Lapping and polishing method and apparatus for planarizing photoresist and metal microstructure layers

• US 5,718,618 A
• Filed: 02/09/1996
• Issued: 02/17/1998
• Est. Priority Date: 02/09/1996
• Status: Expired due to Term

• Current Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Original Assignee: Wisconsin Alumni Research Foundation (University of Wisconsin System)
• Inventors: Mangat, Pawitterjit S., Guckel, Henry
• Primary Examiner(s): Morgan, Eileen P.
• Application Number:
  US08/598,851
• Time in Patent Office: 739 Days
• Field of Search: 457/36, 457/37, 457/41, 457/56, 457/58, 457/285, 457/287, 457/288, 457/289, 457/444, 457/446, 156/636.1, 156/645.1, 437/228, 437/229
• US Class Current: 451/41
• CPC Class Codes: B24B 37/04 designed for working plane surfaces
• CPC Class Codes: B24B 53/017 Devices or means for dressing, cleaning or otherwise conditioning lapping tools
• CPC Class Codes: C01D 1/00 Oxides or hydroxides of sodium, potassium or alkali metals in general
• CPC Class Codes: H01L 21/31053 involving a dielectric removal step
• CPC Class Codes: H01L 21/3212 by chemical mechanical polishing [CMP]

Abstract

A method and apparatus for planarizing photoresist and/or metal microstructure layers is provided. Planarization is achieved by removing material from a workpiece by lapping using a diamond containing lapping slurry. A lapping machine is furnished with a lapping plate made of a soft metal material. The lapping plate is furnished with ridges of controlled height using a diamond conditioning ring with a specified grit size. Free diamonds in a liquid slurry are then sprayed onto the plate and embedded therein by a second conditioning ring. After the lapping plate is conditioned, the piece to be lapped is mounted on the lapping plate. A vacuum hold fixture or flat steel or glass mounting plate may be used. During lapping, additional diamond slurry is sprayed onto the lapping plate and driven into the plate by a ceramic conditioning ring. The size of diamonds in the diamond slurry are selected to control the shear forces applied to the surface being lapped and to achieve a desired surface finish. Polishing, using a cloth covered hard metal polishing plate and loose diamond slurry, may be employed after lapping to provide a smooth optical surface finish. The lapping and polishing method and apparatus of the present invention may be used for z-dimension height control, re-planarization, and surface finishing of precise single or multiple level photoresist-metal layers, or of individual preformed photoresist sheets or laminates thereof.

Claims

1. A method for lapping a workpiece including a microstructure layer formed of photoresist or metal, comprising the steps of:

(a) furnishing a lapping machine with a lapping plate having a lapping surface made of a soft metal;

(b) conditioning the lapping plate to furnish the lapping plate surface with a rough ridged surface;

(c) conditioning the lapping plate by embedding diamonds from a diamond lapping slurry into the lapping surface;

(d) mounting the workpiece to be lapped onto the lapping plate; and

(e) lapping the workpiece to remove material therefrom by rotating the lapping plate surface against the workpiece while periodically applying a diamond lapping slurry onto the lapping plate and placing a conditioning device on the lapping plate to continuously embed diamonds from the lapping slurry into the lapping surface.

2. The method of claim 1 wherein the lapping plate is made of a copper composite material.

3. The method of claim 1 wherein the surface of the lapping plate is concave at a center of the lapping plate with respect to an outer edge of the lapping plate.

4. The method of claim 1 wherein the step of conditioning the lapping plate to furnish the lapping plate surface with ridges includes the step of using a diamond embedded conditioning ring placed on the lapping plate to provide a rough lapping surface finish.

5. The method of claim 1 wherein the step of conditioning the lapping plate by embedding diamonds from a diamond slurry into the lapping plate includes the step of using a ceramic conditioning ring placed on the lapping plate ahead of a diamond slurry spray to embed the diamonds from the slurry into the lapping surface.

6. The method of claim 1 wherein the workpiece is mounted onto the lapping plate using a vacuum hold down mounting fixture having a thickness monitoring gauge, and including the additional step of monitoring an amount of material removed from the workpiece using the thickness gauge during the step of lapping the workpiece.

