Plasma composition for selective high-k etch
View Patent ↗A method for the selective removal of a high-k layer such as HfO 2 over silicon or silicon dioxide is provided. More specifically, a method for etching high-k selectively over silicon and silicon dioxide and a plasma composition for performing the selective etch process is provided. Using a BCl 3 plasma with well defined concentrations of nitrogen makes it possible to etch high-k with at a reasonable etch rate while silicon and silicon dioxide have an etch rate of almost zero. The BCl 3 comprising plasmas have preferred additions of 10 up to 13% nitrogen. Adding a well defined concentration of nitrogen to the BCl 3 /N 2 plasma gives the unexpected deposition of a Boron-Nitrogen (BxNy) comprising film onto the silicon and silicon dioxide which is not deposited onto the high-k material. Due to the deposition of the Boron-Nitrogen (BxNy) comprising film, the etch rate of silicon and silicon dioxide is dropped down to zero. The Boron-Nitrogen (BxNy) comprising film can be removed during the etching process using the right substrate bias (leading to ion bombardment) or after the etching process by a simple water rinse since the Boron-Nitrogen (BxNy) comprising film is water soluble.
1. A method for etching a second material selectively over a first material, the method comprising the steps of:
dry etching using a plasma, wherein during dry etching a protective and water-soluble film is deposited onto a first material such that an etch rate of the first material is dropped to almost zero, and whereby almost no protective and water-soluble film is deposited onto a second material; and
removing the protective and water-soluble film from the first material.
2. The method of claim 1 , wherein the plasma comprises a boron-halogen compound and nitrogen, and wherein a ratio of the boron-halogen compound to nitrogen is from 19:1 to 5.6:1.
3. The method of claim 1 wherein the boron-halogen compound is BCl 3 .
4. The method of claim 3 , wherein a ratio of BCl 3 to nitrogen in the plasma is from 9:1 to 6.7:1.
5. The method of claim 3 , wherein the second material is a high-k material.
6. The method of claim 1 wherein the protective and water-soluble film is a BxNy comprising film.
7. The method of claim 1 , wherein the second material is HfO 2 .
8. The method of claim 1 , wherein the first material is silicon, and wherein a ratio of the boron-halogen compound to nitrogen is 9:1.
9. The method of claim 8 , wherein the silicon is undoped polycrystalline silicon or doped or polycrystalline silicon.
10. The method of claim 1 wherein the first material is silicon dioxide, and wherein a ratio of the boron-halogen compound to nitrogen is from 9:1 to 6.7:1.
11. The method of claim 1 , wherein the protective and water-soluble layer is removed during etching using the plasma by ion bombardment.
12. The method of claim 11 , whereby ion bombardment is conducted by using a substrate bias during plasma etching which is different from zero.
13. The method of claim 12 , wherein the substrate bias during plasma etching is from −30 v to −60V.
14. The method of claim 1 , wherein the protective and water-soluble layer is removed after etching by a wet rinse.
15. The method of claim 1 , wherein a plasma power is from 100 W to 1200 W.
16. The method of claim 1 , wherein a plasma power is about 450 W.
17. The method of claim 1 , wherein a pressure in the plasma is from 5 mT to 80 mT.
18. The method of claim 1 , wherein a pressure in the plasma is 5 mT.