Browse Prior Art Database

Electron Beam Lithography Tools

IP.com Disclosure Number: IPCOM000101962D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 139K

Publishing Venue

IBM

Related People

Newman, TH: AUTHOR

Abstract

Disclosed is a technique for accurately adjusting the quality of the image in shaped electron beam lithography tools. In this method, a compact pattern is generated by the tool which provides visual feedback for the setup of the dynamic focus and dynamic stigmators throughout the deflection field. The pattern is designed to fit within the field of view of a scanning electron microscope so that the optimal settings can be readily determined.

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Electron Beam Lithography Tools

       Disclosed is a technique for accurately adjusting the
quality of the image in shaped electron beam lithography tools.  In
this method, a compact pattern is generated by the tool which
provides visual feedback for the setup of the dynamic focus and
dynamic stigmators throughout the deflection field.  The pattern is
designed to fit within the field of view of a scanning electron
microscope so that the optimal settings can be readily determined.

      Due to the relatively large writing field of high
throughput-shaped electron beam lithography tools, deflection
aberrations are often significant and cause the image quality and
placement accuracy to deteriorate as the beam is moved away from the
optical axis.  Of these, field curvature and astigmatism both degrade
the spot quality substantially, but can be corrected by applying the
appropriate magnetic fields.

      The corrections are functions of position in the deflection
field and are generated dynamically while the beam is scanned.  A
common practice is to adjust the image quality manually at several
points in the deflection field, and then to allow analog circuitry to
generate the desired functional fit by interpolation.  The difficulty
lies in determining the optimal manual adjustments.  With the
extended beam of a shaped beam tool, the simple technique of scanning
over a sharp edge and maximizing the steepness of the collected
electron signal can be used but is not accurate enough for high
resolution lithography.

      To improve upon this, a "stigmator series" can be written in
electron-sensitive resist by exposing patterns over a range of
settings of the focus and stigmators, and then identifying the
optimal settings by examining the developed resist features in a
light microscope.  Due to the poor resolution of light optics, this
technique is limited. Furthermore, what is observed is confused by
other factors that must also be adjusted in a shaped beam tool,
namely aperture rotation and shaping gain.  Misadjustment of the
stigmators causes spot edges to appear to be rotated, but aperture
rotation will produce a similar effect.  Imperfect shaping gain setup
can also be confused with a stigmation problem.

      The purpose of the scanning electron microscope stigmator
series described here is to eliminate the ambiguity of evaluation,
thereby both speeding up the convergence and increasing the accuracy.
It does this by removing three variables from consideration:  1) the
shaping aperture rotation; 2) the shaping gain; and 3) the stigmator
housing rotation.  The adjustment requirements of 1) and 2) are
treated in a separate procedure (not discussed here) once the focus
and stigmation are accurately adjusted.  The stigmator housing
rotation is unimportant, since the correction field can be rotated
electronically.  Physical misalignment of the housing with respect to
the beam edges does not degrade the results obtai...