Surface roughening during plasma-enhanced chemical-vapor deposition of hydrogenated amorphous silicon on crystal silicon substrates

Abstract

The morphology of a series of thin films of hydrogenated amorphous silicon ͑a-Si:H͒ grown by plasmaenhanced chemical-vapor deposition ͑PECVD͒ is studied using scanning tunneling microscopy. The substrates were atomically flat, oxide-free, single-crystal silicon. Films were grown in a PECVD chamber directly connected to a surface analysis chamber with no air exposure between growth and measurement. The homogeneous roughness of the films increases with film thickness. The quantification of this roughening is achieved by calculation of both rms roughness and lateral correlation lengths of the a-Si:H film surface from the height difference correlation functions of the measured topographs. Homogeneous roughening occurs over the film surface due to the collective behavior of the flux of depositing radical species and their interactions with the growth surface. ͓S0163-1829͑97͒04932-1͔

Temperature dependence of the surface roughness evolution during hydrogenated amorphous silicon film growth

“…13 However, for a-Si:H growth by plasmas the reported ␣ and ␤ values are in the range 0.5-1.0 and 0.1-0.5 for ␣ and ␤, respectively. [3][4][5][6][7][8][9] In this letter, we report the scaling behavior of the a-Si:H roughness evolution for a broad range of growth rates R d and substrate temperatures T sub . The films have been deposited by the remote expanding thermal plasma ͑ETP͒ under conditions in which film growth is dominated by SiH 3 and in which ion bombardment is absent.…”

“…4,8,11,18 This provides evidence that physisorbed SiH 3 is not responsible for the decreasing surface roughness of a-Si:H with increasing T sub in accordance with the earlier conclusion that not physisorbed SiH 3 but the position of the dangling bonds on the surface determines the surface roughness. 3,10 The dangling bonds act as growth sites for the SiH 3 radicals and ultimately the SiH 3 radicals will stick at these dangling bonds, even in the case that the physisorbed SiH 3 radicals have diffused over the surface. Note, that from our data we do not exclude the presence of physisorbed SiH 3 radicals.…”

Surface Smoothening Mechanism of Amorphous Silicon Thin Films

“…The T dependence of the surface roughening evolution of a-Si:H films has been analyzed in several experiments, under conditions where the dominant deposition precursor is the SiH 3 radical [7][8][9][10][11]. Smets and co-workers studied the scaling behavior of the growth surface morphology of a-Si:H films and derived an activation energy barrier of 1:0 eV for the smoothening mechanism [8].…”

“…Based on the exceptionally low surface roughness of a-Si:H films grown under these conditions over the temperature (T) range 450 K < T < 750 K [4,5], a ''surface valley-filling'' mechanism has been postulated; according to this mechanism, a mobile surface species, generally assumed to be the SiH 3 radical [5], passivates preferentially dangling bonds (DBs) of Si atoms located in surface valleys [4,6]. Experimental data for the roughness evolution of a-Si:H films provide only indirect interpretations for the smoothening mechanism [7][8][9][10][11] and yield controversial results for the diffusion barrier of the SiH 3 radical on the a-Si:H surface [7,8,12,13]. Moreover, there exists no detailed account of either the role of surface morphology in affecting the incorporation of SiH 3 radicals into the film, or of the preferential locations for growth on the a-Si:H surface.…”

Surface evolution during crystalline silicon film growth by low-temperature hot-wire chemical vapor deposition on silicon substrates

“…The microstructure and surface evolution are especially important because all other properties-optical, electrical, and mechanical-stem from these. Previously, many researchers have reported on the evolution roughness of amorphous Si films with substrate temperature 1,2 and with thickness 3 and of epitaxial films grown by molecular beam epitaxy ͑MBE͒, 4 ion-assisted MBE, 5 and with hyperthermal Si beams. 6 In this study, we address the surface evolution of hot-wire chemical vapor deposited ͑HWCVD͒ crystalline Si thin films ͑epitaxial, twinned epitaxial, and polycrystalline͒ with temperature, thickness, and hydrogen dilution and discuss the resulting growth regime and structure.…”