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Etching action by atomic hydrogen and low temperature silicon epitaxial growth on ECR plasma CVD
Pergamon PII: S0042-207X(98)00250-4
Vacuum/volume 51/number 4/pages 537 to 541/1998 ã 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0042-207X/98 Sl - see front matter
Etching action by atomic hydrogen and low temperature silicon epitaxial growth on ECR plasma CVD K. Sasaki,* H. Tomoda and T. Takada, Department of Electrical and Computer Engineering, Kanazawa University, Kodatsuno 2-40-20, Kanazawa 920, Japan
The stability of hydrogen plasma intensity generated by the ECR technique was investigated. Ha intensity decreased with the increase of temperature of the chamber's inside wall. The square root of the Ha intensity and the etch rate of silicon were proportional to the microwave power. For the deposition of a crystalline silicon film the deposition rate increased with the increase of the hydrogen gas flow rate while for the case of an amorphous silicon film the deposition rate decreased. A silicon epitaxial film with excellent crystalline quality was successfully realized at 4508C. ã 1998 Elsevier Science Ltd. All rights reserved
Introduction Plasma chemical vapor deposition (CVD) technique is widely used for the deposition of insulating ®lms such as SiO2 and SiN in the fabrication technology of the large scale integration. Other applications are deposition of amorphous silicon and related ®lms for large area solar cells and thin ®lm transistors for liquid crystal panels. Recently, SiOF ®lms are attracting attention as an insulating layer of interconnection because of their low dielectric constant. The advantage of this technique is high speed deposition of those ®lms at low substrate temperature. In the plasma CVD process it has been considered that the same ®lms can be formed when the plasma conditions are the same. However, we have indicated that substrate played an important role for the ®lm crystallinity and also we have demonstrated on silicon epitaxial ®lm growth by the rf plasma CVD technique1. We named this phenomenon substrate induced epitaxy. The similar investigation results have been reported by other researchers2±4. Plasma excitation method by means of the electron cyclotron resonance (ECR) phenomenon is expected to be more useful for epitaxial ®lm growth than a conventional glow discharge plasma because ECR plasma contains uniform and low energy ions and can produce highly reactive species. High quality SiO2 and SiN ®lms really fabricated by the ECR plasma CVD technique have been reported5, 6. Hence this technique is expected to be useful even for epitaxial ®lm growth7±9. *Corresponding author. E-mail: [email protected]
We studied the low temperature silicon epitaxial growth by ECR plasma CVD from the view point of contribution of an etching action by atomic hydrogen generated by the ECR plasma. Experiment Figure 1 shows a schematic of the ECR plasma CVD apparatus used for the experiment. Hydrogen gas and 2.45 GHz microwave were introduced into the resonance chamber (R.C.), where a 875 G magnetic ®eld was applied to maintain the ECR condition and hydrogen plasma was excited. The input microwave power and the re¯ection were monitored, there was little re¯ection. High eciency power transformation was realized. The main chamber (M.C.) was evacuated by a turbo molecular pump (550 l/s) to a background pressure of 10ÿ7 Torr. The gas pressure was around 10±60 mTorr at hydrogen gas ¯ow rate of 60±250 sccm. Substrates were heated by ®xing them on a heater block. The substrate temperature was measured by a thermocouple on the substrate surface. The hydrogen plasma was characterized by measuring its optical emission through a quartz window. Silicon (100), (111) substrates were used for investigating etching process by the hydrogen plasma. The substrates were cleaned by organic solvent and followed by the RCA cleaning. Finally by dipping in 5% HF solution the substrate surface treatment was ®nished by the hydrogen termination to prevent surface oxidation. Any special surface treatment such as thermal ¯ash as carried out in MBE technique has not be done. 537
K. Sasaki et al: Etching action by atomic hydrogen
Figure 1. Schematics of ECR plasma CVD apparatus.
