JP2002094151A - Gas discharge laser provided with blade insulation electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas discharge laser provided with a blade insulation electrode for a gas discharge with an erodable electrode capable of withstanding several billions of pulses without adversely affecting a gas flow and without adversely affecting laser beam quality. SOLUTION: This gas discharge laser is provided with a laser chamber with two elongated erodable electrode elements. At least, one of the electrode elements is provided with a generally blunt blade shape comprised of a material having high electrical conductivity with a flow shaping dielectric fairing positioned on each of two sides of the blunt blade-shaped part. A pulse power system provides electrical pulses at the frequency of at least 1 kHz. A blower circulates laser gas between the electrodes at speeds of at least 10 m/s, and a heat exchanger is provided to remove heat produced by the blower and the discharges.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present application is filed on June 9, 2000.
U.S. Patent Application Serial No. 09 / 590,961
Is a continuation-in-part application of that issue, which application is hereby incorporated by reference. The present invention relates to discharge lasers, and more particularly to such lasers having chambers with long-lived electrodes.

[0002]

2. Description of the Prior Art The major components of a prior art KrF excimer laser chamber are shown in FIG. This chamber is part of a laser system used as a light source for integrated circuit lithography. These components are
Includes chamber housing. The housings are approximately 50
two electrodes 84 and 83, approximately 20 mm apart from each other by approximately 20 mm, between the pulse with a pulse repetition rate in the range of 1000 Hz or more (from the discharge area between the two electrodes). A) a blower 4 for circulating the laser gas between the electrodes at a speed fast enough to clear the debris, and water cooling fins for removing heat added to the laser gas by the fan and by the discharge between the electrodes. Attached heat exchanger 6. The chamber also includes vanes and baffles to improve the aerodynamic structure of the chamber. The laser gas consists of a gas mixture consisting of about 0.1 percent fluorine, about 1.0 percent krypton, and the balance neon. Each pulse has a very high voltage potential across the electrodes by a pulsed power supply 8 that can create a gain region of about 20 mm high, 3 mm wide, and 700 mm long by discharging during electrode lasting of about 30 nanoseconds. Is created by applying. The discharge causes about 2.5 J of energy to be stored in the gain region. As shown in FIG. 2, the lasing comprises a grating configured in a Littrow configuration, three prism beam expanders, and an adjusting mirror (both disproportionately expanded, a line narrowing package or LNP). (Referred to as grating base line narrowing unit 2B) and an output coupler 2A. The energy of the output pulse of this prior art KrF lithography laser is typically about 10 mJ. There are many industrial uses for discharge lasers. This is an important application as a light source for integrated circuit lithography machines. Such a laser light source,
The line narrowing KrF laser described above that produces a narrow band pulsed ultraviolet light beam of about 248 nm. These lasers typically operate with pulse bursts at a pulse frequency of about 1000-4000 Hz. Each burst consists of a number of pulses, for example, about 80 pulses, and some bursts are separated by a second part downtime during a lithography machine shift that illuminates between die parts. Irradiates a single die portion of the wafer. When a new wafer is loaded, there is another downtime of a few seconds. Thus, in manufacturing, for example, a KrF excimer laser at 2000 Hz operates at a loading of about 30 percent. Operation is 24 hours a day, 7 days a week, 52 weeks a year. 200 for 24 hours at 30% loading rate
Laser operation at 0 Hz accumulates more than 1.5 billion pulses / month. Product destruction is very costly.
For these reasons, conventional excimer lasers for the lithography industry have a modular configuration that minimizes maintenance downtime.

[0003] Maintaining the high quality of the laser beams produced by these lasers is very important because the lithographic systems in which these laser light sources are used are smaller than 0.25 microns.
This is because there is a current need to create integrated circuits of ever smaller dimensions. Laser beam specifications limit changes in individual pulse energies, changes in the integrated energy of a series of pulses, and changes in laser beam bandwidth size and laser wavelength.

