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Si(III) interface formation: An UPS, LEED and Auger study
Surtdce Saencr 16X (1986) 135-233 North-Holland. Am\terddm
FIRST STAGES OF THE Mo/Si(III) UPS, LEED AND AUGER STUDY H BALASKA,
R C CINTI.
INTERFACE
T T A NGUYEN
FORMATION:
and J DERRIEN
Luhomtorre d’Etudes der Proprteter Electronrqtrrr drc Soltdes. C N R 5 38012 Grenoble Ceder France RecelLed
IO lune
lYX5, nccepted
for pubhc&lon
AN
B P 166.
I? Julv 19X5
The behavlour ot the MO&( 111) interface has been studled under atomically clean condltlons using low-energy electron dlftrdctlon, UV photoemIssIon dnd Auger spectro\coptes At room temperdture, the Auger measurements indicdte d Idyer-hy-ldyer growth where no intermlxmg mvolvlng dtorn]L motion KTOSF the mterfdce occurs. m contrnst with mdn! trdnsltlon-metal-sillcon systems The abrupt Junction IS confirmed by the UPS results which show d MO nd\orbed phase in the coverage range H < 1 monolayer and d rapid recovering of the bulb MO features for mcredsmg 0 The band bending varlatlon detected bl the shift of the SI bulb structure\ on the UPS spectra show< that the Schottky bdrrler I\ termed before completion ot the hrst MO layer The
1. Introduction Metal-semiconductor contacts dre dn Important pdrt of the semiconductor technology, especially m connectlon with very-large-scale Integrated (VLSI) semlconductor devices That has Induced a large amount of fundamental work concerning numerous metal-semiconductor Junctions under various preparation condltlons, m order to describe mlcroscoplcally the interface formation Noble- and near-noble-metal-sdlcon interfaces have been mtenslvely studied m this way, while refractory metals only begin to be explored Among them, molybdenum 1s dttractlve because Its metallurgical, chemical and electrical propertles are good and compatible with the usual fabrlcatlon process used m VLSI technology In spite of this, up to now only few short note\ [l-3] have described the lunctlon formation for the MO-% system and their conclusions have not led to an unambiguous descrlptlon of the nature of the interface This brought us to explore carefully the first steps of the interface form&on m this system The mam questions which we have attempted to elucidate are the determmatlon of a possible mtermlxmg m the interface region and the chdracterization of the electronic densltles m the few first interface layers This paper presents our results concermng these pomts Fl0039-6028/X6/$03 50 0 Elsevler Science Publishers (North-Holland Physics Pubhshmg Dlvlslon)
B V
nally, it gives Some hrst result5 on the effect of controlled mterfdce\
2. Experimental
dnneahng
on \uch
procedure
“In situ” m ‘1 UHV chdmber (ba\e All measurements were performed presxure < 1OF”’ Torr) equipped with LEED, angle-resolved UPS and Auger spectroscopy technique5 PhotoemIssIon spectra were recorded u~ng a He dlrcharge lamp (21 2 eV photon source) ,md only normal ernl\\lon was collected The energy dnd angle re\olutlons were kept ,tt = 150 mV ,md +?“, re\pcctlvely The (111) slhcon wafers (p type, B doped. IO-’ Q cm) were tredted according to the usual way to get nn ordered clean 5urfdce (repetltlve 600 V argon-Ion mild 5puttermg dnd anneahng cycle\ under UHV condltlon\ up to 900°C) After such a treatment. the SI surface showed very sharp 5pot4 of the (7x7) superstructure, no contammant waq tound by Auger spectroscopy ,md the UPS spectra displayed well-developed characten\tlc features ot a clean surface The molybdenum deposits were prepdred by metal subllmatlon onto the S1(7x7) 