Browse Prior Art Database

Optical Line Width Measurement in the Submicron Range

IP.com Disclosure Number: IPCOM000101090D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 110K

Publishing Venue

IBM

Related People

Elsner, G: AUTHOR [+3]

Abstract

The 1 megabit chip used to produce semiconductors is presently fabricated with minimum line widths of ~ 1 mm. Future chip generations will have much smaller line widths of, e.g., 350 nm, which are no longer measurable by currently available optical devices.

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Optical Line Width Measurement in the

Submicron

Range

       The 1 megabit chip used to produce semiconductors is
presently fabricated with minimum line widths of ~ 1 mm. Future chip
generations will have much smaller line widths of, e.g., 350 nm,
which are no longer measurable by currently available optical
devices.

      Essential line widths measurements are those carried out on
photoresist structures, because the results of such measurements
decide whether a structure may be etched or has to be reworked.

      In addition to the resolution which is restricted by the
relatively great wavelength of light, optical measuring methods on
semiconductor structures are impaired by the degree of coherence of
light and thus by interferences on thin layers.

      The approach used to overcome these difficulties, which works
with coherent illumination and less complicated computation to
determine the necessary threshold, has failed in practice.  The
method described below uses a physically defined threshold, which is
independent of the layer thicknesses of the structure, and an
extended resolution.  To obtain a threshold for line width
measurements which is independent of the layer thicknesses of the
structure, incoherent rather than coherent illumination is used,
since with the former type of illumination the threshold (location of
the edge) is precluded by definition at 50% of the intensity and the
interference values (Fig. 1).

      Incoherent illumination cannot be obtained by conventional
optical means, as the degree of coherence is determined by the ratio
of the illuminating aperture to the imaging aperture, with an
infinite value being required for incoherent illumination.  The
required incoherent illumination also contrasts with the extremely
great coherence lengths of short-wave lasers (argon+ and He-Cd)
which, because of their high luminance values, are particularly
suitable for a high resolution.

      The necessary incoherence may also be obtained by means of
laser radiation by destroying the coherence by fluorescence in or on
the object.  The incoherence thus obtained during imaging also
improves the resolution.

      As the fluorescence method is an amplitude method, it is also
possible to use immersions with large numeric a...