7. The method of claim 1 wherein the conditioning steps (b) and (c) are repeated periodically after the step of lapping the workpiece causes the ridges on the roughened polishing surface of the lapping plate to be worn down.

8. The method of claim 1 wherein the workpiece includes a substrate upon which a layer including photoresist and vertically dimensional metal microstructures which are more high than wide has been applied.

9. The method of claim 1 wherein the workpiece includes a pre-formed photoresist sheet which has been exposed in a pattern to radiation to render portions of the photoresist sheet removable using a developer.

10. The method of claim 1 including the additional steps of removing the workpiece from the lapping plate, and finish polishing the workpiece using a polishing machine having a hard polishing plate covered by a polishing cloth which is saturated with a diamond slurry.

11. The method of claim 1 wherein the diamond lapping slurry includes diamond particles having a size between approximately 0.5 and 30 micrometers in diameter.

12. A method for lapping a workpiece including a microstructure layer formed of photoresist or metal, comprising the steps of:

(a) furnishing a lapping machine with a lapping plate having a lapping surface made of a soft metal;

(b) conditioning the lapping plate to furnish the lapping plate surface with a rough ridged surface;

(c) conditioning the lapping plate by embedding diamonds from a diamond lapping slurry into the lapping surface;

(d) mounting the workpiece on a mounting plate made of a material selected from the group of materials consisting of steel and glass, mounting glass support pieces on the mounting plate around the workpiece, and placing weights on the mounting plate to provide contact pressure between the workpiece and the glass support pieces and the lapping plate surface; and

(e) lapping the workpiece to remove material therefrom by rotating the lapping plate surface against the workpiece while periodically applying a diamond lapping slurry onto the lapping plate and continuously embedding diamonds from the lapping slurry into the lapping surface.

13. The method of claim 12 comprising the additional steps of periodically measuring a thickness of the glass support pieces during the lapping step and adjusting positions of the weights on the mounting plate to level the thicknesses of the glass support pieces.

14. A method for lapping a workpiece including a microstructure layer formed of photoresist or metal, comprising the steps of:

(a) furnishing a lapping machine with a lapping plate having a lapping surface made of a soft metal;

(b) conditioning the lapping plate using a diamond embedded conditioning ring placed on the lapping surface to furnish the lapping plate surface with a rough ridged surface;

(c) conditioning the lapping plate by spraying a diamond lapping slurry onto the lapping plate surface and embedding diamonds from the lapping slurry into the surface using a ceramic conditioning ring placed on the lapping plate ahead of the diamond slurry spray;

(d) mounting a workpiece to be lapped onto the lapping plate; and

(e) lapping the workpiece to remove material therefrom by rotating the lapping plate surface against the workpiece while periodically spraying a diamond lapping slurry onto the lapping plate and continuously embedding diamonds from the lapping slurry into the lapping surface using the ceramic conditioning ring.

15. The method of claim 14 wherein the lapping plate is made of a copper composite material.

16. The method of claim 14 wherein the lapping surface of the lapping plate is concave at a center of the lapping plate with respect to an outer edge of the lapping plate.

17. The method of claim 14 wherein the workpiece is mounted onto the lapping plate using a vacuum hold down mounting fixture having a thickness monitoring gauge, and including the additional step of monitoring an amount of material removed from the workpiece using the thickness monitoring gauge during the step of lapping the workpiece.

18. The method of claim 14 wherein the workpiece is mounted onto the lapping plate by mounting the workpiece on a mounting plate made of a material selected from the group of materials consisting of steel and glass, mounting glass support pieces on the mounting plate around the workpiece, and by placing weights on the mounting plate to provide contact pressure between the workpiece and the glass support pieces and the lapping plate surface.

19. The method of claim 18 comprising the additional steps of periodically measuring a thickness of the glass support pieces during the lapping step and adjusting positions of the weights on the mounting plate to level the thicknesses of the glass support pieces.

20. The method of claim 14 wherein the conditioning steps (b) and (c) are repeated periodically after the step of lapping the workpiece causes the ridges on the roughened surface of the lapping plate to be worn down.

