Microelectromechanical microphone with membrane trench reinforcements and method of fabrication

A method for fabricating a Microelectromechanical System (MEMS) microphone, the method comprising:

• depositing, on a frontside of a wafer, a first oxide layer over a silicon nitride thin film and over and adjacent the wafer, wherein the silicon nitride thin film is disposed over the wafer;
• depositing a membrane protection layer over the first oxide layer between a first side of a first cavity formed in the wafer and a second side of a second cavity formed in the wafer;
• depositing a second oxide layer over and adjacent the membrane protection layer;
• depositing a first membrane nitride layer over the second oxide layer;
• depositing a membrane polysilicon layer over the first membrane nitride layer;
• depositing a second membrane nitride layer over the membrane polysilicon layer;
• depositing a third oxide layer over the second membrane nitride layer depositing a fourth oxide layer over the third oxide layer;
• depositing a backplate nitride underlayer over and adjacent the fourth oxide layer and adjacent the third oxide layer;
• depositing a first backplate polysilicon layer over and adjacent the backplate nitride underlayer;
• depositing a fifth oxide layer at respective portions of the first backplate polysilicon layer;
• depositing a second backplate polysilicon layer over the fifth oxide layer and the first backplate polysilicon layer;
• depositing metal over the second backplate polysilicon layer and over the first backplate polysilicon layer;
• defining a cavity on a backside of the wafer, resulting in a defined structure;
• performing a first release of the defined structure;
• removing the membrane protection layer;
• performing a second release of the defined structure;
• and
• depositing a self-assembled monolayer coating.