The Character Research And Simulation Of Anisotropic Wet Etching Of Quartz

Anisotropic wet etching is a powerful tool for the fabrication of quartz devices. This study presents the character and the method to predict the three-dimensional shape of quartz in anisotropic wet etching process based on the geometric model. And the program is developed to simulate the three-dimensional shape of complex micro-structure of crystals in aisotropic wet etching based on Level Set Method. The research on the SEM pictures of Z cut quartz wafer shows that the prediction method is feasible and the simulation program is accurate and effective.And then, discuss how to design the mask to achieve the desired structure. The research work is mainly as the followings.The evolution rules of the geometric shape of a crystal in anisotropic wet etching process have been investigated and the underetching rate plays a decisive role. The surface of convex regions of an etched crystal is increasingly formed by crystallographic planes with high underetching rates, while the surface of concave regions is increasingly formed by crystallographic planes with low underetching rates. The general method to predict the complex shape of an etched crystal is presented which can be summarized as rounding the corner, analyzing the possible crystallographic planes and choosing the planes.Based on Level Set Method, the program to simulate the three-dimensional shape of anisotropic wet etched crystals is developed in MATLAB software which can apply to crystal wafers of many cuts with any mask shape. The program is verified by the comparison between the simulaton results and the SEM pictures of the etched Z cut quartz wafer and can be used to assist in designing the micro-structure and developing the anisotropic wet etching process of crystals.By using a spherical specimen made of alpha-quartz, the etching rates for any crystallographic orientations of alpha-quartz in saturated ammonium bifluoride solution at 80 degrees are measured. Many structures of Z cut quartz wafer with different mask shapes are fabricated, such as mesas, cavities and array structures.The structures are analyzed in detal, especially the angles and underetching rates of the sidewalls of the rectangular grooves with different polar angles from 0° to 60°. Based on the experimental data, the evolution process of the mesas and cavities are explained which verifies the method to predict the etched shape of quartz.