Methods for forming backside alignment markers useable in semiconductor lithography
Disclosed herein are methods for forming photolithography alignment markers on the back side of a substrate, such as a crystalline silicon substrate used in the manufacture of semiconductor integrated circuits. According to the disclosed techniques, laser radiation is used to remove the material (e.g., silicon) from the back side of a substrate to form the back side alignment markers at specified areas. Such removal can comprise the use of laser ablation or laser-assisted etching. The substrate is placed on a motor-controlled substrate holding mechanism in a laser removal chamber, and the areas are automatically moved underneath the laser radiation to removal the material. The substrate holding mechanism can comprise a standard chuck (in which case use of a protective layer on the front side of the substrate is preferred), or a substrate clamping assembly which suspends the substrate at its edges (in which case the protective layer is not necessary). Alternatively, a stencil having holes corresponding to the shape of the back side alignment markers can be placed over the back side of the substrate to mitigate the need to move the substrate to the areas with precision.
1. A method for forming and using an alignment marker on a substrate, comprising:
removing material on a back side of the substrate using radiation to form at least one alignment marker on the back side of the substrate;
forming a photoresist over a front side of the substrate; and
assessing the position of the at least one alignment marker to pattern the photoresist in alignment with the alignment marker.
2. The method of claim 1 , wherein the radiation comprises radiation from a laser.
3. The method of claim 2 , wherein the laser radiation removes the material by ablation.
4. The method of claim 2 , wherein removing the material further comprises exposing the material to an etchant gas, and wherein the laser radiation interacts with the etchant gas to remove the material.
5. The method of claim 1 , wherein assessing the position of the alignment marker comprises an optical assessment.
6. The method of claim 1 , further comprising removing the patterned photoresist and etching a circuit layer underlying the patterned photoresist using non-patterned photoresist as a mask.
7. The method of claim 1 , wherein, when removing material on the back side of the substrate, the front side of the substrate is unprotected.
8. The method of claim 1 , wherein, when removing material on the back side of the substrate, the front side of the substrate is suspended front side down such that the substrate does not substantially come into contact with a work surface.
9. The method of claim 1 , wherein patterning the photoresist comprises aligning the assessed position of the alignment marker with a mask.
10. The method of claim 1 , wherein the material comprises silicon.
11. The method of claim 1 , wherein removing the material comprises masking the radiation with a stencil offset from the substrate by a distance.
12. A method for forming and using an alignment marker on a substrate, comprising:
removing material on a back side of the substrate using laser radiation to form at least one alignment marker on the back side of the substrate;
forming a photoresist over a front side of the substrate; and
assessing the position of the at least one alignment marker to pattern the photoresist in alignment with the alignment marker.
13. The method of claim 12 , wherein the laser radiation removes the material by ablation.
14. The method of claim 12 , wherein removing the material further comprises exposing the material to an etchant gas, and wherein the laser radiation interacts with the etchant gas to remove the material.
15. The method of claim 12 , wherein assessing the position of the alignment marker comprises an optical assessment.
16. The method of claim 12 , wherein the material is removed on the back side of the substrate without using a photoresist.
17. The method of claim 12 , wherein patterning the photoresist comprises aligning the assessed position of the alignment marker with a mask.
18. The method of claim 12 , wherein, when removing material on the back side of the substrate, the front side of the substrate is unprotected.
19. The method of claim 12 , wherein, when removing material on the back side of the substrate, the front side of the substrate is suspended front side down such that the substrate does not substantially come into contact with a work surface.
20. The method of claim 12 , wherein the material comprises silicon.
21. The method of claim 12 , wherein removing the material comprises use of a stencil offset from the substrate by a distance.
22. A method for forming and using an alignment marker on a substrate, comprising:
removing material on a back side of the substrate using laser radiation to form at least one alignment marker on the back side of the substrate, wherein removing the material further comprises exposing the material to an etchant gas, and wherein the laser radiation interacts with the etchant gas to remove the material; and
using the at least one alignment marker to align the substrate during formation of integrated circuitry on a front side of the substrate.
23. The method of claim 22 , wherein, when removing material on the back side of the substrate, the front side of the substrate is unprotected.
24. The method of claim 22 , wherein, when removing material on the back side of the substrate, the front side of the substrate is suspended front side down such that the substrate does not substantially come into contact with a work surface.
25. The method of claim 22 , wherein the material comprises silicon.
26. The method of claim 22 , wherein removing the material comprises masking the radiation with a stencil offset from the substrate by a distance.
27. A method for forming and using an alignment marker on a substrate, comprising:
removing material on a back side of the substrate using a laser and without using a photoresist to form at least one alignment marker on the back side of the substrate; and
using the alignment marker to align the substrate during formation of integrated circuitry on a front side of the substrate.
28. The method of claim 27 , wherein the laser radiation removes the material by ablation.
29. The method of claim 27 , wherein removing the material further comprises exposing the material to an etchant gas, and wherein the laser radiation interacts with the etchant gas to remove the material.
30. The method of claim 27 , wherein, when removing material on the back side of the substrate, the front side of the substrate is unprotected.
31. The method of claim 27 , wherein, when removing material on the back side of the substrate, the front side of the substrate is suspended front side down such that the substrate does not substantially come into contact with a work surface.
32. The method of claim 27 , wherein the material comprises silicon.
33. The method of claim 27 , wherein removing the material comprises use of a stencil offset from the substrate by a distance.
