Method of reducing surface roughness
Surface roughness on a non-planar surface of a silicon substrate with upstanding and/or recessed features can be reduced. A first sequence of plasma processing steps and a second sequence of plasma processing steps can be performed on the silicon substrate to reduce the surface roughness of the upstanding and/or recessed features while retaining these features. The first sequence of plasma processing steps includes i) a plasma deposition step using oxygen and at least one fluorocarbon gas followed by ii) a plasma etch step using oxygen, at least one fluorocarbon etchant gas, and SF 6 . The second sequence of plasma processing steps includes i) an isotropic plasma etch step using oxygen and at least one fluorine containing etchant gas followed by ii) a plasma etch step using at least one fluorine containing or chlorine containing etchant gas.
1. A method of reducing surface roughness on a non-planar surface of a silicon substrate comprising upstanding and/or recessed features, the method comprising the steps of:
providing a silicon substrate having a non-planar surface comprising upstanding and/or recessed features which have an associated surface roughness;
performing a first sequence of plasma processing steps on the silicon substrate; and
performing a second sequence of plasma processing steps on the silicon substrate;
wherein the performance of the first and second sequence of plasma processing steps reduces the surface roughness of the upstanding and/or recessed features while retaining the upstanding and/or recessed features;
wherein the first sequence of plasma processing steps comprises i) a plasma deposition step using oxygen and at least one fluorocarbon gas at a total process pressure of 100 mTorr (13.3 Pa) or greater, with no RF bias or with an RF bias power of less than 100 W, followed by ii) a plasma etch step using oxygen, at least one fluorocarbon etchant gas, and SF 6 at a total process pressure of 100 mTorr (13.3 Pa) or greater, with no RF bias or with an RF bias power of less than 100 W; and
wherein the second sequence of plasma processing steps comprises i) an isotropic plasma etch step using oxygen and at least one fluorine containing etchant gas at a total process pressure of 100 mTorr (13.3 Pa) or greater, with no RF bias or with an RF bias power of less than 100 W, followed by ii) a plasma etch step using at least one fluorine containing or chlorine containing etchant gas at a total process pressure of less than 100 mTorr (13.3 Pa), with an RF bias power of greater than 500 W.
2. The method according to claim 1 , wherein the plasma deposition step i) and plasma etch step ii) of the first sequence of plasma processing steps are alternately repeated.
3. The method according to claim 1 , wherein the plasma deposition step i) of the first sequence of plasma processing steps uses a flow rate of oxygen that is less than a flow rate of the at least one fluorocarbon gas.
4. The method according to claim 1 , wherein in the plasma deposition step i) of the first sequence of plasma processing steps, the at least one fluorocarbon gas is CF 4 .
5. The method according to claim 1 , wherein in the plasma etch step ii) of the first sequence of plasma processing steps, the at least one fluorocarbon etchant gas comprises CF 4 and/or C 4 F 8 .
6. The method according to claim 5 , wherein in the plasma etch step ii) of the first sequence of plasma processing steps uses a process gas mixture which consists essentially of oxygen, SF 6 , CF 4 and C 4 F 8 .
7. The method according to claim 1 , wherein the plasma etch step ii) of the first sequence of plasma processing steps uses flows of oxygen, SF 6 and the at least one fluorocarbon etchant gas, and a flow rate of oxygen is less than a combined flow rate of SF 6 and the at least one fluorocarbon etchant gas.
8. The method according to claim 1 , wherein the plasma etch steps i) and ii) of the second sequence of plasma processing steps are alternately repeated.
9. The method according to claim 1 , wherein in the plasma etch step i) of the second sequence of plasma processing steps, the fluorine containing etchant gas is SF 6 .
10. The method according to claim 1 , wherein in the plasma etch step i) of the second sequence of plasma processing steps, the fluorine containing etchant gas is CF 4 .
11. The method according to claim 1 , wherein in the plasma etch step ii) of the second sequence of plasma processing steps, SF 6 or CF 4 is used as the fluorine containing etchant gas.
12. The method according to claim 1 , wherein the plasma etch step ii) of the second sequence of plasma processing steps uses a Noble gas.
13. The method according to claim 12 , wherein the plasma etch step ii) of the second sequence of plasma processing steps uses a process gas mixture which consists essentially of SF 6 and argon.
14. The method according to claim 1 , wherein the plasma etch step i) of the second sequence of plasma processing steps uses a flow rate of oxygen that is greater than a flow rate of the at least one fluorine containing etchant gas.
15. The method according to claim 1 , wherein the plasma etch step ii) of the second sequence of plasma processing steps is performed in the substantial absence of oxygen.
16. The method according to claim 1 , wherein one or more of the plasma etch step i) of the first sequence of plasma processing steps, the plasma etch step ii) of the first sequence of plasma processing steps, and the plasma etch step i) of the second sequence of plasma processing steps is performed at a total process pressure in a range 100 to 300 mTorr (13.3 to 40.0 Pa).
17. The method according to claim 1 , wherein the plasma etch step ii) of the second sequence of plasma processing steps is performed at a total process pressure in a range 5 to 50 mTorr (0.67 to 6.7 Pa).
18. The method according to claim 1 , wherein the upstanding and/or recessed features comprise one or more of microneedles, vias or trenches.