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Etching of nitride and oxide layers with reactant gases is modulated by etching in different process regimes. High etch selectivity to silicon nitride is achieved in an adsorption regime where the partial pressure of the etchant is lower than its vapor pressure. Low etch selectivity to silicon nitri

Etching of nitride and oxide layers with reactant gases is modulated by etching in different process regimes. High etch selectivity to silicon nitride is achieved in an adsorption regime where the partial pressure of the etchant is lower than its vapor pressure. Low etch selectivity to silicon nitride is achieved in a condensation regime where the partial pressure of the etchant is higher than its vapor pressure. By controlling partial pressure of the etchant, very high etch selectivity to silicon nitride may be achieved.

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1. A method comprising: (a) depositing an etchant on a feature of a surface of a work piece under conditions that thermodynamically provide for condensation of the etchant, wherein an oxide and a liner are on the feature;(b) etching the oxide on the feature;(c) depositing the etchant on the feature

1. A method comprising: (a) depositing an etchant on a feature of a surface of a work piece under conditions that thermodynamically provide for condensation of the etchant, wherein an oxide and a liner are on the feature;(b) etching the oxide on the feature;(c) depositing the etchant on the feature under conditions that thermodynamically provide for adsorption of the etchant; and(d) selectively etching the oxide on the feature without substantially etching the liner. 2. The method of claim 1, wherein the liner is silicon nitride deposited via a process selected from the group consisting of low-pressure chemical vapor deposition, plasma enhanced chemical vapor deposition, atomic layer deposition, and high density plasma chemical vapor deposition. 3. The method of claim 1, wherein the oxide is selected from the group consisting of thermal silicon oxide, flowable silicon oxide, silicon oxide deposited via plasma enhanced chemical vapor deposition, silicon oxide deposited via sub-atmospheric chemical vapor deposition, silicon oxide deposited via atomic layer deposition, silicon oxide deposited via pulsed deposition layer processing, and silicon oxide deposited via high density plasma chemical vapor deposition. 4. The method of claim 1, wherein the oxide is hafnium oxide or zirconium oxide. 5. The method of claim 1, wherein operations (a) to (d) are performed in a single chamber. 6. The method of claim 5, wherein the chamber comprises at least two processing stations, and wherein operations (a) and (c) are performed in different processing stations. 7. The method of claim 1, wherein the conditions that thermodynamically provide for condensation of the etchant are conditions in which a partial pressure of the etchant in a chamber housing the work piece is greater than a vapor pressure of the etchant. 8. The method of claim 7, wherein the partial pressure during (a) is between about 10 and 15 mTorr, and wherein the etchant is selected from the group consisting of ammonium fluoride, ammonium bifluoride, and ammonium fluoride and ammonium bifluoride. 9. The method of claim 7, wherein the partial pressure during (a) is between about 10 and 13 mTorr, and wherein the etchant is selected from the group consisting of ammonium fluoride, ammonium bifluoride, and ammonium fluoride and ammonium bifluoride. 10. The method of claim 1, wherein the conditions that thermodynamically provide for adsorption of the etchant are conditions in which a vapor pressure of the etchant is greater than a partial pressure of the etchant in a chamber housing the work piece. 11. The method of claim 10, wherein the partial pressure during (c) is between about 1 and 10 mTorr, and wherein the etchant is selected from the group consisting of ammonium fluoride, ammonium bifluoride, and ammonium fluoride and ammonium bifluoride. 12. The method of claim 10, wherein the partial pressure during (c) is between about 5 and 8 mTorr, and wherein the etchant is selected from the group consisting of ammonium fluoride, ammonium bifluoride, and ammonium fluoride and ammonium bifluoride. 13. The method of claim 1, wherein the work piece temperature is about 0 to 50° C. during operations (a) to (d). 14. The method of claim 1, wherein the work piece temperature is about 25° C. during operations (a) to (d). 15. The method of claim 1, wherein (a) and/or (c) comprise concurrently introducing a hydrogen-containing species and a fluorine-containing species into a chamber housing the work piece. 16. The method of claim 1, wherein (a) and/or (c) comprise sequentially introducing a hydrogen-containing species and a fluorine-containing species into a chamber housing the work piece. 17. The method of claim 1, wherein (a) and/or (c) comprise introducing ammonia and hydrogen fluoride into a chamber housing the work piece. 18. The method of claim 1, wherein (a) and/or (c) comprise introducing ammonia and nitrogen trifluoride into a chamber housing the work piece. 19. The method of claim 1, wherein the feature is a trench partially filled with the oxide. 20. A method comprising: (a) condensing a layer of an ammonium halide etchant on a feature of a surface of a work piece, wherein an oxide and a nitride are on the feature;(b) etching the oxide on the feature;(c) depositing a partially saturated layer of the ammonium halide etchant on the feature of the surface of the work piece under conditions that thermodynamically provide for deposition of the partially saturated layer; and(d) selectively etching the oxide on the feature without substantially etching the nitride, wherein an etch selectivity for the oxide over the nitride is at least about 50:1. 21. The method of claim 20, wherein the etch selectivity is at least about 100:1. 22. The method of claim 20, wherein the etch selectivity is at least about 200:1. 23. The method of claim 20, wherein the nitride is silicon nitride deposited via a process selected from the group consisting of low-pressure chemical vapor deposition, plasma enhanced chemical vapor deposition, atomic layer deposition, and high density plasma chemical vapor deposition. 24. The method of claim 20, wherein the oxide is selected from the group consisting of thermal silicon oxide, flowable silicon oxide, silicon oxide deposited via plasma enhanced chemical vapor deposition, silicon oxide deposited via sub-atmospheric chemical vapor deposition, silicon oxide deposited via atomic layer deposition, silicon oxide deposited via pulsed deposition layer processing, and silicon oxide deposited via high density plasma chemical vapor deposition. 25. A method comprising: (a) depositing an etchant on a feature of a surface of a work piece under conditions that thermodynamically provide for condensation of the etchant, wherein an oxide and a liner are on the feature;(b) etching the oxide on the feature with the etchant deposited under conditions that thermodynamically provide for condensation of the etchant;(c) removing the etchant from the feature to stop the etching of the oxide on the feature with the etchant deposited under conditions that thermodynamically provide for condensation of the etchant;(d) removing solid reaction product from the etching of the oxide on the feature with the etchant deposited under conditions that thermodynamically provide for condensation of the etchant;(e) depositing the etchant on the feature under conditions that thermodynamically provide for adsorption of the etchant; and(f) selectively etching the oxide on the feature with the etchant deposited under conditions that thermodynamically provide for adsorption of the etchant without substantially etching the liner. 26. A method comprising: (a) depositing an etchant on a feature of a surface of a work piece under conditions that thermodynamically provide for condensation of the etchant, wherein an oxide and a liner are on the feature;(b) etching the oxide on the feature with the etchant deposited under conditions that thermodynamically provide for condensation of the etchant;(c) removing the etchant from the feature to stop the etching of the oxide on the feature with the etchant deposited under conditions that thermodynamically provide for condensation of the etchant;(d) depositing the etchant on the feature under conditions that thermodynamically provide for adsorption of the etchant; and(e) selectively etching the oxide on the feature with the etchant deposited under conditions that thermodynamically provide for adsorption of the etchant without substantially etching the liner.