JP2001230473A - Gas laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize discharging and laser output by nearly unifying flow rates at any place between electrodes to increase the lowest flow rate in a discharge region. SOLUTION: A high voltage-side electrode 2a is installed on an insulation base 11 and folds 11a are formed in a peripheral part of the insulation base 11 around the electrode 2a to prevent creeping discharge. A ground-side electrode 2b is disposed opposite to the upper electrode 2a by a specified distance away from the electrode 2a. By applying a high voltage pulse between the electrodes 2a, 2b to generate discharge, a laser gas is excited. In the laser chamber, a cross flow fan 5 is installed to rapidly circulate the laser gas. On both sides of the ground-side electrode 2b opposite to the folds 11a, air course regulation members 6 made of an insulation material are installed, which makes a cross-sectional area of laser gas circulation spaces formed on both sides of the ground-side electrode nearly the same as that between the electrodes. As a result, the flow rates are nearly uniformed at any place between the electrodes and the lowest flow rate in the discharge region can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge excitation gas laser device, and more particularly, to a discharge excitation gas laser device in which a gas provided between electrodes is circulated by a fan provided in a laser chamber.

[0002]

2. Description of the Related Art With miniaturization and high integration of semiconductor integrated circuits, there is a demand for an improvement in resolution of a projection exposure apparatus. For this reason, the wavelength of the exposure light emitted from the exposure light source has been shortened. As a light source for semiconductor lithography, a discharge excitation gas laser device that emits light having a wavelength shorter than the wavelength of the conventional mercury lamp light is used. (Hereinafter, an excimer laser device will be described as an example).
The excimer laser device is, for example, in a laser chamber,
A laser gas composed of a rare gas such as fluorine (F ₂ ), argon (Ar), and neon (Ne) as a buffer gas is sealed at several hundred kPa. A pair of main discharge electrodes are provided inside the laser chamber, the main discharge electrodes extending in the laser optical axis direction and facing each other at a predetermined interval. By generating a discharge by applying a fast rising high voltage pulse between the main discharge electrodes, a laser gas as a laser medium is excited.

In order to avoid the problem of chromatic aberration in the output mirror and the projection optical system of the exposure apparatus before and after the laser chamber, the spectral width of the laser beam is narrowed so as to stabilize the center wavelength. A narrowing optical system is arranged, and the output mirror and the narrowing optical system constitute a laser resonator. Light emitted from the laser chamber when the laser gas is excited is amplified by the laser resonator, and is extracted as laser light from the output mirror of the laser resonator. In order to generate laser light efficiently, it is necessary to generate a uniform discharge between the main discharge electrodes. However, in order to generate a uniform discharge in a high-pressure gas atmosphere of several hundred kPa, the main discharge is usually performed. Generally, the laser gas existing in the main discharge space between the main discharge electrodes is pre-ionized by the pre-ionization means provided near the discharge electrode before the main discharge starts.

An excimer laser device used as an exposure light source requires several kilohertz of discharge to increase throughput.
High repetition operation at z is beginning to be demanded. However, after the occurrence of the main discharge, discharge products such as ions and fluorides are generated in the main discharge space, and further, thermal disturbance and acoustic disturbance (such as shock waves) also occur, and this state is maintained. Then, the next main discharge becomes unstable, an arc discharge occurs between the main electrodes, and the laser output becomes unstable. In order to avoid such a problem, it is necessary to exchange the gas in the main discharge space before the next discharge occurs. Specifically, a fan is provided in the laser chamber, and the laser gas in the laser chamber is circulated at high speed.

FIG. 6 shows the inside of a conventional laser chamber.
Particularly, a schematic diagram showing a longitudinal section of the electrode and a longitudinal section of the fan is shown. It should be noted that, in the figure, preliminary ionization means, heat exchange means for cooling the laser gas heated by the heat generated by the discharge, and the like are omitted. Further, regarding the entire structure of the laser device and the flow of the wind, for example, US Pat.
See, for example, JP-A-59,840 and JP-A-10-232955. The laser chamber comprises a chamber body 1 and an insulating base 11 which is hermetically mounted on the upper part of the chamber body. The insulating base 11 is made of an insulating material such as ceramics, and has one of a pair of main discharge electrodes (hereinafter referred to as electrodes) 2a and 2b extending in the laser optical axis direction on a surface facing the inside of the laser chamber. An electrode (high voltage side) 2a is provided. The electrode 2a is connected to the high voltage side of the high voltage pulse generator 4 via the current supply member 3. On the other hand, the other electrode (ground side) 2b facing the electrode 2a at a predetermined interval is connected to the ground side of the high-voltage pulse generator 4 via an unillustrated energizing member. As described above, by applying a high-voltage pulse having a rapid rise from the high-voltage pulse generator 4 to the pair of electrodes 2a and 2b to generate a discharge, a laser gas as a laser medium is excited.

