5_Basic_Principles_of_Plasma_Etching

5_Basic_Principles_of_Plasma_Etching - Basic Principles of...

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Basic Principles of Plasma Etching Lecture 4 Thin Film Technology – Basics and Applications
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Basic Principles of Plasma Etching Pattern Formation on Integrated Circuits Isotropic vs. Anisotropic etching Advantages of Plasma Etching over Wet Etch Basics of Plasma Etching
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Plasma Etching Plasma supplies etchants which selectively remove film (not mask or substrate) Chemical reaction: Substrate + Reactant = volatile product Physical sputtering: Substrate + Ar ions = Sputtered material Ion assisted chemistry: Substrate + reactant + Ar ions = volatile product
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Advantages of Plasma Etching over Wet Etching Anisotropic Etching Less Hazardous Materials and Waste Absence of Surface Tension Effects - no resist lifting from capillarity - no wettability problems to hinder etching No Etch Rate Change from Reagent Use Easier to Automate
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S. Gupta Thin Film Technology Etch Anisotropy Isotropic etch horizontal etch velocity = vertical etch velocity Directional etch vertical etch velocity > horizontal etch velocity => less mask undercut Anisotropic etch Vertical etch velocity >> horiziontal etch velocity => vertical sidewalls, no
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S. Gupta Thin Film Technology Selectivity Requirements Tradeoff between anisotropy and selectivity Film: mask > 4:1 Film: substrate > 20:1
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S. Gupta Thin Film Technology Angle of incidence, sputter yield and ion etch rate Sputter yield and etch rate peaks at angle of incidence between 45 0 and 60 0 , depending on material Preferential etching at step corners leading to facetting
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S. Gupta Thin Film Technology Requirements for accurate subtractive pattern transfer • Mask opening = d m • Etched feature (with undercut) = d f • Etch bias = │B│= d m -d f For isotropic etching │B│=2 t f , where t f = film thickness
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S. Gupta Thin Film Technology Ideal Etch Profiles Anisotropic A = 1 Isotropic A = 0 • Degree of anisotropy A = 1 – ν h / ν v • A = 1 – (│B│/2 t f ) • Critical feature size d c = smallest mask opening • d c = 2 d f – d m = d f -│B│(assuming equal lines and spaces) • Pitch = 2 d f = d m + d c • d c = d f [1 – 2 t f / d f (1 – A)]
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S. Gupta Thin Film Technology Selectivity and Dimension Control • Consider patterning film of thickness t f with uniformity α (0 α 1). • Assume mean etch rate
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5_Basic_Principles_of_Plasma_Etching - Basic Principles of...

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