JPH0883945A - Excimer laser oscillator - Google Patents

Abstract

PURPOSE: To improve the flowing velocity of laser gas by making the flow of the gas in a discharge unit uniform by forming a plurality of recesses on the outer surfaces of discharge electrodes. CONSTITUTION: A pair of discharge electrodes 14a, 14b are formed of a plurality of dimples 20 of circular recesses of a circular shape in a flat surface shape on the semispherical outer surface. Thus, the flowing velocity of laser gas near the electrodes l4a, 14b approaches the flowing speed value at the center between the electrodes 14a and 14b. Accordingly, when the flowing velocities near the electrodes 14a, 14b are set to necessary minimum limit values, the velocities of the gas at the center of the electrodes 14a, 14b are not largely altered from those at the wall, and hence waste is reduced. The decrease in the flow rate of the blower 15 contributes to the reduction in the power of the blower, thereby improving the entire efficiency of the laser oscillator 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an excimer laser oscillating device for generating an excimer laser used in semiconductor manufacturing, and more particularly to an excimer laser oscillating device having a pair of discharge electrodes and the like improved.

[0002]

2. Description of the Related Art Conventionally, an example of this type of excimer laser oscillator is shown in FIG. In this excimer laser oscillator 1, a main body case 2 which is a hermetically sealed container is filled with a laser gas 3 and a pair of discharge electrodes 4a, 4b are provided in order to efficiently and rapidly flow the laser gas into a gap between the pair of discharge electrodes 4a, 4b. While narrowing the gap of 4b narrowly,
The other gas flow paths should be wider to reduce the flow resistance.
The laser gas 3 is circulated in the direction of the arrow in the drawing by the blower 5, and the laser gas 3 heated by the discharge is cooled by the pair of left and right heat exchangers 6a and 6b in the drawing.

Then, as shown in FIG. 7, the laser gas 3
When, for example, is flown from left to right in the figure, the laser gas 3
Is heated and ionized by the pulse discharge of the pair of discharge electrodes 4a and 4b. In order to remove this gas and the metal vapor generated by the electrode sputtering from the discharge part, the laser gas 3 responds to the pulse repetition rate. Shed at speed.

Further, such discharge is performed, for example, from two pairs of preionization electrodes 7a and 7b, 8a and 8b to discharge electrodes 4a and 4b.
Are performed in this order, and the preionization electrodes 7a and 7b, 8a and 8b
Then, a very strong arc discharge is instantaneously generated to generate ultraviolet light, and the laser gas 3 between the discharge electrodes 4a and 4b is preionized by the photoionization action of this ultraviolet light. Next, glow discharge is performed between the pair of discharge electrodes 4a and 4b,
The laser gas 3 is excited and the laser light is extracted in the direction perpendicular to the paper surface.

[0005]

However, such a conventional excimer laser oscillator 1 has a problem that a boundary layer easily develops in the flow of the laser gas 3 in the main body case 2.

That is, in order to efficiently flow the laser gas 3 at a high speed in the narrow gap of the discharge part around the pair of discharge electrodes 4a and 4b, the gas flow path is narrowed toward the discharge part on the upstream side of the discharge part. On the other hand, on the downstream side of the discharge part, the gas flow path is expanded again. Therefore, as shown in FIG. 7, the upstream flow passage cross-sectional area of the laser gas 3 is reduced to the cross-section AA, while the downstream flow passage cross-sectional area after the cross-section BB gradually expands along the gas flow direction. Therefore, the gas flow cross section A-A becomes an accelerating flow, while the cross section B-B and thereafter becomes a decelerating flow, and the boundary layer 9 easily develops after the cross section BB.
I mean. Cross-section A where the flow passage cross-sectional area of the laser gas 3 is minimum
-After A, the boundary layer 9 develops rapidly.

