Reliable, modular, production quality narrow-band high rep rate F2 laser

• US RE38,054 E1
• Filed: 03/07/2001
• Issued: 04/01/2003
• Est. Priority Date: 07/18/1997
• Status: Expired due to Fees

• Current Assignee: Cymer Incorporated (ASML Holding NV)
• Original Assignee: Cymer Incorporated (ASML Holding NV)
• Inventors: Rothweil, Daniel A., Sandstrom, Richard L., Das, Palash P., Ishihara, Toshihiko, Hofmann, Thomas, Partlo, William N., Duffey, Thomas P., Ness, Richard M., Besaucele, Herve A., Morton, Richard G., Newman, Peter C., Melchior, John T., Hueber, Jean-Marc
• Primary Examiner(s): Scott, Jr., Leon
• Application Number:
  US09/801,383
• Time in Patent Office: 755 Days
• Field of Search: 372/25, 372/92, 372/38, 372/70, 372/69, 372/58, 372/86, 372/87, 372/102, 372/34, 372/82, 372/37, 372/60, 372/33
• US Class Current: 372/25
• CPC Class Codes: C23C 14/0694 Halides
• CPC Class Codes: C23C 14/16 on metallic substrates or on substrates of boron or silicon
• CPC Class Codes: C23C 14/225 Oblique incidence of vaporised material on substrate
• CPC Class Codes: C23C 14/24 Vacuum evaporation
• CPC Class Codes: G01J 9/00 Measuring optical phase difference devices or arrangements for controlling the phase of light beams G02F1/01; Determining degree of coherence; Measuring optical wavelength spectrometry G01J3/00
• CPC Class Codes: G02B 1/105 Protective coatings
• CPC Class Codes: G02B 5/1852 using mechanical means, e.g. ruling with diamond tool, moulding
• 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 7/70358 Scanning exposure, i.e. relative movement of patterned beam and workpiece during imaging
• 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 3/02 Constructional details housings or packages of fibre lasers H01S3/06704
• CPC Class Codes: H01S 3/03 of gas laser discharge tubes
• 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 3/08009 using a diffraction grating
• CPC Class Codes: H01S 3/097 by gas discharge of a gas laser
• CPC Class Codes: H01S 3/0971 transversely excited H01S3/0975 takes precedence
• CPC Class Codes: H01S 3/1055 one of the reflectors being constituted by a diffraction grating
• CPC Class Codes: H01S 3/134 in gas lasers
• CPC Class Codes: H01S 3/1392 : by using a passive reference, e.g. absorption cell H01S3/1396, H01S3/1398 take precedence
• CPC Class Codes: H01S 3/223 : the active gas being polyatomic, i.e. containing two or more atoms H01S3/227 takes precedence
• CPC Class Codes: H01S 3/225 : comprising an excimer or exciplex
• CPC Class Codes: H01S 3/2251 : ArF, i.e. argon fluoride is comprised for lasing around 193 nm
• CPC Class Codes: H01S 3/2256 : KrF, i.e. krypton fluoride is comprised for lasing around 248 nm
• CPC Class Codes: H03K 17/80 : using non-linear magnetic devices; using non-linear dielectric devices H03K17/95, H03K17/97 take precedence
• CPC Class Codes: H03K 3/57 : the switching device being a semiconductor device

Abstract

The present invention provides a reliable modular production quality excimer laser capable of producing 10 mJ laser pulses in the range of 1000 Hz to 2000 Hz or greater. Replaceable modules include a laser chamber; a pulse power system comprised of three modules; an optical resonator comprised of a line narrowing module and an output coupler module; a wavemeter module, an electrical control module, a cooling water module and a gas control module. Important improvements have been provided in the pulse power unit to produce faster rise time and improved pulse energy control. These improvements include an increased capacity high voltage power supply with a voltage bleed-down circuit for precise voltage trimming, an improved communication module that generates a high voltage pulse from the capacitors charged by the high voltage power supply and amplifies the pulse voltage 23 times with a very fast voltage transformer having a secondary winding consisting of a single four-segment stainless steel rod. A novel design for the compression head saturable inductor greatly reduces the quantity of transformer oil required and virtually eliminates the possibility of oil leakage which in the past has posed a hazard.

