Photocopying – Projection printing and copying cameras – Illumination systems or details
Reexamination Certificate
1998-06-11
2001-07-03
Gray, David M. (Department: 2851)
Photocopying
Projection printing and copying cameras
Illumination systems or details
C355S053000
Reexamination Certificate
active
06256087
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a light intensity measurement system and more particularly, to a light intensity measurement system of a projection illumination system for microlithography.
2. Description of Relevant Art
Such systems are in use in wafer steppers or scanners of the ASM-L Company, with optics of the Carl Zeiss Company, Oberkochen, Germany. International patent publication WO 97/31298 is a related publication. Such systems are also known from European Patent 0 500 393 B1 (FIG. 13
4
).
The measurement of light intensity—and thereby the energy, after integration over time—serves for the precise exposure of photoresists, and also as an input magnitude for control circuits by means of which the effects of the light flux on the optical elements (lens heating, thermal lenses) are stabilized.
Problems of measurement accuracy arise with increasing requirements for the accuracy of the whole exposure system and process, and with increasing variability of the whole system, particularly at the exit of the glass rod used in the system, with the variable adjustment of a reticle masking diaphragm whose diaphragm lamellae give rise to considerable reflections back into the glass rod.
SUMMARY OF THE INVENTION
The invention has as its object the provision of such a system with improved measurement accuracy and with greater flexibility of adjustment of the illumination system.
This object is attained by means of a light intensity measurement system in an illumination system of a projection illumination system for microlithography, with a light-mixing glass rod which includes a deflecting mirror that transmits a fraction of the light intensity, and an energy sensor that senses the transmitted fraction of the light intensity. An adjustable diaphragm is following after the glass rod in the direction of light flow. The diaphragm reflects light back into the glass rod, which light in part reaches the energy sensor. A compensation detector containing a photodetector is arranged near the deflecting mirror, in the main direction of the light reflected by the adjustable diaphragm.
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patent: 296 13 089 U1 (1996-07-01), None
patent: 0 766 144 A1 (1996-09-01), None
patent: 0 500 393 B1 (1997-11-01), None
patent: WO 97/31298 (1997-08-01), None
European Search Report, EP 98 10 8864, Sep. 6, 2000.
Carl-Zeiss-Stiftung
Gray David M.
Nguyen Hung Henry
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