wk 6 - Pattern Transfer with Dry Etching and Additive...

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Pattern Transfer with Dry Etching and Additive Techniques D. T. Shaw EE 415/515 10/6/09
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Silicon as a Mechanical Materials Reference: K. E. Petersen, Proc IEEE, 70(5) May,1982
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Si is brittle, not a good structural material.
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Chapter 4, p185
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[100] [010] [001] (110) (111)
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[100] [010] [001] (100) {100} (001) (010)
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[100] [010] [001] a b c [abc] 1/a 1/b 1/c (abc)
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Si crystal orientation http://www.novagate.com/~ahines/rocks/vir_cris.htm Each site is tetrahedrally coordinated with four other sites in the other sublattice Equivalent planes i.e. families {} More atoms per cm 2 (oxidizes faster than 100) but etches much slower Bulk Micromachining
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Anisotropic etchants etch at different rates depending on the orientation of the exposed crystal plane: Usually alkaline (pH> 12 e.g. KOH) Higher temperatures (> 50 °C e.g. 85 to 115 °C) Reaction rate limited Slower e.g 1 µm/min (for <100> direction) Does not undercut the mask Not very agitation sensitive Masking very difficult e.g. LPCVD Si 3 N 4 Bulk Micromachining
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A Wafer is oxidized after electrochemical wells are etched Electrochemical well B Wafer is oxidized a second time after vias are etched C Metal deposition from the back against oxide window D Metal is etched free by a timed etch. Sensor metal electrode Oxide over the window is only 1/2 of the oxide thickness elsewhere on the wafer Si SiO 2 Example: electrochemical sensor array A typical bulk micromachining example: to make an array of electrochemical sensors in a catheter (e.g. to measure pH, O 2 and CO 2 in blood) The etch stop in this case is a sacrificial oxide layer Yet smaller structurs could be used to experiment in picoliter microvials (e.g. to investigate a single biological cell)-go visit http://pubs.acs.org/hotartcl/chemtech Bulk Micromachining
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Page 183-195
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Homework Use materials in chapter 3, 4 and 5 to reinforce today’s discussions (i.e., read only those sections we discussed) Use the example on mean free path for
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wk 6 - Pattern Transfer with Dry Etching and Additive...

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