Takayuki Oshima

Analysis of H2-Dilution Effects on Photochemical Vapor Deposition of Si Thin Films

Hg-sensitized photochemical vapor deposition (photo-CVD) of Si thin films at low temperatures using a gas mixture of SiH4 and H2 was analyzed and the concentrations of SiH3 and H in the gas phase were theoretically estimated. The results of the calculation were compared with the properties of the Si thin films, and the roles of atomic H were discussed. With the correlations between the radical concentrations near the growing surface and film properties such as film structure, film quality, and the concentration of bonded hydrogen in a-Si films were successfully explained. It is suggested that the roles of atomic H on the growing surface are a termination of dangling bonds on the surface and an extraction of SiH3 radicals from the growing surface. Since the role of atomic H competes with the deposition of Si, the supply balance between the atomic H and the SiH3 radicals is essential to determine the properties of Si thin films.

Selective silicon epitaxy by photo-chemical vapor deposition at a very low temperature of 160° C

We have grown epitaxial Si films by the photo-chemical vapor deposition (photo-CVD) technique with SiH4 and H2 at a very low-temperature of 160°C. Epitaxial films were grown on silicon substrates, while amorphous-like films were deposited on glass substrates. Furthermore, it was found from the atomic hydrogen etching which was produced by photo-dissociation of hydrogen that the etching rate of amorphous silicon was much higher than that of crystal silicon. By using these selectively, we have demonstrated selective epitaxial growth of silicon by the photo-CVD technique followed by the atomic hydrogen photo-etching. Furthermore, heavily phosphorus-doped silicon films (>1 × 1021 cm1−3) were also selectively grown by this novel technique.

Defect Evaluation of Heavily P-Doped Si Epitaxial Films Grown at Low Temperature

Heavily P-doped epitaxial Si films with carrier concentration of 3×1021 cm-3 have been successfully grown by plasma chemical vapor deposition using a gas mixture of SiH4, SiF4, H2 and PH3 at a very low temperature of 250°C. From the annealing characteristics of heavily P-doped Si films, it was found that the electron concentration decreased once after annealing at 600°C but increased subsequently upon raising the annealing temperature. The possibility of the formation of a vacancy-type defect complex, typically (v-P4), a vacancy surrounded by four phosphorus atoms, was proposed to interpret this phenomenon. Furthermore, a positron annihilation experiment was employed to investigate this vacancy-type defect in Si films and good agreement was obtained between thermodynamical calculation based on the v-P4 model and the positron annihilation experiment.

Effects of SiH2Cl2 on low-temperature (≤200°C) Si epitaxy by photochemical vapor deposition

Epitaxial Si films have been grown by the mercury sensitized photo-CVD method using a SiH 4 /H 2 gas mixture with and without SiH 2 Cl 2 at a substrate temperature lower than 200 o C. The effect of SiH 2 Cl 2 on low-temperature Si epitaxy was investigated. The structural properties of the obtained films were characterized by reflection high-energy electron diffraction (RHEED), IR and Raman spectroscopy. It was found that the film quality was improved by the addition of SiH 2 Cl 2 . The most probable role of SiH 2 Cl 2 is etching of the growing surface, resulting in a rigid Si network

Low-temperature epitaxial growth of undoped and n-doped silicon by photochemical vapor deposition using SiH4/SiH2Cl2/H2/PH3 mixtures

Undoped and doped silicon films were grown epitaxially on (100) substrates of the same material from a gas mixture of dichlorosilane, silane, hydrogen and phosphine, employing mercury-sensitized photochemical vapor deposition (photo-CVD). The films were characterized using reflection high energy electron diffraction (RHEED), Raman spectroscopy, infrared transmittance and electrical measurements. RHEED patterns and Raman measurements revealed the formation of single-crystal silicon films grown at temperatures as low as 150 °C. The best crystallinity was observed on films with a low hydrogen content (calculated from infrared measurements) and was equivalent to that reported previously for photo-CVD films grown from Si2H6/SiH2F2/H2 mixtures at lower growth rates. At the phosphine molar fraction 1 × 10−5 used in this work, the electrical properties of n-doped films are affected in an appreciable manner by hydrogen dilution and temperature.

Effects of SiH 2 Cl 2 Addition on the Growth Mechanism of Si Films Prepared by Photochemical Vapor Deposition

Effects of SiH 2 Cl 2 and H 2 addition to SiH 4 on photochemical vapor deposition (photo-CVD) of amorphous Si (a-Si) and epitaxial Si films were investigated, and roles of Cl and H in the growth mechanism were discussed. The surface morphology and the defect density of the obtained a-Si films were evaluated by atomic force microscope (AFM), and constant photocurrent method (CPM), respectively. It was found that the H2 dilution of SiH 4 is effective to prepare the a-Si films with smooth surfaces and low defect density. Furthermore, nearly flat surface with the root mean square (RMS) of the roughness of 0.35nm was obtained by the SiH 2 Cl 2 addition to H 2 -diluted SiH 4 . In the Si epitaxy, the SiH 2 Cl 2 addition is also efficient to improve the film quality. It is suggested that the growing surface is terminated by both Cl and H, and the surface is more stable than that terminated by only H. Therefore, the diffusion on the growing surface of the film precursors such as SiH 3 is enhanced, resulting in the improvement of the surface morphology and the film quality.

Heavily B-Doped Epitaxial Si Films Grown by Photochemical Vapor Deposition at Very Low Temperature ( <200° C)

Heavily B-doped epitaxial Si films were grown by photochemical vapor deposition (photo-CVD) using a gas mixture of SiH4, H2, SiH2Cl2 and B2H6 in the substrate temperature range of 160-210° C. The electrical and optical properties of the obtained films were evaluated. The most striking result was that B atoms in the as-grown films were almost 100% neutralized even though the hole concentration was increased to 1.3×1020 cm-3 by annealing. It was found that the hole concentration increased as a stretched-exponential function of the annealing time, and an infrared absorption band at 2210 cm-1, which is regarded as a B-related band, appeared as the B-doping quantity was increased. The neutralization of B is considered to be related to H atoms in the films.

Low-temperature Si epitaxy by photochemical vapor deposition with SiH2Cl2

Epitaxial Si films were successfully grown by the mercury-sensitized photochemical vapor deposition (photo-CVD) method with SiH2Cl2 at a substrate temperature of as low as 200° C. The electrical and optical properties of the obtained films were characterized by Hall measurement, IR and Raman spectroscopy and transmission electron microscopy. Furthermore, the n-type doping was carried out by the addition of PH3 gas, and the electron concentration was varied from 1016 cm-3 to 1018 cm-3 by varying the PH3/SiH4 gas ratio. It was found from the experiments that there was a strong correlation between the SiH2Cl2 and H2 flow rates for obtaining the epitaxial Si films at a low temperature.