Microelectromechanical system (MEMS) device and fabrication method thereof

A method for fabricating microelectromechanical system (MEMS) device, comprising:

• providing a silicon substrate, having a first side and a second side;
• forming a structural dielectric layer on the first side of the silicon substrate, wherein a plurality of structure elements is embedded in the structural dielectric layer and to be released, the structure elements comprise:
• a first conductive layer, formed over the silicon substrate, wherein the first conductive layer has a plurality of venting holes;
• a supporting layer, formed on the first conductive layer, surrounding the venting holes;
• a second conductive layer, formed on the supporting layer;
• a plurality of protrusion structures, formed on the second conductive layer;
• a cap layer, capping over the first conductive layer, the supporting layer, the second conductive layer and the protrusion structures;
• and
• a diaphragm, formed above the second conductive layer by a distance, wherein a chamber is formed between the diaphragm and the cap layer and is connected to the cavity of the silicon substrate through the venting holes;
• forming a passivation layer over the structural dielectric layer, wherein the passivation layer has an opening to expose the structural dielectric layer at a MEMS region;
• forming a cavity in the silicon substrate at the second side to expose the structural dielectric layer;
• and
• performing isotropic etching process on a dielectric material of the structural dielectric layer to release the structure elements,
• wherein a first side of the diaphragm is exposed by the chamber and faces to the protrusion structures of the conductive backplate and a second side of the diaphragm is exposed to an environment space, wherein the chamber is connected to the cavity of the silicon substrate through the venting holes of the conductive backplate.