3D NAND etch
Methods of etching film stacks to form gaps of uniform width are described. A film stack is etched through a hardmask. A conformal liner is deposited in the gap. The bottom of the liner is removed. The film stack is selectively etched relative to the liner. The liner is removed. The method may be repeated to a predetermined depth.
1. A method of etching a film stack, the method comprising:
etching a film stack having a first thickness to a depth of a second thickness to form a gap with a substantially uniform width, a sidewall and a bottom, the second thickness being less than the first thickness;
depositing a liner comprising boron on the sidewall and the bottom of the gap;
etching the liner from the bottom of the gap;
selectively etching the film stack relative to the liner to a depth of a third thickness to extend a depth of the gap; and
removing the liner by a process comprising an anneal in an oxidizing atmosphere, or if the liner further comprises carbon by a process comprising an oxygen plasma ash.
2. The method of claim 1 , wherein the film stack comprises alternating layers.
3. The method of claim 2 , wherein each alternating layer has a thickness in a range of 100 Å to 3000 Å.
4. The method of claim 2 , wherein the alternating layers comprise an oxide layer and a nitride layer.
5. The method of claim 2 , wherein the alternating layers comprise an oxide layer and a polysilicon stack.
6. The method of claim 1 , further comprising forming a patterned hardmask on the film stack before etching, and wherein openings in the patterned hardmask expose portions of the film stack to be etched.
7. The method of claim 1 , wherein the gap has a width in a range of about 1 nm to about 100 nm.
8. The method of claim 1 , wherein the liner comprises one or more of B, BN, BC, or BCN.
9. The method of claim 1 , wherein the liner is substantially conformal and deposited by atomic layer deposition.
10. The method of claim 1 , wherein the liner has a thickness in a range of about 10 Å to about 50 Å.
11. The method of claim 1 , wherein the liner has a total thickness on the sidewall of the gap which is less than or equal to 50% of the width of the gap.
12. The method of claim 1 , wherein the liner has a thickness on the sidewall of the gap that is greater than a thickness on the bottom of the gap.
13. The method of claim 12 , wherein the thickness of the sidewall of the gap is greater than or equal to 120 percent of the thickness on the bottom of the gap.
14. The method of claim 1 , wherein the liner is removed by a process comprising an anneal in an oxidizing atmosphere.
15. The method of claim 14 , wherein the anneal is performed at a temperature greater than or equal to about 500° C.
16. The method of claim 1 , wherein the liner further comprises carbon and the liner is removed by a process comprising an oxygen plasma ash.
17. The method of claim 16 , wherein the oxygen plasma ash is performed at a temperature in a range of about 300° C. to about 400° C.
18. The method of claim 1 , wherein each etch process is substantially directional.