[0004] The typical operation of a discharge laser as shown in FIG. 1 causes the electrodes to corrode. The corrosion of these electrodes is
Affects the shape of the discharge, which in turn affects the quality of the output beam as well as the laser efficiency. Electrode designs have been proposed to minimize the effects of corrosion by providing the electrodes with protrusions having the same width as the discharge. The same example is described in Japanese Patent No. 26
No. 31607. However, these designs have an adverse effect on gas flow. In these gas discharge lasers, it is practically very important to get all the effects of each pulse out of the discharge area before the next pulse.

[0005] There is a need for a gas discharge with a corroding electrode that can withstand billions of pulses without adversely affecting gas flow and without adversely affecting laser beam quality.

[0006]

SUMMARY OF THE INVENTION The present invention provides a gas discharge laser having a laser chamber with two elongated corrosive electrode elements, wherein at least one of the electrode elements has two of a blunt blade-shaped portion. It has an overall pillow blade shape of high conductivity material with flow shaping insulating fairings positioned on each side. Pulse power systems produce electrical pulses at a frequency of at least 1 KHz. A blower circulates the laser gas between the electrodes at a speed of at least 10 m / s, and a heat exchanger is provided to remove heat generated by the blower and the discharge.

[0007]

FIG. 3 shows the main components of an electrical circuit 8 for providing pulsed power to discharge a gas discharge laser. The pulse power system is standard 208 volts, 3
Operates from phase power. The power supply using rectifier 22, inverter 24, transformer 26 and rectifier 30 has a power of about 500
Charges 8.1 microfarad charge capacitor C ₀ 42 to a voltage level between 乃至 1200 volts. When a pulse is desired that can discharge the energy of C ₀ into the subsequent portion of the pulse power system,
The laser control processor indicates that the IGBT switch 46 is to be closed. C ₀ is charged by the inductor 48
Through the capacitor bank C ₁ 52, and then the saturable inductor 54 and the voltage transformer 5
6 to capacitor bank C _p-1 62, and then through saturable inductor 64 to peak capacitor bank C _p 82. As shown in FIG. 3, the peak capacitor bank C _p is connected electrically in parallel with electrodes 84 and 83.

FIG. 4A shows that after the switch 42 is closed,
Capacitor as a function of time up to microsecond
Bank C₀, C₁, C_p-1And C_pShows the potential of
FIG. 4B cuts out 800 ns immediately before and immediately after discharge.
Are shown. The reader, Peak Capacitor Bank C
_pIs charged to approximately -15,000V just before discharging
It should be noted that The discharge lasts about 30 ns. Release
During the electricity flow, the electron flow first goes to the upper electrode / cathode 84
Flows to the grounded electrode / anode 83 below. FIG.
As all shown in B, the current "overshoot"
Indicates that during the last approximately 15 ns discharge, the electron flow
After flowing from the lower grounded electrode to the upper electrode,
When the flow in the direction is reversed, about + 6000V
Positive value C _pCharge.

Applicants have noted that while electrode corrosion occurs on both electrodes,
The corrosion rate of the grounded electrode (anode 83) was found to be about four times that of the high voltage electrode (cathode 84).
Also, standard operation results in a metal fluoride insulating layer that builds up very slowly on a portion of the anode. Near the end of the life of the electrode, the portion of the discharge surface covered by the layer can be between 50% and even more than 80%. In the area covered by the fluoride layer, the discharge current flows through small holes with a generally circular cross section of typically about 50-100 microns in diameter. The surface covered by the fluorinated layer does not substantially suffer from further corrosion, but the uncoated surface is reduced,
Corrosion rates increase on uncoated discharge surfaces.
(These are manifested in corrosion of the coated surface at the location of the small holes.) Electrode erosion and prior art fluorine build-up are typically severe at about 5-10 billion pulses and the laser beam is severe. No longer meets the quality of the specification.

At this point, generally the laser chamber
Replace with a chamber with new electrodes. Replacement chambers can cost thousands of dollars and require a temporary stoppage of integrated circuit production to replace.

