Electron beam focussing
US4514634A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Mar 1, 1983 |
| Grant date | Apr 30, 1985 |
| Priority date | — |
| Expiry date | Mar 1, 2003 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH01J37/21
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
Abstract
An automatic focussing arrangement for use with scanning electron beam apparatus such as a scanning electron microscope or electron beam microfabrication apparatus sets the focus coil (18) current at each one of a plurality of predetermined values in turn. At each setting, the scanning system (10, 12, 14) is activated to frame-scan the electron beam across a predetermined sharp-edged target. The resultant video signal (22) is monitored for each line of the frame scan to derive the mean value, then the mean value is subtracted from the instantaneous value of the video signal for that line (this may be carried out during a second scan of the same line), and the difference is then squared and integrated. The integrated outputs corresponding to each line scan are monitored to determine the greatest one. This is then stored (32) in association with the corresponding level of the focus drive current, and the process is then repeated. When frame scans have been carried out corresponding to all values of the focus current, the maximum one of all the stored integrated outputs is determined by a computer (38) and this identifies the optimum focus drive current. The focus drive current may th…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.