| 摘要 |
Due to its lack of appreciable thickness, the reticle used in charged-particle-beam (CPB) microlithography is prone to bending and flexing, causing instability in reticle axial height position relative to the projection-lens system, with consequent errors in image focus, rotation and magnification. Apparatus and methods are disclosed for monitoring changes in axial height position of the reticle, to facilitate making compensatory changes. Representative apparatus 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 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 one or more parameters of exposure and/or axial position of the reticle or wafer.
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