Removal of native oxide with high selectivity
Provided are methods and systems for removing a native silicon oxide layer on a wafer. In a non-sequential approach, a wafer is provided with a native silicon oxide layer on a polysilicon layer. An etchant including a hydrogen-based species and a fluorine-based species is introduced, exposed to a plasma, and flowed onto the wafer at a relatively low temperature. The wafer is then heated to a slightly elevated temperature to substantially remove the native oxide layer. In a sequential approach, a wafer is provided with a native silicon oxide layer. A first etchant including a hydrogen-based species and a fluorine-based species is flowed onto the wafer. Then the wafer is heated to a slightly elevated temperature, a second etchant is flowed towards the wafer, and the second etchant is exposed to a plasma to complete the removal of the native silicon oxide layer and to initiate removal of another layer such as a polysilicon layer.
1. A method of removing a native silicon oxide layer from a wafer, the method comprising:
providing a wafer having a native silicon oxide layer on a polysilicon layer;
flowing a first etchant onto the wafer to contact the native silicon oxide layer without exposure to a plasma and including a first hydrogen-based species and a first fluorine-based species, wherein the first hydrogen-based species is hydrogen and the first fluorine-based is nitrogen trifluoride;
heating the wafer to a temperature greater than about 60° C.;
removing at least partially the native silicon oxide layer during the heating of the wafer;
flowing a second etchant including a second hydrogen-based species and a second fluorine-based species towards the wafer;
exposing the second etchant to a plasma; and
removing the remainder of the native silicon oxide layer and removing at least partially the polysilicon layer after exposing the second etchant to the plasma.
2. The method of claim 1 , further comprising:
transferring the wafer to a station for removal of polysilicon and completion of the native oxide removal after flowing the first etchant onto the wafer but prior to heating the wafer.
3. The method of claim 2 , wherein each of the steps occur without breaking vacuum.
4. The method of claim 1 , wherein the first etchant is identical to the second etchant.
5. The method of claim 1 , wherein heating the wafer includes heating the wafer to a temperature of less than about 200° C.
6. The method of claim 1 , wherein the wafer includes an exposed nitride and/or oxide structure.
7. The method of claim 6 , wherein an etch rate of the exposed nitride and/or oxide structure is less than about 3 Å per minute during removal of the native silicon oxide layer.
8. The method of claim 6 , wherein the exposed nitride structure includes silicon nitride and/or titanium nitride.
9. The method of claim 6 , wherein the exposed oxide structure includes thermal silicon oxide.
10. The method of claim 1 , wherein removal at least partially of the polysilicon layer occurs at a selectivity over the exposed nitride and/or oxide structure of greater than about 1000:1.
11. The method of claim 1 , wherein exposing the second etchant to a plasma includes exposing the second etchant to a remote plasma.