Method of producing substrate for liquid ejection head

A method of producing a substrate for a liquid ejection head including a liquid supply port formed therein, comprising:

• forming a sacrifice layer on a first surface of a silicon substrate in a region in which the liquid supply port is to open, the sacrifice layer containing aluminum which is selectively etched with respect to the silicon substrate;
• forming an etching mask on a second surface which is a rear surface of the first surface of the silicon substrate, the etching mask having an opening corresponding to the sacrifice layer;
• a first etching step of etching the silicon substrate by use of the etching mask as a mask and by use of a first etchant containing 8 mass % or more and less than 15 mass % of tetramethylammonium hydroxide;
• and
• after the first etching step, a second etching step of removing the sacrifice layer by use of a second etchant containing 15 mass % or more and 25 mass % or less of tetramethylammonium hydroxide.