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Surface reaction of CH3SiH3 on Ge(100) and Si(100)
Applied Surface Science 162–163 Ž2000. 156–160 www.elsevier.nlrlocaterapsusc
Surface reaction of CH 3 SiH 3 on Gež100/ and Siž100/ Toshinori Takatsuka 1, Masaki Fujiu, Masao Sakuraba, Takashi Matsuura, Junichi Murota) Laboratory for Electronic Intelligent Systems, Research Institute of Electrical Communication, Tohoku UniÕersity, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
Abstract Surface reaction of CH 3 SiH 3 on the GeŽ100. and SiŽ100. surfaces was investigated in the low-temperature region of 400–5008C using ultraclean hot-wall low-pressure chemical vapor deposition ŽCVD. systems, where CH 3 SiH 3 was supplied at a partial pressure of 18 Pa for 0–240 min. On GeŽ100., the concentrations of Si and C deposited at 4008C and 4508C saturate to the value corresponding to the single atomic layer, but those at 5008C increase continuously with exposure time. Nevertheless, at all the temperatures studied, the concentration of deposited Si is nearly the same as that of deposited C. In the case of SiH 4 exposure at 4508C at partial pressures of 6 and 60 Pa, it was found that the Ge atoms segregate on the top surface at the early stage of Si deposition. By comparing these results, it is considered that the adsorption of CH 3 SiH 3 suppresses the Ge segregation. On SiŽ100., the C deposition by CH 3 SiH 3 has a similar tendency to that on GeŽ100., but the initial deposition efficiency is lower than that on GeŽ100.. Moreover, the FTIRrRAS Si-hydride peak shifts to the lower wave numbers after CH 3 SiH 3 exposure. These results suggest that CH 3 SiH 3 is adsorbed without breaking the Si`C bond on GeŽ100. and SiŽ100. at 400–5008C. q 2000 Elsevier Science B.V. All rights reserved. PACS: 68.45.Da; 81.05.Cy; 81.15.Gh Keywords: CH 3 SiH 3 ; Surface reaction; Si; Ge; C; CVD
1. Introduction Atomically controlled process of group IV materials, such as the atomic layer epitaxy and the atomic layer etching, is extremely important for fabrication of novel heterodevices integrated on a Si wafer. Self-limiting control of gas adsorption and reaction
)
Corresponding author. Tel.: q81-22-217-5548; fax: q81-22217-5565. E-mail address: [email protected] ŽJ. Murota.. 1 Present address: Research and Development Department, Asahi Kasei Electronics, 2-1, Samejima, Fuji-city, Shizuoka, 4168501 Japan.
is essential for the process w1,2x. In our previous work, single atomic-layer growth of Ge on the Si surface and of Si on the Ge surface was achieved using GeH 4 and SiH 4 by flash-heating chemical vapor deposition ŽCVD. w3–7x. Using this growth control, a double barrier resonant tunneling diode was fabricated, which showed negative resistance characteristics w6x. From the viewpoint of extending the band engineering potential further, it is interesting to fabricate the atomically controlled SiC and SiGeC superlattices including C, which will make wider the bandgap of group IV materials. In realization of atomically controlled processing, it is important to decrease the reaction temperature in order to
0169-4332r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 Ž 0 0 . 0 0 1 8 5 - 9
T. Takatsuka et al.r Applied Surface Science 162–163 (2000) 156–160
suppress interdiffusion of the atoms deposited and those in the substrate. Recently, Tillack et al. w8x reported atomic-order C growth on Si 1y xGe x Ž100. surface using CH 3 SiH 3 as a source gas. In this work, low-temperature reaction of CH 3 SiH 3 on GeŽ100. and SiŽ100. has been investigated to obtain basic information for fabricating the atomically controlled SiGeC superlattice.
