Deep trenches on microelectromechanical system wafers for stealth dicing

A wafer, comprising:

• a substrate;
• an insulation layer arranged on the substrate;
• a plurality of device layers arranged on the insulation layer, the plurality of device layers including an upper device layer;
• trenches extending into the wafer from the upper device layer and delineating a set of dies in the wafer, the trenches having trench bottoms;
• and
• regions, arranged below the bottoms of the trenches, comprising aligned structural weaknesses,
• wherein each die of the set of dies having an optical microelectromechanical systems (MEMS) surface in the upper device layer and one or more inner cavities below the optical MEMS surface.

A method of manufacturing a plurality of optical microelectromechanical systems (MEMS) dies, the method comprising:

• forming an unreleased wafer assembly including a wafer substrate, an insulation layer formed on the wafer substrate, and a plurality of device layers formed on the insulation layer,
• wherein the plurality of device layers includes an upper device layer and one or more inner cavities,
• wherein the one or more inner cavities contain MEMS actuation structures that are sensitive to particulate, and
• wherein the upper device layer of the plurality of device layers is sealed such that the one or more inner cavities are closed;
• after forming the unreleased wafer assembly and before opening the one or more inner cavities, forming deep trenches along singulation lanes that delineate the optical MEMS dies in the unreleased wafer assembly,
• wherein each deep trench extends from the upper device layer to a depth that is at least partially into the plurality of device layers;
• after forming deep trenches, forming a released wafer assembly by unsealing the upper device layer thereby opening the one or more inner cavities of the unreleased wafer assembly to form a plurality of optical MEMS devices in the plurality of device layers;
• after forming the released wafer assembly, emitting one or more laser beams into the wafer substrate to create defect regions within the singulation lanes of the wafer substrate;
• and
• after emitting the one or more laser beams, separating the released wafer assembly, through the defect regions in the wafer substrate, into the plurality of optical MEMS dies.