wk 7 09 - Wet Etching, Surface Micromachining & Scaling Law...

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Wet Etching, Surface Micromachining & Scaling Law (wk 7) David T. Shaw Fall 2009
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Table of Content Single crystal growth Si lattice structure Miller Indices Wafer flats Isotropic and anisotropic etching Example
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This figure shows a 4 inch 100 plane crystal Silicon wafer, typically between 250-600 microns thick The current fab standards are up to 12 inch wafers 300 mm (11.8 inch) -- "12 inch" Thickness 775 µm – “pizza size” 450 mm ("18 inch"). Thickness 925 µm (2012??) For CMOS work (100) (for MOS) and (111) (for bipolar) wafers are most important. MEMS other orientations are used as well --- especially (110) Wafer flats indicate orientation (primary) and conductivity type (secondary) Bulk Micromachining
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The primary flat on (100) and (110) wafers marks the <110> direction (111) (100) Bulk Micromachining Purpose and Function Orientation for automatic equipment Indicate type and orientation of crystal Primary Flat = The flat of longest length. The primary flat always [110]. Secondary Flat = Indicates the crystal orientation and doping of the wafer. The location of this flat varies. P type <111> No secondary Flat P type <100> 90°±5° Clockwise from Primary Flat N type <111> 45°±5° Clockwise from Primary Flat N type <100> 180°±5° Clockwise from Primary Flat
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(110)
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All Primary flats are in [110] direction No standardization in case of {110} wafers
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(110) (111)
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Isotropic etching (HF:Nitric Acid: Acetic Acid) Anisotropic etching (KOH) (110) (100) Bulk Micromachining
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Bulk Micromachining Isotropic etchants etch in all crystallographic directions at the same rate: Usually acidic HNA (i.e. HF, HNO 3 and CH 3 COOH-- Acetic Acid ) Room temperature or slightly
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This note was uploaded on 02/19/2011 for the course EE 515 taught by Professor Dr.shaw during the Fall '10 term at SUNY Buffalo.

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wk 7 09 - Wet Etching, Surface Micromachining & Scaling Law...

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