2. Experimental CH 3 SiH 3 was exposed to GeŽ100. and SiŽ100. in the low-temperature region 400–5008C at a partial pressure of 18 Pa for 0–240 min using an ultraclean vertical-type hot-wall low-pressure CVD system ŽFig. 1. w9x and another ultraclean horizontal-type hot-wall low-pressure CVD system w10,11x, which were made ultrahigh vacuum compatible with a turbo-molecular pump system, respectively. It was confirmed that the same results were obtained by the same experimental condition using the two low-pressure CVD systems. In order to prevent any contamination from the exhaust line, carrier gas was always supplied to the reactor from the ultraclean gas delivery system. To minimize air contamination into the reactor during wafer load and unload, a transfer chamber with N2 purge is combined. The substrates used were the mirror-polished ptype SiŽ100. wafers. For the GeŽ100. surface, epitax˚ was formed on SiŽ100. ial Ge layer of about 2000 A by ultraclean low-pressure CVD at 3508C using GeH 4 and H 2 gases w12x. The substrates with and without
Fig. 1. Schematic diagram of an ultraclean vertical-type hot-wall low-pressure CVD system.
157
epitaxial Ge layer were loaded into the transfer chamber after removing the native Ge and Si oxide by dipping the substrates into a 2%-diluted HF solution followed by deionized water rinse. To obtain clean surfaces, the substrates were preheated for 30 min at 7508C in H 2 at ; 80 Pa. Subsequently, they were cooled down in H 2 and were exposed to CH 3 SiH 3 at a partial pressure of 18 Pa and a total pressure of 330 Pa with He for 0–240 min at 400– 5008C, and then cooled down in H 2 below 1008C. The Si and C atom concentrations were estimated by the X-ray photoelectron spectroscopy ŽXPS. w13x. The surface structure and hydrogen termination on the Ge and Si surfaces were evaluated by reflection high-energy electron diffraction ŽRHEED. and by Fourier-transform infrared reflection absorption spectroscopy ŽFTIRrRAS., respectively.
3. Results and discussion 3.1. Surface reaction of CH3 SiH3 on Ge(100) The C 1s XPS spectra obtained by exposing the GeŽ100. epitaxial surface to CH 3 SiH 3 for various exposure times are shown in Fig. 2. Two peaks are observed in the C 1s XPS spectra. With increasing exposure time, the peak area at ; 282.8 eV increases, although that at ; 285.0 eV scarcely changes. Therefore, the C 1s peak at ; 282.8 eV has been attributed to C bonded with Si ŽC`Si. and that at ; 285.0 eV results mainly from the surface carbon contamination such as C x H yOz and Si 4 C 4 O4 w9,14x. It is considered that the surface is contaminated during transportation of the sample and evacuation in the XPS load-lock chamber. Contribution from C bonded with Ge ŽC`Ge., which should cause a peak at ; 284.0 eV if it is present w15x, is very small. The C atom concentration only due to CH 3 SiH 3 reaction was estimated using the XPS intensity ratio of the peak area of C`Si Ž; 282.8 eV. to that of Ge3d. Figs. 3 and 4 show the CH 3 SiH 3 exposure time dependence of the deposited Si and C atom concentrations on GeŽ100., respectively. Even at 4008C, CH 3 SiH 3 reacts on the GeŽ100. surface. At a short CH 3 SiH 3 exposure time within 10 min, the deposited Si and C concentrations become the value
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T. Takatsuka et al.r Applied Surface Science 162–163 (2000) 156–160
Fig. 2. The C 1s XPS spectra of the GeŽ100. surface exposed to CH 3 SiH 3 at a partial pressure of 18 Pa at 5008C for various exposure times.
