Liquid ejection head substrate, liquid ejection head, and method of manufacturing liquid ejection head substrate

A liquid ejection head comprising:

• an element substrate;
• a relay wiring portion electrically connected to the element substrate;
• and
• a casing internally storing a liquid to be supplied to the element substrate,
• the element substrate including:
• a base layer;
• a heating resistance element provided over the base layer to generate a heat energy for ejecting the liquid;
• a first insulation layer covering the heating resistance element;
• and
• a protective layer provided on the first insulation layer, having a first region which overlaps the heating resistance element via the first insulation layer and a second region which does not overlap the heating resistance element, the protective layer is formed of a material including a metal which is eluted by an electrochemical reaction,
• wherein the element substrate further includes a second insulation layer provided over a region overlying the base layer and not provided with the protective layer and over the second region of the protective layer, and
• wherein a layer thickness of the first insulation layer in a region uncovered with the protective layer is smaller than a layer thickness of the first insulation layer in a region covered with the protective layer.

A method of manufacturing a liquid ejection head substrate, wherein the liquid ejection head substrate comprising:

• a base layer;
• a heating resistance element;
• an electrode wiring layer;
• a first insulation layer;
• a protective layer;
• and a second insulation layer, the method of manufacturing the liquid ejection head substrate including:
• a first step of providing, over the base layer, the heating resistance element that generates a heat energy for ejecting a liquid;
• a second step of stacking the first insulation layer over the heating resistance element;
• a third step of stacking, over the first insulation layer, the protective layer having a first region overlapping the heating resistance element via the first insulation layer and a second region not overlapping the heating resistance element and formed of a material including a metal which is eluted by an electrochemical reaction;
• a fourth step of partially removing the first insulation layer and the protective layer, so as to make a layer thickness of the first insulation layer in a region uncovered with the protective layer smaller than a layer thickness of the first insulation layer in a region covered with the protective layer;
• and
• a fifth step of stacking the second insulation layer over a region overlying the base layer where the protective layer is not provided and over at least the second region of the protective layer.