Precise [100] crystal orientation determination on  110 -oriented silicon wafers

In this paper we propose a novel pre-etch method to determine the [100] direction on the surface of ⟨110⟩ silicon wafers with a diameter of 100 mm for precise bulk etching. A series of circular windows is arranged in an arc with a radius of 48.9 mm, and bulk etched to form hexagonal shapes for the indication of crystal orientation. The hexagons, which have two angles of 109° and four other angles of 125.5°, are surrounded by four {111} vertical planes and two {111} planes inclined 35.5° to the wafer surface. The corners of the hexagons are used as an alignment reference to indicate the [100] direction on the ⟨110⟩ silicon wafers. Using a calculation from the relationship between the circular windows with different diameters of 153, 74 and 35 μm and the circle center distances of 192, 96 and 48 μm, the alignment accuracy can be determined as ±0.11°, ±0.06° and ±0.03° to the projected [100] orientation, respectively. Experimental results also demonstrate the feasibility of accurately aligning long etching slots along the ⟨111⟩ direction. The misalignment has been determined to be 0.02° from 20 experimental samples, much less than the estimated value of ±0.03° on a 100 mm ⟨110⟩ wafer. This simple, accurate and fast alignment technique is applicable to long slot fabrication on ⟨110⟩ wafers with tight geometry tolerance.