Single crystal silicon substrate, liquid discharge head, and method for manufacturing single crystal silicon substrate

A liquid discharge head, comprising:

• a single crystal silicon substrate that includes
• a substrate surface;
• a first through-hole including an inclined side wall which is inclined with respect to the substrate surface, wherein an angle formed by the inclined side wall with respect to the substrate surface is in a range from 45.0° to 54.7;
• and
• a second through-hole constituting a flow path and including a side wall, wherein
• the side wall is constituted by a vertical side wall which is more vertical to the substrate surface than the inclined side wall is to the substrate surface,
• the first through-hole is formed by crystal anisotropic etching,
• the second through-hole is formed by metal-assisted chemical etching, and
• the substrate surface includes
• a first surface on a side where the inclined side wall is exposed, and
• a second surface opposite to the first surface, wherein
• the first through-hole and the second through-hole extend from the first surface to the second surface, and
• an opening portion of the second through-hole on a first surface side is provided with an inclined surface with respect to the first surface, the inclined surface widening toward the first surface;
• and
• a cavity substrate including a third surface at which a piezoelectric element and a conductive portion electrically coupled to the piezoelectric element are formed, and a fourth surface at least a part of which constitutes the flow path and that is opposite to the third surface, wherein
• the third surface is bonded to the substrate surface with a part of the conductive portion exposed through the first through-hole, and the flow path of the fourth surface communicates with the second through-hole.