Methodology for cleaning of surface metal contamination from electrode assemblies
Systematic and effective methodology to clean capacitively coupled plasma reactor electrodes and reduce surface roughness so that the cleaned electrodes meet surface contamination specifications and manufacturing yields are enhanced. Pre-cleaning of tools used in the cleaning process helps prevent contamination of the electrode being cleaned.
1. A method for cleaning an electrode assembly for generating plasma in a plasma chamber comprising a plasma-exposed silicon surface, the method comprising:
pre-cleaning with a nitric acid solution an inner liner of a bath and a component used to suspend the electrode assembly in the bath, wherein the nitric acid solution comprises less than 10% nitric acid;
suspending the electrode assembly within the pre-cleaned inner liner of the bath using the pre-cleaned component;
soaking the electrode assembly in or cleaning the electrode assembly with ultra-pure water contained within the pre-cleaned inner liner of the bath;
removing the electrode assembly from the pre-cleaned inner liner of the bath; and
removing contaminants from the silicon surface of the electrode assembly by contacting the silicon surface with an acidic solution comprising hydrofluoric acid, nitric acid, acetic acid, and water,
wherein the electrode assembly comprises a showerhead electrode having a plurality of gas outlets.
2. The method of claim 1 , wherein the bath comprises an ultrasonic bath, the method comprising ultrasonically cleaning the electrode assembly with ultra-pure water contained within the pre-cleaned inner liner of the ultrasonic bath.
3. The method according to claim 1 , wherein the inner liner of the bath comprises polyethylene.
4. The method according to claim 1 , wherein the component used to suspend the electrode assembly in the bath comprises polytetrafluoroethylene.
5. The method according to claim 1 , wherein the pre-cleaning with the nitric acid solution comprises wiping with the nitric acid solution, rinsing with ultra-pure water, wiping with isopropyl alcohol, and rinsing with ultra-pure water.
6. The method according to claim 1 , further comprising contacting the silicon surface of the electrode assembly with a wiper wetted with isopropyl alcohol or soaking the electrode assembly in isopropyl alcohol contained in a tank.
7. The method according to claim 1 , wherein contacting the silicon surface with the acidic solution comprises contacting the silicon surface with a wiper wetted with the acidic solution.
8. The method according to claim 1 , further comprising flushing the electrode assembly with ultra-pure water.
9. The method according to claim 1 , further comprising blow drying the electrode assembly, baking the electrode assembly in a vacuum oven, and pre-cleaning with nitric acid solution a component used to support the electrode assembly in the vacuum oven, wherein the nitric acid solution comprises less than 10% nitric acid.
10. The method according to claim 1 , further comprising:
pre-cleaning with nitric acid solution a tank used to transport the electrode assembly to a cleanroom, wherein the nitric acid solution comprises less than 10% nitric acid; and
transporting the electrode assembly in the pre-cleaned tank to a cleanroom in which the silicon of the electrode assembly surface is contacted with the acidic solution comprising hydrofluoric acid, nitric acid, acetic acid, and water.
11. The method according to claim 1 , further comprising:
pre-cleaning with nitric acid solution an appliance that contains the electrode assembly during a power flushing step, wherein the nitric acid solution comprises less than 10% nitric acid, and further wherein the appliance comprises:
an upper cover having one or more inlets connected to at least one supply of pressurized cleaning fluid for the power flushing; and
a lower portion having drainage and in which the electrode assembly is placed; and
power flushing the electrode assembly supported in the pre-cleaned appliance with isopropyl alcohol solution or ultra-pure water, wherein the power flushing comprises supplying pressurized cleaning fluid to the appliance through the one or more inlets, and further wherein the power flushing cleans gas holes and surfaces of the electrode assembly.
12. The method according to claim 1 , wherein the electrode assembly comprises an aluminum backing member elastomer bonded to a silicon electrode.
13. The method according to claim 1 , wherein removed contaminants are selected from the group consisting of Al, Ca, Mg, Na, K, Ni, Fe, Zn, Ti, and combinations thereof.
14. The method according to claim 1 , wherein the acidic solution comprises 0.25 to 1% by volume hydrofluoric acid, 10 to 40% by volume nitric acid, and 10 to 20% by volume acetic acid.
15. The method according to claim 1 , wherein the nitric acid solution used in the pre-cleaning comprises about 2% nitric acid and balance water.
16. The method according to claim 1 , further comprising removing black silicon from the silicon surface of the electrode assembly.
17. The method according to claim 6 , further comprising pre-cleaning with nitric acid solution the tank containing the isopropyl alcohol, wherein the nitric acid solution comprises less than 10% nitric acid.
18. The method according to claim 12 , wherein the aluminum backing member comprises a plate or ring.