1. Etch Process Trends

2. 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 Pressure Gas flow rate A B

3. 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

4. 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?

5. 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 +++

6. 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

7. The effect of increased RF power on Etch Rate Our approach: Increased RF Sub-processes in Etch: Reactants generation Polymer protective layer generation Reactant transport to wafer surface Ion bombardment Etch reaction By-product removal Etch Rate

8. Substrate Dissociation/ ionization of input gases by plasma Gas delivery RF Electrode + + 2+ CH4 CH3+ CH2+ CH3 2+CH 2+ 2+ The effect of increased RF on Reactant Generation

9. Substrate Dissociation/ ionization of input gases by plasma Gas delivery RF Electrode + + 2+ CH4 CH3+ CH2+ CH3 2+CH 2+ 2+ Protective film Photo Resist The effect of increased RF on Protective Film Generation

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

11. * 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. Lower Electrode wafer +++ Protective film +++ Gas Photo Resist 11 Effect on Ion-bombardment Process

12. Effect on Etch Reaction Etch reaction is not just a chemical reaction. It is assisted by RF power.

13. RF power vs. Etch Rate The effect of increased RF power on the sub-processes of etch: Increased RF Sub-processes in Etch: Reactants generation ↑ Polymer protective layer generation ↑ Reactant transport to wafer surface = Ion bombardment ↑ Etch reaction ↑ By-product removal = Etch Rate ?

14. RF power vs. Etch Rate The effect of increased RF power on the sub-processes of etch: Sub-processes in EtchEffectEffect on etch rate Overall trend Reactants generation↑ Polymer protective layer generation ↑ Reactant transport to wafer surface == Ion bombardment↑ Etch reaction ↑ By-product removal ==

15. RF power vs. Etch Rate The effect of increased RF power on the sub-processes of etch: Sub-processes in EtchEffectEffect on etch rate Overall trend Reactants generation↑↑ Polymer protective layer generation ↑↓ Reactant transport to wafer surface == Ion bombardment↑↑ Etch reaction ↑↑ By-product removal ==

16. RF power vs. Etch Rate The effect of increased RF power : Sub-processes in EtchEffectEffect on etch rate Overall trend Reactants generation↑↑ ↑ Polymer protective layer generation ↑ ↓ (off-set by ion bombardment) Reactant transport to wafer surface == Ion bombardment↑↑ Etch reaction ↑↑ By-product removal ==

17. 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

18. Reactant gas flow rate vs. Etch Rate The effect of increased gas flow rate: Sub-processes in EtchEffectEffect on etch rate Overall trend Reactants generation↑↑ ↑ Polymer protective layer generation == Reactant transport to wafer surface ↑ ↑ Ion bombardment== Etch reaction == By-product removal ==

19. 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