Polysilicon etch with high selectivity
Provided are methods and systems for removing polysilicon on a wafer. A wafer can include a polysilicon layer and an exposed nitride and/or oxide structure. An etchant with a hydrogen-based species, such as hydrogen gas, and a fluorine-based species, such as nitrogen trifluoride, can be introduced. The hydrogen-based species and the fluorine-based species can be activated with a remote plasma source. The layer of polysilicon on the wafer can be removed at a selectivity over the exposed nitride and/or oxide structure that is greater than about 500:1.
1. A method of removing polysilicon from a wafer, the method comprising:
providing a wafer, wherein the wafer includes:
a polysilicon layer; and
an exposed nitride and/or oxide structure;
flowing an etchant including a hydrogen-based species and a fluorine-based species towards the wafer, wherein a concentration of the fluorine-based species is between about 0.7% and about 10% by volume and a concentration of the hydrogen-based species is greater than the concentration of the fluorine-based species;
exposing the etchant to a remote plasma to activate the hydrogen-based species and the fluorine-based species; and
removing the polysilicon layer at a selectivity over the exposed nitride and/or oxide structure of greater than about 500:1.
2. The method of claim 1 , wherein the hydrogen-based species includes hydrogen or ammonia.
3. The method of claim 1 , wherein the fluorine-based species includes nitrogen trifluoride or carbon tetrafluoride.
4. The method of claim 1 , wherein removing the polysilicon layer is performed at a selectivity over the exposed nitride and/or oxide structure of greater than about 1000:1.
5. The method of claim 1 , wherein the exposed nitride structure includes silicon nitride or titanium nitride.
6. The method of claim 1 , wherein the exposed oxide structure includes silicon dioxide.
7. The method of claim 1 , wherein removing the polysilicon layer is performed at an etch rate of greater than about 1000 Å per minute.
8. The method of claim 1 , wherein an etch rate of the exposed nitride and/or oxide structure is less than about 5 Å per minute during removal of the polysilicon layer.
9. The method of claim 1 , wherein the remote plasma is generated from a downstream plasma reactor.
10. The method of claim 9 , wherein the downstream plasma reactor includes a ceramic dome.
11. The method of claim 1 , wherein removing the polysilicon layer is performed in a chamber at a temperature between about 60° C. and about 100° C.
12. The method of claim 1 , wherein removing the polysilicon layer is performed in a chamber having a pressure between about 1 Torr and about 3 Torr.
13. The method of claim 1 , wherein the exposed nitride and/or oxide structure are part of a memory device.
14. The method of claim 1 , wherein the hydrogen-based species is hydrogen.
15. The method of claim 14 , wherein the flow rate of hydrogen is about equal to or greater than 2 standard liters per minute.