Research On Wet Etching And Releasing Technology Of Microstructures

Wet etching is one of the key process in micromachining technology.It has the advantages of fast etch rate,good selectivity and uniformity,simple equipment and mass production,so it is widely used in the releasing technology of microstructures.In this paper,three key process of wet etching and releasing technology of microstructures,including the positive releasing of <110> orientation to the micro beam,etching characteristics of BHF-GL solution,and the self-stop etching of concentrated boron were studied.Firstly,the etching characteristics of three kinds of silicon wafers with resistivity of 0.0087,0.015 and 1.6 Ω·cm in 25% TMAH solution were studied.The experimentation has find that when the doping concentration of silicon substrate is lower than the self-stop etching concentration,the etch rate of(100)surface remains unchanged,but the etch rate of(111)surface increases significantly.Based on the anisotropic etching mechanism of silicon,this phenomenon is qualitatively explained.Based on this etching phenomenon,the front side release of <110> orientation micro beam with 85 μm width is realized.This wet etching and releasing technology of microstructures can be used to fabricate pressure,acceleration and other micro sensors based on piezoresistive effect.Silicon dioxide is a common sacrificial layer material in micromachining.When etching silicon dioxide and releasing microstructures,it is usually not desirable to etch the aluminum electrodes and leads.BHF-Gl solution has good etching selectivity to LPCVD silicon dioxide and aluminum,but there are no reports on the etching characteristics of BHF-Gl solution to other commonly used MEMS materials.In this paper,the etching characteristics of insulating materials such as thermal oxidation silicon dioxide,LPCVD and PECVD silicon nitride,metal materials such as aluminum,titanium and chromium and poly-silicon films in BHF-Gl solution were studied.The etch rate of these materials in BHF-Gl solution were tested by experiments.The results show that: in BHF-Gl solution,the etch rate of thermal oxidation silica,PECVD silicon nitride and titanium is fast,that of LPCVD silicon nitride and aluminum is extremely slow,and that of chromium and polysilicon is almost non-etching.This conclusion has a certain reference value for the design of MEMS device structure and process flow.Heavily boron-doped technology is often used to realize the self-stop etching of microstructures.The self-stop etching process in heavily boron-doped uses silicon substrate with low doping concentration,and the impurity concentration difference between the upper and lower surfaces of the micro beam is large.In this paper,heavily boron-doped is carried out on high doping concentration silicon substrate to complete the fabrication of micro cantilever,which reduces the difference of impurity concentration between the upper and lower surfaces of the diffusion layer,and the root of the micro cantilever has a small deflection,which indicates the effectiveness of this method.