F2 laser with visible red and IR control

• US 6,330,260 B1
• Filed: 11/12/1999
• Issued: 12/11/2001
• Est. Priority Date: 03/19/1999
• Status: Expired due to Fees

• Current Assignee: Cymer Incorporated (ASML Holding NV)
• Original Assignee: Cymer Incorporated (ASML Holding NV)
• Inventors: Sandstrom, Richard L., Duffey, Thomas P., Onkels, Eckehard D.
• Primary Examiner(s): Arroyo, Teresa M.
• Assistant Examiner(s): Monbleau, Davienne
• Application Number:
  US09/438,249
• Time in Patent Office: 760 Days
• Field of Search: 372/38.1, 372/38.04, 372/55, 372/57, 372/58, 372/59
• US Class Current: 372/38.04
• CPC Class Codes: G03F 7/70025 by lasers
• CPC Class Codes: G03F 7/70041 by pulsed sources, e.g. multiplexing, pulse duration, interval control or intensity control
• CPC Class Codes: G03F 7/70483 Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
• CPC Class Codes: G03F 7/70558 Dose control, i.e. achievement of a desired dose
• CPC Class Codes: G03F 7/70575 Wavelength control, e.g. control of bandwidth, multiple wavelength, selection of wavelength or matching of optical components to wavelength
• CPC Class Codes: H01S 3/036 Means for obtaining or maintaining the desired gas pressure within the tube, e.g. by gettering, replenishing; Means for circulating the gas, e.g. for equalising the pressure within the tube H01S3/031 takes precedence
• CPC Class Codes: H01S 3/10092 Coherent seed, e.g. injection locking
• CPC Class Codes: H01S 3/225 comprising an excimer or exciplex

Abstract

A reliable, modular, production quality F₂ excimer laser capable of producing, at repetition rates in the range of 1,000 to 2,000 Hz or greater, laser pulses with pulse energies greater than 10 mJ with a full width half, maximum bandwidth of about 1 pm or less at wavelength in the range of 157 nm. Laser gas concentrations are disclosed for reducing unwasted infrared emissions from the laser. Also disclosed are UV energy detectors which are substantially insensitive to infrared light. Preferred embodiments of the present invention can be operated in the range of 1000 to 4000 Hz with pulse energies in the range of 10 to 5 mJ with power outputs in the range of 10 to 40 watts. Using this laser as an illumination source, stepper or scanner equipment can produce integrated circuit resolution of 0.1 μm or less. Replaceable modules include a laser chamber and a modular pulse power system.

Claims

1. A very narrow band reliable modular production quality high repetition rate F₂ excimer laser for producing a narrow band pulsed laser beam at repetition rates of at least about 1000 Hz, said laser comprising:

A. a laser chamber module comprising a laser chamber comprising;

1) two elongated electrodes;

2) a laser gas comprised of

a) fluorine, and

b) a buffer gas mixture comprising helium and neon;

3) a gas circulator for circulating said gas between said electrodes at speeds of at least two cm/millisecond

B. a pulse power system of a power supply and pulse compression and amplification circuits and pulse power controls for producing high voltage electrical pulses of at least 14,000 volts across said electrodes at rates of at least about 1000 Hz; and

C. a laser pulse energy control system for controlling the voltage provided by said pulse power system, said control system comprising a laser pulse energy monitor and a computer processor programmed with an algorithm for calculating, based on historical pulse energy data, electrical pulses needed to produce laser pulses having pulse energies within a desired range of energies.

2. A laser as in claim 1 wherein the mixture defines a neon concentration within a range of 0.4 to 0.95.

3. A laser as in claim 2 wherein the mixture defines a neon concentration within a range of 0.52 to 0.63.

4. A laser as in claim 1 wherein said chamber and said gas circulator define a gas flow path and an upstream direction and said laser also comprises a single preionizer tube located upstream of said electrodes.

5. A laser as in claim 1 wherein each of said electrodes define an electrode length and said single preionizer tube is comprised of a grounded electrically conducting rod positioned along the axis of an Al₂O₃ hollow cylindrical tube having a length longer than said electrode length.

6. A laser as in claim 1 wherein said laser chamber defines a chamber structure and wherein said two elongated electrodes define a cathode and an anode and said cathode is insulated from said chamber structure by a single piece insulator comprised of Al₂O₃ which is attached to a portion of said chamber structure.

7. A laser as in claim 6 wherein said cathode is mounted directly on said single piece insulator.

8. A laser as in claim 1 wherein all seals exposed to said laser gas are metal seals.

9. A laser as in claim 1 wherein said two elongated electrodes define a cathode and an anode and said anode is supported by an anode support bar having a tapered surface positioned to reduce aerodynamic reaction forces on said bearings.

