Cambridge Instruments Inc.

Ian A Cruttwell

John C Barker

William R Knowles

A scanning electron microscope arrangement has an integral image store connected to receive signals from an electron collector which collects the secondary electrons emitted from the specimen surface in response to impingement by the electron beam. The latter is scanned over the specimen by scanning coils driven by a scan generator. A cathode ray tube is provided which has its separate scan generator and responds to the previously stored signals as they are read out from the store under control of a control unit. Because the arrangement has an integral store, the beam scanning rates of the electron beam and the CRT beam can be entirely independent. The scan generator for the electron beam may therefore have a relatively low rate and therefore a low power rating. The CRT can be a standard type and does not need to be high persistance. The signal to noise ratio of the signals in the store can be increased by repeating the scan of the specimen before reading out the signals.

Scannable-beam microscopes and image stores therefor

A defect detection system for classifying defects in reticles (such as used in the manufacture of integrated circuit wafers) is described. An inspection unit, scanning the reticle in real time, compares it with the correct form and inputs signals representing each defect and its position in a store. The stored defects are then used to direct the inspection unit to inspect each defect more slowly. The inspection unit classifies each defect as either being an 'excess metal' or a 'missing metal' defect, and corresponding signals are stored in respective additional stores. The signals stored in these stores are then further processed and compared with the desired form of the reticle so as to classify the 'excess metal' defects as either being a 'pin spot' defect, an 'extension' defect or a 'bridge-type' defect. Similarly, the 'missing metal' defects are classified as either being a 'pinhole' defect an 'intrusion' defect or a 'break-type' defect. A size measuring unit measures the size of each defect.

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Great Chishall, Nr. Royston, United Kingdom

Ian A Cruttwell