Many electric discharge lasers used for integrated circuit lithography utilize brass such as C36000 brass (61.5% copper, 35.5% zinc, 3% lead) as the electrode material. Many other materials have been tested for the discovery of better electrode materials, but, to the applicant's knowledge, have proven to be superior to brass when considering all costs, including laser fabrication and operation. There is nothing. However, in a recent study by the applicant, O.M., sold under Gridcop® and located at Research Triangle Park, North Carolina, USA
A high strength copper material containing sub-micron Al ₂ O ₃ lumps available from OMG Americas is a good electrode material. More recent tests by applicant have shown that copper, aluminum and iron, or copper,
It is shown that zinc and iron alloys and iron and copper alloys with trace amounts of zinc and phosphorus provide improved performance. These tests also show that annealing the electrode material after machining also improves performance. Good alloys are C95400 (85% copper, 11% aluminum, 4% iron) for both the anode and cathode, and C19400 (9% for the cathode).
7.5% Cu, 2.35% Fe, 12% Zn, and 0.1% Cu.
03% Ph). One of the applicants has discovered that a copper alloy known as a spinodal copper alloy is very suitable as an electrode material in a fluorine environment. Many excellent electrode materials are not suitable for violent fluorine reactions in these chambers.

Sputtered metal ions-discharge
In order to produce a critically good laser active medium, a uniform discharge plasma needs to be created between the electrodes. First, the gas in the gap between the electrodes is pre-ionized by the pre-ionization device 12 shown in FIG. As the voltage on the electrode increases, a significant portion of the plasma in the region near the cathode is created by ion sputtering of the electrode material. Metal atoms sputtered from the electrode are mostly in the vapor state, with a significant portion of the metal atoms being ionized, forming a positive ion cathode `` falling '' region immediately adjacent to the surface of the cathode. It creates a very large electric field that can help and contribute to the flow of electrons from the cathode and accelerate the electrons leaving the cathode. This process is first applied to cathode 84 during the first portion of each pulse.
However, as shown in FIG. 4B, since the polarity of the electrode is reversed approximately at the center through the pulse, this effect is due to the anode 8 now functioning as the cathode (ie, negative electrode).
3 also occurs. Depending on the conditions of the rapidly changing electric field,
Both during and after the pulse, metal ions can be attracted back to the electrode, but many are blown away by the circulating laser gas because some of the displaced electrode material is transported across the gas flow boundary layer. It is. Applicants have determined that the erosion loss at the anode is about 3 grams per billion pulses, or about 2.8 × 10
It is estimated to be about 3 × 10 ^-9 grams per pulse corresponding to ¹³ atoms. With a discharge surface of about 1500 square millimeters on the anode, the loss is about 1.2 × 10 ¹⁰ atoms /
Square millimeter / pulse. Each atomic layer of the brass electrode contains about 3 × 10 ¹³ atoms per square millimeter, so that about 2,250 pulses (slightly over 1 second at a pulse rate of 2,000 Hertz) leave the electrode at 1 mm. One atomic layer is lost. After 10 billion pulses, about 4.4 million atomic layers are lost, corresponding to a reduction of about 0.5 millimeters in the vertical position of the electrode discharge surface. In a prior art electrode of the type shown in FIG. 1, this reduction is due to the expansion of the discharge area, the expansion of the discharge, the dislocation,
Or, it involves division and accumulation of a fluoride layer at each part of the anode discharge surface. This usually has a substantial adverse effect on the quality of the laser beam produced by the laser.

[0013] There are five important issues below should be addressed in the development of better electrode for electric discharge lithography laser used problems fluorine containing laser gas.

1) Electrode erosion has a severe effect on beam quality; 2) Electrode erosion currently limits the life of the laser chamber; 3) Anodic erosion is about four times cathodic erosion; 4) Accumulation of the fluoride layer on the anode is a problem, and 5) Maintaining good gas flow conditions in the discharge gap is very important.

[0015] The various embodiments of the invention described herein address these issues. The electrodes satisfy the following criteria.

1) The electrodes include an eroding surface that erodes slowly over billions of laser pulses, with erosion that does not substantially affect beam quality. 2) The eroding surface comprises fluoride in the discharge region. 3) The electrodes allow a repetition rate of 1,000 to 6,000 Hertz or more without significant turbulence in the discharge zone or in the stagnation zone immediately adjacent to the discharge zone. Designed to provide an improved gas flow.

Anode Assembly FIG. 5 shows the serial number 09 / 590,9, the parent application of this application.
1 shows a cross-sectional view of the anode assembly disclosed in No. 61. Corrosive electrode 72A and insulating flow spacers 74A and 76A are attached to anode support bar 80A.

