Recording element substrate and method of manufacturing the same

A recording element substrate, comprising:

• an ejection port forming member in which an ejection port configured to eject liquid is formed;
• and
• a substrate including a liquid supply port configured to supply the liquid to the ejection port, a first surface on which the ejection port forming member is placed, and a second surface that is a rear surface of the first surface,
• wherein the liquid supply port includes a first portion perpendicularly connected to the first surface, a second portion connected to the first portion, and a third portion perpendicularly connected to the second portion,
• wherein an inner wall of the second portion includes an inclined surface that is inclined toward an inner wall of the first portion such that a width of the second portion is gradually increased toward the second surface, and
• wherein a water-repellent film is formed at least on the inner wall of the first portion.

A method of manufacturing a recording element substrate, wherein the recording element substrate includes an ejection port forming member in which an ejection port configured to eject liquid is formed, and a substrate including a liquid supply port configured to supply the liquid to the ejection port, a first surface on which the ejection port forming member is placed, and a second surface that is a rear surface of the first surface, the method comprising:

• preparing the substrate such that the liquid supply port includes a first portion perpendicularly connected to the first surface, a second portion connected to the first portion, a third portion perpendicularly connected to the second portion, and an inner wall of the second portion includes an inclined surface that is inclined toward an inner wall of the first portion such that a width of the second portion is gradually increased toward the second surface;
• forming a hydrophilic film at least on the inner wall of the first portion;
• attaching a tape on the first surface of the substrate including the liquid supply port;
• filling the first portion with an aqueous filler by dropping the aqueous filler on the inclined surface of the inner wall of the second portion;
• removing the tape;
• forming the ejection port forming member on the first surface;
• and
• removing the aqueous filler.