Multistage gas cascade amplifier
AssigneeFEI Company
InventorsMarek Uncovsky, Milos Toth, William Ralph Knowles
Life of this patent
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Abstract
A novel detector for a charged particle beam system which includes multiple gas amplification stages. The stages are typically defined by conductors to which voltage are applied relative to the sample or to a previous stage. By creating cascades of secondary electrons in multiple stages, the gain can be increased without causing dielectric breakdown of the gas.
Claims36
A charged particle beam system, comprising:
- a sample chamber for containing a sample at a sample position;
- a charged particle beam source including a focusing column for forming a beam of charged particles and directing the beam toward the sample chamber;
- and
- a detector for detecting an electron signal emitted as the charged particle beam impacts the sample, the detector comprising:
- a detector volume;
- an anode positioned toward the rear of the detector volume;
- a first electrode positioned between a sample position and the anode;
- and
- a second electrode positioned between the first electrode and the anode;
- the detector volume being defined by an electric field generated by electric potential differences between the sample position, the first electrode, the second electrode, and the anode, the detector amplifying by means of gas cascade amplification an electron imaging signal emitted as the charged particle beam impacts the sample.
A gas cascade amplification detector for use in a charged particle beam system, comprising:
- a housing having an opening;
- a first electrode adjacent the opening of the housing;
- an anode positioned within the housing;
- and
- a second electrode positioned within the housing between the first electrode and the anode, the first and second electrodes being semi-transparent to electrons and positioned so that when electrical potentials are applied to the first electrode, the second electrode, and the anode, regions between the electrodes provide multiple stages of gas cascade amplification, the combined amplification being greater than the maximum amplification available in a single stage.
A method of forming an image of a sample in a scanning electron microscope, comprising:
- providing a first gas cascade amplification region to amplify an electron signal from a sample, the first gas cascade amplification region being defined by an electric potential difference between a sample and a first electrode;
- providing a second gas cascade amplification region to amplify electrons from the first amplification region, the second gas cascade amplification region being defined by an electric potential difference between the first electrode and a second electrode;
- providing a third gas cascade amplification region to amplify electrons from the second amplification region, the third gas cascade amplification region being defined by an electric potential difference between the second electrode and a third electrode;
- and
- forming an image of the sample corresponding to the amplified electron signal,
- whereby the electric potential at the first electrode is greater than the electric potential at the sample surface, the electric potential at the second electrode is greater the electric potential at the first electrode, and the electric potential at the third electrode is greater the electric potential at the second electrode.
A multi-stage gas cascade amplification detector for a scanning electron microscope, comprising:
- a first gas cascade amplification region defined by a first electric field region having a first gain;
- and
- a second gas cascade amplification region being defined by a second electric field region and having a second gain, the second gain being greater than one half of the first gain.
A multi-stage, gas cascade amplification detector for a scanning electron microscope, comprising:
- a detector housing having an opening;
- a first electrode adjacent the opening of the housing;
- and
- an anode positioned within the housing, the first electrode being semi-transparent to electrons and positioned so that when electrical potentials are applied to the first electrode and the anode, regions between the electrodes provide multiple stages of gas cascade amplification, the first electrode and anode being positioned so as to provide a gain between the first electrode and the anode of at least one half the gain available between a sample and the first electrode.
Dependencies are inferred from the claim text.