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Plasma Etch Sub-processes

Plasma Etch Sub-processes. RF. Electrode. CH2+. CH4. CH3+. Gas delivery. +. +. Dissociation/ ionization of input gases by plasma. 2+. CH 2+. CH3 2+. 2+. Substrate. Electrode.

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Plasma Etch Sub-processes

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  1. Plasma Etch Sub-processes

  2. RF Electrode CH2+ CH4 CH3+ Gas delivery + + Dissociation/ ionization of input gases by plasma 2+ CH 2+ CH3 2+ 2+ Substrate Electrode During ionization, plasma can break down reactant gas molecules into many pieces. Each different from another. For example, CH4 can be broken down to CH3+, CH3 2+, CH2 +, or CH 2+, etc. None of these parts of the original molecule are stable, and are thus highly reactive species. They are called reactive radicals. A plasma gas is a soup of mutant monsters. These highly reactive radicals help reactions to occur at much lower temperatures (~300C) for reactions that usually happen at 700C. To etch SiO2 we add gasses containing C and F. Such as CF4, C3F8, etc. Reactant Generation process

  3. RF Electrode CH2+ CH4 CH3+ Gas delivery + + Dissociation/ ionization of input gases by plasma 2+ CH 2+ CH3 2+ 2+ Substrate Electrode Protective Polymer Film Generation Process Protective film Photo Resist Add certain gases to generate protective coating film during the etch process. Etching gas can not penetrate through the protective film. Add gases that contain C and H. They breakdown and re-link into a polymer film. This film is deposited to all the surfaces of the chamber including the wafer.

  4. B Sheath RF supply + + + Ion-bombardment Process * After plasma is ignited and stabilized: * In region B, electric field is very weak * In the sheath region ions see a DC electric potential, attracting them to the lower electrode * This causes a effect called “ion bombardment” of the lower electrode Ions Sheath Lower electrode

  5. + + + + + + Protective film Gas wafer Lower Electrode Ion-bombardment Process * Ion bombardment removes protective film on horizontal surfaces, exposing them to etching gas. It does not touch protective film on vertical surfaces, hence no vertical etch rate. Photo Resist * Summary: RF plasma -- Ion Bombardment -- Anisotropic Etch

  6. RF generator Electrode Electrode 1) Reactants enter chamber Gas delivery 2) Dissociation of reactants by electric fields Exhaust 3) Reactant transport from bulk of plasma to surface of wafer By-product removal Substrate Reactant delivery and by product removal process

  7. The slowest sub-process bottlenecks the overall process. It thus determines the reaction rate. It becomes the dominate sub-process– the overall process behaves like it.

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