Fig. 4. CH 3 SiH 3 exposure time dependence of the C atom concentration on GeŽ100. at various substrate temperatures. The CH 3 SiH 3 partial pressure is 18 Pa.
corresponding to the single atomic layer at 4008C and 4508C. If the C`Si bond in CH 3 SiH 3 is stable at temperatures below 6008C and CH 3 SiH 3 dissociates into CH 3 SiH by breaking the Si`H bonds w16x, it is expected that CH 3 SiH 3 is adsorbed as the single atomic layer on the GeŽ100. surface, which suppresses the further adsorption of CH 3 SiH 3 . On the other hand, the concentrations of the deposited Si and C concentration at 5008C increase continuously over the single atomic layer with increasing CH 3 SiH 3 exposure time. Nevertheless, the concentration of the deposited Si is nearly the same as that of the de-
posited C. This may be caused by the formation of dangling bonds due to dissociation at 5008C of the Si`H bond in the absorbed CH 3 SiH, which is hardly dissociated at 4008C and 4508C. The dependence of the Si deposition rate on the Si atomic layers deposited on GeŽ100. at 4508C for SiH 4 and CH 3 SiH 3 is shown in Fig. 5. In the case of exposure of the GeŽ100. surface to SiH 4 at a partial pressure of 6 Pa, the Si deposition rate is higher until about triple atomic layers and decreases with increasing Si atomic layer. In the case of the SiH 4 partial pressure of 60 Pa, the Si deposition rate becomes constant from the less atomic layer. Therefore, it is
Fig. 3. CH 3 SiH 3 exposure time dependence of the Si atom concentration on GeŽ100. at various substrate temperatures. The CH 3 SiH 3 partial pressure is 18 Pa.
Fig. 5. Dependence of the Si deposition rate on the number of the Si atomic layers deposited on GeŽ100. at 4508C. SiH 4 exposure at 6 and 60 Pa is compared with CH 3 SiH 3 exposure at 18 Pa.
T. Takatsuka et al.r Applied Surface Science 162–163 (2000) 156–160
159
considered that enhancement of the SiH 4 reaction observed at 6 Pa is caused by the reaction with Ge atoms segregated on the top surface. On the other hand, in the case of the CH 3 SiH 3 exposure, the Si deposition occurs only until the single atomic layer. This demonstrates self-limited reaction of CH 3 SiH 3 on GeŽ100. and suppression of the Ge segregation. 3.2. Surface reaction of CH3 SiH3 on Si(100) The CH 3 SiH 3 exposure time dependence of the concentration of the deposited C atoms on SiŽ100. is shown in Fig. 6. The deposited C atom concentration at 4008C and 4508C increases with the CH 3 SiH 3 exposure time and tends to saturate to the value corresponding to the single atomic layer. On the other hand, the C atom concentration at 5008C increases continuously with increasing CH 3 SiH 3 exposure time beyond the value corresponding to the single atomic layer. These results are very similar to those in the case of GeŽ100.. However, the initial deposition efficiency is lower than that on GeŽ100.. Nevertheless, it is considered that the dissociation characteristics of CH 3 SiH 3 on SiŽ100. are very similar to those on GeŽ100.. Fig. 7 shows the FTIRrRAS spectra taken from the initial SiŽ100. surface after H 2-preheating at 7508C and from the Si surface subsequently exposed to CH 3 SiH 3 at 4008C. An absorption peak from the initial SiŽ100. appears clearly at 2098 cmy1 . This
Fig. 7. Typical FTIRrRAS spectra for SiŽ100. exposed to CH 3 SiH 3 at a partial pressure of 18 Pa at 4008C for various exposure times.
peak can be assigned to the Si-hydride stretching mode w17x. Because the two-fold streaks were observed in the RHEED patterns taken from the w011x azimuth for all the samples Ža. – Žf., the Si-hydride species are monohydrides on the dimer structure. The position of the Si-hydride peak shifts to the lower wavenumbers with increasing CH 3 SiH 3 exposure time. Lucovsky’s w18x empirical equation indicates that the peak at 2060cmy1 is caused by the Si-hydride included in the surface admolecule– SiHŽCH 3 .. Therefore, it is suggested that two of the three Si`H bonds in CH 3 SiH 3 are broken, and that the Si atom in the CH 3 SiH 3 molecule makes a bond with the Si atom on the surface. The reaction of CH 3 SiH 3 occurs at a lower substrate temperature than CH 4 w9x, which reacts at 5008C.