Therefore, as shown in FIG. 8 (A), the flow velocity distribution of the laser gas 3 is substantially uniform in the cross section AA because the flow velocity distribution is a reduced flow passage. However, FIG. 8 (B)
As shown in FIG. 5, in the flow passage cross section BB of the laser gas 3, the flow velocity distribution near the flow passage wall surface, for example, the upper and lower wall surfaces becomes slow due to the development of the boundary layer 9.

By the way, in the excimer laser 1, the laser gas 3 between the pair of discharge electrodes 4a and 4b is discharge-excited to obtain a laser output, but this discharge excitation is usually very high energy under a high gas pressure of several atmospheres. Requires a density discharge input. In a high energy density discharge, the gas temperature instantly rises to a high temperature, and the discharge tends to be unstable. Therefore, the discharge can last only a few 100 ns and can be operated only by intermittent pulses.

The high temperature laser gas 3 after the discharge of the pair of discharge electrodes 4a and 4b is removed from the discharge part by the gas flow, and new gas is continuously supplied to the discharge part to be replaced. Due to the development of the layer 9, the gas flow velocity in the vicinity of the wall surface on the downstream side is remarkably reduced.
The replacement of the laser gas 3 on the surfaces of a and 4b was not performed efficiently. Therefore, the flow rate of the discharge part is increased more than necessary to replace the gas in the discharge part.

However, the power required to circulate the laser gas 3 is generally proportional to the cube of the gas flow velocity, and the theoretical value of the conventional excimer laser oscillator 1 is theoretically required for the theoretically required discharge part flow velocity. The gas flow rate is 5 to 10 times higher than that for stable operation. Therefore, 100 to 1000 times the theoretically necessary gas circulation power is wasted for gas circulation.

Further, the laser gas 3 is caused to flow in the discharge part in accordance with the number of pulse repetitions, which is mainly intended to suppress local discharge concentration and to cool the discharge part structure. That is, the discharge concentration lowers the laser output, further damages the discharge electrodes 4a and 4b, and accelerates the deterioration of the laser gas. Therefore, suppressing the discharge concentration is an important technical issue.

By the way, in the discharge of the excimer laser oscillator 1, ultraviolet light is generated by the preionizations 7a and 7b and 8a and 8b, and the pair of discharge electrodes 4a, 4a and
The laser gas 3 flowing between 4b is ionized. The initial electrons generated at this time move toward the anode by electrolysis in the initial stage of voltage application to the discharge electrodes 4a and 4b, and also move the electrons near the cathode, so that an electron-deficient layer is formed on the cathode surface.

However, if this electron-deficient layer is thick, discharge concentration occurs (VG Geinman, et al., "Formation of sel").
f-sustained volume discharges in large interelectr
odegaps. '' Sov.Phys.Tech.Phys., Vol.30, Dec.1985, pp1
394-1397).

Therefore, when the conventional excimer laser oscillator 1 is operated by the high repetition pulse discharge, the electric current is concentrated in several places of the discharge electrodes 4a and 4b, and the discharge electrode 4a in the high repetition operation is characteristic of the electric circuit. , 4
The voltage application to b occurs more slowly than when the pulse repetition is slow. If the voltage application speed is slow, the electron deficient layer becomes thick and current concentration occurs. If current concentration occurs, the discharge current will not be used effectively and the laser oscillation efficiency will deteriorate.

Further, since the outer surfaces of the conventional discharge electrodes 4a and 4b are smooth, when used for a long period of time, a discharge concentration portion from one point to several points is generated due to the action of discharge, and laser gas excitation due to the discharge is concentrated in a part. However, the excitation efficiency of the laser gas 3 deteriorates.

The present invention has been made to solve the above problems, and an object thereof is to provide a highly efficient excimer laser oscillator capable of equalizing the flow of laser gas in the discharge part and improving the flow velocity thereof. The purpose is to do.

[0017]

In order to solve the above problems, the present invention is configured as follows.

