- Email: [email protected]
Organosilicon ion beam for SiC heteroepitaxy
Surface and Coatings Technology 177 – 178 (2004) 260–263
Organosilicon ion beam for SiC heteroepitaxy Masato Kiuchia,*, Takaomi Matsutania, Takae Takeuchib, Takashi Matsumotoc, Satoshi Sugimotoc, Seiichi Gotoc a
National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan b Nara Women’s University, Nara 630-8305, Japan c Osaka University, Suita, Osaka 565-0871, Japan
Abstract A low-energy deposition technique using a beam of organosilicon ions has been developed and successfully applied for heteroepitaxial growth of SiC on a Si substrate at temperatures of 900–1300 K. The process employs gaseous CH3SiH2 CH3 in a Freeman-type ion source to produce CH3Siq fragment ions that are then mass-selected and deposited at 100 eV on a Si wafer. Ion energy was precisely controlled and energy fluctuation was "1 eV. RHEED analysis and AFM observation, respectively, showed that a thin film of SiC had been crystallized heteroepitaxially and in the form of ‘nano-tiles.’ The technique offers the potential for fabrication of self-assembled SiC nanostructures. 䊚 2003 Elsevier B.V. All rights reserved. Keywords: Organosilicon ion beam; SiC heteroepitaxy; Low-energy deposition technique
1. Introduction Ion beam technology has proven to be a effective tool for functional materials fabrication. A wide variety of deposition studies of materials have been undertaken using low-energy deposition processes, in order to discuss the effect of energy and momentum in deposition processes w1x. In studies of low-energy ion beam deposition, atomic ion beams have been discussed and elementary substances have been deposited w2–5x. Compound deposition using low-energy ion beams offers an interesting area for further discussion. In this connection, we developed a molecular ion beam deposition apparatus for use in processes with an organosilicon ion beam. Silicon carbide (SiC) is a wide bandgap semiconductor w6x. Usually SiC films are formed using thermal chemical vapor deposition at a high temperature of 1600 K. For applications in Si technology, a new process at a lower temperature is required. Furthermore, SiC has a large lattice mismatch to Si, making it difficult to achieve good performance from heteroepitaxial growth. In this regard, we have demonstrated the advan*Corresponding author. Tel.: q72-751-9535; fax: q72-751-9637. E-mail address: [email protected] (M. Kiuchi).
tages of the low-energy deposition technique using a molecular ion beam in SiC heteroepitaxy on Si wafers w9,10x. In this paper, a new technology for compound deposition is discussed. 2. Organosilicon ion beam We used a low-energy ion-beam deposition apparatus built at Osaka University (Fig. 1) w7x, and its basic structure is identical to a conventional mass-selected low-energy ion-beam deposition apparatus w1x. The deposition chamber is equipped with a plasma process monitor to evaluate the quality of the ion beams. In our experiments, dimethylsilane (CH3SiH2CH3) was introduced to a Freeman-type ion source and adsorbed on a hot tungsten filament. Dimethylsilane was ionized and frangmented into methylsilicenium ions (CH3Siq) through the surface ionization process. The CH3Siq ions with an energy of 100 eV were deposited on the Si surface, since the displacement energy in crystal is 10–30 eV for every solid, an energy of 100 eV for the incident CH3Siq ions is considered to be sufficient for developing several displacements at the surface and the subsurface. In SiC deposition processes, the difference in the sticking probabilities of Si and C
0257-8972/04/$ - see front matter 䊚 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2003.09.003
M. Kiuchi et al. / Surface and Coatings Technology 177 – 178 (2004) 260–263
Fig. 1. Apparatus for low energy ion beam deposition. A precursor gas is introduced into the Freeman-type ion source. Ions are extracted by a 20 kV electric field and mass-selected by the electro-magnetic sector. The beam is deflected for rejection of high-energy neutrals, and decelerated to the desired energy just before deposition. The deposited films are examined in situ by RHEED. The beam quality is examined by a plasma process monitor before starting deposition.
