Method of manufacturing liquid ejection head

A method of manufacturing a liquid ejection head having a substrate and an ejection port formation member in which a liquid channel is formed between the member and the substrate and ejection ports which communicate with the channel and eject liquid are provided, the method comprising:

• providing a first photosensitive resin layer containing a photodegradable positive photosensitive resin and serving as a mold material of the channel on the substrate;
• providing a gas barrier layer having a film density of 1 g/cm3 or more on the first photosensitive resin layer;
• subjecting the first photosensitive resin layer and the gas barrier layer to pattern exposure, and then performing development to thereby form a mold material of the channel and also removing the gas barrier layer before or simultaneously with the development;
• providing a second photosensitive resin layer serving as the ejection port formation member on the mold material of the channel and the substrate;
• subjecting the second photosensitive resin layer to pattern exposure, and then performing development to thereby form the ejection ports;
• and
• removing the mold material of the channel to form the channel.