Abstract
This thesis is discussing thin film diaphragm problems during the fabricating process that when using bulk micromachining method to fabricate micro-pressure sensors and proffers some solving methods. The film thickness, surface roughness, annealing of films were measured and analysed by n＆k, Atomic force microscopy (AFM), Fourier transform IR spectroscopy (FTIR), and I-V measurment, respectively.Piezoresistors have been used widely for various microsensors, such as accerlerometers and pressure sensors. Piezoresistive sensors are fabricated by placing the piezoresistors on the regions where largest strain would occur. In order to satisfy the measurement sensitivity as well as the fabrication processes, the substrate underneath the microstructures are usually removed through the back-sided etching. Hence, the fabrication processes are complex and time consuming.A thin diaphragm was constructed by bulk micromachining on n-type silicon wafer.Boron was then doped into diaphragm to produce piezoresistors,and these piezoresistors were connected in the form of Wheatstone bridge configuration.Whenever the diaphragm was affected by stress,the resistance of the piezoresistor changes .Through measuring the signals of the output voltage enlarged by the Wheatstone bridge configuration,the stress intensity can be calculated indirectly.This thesis is discussing thin film diaphragm deformation problems during the fabricating process that when using surface micromachining method to fabricate micro-pressure sensors and proffers some solving methods. Because the design principle of micro-pressure sensors is that builds polycrystalline silicon with doped on the top of pressure sensor thin film, so when its deformation happens, the Piezoresistance will change and we can detect sensor point gas pressure value change.Bulk-micromachining techniques are used to fabricate the pressure sensors. Processes like LPCVD, APCVD, dry etching, wet etching, and lithography are applied in this study. Several important issues regarding fabrication process have been raised and discussed.In the research the piezoresistive sensers have been fabricated successfully, and it is proved that the process design is feasible. The testing results showed the approximate sensitivity of these sensors was 57.2μV/V-mmHg.Because the traditional pressure sensors are restricted by its size specification, they are subject to field space and environmental limitations. However, the rapid development of the semiconductor fabrication technology has greatly improved the sensitivity and linearity characteristics of the silicon- base piezzoresistor pressure sensors by the MEMS fabrication process.