Here, the electrode (high voltage side) 2a has ~ 3
Since a high voltage of about 0 kV is applied, creeping discharge may occur between this electrode and the grounded chamber body 1. Therefore, as shown in FIG. 7 (FIG. 7 is a diagram of the insulating base 11 viewed from below in FIG. 6), a fold 11a is formed on the insulating base 11 on which the electrode 2a is installed so as to surround the electrode 2a. In addition, the creeping distance is increased to prevent the occurrence of creeping discharge. The height of the fold 11a in the discharge direction is equal to or slightly (for example, about 1 mm) of the electrode (high voltage side) 2a so as not to block the laser beam generated between the electrodes 2a and 2b. It is formed to be lower. A window 1b through which laser light passes is provided on a side surface of the chamber body 1, and the window 1b is sealed with a window material (not shown). A cross-flow fan 5 is used as means for circulating the laser gas at high speed inside the laser chamber. The cross flow fan 5 is provided at each end with a protrusion 5a substantially coincident with the center axis of the fan, and the protrusion is rotatably held by a rotary bearing 5b. By this cross flow fan 5, the wind flows in the direction from the back of the paper toward the front and rises, flows between the electrodes 2a and 2b from the front of the paper toward the back, descends and reaches the cross flow fan 5. Circulate as you do. For details, refer to the above-mentioned prior art document.

[0007]

As described above, the fold 11a is formed on the insulating base 11 in order to increase the creepage distance between the electrode (high voltage side) 2a and the chamber body 1. Therefore, the cross-sectional area (width A) of the laser gas circulation space at both ends of the electrodes 2a and 2b is larger than that between the electrodes 2a and 2b. Due to the effect of this large space, the electrode 2
The flow velocity distribution of the gas flowing between a and 2b is not uniform. This is schematically shown in FIG. In the figure, the horizontal axis represents the position of the electrodes 2a and 2b in the optical axis direction, and the vertical axis represents the flow velocity distribution. The flow velocity distribution shown here is the optical axis direction of the flow velocity at the center position between the electrodes (the electrode longitudinal direction). ) (Flow velocity distribution at the position indicated by the two-dot chain line in FIG. 8).

As described above, the electrodes 2a, 2a
The laser gas in the laser chamber is circulated at high speed in order to exchange the gas in the main discharge space before the next discharge occurs between b. In recent years, to increase throughput, several kilohertz
There is a demand for a laser operation with a high repetition rate of z, and the minimum flow velocity of the laser gas that can cope therewith is, for example, several tens m / s, depending on the width of the discharge space. However, conventionally, as shown in FIG.
The flow velocity distribution of the gas flowing between b was not uniform, and the required gas flow velocity could not be obtained in a part of the discharge space (both ends in the optical axis direction). In the discharge space where the gas flow rate is lower than the required minimum flow rate, the next main discharge becomes unstable and an arc discharge occurs, and as a result, the laser output becomes unstable.

Here, if attention is paid only to the improvement of the non-uniformity of the gas flow velocity, as a means for solving the problem, the cross-sectional area (width A) of the laser gas circulation space at both ends of the electrodes 2a and 2b.
However, it is conceivable to lengthen the electrode (ground side) 2b by the width A so as not to become larger than that between the electrodes 2a and 2b. However, the electrode (ground side)
When 2b is lengthened, the electric field distribution between the electrode 2b and the electrode (high voltage side) 2a changes, and as a result, the discharge becomes unstable and the above-described arc discharge occurs, and as a result,
The laser output becomes unstable. The present invention has been made in order to solve the above-mentioned problems of the prior art, and the flow velocity distribution between the electrodes is substantially uniform, the discharge is stabilized by increasing the minimum flow velocity in the discharge generation region, and the laser output is improved. Is to provide a discharge-excited gas laser device that can stabilize the gas.

