An etching model to predict minimum-microloading gas pressure

Plasma etching has been widely used in fabricating ultra large-scale integrated circuits (ULSI). One etching problem, however is that the etching rate decreases with decreasing pattern width; this is called microloading. Up to now, ion shadowing microloading was suppressed by using lower gas pressure. However, as the pressure decreases, another type of microloading is caused by reactant limiting or product adsorption. Recently, we found that the etching rate was related to reactant and product surface diffusion in the adsorption process. Our model incorporating this process has shown these types of microloading decrease as the pressure increases, in contrast to ion shadowing microloading. Therefore, there must be an optimum gas pressure that minimizes microloading. We can determine this pressure using our etching model which involves an ion shadowing term. This model is applied here to Cl/sub 2/-gas Si etching and Al etching.