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Exact transmission balanced alternating phase-shifting mask for photolithography

  • US 5,932,377 A
  • Filed: 02/24/1998
  • Issued: 08/03/1999
  • Est. Priority Date: 02/24/1998
  • Status: Expired due to Term
First Claim
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1. A method of eliminating pattern size and placement inaccuracies caused by errors in the relative amount of light transmitted through transparent features of different phase on a phase-shifted photomask, the method comprising the steps of:

  • building design data of said photomask representing pattern size, shape, placement and phase of said transparent features;

    modifying said design data by altering the size or shape of at least one of said phase-shifted features;

    fabricating said photomask with said modified design data by forming opaque and transparent features of said photomask and selectively etching transparent material of said photomask to a depth which establishes the phases of said transparent phase-shifted features, thereby partially reducing said transmission errors; and

    subjecting said photo-mask to an etch-back process comprising adjusting edge locations of said transparent material within said etched features in relation to edge locations of said opaque film of said photomask to a position wherein residual transmission errors between said features having a different phase on said photomask are corrected, thereby eliminating said residual transmission errors that were not previously corrected by a combination of said design data modification step and said fabrication step.

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