Description of the Electrode System General Description FIG. 6 is a cross-sectional view of a laser chamber that has been tested and made by Applicant and shows a practical implementation of the invention. In this chamber, a novel electrode system is provided that provides substantially improved life performance compared to the prior art electrode system described with reference to FIG. In this electrode system, important new elements are an anode assembly 70 consisting of a blade electrode 72 and an insulating fairing 7.
4 and 76; an anode support bar 78 (including base 80 and cooling fins 82); a sharpened cathode 84;
A current return unit 86.

Dull Blade Shaped Anode In this preferred embodiment, anode 72 is shown in FIGS.
B, 7C and 7D. Anode length 2
It is 6.4 inches and 0.439 inches high. 0.2 width at bottom
84 inches and 0.141 inches wide at the top. FIG. 7A
Is a sectional view. FIG. 7B is a side view, and FIG.
Is a bottom view. FIG. 7D shows a preferred cross-sectional shape of the top of the electrode. The cross-sectional shape is again a truncated cone with a 10 degree gradient and is the top of an ellipse as shown in FIG. 7A.
The cross-sectional shape is also similar to that of a dull blade. The bottom of the anode has equally spaced tapped screw holes 72 for attaching the anode to the anode support bar.
A is provided.

[0020] Preferably, the anode material is a copper-based alloy suitable for use of the electrode in a fluorine environment. Preferred choices are C36000, C95400 or C1940
Contains 0. Applicants' tests show that post-machining annealing is substantially inefficient. Another preferred anode material is a spinodal copper alloy, such as the alloy Nicomet®, available from Anchor Bronze and Metals with offices in Bay Village, Ohio. This material contains about 80 percent copper, about 7 percent tin, and about 12.5 percent nickel, and is made using known processes such as spinodal decomposition.

Insulating Fairings Fairings are shown in FIGS. 8A, 8B, 8C and 8D.
As shown, each fairing is 26.4 inches long, 0.410 inches tall at its highest point, and 0.5309 inches wide. FIG. 8A is a plan view and FIG.
Is a side view, and FIG. 8C is a bottom view. FIG. 8D shows a cross-sectional view at the portion A as shown in FIG. 8B. Fairings 74 and 76 are held in place at both ends of anode 72 by screws 88 through holes as shown in FIGS. 8A and 8D. The screw fits loosely via fairings 74 and 76 and the anode support bar 78
To be fixed. This allows the anode support bar 78
Allow the fairings 74 and 76 to expand and contract. The fairings 74 and 76 and the dowel pins 88 are preferably comprised of a high density alumina ceramic having a density of 99.5 percent or greater.

Anode Support Bar An anode support bar 78 is shown in FIGS. 9A, 9B and 9C. FIG. 9A is a plan view. FIG. 9B is a bottom view. FIG. 9C is a perspective view of the anode support bar 78. The holes for the screws for attaching the anode 78 are shown at 90 and the holes for aligning the dowel pins are shown at 92. 9A and 9C each show three regularly spaced small tolerance holes for dowel pins to accurately position the anode on the anode support bar. Corresponding regularly spaced dowel pin holes are provided at the bottom of the anode, but these holes are not shown in FIGS. 7B and 7C.

Cathode The cathode 84 is shown in FIGS. 10A, 10B, 10C, 10D, 1
Shown at 0E and 10F. FIG. 10A is a plan view. FIG.
0B is a cross-sectional view in the longitudinal direction. FIG. 10C is a bottom view. FIG. 10D is a cross-sectional view of the short dimension of the cathode. FIG. 10E shows the surface shape of each end of the cathode. FIG.
F indicates the point of the cathode facing the anode.

As shown in FIG. 1, there are two important differences between this cathode design and the prior art design. First, the short cross-sectional shape of the cathode is generally pointed, giving the cathode a descriptive name, "a pointed cathode." The faces of the cathode facing the anode are flat faces 9 approaching each other at an angle of 130 degrees.
4. The actual midpoint (0.116 inch) has an oval shape and is rounded as shown in FIG. 10F. In this embodiment, fifteen equally spaced screw holes are provided to hold the cathode against the main insulator and electrically connect the cathode to the high voltage pulse power of the laser system, as shown at 85 in FIG. There is. The second difference is the end section of the cathode taper down along the oval path, as shown in FIG. 10E. This shape allows for a more compact configuration than prior art electrodes with rounded end sections.
It essentially improves the electric field distribution.

