Bubble结构牺牲层腐蚀的一种改进模型

A Modified Model for Etching a Sacrificial Layer in Bubble Structures

以往的牺牲层腐蚀模型把扩散系数看作是常数,然而,实验结果和以往模型的计算结果在腐蚀开始一段较短的时间内吻合较好,但随着腐蚀时间的变长两者的差异越来越明显.为了解释这一现象并使模型能够较好地预测腐蚀过程,提出了腐蚀模型应该考虑氢氟酸扩散系数是浓度的函数,并在此基础上得到了改进模型.在改进模型中,浓度的下降会引起扩散系数的增大,这部分补偿了腐蚀前端浓度的下降.另外在改进模型中,扩散系数还是温度的函数.实验表明,改进模型与实验结果吻合地较好.这些结果不仅为对牺牲层腐蚀机理的理解提供新的证据,而且也为溶液在bubble结构里面的扩散提供新的证据.文中所观察到的这些现象也适合于其他类型的牺牲层腐蚀,条件是其腐蚀过程是受扩散限制的.

A previous sacrificial layer etching model treats the diffusion coefficient D as a constant through the etching process. This model fits the experimental data well during a short initial period of the etching time,but it deviates very seriously as the etching progresses. In order to explain this phenomenon and predict the etching process accurately,a modified model is proposed that treats the diffusion coefficient of HF as a function of the solution concentration. In the modified model,a decrease in the HF concentration will cause an increase of the HF diffusion coefficient,which will partly compensate for the decrease in concentration because of the long diffusion distance. In the modified model,the diffusion coefficient is also a function of temperature. In this way, the modified model matches the experimental data very well. These results provide new insight for understanding not only the mechanism of sacrificial layer etching,but also the solution diffusion in complex structures. The observed phenomenon should be applicable to other kinds of sacrificial layer etching if they are diffusion limited.