4. Conclusions Fig. 6. CH 3 SiH 3 exposure time dependence of the C atom concentration on SiŽ100. at various substrate temperatures. The CH 3 SiH 3 partial pressure is 18 Pa.
Even at 400–5008C, CH 3 SiH 3 reacted on the GeŽ100. and SiŽ100. surfaces. Self-limited deposition of about one monolayer CH 3 SiH 3 on GeŽ100.
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T. Takatsuka et al.r Applied Surface Science 162–163 (2000) 156–160
and SiŽ100. was found at 4008C and 4508C. Especially on GeŽ100., it is considered that the adsorption of CH 3 SiH 3 suppresses the surface segregation of Ge atoms. Moreover, on SiŽ100., the position of FTIRrRAS Si-hydride peak was found to shift to the lower wavenumbers. These results suggest that CH 3 SiH 3 is adsorbed without breaking the Si`C bond on the GeŽ100. and SiŽ100. surfaces. Acknowledgements The authors wish to express their thanks to Dr. B. Tillack of Institute for Semiconductor Physics, FrankfurtŽOder., Germany for his useful discussion. The CVD reactor was provided by Kokusai Electric. This study was partially supported by the Research for the Future ŽNo. JSPS-RFTF97P00202. from the Japan Society for Promotion of Science, a Grant-inAid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan, and the Mitsubishi Foundation. References w1x J. Nishizawa, H. Abe, T. Kurabayashi, J. Electrochem. Soc. 132 Ž1985. 1197. w2x Y. Takahashi, H. Ishii, K. Fujinaga, J. Electrochem. Soc. 136 Ž1989. 1826.
w3x M. Sakuraba, J. Murota, N. Mikoshiba, S. Ono, J. Cryst. Growth 115 Ž1991. 79. w4x J. Murota, M. Sakuraba, N. Mikoshiba, S. Ono, J. Phys. IV ŽFrance. 1 Ž1991. C2–C803. w5x J. Murota, M. Sakuraba, S. Ono, Appl. Phys. Lett. 62 Ž1993. 2353. w6x J. Murota, M. Sakuraba, T. Watanabe, T. Matsuura, Y. Sawada, J. Phys. IV ŽFrance. 5 Ž1995. C5–C1101. w7x T. Watanabe, M. Sakuraba, T. Matsuura, J. Murota, Jpn. J. Appl. Phys. 36 Ž1997. 4042. w8x B. Tillack, E. Bugiel, D. Kruger, R. Kurps, K. Glowatzi, ¨ E-MRS’98 Abstracts, Strasbourg, France, Jun. 16–19 Ž1989. D23. w9x A. Izena, M. Sakuraba, T. Matsuura, J. Murota, J. Cryst. Growth 188 Ž1998. 131. w10x J. Murota, N. Nakamura, M. Kano, N. Mikoshiba, T. Ohmi, Appl. Phys. Lett. 54 Ž1989. 1007. w11x J. Murota, S. Ono, Jpn. J. Appl. Phys 33 Ž1994. 2290. w12x J. Murota, M. Kato, R. Kircher, S. Ono, J. Phys. IV ŽFrance. 1 Ž1991. C2–C795. w13x D. Briggs, M.P. Seah, Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, Wiley, New York, 1983. w14x B. Hornetz, H.J. Michel, J. Halbritter, J. Mater. Res. 9 Ž1994. 3088. w15x S. Kumar, H.J. Trodahl, Thin Solid Films 193r194 Ž1990. 72. w16x A.D. Johnson, J. Perrin, J.A. Mucha, D.E. Ibbotson, J. Phys. Chem. 97 Ž1993. 12937. w17x O. Vetal, S. Verhaverbeke, H. Bender, M. Caymax, F. Chollet, B. Vermeire, P. Mertens, E. Andre, M. Heyns, Jpn. J. Appl. Phys. 32 Ž1993. L1489. w18x G. Lucovsky, Solid State Commun. 29 Ž1979. 571.
