Patent ID: 7674722

Claim:
A method of forming a gate insulation film, comprising: processing of plasma nitridation to an oxide film of the insulation film by microwave plasma generated from a process gas of argon gas and nitrogen gas, using a plane antenna, wherein the oxide film is processed by plasma nitridation so as to have nitrogen concentration of 5 to 20% in atomic percentage, wherein processes of the plasma nitridation comprise the steps of: carrying a substrate into a process vessel; subsequently vacuuming the inside of the process vessel to remove residual oxygen in the process vessel; subsequently heating the substrate; subsequently introducing the process gas necessary for a nitridation into the process vessel; and subsequently generating the plasma in the process vessel to perform the processing of plasma nitridation, and wherein said step of generating the plasma in the process vessel to perform the plasma nitridation processing includes the step of igniting the plasma, with pressure in the process vessel set higher than pressure for the plasma nitridation processing and with a flow rate of the argon gas set higher than a flow rate of the argon gas at the time of the plasma nitridation processing.