rf power source 28 supplies rf power to the microwave inlet window 22 argon gas is supplied through an argon gas inlet 30 into the plasma chamber 20 to keep the microwave inlet window 22 clean this technique is described in akabori et al spring 1989 ouyou butsuri gakkai yokou shu 3p 2f 1 p 721 a ticl 4 gas source supplies ticl 4 gas through a mass flow controller mfc and a first gas supply line 40 into the film forming chamber 10 and n 2 gas and h 2 gas are supplied through mass flow controllers mfcs and a second gas supply line 42 into the film forming chamber 10 the gases are discharged from the film forming chamber 10 through a discharge duct 16 a heating system 50 which is the feature of the present invention has heating element buried in the side walls 10a of the film forming chamber 10 to heat the film forming chamber 10 the heating system 50 and the heating element 14 for heating the semiconductor wafer 100 are controlled by a common temperature controller not shown so that the side walls 10a and the semiconductor wafer 100 are heated respectively at desired temperatures in fig1 indicated at 32 is a plasma a process of forming a.