Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-11-28
2003-09-09
Mack, Ricky (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C435S005000
Reexamination Certificate
active
06618185
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to techniques for obtaining improved images by compensation methods. In particular it relates to a method for compensating defective pixels in a Spatial Light Modulator (SLM), used in optical lithography. It also relates to an apparatus for patterning a work piece comprising such a method and a method for detecting defective pixels.
DESCRIPTION OF THE BACKGROUND ART
Lithographic production is useful for integrated circuits, masks, reticles, flat panel displays, micro-mechanical or micro-optical devices and packaging devices, e.g. lead frames and MCM's. Lithographic production may involve an optical system to image a master pattern from a computer-controlled reticle onto a workpiece. A suitable workpiece may comprise a layer sensitive to electromagnetic radiation, for example visible or non-visible light. An example of such a system is described in WO 9945435 with the same inventor and applicant as the present invention.
Said computer controlled reticle may be a Spatial Light Modulator (SLM) comprising a one or two dimensional array or matrix of reflective movable micro mirrors, a one or two dimensional array or matrix of transmissive LCD crystals, or other similar programmable one or two dimensional arrays based on gratings effects, interference effects or mechanical elements (e.g., shutters).
In general, these computer controlled reticles may be used for the formation of images in a variety of ways. These reticles, such as an SLM, include many modulating elements or pixels, in some instances million or more pixels. For example a problem with Spatial Light Modulators is that one or a plurality of pixels in a given SLM may be defective, i.e. they may not respond to a control signal as intended.
These defective pixels in a computer controlled reticle may limiting the resolution and accuracy available for their use in optical imaging; e.g., the production of printed patterns on a workpiece may be limited as to its line widths and accuracy.
Therefore, there is a need in the art for a method, which effectively and precisely finds and compensates for defective pixels in the SLM.
SUMMARY OF THE INVENTION
In view of the foregoing background, the compensation for defective pixels in the SLM, such as for example a mirror elements stuck in a specific position, is useful to form images having sub micron line widths with tolerances approaching 5 nm.
Accordingly, it is an object of the present invention to improve the images formed using spatial light modulators by providing an improved method for the compensation of defective pixels.
In a first embodiment, the invention provides a method for compensating the impact of at least one defective pixel with a known position in a spatial light modulator (SLM) when creating a pattern of the SLM on a work piece covered with a layer sensitive to electromagnetic radiation. Said method comprising the actions of providing a source for emitting electromagnetic radiation, illuminating by said radiation said SLM having a plurality of modulating elements (pixels), projecting in a writing pass an image of said modulator on said work piece, and performing a compensation for defective pixels in at least one other writing pass.
In another embodiment of the invention said electromagnetic radiation is a pulsed laser source.
In another embodiment of the invention a single defective pixel in one writing pass is compensated with a single compensating pixel in another writing pass.
In another embodiment of the invention a single defective pixel in one writing pass is compensated with a plurality of compensating pixel in another writing pass.
In another embodiment of the invention said SLM is illuminated by a radiation dose in the different writing passes.
In another embodiment of the invention said SLM is illuminated by different radiation intensities in the different writing passes.
In another embodiment of the invention said SLM is a transmissive Spatial Light Modulator.
In another embodiment of the invention said SLM is a reflective Spatial Light Modulator.
In another embodiment of the invention the pixels in said SLM is operated in an analog mainer.
The invention relates also to a method for compensating the impact of at least one defective pixel with a known position in a spatial light modulator (SLM) when creating a pattern of the SLM on a work piece covered with a layer sensitive to electromagnetic radiation. Said method comprising the actions of, providing a source for emitting electromagnetic radiation, illuminating by said radiation said SLM having a plurality of modulating elements (pixels), projecting an image of said SLM on the detector arrangement for measuring a dose of radiation, and performing a compensation of said defective pixel by at least one of the most adjacent pixels in the SLM.
In another embodiment of the invention said compensation is performed by assigning said at least one of the most adjacent pixels by a value given by subtraction of an intended pixel value by a actual pixel value divided by the number of most adjacent pixels used for compensation.
The invention relates also to a method for compensating the impact of at least one defective pixel in a spatial light modulator (SLM) when creating a pattern of the SLM on a work piece covered at least partially with a layer sensitive to electromagnetic radiation. Said method comprising the actions of, setting the pixels in said SLM in a predetermined state, illuminating by a radiation source said SLM, projecting the image of the SLM onto the detector arrangement that measures dose of the SLM pixels, identifying defective pixels, and performing a compensation for said defective pixels in at least one writing pass.
The invention relates also to a method for compensating the impact of at least one defective pixel with a known position in a spatial light modulator (SLM) when creating a pattern of the SLM on a work piece covered with a layer sensitive to electromagnetic radiation. Said method comprising the actions of, providing a source for emitting electromagnetic radiation, illuminating by said radiation said SLM having a plurality of modulating elements (pixels), projecting in a first writing pass an image of said modulator on said work piece using a first set of pixels in said SLM, performing a pre compensation for defective pixels in at least one subsequent writing pass in at least one prior writing pass, and projecting in at least a second writing pass said image of said modulator on said work piece using at least a second set of pixels in said SLM.
In another embodiment of the invention, said method further comprising the action of, performing a post compensation for defective pixels in at least one prior writing step in at least one subsequent writing pass.
In another embodiment of the invention a post compensation for defective pixels in at least one prior writing step in at least one subsequent writing pass is performed instead of said pre compensation.
In another embodiment of the invention said electromagnetic radiation is a pulsed laser source.
In another embodiment of the invention, said method further comprising the action of, including at least one pixel in said first set of pixels in said at least second set of pixels.
In another embodiment of the invention a single defective pixel in one writing pass is compensated with a single compensating pixel in another writing pass.
In another embodiment of the invention a single defective pixel in one writing pass is compensated with a plurality of compensating pixels in another writing pass.
In another embodiment of the invention said SLM is illuminated by the same radiation dose in different writing passes.
In another embodiment of the invention said SLM is illuminated by different radiation dose in different writing passes.
In another embodiment of the invention said SLM is a transmissive Spatial Light Modulator.
In another embodiment of the invention said SLM is a reflective Spatial Light Modulator.
In another embodiment of the invention the pixels in said SLM is operate
Beffel, Jr. Ernest J.
Haynes Beffel & Wolfeld LLP
Mack Ricky
Micronic Laser Systems AB
Thomas Brandi N
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