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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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Presentation Transcript
reactant generation process

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
protective polymer film generation process

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.

slide4

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

slide5

+

+

+

+

+

+

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

reactant delivery and by product removal process

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
slide7

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.