JPH0685365A - Excimer laser oscillator - Google Patents

Abstract

PURPOSE:To provide the excimer laser oscillator with high efficiency capable of decreasing the laser gas flow rate during highly repeated laser oscillating operation time while avoiding the local concentration of discharge. CONSTITUTION:In the excimer laser oscillator provided with main discharge electrode 1 exciting a laser gas and preliminary ionizing electrodes 3 before main-discharging the excited laser gas, the preliminary ionizing electrode 3 are arranged on upstream side of the main discharge electrodes 1 while reflecting panels 4 are provided around the preliminary ionizing electrodes 3. On the other hand, the reflecting panels 4 may be substituted with optical fiber devices leading a part of ultraviolet rays from the preliminary ionizing electrodes 3 to the main discharging part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for increasing the repetition rate of an excimer laser used for semiconductor manufacturing.

[0002]

2. Description of the Related Art FIG. 8 shows a structure of a main part of a discharge part of a conventional excimer laser oscillator. Reference numeral 1 is a main discharge electrode, 2 is a preliminary ionization electrode, and the laser gas is flown in the direction of the arrow in the figure. The laser gas is flowed to remove the metal vapor and the warmed gas generated by the discharge from the discharge part. The discharge is performed in the order of the preliminary ionization electrode 2 and the main discharge electrode 1. The preliminary ionization electrode 2 instantaneously performs a very strong arc discharge to generate ultraviolet light, and the generated ultraviolet light causes the main discharge electrode 1 to discharge.
The laser gas between a and 1b is preionized. There, glow discharge is performed at the main discharge electrode 1, laser gas is excited,
The laser light is extracted in the direction perpendicular to the paper surface. The main discharge electrode 1 has a shape like a slender kamaboko in the direction perpendicular to the paper surface of the figure, and a large number of preionization electrodes 2 are arranged in the direction perpendicular to the paper surface of the figure, and are uniform in the laser gas between the main discharge electrodes 1a and 1b. It is designed to emit ultraviolet light.

[0003]

SUMMARY OF THE INVENTION Main discharge electrodes 1a, 1b
In order to uniformly excite the laser gas between them, it is important to preliminarily ionize the laser gas in the main discharge space, and therefore a large number of preionization electrodes 2 are arranged on both sides of the main discharge electrode 1. However, since the discharge in the preionization electrode 2 is an arc discharge, the metal forming the preionization electrode 2 is evaporated during the discharge, and the metal generated in the preionization electrodes 2a, 2b on the upstream side of the main discharge electrode 1 is generated. The vapor rides on the flow of the laser gas and flows into the main discharge space. When the metal vapor exists in the main discharge space, the main discharge concentrates on the portion where the metal vapor exists, and the laser gas is not uniformly excited. In order to completely blow off this metal vapor, a conventional excimer laser oscillator has passed a laser gas at a high speed. For example, assuming that the distance between the main discharge electrode 1 and the preionization electrode 2 is 40 mm, about 60 m / s, 5
A gas flow velocity of 300 m / s is required for the conventional excimer laser oscillator in the repetitive operation of kHz. Therefore, the repetition rate of the conventional excimer laser oscillator is 1 kHz.
It was limited to the extent. Further, when the number of repetitions of laser oscillation increases, the flow rate of laser gas becomes very fast, so the power for circulating the laser gas exceeds the discharge energy for laser oscillation, which deteriorates the efficiency of the system. .

In order to solve the above problems, the preionization electrodes 2a and 2b may not be provided above the main discharge electrode 1, but if the upstream preionization electrodes 2a and 2b are not used, the preionization of the laser gas in the main discharge space is performed. Is insufficient, the discharge is locally concentrated and a sufficient laser output cannot be obtained.

The conventional excimer laser oscillator has a limit to high repetition operation, and the production speed is limited in applications such as semiconductor manufacturing. In addition, the efficiency in high repetition operation was poor. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, to make an excimer laser oscillator highly repetitive, to increase productivity, and to improve the efficiency of the excimer laser oscillator.

[0006]

In order to achieve the above object, in the present invention, a preionization electrode is provided downstream of the laser gas flow with respect to the main discharge electrode, and a reflecting mirror is provided around the preionization electrode. The configuration. The above object can also be achieved by providing an optical fiber device that guides a part of the ultraviolet light from the preionization electrode to the main discharge part instead of providing the reflecting mirror.

[0007]

[Operation] The discharge is performed in the order of the preionization electrode and the main discharge electrode. The preionization electrode instantaneously performs a very strong arc discharge to generate ultraviolet light, and the generated ultraviolet light causes the laser gas between the main discharge electrodes to be discharged. Preionize. The generated ultraviolet light is divided into one that directly reaches the main discharge portion and one that is reflected by the reflection plate 4 and arrives. Next, glow discharge is performed at the main discharge electrode, laser gas is excited, and laser light is extracted.

In the present invention, since the preionization electrode is provided on the downstream side of the main discharge part, impurities such as metal vapor do not flow from the upstream side to the main discharge part, and the laser gas flow is generated in the main discharge part. It is only necessary to blow off the metal vapor and ions, the gas flow velocity can be reduced, and the energy for flowing the gas can be saved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of the main part of the discharge part of an embodiment of an excimer laser oscillator according to the present invention. Reference numeral 1 is a main discharge electrode, 3 is a preliminary ionization electrode, and 4 is a reflector. The preionization electrode 3 is provided only on the downstream side of the laser gas flow, and the reflection plate 4 is installed around the preionization electrode 3.

