Automated active feedback slice and view milling of magnetic head cross-sections
View Patent ↗A dual/beam FIB/SEM system and method for operating such a system are provided. A micrograph of a throat height view of a magnetic writer is obtained through iterative milling and repeated evaluation of the leading bevel angle or pole length. In some cases, the milling depth for a next iteration may be modified based on evaluation of the leading bevel angles of the current iteration.
1. A method, comprising:
obtaining a first micrograph of an air bearing surface of a magnetic head pole;
using the first micrograph, measuring the width of the pole at the air bearing surface and measuring the length of the pole at the air bearing surface;
if the width of the pole at the air bearing surface is greater than a lower width threshold and less than an upper width threshold, then performing the steps of:
determining an initial milling region proximal to an outer edge of the pole;
milling the pole within the initial milling region to form a milled surface; and
performing at least one iteration, each iteration comprising:
obtaining an iterative micrograph of the pole at the milled surface;
using the iterative micrograph, measuring a leading bevel angle and a trailing bevel angle of the pole or measuring the length of the pole at the milled surface; and
if the difference between the leading bevel angle and the trailing bevel angle is greater than a bevel angle threshold or if the difference between the length of the pole at the milled surface and the length of the pole at the air bearing surface is greater than a pole length threshold, then milling the pole by a milling amount and performing a next iteration, or else providing the iterative micrograph for metrology.
2. The method of claim 1 , the first iteration comprising:
using the iterative micrograph, measuring the length of the pole at the milled surface; and
if the difference between the length of the pole at the milled surface and the length of the pole at the air bearing surface is greater than a pole length threshold, then milling the pole by a milling amount and performing a next iteration, or else providing the iterative micrograph for metrology.
3. The method of claim 1 , each iteration after the first iteration comprising:
using the iterative micrograph, measuring a leading bevel angle and a trailing bevel angle of the pole; and
if the difference between the leading bevel angle and the trailing bevel angle is greater than a bevel angle threshold, then milling the pole by a milling amount and performing a next iteration, or else providing the iterative micrograph for metrology.
4. The method of claim 1 , wherein the milling amount varies based on the difference between the leading bevel angle and the trailing bevel angle.
5. The method of claim 4 , wherein milling amount is:
3 nm if the difference between the leading bevel angle and the trailing bevel angle is greater than 15°,
1 nm if the difference between the leading bevel angle and the trailing bevel angle is between 15° and 8°, and
0.5 nm if the difference between the leading bevel angle and the trailing bevel angle is between 8° and 4°.
6. The method of claim 1 , further comprising, if the width of the pole at the air bearing surface is less than the lower width threshold, then providing an indication that the pole is ineligible for milling.
7. The method of claim 1 , further comprising, if the width of the pole at the air bearing surface is greater than the upper width threshold, then performing the steps of:
milling the pole at a location within the width of the pole;
obtaining a micrograph of the pole at the milled location; and
providing the micrograph of the pole for metrology.
8. The method of claim 1 , wherein the lower width threshold is 55 nm and the upper width threshold is 100 nm.
9. A non-transitory computer readable medium having computer program code stored thereon, the computer program code configured to cause a system to perform the steps of:
obtaining a first micrograph of an air bearing surface of a magnetic head pole;
using the first micrograph, measuring the width of the pole at the air bearing surface and measuring the length of the pole at the air bearing surface;
if the width of the pole at the air bearing surface is greater than a lower width threshold and less than an upper width threshold, then performing the steps of:
determining an initial milling region proximal to an outer edge of the pole;
milling the pole within the initial milling region to form a milled surface; and
performing at least one iteration, each iteration comprising:
obtaining an iterative micrograph of the pole at the milled surface;
using the iterative micrograph, measuring a leading bevel angle and a trailing bevel angle of the pole or measuring the length of the pole at the milled surface; and
if the difference between the leading bevel angle and the trailing bevel angle is greater than a bevel angle threshold or if the difference between the length of the pole at the milled surface and the length of the pole at the air bearing surface is greater than a pole length threshold, then milling the pole by a milling amount and performing a next iteration, or else providing the iterative micrograph for metrology.
10. The non-transitory computer readable medium of claim 9 , the first iteration comprising:
using the iterative micrograph, measuring the length of the pole at the milled surface; and
if the difference between the length of the pole at the milled surface and the length of the pole at the air bearing surface is greater than a pole length threshold, then milling the pole by a milling amount and performing a next iteration, or else providing the iterative micrograph for metrology.
