Modeling And Simulation Of Sacrificial Layer Etching

Sacrificial layer etching is one of the important technology in the surface manufacturing process of Micro-eletromechanical System (MEMS), It is highly affected to the MEMS device. Therefore, The controlling and simulation of sacrificial layer etching is the very important instruction to sacrificial layer etching. In the paper, computer aided design (CAD) technology is used to achieve simulation of sacrificial layer etching. Firstly, the mechanism of hydrofluoric acid (HF) etching the silicon dioxide (SiO2) and the kinds of factors that impact the etching are presented in particular. Then the etching mathematical models are introduced in one-dimension space, and then it is extended to two-dimension space. At last, the numerical algorithm is presented and simulation through programming is achieved.According to the etching chemical mechanism of HF etching oxidation silicon (SiO₂), many etching models are founded. Such as Deal-Grove(D-G) model, power law model and Liu.'s combined first-and-second order model . It is not very precise to simulate using D-G model, while simulation is more precise using the following two models. In the paper, introduction of the upwards models is presented, and the power law model is chosen to introduced particularly. Finally, using the etching model, simulation that can simulate the etching process with various etchant and various sacrificial materials is carried out through programming.2-D radial coordinate model from which the combined first-and-second order model is extended is presented. The numerical simulation of the radical diffusion equation is particularly discussed and the algorithm is optimized appropriately. The program in C is compiled to realize the simulation of the etching process. It can implement the simulation of etching the bubble structure.As the etching is affected mostly by diffusion, the 1-D diffusion equation is extended to 2-D. Numerical model based on diffusion equation is constructed. And then the relative boundary conditions are given. Explicit and implicit numerical algorithm of finite-difference method is presented to solve the 2-D diffusion equation, so as to get the value of the concentration at every site at the corresponding time. Then the Topography Model is used to compute the etching state to determine the etch contour at the front. The simulation program that can simulate the different and complex sacrificial structures is implemented.To validate the simulation, many different etching testing structures is designed, such as cantilever, fixed lever, circle, rectangle and many kinds of complex combined structures. Then chips are fabricated and at last the chips are etched and released. The simulation results are consistent to the experimental results in etching shape and etching size through comparing, and its etching size error can be restricted to 10% basically. Therefore, the simulation veracity is validated.