The quality ot this oxide is quite comparable to good thermal oxide as confirmed by the dissolution rate in HF With this method more than 20/~m width silicon islands can be fully isolated The

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convex warpage of the wafer induced by this treatment, which is an important p a r a m e t e r for IC technology, is lower than 40 ,um on 2" wafers This value accords totally with the imperatives of photolithographic processes Fig 4a presents the cross-section SEM mlcrograph of test depletion transistors obtained on the Sl/oXldlzed PS structure The corresponding electrical characteristics are reported in fig 4b The moblhty which IS deduced from these characteristics is lower than expected for the channel doping level (450 c m 2 V -I S I), but quite comfortable for SOl applications 3 3 The CoSl2/Sl and SlepJCOSl2/Sl,ub~trat e structures (MBT)

The metal base transistor

M B T is considered today as a very attractive device for hyperfrequency amplification It supposes the ability to grow both epltaxlal metal films on slllcon and re-epltaxlal silicon films on the metal layer Epitaxial thin slhclde layers, which have metallic properties, have been extensively studied [16-18] The cobalt dlsillclde is particularly interesting for its good lattice matching with silicon It can be obtained either by MBE, l e by co-evaporation ot metal and silicon, or by solid-phase epltaxy (SPE), 1 e by thermal annealing of a Co predeposlted layer on the silicon substrate The SPE formation of COS12 proceeds by different steps, namely the Co2S1, CoSI and finally CoSI~ phases These different steps have been previously evidenced by the AES profiling of both SI and Co peaks during the formation annealing [11] After few minutes at T~ = 650°C the CoSI 2 phase is always obtained However, the quality of this layer is strongly dependent on both the annealing temperature and the layer thickness Typically, If the thickness and the annealing temperature rise above 200 A and 650°C respectively, formation of CoSh Islands Is observed This p h e n o m e n o n can be easily detected by looking at the change of the L E E D pattern from a 1 x 1 to a 7 × 7 superstructure In fact high-resolution electron microscopy [19] observation of the different phases has demonstrated that the reaction is initiated at RT by epitaxy of CoSl on $1 and the first two phases Identified as Co~S! and CoS1 by AES are m fact a mixture ot these phases with Co, the proportions being different These results agree perfectly with those of Derrlen obtained by L E E D , angle-resolved ultraviolet photoemlsslon ( A R U P S ) , and extended electron energy-loss fine structure technique [20] Intenswe electrical characterizations have been also performed Transient capacitance studies have shown that no electron traps assocmted with Co diffusion are detected in the SI bulk Electrically ideal structures have been found for anneahng temperatures below 7{)(I°C and CoSh films thickness below 200 A For the other samples a continuum of states highly localized near the CoSI4SI interface is observed [21] Moreover, tunnehng spectroscopy of electrons between the CoSb metal and the Sdlcon bulk have been shown to yield sharp phonon structures unusually observed be-

F Arnaud d'A ~ttaya et al / Slhcon M B L

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tween - 1 0 0 mV and +100 mV [22] The interpretation of the other sharp structures also observed at higher energy (between - 1 0 0 and - 6 0 0 meV) is not yet clear More recently variations of the superconducting transition temperatures with CoSI2 thickness have been ewdenced [23] Silicon re-epltaxy on COS12 gives rise to quite perfect epltaxlal sandwiches as demonstrated by the T E M observations [24] Plane view of the SkvJCoSl2/ Sl,ub,tr,,t~ structure shows black areas which correspond to grains ot type A (i e grains oriented like the substrate) and white areas corresponds to grains twinned with respect to the substrate orientation (l e grains rotated by 180°

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F Arnaud d'Av~taya et al / Sdtcon M B E recent developments

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with respect to the (11 i ) axis) No dislocation network is observed assessing that the COS12 layer is completely strained On the high-resolution cross section of fig 5 it must be noticed the highly sharp and linear CoSI2/Sl~ub~tr~te and CoSl2/Slep I interfaces over a long range ( > 3000 ,~) However, as the crosssection T E M observations are highly localized It iS really difficult to assess that there are no pinholes The presence of macroscopic pinholes is dramatic because it leads to unintentional PBT and consequently lrreproduclble characteristics from wafer to wafer Moreover, the current flowing through pinholes can create a local heating of the structure and leads to a change, In time, of the electrical characteristics associated with an enlargement of the pinholes Nevertheless, these pinholes may be detected using plane-view T E M imaging on thinned MBT structures Using this technique no pinholes have been observed in our layers (T, < 650°C, COS12 thickness < 200 ,~) Fig 6 shows the energy band diagram of a MBT transistor with pinholes and figs 7a and 7b the common base characteristics of two samples A and B obtained for different experimental conditions Sample A correspond to a COS12 formation temperature of T, = 650°C followed by SI epltaxy at the same T, Sample B corresponds to the same CoSI~ reaction temperature as for sample A but the SI epltaxy temperature was 7", -- 750°C The silicon epitaxial overlayers consist of 2000 A undoped silicon followed by 8000 ,~ Sb-doped silicon at 3 × l() 19 cm -~ and 5 × l0 j7 cm ~ for samples A and B respectively, in order to define a hot electron injector These characteristics do not intercept near the origin which is expected for hot electrons injected from the emlttter above the collector base barrier height However, this effect could be also due to the current flowing through pinholes The electrical method recently described [25] consists in plotting the emitter current I v or the variation of the emitter current I F versus the emitter base voltage for different collector base bias VB( It is assumed that the real MBT current is not affected by the collector base bias because the potential is completely screened by the metal The variation of the emitter current for sample A (fig 8a) is quite negligible, as a matter of fact we assume that there is no pinhole in the CoSi2 sandwiched layer This is not the case for sample B The emitter current characteristics of fig 8b are strongly dependent on the collector base bias This result is indicative of current flowing through macroscopic pinholes and the characteristics of fig 8b are those of an unwanted PBT ~Ihis non-destructive method ,illows one to determine unambiguously the presence ot pinholes in MBT transistors It also opens the possibility ot statistical analysis on entire waters It has been also demonstrated that S~/CoS,./Si structures, realized by MBE at ,i sUttlClCntly low tempcrature (7", < 650°C) le,id~ to real MBT

