Radiant energy – Calibration or standardization methods
Reexamination Certificate
1999-12-07
2001-11-20
Berman, Jack (Department: 2881)
Radiant energy
Calibration or standardization methods
C250S492200, C250S491100
Reexamination Certificate
active
06320187
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to particle beam projection systems and more particularly to calibration of such systems.
2. Description of Related Art
See U.S. Pat. No. 5,763,894 of Enichen et al. for “Calibration Patterns and Techniques for Charged Particle Projection Lithography Systems” and U.S. Pat. No. 5,283,440 Sohda et al. for “Electron-Beam Writing System Used in a Cell Projection Method”.
In an EBPS (Electron-Beam Projection System) the size and orientation (rotation) of the projected cell or subfield must be adjusted in order for subfields or cells being formed to butt against the neighboring subfields or cells without gaps or an overlap between subfields or cells.
Previous calibration methods described in U.S. Pat. No. 5,763,894, supra, and U.S. Pat. No. 5,283,440, supra, have done this adjustment task by projecting an image formed by the reticle onto a matching target in the wafer plane, and the projected image is scanned over the matching target. The degree of matching is evaluated by measuring the peak signal strength of the backscattered electron signal or by measuring the width of the backscattered electron signal at a given threshold. The lenses that control the magnification and rotation of the subfields are stepped through a range of values and data is collected from the backscattered electron detector. The optimum adjustment is determined by the lens setting that maximizes the backscattered electron signal or minimizes the backscattered electron signal width.
The problem with the techniques of U.S. Pat. No. 5,763,894, supra, and U.S. Pat. No. 5,283,440, supra, is that for a single measurement it is impossible to determine the direction in which to make an adjustment. It is necessary to make enough trial adjustments in order to establish a maximum backscattered electron signal or a minimum backscattered electron signal width. A single measurement yields no information on the degree to which the adjustment has approached proximity to an optimum adjustment or in what direction an optimum can be approached.
SUMMARY OF THE INVENTION
In accordance with this invention, a method of calibrating a projection particle beam lithography system, comprises the following steps. Provide a magnification reticle pattern and a magnification target pattern. Provide a rotation reticle pattern and a rotation target pattern. Produce a particle beam. Direct the particle beam through the magnification reticle pattern and onto the magnification target pattern. The projected reticle pattern image is scanned over the magnification target using a calibrated deflection. Determine the distance between peaks of target patterns as indicated by particles backscattered from the magnification target pattern. Calculate the deviation from the ideal for the distance between peaks of a the backscatter signal and calculate the magnification deviation and use the magnification deviation to adjust the particle beam. Direct the particle beam through the rotation reticle pattern and onto the rotation target pattern. Scan the rotation reticle pattern image over the rotation target using a calibrated deflection. Determine the distance between peaks of the signal from the particles backscattered from the rotation target pattern. Calculate the deviation from the ideal for the distance between peaks of the backscatter signal and calculate the rotation value. Then use the rotation value to adjust the rotational orientation of the particle beam.
In accordance with another aspect of this invention, a method of calibrating a projection electron beam lithography system, comprises the following steps. Provide a magnification reticle pattern and a magnification target pattern. Provide a rotation reticle pattern and a rotation target pattern. Produce an electron beam. Demagnify the electron beam. Orient the electron beam. Direct the electron beam through the magnification reticle pattern and onto the magnification target pattern. Scan the image of the magnification reticle pattern over the magnification target elements with a calibrated scan. Determine the distance between peaks of the signal produced by secondary electrons or electrons backscattered from the magnification target pattern. Calculate the deviation from the distance between peaks of an ideal signal and calculate the magnification deviation and use the magnification deviation to adjust the electron beam. Direct the electron beam through the rotation reticle pattern and onto the rotation target pattern. Scan the image of the rotation reticle pattern over the rotation target elements with a calibrated scan. Determine the distance between peaks of the signal produced by secondary electrons or electrons backscattered from the rotation target pattern. Calculate the deviation from the distance between peaks of an ideal signal and calculate the rotation deviation, then use the rotation deviation to adjust the electron beam and using the rotation value to adjust the rotational orientation of the electron beam.
REFERENCES:
patent: 5079112 (1992-01-01), Berger et al.
patent: 5283440 (1994-02-01), Sohda et al.
patent: 5316879 (1994-05-01), Berger et al.
patent: 5763894 (1998-06-01), Enichen et al.
patent: 5766894 (1998-06-01), Enrichen et al.
patent: 5911858 (1999-06-01), Ruffner
patent: 5936252 (1999-08-01), Stickel et al.
patent: 6115108 (2000-09-01), Capodieci
Scalpel, www.bell-labs.com/project/Scalpel (1999) pp. 1-41 (page numbers added).
Berman Jack
Jones II Graham S.
Nikon Corporation
Smith II Johnnie L
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