Epitaxial silicon CMOS-MEMS microphones and method for manufacturing

A method of forming a MEMS microphone, the method comprising:

• depositing an oxide layer on a mono-crystalline silicon layer on a top surface of a monolithic structure;
• etching a plurality of vent hole locations partially through the oxide layer from the top surface of the monolithic structure;
• depositing a poly-crystalline silicon layer of a substantially uniform thickness on the oxide layer on the top surface of the monolithic structure;
• etching the poly-crystalline silicon layer and the oxide layer from the top surface around a perimeter of the monolithic structure to expose the mono-crystalline silicon layer;
• epitaxially depositing a hybrid silicon layer on the poly-crystalline silicon layer and the exposed area of the mono-crystalline silicon layer on the top surface of the monolithic structure,
• the hybrid silicon layer acquiring characteristics of a seed material, wherein the seed material is poly-crystalline silicon in areas where the hybrid silicon layer contacts the poly-crystalline silicon layer and the seed material is mono-crystalline silicon in areas where the hybrid silicon layer contacts the mono-crystalline silicon layer,
• the hybrid silicon layer being formed such that the monolithic structure has a substantially uniform thickness after the hybrid silicon layer is deposited;
• depositing a second oxide layer on the hybrid silicon layer on the top surface of the monolithic structure;
• etching a back cavity through the mono-crystalline silicon layer on a bottom surface of the monolithic structure exposing the oxide layer in the back cavity;
• etching the oxide layer in the back cavity from the bottom surface of the monolithic structure until the poly-crystalline silicon layer is partially exposed in the back cavity in the plurality of vent hole locations;
• and
• creating a plurality of vent holes in the plurality of vent hole locations using the remaining oxide layer as a mask by etching the poly-crystalline silicon layer and the poly-crystalline silicon of the hybrid silicon layer from the bottom surface of the monolithic structure until the second oxide layer is exposed leaving the oxide layer and the hybrid silicon layer intact in areas outside of the plurality of vent hole locations.

A microphone comprising:

• a back cavity formed in a first layer of a first silicon type;
• a hybrid layer positioned monolithically on the first layer, the hybrid layer including a microphone backplate of a second silicon type surrounded by a perimeter of the first silicon type, the hybrid layer begin formed as a single silicon layer in a monolithic microphone structure, the microphone backplate including a plurality of vent holes;
• and
• a CMOS/membrane layer including
• a non-perforated microphone membrane positioned above the microphone backplate, and
• a CMOS-backend system positioned above the perimeter of the first silicon type and supporting the non-perforated microphone membrane.