Current Return The details of the current return 86 are shown in FIGS. 11A, 11B, 11C and 11D. FIG. 11A shows how the current return is (0.015 inch) thick nickel alloy 40 (U
NS ND4400). The current return is formed into a specific shape as shown in FIG. 11B. The rib 90 has a width (0 .0) as shown in FIG.
09 inches) and thickness (0.015 inches), the (0.09 inches) dimension is parallel to the gas flow to minimize flow resistance. FIG. 11D is an enlarged view of one end of the current return showing how the ribs have been cut to facilitate the bending described above. A second current return design is shown in FIGS. This design is laser cut from the same material described above as shown in FIG. 12A. FIG. 12B is an enlarged view of the section of FIG. 12B shown in FIG. 12A. 12C and 12D show FIG.
FIG. 4 is a further enlarged view of the section shown in FIG. FIG. 12E
FIG. 4 is a bottom view of the current return after the rib has been bent into an appropriate shape. FIG. 12F is a side view of the discharge direction.

Other Blade Shapes Many other blade shapes are possible within the general scope of the present invention. FIG. 13A shows a blade design with a vertical side. The sides may be flat, or the sides may include a pattern, as shown in FIG. 13B, that provides a periodic modulation of about 0.3 mm amplitude with the sides being vertical but repeating at about 1.5 cm intervals. The anode shown in FIG. 13C includes a height adjustment to control erosion at the surface of the electrode. The adjustment mechanism may be any of a variety of mechanisms such as cams, racks, and pinions, ramps or lever arms. Adjustments are made manually when adjustments are made during periodic maintenance downtime, or the adjustments are made automatically.
The adjustment mechanism is made very fast by incorporating a piezo driver if the adjustment is made on a real time basis and is used to adjust the laser.

While the present invention has been described in terms of a preferred embodiment, it is to be understood and understood by the reader that many changes and modifications can be made without departing from the spirit of the invention. For example, a downstream fairing may be formed to provide a gradually widened diffusion region to restore gas pressure and substantially eliminate turbulence downstream of the discharge region. Preferably, the diffusion region expands at a rate of about 7 to 15 degrees. The fairing is preferably coated or made of metal fluoride performance. The anode may be configured such that its horizontal position can be adjusted with respect to the anode support bar to accommodate corrosion at the anode surface or to fine tune the laser output. The principle of the present invention is, for example, an ArF laser, F
It can be applied to many other gas discharge lasers other than the KrF laser such as the _two lasers. Therefore, the scope of the invention should be determined by the appended claims and their equivalents.

[Brief description of the drawings]

FIG. 1 shows a sectional view of a chamber of a prior art gas discharge laser.

FIG. 2 illustrates another feature of a prior art laser.

FIG. 3 shows the main features of a prior art gas discharge laser pulse power system.

FIG. 4A shows an electrical pulse shape in the pulse power system of FIG.

FIG. 4B shows an electrical pulse shape in the pulse power system of FIG.

FIG. 5 illustrates features of the anode assembly described in US patent application Ser. No. 09 / 590,961.

FIG. 6 is a sectional view of a laser chamber showing a preferred embodiment of the present invention.

FIG. 7A illustrates a preferred blunt blade shaped anode.

FIG. 7B illustrates a preferred blunt blade shaped anode.

FIG. 7C illustrates a preferred blunt blade shaped anode.

FIG. 7D illustrates a preferred blunt blade shaped anode.

FIG. 8A illustrates a preferred dielectric fairing.

FIG. 8B illustrates a preferred dielectric fairing.

FIG. 8C illustrates a preferred dielectric fairing.

FIG. 8D illustrates a preferred dielectric fairing.

FIG. 9A shows a preferred anode support bar.

FIG. 9B shows a preferred anode support bar.

FIG. 9C illustrates a preferred anode support bar.

FIG. 10A shows a preferred cathode.