Surface reaction of CH 3 SiH 3 on Gež100/ and Siž100/ Toshinori Takatsuka 1, Masaki Fujiu, Masao Sakuraba, Takashi Matsuura, Junichi Murota) Laboratory for Electronic Intelligent Systems, Research Institute of Electrical Communication, Tohoku UniÕersity, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
Abstract Surface reaction of CH 3 SiH 3 on the GeŽ100. and SiŽ100. surfaces was investigated in the low-temperature region of 400–5008C using ultraclean hot-wall low-pressure chemical vapor deposition ŽCVD. systems, where CH 3 SiH 3 was supplied at a partial pressure of 18 Pa for 0–240 min. On GeŽ100., the concentrations of Si and C deposited at 4008C and 4508C saturate to the value corresponding to the single atomic layer, but those at 5008C increase continuously with exposure time. Nevertheless, at all the temperatures studied, the concentration of deposited Si is nearly the same as that of deposited C. In the case of SiH 4 exposure at 4508C at partial pressures of 6 and 60 Pa, it was found that the Ge atoms segregate on the top surface at the early stage of Si deposition. By comparing these results, it is considered that the adsorption of CH 3 SiH 3 suppresses the Ge segregation. On SiŽ100., the C deposition by CH 3 SiH 3 has a similar tendency to that on GeŽ100., but the initial deposition efficiency is lower than that on GeŽ100.. Moreover, the FTIRrRAS Si-hydride peak shifts to the lower wave numbers after CH 3 SiH 3 exposure. These results suggest that CH 3 SiH 3 is adsorbed without breaking the Si`C bond on GeŽ100. and SiŽ100. at 400–5008C. q 2000 Elsevier Science B.V. All rights reserved. PACS: 68.45.Da; 81.05.Cy; 81.15.Gh Keywords: CH 3 SiH 3 ; Surface reaction; Si; Ge; C; CVD
1. Introduction Atomically controlled process of group IV materials, such as the atomic layer epitaxy and the atomic layer etching, is extremely important for fabrication of novel heterodevices integrated on a Si wafer. Self-limiting control of gas adsorption and reaction
)
Corresponding author. Tel.: q81-22-217-5548; fax: q81-22217-5565. E-mail address: [email protected] ŽJ. Murota.. 1 Present address: Research and Development Department, Asahi Kasei Electronics, 2-1, Samejima, Fuji-city, Shizuoka, 4168501 Japan.
is essential for the process w1,2x. In our previous work, single atomic-layer growth of Ge on the Si surface and of Si on the Ge surface was achieved using GeH 4 and SiH 4 by flash-heating chemical vapor deposition ŽCVD. w3–7x. Using this growth control, a double barrier resonant tunneling diode was fabricated, which showed negative resistance characteristics w6x. From the viewpoint of extending the band engineering potential further, it is interesting to fabricate the atomically controlled SiC and SiGeC superlattices including C, which will make wider the bandgap of group IV materials. In realization of atomically controlled processing, it is important to decrease the reaction temperature in order to
0169-4332r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 Ž 0 0 . 0 0 1 8 5 - 9
T. Takatsuka et al.r Applied Surface Science 162–163 (2000) 156–160
suppress interdiffusion of the atoms deposited and those in the substrate. Recently, Tillack et al. w8x reported atomic-order C growth on Si 1y xGe x Ž100. surface using CH 3 SiH 3 as a source gas. In this work, low-temperature reaction of CH 3 SiH 3 on GeŽ100. and SiŽ100. has been investigated to obtain basic information for fabricating the atomically controlled SiGeC superlattice.