SiH4 gas was introduced into the main chamber through a ring shape gas nozzle and was decomposed by mixing with the hydrogen plasma. SiH4 gas ¯ow rate was kept 1 sccm constant for the every deposition experiment. Experiments were carried out by changing the substrate temperature, the hydrogen ¯ow rate and the microwave power. Silicon ®lm growth characteristics were observed on silicon (100) substrates and the crystallinity was evaluated by the re¯ection high energy electron diraction (RHEED) method. Results and discussion Stability of ECR plasma. First of all we mention about stability of ECR plasma because lack of stability induces error in the experiment. To analyze the stability we measured an optical emission from the ECR plasma and surface temperature of the substrate holder for operating time of the ECR plasma apparatus. The wave length of 288 nm which is assigned for silicon atom was monitored. The emission intensity is considered to correspond to the plasma intensity or the electron density. Plasma irradiation induces temperature increase of the apparatus, especially on the substrate holder. The microwave power was ®xed at 900 W for 60 min in the beginning, after that, decreased to 200 W for 60 min. Figure 2 shows the emission intensity and the temperature of the substrate holder surface for the time lapse. It is found that the emission intensity rapidly decreases just after the plasma on, and then the gradual decrease continues for around 30 min. At 60 min the emission intensity abruptly drops with the microwave power change from 900 W to 200 W. After that, the emission intensity, however starts to increase. Also the temperature is found to decrease with the similar time constant as the temperature elevated. Interestingly, this drift of the emission intensity is coincident with the temperature drift. The tendency of the temperature drift at the inside wall of the apparatus is considered to similar at the substrate holder surface. Although the detailed mechanism is unknown, these results show that temperature of inside wall of the apparatus aects the plasma intensity. For reproducible experiment a 30 min preliminary operation of the apparatus was done for following experiments. 538
Figure 2. Drift characteristics of optical emission intensity of Si (288 nm) and substrate surface temperature for apparatus operating time.
Plasma density and etch rate. In this section we discuss fundamental properties among the input microwave power, the density of atomic hydrogen and the silicon etch rate. The etching experiment was carried out under conditions of hydrogen ¯ow rate = 150 sccm and the substrate temperature = 2858C, where no SiH4 gas was supplied. Figure 3 shows dependencies of the etch rate and the square root of Ha (wave length = 656 nm) intensity for the microwave power. The square root of Ha intensity (IHa ) is found to be proportional to microwave power (Pm) from this ®gure, that is,
I 1=2 Ha APm :
1
Figure 3. Dependencies of etch rate and (Ha intensity)1/2 on microwave gas flow rate = 150 sccm and substrate power. (H2 temperature = 2858C).
K. Sasaki et al: Etching action by atomic hydrogen We regard that the emission intensity is proportional to the produced atomic hydrogen density (DH),
IHa ADH :
2
Because the electron motion in the ECR condition is ®xed by the microwave frequency and magnetic ®eld, the electron density should increase in proportion to the input power. Assuming that the electron density (Ne) in the plasma is proportional to the microwave power,
Ne APm
3
Thus we have the next relation,
DH AN 2e :
4
The reason of this relation means that atomic hydrogens are produced by the two-electron-process. Actually the production of atomic hydrogen is known due to the two-electron-process10. This fact suggests that the assumption of Equation (3) is valid. In Figure 3 etch rate (Retch) is found to be proportional to the microwave power, consequently the square root of the atomic hydrogen density, that is
Retch APm AD1=2 H :
and a silicon dangling bond is produced. This dangling bond reacts with another atomic hydrogen. By these processes being repeated, a silicon atom is removed. What we have to pay attention in this process is that the reverse process occurs. That is, even though once a silicon±silicon bond is cut by atomic hydrogens, the bond is possible to recover by the terminated hydrogens being extracted by another atomic hydrogen or dissociating thermally.