10. A laser as in claim 1 wherein said power supply comprises a rectifier for converting AC power to DC power, an inverter for converting the DC power to high frequency AC power, a step-up transformer for increasing the voltage of said high frequency AC power to a higher voltage, a rectifier for converting the higher voltage to charge a charging capacitor to a voltage at or approximately at a command voltage established by said laser pulse energy control system.

11. A laser as in claim 10 wherein said power supply is configured to slightly over charge said charging capacitor and further comprises a bleed circuit to bleed down said charging capacitor to said command voltage.

12. A laser as in claim 10 wherein said pulse power system comprises a solid state switch which upon closing initiates said high voltage electrical pulses by allowing charge to flow from said charging capacitor to a second capacitor to create a high voltage charge on said record capacitor.

13. A laser as in claim 10 and further comprising an inductor, a pulse transformer and a third capacitor wherein said inductor, pulse transformer and said third capacitor are arranged to permit the high voltage charge on said second capacitor to flow to ground through the primary side of said pulse transformer in order to produce a very high voltage pulse at the output of said pulse transformer to be stored temporarily on said third capacitor.

14. A laser as in claim 10 wherein said primary side of said pulse transformer comprises a plurality of hollow spools, each spool defining an axis, connected in series and a secondary side of said pulse transformer is comprised of at least one rod co-aligned with the axis of a plurality of said spools.

15. A laser as in claim 10 wherein said at least one rod is four rods connected in series and defining two leads, one defining a ground lead and the other a very high voltage lead.

16. A laser as in claim 1 wherein said laser pulse power system comprises at least one saturable inductor with a coil emersed in oil contained in a pot which also serves as the high voltage lead of the inductor.

17. A laser as in claim 1 wherein said gas circulator comprises a blower comprising a shaft supported by active at least two magnetic bearings, each bearing comprising a stator and a rotor, said shaft bearing driver by a motor comprising a stator and a rotor, said blower also comprising a sealing means for sealing said rotors within an environment containing said laser gas with said stator outside said laser gas environment.

18. A laser as in claim 1 wherein said gas circulator comprises a blower comprising a shaft supported by at least two ceramic bearings.

19. A laser as in claim 1 and further comprising a purge system having an exit port comprising a long tube having a length and defining an average internal dimension of less than one fiftieth said length, said purge system providing an purge flow to at least one laser optical component outside the laser chamber.

20. A laser as in claim 19 wherein said purge system comprises a flow monitor to detect purge flow.

21. A laser as in claim 1 and further comprising a pulse energy detector comprising a pulse energy insensitive to visible red light and infrared light.

22. A laser as in claim 1 and further comprising a solar-blind energy detector for detecting pulse energy.

23. A very narrow band reliable modular production quality high repetition rate F₂ excimer laser for producing a narrow band pulsed laser beam at repetition rates of at least about 1000 Hz, said laser comprising:

A. a laser chamber module comprising a laser chamber comprising;

1) two elongated electrodes;

2) a laser gas comprised of

a) fluorine, and

b) a buffer gas;

3) a gas circulator for circulating said gas between said electrodes at speeds of at least two cm/millisecond

B. a pulse power system of a power supply and pulse compression and amplification circuits and pulse power controls for producing high voltage electrical pulses of at least 14,000 volts across said electrodes at rates of at least about 1000 Hz;

C. a laser pulse energy control system for controlling the voltage provided by said pulse power system, said control system comprising a laser pulse energy monitor and a computer processor programmed with an algorithm for calculating, based on historical pulse energy data, electrical pulses needed to produce laser pulses having pulse energies within a desired range of energies; and

D. a pulse energy detector sensitive to UV light in the range of 157 nm but insensitive to both visible red light and infrared light.

24. A laser as in claim 23 wherein said detector is a solar-blind detector.

25. A laser as in claim 23 wherein said detector is a phototube.

26. A laser as in claim 23 wherein said detector is a phototube comprising a photocathode material chosen from a group consisting of CsTe, CsI and diamond.

27. A laser as in claim 23 wherein said buffer gas comprises helium.

28. A laser as in claim 23 wherein said buffer gas comprises helium and neon.

29. A laser as in claim 23 wherein said detector comprises at least one mirror configured to preferentially reflect or transmit UV light.

30. A laser as in claim 23 wherein said detector comprises at least one dispersion element configured to disperse UV light in a direction different from visible or IR light present in said beam.

31. A laser as in claim 23 wherein said detector comprises a fluorescing element configured to fluoresce upon exposure to UV light.