CMOS-based MEMS Sensor Process Development for Very Low Capacitive Pressure Application

摘要

Nowadays, the megatrend in MEMS processing are integration with CMOS standard process. With beginning through out of bulk micromachining, the next transformation to use surface micromachining in produced CMOS-based MEMS devices. We have demonstrated the ability to fabricate thin layer membrane for very low capacitive pressure sensor application using CMOS-based MEMS process compatible. The structure of the membrane consists of parallel plate separated with air gap which both top and bottom electrodes were fixed at both sides. A novel fabrication approach is introduced. The novelty of this work lies in the design and fabrication process itself. The discovery of the low pressure chemical vapor deposition (LPCVD) silicon nitride of deposition behaviors is the key factor that allows the seal off multi holes opening. The multi hole openings on the polysilicon membrane were then sealed off by find the ideal combination of etch holes size, nitride deposition method and the thickness so that the holes are perfectly sealed. Another study was carried out to understand the issues related to this design and process fabrication technique. The resultant 1 um thin layer membrane with absolute air gap has been designed and fabricated.