Effects of SiH 2 Cl 2 Addition on the Growth Mechanism of Si Films Prepared by Photochemical Vapor Deposition
- PDF / 2,093,694 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 67 Downloads / 242 Views
ABSTRACT Effects of SiH 2 CI 2 and H 2 addition to SiH 4 on photochemical vapor deposition (photoCVD) 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 CI 2 addition to H 2-diluted SiH 4 . In the Si epitaxy, the SiH 2 CI 2 addition is also efficient to improve the film quality. It is suggested that the growing surface is terminated by both C1 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. INTRODUCTION Improvement of film quality of amorphous silicon (a-Si) is one of the main subjects for developments of a-Si based devices. Previously, we have reported on the photo-CVD of a-Si films using SiH 4 and SiH 2CI 2 1). The quality of the a-Si films are improved by a small addition of SiH 2 CI2 to SiH 4. Furthermore, we also reported on the low-temperature Si epitaxy 2). It was found in the study that the epitaxial growth of Si takes place on Si(100)substrates by photo-CVD with H2 -diluted SiH 4 at 200*C even though a-Si films were deposited on glass substrates under the same growth conditions, and that the film quality of the epitaxial Si films were drastically improved by the addition of SiH 2CI 2 . Accordingly, it is considered that the behavior of film precursors on the growing surface is changed by introducing of H and Cl to the gas phase of the CVD. However, roles of Cl and H in the film growth are unclear. In this study, in order to clarify the roles of Cl and H, changes of the surface morphology of the films by the addition of SiH 2 CI2 and H 2 to SiH 4 were investigated since it is assumed that the surface morphology reflects the growth mechanism. EXPERIMENTAL Mercury sensitized photo-CVD was used to prepare the Si films. Figure 1 shows the schematic diagram of the photo-CVD system. A gas mixture of SiH 4 , H 2 and SiH 2CI 2 was introduced into the reactor with a very small amount of mercury vapor. A 40mW/cm 2 lowpressure mercury lamp was used as the UV source, radiating 253.7nm and 184.9nm resonance lines. SiH 3 and atomic H are generated by mercury-sensitized reactions of SiH 4 and H 2 3,4), respectively; 125 Mat. Res. Soc. Symp. Proc. Vol. 377 © 1995 Materials Research Society
Table I Growth conditions Light source low-pressure mercury lamp 12mW/cm 2 Light power Mercury bath temp. 50°C Substrate Corning 7059 Si(100) Substrate temp. 160-210*C Base pressure 2x 10-6Torr Source gasses SiH 4 , SiH 2CI 2 , H2 SiH4 flow rate 4.6-20scc
Data Loading...
