Patent US3576438A successfully refreshed from Google Patents.
US3576438A
Expired / Lapsed
US
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Focus monitor for electron microscope including an auxiliary electron gun and focusing lens
Assignee: AT&T Inc
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Filing: 1969-04-28
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Granted: 1971-04-27
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Expires: 1989-04-28
Abstract
Abstract The focus of an electron microscope is monitored and stabilized by measuring variations in the focal length of an analyzing lens energized by the same current as the microscope objective lens and utilizing the resulting signal to control either the objective lens current or the electron source voltage.
Inventors
- 👤 Roger F W Pease
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 23:13
CPC Classifications
H; H01; H01J; H01J37/00; H01J37/02; H01J37/21
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
159 words
A focus monitor for a particle beam microscope having a particle source and an objective lens comprising, in combination: an auxiliary particle source; at least one analyzing lens for focusing particles from said auxiliary particle source, said analyzing lens having characteristics matched with the characteristics of said objective lens with respect to the relationship between focal length, lens current, and particle voltage, said analyzing lens being connected in series with said objective lens such that the focal length of each of said lenses is equally affected by any change in current therethrough; means for measuring changes in focal length of said analyzing lenses, said measuring means including target means illuminated by said particles from said auxiliary particle source and having an image thereof formed, said image having dimensional variations proportional to said changes in focal length, and detector means for detecting said dimensional variations and deriving signals therefrom; and control means for utilizing said signals to control said focus.
Claim 2
Dependent Claim
159 words
A focus monitor for a particle beam microscope having a particle source and an objective lens comprising, in combination: an auxiliary particle source; at least one analyzing lens for focusing particles from said auxiliary particle source, said analyzing lens having characteristics matched with the characteristics of said objective lens with respect to the relationship between focal length, lens current, and particle voltage, said analyzing lens being connected in series with said objective lens such that the focal length of each of said lenses is equally affected by any change in current therethrough; means for measuring changes in focal length of said analyzing lenses, said measuring means including target means illuminated by said particles from said auxiliary particle source and having an image thereof formed, said image having dimensional variations proportional to said changes in focal length, and detector means for detecting said dimensional variations and deriving signals therefrom; and control means for utilizing said signals to control said focus.
Claim 3
Dependent Claim
45 words
Apparatus in accordance with claim 1 wherein said target means comprises a plate having a plurality of holes therein, said image comprises projections of said holes upon said detector means, and said dimensional variations are detected by movement of said projections upon said detector means.
Claim 4
Dependent Claim
53 words
Apparatus in accordance with claim 1 wherein said detector means comprises a plurality of particle sensitive devices upon which said image is projected, each of said devices generating an output proportional to the portion of said image projected thereon, and circuit means for combining said outputs to indicate dimensional variations of said image.
Claim 5
Dependent Claim
14 words
Apparatus in accordance with claim 3 wherein each of said devices comprises a diode.
Claim 6
Dependent Claim
40 words
Apparatus in accordance with claim 1 including a spacer of material having a low thermal expansion connecting said target means and said analyzing lenses such that any change in focal length of said analyziNg lens results in said dimensional variations.
Claim 7
Dependent Claim
12 words
Apparatus in accordance with claim 5 wherein said material is fused quartz.
Claim 8
Dependent Claim
36 words
Apparatus in accordance with claim 1 wherein said particle source and said auxiliary particle source are connected in parallel to a common voltage source such that each of said particle sources has the same particle voltage.
Claim 9
Dependent Claim
25 words
Apparatus in accordance with claim 1 wherein said control means utilizes said signals for controlling the current to said objective lens and said analyzing lens.
Claim 10
Dependent Claim
26 words
Apparatus in accordance with claim 1 wherein said control means utilizes said signals for controlling the voltage of said particle source and said auxiliary particle source.
Claim 11
Dependent Claim
57 words
Apparatus in accordance with claim 1 including a plurality of analyzing lenses, each of said lenses having characteristics matched with the characteristics of said objective lens with respect to the relationship between focal length, lens current and particle voltage, said lenses being connected in series such that changes in focal lengths can be detected with increased sensitivity.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-04-26 | 1974-10-26 | 1975-04-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-04-26 | 1978-10-26 | 1979-04-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-04-26 | 1982-10-26 | 1983-04-27 | $7700.00 | Window Closed / Lapsed |