Modified Model for Sacrificial Layer Etching

Sacrificial layer etching with different structures is studied in this work. It is found that the existed model doesn't match with the experimental data well. A modified model is proposed by considering the diffusion coefficient of HF as a function of temperature and concentration in the solution. In the modified model, the decrease of the HF concentration will cause the increase of the HF diffusion coefficient, which will partly compensate the decrease of the concentration caused by the long diffusion distance. In this way, the modified model matches with the experimental data very well both for channel structure and bubble structure. Combined structures are also studied in this work. Some interesting phenomena are observed during the etching of the combined structure, including the etching rate jumps down or up near the joint area. The proposed model can explain these phenomena well.