The invention according to claim 1 of the present application has a device for circulating the laser gas in the body case in a coolable manner, and a pair of discharge electrodes for pulse-discharging the laser gas in the flow path of the laser gas to excite the laser gas. In the excimer laser oscillator, a plurality of recesses are formed on the outer surface of the discharge electrode.

In the invention according to claim 2 of the present application, a plurality of recesses are formed on the wall surface of the divergent laser gas flow path downstream of the discharge electrode along the gas flow direction. Characterize.

Further, the invention according to claim 3 of the present application is
The concave portion is at least one of a circular concave portion and a groove.

Furthermore, the invention according to claim 4 of the present application is characterized in that the circular concave portion is formed so that the area ratio to the total area of the discharge electrode is 78.5% or less.

The invention according to claim 5 of the present application is characterized in that the diameter of the circular recess or the width of the groove is set to 50% or less of the discharge width of the pair of discharge electrodes.

Further, the invention according to claim 6 of the present application is
The circular recess or groove is formed on the cathodes of the pair of discharge electrodes.

Further, in the invention according to claim 7 of the present application, an X-ray tube for irradiating the laser gas with X-rays that penetrate at least a part of the discharge electrode and pre-ionizing the laser gas is provided, while the X-rays are provided. X of the discharge electrode through which
It is characterized in that the thickness of the line-transmissive portion is reduced and a circular concave portion or groove is formed on the outer surface of the thin portion.

[0025]

Since the outer surface of the discharge electrode or the wall surface of the flow path of the laser gas on the downstream side of the discharge electrode is provided with recesses such as dimples and grooves, which are circular recesses, the flow of the laser gas is disturbed in these recesses. . Due to the turbulence of the laser gas, the laser gas having a low velocity (momentum) near the wall surface of the gas channel flows into the center of the flow, and conversely, the laser gas having a large velocity (momentum) at the center portion flows near the wall surface of the channel. Therefore, mixing of laser gas with different momentum occurs,
The flow velocity of the laser gas in the discharge part is made uniform by preventing or reducing the development of the boundary layer. In particular, since the gas flow velocity near the wall surface of the laser gas passage is improved, the efficiency of replacement of the laser gas in the discharge part is improved, and the replacement of the gas is sufficiently performed even if the air volume of the blower is reduced. Therefore, the blower air volume can be reduced. Since the blower power is proportional to, for example, approximately the cube of the blower air volume, even a slight reduction in the blower air volume leads to a significant reduction in the blower power, and the efficiency of the entire laser oscillator can be significantly improved.

[0026]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5, the same or corresponding parts are designated by the same reference numerals.

FIG. 1 is a vertical sectional view showing the overall construction of the first embodiment of the present invention. In FIG. 1, the excimer laser oscillator 11 is filled with a laser gas 13 in a body case 12 of a hermetically sealed container. , A pair of upper and lower discharge electrodes 14a and 14b that perform pulse discharge at a required repetition frequency, a blower 15 that circulates the laser gas 13 in the main body case 12, for example, in the direction of the arrow in the figure, and are disposed on the left and right sides of the blower 15 in the figure. And a pair of heat exchangers 16a and 16b for cooling the laser gas 13 are built in.

On the left and right sides of the pair of discharge electrodes 14a and 14b in the figure, a pair of upper and lower preionization electrodes 17a and 17b,
18a and 18b are provided. As shown in FIG. 2, in the gap between the pair of discharge electrodes 14a and 14b, the laser gas 13 flowing in the vertical direction, that is, in the direction of the arrow in the figure.
The flow passage 19 is formed so that the diameter of the flow passage 19 gradually increases toward the upstream side 19a and the downstream side 19b.

Then, the pair of discharge electrodes 14a, 14b
On the outer surface of the hemisphere, a plurality of dimples 20 each having a circular concave shape in a plan view are formed.

