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Correcting Pattern Distortions in Membrane Masks

IP.com Disclosure Number: IPCOM000100800D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 58K

Publishing Venue

IBM

Related People

Keyser, J: AUTHOR [+2]

Abstract

Disclosed are different ways of predistorting a pattern during its generation such that distortions in the finished mask are corrected. For this purpose, an equation is used which permits calculating the pattern distortion and thus predicting a suitable predistortion.

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Correcting Pattern Distortions in Membrane Masks

       Disclosed are different ways of predistorting a pattern
during its generation such that distortions in the finished mask are
corrected.  For this purpose, an equation is used which permits
calculating the pattern distortion and thus predicting a suitable
predistortion.

      Lithographic shadow projection methods, such as electron beam
proximity printing (EBP) or X-ray lithography, use thin silicon
membranes as substrates for the IC structures to be printed on the
wafer.  A membrane is fabricated by thinning a normal silicon wafer
within the mask window down to a thickness of about 3 mm.  Thus, the
membrane is suspended within a frame of solid silicon. After
fabrication, the membrane is subjected to an internal tensile stress.
This stress keeps the membrane stretched flat within the frame even
when it is slightly heated by the partially absorbed electron or
X-ray beam during exposure. In the case of X-ray lithography, the IC
pattern is provided in the form of gold absorbers which are deposited
on the membrane.  With EBP, holes and slots are etched into the
membrane to let the electrons pass through on their way to the wafer.

      Etching of the structures into the membrane decreases the
elasticity of the perforated pattern area relative to that of the
unperforated surrounding border.  The resulting inhomogeneous
elasticity in combination with the internal stress leads to
distortion of the IC patter...