AVS 46th International Symposium
    Thin Films Division Monday Sessions
       Session TF-MoM

Paper TF-MoM9
Hydrogenated Amorphous Silicon Surface Growth Mechanism Characterized by Fourier Analysis of the Surface Topography

Monday, October 25, 1999, 11:00 am, Room 615

Session: Fundamentals of PECVD
Presenter: K.R. Bray, North Carolina State University
Authors: K.R. Bray, North Carolina State University
A. Gupta, North Carolina State University
L. Smith, North Carolina State University
G.N. Parsons, North Carolina State University
Correspondent: Click to Email
Hydrogenated amorphous silicon (a-Si:H) is widely used for the manufacture of solar cells and for thin film transistors (TFT) in active matrix liquid crystal displays (AMLCD). There have been many studies of the gas-phase reactions occurring in the plasma, but less is known of what takes place on the growing silicon surface. An increased understanding of its growth mechanism is desirable to optimize the quality of the a-Si:H films. Atomic force microscopy (AFM) was used to image the surface topography of PECVD deposited a-Si:H. Surface topography was compared for samples deposited over a wide range of temperatures (25° C - 350° C) and film thicknesses (20 - 2000 Å). The rms surface roughness has been used to characterize surface growth. During the initial 30 seconds of nucleation using 100 sccm of 2% SiH@sub 4@/He, the rms is between 1 - 4 nm. As the deposition continues from 1 to 5 minutes, the rms increases to between 13 and 28 nm. After film coalescence, the rms roughness reduces to between 1 and 4 nm. A Fourier analysis of the surface topography produces an index (i), which has been correlated with different surface growth mechanisms. The Fourier indices for these samples range from i = 3.8 to 4.8, and increase with temperature. These results indicate that surface diffusion (i = 4) is the primary smoothing mechanism during growth. But the deviation from 4 suggests that the actual mechanism is more complex than simple surface diffusion. A shift in i suggests that there is a change in the growth mechanism as the film coalesces. We will discuss correlations between the Fourier index and film quality as deduced from structure and electrical characterizations.