Wafer dicing method and liquid ejection head

A stealth dicing method performed on a wafer having a first substrate, a second substrate bonded to the first substrate, and a hollow portion defined by a concave portion at least partially disposed adjacent to an interface of the first substrate and the second substrate, the second substrate being thinner than the first substrate in a region including the hollow portion, with an X-direction being a direction in which the hollow portion extends, a Z-direction being a direction of a thickness of the wafer, and a Y-direction being a direction orthogonal to the X-direction and the Z-direction, the stealth dicing method comprising:

• a first step of performing laser application on the second substrate to form a modified region in the second substrate, the modified region being a region for dicing and having low crystal strength;
• and
• a second step of performing laser application on the first substrate to form a modified region in the first substrate, wherein
• in one of the first step and the second step, a plurality of the modified regions are formed, arranged in the Z-direction at positions corresponding to both sides of the hollow portion in the Y-direction, and in another one of the first step and the second step, a plurality of the modified regions are formed, arranged in the Z-direction at a position corresponding to one side of the hollow portion in the Y-direction.