AVS 45th International Symposium
    Thin Films Division Monday Sessions
       Session TF-MoP

Paper TF-MoP23
Characterization of PECVD Hydrogenated Amorphous Silicon (a-Si:H)

Monday, November 2, 1998, 5:30 pm, Room Hall A

Session: Thin Films Poster Session
Presenter: T.C. Ang, Nanyang Technological University, Singapore
Authors: T.C. Ang, Nanyang Technological University, Singapore
M.S. Tse, Nanyang Technological University, Singapore
L.H. Chan, Chartered Semiconductor Manufacturing Ltd., Singapore
J.L. Sudijono, Chartered Semiconductor Manufacturing Ltd., Singapore
Correspondent: Click to Email
Unhydrogenated amorphous silicon has a high defect density and this prevents it from being useful for electronic devices. Hydrogen incorporation in a-Si eliminates defects and the quality of a-Si:H depends on the way the hydrogen is incorporated rather than its content in the film. The type of plasma used and the deposition conditions determine the nature of the hydrogen bonding and the film quality. In this paper, the film characteristics of PECVD a-Si:H deposited using pure silane plasma and silane plasma diluted with argon at different deposition temperatures are studied in terms of the deposition rate, hydrogen content, refractive index and film morphology. Fourier transform infrared spectroscopy (FTIR) spectra showed that in a-Si:H films deposited with argon dilution of the silane plasma, hydrogen is bonded to Si only in monohydride groups (SiH) whereas with a monosilane glow discharge plasma, the spectra revealed the presence of SiH, SiH@sub 2@ and (SiH@sub 2@ + SiH@sub n@) bonds. Higher hydrogen content was measured in low temperature deposited films. The RI and absorption coefficient (n, k) values of low temperature deposited films were lower and are consistent with the higher hydrogen content observed in the FTIR spectra. This is mainly due to the decreasing Si densities of the films due to the formation of Si-H and SiH@sub n@ (n>1) bonds in the films. Atomic force microscopy (AFM) was used to investigate the effect of deposition temperature on the film morphology and results showed that smaller grain sizes and tighter packing densities were characteristic of higher temperature deposited films. Results obtained through FTIR and spectroscopic ellipsometry (SE) show a correlation between the hydrogen content and the RI. Films deposited at higher deposition temperatures have lower H content and higher RI values as compared to lower temperature deposited films. Results from electrical tests on a-Si:H films deposited at different temperatures revealed changes in film quality which are consistent with the FTIR and SE observations. @FootnoteText@ W. Beyer and H. Wagner, J. non-crystall. Solids 59/60, 161 (1983). W. Beyer, Tetrahedrally-Bonded Amorphous Semiconductors, Ed. D. Adler and H. Fritzsche, Plenum Press, New York, 129, 1985. W. Beyer, Physica (Utrecht), 170B, 105,1991. R. A. Street, Hydrogenated Amorphous Silicon, Cambridge Solid State Science Series (Cambridge University Press, Cambridge, 1991). Akihisa Matsuda, Plasma Physics Control Fusion, 39, pp.A431,1997.