Pattern generator

• US 6,747,783 B1
• Filed: 08/29/2000
• Issued: 06/08/2004
• 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
• Assistant Examiner(s): CHOI, WILLIAM C
• Application Number:
  US09/623,195
• Time in Patent Office: 1,379 Days
• Field of Search: 359/290, 359/291, 359/295, 359/298, 359/223, 250/492.2, 250/491.1, 250/396.R, 430/5, 430/394-396, 430/22, 430/30, 430/311, 355/53, 355/67
• US Class Current: 359/290
• 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 is provided 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 and a spatial modulator (SLM) having a multitude of modulating elements (pixels). It further includes an electronic data processing and delivery system feeding drive signals to the modulator, a precision mechanical system for moving said workpiece and an electronic control system coordinating the movement of the workpiece, the feeding of the signals to the modulator and the intensity of the radiation, so that said pattern is stitched together from the partial images created by the sequence of partial patterns. The drive signals can set a modulating element to a number of states larger than two.

Claims

1. An apparatus for creating a pattern on a workpiece sensitive to light radiation, 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 being 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 at least one of said workpiece and said 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.

2. The apparatus according to claim 1, where a modulating element modulates at least one of the following properties of the radiation:

intensity

phase

complex amplitude

direction

polarization

wavefront flatness

frequency

where the modulation impressed on the radiation field has at least three different states.

3. The apparatus according to claim 2, having a filter selective to the state of the radiation, thereby translating the modulation across the surface of the spatial modulator to an intensity image at the workpiece.

4. The apparatus according to claim 2, where the modulation impressed on the radiation field has at least four different states.

5. The apparatus according to claim 1, where a compensating linearization function is used in the conversion from the input pattern description to the modulator voltages to correct for a non-linear response from the modulator voltages to the exposure on the workpiece.

6. The apparatus according to claim 5, where the linearization function is based on a theoretical simulation.

7. The apparatus according to claim 5, where the linearization function is based on an empirical characterization of the response.

8. The apparatus according to claim 5, where said response is the physical or chemical result of the exposure of a surface element, or the removal of material mass per surface area by an ablation process.

9. The apparatus according to claim 8, wherein said response is the light absorption of a developed silver halide emulsion, or the removal of material mass per surface area by an ablation process.

10. The apparatus according to claim 5, where the desired responses are computed as digital values and the linearization function is stored in a look-up table generating new corrected digital values used for generation of the modulator drive voltages.

11. The apparatus according to claim 10, where the modulator voltages are created by digital analog converters.

12. The apparatus according to claim 5, where the desired responses are computed as digital values and the values are used to select for each modulating element one of several independently generated voltages, and where said voltages are set to contain the linearization function.

13. The apparatus according to claim 1, where at least two modulator voltage signals are fed to a single modulator element and the modulator element is responsive to the combination of the signals, thereby being driven to a larger number of states than the number of possible voltage values in each signal.

14. The apparatus according to claim 13, wherein there are four binary signals creating sixteen different states of the modulating element.

15. The apparatus according to claim 1, with a look-up table with corrections for different response between modulator elements.

16. The apparatus according to claim 15, where the look-up table is generated during a calibration procedure where the response function of at least two different modulator elements are measured.

17. The apparatus according to claim 15, where said look-up table stores at least one of the following types of data for a modulating element:

An offset voltage

A sensitivity factor

A polynomial response function.

18. The apparatus according to claim 15, where the correction of a modulating element is applied as a digital operation on a digital representation of the desired state of the modulator element.

19. The apparatus according to claim 15, where the correction of a modulating element is applied by an analog operation on the analog drive signal.

20. The apparatus according to claim 1, where the spatial modulator is a two-dimensional array of modulating elements with time-multiplexed loading of the values to the modulating elements and storage of the loaded value at each element.

21. The apparatus according to claim 1, where the modulator is built on a matrix-addressed active circuit.

22. The apparatus according to claim 1, where the modulator is built on top of a semiconductor chip.

23. The apparatus according to claim 1, where the modulator contains a liquid crystal.

24. The apparatus according to claim 1, where the modulator has a viscoelastic layer.

25. The apparatus according to claim 1, where the modulator has an array of micromechanical elements.

26. The apparatus according to claim 25, wherein the micromechanical elements are micromirrors.

27. The apparatus according to claim 26, wherein the micromirrors are pyramidal micromirrors.

28. The apparatus according to claim 1, where the modulator is reflective.

29. The apparatus according to claim 1, where the modulator is transmissive.

30. The apparatus according to claim 1, where the input pattern is decomposed into a number of exposure fields, and said exposure fields are exposed at different positions on the workpiece, thereby stitching together the complete pattern from said exposure fields.

31. The apparatus according to claim 30, where the stage and projection system are adapted to making strokes of continuous travel relative to each other, and the electronic control system coordinates the motion, the loading of the modulator drive signals and the illumination, in such a way that at least two exposure fields are exposed during an uninterrupted stroke.

32. The apparatus according to claim 31, wherein at least ten exposure fields are exposed during an uninterrupted stroke.

33. The apparatus according to claim 30, where at least one of the stage and the optical system is adapted to produce a microlithographic pattern with at least one of features smaller than 30 μ

m and the placement and size accuracy better than 3 μ

m (3 sigma).

34. The apparatus according to claim 1, further comprising a timing unit controlling the timing of the emission of radiation from the light source.

35. The apparatus according to claim 34, whereby the timing unit predicts the time delay for a control signal to the light source emission according to the previous measurements, and compensates for the same.

36. The apparatus according to claim 1, whereby the light source is a laser.

37. The apparatus according to claim 36, wherein the laser is an excimer laser.

38. The apparatus according to claim 1, where the illumination of at least one modulating element of the SLM is pulsed.

39. The apparatus according to claim 38, where the pulse length (full width half maximum or equivalent) of the illumination of a modulating element of the SLM is shorter than the time to travel a distance corresponding to three pixels projected on the workpiece.

40. The apparatus according to claim 38, wherein the illumination of the entire SLM is pulsed.

41. The apparatus according to claim 1, where the illumination of at least one modulating element of the SLM is continuous and scanned.

42. The apparatus according to claim 41, wherein the illumination of the entire SLM is continuous and scanned.

43. The apparatus according to claim 1, where the digital description of the pattern is in a symbolic format.

44. The apparatus according to claim 43, wherein the symbolic format is a vector or algorithmic format.

45. The apparatus according to claim 1, where the pattern is formed in photoresist, photopolymer or photographic emulsion.

46. The apparatus according to claim 1, where the pattern is formed by ablation, a photorefractive effect, a photochemical alteration of a component of the workplace or by a thermal process.

47. The apparatus according to claim 1, where the electronic data processing system has an array of parallel processors for real-time pattern, conversion.

48. The apparatus according to claim 1, where the drive signals and the modulating elements are adapted to create a number of modulation states larger than three.

49. The apparatus according to claim 1, wherein the workpiece sensitive to light radiation is a photomask, a display panel or a microoptical device.