The discharge is performed in the order of the preliminary ionization electrode 3 and the main discharge electrode 1. The preionization electrode 3 instantaneously performs a very strong arc discharge to generate ultraviolet light, and the generated ultraviolet light preionizes the laser gas between the main discharge electrodes. Part of the ultraviolet light generated by the preliminary ionization pins 3a and 3b directly reaches the main discharge portion, and part of the ultraviolet light is reflected by the reflection plate 4 and reaches the main discharge portion. Then, glow discharge is generated at the main discharge electrode 1, excited from the laser gas, and laser light is extracted. The laser gas is made to flow in the direction of the arrow in the figure, and the metal vapor generated by the discharge and the warmed gas are removed from the discharge part. Holes are formed in the reflection plates 4a and 4b at the portions through which the preionization electrodes 3a and 3b pass, and the preionization electrodes 3a and 3b are formed.
Meanwhile, the main discharge electrode 1 and the preliminary ionization electrode 3 are prevented from being electrically short-circuited.

In this embodiment, since the preionization electrode 3 is provided only on the downstream side of the main discharge part, impurities such as metal vapor will not flow into the main discharge part from the upstream side. for that reason,
The laser gas flow need only blow away the metal vapor and ions generated in the main discharge part. If the discharge width of the main discharge part is 10 mm, a gas flow rate of 100 m / s is sufficient even at 5 kHz for 20 m / s repetitive operation at 1 kHz, and energy for flowing gas can be saved. Further, by using the reflector 4 for the ultraviolet light applied to the main discharge part, the same amount of light as when the preliminary ionization electrode is provided on the upstream side can be secured. Further, by devising the shape of the reflection plate 4, the laser gas in the main discharge part can be more uniformly preionized.

FIG. 2 shows another embodiment. In this embodiment, the reflecting mirror 5 is divided and provided like 5a, 5b, 5c, 5d, 5e and 5f, and the same operation as the above embodiment
Although effective, in this example, the ultraviolet light further generated can be effectively used as compared with the example shown in FIG.

3 and 4, a prism 7 is provided in addition to the reflection plate 6, and the reflection plate 6 is formed by using the prism so that the flow path shape is the shape with the least gas flow resistance. Reflected ultraviolet light from the main discharge electrodes 1a, 1b
You can effectively guide in the meantime. The insulating lip 8a is connected to the pre-ionization electrodes 3a and 3a from the main discharge electrode 1 through the reflection plate 6.
It is used to prevent damage to the reflection plate 6 due to the current flowing in b.

FIG. 5 is a view of the reflection plate 6 of FIGS. 3 and 4 as seen from above. In the figure, 3 is a preionization electrode. A very large current instantaneously flows through the preionization electrode 3. A slit 8 is provided on the reflection surface of the reflection plate 6 in order to prevent an induced current from flowing through the reflection surface. Providing the slit 8 not only extends the life of the reflection plate 6, but also reduces the inductance of the preionization electrode 3, so that a large current can be flowed more instantaneously and strong ultraviolet rays can be generated.

In FIG. 6, the ultraviolet light generated by the preionization electrodes 3a and 3b is collected by the condenser lenses 9a and 9b and is irradiated through the optical fibers 10a and 10b between the main discharge electrodes 1a and 1b. is there. In this example, there is an advantage that no metal such as a reflector is used. Also,
Since the optical fiber can be guided to a necessary portion, uniform irradiation of ultraviolet light can be performed.

FIG. 7 shows the shape of the preionization electrode viewed from the downstream side of the laser gas flow. In the figure, 11a and 11b are the preionization electrodes. When the preionization electrodes 11a and 11b are installed in a dogleg shape as shown in the figure so as to face each other, ultraviolet light due to discharge between the preionization electrodes 11a and 11b is also generated on the wall surface side.
Since 11b can reach itself without being blocked, the ultraviolet light generated by installing a reflector on the wall can be used more effectively.

[0017]

As described above, according to the present invention, it is possible to reduce the laser gas flow rate during high repetition operation and obtain a highly efficient high repetition excimer laser device.

[Brief description of drawings]

FIG. 1 is an enlarged view of a discharge part of an excimer laser oscillator according to an embodiment of the present invention.

FIG. 2 is a diagram showing another embodiment of the present invention.

FIG. 3 is a diagram showing another embodiment of the present invention.

FIG. 4 is a diagram showing another embodiment of the present invention.

5 is a view of the reflecting mirror in FIG. 4 seen from above.

FIG. 6 is a diagram showing another embodiment of the present invention.

FIG. 7 is a diagram showing another embodiment of the present invention.

FIG. 8 is an enlarged view of a discharge part of a conventional excimer laser oscillator.

[Explanation of symbols]

 1 ... Main discharge electrode 2, 3, 11 ... Pre-ionization electrode 4, 5, 6 ... Reflector 7 ... Prism 8 ... Slit 9 ... Condenser lens 10 ... Optical fiber

Claims (2)

[Claims] 1. An excimer laser oscillator comprising: a main discharge electrode for exciting a laser gas by pulse discharge; and a preionization electrode for uniformly irradiating the excited laser gas with ultraviolet light for preionization before main discharge. An excimer laser oscillating device characterized in that the preliminary ionization electrode is provided on the downstream side of the laser gas flow with respect to the main discharge electrode, and a reflector is provided around the preliminary ionization electrode. 2. An excimer laser oscillator comprising a main discharge electrode for exciting a laser gas by pulse discharge and a preionization electrode for uniformly irradiating the excited laser gas with ultraviolet light to perform preionization before main discharge, Excimer laser oscillation characterized in that the preliminary ionization electrode is provided on the downstream side of the laser gas flow with respect to the main discharge electrode, and an optical fiber device for guiding a part of the ultraviolet light from the preliminary ionization electrode to the main discharge part is provided. apparatus.