A novel anti-shock silicon etching apparatus for solving diaphragm release problems

This paper presents a novel anti-shock bulk siliconetching apparatus for solving a universal problem which occurs whenreleasing the diaphragm (e.g. SiNx), that the diaphragm tends to beprobably cracked by the impact of heating-induced bubbles, the swirling of heating-inducedetchant, dithering of the hand and imbalanced etchantpressure during the wafer being taken out. Through finite elementmethods, the causes of the diaphragm cracking are analysed.The impact of heating-induced bubbles could be the main factor whichresults in the failure stress of the SiNx diaphragm and the rupture ofit. In order to reduce the four potential effects on the cracking of the releaseddiaphragm, an anti-shock bulk silicon etching apparatus isproposed for using during the last etching process of the diaphragmrelease. That is, the silicon wafer is first put into the regularconstant temperature etching apparatus or ultrasonic plus, and whenthe residual bulk silicon to be etched reaches near theinterface of the silicon and SiNx diaphragm, within a distance of50--80~$mu $m (the exact value is determined by the thickness,surface area and intensity of the released diaphragm), the wafer istaken out carefully and put into the said anti-shock silicon etchingapparatus. The wafer's position is at the geometrical centre, alsothe centre of gravity of the etching vessel. An etchant outlet isbuilt at the bottom. The wafer is etched continuously, andat the same time the etchant flows out of the vessel. Optionally, twosymmetrically placed low-power heating resistors are put in theanti-shock silicon etching apparatus to quicken the etching process.The heating resistors' power should be low enough to avoid theswirling of the heating-induced etchant and the impact of the heating-induced bubbleson the released diaphragm. According to the experimentalresults, the released SiNx diaphragm thus treated is unbroken, whichproves the practicality of the said anti-shock bulk silicon etchingapparatus.