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Method and apparatus for image alignment in ion lithography

  • US 4,967,088 A
  • Filed: 06/02/1988
  • Issued: 10/30/1990
  • Est. Priority Date: 06/02/1987
  • Status: Expired due to Term
First Claim
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1. In an ion projection lithography system, an apparatus for positioning on a substrate or wafer at a target station an ion image of structures provided on a mask, said image produced by an ion beam projected along an axis upon said mask, wherein said mask includes reference marks to provide ion reference beams about the image field, the target station includes marks and the beam of the system is controlled to establish a coincidence of the marks on the mask with the corresponding marks at said target station, said ion projection system including in its optical path an electrostatic multipole, which is adapted to be controlled by a control device, means for rotational adjustment of said image relative to said substrate, and means for correcting the scale of the image, wherein at least some of the marks at said target station are carried on a reference block, said block being disposed in a predetermined position relative to the substrate and having an aperture corresponding in size to the mask image to be formed on the substrate so that the marks on said block are disposed outside the optical path used to generate the image on the substrate, said marks being on the side of said block opposite to the side on which the wafer lies and being in position to coincide with respective reference beams while said ion image is projected along the optical path toward said target station,detectors provided for secondary radiation emitted by the marks on the reference block as a result of the ion reference beams passing through said marks on said mask, said detectors and reference block arranged along said beam path such that said reference block can shield said detectors from any secondary radiation emitted as a result of said beam striking a surface after passing through said apertureand the signals from the detectors adapted to be delivered to the control device for the multipole, the means for relative rotational adjustment of said image on said substrate and to the means for scale correction.

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