This dimple 20 has a reference (Masahiro Kato,
3 others, "Drag, lift, and flow visualization in spherical flying vehicles," Vol.7 Suppl., October 1987, pp.153-156)
As shown in, there is an effect of preventing separation of the fluid flow.
In other words, the dimples formed on the golf ball generate turbulence in the air flow, and the turbulence causes the low-velocity gas flow near the ball surface to flow into the flow center, while the high-velocity gas near the ball flow near the wall surface. . Therefore, the above-mentioned slow gas flow near the wall surface and the fast gas flow near the wall surface are mixed, and the flow velocity on the surface of the golf ball is increased. The flow separation means a state in which the flow velocity near the surface is zero or negative, and therefore the effect of preventing the separation of the dimples is due to the occurrence of this turbulence.

Almost the same as this, a pair of discharge electrodes 14
Similarly, the dimples 20 on the outer surfaces of a and 14b also generate turbulence in the flow of the laser gas 13, and the turbulence causes the laser gas flow of low velocity (momentum) near the discharge electrodes 14a and 14b to flow into the central portion, and conversely to the central portion. Since the laser gas flow having a large velocity (momentum) flows into the vicinity of the wall surface and mixes with each other, the development of the boundary layer 9 of the conventional excimer laser oscillator 1 shown in FIG. 7 is prevented or reduced similarly to the above golf ball. As a result, the flow velocity of the laser gas 13 in the discharge part is made uniform.

Therefore, the efficiency of replacement of the laser gas 13 in the discharge part is improved, and the replacement of the laser gas in the discharge part is sufficiently performed even if the air volume of the blower 15 is low, so that the air volume of the blower can be reduced. Therefore, conventionally, when the laser is operated at high repetition rate, the discharge electrode 14a,
Although it has been dealt with by increasing the blower air volume so that the flow velocity of the laser gas 13 near the outer surface of 14b becomes a required gas flow velocity, conventionally, even if the laser gas flow velocity near the discharge electrodes 14a and 14b is set to a necessary minimum value, Discharge electrode 14a,
The continuous gas flow velocity in the central portion between 14b was much more than the required amount and wasted. On the other hand, when the dimples 20 are provided on the discharge electrodes 14a and 14b as in this embodiment,
The laser gas flow velocity near the discharge electrodes 14a and 14b approaches the flow velocity value at the central portion between the discharge electrodes 14a and 14b. Therefore, if the flow velocity in the vicinity of the discharge electrodes 14a, 14b is set to the necessary minimum value, the gas flow velocity at the central portions of the discharge electrodes 14a, 14b does not significantly change from the flow velocity at the wall surface, so that waste is reduced. Further, since the blower power is proportional to the cube of the blower air volume, reducing the air volume of the blower 15 even a little leads to a significant reduction in the blower power, and the efficiency of the entire laser oscillator 11 can be significantly improved.

By the way, the dimple 20 is connected to the discharge electrode 14
The dimples 20 are formed on the outer surfaces of a and 14b.
Since the electric field is concentrated on the edge portion of the, the electric current is more likely to be concentrated on the edge portion of the dimple 20. Moreover, when the electric field concentration is concentrated at one point or when the area ratio of the concentrated portion to the entire electrode surface is very small, the laser output is reduced. Conventional discharge electrode 4 shown in FIG.
In the case of a and 4b, since the outer surface is smooth, when used for a long period of time, a discharge concentrated portion is generated from one point to several points due to the discharge action, laser gas excitation due to discharge is concentrated in a part, and laser gas excitation efficiency is increased. It gets worse.

On the other hand, the dimple 20 is connected to the discharge electrode 1
In the case of the present embodiment provided on the outer surfaces of 4a and 14b, the electric field concentration portions are evenly distributed on the electrode surface, the discharge is stabilized for a long time, and the laser gas excitation by the discharge is also uniformly performed.

