Near field optical scanning system employing microfabricated solid immersion lens

• US 6,441,359 B1
• Filed: 10/07/1999
• Issued: 08/27/2002
• Est. Priority Date: 10/20/1998
• Status: Expired due to Fees

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Inventors: Soh, Hyongsok T., Fletcher, Daniel A., Cozier, Kenneth B., Kino, Gordon S., Quate, Calvin F.
• Primary Examiner(s): ALLEN, STEPHONE B
• Application Number:
  US09/414,674
• Time in Patent Office: 1,055 Days
• Field of Search: 250/216, 250/234, 250/235, 250/236, 250/227.11, 250/306, 250/307, 359/664, 369/44.14, 369/44.15, 369/44.16, 369/112, 369/13, 369/14
• US Class Current: 250/216
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• CPC Class Codes: G01Q 60/22 Probes, their manufacture, or their related instrumentation, e.g. holders
• CPC Class Codes: G03F 7/70325 Resolution enhancement techniques not otherwise provided for, e.g. darkfield imaging, interfering beams, spatial frequency multiplication, nearfield lenses or solid immersion lenses
• CPC Class Codes: G03F 7/70825 Mounting of individual elements, e.g. mounts, holders or supports workpiece or mask holders G03F7/707
• CPC Class Codes: G11B 11/10534 for recording by magnetising, demagnetising or transfer of magnetisation, by radiation, e.g. for thermomagnetic recording
• CPC Class Codes: G11B 7/1374 Objective lenses optical objectives per se G02B9/00
• CPC Class Codes: G11B 7/1387 using the near-field effect
• CPC Class Codes: Y10S 977/862 Near-field probe

Abstract

A solid immersion lens integrated on a flexible support such as a cantilever or membrane is described, together with a method of forming the integrated structure.

Claims

1. A supported solid immersion lens for use in a near field optical scanning system comprising:

a thin flexible silicon or silicon nitride support, and

a silicon or silicon nitride solid immersion lens having a curved surface and integral tip integral with the flexible support for focusing incident optical radiation to a point opposite the curved surface.

2. A method of performing lithography on photoresist on the surface of a substrate comprising the steps of:

bringing an array of the supported solid immersion lenses as recited in claim 1 adjacent the surface of the substrate,

controlling the distance between the tips and substrate surface so that the surface is within the near field distance of light emerging from the tips, and

scanning the surface relative to the tips while applying light intermittently to the solid immersion lens to expose a predetermined pattern of photoresist.

3. A supported solid immersion lens as in claim 1 in which the lens tip and flexible support are silicon nitride.

4. A supported solid immersion lens as in claim 1 or 3 in which the tip is pyramidical.

5. A supported solid immersion lens as in claim 1 or 3 in which the tip is conical.

6. A supported solid immersion lens as in claim 1 or 3 in which the tip is hemispherical.

7. A supported solid immersion lens as in claims 1 or 3 in which the solid immersion lens is between 1 and 400 microns in diameter.

8. A supported solid immersion lens as in claims 1 or 3 in which the cantilever arm, the tip, and the solid immersion lens are formed by masking and etching steps.

9. A supported solid immersion lens as in claim 8 wherein the solid immersion lens is fabricated by a cavity method.

10. A supported solid immersion lens as in claim 8 wherein the solid immersion lens is fabricated by a reflow method.

11. A solid immersion lens as in claim 8 in which the tip is formed by an oxidation sharpening method.

12. A method of performing lithography on a substrate using a layer of photoresist which comprises the steps of:

providing an array of the supported solid immersion lens as recited in claim 1,

mounting on the substrate opposite the tips within the near field of light emerging from the ends of the tips,

moving the substrate and supported solid immersion lens relative to one another in first and second directions which are generally perpendicular to one another,

applying modulated light to each of said solid immersion lenses whereby to selectively illuminate pixels in selected lithographic patterns.

13. The method of claim 12 in which the light is modulated by deflecting the light into the solid immersion lens.

14. The method of claim 12 in which the distance between the tips and substrate is controlled by forming an interference pattern between light reflected from the substrate and from the pointed tip, and using the interference pattern to control the distance.

15. The method of claim 12 further including the step of controlling the distance between the tip and substrate by bending the flexible supports.

16. The method of claim 15 in which the step of controlling the distance includes the step of applying a superimposed AC/DC signal to a piezoelectric element attached to said cantilevers.

17. A near field optical scanning system for optically scanning an object comprising:

a flexible silicon or silicon nitride cantilever arm having a free end and a fixed end,

a solid immersion lens made of material having a high refractive index for focusing light onto an integral tip, said solid immersion lens and tip being formed integral with said flexible silicon or silicon nitride cantilever arm,

a light source for projecting light into said solid immersion lens whereby it emerges from the end of the tip, focused by the solid immersion lens,

means for holding the object opposite the tip within the near field of focused light emerging from the solid immersion lens, and

a scanner for moving the object relative to the tip whereby the emerging light scans the object.

18. A near field optical system as in claim 17 in which the material having a high refractive index has a refractive index greater than 2.

19. A near field optical scanning system as in claim 17 including:

means for detecting the distance of the tip from the object,

a control system connected to the detection means and providing a distance control signal, and

means for altering the distance of the tip from the object in response to the control signal.