5ubstrdtes The MO source placed dt d distance ot 1_5cm horn the sdmple, was made with d MO wire wrdpped on d tungsten hdlr pm heated by d current-reguldted power supply Well-controlled fluxes were then obt‘uncd, but only In ‘I condcn\,ltlon r,lte r,mgc of few tenth of ‘I monolayer/mlnutc, due to the short llfetlme ot our source ‘tt too high oper‘itmg temperdturc The re\ldu,d pressure durmg the evdpordtlon\. rcmdmed ,tt .m ,Iccept‘Lble value (= 5 x 10 I"Torr) owing to the getterlng ettect ot Mo conden5‘ttmn Depo\lt\ were achieved onto SI \urtace\ mamtdmed .it room tcmperdture
3. Results and discussion At the Inltl,d \tdges ot Mo depo\ltlon LEED ob\cr\dtlon show\ ‘I r,lpld erasing of the orlgmal (7x7) structure At 8 = 0 3 monolayer (ML), only ‘I strong diffuse background remdm5 with trace, ot the (1 x 1) structure which dlrappedr near 0 60 7 ML Compared to the Nl/Sl( 111) ca\e [A] where the two vdm,hmg limits were tound for H = 0 8 dnd 1 .S ML, thl5 r,tpld disdppearante suggests a low moblllty for the MO dtom5 on the subutrnte. the I,uger coverage values found for the NI depo\lts bemg Interpreted In term5 of twodlmenslonal clu\terlng which give\ larger bare SI areds permlttmg (7x7) rcconstructlon At the 5dme time, the MO MVV (186 eV) and the Sl LVV (92 eV) Auger slgnal mtensltles. plotted versus deposItIon time show curve5 typlcal of the layer-by-layer growth mode, where the breaks correspondmg to the completlon of the first and second layer dre well-defmed (fig 1) Our MO Source wa\
H Balaska
et al I Fmt stage7 of MolT~(llI)
717
rnterface formatlot
cahbrated with this well-known phenomenon lmpreclslon (due to thermal drift) of our quartz mlcrobalance system did not permit to determine the exact density (m atoms/cm’) of these so-defmed “monolayers” Indlcatlons on the growth mode are also given by the evolution of the relative Sl LVV Auger slgnal intensity versus the deposit thickness In fig 2, the attenuation coefficient
0
Fig time
5 EXPOSURE
10 TIME
15
20
(mmute)
1 Mo MVV (186 eV) dnd SI LVV (Y? eV) Auger peak mtenslties
COVERAGE
plotted
verb”5 deposit
(M L )
Fig 2 Semi-loguthmlc plot of the attenuation emlwon versus metdl coverage 0
coetfwent
a = log[l~,(0)/Is,(O)]
0t
the Sl LVV
~1= log [I,,(0)lf,,(O)] IS plotted d\ d tunctlon ot the coverage 0. f,,(0) being the medsured Intensity for a given coverdge H dnd Is,(O), the clean SI sub\tr,tte emlsclon With such d defmltlon, d sharp lnterfdce with no dtomlc Interml\mg will show a hnedr dependence ot
ces prepared using dlfterent technique\ Let us consider now the other curves of fig 3 We notlce that deposits of d few tenths of a monolayer era5e rapldly the charactenstlc electromc features of the (7x7) surface, and m the 5ame time a structure derived from metal dstates grows between EF and -5 eV On the first three spectra, we observe that the SI 5p structure. appearmg between -7 and -8 eV. undergoes a shift towdrdv E, This energy shift. materlahzed by the arrow5, lndlcateq a vdrldtlon of the EF posltlon In the gap and hence d modlflcatlon of the mltlal band bending upon metal deposltlon Such an effect has been found before m the interface formation of Al. Gd. In and Ce evdporated on Sl(11 I) [12. I.31 In the present case, It corresponds to a reduction of the curtace band bending of our p-type Si samples Fig 4 displays the EDC\ of thicker depoflts, for which the eml55lon originating from metal d states IS dominant For 8 5 0 8 ML. the MO d state5 give ri?e to a broad peak (- 4 eV FWHM) centered at about -1 5 eV, which
a=000
I
b=oo7
C=olO ML 25
d=O
EV