2. Experimental CH 3 SiH 3 was exposed to GeŽ100. and SiŽ100. in the low-temperature region 400–5008C at a partial pressure of 18 Pa for 0–240 min using an ultraclean vertical-type hot-wall low-pressure CVD system ŽFig. 1. w9x and another ultraclean horizontal-type hot-wall low-pressure CVD system w10,11x, which were made ultrahigh vacuum compatible with a turbo-molecular pump system, respectively. It was confirmed that the same results were obtained by the same experimental condition using the two low-pressure CVD systems. In order to prevent any contamination from the exhaust line, carrier gas was always supplied to the reactor from the ultraclean gas delivery system. To minimize air contamination into the reactor during wafer load and unload, a transfer chamber with N2 purge is combined. The substrates used were the mirror-polished ptype SiŽ100. wafers. For the GeŽ100. surface, epitax˚ was formed on SiŽ100. ial Ge layer of about 2000 A by ultraclean low-pressure CVD at 3508C using GeH 4 and H 2 gases w12x. The substrates with and without
Fig. 1. Schematic diagram of an ultraclean vertical-type hot-wall low-pressure CVD system.
157
epitaxial Ge layer were loaded into the transfer chamber after removing the native Ge and Si oxide by dipping the substrates into a 2%-diluted HF solution followed by deionized water rinse. To obtain clean surfaces, the substrates were preheated for 30 min at 7508C in H 2 at ; 80 Pa. Subsequently, they were cooled down in H 2 and were exposed to CH 3 SiH 3 at a partial pressure of 18 Pa and a total pressure of 330 Pa with He for 0–240 min at 400– 5008C, and then cooled down in H 2 below 1008C. The Si and C atom concentrations were estimated by the X-ray photoelectron spectroscopy ŽXPS. w13x. The surface structure and hydrogen termination on the Ge and Si surfaces were evaluated by reflection high-energy electron diffraction ŽRHEED. and by Fourier-transform infrared reflection absorption spectroscopy ŽFTIRrRAS., respectively.
3. Results and discussion 3.1. Surface reaction of CH3 SiH3 on Ge(100) The C 1s XPS spectra obtained by exposing the GeŽ100. epitaxial surface to CH 3 SiH 3 for various exposure times are shown in Fig. 2. Two peaks are observed in the C 1s XPS spectra. With increasing exposure time, the peak area at ; 282.8 eV increases, although that at ; 285.0 eV scarcely changes. Therefore, the C 1s peak at ; 282.8 eV has been attributed to C bonded with Si ŽC`Si. and that at ; 285.0 eV results mainly from the surface carbon contamination such as C x H yOz and Si 4 C 4 O4 w9,14x. It is considered that the surface is contaminated during transportation of the sample and evacuation in the XPS load-lock chamber. Contribution from C bonded with Ge ŽC`Ge., which should cause a peak at ; 284.0 eV if it is present w15x, is very small. The C atom concentration only due to CH 3 SiH 3 reaction was estimated using the XPS intensity ratio of the peak area of C`Si Ž; 282.8 eV. to that of Ge3d. Figs. 3 and 4 show the CH 3 SiH 3 exposure time dependence of the deposited Si and C atom concentrations on GeŽ100., respectively. Even at 4008C, CH 3 SiH 3 reacts on the GeŽ100. surface. At a short CH 3 SiH 3 exposure time within 10 min, the deposited Si and C concentrations become the value
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Fig. 2. The C 1s XPS spectra of the GeŽ100. surface exposed to CH 3 SiH 3 at a partial pressure of 18 Pa at 5008C for various exposure times.
