High aspect ratio etch with combination mask

1. A method for etching features in a stack, comprising:

forming a combination hardmask, comprising:

forming a first hardmask layer comprising carbon or silicon oxide over the stack;

forming a second hardmask layer comprising metal over the first hardmask layer; and

forming a patterned mask over the second hardmask layer;

patterning the first and second hardmask layers, comprising:

etching the second hardmask layer, comprising:

flowing a second hardmask layer etch gas comprising a halogen component;

forming the second hardmask layer etch gas into a plasma; and

stopping the flow of the second hardmask layer etch gas; and

etching the first hardmask layer, comprising:

flowing a first hardmask layer etch gas comprising oxygen and at least one of COS or SO 2 ;

forming the first hardmask layer etch gas into a plasma; and

stopping the flow of the first hardmask layer etch gas; and

etching the stack through the combination hardmask.

2. The method, as recited in claim 1 , wherein the patterning the first and second hardmask layers removes the patterned mask.

3. The method, as recited in claim 1 , wherein the stack is at least one of a silicon oxide layer, OPOP or ONON.

4. The method, as recited in claim 1 , further comprising ashing the first hardmask layer.

5. The method, as recited in claim 1 wherein the stack is at least one of silicon oxide or polysilicon.

6. The method, as recited in claim 1 , wherein the forming the combination hardmask further comprises forming a third hardmask layer comprising carbon or silicon oxide over the second hardmask layer, and forming a fourth hardmask layer comprising metal over the third hardmask layer, wherein the forming the patterned mask over the second hardmask layer forms the patterned mask over the fourth hardmask layer.

7. The method, as recited in claim 6 , further comprising:

etching the fourth hardmask layer, comprising:

flowing a fourth hardmask layer etch gas comprising a halogen component;

forming the fourth hardmask layer etch gas into a plasma; and

stopping the flow of the fourth hardmask layer etch gas; and

etching the third hardmask layer, comprising:

flowing a third hardmask layer etch gas comprising oxygen and at least one of COS or SO 2 ;

forming the third hardmask layer etch gas into a plasma; and

stopping the flow of the third hardmask layer etch gas.

8. The method, as recited in claim 1 , wherein the first hardmask layer is of amorphous carbon.

9. The method, as recited in claim 8 , wherein the second hardmask layer is of titanium nitride.

10. The method, as recited in claim 9 , wherein the patterned mask is of silicon nitride.

11. The method, as recited in claim 1 , wherein the second hardmask layer comprises at least one of elemental metal, a metal alloy, a metal oxide, metal carbide, or a metal nitride.

12. The method, as recited in claim 11 , wherein the stack is at least one of a silicon oxide layer, OPOP or ONON.

13. The method, as recited in claim 12 , wherein the forming the combination hardmask further comprises forming a third hardmask layer comprising carbon or silicon oxide over the second hardmask layer, and forming a fourth hardmask layer comprising metal over the third hardmask layer.

14. The method, as recited in claim 13 , further comprising:

etching the fourth hardmask layer, comprising:

flowing a fourth hardmask layer etch gas comprising a halogen component;

forming the fourth hardmask layer etch gas into a plasma; and

stopping the flow of the fourth hardmask layer etch gas; and

etching the third hardmask layer, comprising:

flowing a third hardmask layer etch gas comprising oxygen and at least one of COS or SO 2 ;

forming the third hardmask layer etch gas into a plasma; and

stopping the flow of the third hardmask layer etch gas.

15. The method, as recited in claim 14 , wherein the patterning the first and second hardmask layers removes the patterned mask.

16. The method, as recited in claim 15 , further comprising ashing the first hardmask layer.