Process Modeling of Anisotropic Chemical Etching of Silicon

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We investigated orientation-dependent anisotropic etching of single-crystal silicon. The group of Nagoya University measured etching rates of silicon using alkaline solutions such as potassium-hydroxide (KOH) and tetramethyl-ammonium-hydroxide (TMAH) water solutions. They evaluated the orientation dependence in the etching rate for a number of crystallographic orientations under wide ranges of etching conditions in temperature and etchant concentrations.The group of the Univ. of Twente and the Univ. of Nijmegen tried to describe such orientation dependence using a limited number of physical parameters, which used to be used in crystal growth that is the reverse process of etching. They introduced 9 parameters, and by fitting those values to experimental data provided from Nagoya Univ., they succeeded in describing etching rates within an error of 5% for one etching condition using KOH water solution. The results were presented in two international conferences, and will be published in Sensors and Actuators : A. It is our future work to describe orientation dependence for a wide range of etching conditions, because the orientation dependence significantly varies according to the conditions.The group of LAAS/CNRS simulated the etching process in atomic scale using Monte Carlo method based on a model, which considers weakening of silicon back-bonds according to the increase in the number of OH attached to the silicon surface-atom. The simulated orientation dependence was similar to that of the experimental results of TMAH rather than KOH both measured by Nagoya Univ.We organized a workshop focused on silicon anisotropic etching. The first workshop was held in 1998 in Holten, the Netherlands, and going to be held in 2000 in Toulouse, France. We are planning the third in 2002 in Japan.