Modulator design for pattern generator

• US 6,504,644 B1
• Filed: 08/31/2000
• Issued: 01/07/2003
• Est. Priority Date: 03/02/1998
• Status: Expired due to Term

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: Micronic Laser Systems AB (Mycronic AB)
• Inventors: Sandstrom, Torbjorn
• Primary Examiner(s): Ben, Loha
• Application Number:
  US09/623,311
• Time in Patent Office: 859 Days
• Field of Search: 359/298, 359/290, 359/291, 359/318, 359/392, 359/285, 359/281, 250/492.1, 250/492.2, 430/5, 430/394, 430/395, 430/30, 430/22, 355/53, 355/67, 345/84, 348/760, 348/771
• US Class Current: 359/291
• CPC Class Codes: B23K 26/032 using optical means
• CPC Class Codes: B23K 26/064 by means of optical elements, e.g. lenses, mirrors or prisms
• CPC Class Codes: B23K 26/0648 comprising lenses
• CPC Class Codes: B41J 2/465 using masks, e.g. light-switching masks
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 27/0043 in projection exposure systems, e.g. microlithographic systems
• CPC Class Codes: G02B 27/4205 having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant
• CPC Class Codes: G03F 7/2022 Multi-step exposure, e.g. hybrid; backside exposure; blanket exposure, e.g. for image reversal; edge exposure, e.g. for edge bead removal; corrective exposure
• CPC Class Codes: G03F 7/70041 by pulsed sources, e.g. multiplexing, pulse duration, interval control or intensity control
• CPC Class Codes: G03F 7/70283 Mask effects on the imaging process
• CPC Class Codes: G03F 7/70291 Addressable masks, e.g. spatial light modulators [SLMs], digital micro-mirror devices [DMDs] or liquid crystal display [LCD] patterning devices
• CPC Class Codes: G03F 7/704 Scanned exposure beam, e.g. raster-, rotary- and vector scanning mask projection exposure involving relative movement of patterned beam and workpiece during imaging G03F7/70358
• CPC Class Codes: G03F 7/70475 Stitching, i.e. connecting image fields to produce a device field, the field occupied by a device such as a memory chip, processor chip, CCD, flat panel display
• CPC Class Codes: G03F 7/70725 control
• CPC Class Codes: G09G 3/2007 Display of intermediate tones
• CPC Class Codes: G09G 3/346 based on modulation of the reflection angle, e.g. micromirrors micromirrors devices per se G02B26/0833
• CPC Class Codes: H04N 1/195 the array comprising a two-dimensional array or a combination of two-dimensional arrays
• CPC Class Codes: H04N 2201/0414 Scanning an image in a series of overlapping zones
• CPC Class Codes: H04N 5/7458 the modulator being an array of deformable mirrors, e.g. digital micromirror device [DMD]

Abstract

An apparatus for creating a pattern on a workpiece sensitive to radiation, such as a photomask, a display panel or a microoptical device. The apparatus includes a radiation source, a spatial modulator (SLM) having a multitude of modulating elements (pixels), a projection system, an electronic data processing and delivery system controlling said modulator, a precision mechanical system for moving said workpiece and an electronic control system. Specifically, the drive signals can set the pixels in a number of states larger than two, and intermediate modulation states are used for pixels along edges of pattern features. The design of the modulating elements and the exposure method create, for differently placed and/or differently oriented edges in the pattern, a symmetry in the aperture stop of the projection system.

Claims

1. An apparatus for creating a pattern on a workpiece sensitive to light radiation, such as a photomask, a display panel or a microoptical device, comprising:

a source for emitting light in the wavelength range from EUV to IR,

a spatial light modulator (SLM) having a multitude of modulating elements (pixels), adapted to be illuminated by said radiation,

a projection system creating an image of the modulator on the workpiece,

an electronic data processing and delivery system receiving a digital description of the pattern to be written, converting said pattern to modulator signals, and feeding said signals to the modulator,

a precision mechanical system for positioning said workpiece and/or projection system relative to each other, an electronic control system controlling the position of the workpiece, the feeding of the signals to the modulator and the intensity of the radiation, so that said pattern is printed on the workpiece,

where the drive signals and the modulating elements are adapted to create a number of modulation states larger than two, where intermediate modulation states are used for pixels along edges of pattern features, and the design of the modulating elements and the exposure method are adapted to create, for differently placed and/or differently oriented edges in the pattern, a symmetry in an aperture stop of the projection system.