[0010]

The present invention solves the above-mentioned problems as follows. (1) A laser chamber in which a laser gas is sealed, a pair of electrodes facing each other at a predetermined interval disposed in the laser chamber, and having a shape extending in the laser optical axis direction, and flowing the laser gas between the electrodes. A gas laser device having a gas circulating means for circulating a flow, and having an insulating member (for example, a fold) for ensuring a creeping distance around a longitudinal direction of the high-voltage side electrode of the pair of electrodes. An air passage regulating member is provided at both ends in the longitudinal direction of the low voltage side electrode at positions facing the insulating member. (2) a laser chamber in which the laser gas is sealed, a pair of electrodes arranged in the laser chamber, facing each other at a predetermined interval, and having a shape extending in the laser optical axis direction, and flowing the laser gas between the electrodes; In a gas laser device having a gas circulating means for circulating a flow, air flow regulating members are provided at both longitudinal ends of the pair of electrodes. (3) In (1) and (2), the height of the air flow path regulating member in the discharge direction is made equal to the height of the pair of electrodes in the discharge direction. (4) In the above (1) and (2), the cross-sectional shape of the air flow path regulating member and the cross-sectional shape of the electrode when cut along a plane perpendicular to the longitudinal direction of the electrode are made substantially equal. Claims 1 and 2 of the present invention
In the present invention, since the air flow regulating members are provided at both ends in the longitudinal direction of the electrodes as described above, the flow velocity distribution between the electrodes can be made substantially uniform, and the minimum flow velocity in the discharge generation region can be increased. Therefore, the discharge can be stabilized, and the laser output can be stabilized. According to the third aspect of the present invention, since the height of the air flow regulating member in the discharge direction is equal to the height of the pair of electrodes in the discharge direction, the sectional area of the laser gas circulation space at both ends of the electrodes is reduced. Can be made substantially equal to the cross-sectional area between the electrodes, the flow velocity distribution between the electrodes can be made more uniform, and the minimum flow velocity in the discharge generation region can be further increased. The invention according to claim 4 of the present invention is to reduce the turbulence of the flow of the laser gas because the cross-sectional shape of the air flow path regulating member and the cross-sectional shape of the electrode when cut along a plane perpendicular to the longitudinal direction of the electrode are substantially equal. Can be.

[0011]

FIG. 1 is a diagram showing the configuration of a first embodiment of the present invention. Note that, as in FIG. 5, the pre-ionization means, the heat exchange means for cooling the laser gas heated by the heat generated by the discharge, and the like are omitted in FIG. In FIG. 1, a laser chamber is a chamber body 1.
And an insulating base 11 air-tightly mounted on the upper part of the chamber main body 1. The insulating base 11 is made of an insulating material such as ceramics, and has a pair of electrodes 2a and 2a extending in the laser optical axis direction on a surface facing the inside of the laser chamber.
2b is provided with one electrode (high voltage side) 2a.
The electrode 2a is connected to the high voltage side of the high voltage pulse generator 4 via the current supply member 3. As shown in FIG. 7, the electrode 2a is provided on the insulating base 11 on which the electrode 2a is installed.
A fold 11a is formed so as to surround a, and the creepage distance is increased to prevent the occurrence of creeping discharge. On the other hand, the other electrode (ground side) 2b facing the electrode (high voltage side) 2a at a predetermined interval is connected to the ground side of the high voltage pulse generator 4 via a conducting member (not shown). .

The electrode (ground side) 2b is attached to a plate-like electrode holder 21 having both ends in the optical axis direction made of alumina and a central part made of metal. Plate-shaped electrode holder 21
Is formed of alumina at both ends, insulation between the electrode 2b and the chamber body 1 can be ensured. Even if the voltage of the electrode 2b transiently increases due to the discharge current during discharge, the electrode 2b An arc discharge or the like can be prevented from being generated between the chamber body 1 and the chamber. As described above, the high-voltage pulse generator 4 is provided between the pair of electrodes 2a and 2b.
By generating a discharge by applying a high-voltage pulse having a faster rise, a laser gas as a laser medium is excited. A window 1b through which laser light passes is provided on a side surface of the chamber body 1, and the window 1b is sealed with a window material (not shown). Further, in order to circulate the laser gas at a high speed inside the laser chamber, a cross flow fan 5 is provided, and the cross flow fan 5 is provided with protrusions 5a substantially coincident with the center axis of the fan at both ends as described above. The protrusion 5a is rotatably held by the rotary bearing 5b.

