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An oxygen-free hydrogen plasma ashing process particularly useful for low-k dielectric materials based on hydrogenated silicon oxycarbide materials. The main ashing step includes exposing a previously etched dielectric layer to a plasma of hydrogen and optional nitrogen, a larger amount of water vap

An oxygen-free hydrogen plasma ashing process particularly useful for low-k dielectric materials based on hydrogenated silicon oxycarbide materials. The main ashing step includes exposing a previously etched dielectric layer to a plasma of hydrogen and optional nitrogen, a larger amount of water vapor, and a yet larger amount of argon or helium. Especially for porous low-k dielectrics, the main ashing plasma additionally contains a hydrocarbon gas such as methane. The main ashing may be preceded by a short surface treatment by a plasma of a hydrogen-containing reducing gas such as hydrogen and optional nitrogen.

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The invention claimed is: 1. An ashing process comprising a main ashing step, comprising: supplying to a remote plasma source a main ashing gas comprising a first amount of a reducing gas selected from the group consisting of hydrogen gas and ammonia gas, a second amount of water vapor, and a third

The invention claimed is: 1. An ashing process comprising a main ashing step, comprising: supplying to a remote plasma source a main ashing gas comprising a first amount of a reducing gas selected from the group consisting of hydrogen gas and ammonia gas, a second amount of water vapor, and a third amount of a diluent gas selected from the group consisting of argon and helium, wherein the second amount is greater than the first amount, wherein the third amount is greater than the second amount, and wherein the main ashing gas does not contain an amount of oxygen gas effective at ashing the substrate during the main ashing step; generating in the remote plasma source a plasma from the main ashing gas; removing ions from the plasma in a charged particle filter; and applying to the substrate the plasma output by the charged particle filter. 2. The process of claim 1, wherein the reducing gas comprises hydrogen gas. 3. The process of claim 1, wherein the reducing gas comprises ammonia gas. 4. An ashing process comprising a main ashing step of applying to a substrate a plasma of a main ashing gas comprising a first amount of a reducing gas selected from the group consisting of hydrogen gas and ammonia gas, a second amount of water vapor, a third amount of a diluent gas selected from the group consisting of argon and helium, and a fourth amount of a hydrocarbon gas, wherein the second amount is greater than the first amount, wherein the third amount is greater than the second amount, and wherein the main ashing gas does not contain an amount of oxygen gas effective at ashing the substrate during the main ashing step. 5. The process of claim 4, wherein the fourth amount is less than the first amount. 6. The process of claim 4, wherein the hydrocarbon gas comprises methane. 7. The process of claim 5, wherein the substrate includes a dielectric layer having a hole therein that is subject to the ashing process. 8. The process of claim 7, further comprising a preceding step of etching the hole in the dielectric layer according to a photoresist mask. 9. The process of claim 1, further comprising an initial ashing step, performed prior to the main ashing step, of applying to the substrate a plasma of an initial ashing gas including a fourth amount of a hydrogen-containing reducing gas and no amount of water vapor or of a hydrocarbon which would be effective at ashing the substrate during the initial ashing step, wherein the initial ashing gas and the main ashing gas include respective constituent gases differing between the initial and main ashing gases. 10. The process of claim 9, wherein the hydrogen-containing reducing gas comprises hydrogen gas. 11. The process of claim 10, wherein the initial ashing gas further comprises a fifth amount of nitrogen gas which is smaller than the fourth amount. 12. The process of claim 9, wherein the substrate includes a dielectric layer having a hole therein that is subject to the ashing process. 13. The process of claim 12, further comprising the preceding step of etching the hole in the dielectric layer according to a photoresist mask. 14. A process of ashing a substrate having dielectric layer with a hole previously etched therein, comprising the steps performed in a plasma etch chamber in which the substrate is disposed and ancillary apparatus: a first step of exciting into a first plasma a first gas mixture comprising a first amount of hydrogen gas and no amounts of oxygen and water vapor effective at ashing the substrate during the first step; a subsequent second step of exciting into a second plasma a second gas mixture comprising a second amount of hydrogen gas, a third amount of water vapor, and a fourth amount of an inactive gas selected from the group consisting of argon and helium, wherein the second gas mixture contains no amount of oxygen which would be effective at ashing the substrate during the second step; wherein the first and second gas mixtures contain respective gas components differing between the first and second gas mixtures. 15. The process of claim 14, wherein the second step is performed for a longer time than the first step. 16. The process of claim 14, wherein the ancillary apparatus includes a remote plasma source in which the first and second plasmas are excited and thereafter flow into the chamber through a charged particle filter to remove ions from the first and second plasmas. 17. The process of claim 14, wherein the first gas mixture additionally comprises nitrogen. 18. The process of claim 14, wherein the second gas mixture additionally comprises a fifth amount of a hydrocarbon gas and the first gas mixture includes no hydrocarbon gas effective at ashing the substrate during the first step. 19. The process of claim 18, wherein the hydrocarbon gas comprises methane. 20. The process of claim 14, wherein the third amount is greater than the second amount and less than the fourth amount.