on SiC causes problems for stoichiometric deposition. A methylsilicenium ion has one silicon atom and one carbon atom in a molecular ion and these are bound chemically. So, stoichiometric deposition is considered to be possible (Fig. 2). The ion beam extracted from the ion source contains several kinds of ions. They were analyzed by a mass selector. In Fig. 3, a variety of ions produced in the ion source are shown by scanning driving current of the mass selector. The dominant ion for SiC deposition was the myz 43 ion. The myz 43 ion was identified as the methylsilicenium ions by ab initio molecular orbital
Fig. 2. Schematic illustration of SiC heteroepitaxy using low energy methylsilicenium ion beam deposition. Crystallization in a stoichiometric ratio is considered to be possible as the ion has one Si atom and one C atom. As the substrate temperature is above 600 8C, hydrogen will be removed under deposition.
261
Fig. 3. Ion species obtained by the Freeman-type ion source with dimethysilane gas. By scanning the driving current of the mass-selecting magnet, a variety of fragment ions are observed.
calculations w8x. In the case of methylsilane (CH3SiH3) gas, methylsilylene ions (CH3SiHq) were obtained, however, the current was not enough for deposition. Accordingly, we used CH3SiH2CH3 and deposited CH3Siq ions. Methylsilicenium ions were introduced to the deposition chamber and decelerated. Before starting deposition, the quality of the beam was evaluated by a plasma process monitor with an energy analyzer and a Q-mass analyzer w9x. As shown in Fig. 4, the energy of the ions was 100"1 eV. As the electric potential of the ion source using a DC power supply was set at 100 V from the ground, the ions should have an energy of 100 eV gained from the DC power supply and an energy gained by the plasma potential. In this case, the plasma potential was zero and the energy fluctuation was negligible because of the surface ionization on the tungsten surface. In case of noble gases (Ne, Ar, Xe, etc.), the plasma potential was 2–5 eV and the energy fluctuation was on the order of several electronvolts in the Freemantype ion source. The plasma potential and the energy fluctuation will be important in a detailed study to discuss the energy effect.
Fig. 4. Quality of methylsilicenium ions produced by surface ionization on a hot tungsten filament. The plasma potential is zero and the energy fluctuation is "1.
262
M. Kiuchi et al. / Surface and Coatings Technology 177 – 178 (2004) 260–263
Using this apparatus and the methylsilicenium ion beam, precise control of deposition process becomes possible. 3. SiC heteroepitaxy Si wafers (100) and (111) were used as substrates for heteroepitaxial growth of SiC. Before deposition, wafers were annealed at 1300 K to remove native oxides, and the superlattice structure of Si surfaces was observed by reflection high-energy electron diffraction (RHEED). Methylsilicenium ions with an energy of 100 eV were deposited on decontaminated Si surfaces. The energies of C and Si atoms were 28 eV and 65 eV, respectively. The energies of rotation and vibration were not included. The range over which temperature was elevated during deposition was 873–1273 K. The current density was 0.20 mA and the beam spot size was 10 mm. The pressure under deposition was 1=10y6 Pa. The average
Fig. 6. AFM image of surface profile of heteroepitaxial 3C– SiC(001)ySi(001). The sample was produced by deposition of 100 eV methylsilicenium ions at 1023 K.
thickness of films calculated by the total current of the beam was approximately 10 nm w10x. Fig. 5 shows the RHEED pattern of the 3C–SiC(001) film deposited on a Si(001) surface. Deposition was performed using CH3Siq ions with an energy of 100"1 eV at 1023 K. This figure confirms the heteroepitaxial growth of 3C–SiC(001) on Si(100). Fig. 6 shows the AFM surface profile of 3C– SiC(001) produced at 1023 K. SiC was crystallized in a shape of self-assembled nano-sized tiles. To our knowledge this the first report of a nano-tiled SiC structure. The nano-tile structure varies with deposition temperature, the details of which will be published elsewhere. 4. Concluding remarks We developed a low-energy organosilicon ion beam deposition technique. With this, SiC was successfully deposited heteroepitaxially on a Si substrate at 873– 1273 K using CH3Siq ions with an energy of 100 eV. We also observed that the mode of crystallization could be varied to produce hexagonal SiC using lower energy ions, further study of which will follow. References
Fig. 5. RHEED pattern of the heteroepitaxial 3C–SiC(001) on Si(001) produced by methylsilicenium ion beam deposition.