34. A method for forming and using an alignment marker on a substrate, comprising:
removing material on a back side of the substrate using radiation to form at least one alignment marker on the back side of the substrate;
forming a photoresist over a circuit layer on a front side of the substrate;
using the at least one alignment marker to align the substrate with a mask;
patterning the photoresist using the mask;
removing the patterned photoresist to expose portions of the circuit layer; and etching the exposed portions of the circuit layer.
35. The method of claim 34 , wherein the radiation comprises radiation from a laser.
36. The method of claim 35 , wherein the laser radiation removes the material by ablation.
37. The method of claim 35 , wherein removing the material further comprises exposing the material to an etchant gas, and wherein the laser radiation interacts with the etchant gas to remove the material.
38. The method of claim 34 , wherein, when removing material on the back side of the substrate, the front side of the substrate is unprotected.
39. The method of claim 34 , wherein, when removing material on the back side of the substrate, the front side of the substrate is suspended front side down such that the substrate does not substantially come into contact with a work surface.
40. The method of claim 34 , wherein the material comprises silicon.
41. The method of claim 34 , wherein removing the material comprises masking the radiation with a stencil offset from the substrate by a distance.
42. A method for forming and using an alignment marker on a substrate, comprising:
removing material on a back side of the substrate without using a photoresist to form at least one alignment marker on the back side of the substrate;
forming a photoresist over a circuit layer on a front side of the substrate;
using the at least one alignment marker to align the substrate with a mask;
patterning the photoresist using the mask;
removing the patterned photoresist to expose portions of the circuit layer; and
etching the exposed portions of the circuit layer.
43. The method of claim 42 , wherein the removing the material comprises the use of laser radiation.
44. The method of claim 43 , wherein the laser radiation removes the material by ablation.
45. The method of claim 43 , wherein removing the material further comprises exposing the material to an etchant gas, and wherein the laser radiation interacts with the etchant gas to remove the material.
46. The method of claim 42 , wherein, when removing material on the back side of the substrate, the front side of the substrate is unprotected.
47. The method of claim 42 , wherein, when removing material on the back side of the substrate, the front side of the substrate is suspended front side down such that the substrate does not substantially come into contact with a work surface.
48. The method of claim 42 , wherein the material comprises silicon.
49. The method of claim 42 , wherein removing the material comprises use of a stencil offset from the substrate by a distance.
50. A method for forming and using an alignment marker on a substrate, comprising:
removing material on a back side of the substrate without using a photoresist to form at least one alignment marker on the back side of the substrate;
forming a photoresist over a front side of the substrate;
assessing the position of the at least one alignment marker to pattern the photoresist in alignment with the alignment marker; and
removing the patterned photoresist and etching a circuit layer underlying the patterned photoresist using non-patterned photoresist as a mask.
51. The method of claim 50 , wherein the removing the material comprises the use of laser radiation.
52. The method of claim 51 , wherein the laser radiation removes the material by ablation.
53. The method of claim 51 , wherein removing the material further comprises exposing the material to an etchant gas, and wherein the laser radiation interacts with the etchant gas to remove the material.
54. The method of claim 50 , wherein assessing the position of the alignment marker comprises an optical assessment.
55. The method of claim 50 , wherein patterning the photoresist comprises aligning the assessed position of the alignment marker with a mask.
56. The method of claim 50 , wherein, when removing material on the back side of the substrate, the front side of the substrate is unprotected.
57. The method of claim 50 , wherein, when removing material on the back side of the substrate, the front side of the substrate is suspended front side down such that the substrate does not substantially come into contact with a work surface.
58. The method of claim 50 , wherein the material comprises silicon.
59. The method of claim 50 , wherein removing the material comprises use of a stencil offset from the substrate by a distance.
60. A method for forming and using an alignment marker on a substrate, comprising:
removing material on a back side of the substrate using radiation to form at least one alignment marker on the back side of the substrate, wherein, when removing material on the back side of the substrate, a front side of the substrate is unprotected; and
using the at least one alignment marker to align the substrate during formation of integrated circuitry on the front side of the substrate.
61. The method of claim 60 , wherein the radiation comprises radiation from a laser.
62. The method of claim 61 , wherein the laser radiation removes the material by ablation.
63. The method of claim 61 , wherein removing the material further comprises exposing the material to an etchant gas, and wherein the laser radiation interacts with the etchant gas to remove the material.
64. The method of claim 60 , wherein, when removing material on the back side of the substrate, the front side of the substrate is suspended front side down such that the substrate does not substantially come into contact with a work surface.
65. A method for forming and using an alignment marker on a substrate, comprising:
removing material on a back side of the substrate using radiation to form at least one alignment marker on the back side of the substrate, wherein, when removing material on the back side of the substrate, a front side of the substrate is suspended front side down such that the substrate does not substantially come into contact with a work surface; and
using the at least one alignment marker to align the substrate during formation of integrated circuitry on the front side of the substrate.
66. The method of claim 65 , wherein the radiation comprises radiation from a laser.
67. The method of claim 66 , wherein the laser radiation removes the material by ablation.
68. The method of claim 66 , wherein removing the material further comprises exposing the material to an etchant gas, and wherein the laser radiation interacts with the etchant gas to remove the material.
69. A method for forming and using an alignment marker on a substrate, comprising:
removing material on a back side of the substrate using radiation to form at least one alignment marker on the back side of the substrate, wherein removing the material comprises masking the radiation with a stencil offset from the substrate by a distance; and
using the at least one alignment marker to align the substrate during formation of integrated circuitry on a front side of the substrate.