holes defined in the plasma electrode 12 an oxidizing gas of dinitrogen monoxide n 2 o which is stored in a cylinder 19 is supplied through a pipe connected to the cylinder 19 into the pipe from the temperature regulator 17 immediately before the plasma reaction chamber 11 as is well known in the art the carrier gas may be of nitrogen n 2 helium he or xenon xe other than argon using the high frequency plasma cvd system shown in fig2 a film of tantalum oxide was formed as follows the cylinder 18 containing a certain quantity of tantalum v chloride tacl 5 was heated to 160 u00b0 c by the temperature regulator 17 thus generating a vapor or gas of tantalum chloride the gas of tantalum chloride was then mixed with a carrier gas of argon and the mixture gas was supplied to the plasma reaction chamber 11 an oxidizing gas of dinitrogen monoxide n 2 o was supplied from the cylinder 19 and mixed with the mixture gas of tantalum chloride and argon immediately before the plasma reaction chamber 11 the mixed gas was then introduced into the plasma reaction chamber 11 the gas of tantalum chloride was supplied at a rate of 10 sccm and the gas of dinitrogen monoxide at a rate of 100 sccm the pressure in the plasma reaction chamber was 0 6 torr a silicon substrate 21 supported by the susceptor 13 was heated to 450 u00b0 c by a heater not shown.