Experimental verification of the diffusion theory for wet isotropic etching of si via circular mask openings

摘要

Isotropic etching of silicon in HF based solutions is expected to be controlled by the diffusion offluorine to the silicon surface. In order to gain quantitative understanding of the process we studiedetching of Si in HF/HNO3/H2O via circular mask openings and compared the results with the theoreticalexpectations. The cavity edges due to etching under the mask were analyzed with a high precision byprocessing the optical microscope images. Dependence on the etching time and opening size wasinvestigated. The time dependence was verified with 1% precision. Dependence on the opening sizepredicted theoretically is not fully supported by the experiment. There is a small (4%) but clearlyobservable deviation from the theory. A small anisotropy was observed in perfect agreement with thecrystal orientation symmetry. The anisotropy becomes larger with the decrease of the opening size for(100) and (110) wafers.