Provided is a process for producing a substrate for a liquid ejection head, including forming a liquid supply port in a silicon substrate, the process including the steps of (a) forming an etch stop layer at a portion of a front surface of the silicon substrate at which portion the liquid supply port is to be formed; (b) performing dry etching using a Bosch process from a rear surface side of the silicon substrate up to the etch stop layer with use of an etching mask formed on a rear surface of the silicon substrate to thereby form the liquid supply port; and (c) simultaneously removing the etch stop layer and a deposition film formed inside the liquid supply port.