Correction of astigmatism in electron beam instruments
US4567369A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 16, 1983 |
| Grant date | Jan 28, 1986 |
| Priority date | — |
| Expiry date | Jun 16, 2003 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH01J37/153
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
Abstract
An electron beam instrument having an objective lens coil 14 and stigmator coils 18 has its astigmatism corrected for by measurement of the contrast in the final image. The currents through the objective lens and the stigmator coils are adjusted in sequence iteratively to optimize the contrast. The optimum contrast may be either a maximum contrast or a minimum contrast depending on the nature of the instrument and its mode of operation. Measurement of contrast may be made by measuring the magnitudes of successive points of an image and calculating the variance. Alternatively two measurements of magnitude at each point of an image may be made and the covariance calculated.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.