The dimples 20 are the discharge electrodes 14
Since it is formed to give turbulence to the laser gas flow on the outer surfaces of a and 14b, a plurality of grooves are formed on the outer surfaces of the discharge electrodes 14a and 14b instead of the dimples 20 if the shape is such that the flow of the laser gas 13 is disturbed. However, substantially the same effect as that of the above-described embodiment can be obtained. This groove may be formed in a grid pattern or may be spiral. The shape of the groove and the dimple 20 may be any shape as long as it is not a projection, and the shape of the cathode and the anode of the pair of discharge electrodes 14a and 14b may be changed. It should be noted that although similar effects can be obtained from the protrusions in terms of hydrodynamics, when the protrusions are used, an electric current is concentrated on the protrusions during discharge and arc discharge is likely to occur. In this case, laser output can be reduced, but laser oscillation can be performed.

In the case of the first embodiment, if the size of each dimple 20 formed on the outer surface of the discharge electrodes 14a and 14b is too large, the laser gas in the concave portion of the dimple 20 will not be excited by discharge and the above effect will be obtained. It may not be obtained. That is, the size of each dimple 20 needs to have a diameter (width in the case of a groove) smaller than at least the discharge width (distance between discharges).
An appropriate size is 0% or less. In addition, the pitch of the dimples 20 also becomes unstable if the area of the portion excluding the dimple recesses related to the discharge becomes too small. Therefore, the total area of the recesses of the dimples 20 is set to the discharge electrodes 14a, 14b.
It is necessary that the area ratio to the total area of 78.5% or less.

FIG. 3 is a longitudinal sectional view of a main part of a second embodiment of the present invention, which shows a laser gas flow path 19b on the downstream side of the electrode part.
The inner wall surface 19c is characterized in that a plurality of dimples 20a are formed.

According to the second embodiment, the separation of the flow of the laser gas 13 can be prevented by providing the plurality of dimples 20a on the wall surface 19c of the downstream laser gas passage 19b. That is, when the flow of the laser gas 13 is separated, the laser gas 13 stagnates near the wall surface of the flow path. The laser gas 13 after the discharge is ionized and contains metal vapor, so that the electric resistance is low.
Therefore, the laser gas 13 is discharged to the discharge electrodes 14a and 14b.
In the case of staying in the vicinity of, the discharge current flows through the portion having a low electric resistance, so that the laser gas 13 is not effectively excited and the laser oscillation efficiency is deteriorated.

On the other hand, in this second embodiment, since the dimples 20 and 20a are provided on the outer surfaces of the pair of discharge electrodes 14a and 14b and the flow passage wall surface 19c, the circulation of the laser gas 13 is improved, and therefore the discharge is performed. Current is laser gas 13
It is effectively used to excite laser and can improve laser oscillation efficiency.

FIG. 4 is a vertical cross-sectional view of a main portion of a third embodiment of the present invention. In this embodiment, the preionization electrodes 17a and 17b and 18a and 18b in the first embodiment are replaced with an X-ray tube 21. The point is characteristic. The X-ray tube 21 is inserted into one of the pair of discharge electrodes 14a and 14b, for example, 14b from the recess 14b1 on the back surface thereof, and transmits the X-rays to the laser gas 13 through the transmitting portion 14b2 which is ahead of the tip thereof. The laser gas 13 is pre-ionized by irradiation.

A plurality of dimples 20 or grooves are also provided on the outer surface of the X-ray transmitting portion 14b2 of the one discharge electrode 14b. Because of this, the dimples 20 or grooves are X
Since it has the effect of scattering the X-rays from the radiation tube 21, the laser gas 13 can be preionized more uniformly, and the discharge becomes more uniform, so that the excitation efficiency of the laser gas 13 can be improved. Further, as shown in FIG. 5, by making the thickness of the X-ray transmitting portion 14b2 of the discharge electrode thinner, the X-ray transmittance of this portion is increased and the preliminary ionization efficiency is further increased.
The laser gas excitation efficiency can be improved.