Fig. 4. CH 3 SiH 3 exposure time dependence of the C atom concentration on GeŽ100. at various substrate temperatures. The CH 3 SiH 3 partial pressure is 18 Pa.
corresponding to the single atomic layer at 4008C and 4508C. If the C`Si bond in CH 3 SiH 3 is stable at temperatures below 6008C and CH 3 SiH 3 dissociates into CH 3 SiH by breaking the Si`H bonds w16x, it is expected that CH 3 SiH 3 is adsorbed as the single atomic layer on the GeŽ100. surface, which suppresses the further adsorption of CH 3 SiH 3 . On the other hand, the concentrations of the deposited Si and C concentration at 5008C increase continuously over the single atomic layer with increasing CH 3 SiH 3 exposure time. Nevertheless, the concentration of the deposited Si is nearly the same as that of the de-
posited C. This may be caused by the formation of dangling bonds due to dissociation at 5008C of the Si`H bond in the absorbed CH 3 SiH, which is hardly dissociated at 4008C and 4508C. The dependence of the Si deposition rate on the Si atomic layers deposited on GeŽ100. at 4508C for SiH 4 and CH 3 SiH 3 is shown in Fig. 5. In the case of exposure of the GeŽ100. surface to SiH 4 at a partial pressure of 6 Pa, the Si deposition rate is higher until about triple atomic layers and decreases with increasing Si atomic layer. In the case of the SiH 4 partial pressure of 60 Pa, the Si deposition rate becomes constant from the less atomic layer. Therefore, it is
Fig. 3. CH 3 SiH 3 exposure time dependence of the Si atom concentration on GeŽ100. at various substrate temperatures. The CH 3 SiH 3 partial pressure is 18 Pa.
Fig. 5. Dependence of the Si deposition rate on the number of the Si atomic layers deposited on GeŽ100. at 4508C. SiH 4 exposure at 6 and 60 Pa is compared with CH 3 SiH 3 exposure at 18 Pa.
T. Takatsuka et al.r Applied Surface Science 162–163 (2000) 156–160
159
considered that enhancement of the SiH 4 reaction observed at 6 Pa is caused by the reaction with Ge atoms segregated on the top surface. On the other hand, in the case of the CH 3 SiH 3 exposure, the Si deposition occurs only until the single atomic layer. This demonstrates self-limited reaction of CH 3 SiH 3 on GeŽ100. and suppression of the Ge segregation. 3.2. Surface reaction of CH3 SiH3 on Si(100) The CH 3 SiH 3 exposure time dependence of the concentration of the deposited C atoms on SiŽ100. is shown in Fig. 6. The deposited C atom concentration at 4008C and 4508C increases with the CH 3 SiH 3 exposure time and tends to saturate to the value corresponding to the single atomic layer. On the other hand, the C atom concentration at 5008C increases continuously with increasing CH 3 SiH 3 exposure time beyond the value corresponding to the single atomic layer. These results are very similar to those in the case of GeŽ100.. However, the initial deposition efficiency is lower than that on GeŽ100.. Nevertheless, it is considered that the dissociation characteristics of CH 3 SiH 3 on SiŽ100. are very similar to those on GeŽ100.. Fig. 7 shows the FTIRrRAS spectra taken from the initial SiŽ100. surface after H 2-preheating at 7508C and from the Si surface subsequently exposed to CH 3 SiH 3 at 4008C. An absorption peak from the initial SiŽ100. appears clearly at 2098 cmy1 . This
Fig. 7. Typical FTIRrRAS spectra for SiŽ100. exposed to CH 3 SiH 3 at a partial pressure of 18 Pa at 4008C for various exposure times.
peak can be assigned to the Si-hydride stretching mode w17x. Because the two-fold streaks were observed in the RHEED patterns taken from the w011x azimuth for all the samples Ža. – Žf., the Si-hydride species are monohydrides on the dimer structure. The position of the Si-hydride peak shifts to the lower wavenumbers with increasing CH 3 SiH 3 exposure time. Lucovsky’s w18x empirical equation indicates that the peak at 2060cmy1 is caused by the Si-hydride included in the surface admolecule– SiHŽCH 3 .. Therefore, it is suggested that two of the three Si`H bonds in CH 3 SiH 3 are broken, and that the Si atom in the CH 3 SiH 3 molecule makes a bond with the Si atom on the surface. The reaction of CH 3 SiH 3 occurs at a lower substrate temperature than CH 4 w9x, which reacts at 5008C.
