tailieunhanh - Microengineering MEMs and Interfacing - Danny Banks Part 5

Tham khảo tài liệu 'microengineering mems and interfacing - danny banks part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 60 Microengineering MEMS and Interfacing A Practical Guide FIGURE KOH-etched pit and groove. FIGURE Illustration of how KOH etching eventually becomes limited by crystal planes given an arbitrary mask opening pits viewed from above . View from above Etch mask a Etch b FIGURE Mesa structures. Copyright 2006 Taylor Francis Group LLC Silicon Micromachining 61 a b c FIGURE Corner compensation structures a square b 110 directed bar c T shapes which may be multiplied not to scale . These compensation structures are designed so that they are etched away entirely when the mesa is formed to leave 90 corners. One problem with using compensation structures to form right-angled mesa corners is that they put a limit on the minimum spacing between the mesas. Some examples of mask designs for corner compensation structures are shown in Figure . These are aligned with specific crystal planes and are designed to be etched completely away when the desired KOH etch depth has been reached. The 110 aligned structures provide almost perfect corner compensation but tend to be quite large. The exact dimensions of each structure have to be computed based on the etching conditions experienced in the clean room. Details are provided in papers by Puers and Sansen 6 and Sandmaier et al. 7 . The simplest structure to implement is the square corner compensation structure Figure . The dimensions of this half of one side of the square can be approximated by X -10 X where h is the etching depth height of the mesa and the units are all in micrometers. Equation was derived from Puers and Sansen s etch rates experienced with KOH IPA solution IPA is isopropyl alcohol which some find improves the quality of KOH etches and Equation was derived from their results with KOH. Alignment to Crystal Planes Do not rely on flats ground onto wafers to provide alignment to crystal planes. These are mechanically ground on and will be aligned to within a .