5
This result, however, does not agree with a simple consideration about the etching mechanism that atomic hydrogens etch away silicon atoms, consequently the etch rate increases with proportional to the etchant amount. To explain this result successfully it may be necessary that a complicated reaction process between the atomic hydrogen and the silicon atom has to be taken into account. On the other hand the etch rate dierence between (100) and (111) is explained by considering the bond formation of Si atom at the each surface. The details are reported elsewhere11. Figure 4 shows elementary processes of the silicon etching by the atomic hydrogen. In this picture we assume that a silicon atom is etched away in SiH4 molecule. First, an atomic hydrogen attacks a silicon bond then it reacts with the silicon
Deposition rate. To analyze ®lm growth mechanism on the ECR plasma ®lm deposition, the ®lm deposition rate was measured for two deposition conditions. One is for growing crystalline silicon ®lms, the other is for amorphous silicon ®lms. The crystalline silicon ®lms were deposited under conditions of a high microwave power of 900 W and a high substrate temperature of 2858C, while amorphous silicon ®lms were deposited under conditions of a low microwave power of 200 W and a low substrate temperature of 608C. The ®lm deposition was carried out with changing hydrogen gas ¯ow rate. Figure 5 shows the deposition rate for the hydrogen gas ¯ow rate. For the condition of crystalline ®lm growth, the deposition rate is increasing with increase of the hydrogen gas ¯ow rate and saturating at around the hydrogen gas ¯ow rate of 150 sccm. This behavior is interpreted that in a low hydrogen gas ¯ow rate region SiH4 gas decomposition eciency increases with increase of the hydrogen gas ¯ow rate then the eciency reaches its limitation resulting in saturation. While, for the condition of amorphous silicon ®lm growth, deposition rate is decreasing monotonously with the hydrogen gas ¯ow rate. This behavior is interpreted that although decomposition eciency of SiH4 gas molecules increases with the hydrogen gas ¯ow rate, etching process by atomic hydrogens dominates the net deposition rate. Silicon bonds in amorphous ®lms are considered weak so that easily to be etched12. The fact of etch rate dierence for crystallinity is useful for ®lm deposition of good crystalline quality, moreover is applicable for selective ®lm deposition11.
Figure 4. Illustration of elemental etching process of silicon by atomic hydrogen.
539
K. Sasaki et al: Etching action by atomic hydrogen
Figure 5. Deposition rate of crystalline silicon film and amorphous silicon film. (Crystalline film: m Ð Wave power 900 W, Tsub.=2858C, amorphous film: m Ð Wave power = 200 W, Tsub.=608C).
Low temperature epitaxial growth of silicon ®lms. As we have been observing so far, it is clear that the etching process occurs simultaneously with the deposition process. This process mixture brings about rearrangement of silicon atoms at the surface, which contributes to improve ®lm crystallinity. In other words, weak bonds in amorphous region are etched but silicon atoms locating at the stable lattice site remain, so that crystalline growth takes place easily. In order to con®rm the above consideration empirically we demonstrate the results of silicon epitaxial growth carried out on silicon (100) substrates by changing deposition conditions variously. An example of RHEED pattern for a silicon epitaxial ®lm is shown in Figure 6. As can be seen in this ®gure, crystalline quality of the ®lm is so excellent that Kikuchi-line is observed. Crystallinity dependence on both substrate temperature and ®lm thickness is summarized in Figure 7. For very thin ®lm thickness of around 10 nm, regardless of substrate temperature the epitaxial growth takes place with excellent reproducibility,
Figure 7. Summary of crystalline quality dependence on substrate temperature and film thickness evaluated by RHEED observation.
which implies that the initial surface has been clean. Etching action by the atomic hydrogen, which is inherent in this process, is considered to have function to clean silicon surface automatically. From this ®gure, crystalline growth property is found to be divided into 3 regions, that is, non-epitaxial region containing amorphous and polycrystalline, single crystalline containing twin defect and pure single crystalline. The limiting thickness determined by the boundary between the ®rst and the second region increases with being proportional to substrate temperature. This limiting thickness is comparable or superior to that of MBE technique. Therefore, we can say that the silicon atom rearrangement action by the atomic hydrogen is useful for low temperature silicon epitaxial growth.
Conclusion We characterized the hydrogen plasma produced by the ECR technique. The plasma intensity was drifted by temperature of chamber inside wall, which suggests a certain interaction between plasma and chamber inside wall. Control of the temperature is signi®cant for reproducible experiments. A remarkable silicon etching by atomic hydrogen occurred. The elementary etching process of a silicon atom by atomic hydrogen may be complicated because of two processes that hydrogen atom reacts with a silicon atom while the bonded hydrogen atoms dissociate. The ®lm deposition process contains etching process. This process mixture is considered to give rise to epitaxial growth eectively at low temperature. We succeeded excellent silicon epitaxial growth at 4508C.