An air flow regulating member 6 made of an insulating material such as alumina according to the present invention is attached to the electrode holder 21 at a position facing the fold 11a and at both longitudinal ends thereof. Have been. The air passage regulating member 6 includes:
As shown in FIG. 2, the height in the discharge direction is equal to or slightly (for example, about 5 mm, preferably about 1 mm) in the discharge direction so as not to block the laser light generated between the electrodes 2a and 2b. It is formed so as to be low, and restricts the flow of wind to the space formed on both sides in the longitudinal direction of the electrode (ground side) 2b. Considering the processing accuracy, the mounting accuracy of the air passage regulating member 6, the alignment accuracy of the laser resonator disposed outside the laser chamber, and the like, as described above, the height of the air passage regulating member is equal to the height of the ground electrode. Is desirably formed to be slightly lower than the height (Δh in FIG. 2). In addition, the length of the air path regulating member 6 in the optical axis direction is
1a is a length (length in the optical axis direction) equivalent to the width (width A) of the region occupied in the optical axis direction. With such a configuration, the cross-sectional area of the laser gas circulation space at both ends of the ground-side electrode can be made substantially equal to that between the electrodes. Here, the space A between the air passage regulating member 6 and the electrode (ground side) 2b shown in FIG.
The laser gas hardly flows in the area where a exists.
Therefore, as described above, the cross-sectional area of the laser gas circulation space on both ends of the ground-side electrode is substantially equal to that between the electrodes 2a and 2b.

As shown in FIGS. 1 and 2, the airflow regulating member 6 was attached, and the flow velocity distribution of the gas flowing between the electrodes 2a and 2b was observed. FIG. 3 schematically shows the results. The flow velocity distribution shown here is the distribution of the flow velocity at the center position between the electrodes in the optical axis direction (longitudinal direction of the electrodes) (distribution at the position shown by the two-dot chain line in FIG. 3). As described above, in this embodiment, the cross-sectional area of the laser gas circulation space at both ends of the electrode (ground side) 2b can be made substantially equal to that between the electrodes 2a and 2b. The distribution can be made substantially uniform, and the gas flow rate does not fall below the required minimum flow rate in the discharge generation region. For this reason, the discharge was stabilized and no arc discharge occurred, and as a result, the laser output could be stabilized.

FIG. 4 is a view showing a second embodiment of the present invention. This embodiment shows an embodiment in which the fold 11a is not formed on the insulating base 11 on which the electrode (high voltage side) 2a is installed. In FIG. 4, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and the laser chamber comprises a chamber main body 1 and an insulating base 11, as in FIG. An electrode (high-voltage side) 2a extending in the laser optical axis direction is provided on a surface of the insulating base 11 made of an insulating material such as ceramics and facing the inside of the laser chamber. The electrode 2a is connected to the high voltage side of the high voltage pulse generator 4 via the current supply member 3. Although the fold 11a as shown in FIG. 7 is not formed on the insulating base 11 on which the electrode (high voltage side) 2a is installed, the size of the insulating base 11 is different from the side wall of the chamber body 1 and the electrode (high). (The voltage side) 2a is separated by a distance that does not cause creeping discharge.

On the other hand, the other electrode 2b opposed to the electrode (high-voltage side) 2a at a predetermined interval is connected to the ground side of the high-voltage pulse generator 4 via a current-carrying member (not shown). . The electrode (ground side) 2b is attached to a plate-like electrode holder 21 having both ends in the optical axis direction made of alumina and a center part made of metal, similarly to the electrode shown in FIG. By applying a high-voltage pulse having a rapid rise from the high-voltage pulse generator 4 to the discharge between the pair of electrodes 2a and 2b as described above, a laser gas as a laser medium is excited. A window 1b through which laser light passes is provided on a side surface of the chamber body 1, and the window 1b is sealed with a window material (not shown). Further, in order to circulate the laser gas at a high speed inside the laser chamber, a cross flow fan 5 is provided, and the cross flow fan 5 is provided with protrusions 5a substantially coincident with the center axis of the fan at both ends as described above. The protrusion is rotatably held by the rotary bearing 5b.

On the insulating base 11 at both ends in the longitudinal direction of the electrode (high-pressure side) 2a, an air passage regulating member 6a made of an insulating material such as alumina is attached. At a position facing the air passage regulating member 6a, an air passage regulating member 6b formed of an insulating material such as alumina is attached. The air path regulating members 6a, 6
b, as in the first embodiment, the height in the discharge direction is equal to or slightly (for example, about 5 mm, preferably about 1 mm) so that the laser beam generated between the electrodes is not shielded. ) It is formed to be lower. The length of the air path regulating members 6a and 6b in the optical axis direction is equal to the length of the electrodes 2a and
The length is such that the flow velocity distribution between 2b is substantially uniform. For example, the length may be equal to the width A in the first embodiment.

