Ultrahigh selective polysilicon etch with high throughput
Provided are methods and apparatuses for removing a polysilicon layer on a wafer, where the wafer can include a nitride layer, a low-k dielectric layer, an oxide layer, and other films. A plasma of a hydrogen-based species and a fluorine-based species is generated in a remote plasma source, and the wafer is exposed to the plasma at a relatively low temperature to limit the formation of solid byproduct. In some implementations, the wafer is maintained at a temperature below about 60° C. The polysilicon layer is removed at a very high etch rate, and the selectivity of polysilicon over the nitride layer and the oxide layer is very high. In some implementations, the wafer is supported on a wafer support having a plurality of thermal zones configured to define a plurality of different temperatures across the wafer.
1. A method of removing a polysilicon layer from a wafer, the method comprising:
providing a wafer having a polysilicon layer;
flowing an etchant including a hydrogen-based species and a fluorine-based species into a remote plasma source, wherein a concentration of the hydrogen-based species is greater than a concentration of the fluorine-based species;
generating a remote plasma in the remote plasma source, wherein the remote plasma includes radicals of the hydrogen-based species and the fluorine-based species; and
exposing the wafer to the remote plasma to remove the polysilicon layer, wherein the wafer is maintained within a temperature range that is less than about 60° C. so that the wafer is substantially free of solid byproduct residue during exposure to the remote plasma and during removal of the polysilicon layer.
2. The method of claim 1 , wherein the wafer includes an exposed nitride and/or oxide structure.
3. The method of claim 2 , wherein the exposed nitride structure includes at least one of silicon nitride and titanium nitride, and wherein the exposed oxide structure includes at least thermal silicon oxide.
4. The method of claim 2 , wherein the selectivity of polysilicon over the exposed nitride and/or oxide structure is greater than about 500:1 during removal of the polysilicon layer.
5. The method of claim 1 , wherein the hydrogen-based species includes hydrogen or ammonia, and wherein the fluorine-based species includes nitrogen trifluoride or carbon tetrafluoride.
6. The method of claim 1 , wherein the wafer is maintained at the temperature range of less than about 60° C. to inhibit the formation of the solid byproduct residue.
7. The method of claim 1 , wherein the wafer is exposed to the remote plasma in a chamber having a pressure less than about 5 Torr.
8. The method of claim 7 , wherein the wafer is exposed to the remote plasma in a chamber having a pressure less than about 1 Torr.
9. The method of claim 1 , wherein the wafer is supported on an electrostatic chuck a plurality of thermal zones configured to define a plurality of different temperatures across the wafer.
10. The method of claim 9 , further comprising:
applying a plurality of different temperatures in the thermal zones of the electrostatic chuck during exposure of the wafer to the remote plasma for improved uniformity of removal of the polysilicon layer.
11. The method of claim 1 , wherein the polysilicon layer is removed at an etch rate of greater than about 2000 Å per minute.
12. The method of claim 1 , wherein the concentration of the fluorine-based species is between about 0.7% and about 10% by volume, and wherein the concentration of the hydrogen-based species is greater than about 50% by volume.
13. The method of claim 1 , wherein the etchant further includes a modifying gas species different from the fluorine-based species, wherein the modifying gas species includes at least one of nitrogen trifluoride, carbon tetrafluoride, fluoromethane, and sulfur hexafluoride.
14. The method of claim 13 , wherein a concentration of the modifying gas species is less than about 10% by volume.
15. The method of claim 1 , wherein the wafer is supported on an electrostatic chuck and further comprises a native oxide layer on the polysilicon layer, the method further comprising:
applying a bias to the electrostatic chuck to generate a capacitively-coupled plasma of at least a fluorine-based etchant between the remote plasma source and the electrostatic chuck; and
exposing the wafer to the capacitively-coupled plasma to remove the native oxide layer, wherein removal of the native oxide layer is performed in situ with removal of the polysilicon layer.