The the μc-Si:H and a-Si:H films were prepared by plasma enhanced chemical vapor deposition(PECVD). The μc-Si:H films were deposited at various Ar dilution {Ar/$(Ar+SiH_4)×$100%} by varying Ar gas flow rate and RF power(70W∼85W) and the a-Si:H films were deposited at various hydrogen dilution ratios ($H_2$/$SiH_4$) by varying $H_2$ gas flow rate and deposition temperature(200℃~300℃). Also those a-Si:H and bilayer(bottom layer:μc-Si:H and top layer:a-Si:H) films were annealed in the conventional furnace under the high vacuum condition($5×10^{-6}torr$) at 600℃. Phases of films were analyzed by Raman spectroscopy, roughness of films by AFM(Atomic Force Microscopy) and the final grain sizes were measured from the TEM(Transmission Electron Microscopy) images.
μc-Si:H films were deposited under heavy Ar dilution(98%) and high RF power(70, 85W). When RF power was 85W, density of μc-Si was low. To study the effects of hydrogen dilution ratios and deposition temperature on the crystallization of a-Si:H films, a-Si:H films were deposited under $H_2$/$SiH_4$ dilution ratios from 20:5 to 60:5, deposition temperature from 200℃ to 300℃ at constant RF power and pressure of 30W, 0.7torr, respectively, and then annealed at 600℃. As hydrogen dilution ratio was decreased and deposition temperature was increased, crystallization rate of a-Si:film was increased. Raman analysis revealed that the increased crystallization rate was due to the lowered structural disorderness.
To study the effects of bottom and top layer on SPC of bilayer films, bilayer(bottom layer:μc-Si:H and top layer:a-Si:H) films were annealed at 600℃.
Raman and TEM analysis showed that, as density of μc-Si in bottom layer and structure disorderness in top layer were low, poly-Si films with large grain(0.7 ㎛) were acquired at short crystallization time(24h).
The effect of interface in bilayer films was investigated. After deposition of μc-Si:H films for bottom layer, $H_2$ and Ar plasma treatment were conducted on the surfaces of μc-Si:H films and then a-Si:H films were deposited on the plasma treated surfaces of μc-Si: films for bilayer films. Those bilayer films were annealed at 600℃ From the Raman and TEM analysis, it was concluded that $H_2$ plasma treatment was very effective for reducing the crystallization time(15h) of bilayer films. AFM analysis showed that selective etchings of amorphous Si were occurred in the case of $H_2$ plasma treatment but not occurred in the case of Ar plasma treatment. Therefore this reduced crystallization time was due to the selective etching of amorphous Si relative to crystalline Si by $H_2$ plasma treatment on the interface in bilayer films.