Precise identification of <1 0 0> directions on Si{0 0 1} wafer using a novel self-aligning pre-etched technique

• Published in: Journal of micromechanics and microengineering Vol. 26; no. 2; pp. 25012 - 25016
• Main Authors: Singh, S S, Veerla, S, Sharma, V, Pandey, A K, Pal, P
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.02.2016
• Subjects: Angle of reflection; Arrays; crystallographic directions; Etching; Planes; pre-etched patterns; Self alignment; Standard deviation; Wafers; Walls; wet etching
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/26/2/025012

Micromirrors with a tilt angle of 45° are widely used in optical switching and interconnect applications which require 90° out of plane reflection. Silicon wet bulk micromachining based on surfactant added TMAH is usually employed to fabricate 45° slanted walls at the direction on Si wafers. These slanted walls are used as 45° micromirrors. However, the appearance of a precise 45° wall is subject to the accurate identification of the direction. In this paper, we present a simple technique based on pre-etched patterns for the identification of directions on the Si surface. The proposed pre-etched pattern self-aligns itself at the direction while becoming misaligned at other directions. The direction is determined by a simple visual inspection of pre-etched patterns and does not need any kind of measurement. To test the accuracy of the proposed method, we fabricated a 32 mm long rectangular opening with its sides aligned along the direction, which is determined using the proposed technique. Due to the finite etch rate of the plane, undercutting occurred, which was measured at 12 different locations along the longer edge of the rectangular strip. The mean of these undercutting lengths, measured perpendicular to the mask edge, is found to be 13.41 μm with a sub-micron standard deviation of 0.38 μm. This level of uniform undercutting indicates that our method of identifying the direction is precise and accurate. The developed method will be extremely useful in fabricating arrays of 45° micromirrors.