Alignment of substrate cavity

A packaged integrated circuit comprising:

• a substrate of a first material having opposing first side and second side, the substrate including:
• a cavity that that extends from the second side;
• and
• a first layer and a second layer of a second material that extends from the first side of the substrate and forming at least parts of opposing side walls of the cavity, in which at least one of:
• the second material is different from the first material, or the substrate is separated from the first layer and the second layer by a layer of a third material different from the first material.

A method comprising:

• forming a first trench structure and a second trench structure that extend from a first side of a substrate comprising a first material;
• filling the first and second trench structures with a second material;
• forming one or more device on the first side of the substrate;
• and
• forming a cavity that extend from a second side of the substrate to the first side by removing parts of the substrate between the first and second trench structures, in which the second material in the first and second trench structures form at least parts of opposing side walls of the cavity.