JPH04775A - Gas laser apparatus and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent the flatness of a discharger section and the widthwise expansion of glow discharge and increase durability by coating the electrode surface of a discharge electrode, except a surface where discharged occurs, with an insulator formed of an inorganic substance. CONSTITUTION:A main discharge electrode 11 comprises a main body section 11m composed of stainless steel and a discharge section 11c, disposed in the top end thereof, composed of tantalum-chromium alloy. In the discharge section 11c, a tantalum-chromium alloy is formed and a shaping process is performed thereon. A chrome-plated coated film 12 is formed except in an area of a width W suited to obtain a discharge width W'. The discharge section 11c is bonded to the main body section 11m. An excimer laser apparatus first performs a preliminary ionization while a voltage is being applied between preliminary ionization electrodes, then causes discharged to be generated between the main discharge electrodes, causing a suppled laser medium gas containing Kr and F2 to be excited. Thus, oscillation is performed. The main discharge electrode 11 formed in this manner reacts with F2 in the laser medium gas during an initial period of the oscillation, and a chromium fluoride 13 is formed on the surface thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas laser device and a method of manufacturing the same, and particularly to a discharge electrode structure of a laser such as an excimer laser containing a corrosive gas in the laser medium.

[Conventional technology]

Since the excimer laser has a short wavelength (for example, the KrF Rayleigh wavelength is about 248.4 nm), there is a possibility that the resolution limit of optical exposure can be extended to 0.5 μm or less, and if the resolution is the same, it can be compared with the conventional mercury lamp. The depth of focus is deeper than that of G-line and I-line, and the numerical aperture (NA) of the lens is
It has many excellent advantages, such as being small in size, allowing for a large exposure area, and being able to obtain high power, making it suitable for use as an industrial laser as a light source for reduction projection exposure equipment used in the manufacture of semiconductor devices. The use of is attracting attention.

An excimer laser device, as shown in FIG. 1
A discharge is generated while circulating a gas containing rare gas and halogen gas such as Ar and F2 as a laser medium between the electrodes, and the discharge energy excites the laser medium existing between the electrodes, producing laser light. It was designed to obtain the following.

Since such excimer lasers use corrosive HCI, F2 scum, etc. as the laser medium, the parts that come into contact with the gas, such as the container, are made of highly corrosion-resistant materials such as Teflon, stainless steel, and nickel. The main discharge electrode 1 and the preliminary ionization electrode 2 also require corrosion resistance, so nickel or aluminum coated with nickel is usually used.

For example, if an excimer laser device containing F2 dregs as the laser medium is configured using Ni electrodes with a predetermined distance between the electrodes, the main discharge electrode will be consumed by approximately 108 oscillations, and the energy required for a stepper will be insufficient. It was no longer possible to oscillate a laser beam with a

This is thought to be because the melting point of Ni is low, so the discharge portion melts and is consumed due to sputtering and electron impact caused by discharge. In other words, the main discharge electrode is normally configured to form a part of a spherical surface, but as the discharge part wears out, it becomes flat, and the width of the generated claw discharge expands, reducing the energy and density of the laser beam. Figure 7 (a
) and FIG. 7(b) show the positions of the electrode parts and the energy density distribution of the discharge pulse, the discharge density appears unevenly, and the beam eventually splits.

In order to prevent such drawbacks, a method has been proposed in which the electrode surface, excluding the part where discharge is to be generated, is coated with an organic substance such as Epoquine resin or insulating rubber (Japanese Patent Laid-Open No. 63-227069). issue).

However, when the electrode is coated with an organic material, the heat generated on the electrode surface during discharge decomposes the organic material coating, causing the discharge to become louder and wider. In addition, the decomposed organic matter mixes into the laser medium gas, causing instability of the discharge and staining the window from which the laser beam is extracted, resulting in a significant deterioration in the performance of the laser device.

(Problem to be Solved by the Invention) Conventionally, the discharge section becomes flat due to wear and tear, and the width of the generated claw discharge increases, reducing the energy density of the laser beam or causing the discharge density to appear uneven. There was a problem, and there was no good way to solve this problem.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to improve the durability of a gas laser device by preventing the discharge portion from flattening due to consumption and expanding the width of the glow discharge generated.