- -0 -6 Fig 3 Normal emlsvon dnd 0 2 monoldycr
-4
-2
spectra for the clean (7x7) surface (lower curve) and tor 0 = 0 (15 0 Arrows emphasize the progressive $hlft of the hulk structures near 7 5 tV
1
bz06
Fg 4 Normal emlsslon spectra \howmg changes ot the valence band emlsvon durmg tormatlon ot the Mo/Sl mtertxr The dotted EDC refer\ to the clean (7x7) \urfxe for compdrtson
reflects the metal-S1 bondmg dt the interface Above. this structure IS rdpldly drowned out by the metallic MO spectrum which 15 fully developed at 0 L 1 ML This observation 1s m agreement with the layer-by-layer growth model already deduced from AES measurements The remarkable \lmllarlty between the 0 4 ML and 0 6 ML EDCs, both m shape dnd m energy position, Indicate5 a \ame band bending dt these coverageq. thl$ strongly suggests thdt the Schottky barrier 19 fulfilled at lower coverage range The completion of the barrier formation at such low metal coverage has been already observed. for example with the Ce/Sl( 11 I) \yctem [13] where the band bendmg evolution has also been found to end up before UPS spectra \how a recovery of the metallic character of the deposit It 15 worth mentlomng that the metallic spectrum obtained on the thicker deposits 15 clearly different from the broad EDC, with three peaks, found on polycry\tallme MO [17] Its relative narrowness and its unstructured shape highly suggest that our angle-resolved
H Bulaska et ul I Fmt stages of MoIS~(lll)
EV 4
’
-6
-&
interface formation
731
-2
FIN 5 Normdl emw~on spectra \howng VdrldtlOn5 of the valence emlwon annealmg to mcreasmg temperatures The uutlal MO coverage IS H = ?. ML
dtter
succewvc
measurements reflect mamly mlxed contrlbutlons emitted normally from lowmdex planes Such narrow EDCs have been observed on (110) and (001) MO surfaces m ARUPS spectra They orlgmate from high-density states near the f pomt of the Brllloum zone (via a surface emission process) and from surface states [18] Based on this argument we believe that our MO films are textured, with high atomic density planes parallel to the substrate, as often observed on metalhc evaporated thm films In order to investigate the thermal stabrhty of these abrupt interfaces and to examme the M-5 reactlon, we have carried out UPS measurements on deposits submltted to annealing at mcreasmg temperature In fig 5 are reported the EDCs collected with a 8 = 2 ML deposit, which are representative of the results obtamed m the 8 < 10 ML range we explored A 10 mm dnnealmg was used at each cycle Up to 300°C. no change 1s detected m the UPS spectra Above this temperature, the peak near EF undergoes a relative decrease m comparison with the second MO-derived structure (at about 2 3 eV
below EF) This shape I\ mamtamed until =6OO”C The MO!%, EDC [ 141 appears between 600 and 700°C and remalnh stable up to =YOO”C It I\ worthy of note that the formatlon of MoS1, slhclde at 700°C I\ dccompamed with d weak (1 x I) LEED structure which becomes more defined at 800°C Two probable causes can be evocated for the dppedrance of this ordered \urf,tce structure cluctermg of the slllclde phase. d\ has been observed by high-re\olutlon electron microscopy of thm MO layer\ on Sl( 100) [ 15. Ih], or ‘I prefcrcnteal orlentatlon ot the MoSI, layer Further lnve\tlgatlon$ ‘Ire needed to find ‘i detmltl\e answer to that que\tlon
