Sidewall stopper for MEMS device

A MEMS device, comprising:

• a substrate having an opening disposed through the substrate;
• a first backplate disposed over the substrate and facing the opening of the substrate;
• a second backplate disposed over the first backplate;
• a diaphragm located between the first backplate and the second backplate and including an opening disposed therethrough, wherein the diaphragm is spaced apart from the first backplate by a first distance and spaced apart from the second backplate by a second distance;
• and
• a sidewall stopper disposed along sidewalls of the opening of the diaphragm.

A MEMS device, comprising:

• a first interlayer dielectric layer disposed over a substrate;
• a diaphragm disposed over the first interlayer dielectric layer;
• a second interlayer dielectric layer disposed over the diaphragm;
• and
• a sidewall stopper disposed along a first sidewall of the diaphragm, wherein the sidewall stopper extends into recesses of the first interlayer dielectric layer and the second interlayer dielectric layer above and below the diaphragm.