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 . An apparatus for removing polysilicon from a wafer, the apparatus comprising:
a reaction chamber comprising the wafer, wherein the wafer includes:
a polysilicon layer; and
an exposed nitride and/or oxide structure
a plasma source coupled to the reaction chamber and configured to generate a plasma outside the reaction chamber; and
a controller with instructions for performing the following operations:
(a) 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;
(b) exposing the etchant to the plasma to activate the hydrogen-based species and the fluorine-based species; and
(c) removing the polysilicon layer at a selectivity over the exposed nitride and/or oxide structure of greater than about 500:1.
2 . The apparatus of claim 1 , wherein the plasma source comprises a remote downstream plasma reactor.
3 . The apparatus of claim 1 , wherein the hydrogen-based species includes hydrogen or ammonia.
4 . The apparatus of claim 1 , wherein the fluorine-based species includes nitrogen trifluoride or carbon tetrafluoride.
5 . The apparatus of claim 1 , wherein the exposed nitride structure includes silicon nitride or titanium nitride.
6 . The apparatus of claim 1 , wherein the exposed oxide structure includes silicon dioxide.
7 . The apparatus of claim 1 , wherein an etch rate of the polysilicon layer is greater than about 1000 Å per minute and 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.
8 . The apparatus of claim 1 , wherein the temperature of the wafer is between about 60° C. and about 100° C.
9 . The apparatus of claim 1 , wherein the hydrogen-based species is hydrogen.
10 . The apparatus of claim 9 , wherein the flow rate of hydrogen is about equal to or greater than 2 standard liters per minute.