w1x J.W. Rabalais, Low Energy Ion–Source Interactions, John Wiley and Sons, 1994. w2x S. Shimizu, O. Tsukakoshi, S. Komiya, Y. Makita, Jpn. J. Appl. Phys. 24 (1985) 1130. w3x J. Ishikawa, Y. Takeiri, T. Takagi, Rev. Sci. Instrum. 57 (1986) 1512. w4x J.S. Gordon, D.G. Armour, S.E. Donnelly, J.A. van den Berg, D. Marton, J.W. Rabalais, Nucl. Instrum. Meth. B 59–60 (1991) 312. w5x W.M. Lau, X. Feng, I. Bello, S. Sant, K.K. Foo, R.P.W. Lawson, Nucl. Instrum. Meth. B 59–60 (1991) 316.
M. Kiuchi et al. / Surface and Coatings Technology 177 – 178 (2004) 260–263 w6x H. Matsunami, T. Kimoto, Mater. Sci. Eng. R 20 (1997) 125. w7x T. Matsumoto, K. Mimoto, S. Goto, M. Ohba, Y. Agawa, M. Kiuchi, Rev. Sci. Instrum. 71 (2000) 1168. w8x T. Matsutani, M. Kiuchi, T. Takeuchi, T. Matsumoto, K. Mimoto, S. Goto, Vacuum 59 (2000) 152.
263
w9x M. Kiuchi, T. Matsumoto, K. Mimoto, T. Takeuchi, S. Goto, Rev. Sci. Instrum. 71 (2000) 1157. w10x T. Matsumoto, M. Kiuchi, S. Sugimoto, S. Goto, Surf. Sci. 493 (2001) 426.
Organosilicon ion beam for SiC heteroepitaxy Masato Kiuchia,*, Takaomi Matsutania, Takae Takeuchib, Takashi Matsumotoc, Satoshi Sugimotoc, Seiichi Gotoc a
National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan b Nara Women’s University, Nara 630-8305, Japan c Osaka University, Suita, Osaka 565-0871, Japan
Abstract A low-energy deposition technique using a beam of organosilicon ions has been developed and successfully applied for heteroepitaxial growth of SiC on a Si substrate at temperatures of 900–1300 K. The process employs gaseous CH3SiH2 CH3 in a Freeman-type ion source to produce CH3Siq fragment ions that are then mass-selected and deposited at 100 eV on a Si wafer. Ion energy was precisely controlled and energy fluctuation was "1 eV. RHEED analysis and AFM observation, respectively, showed that a thin film of SiC had been crystallized heteroepitaxially and in the form of ‘nano-tiles.’ The technique offers the potential for fabrication of self-assembled SiC nanostructures. 䊚 2003 Elsevier B.V. All rights reserved. Keywords: Organosilicon ion beam; SiC heteroepitaxy; Low-energy deposition technique
1. Introduction Ion beam technology has proven to be a effective tool for functional materials fabrication. A wide variety of deposition studies of materials have been undertaken using low-energy deposition processes, in order to discuss the effect of energy and momentum in deposition processes w1x. In studies of low-energy ion beam deposition, atomic ion beams have been discussed and elementary substances have been deposited w2–5x. Compound deposition using low-energy ion beams offers an interesting area for further discussion. In this connection, we developed a molecular ion beam deposition apparatus for use in processes with an organosilicon ion beam. Silicon carbide (SiC) is a wide bandgap semiconductor w6x. Usually SiC films are formed using thermal chemical vapor deposition at a high temperature of 1600 K. For applications in Si technology, a new process at a lower temperature is required. Furthermore, SiC has a large lattice mismatch to Si, making it difficult to achieve good performance from heteroepitaxial growth. In this regard, we have demonstrated the advan*Corresponding author. Tel.: q72-751-9535; fax: q72-751-9637. E-mail address: [email protected] (M. Kiuchi).
