Etch improvement

1. A method comprising:

exposing a first material disposed across a first plane on a first substrate during a first time period to an ion beam to form a first plurality of structures in the first material, the ion beam directed at the first material at an ion beam angle ϑ relative to a surface normal of the first substrate, wherein

the first substrate is positioned at a first rotation angle ϕ 1 between the ion beam and a first vector of the first plurality of structures during the first time period,

the first vector is perpendicular to a direction in which the first plurality of structures extend across the first plane,

the first material is exposed to the ion beam incrementally along a first direction during the first time period, and

exposure of the first material to the ion beam is varied along the first direction to generate a depth variation between the first plurality of structures in the first direction; and

exposing the first material disposed to the ion beam during a second time period to modify the depth of at least some of the first plurality of structures, wherein

the substrate is positioned at a second rotation angle ϕ 2 between the ion beam and the first vector of the first plurality of structures during the second time period,

the second rotation angle ϕ 2 is the negative angle of the first rotation angle ϕ 1 .

2. The method of claim 1 , wherein

the first plurality of structures are formed to have a first slant angle ϑ 1 ′ relative to a surface normal of the first substrate,

the first rotation angle ϕ 1 is selected by an equation ϕ 1 =cos −1 (tan(ϑ 1 ′)/tan(ϑ)), and

the depths of the first plurality of structures are modified during the second period while maintaining the first slant angle ϑ 1 ′ of the first plurality of structures.

3. The method of claim 1 , wherein a duty cycle used to generate the ion beam is varied for different sections of the first material to generate the depth variation between the first plurality of structures as the first material is exposed to the ion beam incrementally along the first direction.

4. The method of claim 1 , wherein a time of exposure to the ion beam is varied for different sections of the first material to generate the depth variation between the first plurality of structures as the first material is exposed to the ion beam incrementally along the first direction.

5. The method of claim 1 , wherein a power used to generate the ion beam is varied for different sections of the first material to generate the depth variation between the first plurality of structures as the first material is exposed to the ion beam incrementally along the first direction.

6. The method of claim 1 , wherein the first substrate is positioned at the first rotation angle ϕ 1 on a substrate support.

7. The method of claim 6 , further comprising

removing the first substrate from the substrate support;

positioning a second substrate on the substrate support; and

exposing a second material disposed across a second plane on the second substrate to the ion beam to form a second plurality of structures in the second material, the ion beam directed at the second material at the ion beam angle ϑ, wherein

the second substrate is positioned at a third rotation angle ϕ 3 between the ion beam and a second vector of the second plurality of structures,

the second vector is perpendicular to a direction in which the second plurality of structures extend across the second plane, and

positioning the second substrate to be at the third rotation angle ϕ 3 comprises rotating the substrate support relative to an orientation of the substrate support when the first plurality of structures were formed on the first substrate.

8. The method of claim 7 , wherein

the second material is exposed to the ion beam incrementally along the first direction, and

exposure of the second material to the ion beam is varied along the first direction to generate a depth variation between the second plurality of structures in the first direction.

9. The method of claim 8 , wherein a duty cycle used to generate the ion beam is varied for different sections of the second material to generate the depth variation of the second plurality of structures as the second material is exposed to the ion beam incrementally along the first direction.

10. The method of claim 7 , wherein

the second plurality of structures are formed to have a second slant angle ϑ 2 ′ relative to a surface normal of the second substrate, and

the third rotation angle ϕ 3 is selected by an equation ϕ 3 =cos −1 (tan(ϑ 2 ′)/tan(ϑ)).

11. A method comprising:

exposing a first material disposed across a first plane on a substrate to an ion beam during a first time period to form a first plurality of structures in the first material, the ion beam directed at the first material at an ion beam angle ϑ relative to a surface normal of the substrate, wherein the substrate is positioned at a first rotation angle ϕ 1 between the ion beam and a first vector of the first plurality of structures during the first time period and the first vector is perpendicular to a direction in which the first plurality of structures extend across the first plane; and

exposing the first material disposed to the ion beam during a second time period to modify the depth of at least some of the first plurality of structures, wherein

the substrate is positioned at a second rotation angle ϕ 2 between the ion beam and the first vector of the first plurality of structures during the second time period, and

the second rotation angle ϕ 2 is the negative angle of the first rotation angle ϕ 1 .