[Purpose of the invention]

(Means for Solving the Problems) Therefore, in the gas laser device of the present invention, the electrode surface of the discharge electrode other than the discharge generating surface is coated with an insulator made of an inorganic material.

Preferably, the electrode surface of the discharge electrode other than the discharge generation surface is coated with a metal such as chromium, which reacts with the halogen in the laser medium to form an inorganic insulator, and when the discharge starts, the halogen such as chromium halide is removed. It allows metals to form.

In addition, in the method for manufacturing a gas laser device of the present invention, after shaping the discharge part of the discharge electrode made of a high-melting point metal, a chromium plating layer is formed on the surface of the discharge electrode, and the discharge part is heat-treated in this state, so that the chromium plating is removed. After forming a chromium-doped layer by diffusing chromium ions from the layer into the discharge section, the region corresponding to the discharge surface of the discharge section is selectively polished to a depth that achieves the desired chromium concentration, exposing the chromium-doped layer on the discharge surface. At the same time, the chromium plating layer is formed so as to remain in areas other than the discharge surface.

[Effect]

With the above configuration, the electrode surface of the discharge electrode other than the discharge generation surface is covered with an inorganic insulator, so even if the electrode surface becomes flat due to wear and tear on the discharge part, the generated glow discharge will not be affected. The width does not widen, and since this insulator is not organic, decomposed organic matter may mix into the laser medium gas, causing instability of the discharge or staining the window from which the laser light is extracted. , there is no significant deterioration in the performance of the laser device.

In addition, in the case of inorganic insulators that are formed by reacting with halogen in the laser medium, since the film is formed by a chemical reaction, it can be formed thinner than an organic insulator film formed by coating, and the main discharge It does not significantly affect the electric field distribution between the electrodes. Furthermore, there are no pinholes that could cause dielectric breakdown.

In this way, it is possible to obtain a highly durable and reliable Kaslaser device.

Further, according to the method of the present invention, a chromium plating layer is formed on the entire surface of the discharge part made of a high-melting point metal, and after chromium ions are diffused by heat treatment, the chromium plating layer is sandwiched in the area corresponding to the discharge surface. Since the layer is polished away to obtain the desired chromium concentration, it is extremely easy to provide a long-life discharge electrode in which the chromium concentration on the discharge surface is well controlled.

(Example) Examples of the present invention will be described in detail below with reference to the drawings.

Embodiment 1 FIG. 1 is a diagram showing a cross section perpendicular to the laser oscillation direction of an electrode portion of an ultraviolet pre-ionization type excimer laser device according to a first embodiment of the present invention.

A pair of main discharge electrodes 11 are provided on an electrode support part (not shown) made of Teflon resin disposed within a laser chamber (not shown), and a pair of preliminary ionization electrodes ( (not shown) are arranged, and this main discharge electrode consists of a main body part 11m made of stainless steel and a main body part 11m made of stainless steel.
A tank chrome alloy (Ta-2,
5% Cr alloy). As shown in an enlarged view of the main part in FIG. 2, a chromium plating film 2 is formed on the surface of the discharge portion 11c, except for an area with a width W suitable for obtaining the discharge width W'. A chromium fluoride layer 13 is formed on the surface of this chromium plating film 12.

The discharge portion of this electrode is manufactured as follows.

First, a tantalum-chromium alloy is formed by melting the material using an electron beam melting method, and this is processed into a desired shape.

Thereafter, selective plating is performed with the region of width W that will become the discharge surface coated with resist, and a chromium plating film 12 is formed in the region excluding the region of width W that will become the discharge surface.

Then, this discharge section is formed by joining to the main body section.

This excimer laser device first performs pre-ionization while applying a voltage between the pre-ionization electrodes, then generates a discharge between the main discharge electrodes, and Kr and F are supplied between the main discharge electrodes.
Laser medium gas containing 2 is excited to generate oscillation.

