Designer atomic layer etching
Methods for evaluating synergy of modification and removal operations for a wide variety of materials to determine process conditions for self-limiting etching by atomic layer etching are provided herein. Methods include determining the surface binding energy of the material, selecting a modification gas for the material where process conditions for modifying a surface of the material generate energy less than the modification energy and greater than the desorption energy, selecting a removal gas where process conditions for removing the modified surface generate energy greater than the desorption energy to remove the modified surface but less than the surface binding energy of the material to prevent sputtering, and calculating synergy to maximize the process window for atomic layer etching.
1. A method of etching a material on a substrate, the method comprising:
identifying process conditions for an atomic layer etching process of the material using a modification gas and a removal gas; and
performing the atomic layer etching process on the material on the substrate by:
exposing the substrate to the modification gas to modify a surface of the material, the modification gas having a modification energy and a desorption energy with respect to the material to be etched, and
exposing the modified surface to the removal gas and igniting a plasma to remove the modified surface,
wherein the modification energy is less than the desorption energy, and the desorption energy is less than a surface binding energy of the material;
wherein the identifying the process conditions comprises selecting a substrate temperature for performing the exposing the substrate to the modification gas, wherein the ion energy provided by the substrate temperature is between the modification energy and the desorption energy; and
further comprising cooling the substrate to a temperature less than about 0° C. prior to performing the atomic layer etching process, and wherein the material is tantalum.
2. The method of claim 1 , wherein the identifying the process conditions further comprises selecting a bias power for applying a bias during the exposing the modified surface to the removal gas, wherein the ion energy provided by the bias is between the desorption energy and the surface binding energy.
3. The method of claim 1 , wherein the modification gas is selected to adsorb to the material without etching the material.
4. The method of claim 1 , wherein the removal gas is selected to remove the modified surface without etching underlying unmodified material.
5. The method of claim 1 , wherein the process conditions are selected from the group consisting of temperature, chamber pressure, plasma power, bias power, modification gas flow, and exposure time.
6. The method of claim 1 , further comprising modifying the process conditions within a process window.
7. The method of claim 1 , wherein the modification gas is a halogen-containing gas.
8. The method of claim 1 , wherein the removal gas is an inert gas.
9. The method of claim 1 , wherein atomic layer etching further comprises purging a chamber housing the substrate between the exposing the substrate to the modification gas and the exposing the substrate to the removal gas.