Atomic layer etching of tantalum
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 tantalum on a substrate, the method comprising: providing the substrate comprising tantalum; cooling the substrate to a temperature less than about 0° C.; and performing atomic layer etching of the tantalum by: exposing the substrate to a modification gas to modify a surface of the tantalum, the modification gas having a modification energy and a desorption energy with respect to the tantalum; and exposing the modified surface to a removal gas and igniting a plasma to remove the modified surface of the tantalum; wherein the modification energy is less than the desorption energy, and the desorption energy is less than a surface binding energy of the tantalum; wherein an ion energy provided by the substrate temperature is between the modification energy and the desorption energy.
2. The method of claim 1 , wherein the substrate is exposed to the modification gas at a substrate temperature less than about 0° C.
3. The method of claim 1 , wherein the temperature is between about −20° C. and about 0° C.
4. The method of claim 1 , wherein the substrate comprises a layer of tantalum.
5. The method of claim 1 , wherein the substrate comprises tantalum nitride.
6. The method of claim 1 , wherein the substrate comprises two or more layers of tantalum and/or tantalum nitride.
7. The method of claim 1 , wherein the substrate temperature of less than about 0° C. achieves self-limiting etching.