tages of the low-energy deposition technique using a molecular ion beam in SiC heteroepitaxy on Si wafers w9,10x. In this paper, a new technology for compound deposition is discussed. 2. Organosilicon ion beam We used a low-energy ion-beam deposition apparatus built at Osaka University (Fig. 1) w7x, and its basic structure is identical to a conventional mass-selected low-energy ion-beam deposition apparatus w1x. The deposition chamber is equipped with a plasma process monitor to evaluate the quality of the ion beams. In our experiments, dimethylsilane (CH3SiH2CH3) was introduced to a Freeman-type ion source and adsorbed on a hot tungsten filament. Dimethylsilane was ionized and frangmented into methylsilicenium ions (CH3Siq) through the surface ionization process. The CH3Siq ions with an energy of 100 eV were deposited on the Si surface, since the displacement energy in crystal is 10–30 eV for every solid, an energy of 100 eV for the incident CH3Siq ions is considered to be sufficient for developing several displacements at the surface and the subsurface. In SiC deposition processes, the difference in the sticking probabilities of Si and C
0257-8972/04/$ - see front matter 䊚 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2003.09.003
M. Kiuchi et al. / Surface and Coatings Technology 177 – 178 (2004) 260–263
Fig. 1. Apparatus for low energy ion beam deposition. A precursor gas is introduced into the Freeman-type ion source. Ions are extracted by a 20 kV electric field and mass-selected by the electro-magnetic sector. The beam is deflected for rejection of high-energy neutrals, and decelerated to the desired energy just before deposition. The deposited films are examined in situ by RHEED. The beam quality is examined by a plasma process monitor before starting deposition.
on SiC causes problems for stoichiometric deposition. A methylsilicenium ion has one silicon atom and one carbon atom in a molecular ion and these are bound chemically. So, stoichiometric deposition is considered to be possible (Fig. 2). The ion beam extracted from the ion source contains several kinds of ions. They were analyzed by a mass selector. In Fig. 3, a variety of ions produced in the ion source are shown by scanning driving current of the mass selector. The dominant ion for SiC deposition was the myz 43 ion. The myz 43 ion was identified as the methylsilicenium ions by ab initio molecular orbital
Fig. 2. Schematic illustration of SiC heteroepitaxy using low energy methylsilicenium ion beam deposition. Crystallization in a stoichiometric ratio is considered to be possible as the ion has one Si atom and one C atom. As the substrate temperature is above 600 8C, hydrogen will be removed under deposition.
261
Fig. 3. Ion species obtained by the Freeman-type ion source with dimethysilane gas. By scanning the driving current of the mass-selecting magnet, a variety of fragment ions are observed.
calculations w8x. In the case of methylsilane (CH3SiH3) gas, methylsilylene ions (CH3SiHq) were obtained, however, the current was not enough for deposition. Accordingly, we used CH3SiH2CH3 and deposited CH3Siq ions. Methylsilicenium ions were introduced to the deposition chamber and decelerated. Before starting deposition, the quality of the beam was evaluated by a plasma process monitor with an energy analyzer and a Q-mass analyzer w9x. As shown in Fig. 4, the energy of the ions was 100"1 eV. As the electric potential of the ion source using a DC power supply was set at 100 V from the ground, the ions should have an energy of 100 eV gained from the DC power supply and an energy gained by the plasma potential. In this case, the plasma potential was zero and the energy fluctuation was negligible because of the surface ionization on the tungsten surface. In case of noble gases (Ne, Ar, Xe, etc.), the plasma potential was 2–5 eV and the energy fluctuation was on the order of several electronvolts in the Freemantype ion source. The plasma potential and the energy fluctuation will be important in a detailed study to discuss the energy effect.