12. The method of claim 11 , wherein

a first section of the first material is exposed to the ion beam during the first time period,

a second section of the first material is exposed to the ion beam during the second time period, and

the second section includes at least a portion that was unexposed to the ion beam during the first time period.

13. The method of claim 12 , wherein the first section and the second section share a common portion.

14. The method of claim 11 , wherein

the first material is exposed to the ion beam incrementally along a first direction during the first time period, and

exposure of the first material to the ion beam is varied along the first direction during the first time period to generate a depth variation between the first plurality of structures in the first direction.

15. The method of claim 14 , wherein

the first material is exposed to the ion beam incrementally along the first direction during the second time period, and

exposure of the first material to the ion beam is varied along the first direction during the second time period to generate a modified depth variation between the first plurality of structures in the first direction.

16. The method of claim 11 , wherein

the first plurality of structures are formed to have a first slant angle ϑ 1 ′ relative to a surface normal of the substrate during the first time period,

the first rotation angle ϕ 1 is selected by an equation ϕ 1 =cos −1 (tan(ϑ 1 ′)/tan(ϑ)), and

exposing the first plurality of structures modifies the depths of at least some of the first plurality of structures during the second period while maintaining the first slant angle ϑ 1 ′ of the first plurality of structures.

17. A method comprising:

exposing a first material disposed across a first plane on a substrate to an ion beam during a first time period to form a first plurality of structures in the first material, the ion beam directed at the first material at an ion beam angle ϑ relative to a surface normal of the substrate, wherein the substrate is positioned at a first rotation angle ϕ 1 between the ion beam and a first vector of the first plurality of structures during the first time period and the first vector is perpendicular to a direction in which the first plurality of structures extend across the first plane; and

exposing the first material disposed to the ion beam during a second time period, wherein

the substrate is positioned at a second rotation angle ϕ 2 between the ion beam and the first vector of the first plurality of structures during the second time period,

the second rotation angle ϕ 2 is the negative angle of the first rotation angle ϕ 1 ,

a duty cycle used to generate the ion beam is varied according to a first profile during the first time period, and

the duty cycle used to generate the ion beam is varied according to a second profile during the second time period.

18. A method comprising:

exposing a first material disposed across a first plane on a substrate to an ion beam during a first time period to form a first plurality of structures in the first material, the ion beam directed at the first material at an ion beam angle ϑ relative to a surface normal of the substrate, wherein

the substrate is positioned at a first rotation angle ϕ 1 between the ion beam and a first vector of the first plurality of structures during the first time period,

the first vector is perpendicular to a direction in which the first plurality of structures extend across the first plane,

the first plurality of structures are formed to have a first slant angle ϑ 1 ′ relative to a surface normal of the substrate during the first time period, and

the first rotation angle ϕ 1 is selected by an equation ϕ 1 =cos −1 (tan(ϑ 1 ′)/tan(ϑ)); and

exposing the first material to the ion beam during a second time period, wherein the substrate is positioned at a second rotation angle ϕ 2 between the ion beam and the first vector of the first plurality of structures during the second time period, wherein

the second rotation angle ϕ 2 is the negative angle of the first rotation angle ϕ 1 ,

a duty cycle used to generate the ion beam is varied according to a first profile during the first time period, and

the duty cycle used to generate the ion beam is varied according to a second profile during the second time period.

19. The method of claim 18 , wherein

a first section of the first material is exposed to the ion beam during the first time period,

a second section of the first material is exposed to the ion beam during the second time period, and

the second section includes at least a portion that was unexposed to the ion beam during the first time period.

20. The method of claim 19 , wherein the first section and the second section share a common portion.