Page 152 - Sami Franssila Introduction to Microfabrication

Etching 131

4. How much underlying oxide is lost when a tungsten
Profile A:S selectivity
film of 500 nm thickness is etched from a sample that
has 300 nm steps on it? Tungsten: oxide selectivity anisotropic ∞
is 10:1. anisotropic 5:1
5. Etch rate could basically be measured easily by anisotropic 1:1
isotropic ∞
weighing the sample before and after etching, and
isotropic 5:1
translating that into the rate by taking the area into
isotropic 1:1
account. What resolution scale is needed to determine
rates for:
9. How much dimensional error does chromium wet
– tungsten etching, 500 nm thickness etching introduce to (a) 1X photomasks and (b) 5X
– silicon etching, 20 nm thickness. reticles?
3
Densities: W – 19.5 g/cm , Si – 2.65 g/cm 3
6. How can the porosity of porous silicon be measured REFERENCES AND RELATED READINGS
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