GB1388110A - Electron beam specimen analysis - Google Patents

Abstract

1388110 Scanning electron microscope image analysis IMAGE ANALYSING COMPUTERS Ltd 11 April 1972 [20 April 1971] 10288/71 Heading G4D [Also in Division G1] In the analysis of specimens by, e.g. a scanning electron microscope, metallic inclusions are identified as such by a signal representative of the sensed specimen current from 16 exceeding a reference level set in comparator 20, and the resulting signals which occur at 24 used (direct or after, e.g. skrinking, stretching &c), to gate at 30 the output of, e.g. a sensor of X- rays 18. The X-ray probe may be an X-ray spectrometer in which case the wavelength of X-rays to be detected may be chosen at 19 so that the signals gated for further processing are representative of a particular metal only. The invention is generally applicable to analysis by scanning with an electron beam and the gated signals may alternatively be due to backscatter, cathode luminescence, secondary electron emission, specimen E.M.F. and direct transmission; the object is to increase scanning speeds. The reference level 22 may be simply to differentiate a metallic inclusion from background noise, but could theoretically also be used to discriminate between metals, if these produce differing amplitude levels. While the reference voltage is being adjusted, the number of line scans per field scan is reduced. The circuit of Fig. 4 is designed to determine one particular metal in a field which may include inclusions of other metals (see e.g. features 10, 12 of different metals, Fig. 1). The wavelength 7 characteristic of the particular metal is selected at 19. However, pulses will be gated at 30 not only within the feature predominantly of the particular metal but to a lesser extent within the other features. To differentiate between these features the ratio N/A is calculated at 44, where N is the number of X-ray pulses for each feature calculated by computer 38 and A is the area of each feature. If N/A is within range JK, the feature is of the required metal. The number of features in the field having the required N/A value are counted at 48. Also calculated are the total X-ray pulse count for a field #N, the total area #A and the average N/A value #N/A (for a given #). In a modification, Fig. 7, not shown, two wavelengths are selected simultaneously so that two types of metal may be determined, there being provided two channels, each comprising an amplifier, number N computer, divider and comparator, a common area computer being sufficient to operate with both the channels. Accumulators for #A for the two wavelengths are provided.