We have assembled a reactor to perform KOH etching which, besides fine control of etching temperature, stirring and solution concentration, allows etching with and without 25 kHz ultrasound. To study the etch rate and morphology of the etched surfaces we use plain and lithographycally masked <100> silicon wafers. The roughnes of the plain wafers after etching was quantifled by the ratio of the diffuse and specular
reflectances in the 800-240 nm range. The mask windows are parallelograllls oriented at different angles and were designed 10 allow a 2-step etch. The first step reveals slowly etching planes and, after selective removal of predetermined regions of the mask, the second step of etching reveals fast etching planes. For the geometrical measurements of the resulting facets we use plane and cross-section image capture and quantitative image processing techniques, and stylus profilometry. We have obtained a relative improvement of the etched surface by the use of ultrasound.