The main discharge electrode formed in this manner reacts with F2 in the laser medium gas at the beginning of oscillation, and forms a chromium fluoride layer 13 on the surface as shown in FIG.

After this, a stable discharge width can be obtained over a long period of time, and since the electrode surface other than the discharge part is covered with an insulating material, unauthorized discharge to metal near the electrode can be prevented. can.

As a result, the cross-sectional area of the main discharge circuit can be reduced, making it possible to manufacture a main discharge circuit with small stray inductance, and providing a laser device with high oscillation efficiency.

In addition, the discharge surface is a tantalum-chromium alloy (Ta-25%
Since it is made of a Cr alloy, the amount of electrode wear is extremely small and stable oscillation can be maintained.

Furthermore, since this fluorinated ROM layer 13 is a film formed by a chemical reaction, it can be formed thinner than an organic insulating film formed by coating, and has a large effect on the electric field distribution between the main discharge electrodes. I have nothing to give. Furthermore, there are no pinholes that could cause dielectric breakdown.

Example 2 Next, a second embodiment of the present invention will be described.

FIG. 3 is a diagram showing a main part of an electrode section of an ultraviolet pre-ionization type excimer laser device according to a second embodiment of the present invention.

In Example 1, a tantalum-chromium alloy (Ta-2.5%) was bonded to the tip of the main body made of stainless steel.
The discharge part 11c made of Cr alloy is coated with a chromium plating film except for the discharge surface. Here, the discharge part 21c is made of tantalum, and the discharge surface is doped with chromium to a desired depth. The device is characterized in that it is composed of a chromium-doped layer 23 and that the region other than the discharge surface is covered with a chromium plating layer 22. Note that, as in the above embodiment, a chromium fluoride layer 24 is formed on the surface of the chromium plating layer 22.

That is, in this electrode structure, a chromium plating layer 22 is formed on the entire surface of the discharge part 2]c except for the joint surface with the main body, and then heat treatment is performed to dope chromium to a desired depth to form a chromium-doped layer 23. The chromium plating layer 22 on the discharge surface is selectively removed, and a chromium doped layer 2 is formed on the discharge surface.
It is designed to expose 3.

Next, a method for manufacturing this discharge section 21c will be described in detail.

First, as shown in FIG. 4(a), tantalum is shaped to form a discharge portion 21c.

Thereafter, as shown in FIG. 4(b), a chromium plating layer 22 is formed on the entire surface of the discharge section 21C except for the joint surface with the main body.

Further, an annealing treatment (heat treatment) is performed to diffuse chromium through the surface plating layer 22 into the discharge portion made of tantalum, and as shown in FIG. 4(C), chromium is doped to a desired depth to form a chromium-doped layer 23. Form.

Then, as shown in FIG. 4(d), by surface polishing,
selectively removing the chromium plating layer 22 in a desired region on the discharge surface to expose the chromium doped layer 23 on the discharge surface;
It is joined to the main body part, and a discharge electrode as shown in FIG. 3 is completed.

At this time, the results of measuring changes in the chromium diffusion concentration distribution before and after the annealing treatment are shown in FIGS. 5(a) and 5(b).

Therefore, in this example, the thickness of the plating layer and the annealing conditions are set so that the chromium concentration on the surface of the discharge part made of tantalum after annealing #ItI treatment is 25% or more, and the thickness is adjusted to the required width of the discharge surface. The surface is polished so that the chromium concentration on the polished surface, that is, the discharge surface, is 25% or less, which is sufficient to prevent tantalum, which is a high melting point material, from being attacked by fluorine.

In the case of the second discharge electrode, as in the case of the discharge electrode of Example 1, it is possible to obtain a stable discharge width over a long period of time.
Furthermore, since the electrode surface outside the discharge area is covered with an insulating material, it is possible to prevent unauthorized discharge to the metal near the electrode, and it is possible to obtain extremely long-life and highly reliable discharge.

In addition, in the above embodiments, Ta-2.5% Cr alloy and Ta were used in the discharge part.
Any alloy containing tantalum as a main component and at least one of chromium, cerium, and strontium may be used, such as an a-Cr-Ni alloy.

