Measurement of the Townsend first ionization coefficient in tetraethoxysilane

The present paper reports the ionization coefficient in tetraethoxysilane determined experimentally by the steady state Townsend method for E/N in the range 450-2000 Td. Low-temperature plasmas of tetraethoxysilane mixtures may be used to perform plasma-enhanced chemical vapour deposition of silicon dioxide thin films for microelectronics at low substrate temperatures. Since tetraethoxysilane is a low-vapour-pressure liquid at room temperature, heating coils are attached to the ionization chamber to maintain the temperature of the chamber higher than that of the tetraethoxysilane source so that the required vapour pressure is obtained yet no condensation of tetraethoxysilane occurs on the chamber walls. Measurements indicate that the ionization coefficient increases very rapidly at about E/N of 450 Td, at which the value is 7.7*10 -18 cm 2 , then the increase tends to saturate and reaches a value of 4.9*10 -16 cm 2 at E/N of 2000 Td. Furthermore, it is found that the logarithm of the current has a linear dependence on electrode separation. This suggests that electron attachment is very small or practically absent in this vapour.