Methods for wordline separation in 3D-NAND devices
Methods of wordline separation in semiconductor devices (e.g., 3D-NAND) are described. A metal film is deposited in the wordlines and on the surface of a stack of spaced oxide layers. The metal film is removed by high temperature oxidation and etching of the oxide or low temperature atomic layer etching by oxidizing the surface and etching the oxide in a monolayer fashion. After removal of the metal overburden, the wordlines are filled with the metal film.
1. A method of processing a substrate, the method comprising:
providing a substrate having a stack of spaced oxide layers with gaps between the oxide layers, the stack having a top and sides, each gap can form a wordline;
depositing a metal on the stack so that the metal fills the gaps and covers the top and sides of the stack with a thickness of metal overburden;
oxidizing the metal to a depth within about ±1 Å of the side of the stack to form a metal oxide on the top and sides of the stack and leaving the metal in the gaps as wordlines; and
etching the metal oxide from the top and sides of the stack leaving the metal in the wordlines.
2. The method of claim 1 , metal comprises tungsten and the metal oxide comprises tungsten oxide.
3. The method of claim 1 , wherein the metal consists essentially of tungsten.
4. The method of claim 1 , further comprising forming a barrier layer on the oxide layers and the metal is deposited on the barrier layer.
5. The method of claim 4 , wherein the barrier layer comprises TiN with a thickness in the range of about 20 Å to about 50 Å.
6. The method of claim 1 , wherein there are greater than 50 wordlines.
7. The method of claim 1 , wherein after etching the metal oxide, the metal overburden is removed and the metal in the gaps forming wordlines is substantially even with the sides of the stack.
8. The method of claim 1 , wherein the oxidation and etching occur at a temperature greater than or equal to about 400° C.
9. The method of claim 1 , wherein etching the metal oxide comprises exposing the metal oxide to a metal halide etchant.
10. The method of claim 9 , wherein the metal halide etchant comprises the same metal species as the metal oxide.
11. The method of claim 9 , wherein the metal halide etchant comprises a different metal species than a metal species of the metal oxide.
12. The method of claim 1 , wherein oxidizing the metal comprises exposing the metal to O 2 .
13. The method of claim 1 , wherein the thickness of metal overburden is greater than or equal to about 5 Å.