Claims

1. A very narrow band reliable modular production quality high repetition rate ArF 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 quickly replaceable laser chamber module comprising a laser chamber comprising;

1) two elongated electrodes;

2) a laser gas comprised of

a) fluorine, and

b) a noble gas;

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

B. a modular pulse power system comprised of at least one quickly replaceable module, said system being comprised 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 said chamber, said pulse power system, said line narrowing system, said energy control system and substantially all electrical, optical and mechanical components of said laser are contained in quickly replaceable modules.

3. A laser as in claim 2 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.

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 all of said at least three prisms are comprised of calcium fluoride.

7. A laser as in claim 1 wherein said two elongated electrodes define a cathode and an anode and said anode support bar comprises cooling fins.

8. A laser as in claim 7 herein said anode and said anode support bar together have a combined mass of at least about 3.4 kg.

9. A laser as in claim 1 wherein said two elongated electrodes define a cathode and an anode and said anode comprises cooling fins.

10. A laser as in claim 1 wherein said modular pulse power system is comprised of at least three modules which each of which are designed for quick removal and replacement.

11. 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.

12. A laser as in claim 11 wherein the portion of said chamber structure to which said single piece insulator is comprised of a material having a coefficient of thermal expansion similar to that of Al₂O₃.

13. A laser as in claim 12 wherein said structure material is ASTM A36 steel.

14. A laser as in claim 13 wherein said cathode is mounted directly on said single piece insulator.

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

16. A laser as in claim 1 further comprising flow vane structures comprised of monel.

17. A laser as in claim 1 and further comprising acoustic baffles.

18. 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.

19. A laser as in claim 18 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.

20. A laser as in claim 19 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.

21. A laser as in claim 20 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.

22. A laser as in claim 21 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.

23. A laser as in claim 22 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.

24. 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.

25. 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.

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

27. A laser as in claim 1 and further comprising an N₂ purge system providing an N₂ purge flow to all laser optical components outside the laser chamber wherein said purge flow is contained at a pressure of less than 10 pascals.

28. A laser as in claim 1 and further comprising a means of measuring the rate of change of pulse energy with changing voltage Δ

E/Δ

V, and a computer controller programmed with an algorithm for controlling pulse energy and integrated energy dose in a burst of pulses defining present burst pulses, P₁, P₂ . . . P_N . . . P_k. P_k+1, P_k+2 . . . P_K+N . . . P₁. P₂ . . . P<sub>N−

1</sub>, P_N, from said laser having a pulse power system including a high voltage charging system defining a charging voltage, said algorithm comprising the steps of;

A) measuring the energy in each pulse of said burst of pulses,

B) determining a rate of change of pulse energy with charging voltage, Δ

E/Δ

V,

C) controlling the pulse energy of each pulse P_N in the first K pulses, in said burst of pulses by regulating the charging voltage of the laser utilizing a computer processor programmed with a first algorithm which;

(1) determines for each P_N a pulse energy error, ε

, based on a measured energy of at least one previous pulse in said burst and a predetermined target pulse energy value,

(2) determines for each P_N an integrated dose error, D, of all previous pulses P₁ through P<sub>N−

1</sub> in said burst,

(3) determines a charging voltage V_N, for each of said pulses, P_N, in said first plurality of pulses using;

(i) said Δ

E/Δ

V

(ii) said ε

(iii) said D

(iv) a reference voltage based on specified voltages for PN in a plurality of previous bursts,

D) controlling the pulse energy of each pulse P_K+N, in pulses following P_K in said burst of pulses by regulating the charging voltage of the laser utilizing a computer processor programmed with a second algorithm which;

(1) determines for each P_N a pulse energy error, ε

, based on a measured energy of at least one previous pulse in said burst and a predetermined target pulse energy value,

(2) determines for each P_N an integrated dose error, D, of all previous pulses, P₁ through P<sub>N−

1</sub> in said burst,

(3) determines a charging voltage, V_N, for each of said pulses, P_N in said first plurality of pulses using;

(i) said Δ

E/Δ

V

(ii) said ε

(iii) said D

(iv) a reference voltage based on specified voltages for P_N in a plurality of previous bursts,

wherein said V_N'"'"'s in said fast and second algorithms are functions of at least said Δ

E/Δ

V, said ε

, said D and said at least one reference voltage and said V_N'"'"'s when calculated one utilized to adjust said charging voltage to control both the individual pulse energy and the integrated energy dose to desired values.

29. A laser as in claim 1 and further comprising an anode support means comprising a tapered surface for reducing the magnitude of aerodynamic reaction forces resulting from laser gas exiting said blower and being redirected by said anode support means.