4. Conclusion The mdln conclu\lons of this work can be \ummanzed d\ follow\ (I) In our experlmentdl condltlon\. ulth SI( 111)(7x7) surface\. the Mo/Sl Intertace remams unredcted. no mlxlng of atoms dcros\ the Interface occur4 ‘14 \een with Auger \pectroccopy (II) UPS data conflrm the layer-by-layer growth mode Spectra 4how the tlr\t MO layer forms a cheml\orbed state on the SI surf‘lce The UPS bulk Mo tcatures are rdpldly recovered for mcrensmg thlckne\\ (111) The Schottky barrier height 1s flxcd betore the complctlon of the tlrst ‘idsorbed Mo layer (IV) Such thin unreacted mterfdce (Inltlal Mo coverage < IO ML) are \tdblc upon anneahng up to 300°C Above that temperature MO-% reactlon occur4 dnd give\ the MoSll \lllclde at =6OO”C
References [I] G Row. I Abbnti. L Br,uco\ILh J Landau W t Spacer U d~i Pennlno .md S N,mn,lronc. Phyw‘t I1711 188 (lYH3) 795 E Puppln and A RIZZI Solid \t,ltc [2] I Abhatl, L Bracowch, B de bIlchell\. A F.~ww Commun 57 ( lY83) 731 [3] T T 4 Nguven dnd R C Cmtl I de Phyvque C 5 -15 (I%-!) 435 [J] A Ddoudt T T A Nguytn And R C (mtl to he puhllshrd [5] D E Eastmdn. F J Hlmpsel .md F J vdn der VLLn. Sohd State Commun 35 (IYXO) 315 [6] t J Chahdl J E Rov,e and D A Z&rmer. Phy\ Re\ Letttrs 46 (19X1) 600 [7] T Yokotsuka, S Kono. 9 Suaul\~ dnd T S,q,w,~ Tolld State Commun 39 (19X1)1001 [X] F Houzay. G M Gtnchar. R Plnchdux. P Thor\? ‘r Petrott and D Dagneaux. Surtax %I YY (IYXO) 2x [Y] J b Rowe S B Chrl\tm,rn ad H Ihach Phks Rr\ Lcttcr\ 3-l (lY75) 873 [IO] F J Hlmp\el, P Hamann and I> E Eatmdn Phy\ Re\ 823 (19X1) 2003 [II] H Froltzhelm U Kohler and H Lammermg Ph?\ Reb BiO (IYHJ) 5771 [ 171 G Mnrg,irltondo J E Roue and S B Chrl\tm,m Ph\\ Rc\ BI1 (lY76) 5396 [ 131 hl Grmm, J Joyce. S A Chamber\ D G O’Ne~ll. M del Gludlce ,md J H Wedrcr, Phv\ Rev Letters 53 (19x4) 7331
H [l-1] J H Weaver
Bnlatha
et al
V L Moruzzl
I Ftnr ylagec of hfol S1(111) ad
F A Schmidt.
Phy\
Rev
interfaceforrnallon B3
(19X1) 2Ylh
[ 151F Arnnud d’Awtaya. prwdte communlcatlon [ 161 A Perlo. J Terra. G Bomchll, F Arnaud d’Avltdyd and R Pdntcl (lY84) x57 [ 171 E Al Khourk, R C Cmtl and J B Hudwn. [IX] R C Cmtl, E Al Khourq B K Ch&ra\erty 3106
133
Appl
Ph)s
J de Phy\quL 35 (lY7-l) L17Y ,md N E Chrlstcn\en Phys Rev
Lctter\15
B1-l (lY7h)
FIRST STAGES OF THE Mo/Si(III) UPS, LEED AND AUGER STUDY H BALASKA,
R C CINTI.
INTERFACE
T T A NGUYEN
FORMATION:
and J DERRIEN
Luhomtorre d’Etudes der Proprteter Electronrqtrrr drc Soltdes. C N R 5 38012 Grenoble Ceder France RecelLed
IO lune
lYX5, nccepted
for pubhc&lon
AN
B P 166.
I? Julv 19X5
The behavlour ot the MO&( 111) interface has been studled under atomically clean condltlons using low-energy electron dlftrdctlon, UV photoemIssIon dnd Auger spectro\coptes At room temperdture, the Auger measurements indicdte d Idyer-hy-ldyer growth where no intermlxmg mvolvlng dtorn]L motion KTOSF the mterfdce occurs. m contrnst with mdn! trdnsltlon-metal-sillcon systems The abrupt Junction IS confirmed by the UPS results which show d MO nd\orbed phase in the coverage range H < 1 monolayer and d rapid recovering of the bulb MO features for mcredsmg 0 The band bending varlatlon detected bl the shift of the SI bulb structure\ on the UPS spectra show< that the Schottky bdrrler I\ termed before completion ot the hrst MO layer The
1. Introduction Metal-semiconductor contacts dre dn Important pdrt of the semiconductor technology, especially m connectlon with very-large-scale Integrated (VLSI) semlconductor devices That has Induced a large amount of fundamental work concerning numerous metal-semiconductor Junctions under various preparation condltlons, m order to describe mlcroscoplcally the interface formation Noble- and near-noble-metal-sdlcon interfaces have been mtenslvely studied m this way, while refractory metals only begin to be explored Among them, molybdenum 