20. A near field optical scanning system as in claim 19 in which the means for altering the distance of the tip from the object is a piezoelectric transducer.

21. A near field optical system as in claim 17 in which the tip and solid immersion lens are made of a high refractive index material.

22. A near field optical system as in claim 21 in which the high refractive index material is selected from silicon nitride, silicon, silicon oxide, strontium titanate, lead sulfide or gallium phosphide.

23. A near field optical scanning system as in claim 17 including means for deflecting the light which strikes the solid immersion lens whereby pixels are formed when the light strikes the solid immersion lens as the object is scanned.

24. The near field optical scanning system of claim 23 wherein the light is controllably deflected by a mirror.

25. An optical scanning system for scanning an object comprising:

a plurality of cantilevers formed in a wafer, each cantilever including;

a flexible cantilever arm having a free end and a fixed end,

an integral transparent tip comprising a sharp end and a solid immersion lens for focusing light into the sharp end of the tip, said tip carried at the free end of said cantilever arm with the sharp end extending perpendicular to the longitudinal axis of the cantilever arm,

an aperture at the sharp end of the tip,

a piezoelectric transducer means on said arm for positioning the free end of the arm to position the sharp end so that near field from the sharp end impinges on the object, and

means for controllably applying light to said solid immersion lens.

26. The optical scanning system as in claim 25 in which the solid immersion lens forms part of a confocal scanning microscope.

27. An optical scanning system as in claim 25 including:

means for moving the object relative to the cantilevers to scan the surface of the object with the light.

28. The optical scanning system of claim 27 in which the surface of the object is provided with a photoresist, and the light is controlled to expose a selected pattern on the photoresist.

29. The optical scanning system as in claim 27 in which the object has a magneto-optic surface and the light is controlled to magneto-optically record information on the medium.

30. A cantilever for use in an optical scanner, the cantilever comprising:

a flexible cantilever member made of silicon or silicon nitride having a free end and a fixed end,

a solid immersion lens formed integral with and near the free end of the cantilever member, the solid immersion lens having a curved surface for receiving light and a tip opposite the curved surface for receiving light transiftted through the solid immersion lens.

31. The cantilever of claim 30 wherein the solid immersion lens is fabricated from a material having a refractive index greater than about 1.5.

32. The cantilever of claim 30 wherein the solid immersion lens and the cantilever member are monolithic.

33. The cantilever of claim 30 wherein the material comprising the solid immersion lens is selected from the group consisting of silicon nitride, strontium titanate, lead sulfide, and gallium phosphide.

34. The cantilever of claim 30 wherein the material comprising the solid immersion lens is silicon nitride.

35. A method of fabricating a solid immersion lens integrated with a cantilever, the method comprising the steps of:

forming a cavity in a layer of silicon material,

applying a layer of high refractive index material on the surface of said silicon layer to fill said cavity and form a layer on the surface of said first layer,

forming a tip in said high refractive index material on a side opposite said hemispherical cavity, and

etching away said first layer to release said high refractive index material to provide a cantilever with an integral solid immersion lens.

36. The method of fabricating a solid immersion lens integrated with a cantilever, as in claim 35 including the additional step of coating said tip with a metal selected from the group consisting of aluminum, gold, silver, titanium and chrome.

37. A method of fabricating a solid immersion lens integrated with a cantilever, the method comprising the steps of:

forming a cavity in a substrate layer to define a solid immersion lens,

filling said cavity and coating the surface of said substrate with a high refractive index material,

planarizing said high refractive index material to remove a conformal depression,

forming a tip in said high refractive index material on a side of said high refractive index material opposite said cavity,

removing part of said coating of high refractive index material to define a cantilever, and

etching said silicon substrate layer to release said cantilever and the solid immersion lens defined by said cavity.

38. The method of claim 37 wherein said high refractive index lens material comprises silicon nitride.

39. The method of claim 37 which includes the additional step of coating the tip with metal.

40. The method of claim 39 wherein said metal coated tip includes an aperture formed by the steps comprising:

applying a positive voltage to said tip,

contacting said tip to an insulating layer of an insulator-metal composite at ground potential, thereby oxidizing said metal at an apex of said tip.

41. The method of claim 39 wherein said metal coated tip includes an aperture formed by the steps comprising:

conformally depositing a layer of silicon nitride over said tip,

selectively depositing a masking layer, keeping an apex of said tip free of said masking layer,

performing a timed etch to completely remove said silicon nitride and said metal at said apex of said tip, thereby creating an aperture at said apex.

42. The method of claim 39 wherein said metal coated tip includes an aperture formed by the steps comprising:

depositing a protective layer over said tip,

planarizing said protective layer to expose the apex of said tip,

etching said metal at said apex of said tip, thereby creating an aperture at said apex.

43. The method of fabricating a solid immersion lens and tip integrated with a cantilever which comprises:

forming a layer of high refractive index material,

forming a lens shaped member of material which resists etching on the surface of said layer,

etching the layer whereby to transfer the lens shape to the high refractive index material,

forming a tip-shaped member of material which resists etching on the surface of the high refractive index material opposite the transferred lens shape etching the layer whereby to form at tip, and

selectively etching the high refractive index material to define a cantilever with the lens at one end of the cantilever.