Browse Prior Art Database

Ultra-resolution Image Transfer

IP.com Disclosure Number: IPCOM000107560D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 5 page(s) / 203K

Publishing Venue

IBM

Related People

Korth, HE: AUTHOR

Abstract

This article describes a new system for ultra-resolution photolithography. A combination of optical imaging and ultra-resolving scanning through a pair of pinhole arrays allows a mask to wafer image transfer which overcomes the classical diffraction limit. A resolution of 100 nm or better is achieved by using visible or near-UV light. Thus, the light wavelength is arbitrarily selectable for maximum efficiency (source, photoresist, optics, image field).

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Ultra-resolution Image Transfer

       This article describes a new system for ultra-resolution
photolithography.  A combination of optical imaging and
ultra-resolving scanning through a pair of pinhole arrays allows a
mask to wafer image transfer which overcomes the classical
diffraction limit.  A resolution of 100 nm or better is achieved by
using visible or near-UV light.  Thus, the light wavelength is
arbitrarily selectable for maximum efficiency (source, photoresist,
optics, image field).

      The structural density of semiconductor devices is limited by
the physics of the photolithographic imaging process (Abbe
condition).  The Abbe condition applies only to imaging processes.
It is possible to feed light through a pinhole having a diameter of
only a fraction of the light wavelength.  If the pinhole is close to
a photosensitive surface, a pixel of similar dimension will be
generated.

      A pinhole in close vicinity to a photosensitive surface is used
to generate a spot image.  The spot diameter depends on the pinhole
diameter, the pinhole to object surface distance, and the
illumination.  For small spots close to the surface, the spot
diameter is considerably smaller than the wavelength of the
illuminating light.  Controlled sequential generation of such spot
images allows generating an arbitrary image pattern.

      The pattern to be imaged is stored on a mask.  The mask is
projected (demagnified) onto the object (wafer) surface. A conjugate
pinhole close to the mask is used to transmit only the desired pixel,
the rest of the mask being shielded. Even if the lateral resolution
of the imaging lens system is not as small as the pixel size, the
pixel is still resolvable at that stage.

      Effective exposure at a given object location depends on the
double convolution of the mask pattern with each of the conjugate
pinholes.  The image contrast, which is close to unity for extended
structures, decays rapidly to a value below 0.5 when the imaged line
width becomes smaller than the pinhole diameter.  The depth of focus
of the system depends on the numerical aperture of the lens and the
gap between the pinhole carrier and the object surface.  To generate
a smooth photosensitive surface on structured wafers, a planarization
layer may become necessary before the photoresist is applied.

      Polarized light causes an anisotropic coupling into the narrow
gap, so that focus and lateral resolution will also exhibit
anisotropy.  This enhances the imaging process in one direction still
further.

      A multitude of pixels may be transmitted in parallel by using a
pair of conjugate plates having a regular hexagonal or rectangular
pinhole array pattern.  The pinholes must be adequately spaced to
avoid crosstalk between adjacent pixels.

      Linear movement of the pinhole arrays relative to the image
allows covering all image locations.  This may be done in various
ways:  A synchronous scann...