1s dttractlve because Its metallurgical, chemical and electrical propertles are good and compatible with the usual fabrlcatlon process used m VLSI technology In spite of this, up to now only few short note\ [l-3] have described the lunctlon formation for the MO-% system and their conclusions have not led to an unambiguous descrlptlon of the nature of the interface This brought us to explore carefully the first steps of the interface form&on m this system The mam questions which we have attempted to elucidate are the determmatlon of a possible mtermlxmg m the interface region and the chdracterization of the electronic densltles m the few first interface layers This paper presents our results concermng these pomts Fl0039-6028/X6/$03 50 0 Elsevler Science Publishers (North-Holland Physics Pubhshmg Dlvlslon)
B V
nally, it gives Some hrst result5 on the effect of controlled mterfdce\
2. Experimental
dnneahng
on \uch
procedure
“In situ” m ‘1 UHV chdmber (ba\e All measurements were performed presxure < 1OF”’ Torr) equipped with LEED, angle-resolved UPS and Auger spectroscopy technique5 PhotoemIssIon spectra were recorded u~ng a He dlrcharge lamp (21 2 eV photon source) ,md only normal ernl\\lon was collected The energy dnd angle re\olutlons were kept ,tt = 150 mV ,md +?“, re\pcctlvely The (111) slhcon wafers (p type, B doped. IO-’ Q cm) were tredted according to the usual way to get nn ordered clean 5urfdce (repetltlve 600 V argon-Ion mild 5puttermg dnd anneahng cycle\ under UHV condltlon\ up to 900°C) After such a treatment. the SI surface showed very sharp 5pot4 of the (7x7) superstructure, no contammant waq tound by Auger spectroscopy ,md the UPS spectra displayed well-developed characten\tlc features ot a clean surface The molybdenum deposits were prepdred by metal subllmatlon onto the S1(7x7) 5ubstrdtes The MO source placed dt d distance ot 1_5cm horn the sdmple, was made with d MO wire wrdpped on d tungsten hdlr pm heated by d current-reguldted power supply Well-controlled fluxes were then obt‘uncd, but only In ‘I condcn\,ltlon r,lte r,mgc of few tenth of ‘I monolayer/mlnutc, due to the short llfetlme ot our source ‘tt too high oper‘itmg temperdturc The re\ldu,d pressure durmg the evdpordtlon\. rcmdmed ,tt .m ,Iccept‘Lble value (= 5 x 10 I"Torr) owing to the getterlng ettect ot Mo conden5‘ttmn Depo\lt\ were achieved onto SI \urtace\ mamtdmed .it room tcmperdture
3. Results and discussion At the Inltl,d \tdges ot Mo depo\ltlon LEED ob\cr\dtlon show\ ‘I r,lpld erasing of the orlgmal (7x7) structure At 8 = 0 3 monolayer (ML), only ‘I strong diffuse background remdm5 with trace, ot the (1 x 1) structure which dlrappedr near 0 60 7 ML Compared to the Nl/Sl( 111) ca\e [A] where the two vdm,hmg limits were tound for H = 0 8 dnd 1 .S ML, thl5 r,tpld disdppearante suggests a low moblllty for the MO dtom5 on the subutrnte. the I,uger coverage values found for the NI depo\lts bemg Interpreted In term5 of twodlmenslonal clu\terlng which give\ larger bare SI areds permlttmg (7x7) rcconstructlon At the 5dme time, the MO MVV (186 eV) and the Sl LVV (92 eV) Auger slgnal mtensltles. plotted versus deposItIon time show curve5 typlcal of the layer-by-layer growth mode, where the breaks correspondmg to the completlon of the first and second layer dre well-defmed (fig 1) Our MO Source wa\
H Balaska
et al I Fmt stage7 of MolT~(llI)
717
rnterface formatlot