21. The method of claim 14 wherein the workpiece includes a substrate upon which a layer including photoresist and metal microstructures has been applied.

22. The method of claim 14 wherein the workpiece includes a pre-formed photoresist sheet which has been exposed in a pattern to radiation to render portions of the photoresist sheet removable using a developer.

23. The method of claim 14 including the additional steps of removing the workpiece from the lapping plate, and finish polishing the workpiece using a polishing machine having a hard polishing plate covered by a polishing cloth which is saturated with a diamond slurry.

24. The method of claim 14 wherein the diamond lapping slurry includes diamond particles having a size between approximately 0.5 and 30 micrometers in diameter.

25. A lapping apparatus for lapping a workpiece including a microstructure layer formed of photoresist or metal, comprising:

(a) a lapping machine with a lapping plate having a lapping surface made of a soft metal and wherein the lapping plate is conditioned such that the lapping plate surface has a rough ridged surface and such that diamonds from a diamond lapping slurry are embedded into the rough ridged surface;

(b) mounting means for mounting the workpiece to be lapped onto the lapping plate for lapping the workpiece;

(c) means for periodically applying a diamond lapping slurry onto a location on the lapping plate while lapping the workpiece to remove material therefrom; and

(d) conditioning means for continuously embedding diamonds from the lapping slurry into the lapping surface while lapping the workpiece, the conditioning means placed on the lapping plate between the location on the lapping plate where the diamond lapping slurry is applied and the workpiece.

26. The lapping apparatus of claim 25 wherein the lapping plate is made of a copper composite material.

27. The lapping apparatus of claim 25 wherein the surface of the lapping plate is concave at a center of the lapping plate with respect to an outer edge of the lapping plate.

28. The lapping apparatus of claim 25 wherein the mounting means includes a vacuum hold down mounting fixture having a thickness monitoring gauge for monitoring an amount of material removed from the workpiece during lapping of the workpiece.

29. The lapping apparatus of claim 25 wherein the conditioning means for continuously embedding diamonds from the lapping slurry into the lapping plate surface includes a ceramic conditioning ring placed on the lapping plate between a lapping slurry spray and the workpiece being lapped.

30. A lapping apparatus for lapping a workpiece including a microstructure layer formed of photoresist or metal, comprising:

(a) a lapping machine with a lapping plate having a lapping surface made of a soft metal and wherein the lapping plate is conditioned such that the lapping plate surface has a rough ridged surface and such that diamonds from a diamond lapping slurry are embedded into the rough ridged surface;

(b) mounting means for mounting the workpiece to be lapped onto the lapping plate for lapping the workpiece including a mounting plate made of a material selected from the group of materials consisting of steel and glass upon which the workpiece is mounted along with glass support pieces of equal thickness mounted on the mounting plate around the workpiece, and weights on the mounting plate to provide contact pressure between the workpiece and the glass support pieces and the lapping plate surface;

(c) means for periodically applying a diamond lapping slurry onto the lapping plate while lapping the workpiece to remove material therefrom; and

(d) means for continuously embedding diamonds from the lapping slurry into the lapping surface while lapping the workpiece.

31. A method of forming metal microstructures, comprising the steps of:

(a) applying a photoresist in a layer onto a substrate base;

(b) exposing the photoresist in a pattern to radiation to render the photoresist dissolvable in a pattern;

(c) removing the dissolvable photoresist;

(d) depositing a first layer of metal onto the substrate base into the area from which the photoresist has been removed to form a photoresist-metal layer; and

(e) planarizing the photoresist-metal layer by;

(1) mounting the substrate base on a lapping machine with a lapping plate having a lapping surface made of a soft metal wherein the lapping plate is conditioned such that the lapping plate surface has a rough ridged surface and such that diamonds from a diamond lapping slurry have been embedded into the rough ridged surface, and

(2) lapping the photoresist-metal layer to remove material therefrom by rotating the lapping plate surface against the photoresist-metal layer while periodically applying a diamond lapping slurry onto the lapping plate and placing a conditioning device on the lapping plate to continuously embed diamonds from the lapping slurry into the lapping surface.