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4. Conclusion The three examples biguously

which have been presented

the potentmhty

of slhcon MBE

here demonstrate

for fundamental

unam-

studms as well as

for technological appheat~ons The important problem of doping can be solved by using electron ~rradlat~on during the growth However, the mechanism w h i c h ~s r e v o l v e d is n o t y e t c l e a r l y u n d e r s t o o d t h a t e p ~ t a x y o n P S is a w a b l e t e c h n o l o g y t e n t i o n ~s p a i d t o t h e P S p r e p a r a t i o n

It h a s a l s o b e e n d e m o n s t r a t e d

for SOI application

if p a r n c u l a r

at-

~tself F m a l l y , ~t is s h o w n t h a t h~gh q u a l -

ity s t r a i n e d SffCoSI2/S~ s t r u c t u r e s c a n b e o b t a i n e d a n d t h a t t h e d e t e c n o n o l p i n h o l e s , w h i c h ~s o f m a j o r i m p o r t a n c e f o r t h e s t u d y o f r e a l M B T t r a n s i s t o r s , is e a s i l y a c h m v e d b y e l e c t r i c a l m e a s u r e m e n t s

References [1] F Ro,Lmcher S Delage Y (ampldelh and F Arnaud d A~mlya Electron LuUers 211 (1084) 762 [2] K l,,hlba,,hl and S Furuka~sa, IEDM Tech Digest (1984) 868 [3,] I ~X~ano, H lshlwaraand N Kaltu Japan J Appl P h ~ 22(198:0 1474 [4] F Arnaud d Avltaya, K Barla, R Hermo and G Bom~hd, Proc Ist lnt~_rn S~mp on Sillcon Molecular Beam Epltaxy Toronto, 14-17 May 198'~, I Ele~.trot.hem Soc to bc pubhshud [~] "1 Ota I Vacuum %~.1 Technol A2(1984)~,9"~ [6] R A A Ixubmk W h' Lcong and E H ( Parkt.r Appl Ph'~s [~.ttt.rs 46 (198~) %S [7] H Jorke A Casel K H Hluber and H K~bbel, 3rd European Workshop on Mole~_ular Beam Fpltaxx, Atp,nols France 18-20 Mard~ I985 [8] S Dclagt. ',, Fatarenko, J C Obcrhn "~ Campldclh and F Arnaud d'A~lta,.i MR", Europe Meutmg, Strasbourg, France 13-15 Ma', 198S, J de Ph}'qquc to b~_ pubhsh~.d [91 ~, Konaka, M T a b e a n d T Sak,u Appl l'h~,,, [utlep, 41 (19S2) 86 [10] H Baumgart F Phdlpp and G K Ccllt.r ( onl on MJ~_ro,,t.op,~ o! ~,emu_onducmlg Maturials Oxtord March 1983 [11] F A r n a u d d A v J t a v a S Dcla D. E Ros~.nchurandJ Dernen J Vat.uum~,~_l I t.t.hnol P,t (ItJ,RS) 770 [12] A l',hl/akd k Nakagawa and "~ %lurakl, 2nd Inturn ( o n l on Molt.~.ular Ikam [ pfl,l\\ and ( It.an ",urlace "Iet.hmquc,, Tok,~o 27 30 Augu',t 19~2 [13] R A Mctzgcr and F G Allen, J Appl Ph'y'~ q'~ (19~4) 9~;[ [14] % A Barntn and J E Grt.~.ne, %urlace %c~ ISI (198S)67 [lq] (, Bomuhfl R Hcrmo, k Barla and J ( Phster, J Elet_trod~em Not. l'~0 (19S:;)ll~ll [16] R 1 Ttmg I C Bean I M (hbson J M Poatt. and D ( Jat.obson -Xppl Phxs l t_tlurs 40 { 19821 684 [17] K Istubash~ and % [ urukax~a Appl Ph'~', 1 etlcp, 43 {19811 6611 IlSl Ix b, hfl~ash~ H l',h~wa~a and % [ urukawa ISth ( onl o11 ~,ohd Nt,llt_ l)t'~lt_t_s blalt_~al,, 1ok\o 19£3 II. I ( d &ntu~roche ~, SurIacc St.~ I(~S (1980) 7"31 [2(I] J l)t.rncn, "oullact. Sol 168 (19~61 171 [21] [ Roscnchcr S I)elagc and F Arnaud d Ax~ta',a I \ acuum Su~ Tt_~.hnol 17,~,(It~sq) 7~2

F Arnaud d Avttava et al / Szhcon M B E recent development~

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[22] E Rosencher, P A Badoz, A Bnggs, Y Campldelh and F Arnaud d'Avltaya, 1st Intern Syrup on Sdlcon Molecular Beam Epltax}, Toronto 14-17 May 1985, J Electrochem Soc , to be pubhshed [23] P A Badoz A Bnggs E Rosencber and F Arnaud d'Avltaya J Phvs Letters, to be pubIi~,hed [24] C d'Anterroches and F Arnaud d'Avltaya, Thin Solid Films, to be published [25] E Ro~encher, S Delage and F Arnaud d'Avltaya, to be published