Aqueous KOH etching of silicon (110) - Etch characteristics and compensation methods for convex corners

This paper investigates the anistropic etching characteristics and convex corner undercut mechanism of (110)-oriented silicon in aqueous potassium hydroxide solutions; First, the crystal planes governing the etch front of the undercut are determined, and their etch rates are measured. Then, based on the measured data, several methods for convex corner compensation techniques are examined. Conventionally, <111> direction beams are used to compensate for the undercut on convex corners. This method is found to produce good results for acute convex corners, but results in the emergence of large residue structures with (111) crystal planes on the obtuse convex corners. To alleviate this problem, new corner compensation methods that use triangular and rhombic patterns are developed based on the measured etch front planes. The effectiveness of the proposed corner compensation patterns in reducing the undercut and residues is evaluated in detail. It is found that for obtuse convex corners the rhombic corner compensation provides the best result, and for acute convex corners both the rhombic and <111> beam patterns are effective.