A substrate processing method forming an oxynitride film by nitriding an oxide film formed on a silicon substrate includes a nitridation processing step that nitrides a surface of the oxide film by radicals or ions formed by exciting a nitrogen gas by microwave-excited plasma, the nitridation processing is conducted at a substrate temperature of 500\xb0 C. The portions 11, 12 divided by the second groove 7 have their outer peripheral surfaces extending obliquely so that a diameter of the male screw 1 reduces progressively downward from the head 2. The first layer has an overhanging portion extending into the opening. If the pixel electrode is at a high voltage level at this time point, a voltage at a node is boosted and a first transistor turns ON to supply a reference voltage to the pixel electrode as a refreshing voltage.