the organosilicon oxide film the results of ashing resistance evaluation performed on the obtained organosilicon oxide film and sih 4 film are shown in the table below and fig2 the vertical axis indicates change in film thickness based on the initial value of 1 compared to the sih 4 film the organosilicon oxide film presents virtually no change in film quality due to ashing indicating superior ashing resistance as shown in the table below good ashing resistance is also achieved at a film forming temperature of 200 u00b0 c or below if teos is used the present invention includes the above mentioned embodiments and other various embodiments including the following 1 an oxide film forming method which is a method of forming an oxide film by capacitively coupled plasma cvd comprising a step in which a substrate is processed at a temperature of 300 u00b0 c or below a step in which processing gases including silicon source gas being teos and oxidizing gas being o 2 are introduced to a reaction chamber in such a way that the total pressure becomes 300 to 600 pa a step in which a first rf power with a frequency range of 10 to 30 mhz such as 13 56 mhz or 27 mhz and a second rf power with a frequency range of 350 to 500 khz such as 400 khz or 430 khz are applied on top of each other to generate a plasma reaction field in the reaction chamber and a step in which the flow rate of each aforementioned gas and output of each aforementioned high frequency power are controlled 2 an oxide film forming method according to 1 above wherein teos o 2 is in a range of 0 01.