11. The non-transitory computer readable medium of claim 9 , each iteration after the first iteration comprising:
using the iterative micrograph, measuring a leading bevel angle and a trailing bevel angle of the pole; and
if the difference between the leading bevel angle and the trailing bevel angle is greater than a bevel angle threshold, then milling the pole by a milling amount and performing a next iteration, or else providing the iterative micrograph for metrology.
12. The non-transitory computer readable medium of claim 9 , wherein the milling amount varies based on the difference between the leading bevel angle and the trailing bevel angle.
13. The non-transitory computer readable medium of claim 12 , wherein milling amount is:
3 nm if the difference between the leading bevel angle and the trailing bevel angle is greater than 15°,
1 nm if the difference between the leading bevel angle and the trailing bevel angle is between 15° and 8°, and
0.5 nm if the difference between the leading bevel angle and the trailing bevel angle is between 8° and 4°.
14. The non-transitory computer readable medium of claim 9 , the steps further comprising, if the width of the pole at the air bearing surface is less than the lower width threshold, then providing an indication that the pole is ineligible for milling.
15. The non-transitory computer readable medium of claim 9 , the steps further comprising, if the width of the pole at the air bearing surface is greater than the upper width threshold, then performing the steps of:
milling the pole at a location within the width of the pole;
obtaining a micrograph of the pole at the milled location; and
providing the micrograph of the pole for metrology.
16. The non-transitory computer readable medium of claim 9 , wherein the lower width threshold is 55 nm and the upper width threshold is 100 nm.
17. A focused ion beam scanning electron microscope, comprising:
a focused ion beam milling module;
a scanning electron microscope module; and
a control system configured to perform the steps of:
obtaining a first micrograph of an air bearing surface of a magnetic head pole;
using the first micrograph, measuring the width of the pole at the air bearing surface and measuring the length of the pole at the air bearing surface;
if the width of the pole at the air bearing surface is greater than a lower width threshold and less than an upper width threshold, then performing the steps of:
determining an initial milling region proximal to an outer edge of the pole;
milling the pole within the initial milling region to form a milled surface; and
performing at least one iteration, each iteration comprising:
obtaining an iterative micrograph of the pole at the milled surface;
using the iterative micrograph, measuring a leading bevel angle and a trailing bevel angle of the pole or measuring the length of the pole at the milled surface; and
if the difference between the leading bevel angle and the trailing bevel angle is greater than a bevel angle threshold or if the difference between the length of the pole at the milled surface and the length of the pole at the air bearing surface is greater than a pole length threshold, then milling the pole by a milling amount and performing a next iteration, or else providing the iterative micrograph for metrology.
18. The microscope of claim 17 , the first iteration comprising:
using the iterative micrograph, measuring the length of the pole at the milled surface; and
if the difference between the length of the pole at the milled surface and the length of the pole at the air bearing surface is greater than a pole length threshold, then milling the pole by a milling amount and performing a next iteration, or else providing the iterative micrograph for metrology.
19. The microscope of claim 17 , each iteration after the first iteration comprising:
using the iterative micrograph, measuring a leading bevel angle and a trailing bevel angle of the pole; and
if the difference between the leading bevel angle and the trailing bevel angle is greater than a bevel angle threshold, then milling the pole by a milling amount and performing a next iteration, or else providing the iterative micrograph for metrology.
20. The microscope of 17 , wherein the milling amount varies based on the difference between the leading bevel angle and the trailing bevel angle.
21. The microscope of claim 20 , wherein milling amount is:
3 nm if the difference between the leading bevel angle and the trailing bevel angle is greater than 15°,
1 nm if the difference between the leading bevel angle and the trailing bevel angle is between 15° and 8°, and
0.5 nm if the difference between the leading bevel angle and the trailing bevel angle is between 8° and 4°.
22. The microscope of claim 17 , the steps further comprising, if the width of the pole at the air bearing surface is less than the lower width threshold, then providing an indication that the pole is ineligible for milling.
23. The microscope of claim 17 , the steps further comprising, if the width of the pole at the air bearing surface is greater than the upper width threshold, then performing the steps of:
milling the pole at a location within the width of the pole;
obtaining a micrograph of the pole at the milled location; and
providing the micrograph of the pole for metrology.
24. The microscope of claim 17 , wherein the lower width threshold is 55 nm and the upper width threshold is 100 nm.