As described above, in this embodiment, the cross-sectional area of the laser gas circulation space at both ends of the electrodes 2a and 2b can be made substantially equal to that between the electrodes 2a and 2b. As in the example, the flow velocity distribution between the electrodes can be made substantially uniform, and the gas flow velocity does not fall below the required minimum flow velocity in the discharge generation region. For this reason, the discharge was stabilized and no arc discharge occurred, and as a result, the laser output could be stabilized. In the first and second embodiments, the air passage regulating members 6, 6a, 6
It is desirable that the portion b facing the direction in which the laser gas flows is a curved surface. This is because the curved surface reduces turbulence in the flow of the laser gas when the laser gas collides with the airflow path regulating members 6, 6a, 6b. In particular, as shown in FIG. 5, if the cross-sectional shape of the air passage regulating members 6, 6a, 6b when cut along a plane perpendicular to the longitudinal direction of the electrodes is made substantially equal to the cross-sectional shape of the electrodes 2a, 2b, the laser gas The turbulence of the flow can be further reduced.

[0019]

As described above, in the present invention,
The following effects can be obtained. (1) Since the airflow regulating members are provided at both ends in the longitudinal direction of the electrodes, the flow velocity distribution between the electrodes can be made substantially uniform, the minimum flow velocity in the discharge region can be increased, and the discharge can be stabilized. As a result, the laser output can be stabilized. (2) By making the height of the air flow regulating member in the discharge direction equal to the height of the pair of electrodes in the discharge direction, the cross-sectional area of the laser gas circulation space at both ends of the electrodes is made equal to the cross-sectional area between the electrodes. It can be made substantially equal, and the flow velocity distribution between the electrodes can be made more uniform, and the minimum flow velocity in the discharge region can be further increased. (3) By making the cross-sectional shape of the air flow path regulating member and the cross-sectional shape of the electrode substantially equal when cut on a plane perpendicular to the longitudinal direction of the electrode, the turbulence of the flow of the laser gas can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a relationship between an airflow regulating member and a height of an electrode in a discharge direction.

FIG. 3 is a diagram schematically showing a flow velocity distribution of a gas flowing between electrodes in the present invention.

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

FIG. 5 is a diagram showing an example of a cross-sectional shape of the airflow path regulating member when cut along a plane perpendicular to the longitudinal direction of the electrode.

FIG. 6 is a schematic view showing the inside of a conventional laser chamber.

FIG. 7 is a view showing a fold formed on an insulating base on which a high-voltage side electrode is installed.

FIG. 8 is a diagram schematically showing a flow velocity distribution of a gas flowing between electrodes in a conventional apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Chamber main body 11 Insulation base 2a, 2b Electrode 21 Electrode holder 3 Current supply member 4 High-voltage pulse generator 5 Cross flow fan 6, 6a, 6b Airway regulation member

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takeshi Minobe 6409 Motoishikawacho, Aoba-ku, Yokohama-shi, Kanagawa Fushio Electric Co., Ltd. F-term (reference) 5F071 DD01 DD08 EE04 FF05 FF09 GG05 JJ05

Claims (4)

[Claims] 1. A laser chamber in which a laser gas is sealed, a pair of electrodes facing each other and spaced apart from each other by a predetermined distance and arranged in the laser chamber, and having a shape extending in a laser optical axis direction. A gas laser device having a gas circulating means for a circulating flow flowing therethrough, provided with an insulating member for ensuring a creeping distance around a longitudinal direction of the high-pressure side electrode of the pair of electrodes, A gas laser device, wherein an air passage regulating member is provided at a position facing the insulating member at both ends in the longitudinal direction of the low-voltage side electrode. 2. A laser chamber in which a laser gas is sealed, a pair of electrodes arranged in the laser chamber, facing each other at a predetermined interval, and having a shape extending in a laser optical axis direction; 1. A gas laser device comprising: a gas circulating means for producing a circulating flow flowing through a pair of electrodes, wherein air flow regulating members are provided at both ends in a longitudinal direction of the pair of electrodes. 3. The height of the air flow regulating member in the discharge direction is:
3. The gas laser device according to claim 1, wherein the height of the pair of electrodes is equal to the height in the discharge direction. 4. The gas laser device according to claim 1, wherein the cross-sectional shape of the airflow regulating member when cut along a plane perpendicular to the longitudinal direction of the electrode is substantially equal to the cross-sectional shape of the electrode.