Abstract: HF etching of sacrificial layers with different structures,namely channel,bubble,and joint-channel,is studied.The existing model cannot fit the experimental data well.The error of etching rate between the existing model and the experimental data increases with etching time.A modified model considering the diffusion coefficient as a function of HF concentration and temperature is proposed.The etching rate coefficient as a function of temperature and the effect of reaction production are also considered in the modified model.For the joint-channel structure,a new mathematical model for the etching profile is also adopted.Experimental data obtained with channel,bubble,and joint-channel structures are compared with the modified model and the previous model.The results show that the modified model matches the experiments well.

Key words: diffusion coefficient, etching rate, sacrificial oxide, TDC model