Advanced processing technique and system for preserving tungsten in a device structure

1. A method for removing photoresist from a workpiece during an intermediate stage of processing when a region of tungsten is exposed as part of the workpiece, said method comprising:

generating a plasma from a gas input consisting essentially of hydrogen gas and oxygen gas in a predetermined ratio; and

exposing the workpiece to the plasma such that said predetermined ratio causes the photoresist to be substantially removed from the workpiece while the region of tungsten is left substantially the same as prior to the exposure to the plasma.

2. The method of claim 1 wherein said exposing results in essentially no loss of the tungsten by oxidation.

3. The method of claim 1 wherein said gas input is approximately nitrogen free.

4. The method of claim 1 wherein said gas input includes no more than 20 percent of nitrogen as part of a total flow rate of the gas input.

5. The method of claim 1 wherein said gas input includes hydrogen gas at a rate of flow of 20% to 30% of a total flow rate of the gas input, in said predetermined ratio, when said plasma is generated by an in-situ plasma reactor.

6. The method of claim 5 wherein said total flow rate is at least approximately 500-1000 sccm.

7. The method of claim 1 wherein said gas input includes hydrogen gas at a rate of flow of 10% to 15% of a total flow rate of the gas input, in said predetermined ratio, when said plasma is generated by a downstream plasma reactor.

8. The method of claim 7 wherein said total flow rate is at least approximately 1000 sccm to 5000 sccm.

9. The method of claim 1 wherein said tungsten region forms part of a gate electrode structure with a major surface of the tungsten region subject to said exposing as the photoresist is removed.

10. The method of claim 1 wherein said photoresist includes a crust previously formed by a high dose ion implantation and said exposing removes the crust.

11. A method for removing photoresist from a workpiece during an intermediate stage of processing when a region of tungsten is exposed as part of the workpiece, said method comprising:

providing a downstream plasma system for exposing the workpiece to a downstream plasma;

feeding a gas mixture to the downstream plasma system for generating said downstream plasma and exposing the workpiece to the downstream plasma;

using hydrogen gas and oxygen gas as the gas mixture for generating the downstream plasma to remove said photoresist such that a removal rate of said photoresist changes with changes in a ratio of the hydrogen gas to the oxygen gas and a loss of said tungsten during the removal of the photoresist changes with changes in said ratio; and

adjusting the ratio of the hydrogen gas to the oxygen gas to a particular value which causes the photoresist to be removed at about a maximum removal rate that corresponds to a minimum tungsten loss rate of about zero.

12. The method of claim 11 wherein the gas mixture consists of hydrogen gas and oxygen gas.

13. The method of claim 11 wherein changing the ratio of the hydrogen gas to the oxygen gas defines a peak in the removal rate of the photoresist at about said particular value of said ratio.

14. The method of claim 11 wherein the removal rate of the photoresist is within 5 percent of the maximum removal rate and the tungsten loss rate is less than 1 Å at said particular value of the ratio.