Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1999-07-30
2001-06-12
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S379000
Reexamination Certificate
active
06246190
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electron guns, and more specifically, to the electrical connections between a power supply and an associated electron gun.
BACKGROUND
Electron guns are well known to produce electron beams and are used in several fields, including television receivers, scanning electron microscopes, defect detection instruments, VLSI testing equipment and electron beam lithography. The electron gun power supply typically used is a DC high voltage power supply (HYPS). High voltages are required to power the various electrodes, which accelerate, focus, and deflect the electron beams within an electron beam (e-beam) column which is a typical use of an electron gun. Typically, the power supplies operate at a floating potential between 10 kV and 100 kV in, for example, e-beam columns in lithography systems. In many of these applications, the electron gun is an assembly mounted on the upper portion of an electron beam column.
It is a well known deficiency that an interconnecting cable must be used to electrically connect the HVPS to the electron gun (see FIG.
1
). Typically, a computer or controller (not shown) controls a module
103
which includes a DC power supply (a HVPS), which in turn supplies a high voltage, and other signals, to an electron gun
105
, which is mounted at one end of an electron beam column
107
. Being very sensitive to vibration, the electron gun
105
and electron beam column
107
are mounted on a vibration-isolated floating work table
113
. Having large, heavy transformers and power conditioning circuits, the module typically weighs 50 to 80 pounds, and thus cannot be mounted directly on the electron gun, but is mounted on a stand-alone structure
115
in contact with the ground (hence, it is often called a rack-mounted HVPS design). A heavy high voltage cable
109
routes the power and signals from the module
103
to the electron gun
105
. Vibrations on the ground or from the rack itself can transmit through the heavy, stiff cable to the electron gun and produce vibrations in the electron beam column which is not acceptable when conducting electron beam lithography.
The cable is very expensive, especially when used in conjunction with a Thermal Field Emission (TFE) electron gun, and may represent a significant portion of the cost of the entire system. The cable is expensive in large part because it is difficult to make; the insulation material must be a high-quality silicone rubber, which is free from air pockets which contribute to arcing. Moreover, it must be flexible enough to prevent vibrations, both internally and externally produced by the HVPS, from being transmitted along the cable to the vibration-sensitive electron gun. The heavy, complex mating assemblies
111
between the high voltage cable and the electron gun on one end, and between the cable and the power supply on the other end, must be nearly perfect; if they are not, electrical current will be discharged to the surrounding air (arcing).
Another disadvantage of the cable is its high capacitance. When arcing does occur from the cable, which is at a high operating voltage (for example, 50,000 V) and a high capacitance, a great deal of energy is released. This energy is often transmitted to the electron gun or the HVPS, often resulting in damage to these components.
SUMMARY
According to the present invention, an electron gun suitable for use with a conventional electron beam column integrates electronic circuitry to power the electron gun together with the electron gun itself in one assembly. The electronic circuitry portion of the assembly has two sections: an active electronics section (which contains a digital to analog converter, interface to a control computer, and analog outputs to control the high voltage electronics) and a high voltage electronics section (which contains high-voltage multiplying circuits and feedback and filtering elements).
The electronic circuitry portion of the assembly weighs about 10 pounds in one example, and is seated on top of the electron gun. A DC power supply is used, along with a digital to analog converter, which is more easily serviceable than a large AC power supply. The control computer is electrically connected to the electronic circuits portion of the assembly via a control cable. The entire assembly is housed in a conductive enclosure and is seated on top of an electron beam column.
The most important aspect of the present invention is that it eliminates the bulky, complex, expensive cables relied on in previous HVPS designs to connect the high voltage electronics to the various gun electrodes. The present invention joins the critical electronic circuitry and the electron gun in one integrated assembly, so that design considerations for the electron gun, regarding the cable's diameter and weight, are eliminated. This, in turn, lowers the cost of the assembly. Moreover, the few soldered wires connecting the high voltage electronics to the electron emitter have much lower capacitance than the prior art interconnecting cables, reducing the likelihood of damage to the electron gun or the power supply if arcing does occur. Another feature of the present invention is that its configuration improves serviceability in the field.
Two embodiments of the invention are described. In a first embodiment, the electronic circuits are partitioned into two sections: a control section, which includes the active electronics and is contained within an internal enclosure inside the assembly, and a high voltage electronics section, which has a lower failure rate. The entire control section is field-replaceable. Advantageously, the internal enclosure and its components are easily detached from the high voltage electronics section and the remainder of the electron gun assembly by disconnecting mating connectors. Thus, in this embodiment, the module may be serviced in the field by removal and replacement of the internal enclosure, without disturbing the critical connection between the high voltage electronics and the electron gun.
In a second embodiment, both the control section and the high voltage electronics section are contained within the internal enclosure. However, the field replaceable unit here is the printed circuit boards which contain the active electronics. The active electronics section is electrically connected to the high voltage electronics section and the electron emitter via a standard, low voltage mating connector. This embodiment provides quick, easy replacement of the active electronics section (which is more likely to fail than the high voltage electronics) in the field by disconnecting the printed circuit boards from the mating connector. A removable cap allows access to the active electronics in both embodiments.
The invention and its various embodiments are further discussed along with the following figures and accompanying text.
REFERENCES:
patent: 3795837 (1974-03-01), Chang
patent: 3894271 (1975-07-01), Pfeiffer et al.
patent: 4153848 (1979-05-01), Pease
patent: 4543512 (1985-09-01), Nakasuji et al.
patent: 4703234 (1987-10-01), Kato
patent: 4820927 (1989-04-01), Langner et al.
patent: 0 689 224 A1 (1995-12-01), None
patent: 2 129 031 (1972-10-01), None
Revell et al., “PSU for a scanning electron microscope,” Mar. 1998, Electronic Engineering, GB, vol. 70, No. 855.
Etec Systems, Inc.
Kuo Jung-hua
Nguyen Hoang
Wong Don
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