In the excimer laser operating at high repetition rate, the flow velocity of the laser gas 13 is very high. In this case, the laser gas 13 flowing in the flow path 19 between the discharge electrodes 14a and 14b
Is completely turbulent, and the boundary layer 9 (see FIG. 7) is not well developed. Even in such a case, the discharge electrode 14a,
By providing the dimple 20 on the cathode side of 14b, the effect of preventing discharge concentration can be obtained. That is, the temple 2
When 0 is provided, the electric field is concentrated at the edge portion of the dimple 20, but when the dimple 20 is provided at the cathode, electrons are emitted from the electric field concentrated portion from the initial stage of voltage application. Then, as described above, at the time of high repetition operation, the electron depletion layer near the cathode surface becomes thick, which causes discharge current concentration and lowers the laser oscillation efficiency. However, when the dimple 20 is provided on the cathode, it is emitted from the edge portion of the dimple. The generated electrons make up for this, and an electron-deficient layer does not occur. Therefore, it is possible to avoid the concentration of the discharge current peculiar to the high repetition operation, so that it is possible to prevent the efficiency from decreasing during the high repetition operation.

[0043]

As described above, according to the present invention, the outer surface of the discharge electrode, or the flow path wall surface of the laser gas on the downstream side thereof,
Since a plurality of recesses such as dimples and grooves which are circular recesses are formed, it is possible to reduce or prevent the formation of a boundary layer in the flow path by giving a turbulent flow to the laser gas flow by these recesses. Therefore, the blower power required for circulating the laser gas can be reduced, and the laser gas flow velocity can be increased to smoothly replace the laser gas heated in the discharge region, so that the laser oscillation efficiency can be improved. .

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing the overall configuration of a first embodiment of an excimer laser oscillator according to the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is an enlarged view of a main part of the second embodiment of the present invention.

FIG. 4 is an enlarged view of a main part of a third embodiment of the present invention.

FIG. 5 is an enlarged view of a main part of a fourth embodiment of the present invention.

FIG. 6 is a vertical sectional view showing the overall configuration of a conventional excimer laser oscillator.

7 is a partially enlarged view of FIG.

8A is a laser gas flow velocity distribution diagram of AA portion shown in FIG. 7, and FIG. 8B is a laser gas flow velocity distribution diagram of BB portion shown in FIG.

[Explanation of symbols]

 11 Excimer Laser Oscillator 12 Body Case 13 Laser Gas 14a, 14b Pair of Discharge Electrodes 15 Blowers 16a, 16b Heat Exchanger 17a and 17b, 18a and 18b 2 Pairs of Pre-ionization Electrodes 19 Channel 19b Downstream Channel 19c Channel Wall 20,20a dimple

Claims (7)

[Claims] 1. An excimer laser oscillating device comprising: a device for circulating a laser gas in a main body case in a freely coolable manner; and a pair of discharge electrodes for pulse-discharging the laser gas in a flow path of the laser gas to excite the laser gas. An excimer laser oscillating device having a plurality of recesses formed on the outer surface thereof. 2. The excimer laser oscillation according to claim 1, wherein a plurality of recesses are formed on the wall surface of the divergent laser gas flow path downstream of the discharge electrode along the gas flow direction. apparatus. 3. The excimer laser oscillator according to claim 1, wherein the concave portion is at least one of a circular concave portion and a groove. 4. The excimer laser oscillating device according to claim 3, wherein the circular concave portion is formed so that an area ratio with respect to the total area of the discharge electrode is 78.5% or less. 5. The excimer laser oscillator according to claim 3, wherein the diameter of the circular recess or the width of the groove is set to 50% or less of the discharge width of the pair of discharge electrodes. 6. The excimer laser oscillator according to claim 3, wherein the circular recess or groove is formed on the cathodes of the pair of discharge electrodes. 7. X which penetrates at least a part of the discharge electrode
The X-ray tube for irradiating the laser gas with the laser gas and pre-ionizing the laser gas is provided, while reducing the thickness of the X-ray transmitting portion of the discharge electrode through which the X-ray is transmitted, and the outer surface of the thin portion has a circular recess or The excimer laser oscillation device according to claim 3, wherein a groove is formed.