Removal of native oxide with high selectivity

A method of removing a native silicon oxide layer from a wafer, the method comprising:

• providing a wafer having a native silicon oxide layer;
• flowing a first etchant including a first hydrogen-based species and a first fluorine-based species onto the wafer to contact the native silicon oxide layer, wherein the first hydrogen-based species or the first fluorine-based species includes nitrogen;
• heating the wafer to a temperature greater than about 60° C.;
• 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 native silicon oxide layer.

An apparatus for removing native silicon oxide from a wafer, the apparatus comprising:

• a reaction chamber comprising the wafer, wherein the wafer includes:
• a polysilicon layer;
• a native silicon oxide layer over the polysilicon layer;
• 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 a first etchant including a first hydrogen-based species and a first fluorine-based species onto the wafer, wherein the first fluorine-based or the first hydrogen-based species includes nitrogen;
• (b) heating the wafer to a temperature greater than about 60° C.;
• (c) flowing a second etchant including a second hydrogen-based species and a second fluorine-based species towards the wafer;
• (d) exposing the second etchant to the plasma;
• (e) removing the native silicon oxide layer from the polysilicon layer, 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 oxide layer;
• and
• (f) removing at least partially the polysilicon layer, wherein removal of the polysilicon layer occurs at a selectivity over the exposed nitride and/or oxide structure of greater than about 1000:1