Influence of pressure and radio frequency power on deposition rate and structural properties of hydrogenated amorphous silicon thin films prepared by plasma deposition

Abstract

The influence of radio frequency (rf) power and pressure on deposition rate and structural properties of hydrogenated amorphous silicon (a-Si:H) thin films, prepared by rf glow discharge decomposition of silane, have been studied by phase modulated ellipsometry and Fourier transform infrared spectroscopy. It has been found two pressure regions separated by a threshold value around 20 Pa where the deposition rate increases suddenly. This behavior is more marked as rfpower rises and reflects the transition between two rf discharges regimes (a and r). The best quality films have been obtained at low pressure and at low rf power but with deposition rates below 0.2 nm/s. In the high pressure region, the enhancement of deposition rate as rf power increases first gives rise to a reduction of film density and an increase of content of hydrogen bonded in poly hydride form because of plasma polymerization reactions. Further rise of rf power leads to a decrease of polyhydride bonding and the material density remains unchanged, thus allowing the growth of a-Si:H films at deposition rates above I nmls without any important detriment of material quality. This overcoming of deposition rate limitation has been ascribed to the beneficial effects of ion bombardment on the a-Si:H growing surface by enhancing the surface mobility of adsorbed reactive species and by eliminating hydrogen bonded in polyhydride configurations.

Size dependence of nanostructures: Impact of bond order deficiency

“…The Raman shifts of TiO 2 particles are attributed to the effects of decreasing particle size on the force constants and vibrational amplitudes of the nearest-neighbor bonds [457]. However, the effect of stress can usually be ignored for hydrogenated silicon [458,459], in which hydrogen atoms terminate the surface dangling bonds, which reduce the bond strains and hence the residual stress. The phonon confinement model [455] attributes the redshift of the asymmetric Raman line to relaxation of the q-vector selection rule for the excitation of the Raman active phonons due to their localization.…”

Lattice Dynamics: Phonon Relaxation

“…The Raman shifts of TiO 2 particles are attributed to the effects of decreasing particle size on the force constants and vibrational amplitudes of the nearest neighbor bonds [25]. However, the effect of stress can usually be ignored for hydrogenated silicon [26,27], in which hydrogen atoms terminate the surface dangling bonds to reduce the bond strains and hence the residual stress.…”

Atomistic origin and temperature dependence of Raman optical redshift in nanostructures: a broken bond rule

“…The Raman shifts of TiO 2 particles are attributed to the effects of decreasing particle size on the force constants and the amplitudes of vibration of the nearest atomic neighbors. 23 However, the effect of stress can usually be ignored for hydrogenated silicon, 24,25 in which hydrogen atoms terminate the surface dangling bonds, which reduce the bond strains and hence the residual stress. The phonon quantum confinement argument 16 attributes the redshift of the asymmetric Raman line to the relaxation of the q-vector selection rule for the excitation of the Raman active phonons due to their localization.…”