Acknowledgements Figure 6. An example of RHEED image of deposited silicon film. Electron beam incident azimuth: [110]. (Sub. temp. = 4508C, Film thick. = 100 nm, H2 gas flow rate = 150 sccm, m Ð wave power = 900 W).
540
The authors would like to thank Professor T. Hata at Kanazawa University for his useful discussion and encouragement.
K. Sasaki et al: Etching action by atomic hydrogen References 1. Furukawa, S. and Sasaki, K., Springer Proc. Phys., 1992, 71, 298. 2. Jai, Y., Oshima, T., Yamada, A., Konagai, M. and Takahashi, K., Jpn. J. Appl. Phys., 1993, 32, 1884. 3. Baert, K. et al., Appl. Phys. Lett., 1987, 51, 1922. 4. Uematsu, T. et al., Jpn. J. Appl. Phys., 1988, 27, L493. 5. Machida, K. and Oikawa, H., Ext. Abs. of 17th SSDM, 1985, A4-5, 329. 6. Matsuo, S. and Kiuchi, M., Jpn. J. Appl. Phys., 1983, 22, L210.
7. Mui, D. S. L., Fang, S. F. and Morkoc, H., Appl. Phys. Lett., 1991, 59, 1887. 8. Fukuda, K., Murota, J. and Ono, S., Appl. Phys. Lett., 1991, 59, 2853. 9. Heung-Sik, T. et al., Appl. Phys. Lett., 1994, 64, 1021. 10. Kampas, F. J. and Grith, R. W., J. Appl. Phys., 1981, 52, 1285. 11. Sasaki, K. and Takada, T., Jpn. J. Appl. Phys. 1998, 37, 402. 12. Nagayoshi, H., Yamaguchi, M., Kamisako, K., Horigome, T. and Tarui, Y., Jpn. J. Appl. Phys., 1994, 33, L621.
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Vacuum/volume 51/number 4/pages 537 to 541/1998 ã 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0042-207X/98 Sl - see front matter
Etching action by atomic hydrogen and low temperature silicon epitaxial growth on ECR plasma CVD K. Sasaki,* H. Tomoda and T. Takada, Department of Electrical and Computer Engineering, Kanazawa University, Kodatsuno 2-40-20, Kanazawa 920, Japan
The stability of hydrogen plasma intensity generated by the ECR technique was investigated. Ha intensity decreased with the increase of temperature of the chamber's inside wall. The square root of the Ha intensity and the etch rate of silicon were proportional to the microwave power. For the deposition of a crystalline silicon film the deposition rate increased with the increase of the hydrogen gas flow rate while for the case of an amorphous silicon film the deposition rate decreased. A silicon epitaxial film with excellent crystalline quality was successfully realized at 4508C. ã 1998 Elsevier Science Ltd. All rights reserved
Introduction Plasma chemical vapor deposition (CVD) technique is widely used for the deposition of insulating ®lms such as SiO2 and SiN in the fabrication technology of the large scale integration. Other applications are deposition of amorphous silicon and related ®lms for large area solar cells and thin ®lm transistors for liquid crystal panels. Recently, SiOF ®lms are attracting attention as an insulating layer of interconnection because of their low dielectric constant. The advantage of this technique is high speed deposition of those ®lms at low substrate temperature. In the plasma CVD process it has been considered that the same ®lms can be formed when the plasma conditions are the same. However, we have indicated that substrate played an important role for the ®lm crystallinity and also we have demonstrated on silicon epitaxial ®lm growth by the rf plasma CVD technique1. We named this phenomenon substrate induced epitaxy. The similar investigation results have been reported by other researchers2±4. Plasma excitation method by means of the electron cyclotron resonance (ECR) phenomenon is expected to be more useful for epitaxial ®lm growth than a conventional glow discharge plasma because ECR plasma contains uniform and low energy ions and can produce highly reactive species. High quality SiO2 and SiN ®lms really fabricated by the ECR plasma CVD technique have been reported5, 6. Hence this technique is expected to be useful even for epitaxial ®lm growth7±9. *Corresponding author. E-mail: [email protected]
