Method to improve profile control during selective etching of silicon nitride spacers

1. A cyclic etch method, the method comprising the steps of:

i) exposing a SiN layer covering structures on a substrate in a reaction chamber to a plasma of hydrofluorocarbon (HFC) to form a polymer layer deposited on the SiN layer that modifies the surface of the SiN layer, the HFC having a formula C x H y F z where x=2-5, y>z, the HFC being a saturated or unsaturated, linear or cyclic HFC;

ii) exposing the polymer layer deposited on the SiN layer to a plasma of an inert gas, the plasma of the inert gas removing the polymer layer deposited on the SiN layer and the modified surface of the SiN layer on etch front; and

iii) repeating the steps of i) and ii) until the SiN layer covered on the etch front is removed thereby forming vertical straight SiN spacers with the SiN layer covered on the sidewalls of the structures,

wherein the plasma of the HFC in step i), the plasma of the inert gas in step ii) or both are pulsed plasma.

2. The cyclic etch method of claim 1 , further comprising the steps of,

after the step of i),

pumping the reaction chamber to a vacuum;

purging the reaction chamber with Ar;

pumping the reaction chamber to the vacuum; and

introducing the inert gas into the reaction chamber to generate the pulsed plasma of the inert gas; and

after the step of ii),

pumping the reaction chamber to a vacuum;

purging the reaction chamber with Ar;

pumping the reaction chamber to the vacuum; and

introducing the HFC into the reaction chamber to generate the pulsed plasma of the HFC.

3. The cyclic etch method of claim 1 , wherein the hydrofluorocarbon (HFC) is mixed with an oxygen-containing gas selected from O 2 , O 3 , CO, CO 2 , NO, NO 2 , N 2 O, SO 2 , COS, H 2 O or combinations thereof.

4. The cyclic etch method of claim 1 , wherein the HFC, the inert gas or both are presented in pulse.

5. The cyclic etch method of claim 1 , wherein a single or multiple RF sources are applied to generate the pulsed plasma of the HFC in the step of i) and to generate the pulsed plasma of the inert gas in the step of ii), respectively.

6. The cyclic etch method of claim 1 , wherein the inert gas is N 2 , Ar, Kr or Xe.

7. The cyclic etch method of claim 1 , wherein the HFC is C 2 H 5 F or C 3 H 7 F.

8. The cyclic etch method of claim 1 , wherein the HFC selectively etches the SiN layer over the structures.

9. The cyclic etch method of claim 1 , wherein less to no footings are formed at each corner between the vertical straight SiN spacer and the substrate.

10. A cyclic etch method for forming vertical straight SiN spacers, the method comprising the steps of:

i) exposing a SiN layer covering structures on a substrate in a reaction chamber to a plasma a mixture of a hydrofluorocarbon (HFC) and an oxygen-containing gas to form a polymer layer deposited on the SiN layer that modifies the surface of the SiN layer, the HFC having a formula C x H y F z where x=2-5, y>z, the HFC being a saturated or unsaturated, linear or cyclic HFC,

wherein the oxygen-containing gas is selected from O 2 , O 3 , CO, CO 2 , NO, NO 2 , N 2 O, SO 2 , COS, H 2 O or combinations thereof;

ii) exposing the polymer layer deposited on the SiN layer to a plasma of an inert gas, the plasma of the inert gas removing the polymer layer deposited on the SiN layer and the modified surface of the SiN layer on the etch front; and

iii) repeating the steps of i) and ii) until the SiN layer covered on the etch front is removed thereby forming the vertical straight SiN spacers with the SiN layer covered on the sidewalls of the structures,

wherein the plasma of the mixture in step i), the plasma of the inert gas in step ii) or both are pulsed plasma.

11. The cyclic etch method of claim 10 , wherein the mixture of the hydrofluorocarbon (HFC) and oxygen-containing gas, the inert gas or both are presented in pulse.

12. The cyclic etch method of claim 10 , wherein a single or multiple RF sources are applied to generate the pulsed plasma of the HFC in the step of i) and to generate the pulsed plasma of the inert gas in the step of ii), respectively.

13. The cyclic etch method of claim 10 , wherein the HFC is C 2 H 5 F or C 3 H 7 F.

14. The cyclic etch method of claim 10 , wherein the HFC selectively etches the SiN layer over the structures.

15. The cyclic etch method of claim 10 , wherein less to no footings are formed at each corner between the vertical straight SiN spacer and the substrate.

16. A cyclic etch method for forming vertical straight SiN gate spacers, the method comprising the steps of:

i) exposing a SiN layer covering gate stacks on a substrate in a reaction chamber to a plasma of hydrofluorocarbon (HFC) selected from the group consisting of C 2 H 5 F and C 3 H 7 F to form a polymer layer deposited on the SiN layer that modifies the surface of the SiN layer;

ii) exposing the polymer layer deposited on the SiN layer to Ar plasma, the Ar plasma removing the polymer layer deposited on the SiN layer and the modified surface of the SiN layer on etch front; and

iii) repeating the steps of i) and ii) until the SiN layer covered on the etch front is removed thereby forming the vertical straight SiN gate spacers with the SiN layer covered on the sidewalls of the gate stacks,

wherein the plasma of the mixture in step i), the plasma of the inert gas in step ii) or both are pulsed plasma.

17. The cyclic etch method of claim 16 , wherein a single or multiple RF sources are applied to generate the pulsed plasma of the HFC in the step of i) and to generate the pulsed Ar plasma in the step of ii), respectively.

18. The cyclic etch method of claim 16 , wherein less to no footings are formed at each corner between the SiN gate spacer and the substrate.

19. The cyclic etch method of claim 16 , wherein the hydrofluorocarbon (HFC) is mixed with an oxygen-containing gas selected from O 2 , O 3 , CO, CO 2 , NO, NO 2 , N 2 O, SO 2 , COS, H 2 O or combinations thereof.

20. The cyclic etch method of claim 16 , wherein the HFC, Ar or both are presented in pulse.