Measurement of the ionisation and attachment coefficients in monosilane and disilane

Abstract

The ionisation alpha /p0, electron attachment eta /p0 and effective ionisation alpha /p0(= alpha /p0- eta /p0) coefficients for monosilane (SiH4) and disilane (Si2H6) were measured by the steady-state Townsend method for 60<E/p0<270 V cm-1 Torr-1, where E is the electric field and p0 is the gas pressure reduced to 0 degrees C. The results show that the values of alpha /p0 and alpha /p0 for SiH4 and Si2H6 are smaller than that of CH4, and the value of alpha /p0 for Si2H6 is about 1/3 of that for SiH4. The value of eta /p0 is found smaller than about 5*10-2 cm-1 Torr-1 for the E/p0 values studied here. It appears that the present work is the first to report the value of these parameters. The limiting E/p0, at which alpha /p0= eta /p0, for SiH4 and Si2H6, is determined to be about 65 and 125 V cm-1 Torr-1, respectively. The total secondary ionisation coefficient gamma T for these gases are also measured for E/p0>150 V cm-1 Torr-1 and found to be less than 10-5.