Etch Process Trends

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 B Pressure A Gas flow rate

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:

8. 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

9. 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

10. 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

11. + + + + + + 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

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: ?

14. RF power vs. Etch Rate • The effect of increased RF power on the sub-processes of etch:

15. RF power vs. Etch Rate • The effect of increased RF power on the sub-processes of etch:

16. RF power vs. Etch Rate • The effect of increased RF power :

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:

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