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Improving the Focal Depth And Resolution of Optical Devices

IP.com Disclosure Number: IPCOM000100802D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 64K

Publishing Venue

IBM

Related People

Makosch, G: AUTHOR [+3]

Abstract

The use of optical devices in the future production of semiconductors is limited by the minimum contrast required for imaging very fine lines. Because of the wave nature of light, the contrast is determined by resolution and focal depth. The method described in this article improves both in a practicable manner. (Image Omitted)

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Improving the Focal Depth And Resolution of Optical Devices

       The use of optical devices in the future production of
semiconductors is limited by the minimum contrast required for
imaging very fine lines.  Because of the wave nature of light, the
contrast is determined by resolution and focal depth.  The method
described in this article improves both in a practicable manner.

                            (Image Omitted)

      By means of a laser-scanning microscope, fine lines on a Cr
mask were tested with blue light (g = 0.488 mm). Dark-field imaging
was used to demonstrate the resolution and focal depth.  The signals
ob tained are shown in Fig. 1.  The edges of a 0.85 mm wide line
are imaged with a modulation of N 20% and a focal depth of + 2
mm (Fig.  1A).

      By inserting in the aperture plane in front of the objective a
circular diaphragm having a diameter half the size of the aperture
diaphragm, signals as shown in Fig. 1B are obtained.  In this case,
modulation doubles to 40%, which improves the resolution by > 10% and
doubles the focal depth to + 4 mm.  These values are obtained at the
expense of a slight increase of the secondary maxima.

      It is basically possible to implement the above-described
"apodized" optical excimer laser lithography with a considerably
increased resolution and focal depth. However, the annular laser beam
cross- section required for this purpose should not be produced by a
diaphr...