We studied the low temperature silicon epitaxial growth by ECR plasma CVD from the view point of contribution of an etching action by atomic hydrogen generated by the ECR plasma. Experiment Figure 1 shows a schematic of the ECR plasma CVD apparatus used for the experiment. Hydrogen gas and 2.45 GHz microwave were introduced into the resonance chamber (R.C.), where a 875 G magnetic ®eld was applied to maintain the ECR condition and hydrogen plasma was excited. The input microwave power and the re¯ection were monitored, there was little re¯ection. High eciency power transformation was realized. The main chamber (M.C.) was evacuated by a turbo molecular pump (550 l/s) to a background pressure of 10ÿ7 Torr. The gas pressure was around 10±60 mTorr at hydrogen gas ¯ow rate of 60±250 sccm. Substrates were heated by ®xing them on a heater block. The substrate temperature was measured by a thermocouple on the substrate surface. The hydrogen plasma was characterized by measuring its optical emission through a quartz window. Silicon (100), (111) substrates were used for investigating etching process by the hydrogen plasma. The substrates were cleaned by organic solvent and followed by the RCA cleaning. Finally by dipping in 5% HF solution the substrate surface treatment was ®nished by the hydrogen termination to prevent surface oxidation. Any special surface treatment such as thermal ¯ash as carried out in MBE technique has not be done. 537
K. Sasaki et al: Etching action by atomic hydrogen
Figure 1. Schematics of ECR plasma CVD apparatus.
SiH4 gas was introduced into the main chamber through a ring shape gas nozzle and was decomposed by mixing with the hydrogen plasma. SiH4 gas ¯ow rate was kept 1 sccm constant for the every deposition experiment. Experiments were carried out by changing the substrate temperature, the hydrogen ¯ow rate and the microwave power. Silicon ®lm growth characteristics were observed on silicon (100) substrates and the crystallinity was evaluated by the re¯ection high energy electron diraction (RHEED) method. Results and discussion Stability of ECR plasma. First of all we mention about stability of ECR plasma because lack of stability induces error in the experiment. To analyze the stability we measured an optical emission from the ECR plasma and surface temperature of the substrate holder for operating time of the ECR plasma apparatus. The wave length of 288 nm which is assigned for silicon atom was monitored. The emission intensity is considered to correspond to the plasma intensity or the electron density. Plasma irradiation induces temperature increase of the apparatus, especially on the substrate holder. The microwave power was ®xed at 900 W for 60 min in the beginning, after that, decreased to 200 W for 60 min. Figure 2 shows the emission intensity and the temperature of the substrate holder surface for the time lapse. It is found that the emission intensity rapidly decreases just after the plasma on, and then the gradual decrease continues for around 30 min. At 60 min the emission intensity abruptly drops with the microwave power change from 900 W to 200 W. After that, the emission intensity, however starts to increase. Also the temperature is found to decrease with the similar time constant as the temperature elevated. Interestingly, this drift of the emission intensity is coincident with the temperature drift. The tendency of the temperature drift at the inside wall of the apparatus is considered to similar at the substrate holder surface. Although the detailed mechanism is unknown, these results show that temperature of inside wall of the apparatus aects the plasma intensity. For reproducible experiment a 30 min preliminary operation of the apparatus was done for following experiments. 538
Figure 2. Drift characteristics of optical emission intensity of Si (288 nm) and substrate surface temperature for apparatus operating time.
Plasma density and etch rate. In this section we discuss fundamental properties among the input microwave power, the density of atomic hydrogen and the silicon etch rate. The etching experiment was carried out under conditions of hydrogen ¯ow rate = 150 sccm and the substrate temperature = 2858C, where no SiH4 gas was supplied. Figure 3 shows dependencies of the etch rate and the square root of Ha (wave length = 656 nm) intensity for the microwave power. The square root of Ha intensity (IHa ) is found to be proportional to microwave power (Pm) from this ®gure, that is,
I 1=2 Ha APm :
1
Figure 3. Dependencies of etch rate and (Ha intensity)1/2 on microwave gas flow rate = 150 sccm and substrate power. (H2 temperature = 2858C).
