Method and apparatus for suppressing disturbances in the measurement of signals with a particle probe
AssigneeSiemens Aktiengesellschaft
InventorsHans-Peter Feuerbaum, Reinhold Schmitt
Life of this patent
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Abstract
A method and apparatus suppress a disturbance in the measurement of signals with a particle probe by providing and measuring a known reference voltage on a specimen at at least one time and using the measurement for eliminating the drift phenomena appearing in a measured signal and enables a significant increase in the precision of the measurement of signals. A secondary electron signal which results from a measurement of a reference voltage controls the operating point of a feedback circuit for suppressing the disturbance.
Claims15
A method of suppressing a disturbance in measuring signals with a particle probe in which a primary electron beam is directed onto test points of a speciman and the secondary electrons emitted from the specimen are detected and measured as representing signals at those test points, comprising the steps of:
- applying a known reference voltage to a reference test point on a specimen to produce a known test signal at the reference test point;
- directing a primary electron beam, at least one time, during a reference phase, to the reference test point causing secondary electron emission;
- generating a control field with a retarding field generator;
- detecting the secondary electrons through the control field and generating a measured secondary electron signal;
- and
- feeding back the measured secondary electron signal as a reference signal to the field generator to control the field intensity during measurement of unknown signals at other test points on the specimen during a measuring phase to compensate for operating point shifts due to electron beam fluctuations and specimen contamination and maintain a specific operating point.
Apparatus for suppressing a disturbance in measuring signals, in which a primary electron beam is directed onto test points of a specimen and secondary electrons are emitted from the specimen and measured as representing signals at those test points, said apparatus comprising:
- means for applying a known reference voltage to a reference test point to produce a known test signal at the reference test point;
- beam control means operable to direct a primary electron beam onto the reference test point, at least one time during a reference phase, to cause secondary electron emission;
- retarding field generator means adjacent the specimen operable to produce a control field;
- detection means adjacent said retarding field generator means for detecting secondary electrons which permeate the control field, including detecting means and generator means for generating a respective measured secondary electron signal;
- and
- feedback means connected between said detection means and said retarding field generator for applying the measured secondary electron signal as a reference signal to control field intensity during measurement of unknown signals at other test points on the specimen during a measuring phase to compensate for operating point shifts due to electron beam fluctuations and specimen containination and maintain a specific operating point.
Dependencies are inferred from the claim text.