Abstract

The rapid progress in Micro-Electro Mechanical Systems necessitated the development of a micromachining technique in order to release micro-mechanical device in integrated chips. In the late 1990's there was a quest for a dry etchant that would not require an expensive setup, and overcome the problems related to wet etching, such as, stiction and etching slowdown due to bubble formation. A good alternative to wet etching would have been plasma etching, but fine tuning of the process parameters to achieve an effective control of the process, combined with the expensiveness of the equipment made plasma etching a less affordable etching method for many small labs. In gaseous phase, xenon difluoride was found to etch silicon isotropically and the required process setup is quite simple compared to other isotropic etching equipment for silicon. In the present work, a new and computer-controlled xenon difluoride etching equipment for silicon was designed and installed. A model for the XeF 2 isotropic etching of silicon based on an atomic approach and fine tuned through pressure increase in the reaction chamber due to formation of the reaction products is presented. The shape of the etch features is predicted by a Matlab ® code, based on the developed model. The etch depth and lateral under-etch can be calculated for a given feature and the chamber loading. The effect of concave corners is ignored in the model although the experimental results indicated a slow down etch rate at such locations. Using the designed and fully in house built etching equipment, experiments were carried on silicon samples with square and circular mask openings in order to validate the proposed etching model. The pressure in the etching chamber was monitored during experimental work and the values were used to be used later in the Matlab ® script for verification purpose. The experimental values were compared with the theoretical ones and were found to be in good agreement. The equipment, as designed and built, has embedded safety features required by toxic gas handling equipment codes