A study on the thermal behavior in microaccelerometer manufacturing processes

Single crystal silicon (SCS) is used in a variety of microsensor applicatio ns in which stresses and other mechanical effects may dominate device perfo rmance. One of major problems associated with the manufacturing processes o f the microaccelerometer based on the tunneling current concept is temperat ure gradient and thermal stressess. This paper deals with finite element an alyses of residual stresses causing popping up, which are induced in microm achining processes of a microaccelerometer. The authors model temperature-d ependent mechanical properties during focused ion beam(FIB) cutting and Pt deposition processes. The maximum thermal strain of 0.0012 occurred at the readout gap of the microaccelerometer during the Pt deposition process. The stress produced during the heating process of FIB cut was also found to be about 33 similar to 36 MPa and cooling process the maximum equivalent stre ss of about 34 MPa still at the right corner of readout gap. The calculated maximum displacement occurred at the readout gap was 0.14 mu m This is sti ll smaller than the popping up of about 2 mu m observed in the experiment. The reason for this popping up phenomenon in munufacturing processes of mic roaccelerometer may be the bending of the whole wafer or it may come from t he way the underetch occurs. Different SOI material and a new geometry of t he accelerometer are under investigation. We want to seek after the real ca use of this pop up phenomenon and diminish this by changing munufacturing p rocesses of microaccelerometer.