LIQUID EJECTION HEAD, ELEMENT SUBSTRATE, AND MANUFACTURING METHODS THEREOF

A method for manufacturing an element substrate of a liquid ejection head, the method includes forming a silicon-based film layer including carbon on one surface of a base substrate, laminating a silicon substrate on the film layer formed on the one surface of the base substrate and bonding the silicon substrate to the film layer, processing the silicon substrate bonded to the film layer using the film layer as a stop layer and forming a lower hole portion, processing the base substrate using the film layer as the stop layer and removing the base substrate to expose the film layer, and forming an opening portion communicating with the lower hole portion in the exposed film layer.