FIG. 10B shows a preferred cathode.

FIG. 10C shows a preferred cathode.

FIG. 10D shows a preferred cathode.

FIG. 10E shows a preferred cathode.

FIG. 10F shows a preferred cathode.

FIG. 11A shows a first preferred current return.

FIG. 11B shows a first preferred current return.

FIG. 11C shows a first preferred current return.

FIG. 11D shows a first preferred current return.

FIG. 12A shows a second preferred current return.

FIG. 12B shows a second preferred current return.

FIG. 12C shows a second preferred current return.

FIG. 12D shows a second preferred current return.

FIG. 12E shows a second preferred current return.

FIG. 12F shows a second preferred current return.

FIG. 13A shows an additional blade electrode.

FIG. 13B shows an additional blade electrode.

FIG. 13C illustrates an additional blade electrode.

Continued on the front page (72) Inventor Michael Sea Cates United States of America 92029 Escondido Avenida Sierra 3359 (72) Inventor Richard G. Morton United States of America 92127 San Diego Aguamir 17786 (72) Inventor Gene-Mark Huber United States of America California 92037 La Jolla Nautilus Street 347 (72) Inventor Los Angeles Winnick 92129, California, USA San Diego Donacker Street 8918 F-term (reference) 5F071 AA06 CC01 CC03 CC10 EE04 GG05 HH07 JJ05 JJ08

Claims (17)

[Claims] 1. A laser chamber containing a laser gas; and B) two elongated corrosive electrode elements disposed in the laser chamber, at least one of the electrode elements comprising: A pillow blade-shaped portion made of a highly electrically conductive material, a first flow-shaping insulating fairing positioned on a first side of the blade-shaped portion, and a second flow-shaping insulating fairing, C) a pulse power system positioned on a second side of said blade-shaped portion and configured to provide an electrical pulse to said electrode at a frequency greater than 1000 Hz to create a discharge. D) to circulate said laser gas between two electrodes at a speed exceeding 5 m / s B) a blower system; E) a heat exchanger with sufficient capacity to remove heat from the blower system and the laser gas generated by the discharge; and F) when the electrodes are new or Gas flow guiding means for guiding a gas flow through the corrosive electrode without creating significant turbulence in the gas, either when corroded to a lifetime shape. laser. 2. A flow wherein one of said electrode elements at least partially constitutes a diffusion region that is gradually enlarged to restore gas pressure and eliminate substantial flow turbulence downstream of said discharge region. 2. The apparatus according to claim 1, wherein the apparatus is configured to function as a shaper and an anode.
A laser according to claim 1. 3. The laser of claim 2, wherein said gradually expanding diffusion region comprises a cone with an angle of about 7 to 15 degrees. 4. The laser according to claim 1, wherein said insulating fairing is made of metal fluoride. 5. The laser according to claim 1, wherein said insulating fairing is made of alumina. 6. The laser according to claim 1, wherein said insulating fairing is made of metal fluoride. 7. The laser according to claim 1, wherein at least one of the corrosive portions of the corrosive electrode element is adjustably positioned with respect to the electrode support. 8. The laser according to claim 1, wherein said pillow blade-shaped portion is made of a copper alloy. 9. The laser according to claim 8, wherein said copper alloy includes copper, aluminum, and iron. 10. The laser of claim 8, wherein said copper alloy comprises about 97.5 percent copper, 2.35 percent iron, and 0.12 percent zinc. 11. The laser of claim 8, wherein said copper alloy comprises about 85 percent copper, 11 percent aluminum, and 4 percent iron. 12. The laser of claim 8, wherein the pillow blade-shaped portion is formed by a machining process and annealed after machining. 13. The laser according to claim 8, wherein said copper alloy is a spinodal copper alloy. 14. The laser of claim 1, wherein one of said electrode elements is a cathode having a generally pointed cross section. 15. The laser of claim 14, wherein said cathode has two surfaces approaching each other at an angle of about 130 degrees. 16. The invention of claim 1 wherein one of said electrode elements is a cathode having two tapered edges sloped to create a uniform electric field along the edges. laser. 17. The laser of claim 16, wherein each of said tapered edges is tapered along a path that approximates an elliptical portion.