cahbrated with this well-known phenomenon lmpreclslon (due to thermal drift) of our quartz mlcrobalance system did not permit to determine the exact density (m atoms/cm’) of these so-defmed “monolayers” Indlcatlons on the growth mode are also given by the evolution of the relative Sl LVV Auger slgnal intensity versus the deposit thickness In fig 2, the attenuation coefficient
0
Fig time
5 EXPOSURE
10 TIME
15
20
(mmute)
1 Mo MVV (186 eV) dnd SI LVV (Y? eV) Auger peak mtenslties
COVERAGE
plotted
verb”5 deposit
(M L )
Fig 2 Semi-loguthmlc plot of the attenuation emlwon versus metdl coverage 0
coetfwent
a = log[l~,(0)/Is,(O)]
0t
the Sl LVV
~1= log [I,,(0)lf,,(O)] IS plotted d\ d tunctlon ot the coverage 0. f,,(0) being the medsured Intensity for a given coverdge H dnd Is,(O), the clean SI sub\tr,tte emlsclon With such d defmltlon, d sharp lnterfdce with no dtomlc Interml\mg will show a hnedr dependence ot
ces prepared using dlfterent technique\ Let us consider now the other curves of fig 3 We notlce that deposits of d few tenths of a monolayer era5e rapldly the charactenstlc electromc features of the (7x7) surface, and m the 5ame time a structure derived from metal dstates grows between EF and -5 eV On the first three spectra, we observe that the SI 5p structure. appearmg between -7 and -8 eV. undergoes a shift towdrdv E, This energy shift. materlahzed by the arrow5, lndlcateq a vdrldtlon of the EF posltlon In the gap and hence d modlflcatlon of the mltlal band bending upon metal deposltlon Such an effect has been found before m the interface formation of Al. Gd. In and Ce evdporated on Sl(11 I) [12. I.31 In the present case, It corresponds to a reduction of the curtace band bending of our p-type Si samples Fig 4 displays the EDC\ of thicker depoflts, for which the eml55lon originating from metal d states IS dominant For 8 5 0 8 ML. the MO d state5 give ri?e to a broad peak (- 4 eV FWHM) centered at about -1 5 eV, which
a=000
I
b=oo7
C=olO ML 25
d=O
EV
- -0 -6 Fig 3 Normal emlsvon dnd 0 2 monoldycr
-4
-2
spectra for the clean (7x7) surface (lower curve) and tor 0 = 0 (15 0 Arrows emphasize the progressive $hlft of the hulk structures near 7 5 tV
1
bz06
Fg 4 Normal emlsslon spectra \howmg changes ot the valence band emlsvon durmg tormatlon ot the Mo/Sl mtertxr The dotted EDC refer\ to the clean (7x7) \urfxe for compdrtson
reflects the metal-S1 bondmg dt the interface Above. this structure IS rdpldly drowned out by the metallic MO spectrum which 15 fully developed at 0 L 1 ML This observation 1s m agreement with the layer-by-layer growth model already deduced from AES measurements The remarkable \lmllarlty between the 0 4 ML and 0 6 ML EDCs, both m shape dnd m energy position, Indicate5 a \ame band bending dt these coverageq. thl$ strongly suggests thdt the Schottky barrier 19 fulfilled at lower coverage range The completion of the barrier formation at such low metal coverage has been already observed. for example with the Ce/Sl( 11 I) \yctem [13] where the band bendmg evolution has also been found to end up before UPS spectra \how a recovery of the metallic character of the deposit It 15 worth mentlomng that the metallic spectrum obtained on the thicker deposits 15 clearly different from the broad EDC, with three peaks, found on polycry\tallme MO [17] Its relative narrowness and its unstructured shape highly suggest that our angle-resolved
H Bulaska et ul I Fmt stages of MoIS~(lll)
EV 4
’
-6
-&
interface formation
731
-2
FIN 5 Normdl emw~on spectra \howng VdrldtlOn5 of the valence emlwon annealmg to mcreasmg temperatures The uutlal MO coverage IS H = ?. ML
dtter
succewvc
