Coaxial laser pulser with solid dielectrics

Details Coaxial laser pulser with solid dielectrics Coaxial laser pulser with solid dielectrics

1999-09-03

2001-03-06

Scott, Jr., Leon (Department: 2881)

Coherent light generators

Particular pumping means

Electrical

C372S081000, C372S082000, C372S025000

Reexamination Certificate

active

06198761

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a coaxial laser pulser which utilizes solid dielectric compounds and provides pulses of electrical energy.
DESCRIPTION OF RELATED ART
The lithographic process employed in fabrication of microprocessor chips often employs an excimer laser as a short wavelength source of illumination. Specific types of excimer lasers include KrF, emitting at 248 nm, ArF, emitting at 193 nm, and F
2
, radiating at 157 nm. Such a laser is direct discharge pumped, normally at voltages in the range of 30 kV, and at pulse repetition rates above 1 KHz. Peak electrical power input to the laser can be several tens of megawatts. Furthermore, to make the lithographic process commercially viable the equipment must not exhibit unscheduled down time and must deliver pulses of the highest stability, uniformity, and spectral quality for uninterrupted periods of weeks at a time.
These requirements have in recent time led to the development of pulsers driven by solid state switches as an improvement on switch life. Replacement of the gaseous thyratron with a solid state switch has been proven to greatly extend laser service intervals and hence reduce operating costs, but whereas the thyratron operating range covers voltages of 20-30 kV, best utilization of solid state switch capabilities occurs at lower voltages, typically in the range of 1-5 kV. Connecting solid state devices in series to reach the thyratron operating voltage range is not cost effective, and in addition solid state switches of the type utilized do not possess sufficient di/dt capability to provide the required voltage risetime of 50-100 ns. Hence the solid state switch is normally used to drive a step-up pulse transformer and a multi-stage pulse compressor to reach correct laser operating voltage and voltage risetime. The attainment of the necessary voltage level, in the range of 30 kV, with sufficiently low circuit inductance, in the range of tens of nH or less, at multikilowatt average power levels is typically done with transformer oil, vapor phase coolants, or pressurized gas such as sulfur hexafluoride or nitrogen. Examples of some pulsers are seen in U.S. Pat. Nos. 5,142,166 and 5,313,481 and 5,177,754.
Atmospheric air does not possess sufficient dielectric strength to withstand the necessary voltage stress or the necessary thermal properties to dissipate the generated heat. Leak-free containment of oil over long time periods is known to be difficult. Vapor phase coolants are expensive and primarily suited for heat removal rather than voltage insulation. Gas containment at the necessary several atmospheres pressure requires use of thick-walled pressure vessels and elaborate seals. In addition, for the above approaches a heat exchanger and pump are required to extract heat from the cooling medium. Using solid dielectrics such as thermal compounds in paste form in present pulser designs is cost prohibitive and would generate excessive temperature gradients due to their basic thermal properties.
The low voltage portion of such a pulser operates at high effective currents which require cooling and the high voltage portion requires positive air displacement to prevent corona generation and resulting breakdown. These requirements exist due to the high voltages, currents, and rates of change of these voltages and currents and the dimensional constraints imposed by the geometry of the laser system. The laser electrode system is typically driven from a point which is centrally located on the chamber so as to present the lowest possible inductance to the energy transfer system. What is needed is a pulser which generates the voltage necessary to drive a laser, but which does not require liquid or gaseous dielectric compounds and exhibits radial symmetry thereby providing law-transfer impedance.
A great deal of work has been done in the area of designing pulse compressors, transformers and the like. One example of a reference dealing with leakage inductance and flux considerations of transformers is Flanagan, William M.
Handbook of Transformer Applications
, Second Ed., New York: McGraw Hill, 1993. An example of a work providing detailed background on inductance calculations is Grover, Frederick W.
Inductance Calculations
New York: D. van Nostrand Company, Inc., 1946. A seminal work relating to pulse compressor theory and circuit description is Melville, W. S., “The Use of Saturable Reactors as Discharge Devices for Pulse Generators”, Proceedings of the Institution of Electrical Engineers, Radio and Communications, London, England, Vol 93, p185, 1951. Another work relating to pulse compressor theory is von Bergmann, H. M., Swart, P. H., “Thyristor-Driven Pulsers for Multikilowatt Average Power Lasers”, IEE Proceedings -B, Vol 139, No. 2, March 1992. A work providing background on compressor stage optimization is Greenwood, M. and Gowar, J., “An Optimization Strategy for Efficient Pulse Compression”, University of Bristol, Industrial Electronics Group, Queen's Building, University Walk, Bristol BS8 1TR, United Kingdom, IEEE publication 1990. Another work providing background on compressor stage optimization is Druckman, I., Gabay, S., and Smilanski, I., “A New Algorithm for the Design of Magnetic Pulse Compressors”, NRCN, P.O. Box 9001, 84190 Beer Sheva, Israel. Also published in 1992 by IEEE.
SUMMARY OF THE INVENTION
The invention eliminates the need for liquid and gaseous dielectric compounds in the pulser. An objective of one embodiment of this invention is to provide a pulser which obviates the need for liquid or gaseous dielectric compounds and thereby avoids leakage of a dielectric liquid or gas which can create a contaminated environment which is highly detrimental to the lithographic process. In the preferred embodiment this is achieved using a coaxial pulse compressor and pulse transformer in conjunction with a conformal solid dielectric material as disclosed herein and the equivalents thereof as disclosed herein. Numerous other advantages can be obtained by providing a pulser as described herein. First, leakage of a dielectric liquid or gas can cause failure or unscheduled shutdown of the lithographic equipment. Second, service or modular replacement of laser components as presently constructed requires several personnel and often power assisted lift or transport mechanisms due to the size and weight of such components. This invention eliminates several tens of liters of transformer oil and the attendant weight as well as the need for an oil tight tank. Third, elimination of circulating pumps and heat exchangers reduce the count of moving parts, shaft seals, gaskets, and galvanic contact of dissimilar metals and hence improves the reliability of the pulser. The present invention uses a solid dielectric compound and does not require dielectric liquids or gases and hence offers considerable size and weight reduction. A further advantage of an embodiment of the invention is that the space and special handling and storage requirements for replacement pulsers are reduced due to the considerable weight reduction.


REFERENCES:
patent: 4718072 (1988-01-01), Marchetti et al.
patent: 4763093 (1988-08-01), Cirkel et al.
patent: 4928020 (1990-05-01), Birx et al.
patent: 4983859 (1991-01-01), Nakajima et al.
patent: 5090021 (1992-02-01), Nakatani et al.
patent: 5142166 (1992-08-01), Birx
patent: 5177754 (1993-01-01), Ball et al.
patent: 5181217 (1993-01-01), Sato et al.
patent: 5305338 (1994-04-01), Wakata et al.
patent: 5313481 (1994-05-01), Cook et al.
patent: 5315611 (1994-05-01), Ball et al.
patent: 5319665 (1994-06-01), Birx
patent: 5729562 (1998-03-01), Birx et al.
patent: 5754579 (1998-05-01), Mizoguchi et al.
patent: 5914974 (1999-06-01), Partlo et al.
patent: 38 42 492 (1988-12-01), None
patent: 2267790 (1993-06-01), None
patent: WO 96/25778 (1996-08-01), None
I. Smilanski et al., Electrical excitation of an XeCl laser using magnetic pulse compression,Appl. Phys. Lett., vol. 40, No. 7, Apr. 1, 1982, pp. 547-548.
O. Kobayashi et al., “High power repetitive excimer lasers pumped by an all s

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