AFM STUDY OF SURFACE FINISH IMPROVEMENT BY ULTRASOUND IN THE ANISOTROPIC ETCHING OF SI[100] IN KOH FOR MICROMACHINING APPLICATIONS

A new procedure for the production of smooth and defect-free surfaces in the anisotropic etching of silicon in alkaline solutions is describ ed. It has been found that etching in an ultrasonic bath results in th e facilitated detachment of hydrogen bubbles at the surface which is s uggested to be one of the causes for surface roughening. In the presen ce of mild ultrasound radiation a significant improvement in surface f inish of the {100} orientation has been observed. The inclusion in the bath of oxygen and/or isopropanol results in root mean square roughne ss values smaller than 20 nm. The effectiveness of bath additives has been related to changes of the contact angle between the liquid/gas/et ching interface. Quantitative determination of roughness and surface i maging have been obtained by atomic force microscopy; dissolution rate s were studied by profilometry. Etching under ultrasound conditions an d the use of additives does not change the etch kinetics, indicating t hat additional convection only changes hydrogen bubble detachment.