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Publication Date: 2002-Nov-19
Document File: 1 page(s) / 21K

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us 6 285 488: PATENT


Homogenous light intensity is a key element in a lithographic patterning process. A spatial light modulator (SLM) can be used to homogenize intensity distribution in a beam spot used in a lithographic patterning process. A detector device detects the original intensity distribution and sends information to the SLM to adjust certain pixels in order to achieve a desired intensity pattern.

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Figure 1 Illustrates an inventive set-up for correcting illumination variations (depicted in the lower diagram in said figure) from an illumination source, which is intended to be impinged onto a spatial light modulator for pattern formation. The depicted set-up in figure 1 comprises an illumination source (not shown) a beamspliter,1 a SLM1, a beamsplitter2, a CCD, a beamsplitter3, a SLM2, a Fourier lens, an aperture, a final lens and a workpiece. Electromagnetic radiation, in the form of laser light (continuous or pulsed), is adjusted by SLM1 in order to fit the desired application. In a lithographic pattern generator using the SLM2 to form the desired pattern illumination on said SLM2 is critical. The illumination has to be homogenous (see upper diagram in figure 1) and not vary in intensity over the SLM2 surface as depicted in the lower diagram. Unadjusted electromagnetic radiation may have some variation in intensity over an area of a beam spot. SLM1 can be set to equalize variations in illumination intensity at the cost of output intensity.

For instance, the incoming electromagnetic radiation may by SLM1 be set to the lowest intensity peak by restraining the higher intensity values. A CCD camera may be used to detect intensity variations in the electromagnetic beam. There is a known relationship between pixels in the spatial light modulator (SLM1) and the pixels in the CCD camera. Changing appropriate pixels in the SLM1 performs this restraining and may change the detec...