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Micro Electro Mechanical System Design - James J. Allen Part 3

Tham khảo tài liệu 'micro electro mechanical system design - james j. allen part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 40 Micro Electro Mechanical System Design FIGURE 2.21 Directional etching of crystalline silicon. TABLE 2.6 Common Crystalline Silicon Etchant Selectivity and Etch Rates Etchant Etch rate 18HF 4HNO3 3Si 2H2SiF6 4NO 8H2O Si H2O2 2KOH K2Sìo3 2H2 Ethylene diamine pyrocatechol EDP Tetramethylammonium hydroxide TMAH Nonselective 100 0.14 gm min 111 0.0035 gm min SiO2 0.0014 gm min SiN4 not etched 100 0.75 gm min 111 0.021 gm min SiO2 0.0002 gm min SiN4 0.0001 gm min 100 1.0 gm min 111 0.029 gm min SiO2 0.0002 gm min SiN4 0.0001 gm min Easy to start and stop the etch process Repeatable etch process Anisotropic etches Few particulates Plasma etching includes a large variety of etch processes and associated chemistries that involve varying amounts of physical and chemical attack. The plasma provides a flux of ions radicals electrons and neutral particles to the surface to be etched. Ions produce physical and chemical attack of the surface 2005 by Taylor Francis Group LLC Fabrication Processes 41 B B B B B B B B B B B B B B B B B B B B B B B B MUUUUUUUUUUU Single Crystal Silicon a. Implant Boron in Single Crystal Silicon wafer b. Deposit and Pattern Silicon Dioxide Etch Mask B B B B B B B B B B B B B B B B B B B B B B B B c. KOH etch FIGURE 2.22 Boron-doped silicon used to form features or an etch stop. and the radicals contribute to chemical attack. The sequence of events that occur in a plasma etch chamber Figure 2.23 are listed below Plasma breaks down the feed gases into chemically reactive species. Reactive species diffuse to the wafer surface and are adsorbed. Surface diffusion of reactive species takes place until they chemically react. Reaction product desorption occurs. Reaction products diffuse away from the surface. Reaction products are transported out of the chamber The details and types of etch chemistries involved in plasma etching are varied and quite complex. This topic is too voluminous to be discussed in detail here but a number of excellent references on