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1985
Journal Article
Titel
Overlay measurement for x-ray lithography
Abstract
The metrology in submicron lilthography is an increasingly difficult task. Especially the control of the stability of the x-ray masks, which needs resolution better than 0.1 micrometer over a large area, supplies a lot of problems. Some of them can be investigated by double exposures evaluated with overlay measurement methods. We use a method that needs a minimum of process steps. Both exposures are made within the same resist. The resist patterns are measured directly. No additional processing step other than lithography and resist developing are necessary. We built an experimental alignment system for x-ray lithography in a vacuum chamber, so we can expose in vacuum or in a He atmosphere. A swivel-mounted microscope allows the observation of the alignment marks on the mask and on the wafer. With six motordriven screws we can adjust wafer to mask. With another setup it is possible to make tilted exposures. After the double exposure we measure the relative position of special metrology marks with light optics on an accuracy of 30 nm (3 delta value). The assembly consists of a LEITZ linewidth measuring microscope, a high precision motordriven x-y-z table, and a microcomputer. The automatic measuring procedure is performed under the control of the computer. With these measuring and evaluation methods we could measure the alignment accuracy, and changes of the x-ray masks due to heating by the synchrotron radiation.