2. An apparatus according to claim 1, where asymmetry between edges placed at different positions relative to the pixel grid is reduced by overlaying at least two images with different placement of the pixel grid relative to the pattern.

3. An apparatus according to claim 1, where the SLM is a deflection type SLM and the symmetry relates to the intensity distribution.

4. An apparatus according to claim 3, where the modulating elements are deflecting the light symmetrically relative to the center of the aperture stop.

5. An apparatus according to claim 3, where the modulating elements deflecting the light asymmetrically relative to the center of the aperture stop, at least two exposures having opposite directions of deflection for a pixel in the image are overlayed.

6. An apparatus according to claim 3, where the modulating elements are deflecting the light asymmetrically relative to the center of the aperture stop, and deflecting the light from a modulating element at an edge of a feature in the pattern is controlled to be in a direction having a fixed geometrical relation to the orientation of the edge, e.g. in a direction perpendicular to the edge and toward the interior of the feature.

7. An apparatus according to claim 1, where the SLM is a diffraction type SLM.

8. An apparatus according to claim 7, where the differences between differently placed and/or oriented edges are reduced by overlaying at least two exposures using complementary states of the modulator with opposite phase maps.

9. An apparatus according to claim 7, where the modulating elements have essentially constant average phase for different modulation states.

10. An apparatus according to claim 9, where a modulating element gives an average complex amplitude essentially limited to real values, said real values being in the range −

1 to 1.

11. An apparatus according to claim 9, where a modulating element gives an average complex amplitude essentially limited to real values, said real values being most preferably in the range −

0.5 to 0.

12. An apparatus according to claim 1, where a modulating element is a reflective micromirror with at least one pivoting surface elements.

13. An apparatus according to claim 1 where a modulating element is a reflective micromirror with at least one deforming surface element having an essentially constant phase for varying deformation.

14. An apparatus according to claim 1, where the pattern consists of areas with an essentially uniform exposure dose and a background having a different dose, and where at least one modulating element is driven to a state where its complex amplitude is negative relative to the state corresponding to the highest of two uniform exposure doses.

15. An apparatus according to claim 1 where adjacent modulating element are driven to different states selected to provide in the image a complex amplitude essentially limited to being real.

16. An apparatus according to claim 1, where a modulating element has an N-fold rotational symmetry, N being at least 2.

17. An apparatus according to claim 1, where a modulating element is rotationally asymmetric and rotational symmetry is created in the pattern by multiple exposure with different modulation states.

18. An apparatus according to claim 1 where the light intensity in the pupil plane of the projection system is asymmetrical for intermediate states of modulation, and a sequence of overlayed exposures gives an average symmetrical distribution for said intermediate states.

19. An apparatus according to claim 1, adapted to write patterns with areas with essentially two uniform exposure doses, and where the state of the modulating elements corresponding to the smallest dose has a complex amplitude that is negative relative to the state corresponding to the highest exposure dose.

20. An apparatus according to claim 1 adapted to write patterns with pattern with areas with essentially two uniform exposures, and where near the boundaries between the areas at least one modulating element is driven to a state corresponding to an exposure outside the range between the two uniform exposures.

21. An apparatus according to claim 1 where for two exposed areas in the pattern separated by a narrow unexposed line the SLM is driven to create opposite phase on the sides of the line.

22. An apparatus according to claim 1, where a modulating element is a reflective micromirror with at least four pivoting surface elements.

23. An apparatus according to claim 1, where the modulation element has an N-fold rotational symmetry, N being preferably at least 4.