30. A laser as in claim 1 and further comprising a fluorine injection system comprising a processor programmed with an algorithm designed to cause fluorine to be injected continuously or at intervals of less than 30 minutes in order to maintain fluorine concentration substantially constant at a desired concentration over extended time periods of at least several days.

31. A laser as in claim 30 wherein said fluorine injection system and further comprising a feedback providing to said processor a voltage signal representative of laser discharge voltages which signal is used by said processor to maintain said signal within a predetermined range.

32. A laser as in claim 31 wherein said predetermined range is revised periodically in order to keep the laser operating with a fluorine concentration within a desired range.

33. A laser as in claim 32 further comprising a means for periodically determining a laser parameter representative of a temporal pulse width of the laser pulses.

34. A laser as in claim 30 wherein said determined parameter is the integral square pulse width.

35. A reliable modular production quality high repetition rate excimer laser for producing a narrow band pulsed laser beam at a repetition rate of at least about 1Khz, said laser comprising:

A. a quickly replaceable laser chamber module comprising;

1) two elongated electrodes

2) a laser gas comprised of fluorine and a buffer gas,

3) a gas circulator system for circulating said laser gas between said electrodes at at least two cm/millisecond comprising;

a) a braze-free blade structure defining a shaft,

b) a brushless motor for rotating said shaft,

c) magnetic bearings for supporting said shaft said motor and said bearings having rotors attached to said shaft and sealed within an environment exposed to said laser gas and said motor and said bearings having a stator outside of said laser gas environment.

B. a pulse power system substantially contained within at least one quickly replaceable module and comprising;

1) a processor controlled high voltage power supply for periodically, at rates of at least about 1000 Hz, charging with electrical energy a charging capacitor to a predetermined pulse control voltage,

2) a compression and amplification circuit for connecting electrical energy stored on said charging capacitor into a high voltage electrical pulses of at least 14,000 volts across said electrodes.

36. A laser as in claim 35 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 electrode and 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.

37. A laser as in claim 35 and further comprising a means of measuring the rate of change of pulse energy with changing voltage Δ

E/Δ

V, and a computer controller programmed with an algorithm for controlling pulse energy and integrated energy dose in a burst of pulses defining present burst pulses, P₁, P₂ . . . P_N . . . P_k,P_K+1, P_K+2 . . . P_K+n, . . . P₁, P₂ . . . P<sub>N−

1</sub>, P_N, from said laser having a pulse power system including a high voltage charging system defining a charging voltage, said algorithm comprising the steps of;

A) measuring the energy in each pulse of said burst of pulses,

B) determining a rate of change of pulse energy with charging voltage, Δ

E/Δ

V,

C) controlling the pulse energy of each pulse P_N in the first K pulses, in said burst of pulses by regulating the charging voltage of the laser utilizing a computer processor programmed with a first algorithm which;

(1) determines for each P_N a pulse energy error, ε

, based on a measured energy of at least one previous pulse in said burst and a predetermined target pulse energy value,

(2) determines for each P_N an integrated dose error, D, of all previous pulses P₁ through P<sub>N−

1</sub> in said burst.

(3) determines a charging voltage V_N, for each of said pulses, P_N, in said first plurality of pulses using;

(i) said Δ

E/Δ

V

(ii) said ε

(iii) said D

(v) a reference voltage base on specified voltages for PN in a plurality of previous bursts,

D) controlling the pulse energy of each pulse P_K+N, in pulses following P_K in said burst of pulses by regulating the charging voltage of the laser utilizing a computer processor programmed with a second algorithm which;

(1) determines for each P_N a pulse energy error, ε

, based on a measured energy of at least one previous pulse in said burst and a predetermined target pulse energy value,

(2) determines for each P_N an integrated dose error, D, of all previous pulses P₁ through P<sub>N−

1</sub> in said burst,

(3) determines a charging voltage, V_N, for each of said pulses, P_N in said first plurality of pulses using;

(i) said Δ

E/Δ

V

(ii) said ε

(v) said D

(vi) a reference voltage based on specified voltages for P_N in a plurality of previous bursts,

wherein said V_N'"'"'s in said first and second algorithms are functions of at least said Δ

E/Δ

V, said ε

, said D and said at least one reference voltage and said V_N'"'"'s when calculated one utilized to adjust said charging voltage to control both the individual pulse energy and the integrated energy dose to desired values.