32. The method of claim 31 wherein the substrate base is mounted on the lapping machine using a vacuum hold down mounting fixture having a thickness monitoring gauge, and including the additional step of monitoring an amount of material removed from the photoresist-metal layer using the thickness monitoring gauge during the step of lapping the photoresist-metal layer.

33. The method of claim 31 comprising the additional step of periodically reconditioning the lapping plate to have a rough ridged surface with diamonds from a lapping slurry embedded therein after the step of lapping the photoresist-metal layer causes ridges on the roughened surface of the lapping plate to be worn down.

34. The method of claim 31 including the additional steps of removing the substrate base from the lapping machine and finish polishing the photoresist-metal layer using a polishing machine having a hard polishing plate covered by a polishing cloth which is saturated with a diamond slurry.

35. The method of claim 31 wherein the diamond lapping slurry includes diamond particles having a size between approximately 0.5 and 30 micrometers in diameter.

36. The method of claim 31 comprising additionally the steps of:

(a) applying a photoresist in a second layer onto the lapped photoresist-metal layer;

(b) exposing the second layer of photoresist in a pattern to radiation to render the photoresist dissolvable in a pattern;

(c) removing the dissolvable photoresist from the second layer of photoresist; and

(d) depositing a second layer of metal onto the first layer of metal and into the area from which the photoresist from the second layer of photoresist has been removed to form a multi-level metal structure.

37. A method of forming metal microstructures, comprising the steps of:

(a) applying a photoresist in a layer onto a substrate base;

(b) exposing the photoresist in a pattern to radiation to render the photoresist dissolvable in a pattern;

(c) removing the dissolvable photoresist;

(d) depositing a first layer of metal onto the substrate base into the area from which the photoresist has been removed to form a photoresist-metal layer; and

(e) planarizing the photoresist-metal layer by;

(1) mounting the substrate base on a lapping machine by mounting the substrate base on a mounting plate, mounting glass support pieces on the mounting plate around the substrate base, and by placing weights on the mounting plate to provide contact pressure between the photoresist-metal layer and the glass support pieces and a lapping plate surface, wherein the lapping plate surface is made of a soft metal and wherein the lapping plate is conditioned such that the lapping plate surface has a rough ridged surface and such that diamonds from a diamond lapping slurry have been embedded into the rough ridged surface, and

(2) lapping the photoresist-metal layer to remove material therefrom by rotating the lapping plate surface against the photoresist-metal layer while periodically applying a diamond lapping slurry onto the lapping plate and continuously embedding diamonds from the lapping slurry into the lapping surface.

38. A method of forming microstructures, comprising the steps of:

(a) providing a first preformed sheet of photoresist material which can be exposed to radiation to affect its susceptibility to a developer;

(b) exposing the photoresist sheet in a pattern to radiation which will change its susceptibility to a developer; and

(c) removing the material of the photoresist sheet to reduce the thickness of the sheet to a desired thickness by;

(1) mounting the photoresist sheet on a lapping machine with a lapping plate having a lapping surface made of a soft metal wherein the lapping plate is conditioned such that the lapping plate surface has a rough ridged surface and such that diamonds from a diamond lapping slurry have been embedded into the rough ridged surface, and

(2) lapping the photoresist sheet to remove material therefrom by rotating the lapping plate surface against the photoresist sheet while periodically applying a diamond lapping slurry onto the lapping plate and placing a conditioning device on the lapping plate to continuously embed diamonds from the lapping slurry into the lapping surface.

39. The method of claim 38 wherein the photoresist sheet is mounted on the lapping machine using a vacuum hold down mounting fixture having a thickness monitoring gauge, and including the additional step of monitoring an amount of material removed from the photoresist sheet using the thickness monitoring gauge during the step of lapping the photoresist sheet.

40. The method of claim 38 comprising additionally the steps of:

(a) providing a second preformed sheet of photoresist material which may be exposed to radiation to affect its susceptibility to a developer;

(b) exposing the second photoresist sheet in a pattern to radiation to change its susceptibility to a developer; and

(c) adhering the second photoresist sheet to the lapped surface of the first photoresist sheet.