Bias-variant photomultiplier tube
AssigneeKLA-Tencor Corporation
InventorsDerek Mackay, Paul Donders, Kai Cao, Jeongsik Lim
Life of this patent
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Abstract
A bias-variant photomultiplier tube (PMT) includes a photocathode that when operating absorbs photons and emits photoelectrons responsive to the absorbed photons. The bias-variant PMTO also includes a plurality of dynodes that receive the photoelectrons emitted by the photocathode. The plurality of dynodes include a first pair of dynodes having a first bias difference and at least a second pair of dynodes having a second bias difference. The second bias difference is greater than the first bias difference. The bias-variant PMTO also includes an anode to receive photoelectrons directed from the plurality of dynodes.
Claims17
A bias-variant photomultiplier tube (PMT) comprising:
- a photocathode configured to absorb photons and emit photoelectrons responsive to the absorbed photons;
- a plurality of dynodes including a first pair of successive dynodes having a first bias difference and a second pair of successive dynodes having a second bias difference greater than the first bias difference, wherein the first pair of successive dynodes is configured to receive the photoelectrons emitted from the photocathode;
- and
- an anode, wherein the anode is configured to receive photoelectrons from the second pair of successive dynodes.
A method for biasing a photomultiplier tube (PMT) comprising:
- generating an initial set of photoelectrons through secondary emission via the absorption of photons with a photocathode;
- directing the initial set of photoelectrons to a first pair of successive dynodes of a plurality of dynodes, wherein the first pair of successive dynodes has a first bias difference;
- amplifying the initial set of photoelectrons to form a second set of photoelectrons with the first pair of successive dynodes;
- amplifying the second set of photoelectrons to form a third set of photoelectrons with a second pair of successive dynodes of the plurality of dynodes, wherein the second pair of successive dynodes has a second bias difference greater than the first bias difference;
- and
- receiving the third set of photoelectrons with an anode.
An optical system comprising:
- an illumination source configured to generate illumination;
- a set of illumination optics configured to direct and focus the illumination onto the sample surface;
- a bias-variant photomultiplier tube (PMT) sensor configured to detect at least a portion of light scattered, reflected, or defracted from the surface of the sample, wherein the bias-variant PMT sensor comprises:
- a photocathode configured to absorb photons and emit photoelectrons responsive to the absorbed photons;
- a plurality of dynodes including a first pair of successive dynodes having a first bias difference and a second pair of successive dynodes having a second bias difference greater than the first bias difference, wherein the first pair of successive dynodes is configured to receive the photoelectrons emitted from the photocathode;
- and
- an anode, wherein the anode is configured to receive photoelectrons from the second pair of successive dynodes;
- and
- a set of collection optics configured to direct and focus at least a portion of light scattered from the surface of the sample to an input of the bias-variant PMT sensor.
Dependencies are inferred from the claim text.