24. An apparatus for creating a pattern on a workpiece sensitive to light radiation, such as a photomask a display panel or a microoptical device, comprising:

a source for emitting light in the wavelength range from EUV to IR,

a spatial light modulator (SLM) having a multitude of modulating elements (pixels), adapted to be illuminated by said radiation,

a projection system creating an image of the modulator on the workpiece, an electronic data processing and delivery system receiving a digital description of the pattern to be written, converting said pattern to modulator signals, and feeding said signals to the modulator,

a precision mechanical system for positioning said workpiece and/or projection system relative to each other, an electronic control system controlling the position of the workpiece, the feeding of the signals to the modulator and the intensity of the radiation, so that said pattern is printed on the workpiece,

where the drive signals and the modulating elements are adapted to create a number of modulation states preferably larger than three, where intermediate modulation states are used for pixels along edges of pattern features, and the design of the modulating elements and the exposure method are adapted to create, for differently placed and/or differently oriented edges in the pattern, a symmetry in an aperture stop of the projection system.

25. An apparatus according to claim 24, where asymmetry between edges placed at different positions relative to the pixel grid is reduced by overlaying at least two images with different placement of the pixel grid relative to the pattern.

26. An apparatus according to claim 24, where the SLM is a deflection type SLM and the symmetry relates to the intensity distribution.

27. An apparatus according to claim 26, where the modulating elements are deflecting the light symmetrically relative to the center of the aperture stop.

28. An apparatus according to claim 26, where the modulating elements deflecting the light asymmetrically relative to the center of the aperture stop, at least two exposures having opposite directions of deflection for a pixel in the image are overlayed.

29. An apparatus according to claim 26, where the modulating elements are deflecting the light asymmetrically relative to the center of the aperture stop, and deflecting the light from a modulating element at an edge of a feature in the pattern is controlled to be in a direction having a fixed geometrical relation to the orientation of the edge, e.g. in a direction perpendicular to the edge and toward the interior of the feature.

30. An apparatus according to claims 24, where the SLM is a diffraction type SLM.

31. An apparatus according to claim 30, where the differences between differently placed and/or oriented edges are reduced by overlaying at least two exposures using complementary states of the modulator with opposite phase maps.

32. An apparatus according to claim 30, where the modulating elements have essentially constant average phase for different modulation states.

33. An apparatus according to claim 32, where a modulating element gives an average complex amplitude essentially limited to real values, said real values being in the range −

1 to 1.

34. An apparatus according to claim 32, where a modulating element gives an average complex amplitude essentially limited to real values, said real values being most preferably in the range −

0.5 to 0.

35. An apparatus according to claim 24, where a modulating element is a reflective micromirror with at least one pivoting surface element.

36. An apparatus according to claim 24, where a modulating element is a reflective micromirror with at least one deforming surface element having an essentially constant phase for varying deformation.

37. An apparatus according to claim 24, where the pattern consists of areas with an essentially uniform exposure dose and a background having a different dose, and where at least one modulating element is driven to a state where its complex amplitude is negative relative to the state corresponding to the highest of two uniform exposure doses.

38. An apparatus according to claim 24, where adjacent modulating element, are driven to different states selected to provide in the image a complex amplitude essentially limited to being real.

39. An apparatus according to claim 24, where a modulating element has an N-fold rotational symmetry, N being at least 2.

40. An apparatus according to claim 24, where a modulating element is rotationally asymmetric and rotational symmetry is created in the pattern by multiple exposure with different modulation states.

41. An apparatus according to claim 24, where the light intensity in the pupil plane of the projection system is asymmetrical for intermediate states of modulation, and a sequence of overlayed exposures gives an average symmetrical distribution for said intermediate states.

42. An apparatus according to claim 24, adapted to write patterns with areas with essentially two uniform exposure doses, and where the state of the modulating elements corresponding to the smallest dose has a complex amplitude that is negative relative to the state corresponding to the highest exposure dose.

43. An apparatus according to claim 24, adapted to write patterns with areas with essentially two uniform exposures, and where near the boundaries between the areas at least one modulator element is driven to a state corresponding to an exposure outside the range between the two uniform exposures.

44. An apparatus according to claim 24, where for two exposed areas in the pattern separated by a narrow unexposed line the SLM is driven to create opposite phase on the sides of the line.

45. An apparatus according to claim 24, where a modulating element is a reflective micromirror with at least four pivoting surface elements.

46. An apparatus according to claim 24, where a modulating element has an N-fold rotational symmetry, N being preferably at least 4.