Identification of Si and SiH in catalytic chemical vapor deposition of SiH4 by laser induced fluorescence spectroscopy

Abstract

Radical species produced in catalytic chemical vapor deposition (CVD), often called hot-wire CVD, processes were identified by using a laser induced fluorescence technique. Ground state Si atoms could be detected at low pressures where collisional processes in the gas phase could be ignored. The electronic temperature of Si atoms just after the formation on the catalyzer (tungsten) surfaces was 1320±490 K, when the catalyzer temperature was 2300 K. By the addition of 0.5 Pa of Ar, the electronic temperature was lowered down to 450±30 K. The absolute density of Si atoms was ${\text{3±1×10}}^9 {\mathrm{cm}}^{\text{−3}}$ at 10 cm below the catalyzer when the flow rate and the pressure of ${\mathrm{SiH}}_4$ were 0.5 sccm and 4 mPa, respectively. This density is just 0.3% of that of the parent ${\mathrm{SiH}}_4$ molecules. However, since the decay rate of Si atoms is fast, it can be concluded that atomic silicon is one of the major products on the heated catalyzer surfaces. SiH radicals could also be detected, but the production rate of this species is two orders of magnitude less than that of Si atoms. It was also discovered that volatile ${\mathrm{SiH}}_4$ molecules are produced by the atomic hydrogen attack on the amorphous silicon deposited on the chamber walls.