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Compact, integrated electron beam imaging system
| Details |
Inventors: Chang, Tai-Hon P.; Mamin, Harry J.; Rugar, Daniel;
Assignee: International Business Machine Corporation (Armonk, NY)
Primary Examiner: Berman; Jack I.
Assistant Examiner:
Attorney, Agent or Firm: Perman & Green
An electron beam imaging system is described wherein a sharp-tip electron source is biased to produce an electron flow and a conductive target is placed in the path of the electron flow. A planar, electrostatic lens is positioned in the electron flow path and between the electron source and target. The lens includes an aperture; at least a first conductive plane that is biased less negative than the electron source; and one or more conductive planes separated by dielectric layers. A secondary electron detector is formed on the surface of the electrostatic lens that is closest to the conductive target, whereby the lens may be positioned close to the target and still not obstruct secondary electrons emitted from the target from impinging on the secondary electron detector. |
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DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG.
1, an electron beam imaging system constructed in accordance with the invention comprises a sharp tip electron source 10, a planar electrostatic lens 12, a substrate 14 and a stage 16 which may, for instance, be a known PZT actuator.
Electron source 10 is provided with a tip 18 that has a voltage -V1 applied which enables it to operate in the field emission mode.
Electrostatic lens 12 comprises a conductive sheet 20 and a juxtaposed dielectric layer 22.
An annular ring of conductor 24 is emplaced on the lower surface of dielectric layer 22 and about an aperture 25 that passes through each of the aforesaid layers.
Potential sources V2 and V3 are respectively connected to conductors 20 and 24 so as to create an electrostatic focusing action on the emitted electrons from tip 18.
To extract electrons into free space, the electrons must experience an overall accelerating voltage.
In this case, that implies V3-(-V1)>0.
In the case of three or more conducting layers, the condition is that Vf-(-V1)>0, where Vf is the voltage on the electrode closest to the sample.
In the case shown here, the potential difference V3-(-V1)) is generally greater than the difference (V2-(-V1)) in order to achieve focusing action.
Generally the target will be held at potential V3, so that no electric field exists in the free space region between the lens and the target.
It is possible, however, to place a different bias voltage on the target, in which case the target can be considered as part of the lens and can provide additional electrostatic focusing.
Alternatively, the target may be held at a potential which is slightly negative with respect to the secondary detector in order to enhance the collection of the secondary electrons.
As a result of the focusing action of microlens 12, emitted electrons from tip 18 are focused onto a conductive surface 26 of sample 14 and cause secondary electrons to be emitted therefrom.
Those secondary electrons travel back towards the underside of microlens 12 and impinge upon a conductive region 28
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