各向异性湿法刻蚀z切石英后结构侧壁形貌的预测

基于石英晶体各晶面的湿法刻蚀速率,研究了石英微结构侧壁形貌的预测方法,讨论了各向异性湿法刻蚀石英的规律.首先,总结了石英各主要晶面的相对刻蚀速率,分别绘制了x、y族刻蚀速率矢量图.然后,在掩模层的边缘处,通过绘制相应的晶面刻蚀速率矢量图,得到各速率矢量的晶面线,晶面线所围成的最小轮廓即是石英微结构的刻蚀形貌.最后,利用该方法预测了x向和y向石英梁的侧壁形貌.在70℃的氢氟酸和氟化铵混合溶液内刻蚀5h,制作了厚度均为500μm的x向和y向两种石英微梁.结果显示,y向梁的-x向侧壁有一均匀整齐的晶棱,棱高210 μm,而+z向侧壁平滑.x向梁的侧壁均有晶棱,+y向晶棱较大,棱高为450 μm,-y向晶棱棱高为240 μm.所制作梁的侧壁形貌与预测结论基本吻合,验证了预测方法的正确性.基于该方法可在石英微结构的设计阶段,通过引入工艺因素对微结构进行优化.

Forecast of structure sidewall profiles for z-cut quartz after anisotropic wet etching

In order to characterize the anisotropic wet etching rule of quartz crystals,a method to forecast the sidewall profiles of quartz microstructures was studied based on wet etching rates of quartz crystal planes.First,etching rates of quartz crystal planes were summarized and the etching rate vector graphs of crystal planes were plotted for x and y groups.Then,the plane lines denoting their crystal planes were obtained by plotting etching rate vector graphs at each edge of a mask,and the etching shape was the minimum profile enclosed by plane lines.Finally,sidewall profiles of quartz beams at x and y directions were forecasted according to this method.An x direction quartz micro-beam and a y direction quartz micro-beam with a thickness of 500 μm were fabricated after 5 h wet etching process in a mixture of hydrofluoric acid and ammonium fluoride at 70 ℃.Experimental results indicate that-x sidewall of the y direction micro-beam presents a crystal facet with a height of 210 μm and +x sidewall is smooth;and crystal facets with the height of 450 μm and 240 μm appear on ±y sidewalls of x direction micro-beam respectively.These sidewall profiles of the beams are in agreement with the analysis results,which validates the forecasting method of wet etching profile.Results demonstrate that the quartz micromachined structure can be optimized by introducing fabrication processes based on the proposed method in designed steps.