Fabrication of microdiaphragm utilizing wafer direct bonding

The process of fabricating a 100 mu m by 100 mu m microdiaphragm was developed through wafer direct bonding, preferential polishing for surface smoothing of the polysilicon embedded in the cavity, and anisotropic etching of [100] and [110] silicon wafers. By adapting the structure developed by this process to the pressure sensor, a small pressure sensor with perpendicular walls and independent pressure inlet ports provided in the back side of the chip was fabricated. The microdiaphragm of this structure minimizes fluctuations in element characteristics which can develop under the influence of excessive moisture, contamination, or other factors since the component side can be provided with a vacuum reference pressure chamber. One of the attractive features of the microdiaphragm pressure sensors mounted on a chip is that pressures of different levels can be measured since each has an independent pressure inlet port.<>