K. Sasaki et al: Etching action by atomic hydrogen We regard that the emission intensity is proportional to the produced atomic hydrogen density (DH),
IHa ADH :
2
Because the electron motion in the ECR condition is ®xed by the microwave frequency and magnetic ®eld, the electron density should increase in proportion to the input power. Assuming that the electron density (Ne) in the plasma is proportional to the microwave power,
Ne APm
3
Thus we have the next relation,
DH AN 2e :
4
The reason of this relation means that atomic hydrogens are produced by the two-electron-process. Actually the production of atomic hydrogen is known due to the two-electron-process10. This fact suggests that the assumption of Equation (3) is valid. In Figure 3 etch rate (Retch) is found to be proportional to the microwave power, consequently the square root of the atomic hydrogen density, that is
Retch APm AD1=2 H :
and a silicon dangling bond is produced. This dangling bond reacts with another atomic hydrogen. By these processes being repeated, a silicon atom is removed. What we have to pay attention in this process is that the reverse process occurs. That is, even though once a silicon±silicon bond is cut by atomic hydrogens, the bond is possible to recover by the terminated hydrogens being extracted by another atomic hydrogen or dissociating thermally.
5
This result, however, does not agree with a simple consideration about the etching mechanism that atomic hydrogens etch away silicon atoms, consequently the etch rate increases with proportional to the etchant amount. To explain this result successfully it may be necessary that a complicated reaction process between the atomic hydrogen and the silicon atom has to be taken into account. On the other hand the etch rate dierence between (100) and (111) is explained by considering the bond formation of Si atom at the each surface. The details are reported elsewhere11. Figure 4 shows elementary processes of the silicon etching by the atomic hydrogen. In this picture we assume that a silicon atom is etched away in SiH4 molecule. First, an atomic hydrogen attacks a silicon bond then it reacts with the silicon
Deposition rate. To analyze ®lm growth mechanism on the ECR plasma ®lm deposition, the ®lm deposition rate was measured for two deposition conditions. One is for growing crystalline silicon ®lms, the other is for amorphous silicon ®lms. The crystalline silicon ®lms were deposited under conditions of a high microwave power of 900 W and a high substrate temperature of 2858C, while amorphous silicon ®lms were deposited under conditions of a low microwave power of 200 W and a low substrate temperature of 608C. The ®lm deposition was carried out with changing hydrogen gas ¯ow rate. Figure 5 shows the deposition rate for the hydrogen gas ¯ow rate. For the condition of crystalline ®lm growth, the deposition rate is increasing with increase of the hydrogen gas ¯ow rate and saturating at around the hydrogen gas ¯ow rate of 150 sccm. This behavior is interpreted that in a low hydrogen gas ¯ow rate region SiH4 gas decomposition eciency increases with increase of the hydrogen gas ¯ow rate then the eciency reaches its limitation resulting in saturation. While, for the condition of amorphous silicon ®lm growth, deposition rate is decreasing monotonously with the hydrogen gas ¯ow rate. This behavior is interpreted that although decomposition eciency of SiH4 gas molecules increases with the hydrogen gas ¯ow rate, etching process by atomic hydrogens dominates the net deposition rate. Silicon bonds in amorphous ®lms are considered weak so that easily to be etched12. The fact of etch rate dierence for crystallinity is useful for ®lm deposition of good crystalline quality, moreover is applicable for selective ®lm deposition11.
Figure 4. Illustration of elemental etching process of silicon by atomic hydrogen.
539
K. Sasaki et al: Etching action by atomic hydrogen
Figure 5. Deposition rate of crystalline silicon film and amorphous silicon film. (Crystalline film: m Ð Wave power 900 W, Tsub.=2858C, amorphous film: m Ð Wave power = 200 W, Tsub.=608C).
