| 摘要 |
The thickness of the reticle used in charged-particle-beam (CPB) microlithography is a few microns at most. Hence, the reticle bends easily and flexes when subject to vibration, causing instability in reticle axial height position relative to the projection-lens system, and errors in image focus, rotation and magnification. Apparatus are disclosed that include a device for detecting the axial height position of the reticle. The device produces one or more beams of light (IR to visible) to strike the reticle at an oblique (not 0 degrees) angle of incidence, detects light reflected from the reticle surface, and detects lateral shifts of the reflected light as received by a height detector. Hence, reticle focus is detected easily and in real time. Multiple detection beams can be used, thereby allowing detection of both axial height position and inclination of the reticle with high accuracy. Reticle-position data can be used to regulate operation of, e.g., an exposure meter.
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