Diffusion of Si atoms and thin film deposition in a silane-argon plasma

Abstract

Time dependences of the Si atom density in a pulsed RF discharge in a mixture of 5% silane and 95% argon have been investigated by absorption spectroscopy. Decay of the Si atom density in afterglow was exponential in a low power and low flow rate limit. The time constant of the decay was proportional to the gas pressure in the measured range of 0.2 to 2 Torr. This relation yields the diffusion coefficient of Si atoms in the mixture to be 1.5*10¹⁹ cm^-1 s^-1 at unit gas density and at 300K. From the diffusion coefficient and the absolute density of Si atoms in the plasma the deposition rate is calculated with the mass density of the deposited film measured by a combination of a multiple beam interferometry and an oscillating quartz microbalance technique. The calculated value is smaller than the measured one by about 30%. The difference is attributed to the deposition of other radicals produced in the plasma.