Low temperature epitaxial growth of silicon ®lms. As we have been observing so far, it is clear that the etching process occurs simultaneously with the deposition process. This process mixture brings about rearrangement of silicon atoms at the surface, which contributes to improve ®lm crystallinity. In other words, weak bonds in amorphous region are etched but silicon atoms locating at the stable lattice site remain, so that crystalline growth takes place easily. In order to con®rm the above consideration empirically we demonstrate the results of silicon epitaxial growth carried out on silicon (100) substrates by changing deposition conditions variously. An example of RHEED pattern for a silicon epitaxial ®lm is shown in Figure 6. As can be seen in this ®gure, crystalline quality of the ®lm is so excellent that Kikuchi-line is observed. Crystallinity dependence on both substrate temperature and ®lm thickness is summarized in Figure 7. For very thin ®lm thickness of around 10 nm, regardless of substrate temperature the epitaxial growth takes place with excellent reproducibility,
Figure 7. Summary of crystalline quality dependence on substrate temperature and film thickness evaluated by RHEED observation.
which implies that the initial surface has been clean. Etching action by the atomic hydrogen, which is inherent in this process, is considered to have function to clean silicon surface automatically. From this ®gure, crystalline growth property is found to be divided into 3 regions, that is, non-epitaxial region containing amorphous and polycrystalline, single crystalline containing twin defect and pure single crystalline. The limiting thickness determined by the boundary between the ®rst and the second region increases with being proportional to substrate temperature. This limiting thickness is comparable or superior to that of MBE technique. Therefore, we can say that the silicon atom rearrangement action by the atomic hydrogen is useful for low temperature silicon epitaxial growth.
Conclusion We characterized the hydrogen plasma produced by the ECR technique. The plasma intensity was drifted by temperature of chamber inside wall, which suggests a certain interaction between plasma and chamber inside wall. Control of the temperature is signi®cant for reproducible experiments. A remarkable silicon etching by atomic hydrogen occurred. The elementary etching process of a silicon atom by atomic hydrogen may be complicated because of two processes that hydrogen atom reacts with a silicon atom while the bonded hydrogen atoms dissociate. The ®lm deposition process contains etching process. This process mixture is considered to give rise to epitaxial growth eectively at low temperature. We succeeded excellent silicon epitaxial growth at 4508C.
Acknowledgements Figure 6. An example of RHEED image of deposited silicon film. Electron beam incident azimuth: [110]. (Sub. temp. = 4508C, Film thick. = 100 nm, H2 gas flow rate = 150 sccm, m Ð wave power = 900 W).
540
The authors would like to thank Professor T. Hata at Kanazawa University for his useful discussion and encouragement.
K. Sasaki et al: Etching action by atomic hydrogen References 1. Furukawa, S. and Sasaki, K., Springer Proc. Phys., 1992, 71, 298. 2. Jai, Y., Oshima, T., Yamada, A., Konagai, M. and Takahashi, K., Jpn. J. Appl. Phys., 1993, 32, 1884. 3. Baert, K. et al., Appl. Phys. Lett., 1987, 51, 1922. 4. Uematsu, T. et al., Jpn. J. Appl. Phys., 1988, 27, L493. 5. Machida, K. and Oikawa, H., Ext. Abs. of 17th SSDM, 1985, A4-5, 329. 6. Matsuo, S. and Kiuchi, M., Jpn. J. Appl. Phys., 1983, 22, L210.
7. Mui, D. S. L., Fang, S. F. and Morkoc, H., Appl. Phys. Lett., 1991, 59, 1887. 8. Fukuda, K., Murota, J. and Ono, S., Appl. Phys. Lett., 1991, 59, 2853. 9. Heung-Sik, T. et al., Appl. Phys. Lett., 1994, 64, 1021. 10. Kampas, F. J. and Grith, R. W., J. Appl. Phys., 1981, 52, 1285. 11. Sasaki, K. and Takada, T., Jpn. J. Appl. Phys. 1998, 37, 402. 12. Nagayoshi, H., Yamaguchi, M., Kamisako, K., Horigome, T. and Tarui, Y., Jpn. J. Appl. Phys., 1994, 33, L621.
541