measurements reflect mamly mlxed contrlbutlons emitted normally from lowmdex planes Such narrow EDCs have been observed on (110) and (001) MO surfaces m ARUPS spectra They orlgmate from high-density states near the f pomt of the Brllloum zone (via a surface emission process) and from surface states [18] Based on this argument we believe that our MO films are textured, with high atomic density planes parallel to the substrate, as often observed on metalhc evaporated thm films In order to investigate the thermal stabrhty of these abrupt interfaces and to examme the M-5 reactlon, we have carried out UPS measurements on deposits submltted to annealing at mcreasmg temperature In fig 5 are reported the EDCs collected with a 8 = 2 ML deposit, which are representative of the results obtamed m the 8 < 10 ML range we explored A 10 mm dnnealmg was used at each cycle Up to 300°C. no change 1s detected m the UPS spectra Above this temperature, the peak near EF undergoes a relative decrease m comparison with the second MO-derived structure (at about 2 3 eV
below EF) This shape I\ mamtamed until =6OO”C The MO!%, EDC [ 141 appears between 600 and 700°C and remalnh stable up to =YOO”C It I\ worthy of note that the formatlon of MoS1, slhclde at 700°C I\ dccompamed with d weak (1 x I) LEED structure which becomes more defined at 800°C Two probable causes can be evocated for the dppedrance of this ordered \urf,tce structure cluctermg of the slllclde phase. d\ has been observed by high-re\olutlon electron microscopy of thm MO layer\ on Sl( 100) [ 15. Ih], or ‘I prefcrcnteal orlentatlon ot the MoSI, layer Further lnve\tlgatlon$ ‘Ire needed to find ‘i detmltl\e answer to that que\tlon
4. Conclusion The mdln conclu\lons of this work can be \ummanzed d\ follow\ (I) In our experlmentdl condltlon\. ulth SI( 111)(7x7) surface\. the Mo/Sl Intertace remams unredcted. no mlxlng of atoms dcros\ the Interface occur4 ‘14 \een with Auger \pectroccopy (II) UPS data conflrm the layer-by-layer growth mode Spectra 4how the tlr\t MO layer forms a cheml\orbed state on the SI surf‘lce The UPS bulk Mo tcatures are rdpldly recovered for mcrensmg thlckne\\ (111) The Schottky barrier height 1s flxcd betore the complctlon of the tlrst ‘idsorbed Mo layer (IV) Such thin unreacted mterfdce (Inltlal Mo coverage < IO ML) are \tdblc upon anneahng up to 300°C Above that temperature MO-% reactlon occur4 dnd give\ the MoSll \lllclde at =6OO”C
References [I] G Row. I Abbnti. L Br,uco\ILh J Landau W t Spacer U d~i Pennlno .md S N,mn,lronc. Phyw‘t I1711 188 (lYH3) 795 E Puppln and A RIZZI Solid \t,ltc [2] I Abhatl, L Bracowch, B de bIlchell\. A F.~ww Commun 57 ( lY83) 731 [3] T T 4 Nguven dnd R C Cmtl I de Phyvque C 5 -15 (I%-!) 435 [J] A Ddoudt T T A Nguytn And R C (mtl to he puhllshrd [5] D E Eastmdn. F J Hlmpsel .md F J vdn der VLLn. Sohd State Commun 35 (IYXO) 315 [6] t J Chahdl J E Rov,e and D A Z&rmer. Phy\ Re\ Letttrs 46 (19X1) 600 [7] T Yokotsuka, S Kono. 9 Suaul\~ dnd T S,q,w,~ Tolld State Commun 39 (19X1)1001 [X] F Houzay. G M Gtnchar. R Plnchdux. P Thor\? ‘r Petrott and D Dagneaux. Surtax %I YY (IYXO) 2x [Y] J b Rowe S B Chrl\tm,rn ad H Ihach Phks Rr\ Lcttcr\ 3-l (lY75) 873 [IO] F J Hlmp\el, P Hamann and I> E Eatmdn Phy\ Re\ 823 (19X1) 2003 [II] H Froltzhelm U Kohler and H Lammermg Ph?\ Reb BiO (IYHJ) 5771 [ 171 G Mnrg,irltondo J E Roue and S B Chrl\tm,m Ph\\ Rc\ BI1 (lY76) 5396 [ 131 hl Grmm, J Joyce. S A Chamber\ D G O’Ne~ll. M del Gludlce ,md J H Wedrcr, Phv\ Rev Letters 53 (19x4) 7331
H [l-1] J H Weaver
Bnlatha
et al
V L Moruzzl
I Ftnr ylagec of hfol S1(111) ad
F A Schmidt.
Phy\
Rev
interfaceforrnallon B3
(19X1) 2Ylh
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