4. Conclusions Fig. 6. CH 3 SiH 3 exposure time dependence of the C atom concentration on SiŽ100. at various substrate temperatures. The CH 3 SiH 3 partial pressure is 18 Pa.
Even at 400–5008C, CH 3 SiH 3 reacted on the GeŽ100. and SiŽ100. surfaces. Self-limited deposition of about one monolayer CH 3 SiH 3 on GeŽ100.
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and SiŽ100. was found at 4008C and 4508C. Especially on GeŽ100., it is considered that the adsorption of CH 3 SiH 3 suppresses the surface segregation of Ge atoms. Moreover, on SiŽ100., the position of FTIRrRAS Si-hydride peak was found to shift to the lower wavenumbers. These results suggest that CH 3 SiH 3 is adsorbed without breaking the Si`C bond on the GeŽ100. and SiŽ100. surfaces. Acknowledgements The authors wish to express their thanks to Dr. B. Tillack of Institute for Semiconductor Physics, FrankfurtŽOder., Germany for his useful discussion. The CVD reactor was provided by Kokusai Electric. This study was partially supported by the Research for the Future ŽNo. JSPS-RFTF97P00202. from the Japan Society for Promotion of Science, a Grant-inAid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan, and the Mitsubishi Foundation. References w1x J. Nishizawa, H. Abe, T. Kurabayashi, J. Electrochem. Soc. 132 Ž1985. 1197. w2x Y. Takahashi, H. Ishii, K. Fujinaga, J. Electrochem. Soc. 136 Ž1989. 1826.
w3x M. Sakuraba, J. Murota, N. Mikoshiba, S. Ono, J. Cryst. Growth 115 Ž1991. 79. w4x J. Murota, M. Sakuraba, N. Mikoshiba, S. Ono, J. Phys. IV ŽFrance. 1 Ž1991. C2–C803. w5x J. Murota, M. Sakuraba, S. Ono, Appl. Phys. Lett. 62 Ž1993. 2353. w6x J. Murota, M. Sakuraba, T. Watanabe, T. Matsuura, Y. Sawada, J. Phys. IV ŽFrance. 5 Ž1995. C5–C1101. w7x T. Watanabe, M. Sakuraba, T. Matsuura, J. Murota, Jpn. J. Appl. Phys. 36 Ž1997. 4042. w8x B. Tillack, E. Bugiel, D. Kruger, R. Kurps, K. Glowatzi, ¨ E-MRS’98 Abstracts, Strasbourg, France, Jun. 16–19 Ž1989. D23. w9x A. Izena, M. Sakuraba, T. Matsuura, J. Murota, J. Cryst. Growth 188 Ž1998. 131. w10x J. Murota, N. Nakamura, M. Kano, N. Mikoshiba, T. Ohmi, Appl. Phys. Lett. 54 Ž1989. 1007. w11x J. Murota, S. Ono, Jpn. J. Appl. Phys 33 Ž1994. 2290. w12x J. Murota, M. Kato, R. Kircher, S. Ono, J. Phys. IV ŽFrance. 1 Ž1991. C2–C795. w13x D. Briggs, M.P. Seah, Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, Wiley, New York, 1983. w14x B. Hornetz, H.J. Michel, J. Halbritter, J. Mater. Res. 9 Ž1994. 3088. w15x S. Kumar, H.J. Trodahl, Thin Solid Films 193r194 Ž1990. 72. w16x A.D. Johnson, J. Perrin, J.A. Mucha, D.E. Ibbotson, J. Phys. Chem. 97 Ž1993. 12937. w17x O. Vetal, S. Verhaverbeke, H. Bender, M. Caymax, F. Chollet, B. Vermeire, P. Mertens, E. Andre, M. Heyns, Jpn. J. Appl. Phys. 32 Ž1993. L1489. w18x G. Lucovsky, Solid State Commun. 29 Ž1979. 571.