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Method of Directly Measuring Line Width Deviations

IP.com Disclosure Number: IPCOM000121064D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 3 page(s) / 121K

Publishing Venue

IBM

Related People

Korth, HE: AUTHOR

Abstract

Dark-field observation of a test grid structure with a modulated line width gradient allows detecting the location of features printed with nominal line width. By means of this method, line width tolerances in photolithographic processes may be controlled with sub-nanometer precision. Sub-(half)micron lines may be measured by visible light with grazing incidence, and the line width of latent images in exposed photoresist may be analyzed.

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Method of Directly Measuring Line Width Deviations

      Dark-field observation of a test grid structure with a
modulated line width gradient allows detecting the location of
features printed with nominal line width.  By means of this method,
line width tolerances in photolithographic processes may be
controlled with sub-nanometer precision. Sub-(half)micron lines may
be measured by visible light with grazing incidence, and the line
width of latent images in exposed photoresist may be analyzed.

      The described method essentially compares a number of
equidistant lines of gradually varying width with the grating
constant of a printed test structure.  If the line width LW thus
determined is exactly half the grating constant a, then the second
(even) order diffraction will be suppressed.  This well-known effect
may be explained by the fact that the second order grating
diffraction coincides with the first diffraction minimum of a single
line of half the width value.  For nearly normal light incidence and
a flat surface topography, the effect does not depend on the type of
line (phase and amplitude mix) or on the light wavelength or
coherence.

      Double modulation of the test structure, i.e., an additive
width increment for every other line, produces a visible fringe
structure on the test pattern image with fringe contrast inversion at
the point of the nominal line width (Fig. 1).  Such a double
modulation pattern may be highly sensitively evaluated by human or
mechanical vision.

      As the width of the line producing the nominal line width value
can be determined, the width deviation ocurring when that line is
printed can also be determined.  In the case of large deviations, for
example, measuring the deviation for two sets of lines with different
nominal width will allow approximating their functional relation,
unless the interdependence of line width and deviation is negligible.

      A sim...