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Original Publication Date: 1996-Nov-01
Included in the Prior Art Database: 2002-Apr-29

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John Gunnison Mark Schoenberg


Wet chemical etching ofunmasked silicon regions is performed in semiconductor discrete processing to form deep moat and mesa device terminations. The contour of resulting moat/mesa silicon sidewall is very steep and leads to inadequate (thin or miss- ing) photoglass at the top of the silicon step (see Figure 1). In addition, the sidewall's large negative contour angle acts to limit the junction's bulk break- down voltage. An improved moat/mesa silicon contouring process was achieved using overlapping silicon etch regions. The following four factors were found to control the moat/mesa contour: 1) Mesa 2-to-Mesa 1 overlap spacing 2) Mesa 1 and Mesa 2 etch depths 3) Mesa 1 and Mesa 2 etch depth sequence 4) Choice of mask sequence The Mesa 1 photo/etch process is followed by a second photo/etch process that utilizes an oversized Mesa 2 mask. By proper selection of the Mesa 1 and Mesa 2 etch depths, respectively, the moat/mesa side- walls can be optimally recontoured (see Figure 2 and 3). Recontoured sidewalls have a much smaller contour angle which offers superior photoglass step coverage and improved electrical parameters.