Analysis of the Local Bonding Structure in Silicon Nitride (Oxide) Films Deposited by Plasma-Enhanced CVD in Terms of a Charge-Transfer Model

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Silicon nitride (SiN_x : H) and Si oxide (SiO_x : H) films are deposited using a plasma-enhanced CVD method, and the vibrational properties, the film stress, and the structure of defects are investigated as a function of the deposition conditions. The results might be summarized as :1) In Si nitride films with a near-stoichiometric composition, the films satisfying all of the low stress, the high break-down strength, and the low etching rate can be obtained as they were deposited under conditions of both high H dilution ratio and high rf power supply. An improvement in properties of the films as insulators can be connected with a change in the local bonding structure : when the density of Si-NH-Si bonds relative to that of N-Si_3 bonds decreases, high quality films can be obtained.2) The oscillator strength for the SiH stretching absorption is a function of the effective charge of the SiH dipole, and the values of the effective charge can be calculated using a charge-transfer model combined with the random bonding model. The calculated values of the oscillator strength for SiN_x : H and SiO_x : H films were in excellent agreement with their experimental values. The frequencies of the SiN and SiO stretching absorption are mainly dominated by the bond length and the bond angle for these bonds. It has been shown that the values of these bond length and bond angle can also connected with the sum of the partial charge on the Si and the N or O atoms.3) The frequency of the SiH bending absorption in SiO_x : H flms, which occur in the range of 500-900 cm^<-1>, was analyzed using a molecular-orbital calculation (MOC) method. Further, the dependence of the electron spin resonance spectra as a function of the film composition, arising from Si dangling bonds, was also analyzed on the basis of the MOC.