Fig. 4. Quality of methylsilicenium ions produced by surface ionization on a hot tungsten filament. The plasma potential is zero and the energy fluctuation is "1.
262
M. Kiuchi et al. / Surface and Coatings Technology 177 – 178 (2004) 260–263
Using this apparatus and the methylsilicenium ion beam, precise control of deposition process becomes possible. 3. SiC heteroepitaxy Si wafers (100) and (111) were used as substrates for heteroepitaxial growth of SiC. Before deposition, wafers were annealed at 1300 K to remove native oxides, and the superlattice structure of Si surfaces was observed by reflection high-energy electron diffraction (RHEED). Methylsilicenium ions with an energy of 100 eV were deposited on decontaminated Si surfaces. The energies of C and Si atoms were 28 eV and 65 eV, respectively. The energies of rotation and vibration were not included. The range over which temperature was elevated during deposition was 873–1273 K. The current density was 0.20 mA and the beam spot size was 10 mm. The pressure under deposition was 1=10y6 Pa. The average
Fig. 6. AFM image of surface profile of heteroepitaxial 3C– SiC(001)ySi(001). The sample was produced by deposition of 100 eV methylsilicenium ions at 1023 K.
thickness of films calculated by the total current of the beam was approximately 10 nm w10x. Fig. 5 shows the RHEED pattern of the 3C–SiC(001) film deposited on a Si(001) surface. Deposition was performed using CH3Siq ions with an energy of 100"1 eV at 1023 K. This figure confirms the heteroepitaxial growth of 3C–SiC(001) on Si(100). Fig. 6 shows the AFM surface profile of 3C– SiC(001) produced at 1023 K. SiC was crystallized in a shape of self-assembled nano-sized tiles. To our knowledge this the first report of a nano-tiled SiC structure. The nano-tile structure varies with deposition temperature, the details of which will be published elsewhere. 4. Concluding remarks We developed a low-energy organosilicon ion beam deposition technique. With this, SiC was successfully deposited heteroepitaxially on a Si substrate at 873– 1273 K using CH3Siq ions with an energy of 100 eV. We also observed that the mode of crystallization could be varied to produce hexagonal SiC using lower energy ions, further study of which will follow. References
Fig. 5. RHEED pattern of the heteroepitaxial 3C–SiC(001) on Si(001) produced by methylsilicenium ion beam deposition.
w1x J.W. Rabalais, Low Energy Ion–Source Interactions, John Wiley and Sons, 1994. w2x S. Shimizu, O. Tsukakoshi, S. Komiya, Y. Makita, Jpn. J. Appl. Phys. 24 (1985) 1130. w3x J. Ishikawa, Y. Takeiri, T. Takagi, Rev. Sci. Instrum. 57 (1986) 1512. w4x J.S. Gordon, D.G. Armour, S.E. Donnelly, J.A. van den Berg, D. Marton, J.W. Rabalais, Nucl. Instrum. Meth. B 59–60 (1991) 312. w5x W.M. Lau, X. Feng, I. Bello, S. Sant, K.K. Foo, R.P.W. Lawson, Nucl. Instrum. Meth. B 59–60 (1991) 316.
M. Kiuchi et al. / Surface and Coatings Technology 177 – 178 (2004) 260–263 w6x H. Matsunami, T. Kimoto, Mater. Sci. Eng. R 20 (1997) 125. w7x T. Matsumoto, K. Mimoto, S. Goto, M. Ohba, Y. Agawa, M. Kiuchi, Rev. Sci. Instrum. 71 (2000) 1168. w8x T. Matsutani, M. Kiuchi, T. Takeuchi, T. Matsumoto, K. Mimoto, S. Goto, Vacuum 59 (2000) 152.
263
w9x M. Kiuchi, T. Matsumoto, K. Mimoto, T. Takeuchi, S. Goto, Rev. Sci. Instrum. 71 (2000) 1157. w10x T. Matsumoto, M. Kiuchi, S. Sugimoto, S. Goto, Surf. Sci. 493 (2001) 426.