Pattern generator for avoiding stitching errors

• US 6,285,488 B1
• Filed: 08/31/2000
• Issued: 09/04/2001
• 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:
  US09/623,310
• Time in Patent Office: 369 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, 430/395, 430/396, 355/67, 355/53
• 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

The present invention relates to an apparatus for creating a pattern on a workpiece, such as a photomask, a semiconductor wafer, an electronic interconnect device, a printed circuit board, a display panel, a microoptical device or a printing plate, whereby a pattern with less visible edges is created. The apparatus comprises a source for emitting light pulses, a spatial modulator (SLM) having several pixels, a projection system, an electronic data delivery system, and a precision mechanical system moving said workpiece relative to said projection system. Further, it comprises an electronic control system coordinating the workpiece, the modulator and light sources, so that a large pattern is stitched together from the partial images created by the sequence of radiation pulses, where adjacent images being stitched together are overlapping at the common boundary, and the overlapping images have essentially the same pattern in the overlap region and a reduced light intensity.

Claims

1. An apparatus for creating a pattern on a workpiece, such as a photomask, a semiconductor wafer, an electronic interconnect device, a printed circuit board, a display panel, a microoptical device or a printing plate, whereby a pattern with less visible edges is created, comprising

a source for emitting electromagnetic radiation with energy content in the wavelength range from EUV to IR,

a spatial light modulator having multitude of modulating elements, illuminated by said radiation,

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

an electronic data delivery system accepting a digital description of the pattern to be written, extracting a sequence of partial patterns from the digital pattern description, converting said partial patterns to modulator signals, and feeding said signals to the modulator,

a precision mechanical system moving said workpiece relative to said projection system,

an electronic control system coordinating the movement of the workpiece, the feeding of the signals to the modulator and the emitted radiation, so that a large pattern is stitched together from the partial images created by the sequence of partial patterns,

where at least two adjacent images being stitched together are overlapping at the common boundary, each of said overlapping images having essentially the same pattern and a reduced exposure dose in the overlapping area.

2. An apparatus according to claim 1, with the exposure in overlapping areas being stepwise constant.

3. An apparatus according to claim 1, with the exposure in overlapping areas having a gradual transition from one image to the adjacent one.

4. An apparatus according to claim 1, with the exposure in overlapping areas being adjustable.

5. An apparatus according to claim 1, with the boundaries of overlapping areas being adjustable.

6. An apparatus according to claim 5, with the boundaries in the overlapping areas being placed to avoid edges and critical features.

7. An apparatus according to claim 1, with a data processing and delivery system that breaks the input pattern description into exposure fields, one field corresponding to one light pulse, and where adjacent fields have an overlap at the common boundary.

8. An apparatus according to claim 1, with a mask, for example a transmission mask or a mirror with a varying reflectivity across its area, in the optical path to generate the reduced exposure in the overlapping area.

9. An apparatus according to claim 8, with the mask having an open area and graded transmission along the edge.

10. An apparatus according to claim 9, with the mask being an analog spatial light modulator.

11. An apparatus according to claim 8, the mask having a clear area at the center and a sharp edge around the clear area, said mask being placed so that an unsharp image of it is created at the workpiece.

12. An apparatus according to claim 8, with the mask placed between the light source and the spatial light modulator.

13. An apparatus according to claim 8, with the mask placed between the spatial light modulator and the workpiece.

14. An apparatus according to claim 8, with the mask being a second spatial light modulator.

15. An apparatus according to claim 1, with the reduced exposure created by the same spatial light modulator that creates the pattern.

16. An apparatus according to claim 15, with the spatial light modulator having a reduced static light efficiency in those areas which will be overlapping in the pattern on the workpiece, thereby creating a reduced exposure in those areas.

17. An apparatus according to claim 15, with an additional coating on the spatial light modulator in the overlap areas that reduce the light efficiency.

18. An apparatus according to claim 15, with the spatial light modulator being an analog spatial light modulator and said reduced exposure is created by the analog function of the modulator.

19. An apparatus according to claim 18, with the reduced exposure being controlled by the data fed to the analog spatial light modulator.

20. An apparatus according to claim 18, with the reduced exposure being controlled by the data fed to the analog spatial light modulator, and said reduced exposure data is added to the pattern data during the conversion from the input description to pixel data suitable for the analog spatial light modulator.

21. An apparatus according to claim 18, with the reduced exposure being controlled by the data fed to the analog spatial light modulator, and said reduced exposure data is added to the pattern data by a special hardware unit.