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Etch Process Trends. Etch process trends. Most trends are not consistent. They depend on the specific values of input parameters. At point A, pressure increases causes etch rate increase but at pint B, the trend is the inverse. Etch rate. B. Pressure. A. Gas flow rate.

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etch process trends1
Etch process trends
  • Most trends are not consistent. They depend on the specific values of input parameters.
  • At point A, pressure increases causes etch rate increase but at pint B, the trend is the inverse

Etch rate

B

Pressure

A

Gas flow rate

etch process consistent trends
Etch process consistent trends
  • 1. P vs. vertical profile
  • 2. RF vs. etch rate
  • 3. Reactant gas flow rates vs. etch rate
  • 4. Gap vs. uniformity
p vs anisotropy
P vs. anisotropy
  • The vertical profile is determined by the ion bombardment sub-process and the sidewall protective polymer film formation sub-process.
  • How does P affect ion bombardment?
p vs vertical profile

+

+

+

P vs. vertical profile
  • How does P affect ion bombardment?

Answer: higher pressure means more molecules to collide into for the ions in their trajectory (i.e. smaller Mean Free Path). Thus the their trajectory will be more scattered and thus less vertical  less anisotropy.

Protective film

p vs vertical profile1
P vs. vertical profile
  • How does P affect ion bombardment?

Answer: higher pressure means more molecules to collide into for the ions in their trajectory (i.e. smaller Mean Free Path). Thus the their trajectory will be more scattered and thus less vertical  less anisotropy.

Less like this

More like this

the effect of increased rf on reactant generation

RF

Electrode

CH2+

CH4

CH3+

Gas delivery

+

+

Dissociation/ ionization

of input gases by plasma

2+

CH 2+

CH3 2+

2+

Substrate

Electrode

The effect of increased RF on Reactant Generation
the effect of increased rf on protective film generation

RF

Electrode

CH2+

CH4

CH3+

Gas delivery

+

+

Dissociation/ ionization

of input gases by plasma

2+

CH 2+

CH3 2+

2+

Substrate

Electrode

The effect of increased RF on Protective Film Generation

Protective film

Photo Resist

effect on 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

Effect on Reactant delivery and by product removal process
slide11

+

+

+

+

+

+

Protective film

Gas

wafer

Lower Electrode

Effect on Ion-bombardmentProcess

* 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

effect on etch reaction
Effect on Etch Reaction
  • Etch reaction is not just a chemical reaction. It is assisted by RF power.
rf power vs etch rate
RF power vs. Etch Rate
  • The effect of increased RF power on the sub-processes of etch:

?

rf power vs etch rate1
RF power vs. Etch Rate
  • The effect of increased RF power on the sub-processes of etch:
rf power vs etch rate2
RF power vs. Etch Rate
  • The effect of increased RF power on the sub-processes of etch:
rf power vs etch rate3
RF power vs. Etch Rate
  • The effect of increased RF power :
effect of increased gap distance vs uniformity
Effect of increased gap distance vs. uniformity
  • Center to edge difference: caused by electric field strength difference
  • If the gap is infinitely small, almost all points on the electrode are like center points.
  • If the gap is large, many points will experience the edge effect.
  • Thus the larger the gap, the worse the center to edge uniformity

Region that feels the edge effect

reactant gas flow rate vs etch rate
Reactant gas flow rate vs. Etch Rate
  • The effect of increased gas flow rate:
summary of trends
Summary of Trends
  • . P upMFPdown less anisotropy
  • 2. RF power up etch rate up (most likely)
  • 3. Reactant gas flow rates up etch rate up
  • 4. Gap up  uniformity down