Further, in the above embodiments, a KrF ekin laser device has been described, but the present invention is applicable to any gas laser device that uses highly corrosive gas as a laser medium.

Furthermore, the surface of the discharge section other than the discharge surface may turn into a ceramic state due to the thermal energy caused by the discharge, and in this case, it becomes possible to maintain the discharge width even more firmly.

In addition, in the first and second embodiments, the present invention is applied to the production of main discharge electrodes, but the present invention can also be applied to the production of pre-ionization electrodes, and the same effects as in the above embodiments can be obtained. be able to.

〔Effect of the invention〕

As explained above, according to the gas laser device of the present invention, since the electrode surface of the discharge electrode other than the discharge generation surface is coated with an insulating material made of an inorganic substance, the electrode surface is Even if it becomes flat, the width of the generated glow discharge does not widen, making it possible to obtain a highly durable and reliable gas laser device.

Further, according to the method of the present invention, a chromium plating layer is formed on the entire surface of the discharge section made of a high-melting point metal, and after chromium ions are diffused by heat treatment, the chromium plating layer in the area corresponding to the discharge surface and other surfaces are Since the layer is selectively polished away to obtain the desired chromium concentration, manufacturing is easy and the chromium concentration on the discharge surface can be extremely easily controlled.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the electrode section of a gas racer device according to the second embodiment of the present invention, FIG. 2 is a diagram showing the main part of FIG. 1, and FIG. 4(a) to 4(d) are diagrams showing the manufacturing process of the electrode of the second embodiment. FIGS. 5(a> to 5(b) are diagrams showing the electrode part of the device. A diagram showing the relationship between chromium concentration and depth before and after annealing treatment in the same example, FIG. 6 is a diagram showing a normal gas laser device, and FIGS. 7(a) and 7(b) are a diagram showing a conventional gas laser device. It is a diagram showing the electrode part of the device, and a diagram showing the position of the electrode part and the energy density distribution of the discharge pulse. 1. Main discharge electrode, 2. Preliminary ionization electrode,] 1. Main discharge electrode, l1m Main discharge Electrode body part, Co-1c... Main discharge electrode discharge part, 12... Chromium plating layer, 13... Chromium doped (diffusion) layer, 21... Main discharge electrode, 22... Chrome plating layer, 23... Chromium dope (diffusion) layer, 2
4...Chromium fluoride layer. (0) Black, -, ■ Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6゜Contents of the amendment Page 16 of the specification of the present application] Line O to the same page, Line 1 to 7 [Fig. 7 (a) and Figure 7 (1 is a diagram showing the electrode section of a conventional gas laser device" is corrected to "Figure 7 is an electrode section of a conventional gas laser device.'' 1999 Patent Application No. 333409 Gas Laser Equipment and its manufacturing method (1'23) Komatsu Ltd.

Claims (5)

[Claims] (1) In a gas laser device that generates a discharge between discharge electrodes arranged in a container to excite laser gas and emit laser light, the electrode surface of the discharge electrode other than the discharge generation surface is made of an inorganic material. A gas laser device characterized by being coated with an insulating material. (2) The gas laser device according to claim 1, wherein the insulator is a metal halide formed by reacting with halogen in the laser medium. (3) The gas laser device according to claim 2, wherein the metal is chromium or an alloy containing chromium. (4) In a method for manufacturing a gas laser device in which a discharge is generated between discharge electrodes disposed in a container to excite laser gas and emit laser light, the step of manufacturing the discharge electrode includes a discharge made of a high melting point metal. a plating step to form a chromium plating layer on the surface; and a heat treatment step to heat treat the discharge part and diffuse chromium ions from the chromium plating layer into the discharge part to form a chromium doped layer. A method for manufacturing a gas laser device, comprising: selectively polishing a region corresponding to the discharge surface of the discharge portion to a depth that provides a desired chromium concentration to expose the discharge surface. (5) The method for manufacturing a gas laser device according to claim (4), wherein the high melting point metal is tantalum.