Gate dielectric layer forming method

The invention discloses a method used for forming a grid dielectric layer. The method comprises the steps as follows: forming a silica layer on a substrate; carrying out plasma nitrogenization treatment for the silica layer; carrying out first thermal annealing treatment for the substrate in the nitrogen environment; and carrying out second thermal annealing treatment for the substrate in the oxygen environment. The method for forming the grid dielectric layer is adopted to increase the concentration of nitrogen present in the surface layer of silica. Moreover, the method can ensure that the concentration of nitrogen present in the surface layer of silica can meet the requirement in spite of a device with a relatively low power or a short-lived plasma treatment, thereby preventing the substrate from damages due to the plasma nitrogenization, and enhancing the performance of the device.