Measurement of the Townsend first ionization coefficient in tetraethoxysilane and oxygen mixtures

The present paper reports the Townsend first ionization coefficient in tetraethoxysilane (TEOS) vapour and oxygen mixtures determined experimentally by the steady state Townsend method for E/N from 350 to 2000 Td (1 Td = 10(-21) V m(2)). This gas mixture is used as a process gas when silicon dioxide films are deposited by using plasma enhanced chemical vapour deposition at low substrate temperatures. The result shows that remarkable synergism for the ionization coefficient exists in the mixtures. The maximum value of the coefficient reaches about 140% of that estimated by a linear interpolation between the values in pure TEOS vapour and pure oxygen. It is also shown that the fractional O-2 percentage pressure of the mixture which gives the maximum values of the ionization coefficient linearly decreases with increasing E/N in the present measurement.