JPH04137777A - Discharge excitation excimer laser apparatus - Google Patents

Abstract

PURPOSE:To eliminate ununiformity of gas mixing ratio after a laser medium gas is supplied to a pressure vessel by providing a cross blow fan and an axial flow fan with the rotating axes matched. CONSTITUTION:During operation of a laser, the laser medium gas is circulated by a cross blow fan 12 within a pressure vessel 1 and drop of laser pulse energy between the exciation and discharge electrodes 2, 2 is suppressed. However, the energy is gradually lowered due to reduction of halogen gas as the number of times of oscillation increases. For a while, drop of energy can be prevented by gradually raising a charging voltage. But, a high voltage power supply has a limit of capacity and therefore gas is deteriorated to a certain degree, drop of output cannot be compensated. In this timing, a gas supplying apparatus 9 supplies the halogen gas into the pressure vessel 1 from a gas supply port 10 and the deteriorated gas is exhausted from an exhaust port 11 in order to keep the gas pressure to a constant. The supplied gas is guided into a fan 12 by an axial flow fan 13. With the effects of both fans, the supplied gas quickly diffuses within the pressure vessel 1, eliminating fluctuation of mixing ratio.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a discharge excited excimer laser device.

BACKGROUND OF THE INVENTION A rare gas halogen excimer laser is a high-output gas laser that oscillates in the ultraviolet region, and is used as a light source for ultrafine processing in a wide range of applications such as semiconductor phosphorography and chemical processes. There are two types of excitation methods for rare gas halogen excimer lasers: electron beam excitation and discharge excitation, and the latter is widely used because it has a relatively simple configuration and is capable of high repetition oscillation.

A conventional discharge-excited excimer laser device will be described below.

Figure 4 (fat) is a cross-sectional view of the pressure vessel of a three-axis orthogonal ultraviolet preionization discharge-excited excimer laser device, which is the most common type among discharge-excited excimer lasers; It is a figure. Pressure vessel 1
A laser medium gas consisting of rare gas and halogen gas is sealed inside at a high pressure higher than atmospheric pressure. The laser medium gas in the excitation discharge region is excited by generating a --like pulse discharge between a pair of elongated excitation discharge electrodes 2, 2 provided inside the pressure vessel 1.

The discharging circuit shown in FIG. 4 (bl) will be explained. While the switch 3 is open, the charging capacitor 5 is charged via the charging coil 4. When the switch 3 is closed, the charging capacitor 5 is charged. transfers to the peaking capacitor 6, the pre-ionization discharge gap 7 discharges to generate ultraviolet light, and subsequently, when the voltage between the terminals of the peaking capacitor 6 reaches the discharge starting voltage of the excited discharge electrode 2, an excited discharge occurs.

This completes one laser operation, but generally a thyratron or the like is used for the switch 3, and the laser operation is repeated.

For a while after the excitation discharge ends, impurities generated by the discharge remain in the laser medium gas in the excitation discharge region, as well as pressure unevenness and electrical nonuniformity, so the number of oscillation repetitions is increased. As time goes by, the subsequent excited discharge becomes unstable and the output decreases. If the oscillation repetition rate is further increased, a uniform excited discharge can no longer be obtained and laser oscillation becomes impossible. In order to achieve high repetition rate oscillation of several tens of Hz or more, it is necessary to return the laser medium gas in the excited discharge region to a homogeneous and clean state immediately after the end of the excited discharge. To this end, a fan for circulating the laser medium gas is housed inside the pressure vessel 1, which forcibly removes the laser medium gas within the excited discharge area after the excited discharge, and keeps it in a clean and homogeneous state at all times. That's what I do. A cross flow fan 8 is generally used as the circulation fan.

In this way, by circulating the laser medium gas, a decrease in laser output during repeated operations can be suppressed. However, in the long term, a decrease in laser output due to deterioration of the laser medium gas is unavoidable. This is because halogen gas such as fluorine used in the excimer laser has extremely high reactivity and is therefore reduced by adsorption to the inner wall of the pressure vessel 1 and reaction with discharge products. In order to maintain the laser output, the charging voltage of the charging capacitor 5 is gradually increased to increase the energy input to the excitation discharge. Furthermore, when the deterioration of the laser medium gas progresses and the decrease in laser output cannot be compensated for simply by increasing the charging voltage, halogen gas may be replenished from the laser medium gas supply device 9 through the gas supply port 10, or the laser medium gas may be partially replaced or Perform continuous replacement while the laser is operating. Note that 11 is a gas exhaust port.

Problems to be Solved by the Invention The laser medium supply device 9 has a gas supply port 10 of the pressure vessel 1.
and is connected to the gas exhaust port 11. It is desirable to provide the gas exhaust port 11 and the gas supply port 10 as far apart as possible in order to increase the gas exchange efficiency. However, if they are provided at both ends of the pressure vessel 1 as shown in Fig. 4 fa), A difference arises between the gas mixture ratio and the gas mixture ratio on the supply port 10 side. Since the cross-flow fan 8 for gas circulation does not move the gas quickly in the direction of its rotation axis, the gases in the pressure vessel 1 are not mixed smoothly, and the non-uniformity of the gas mixture ratio is difficult to eliminate. This causes variations in the gas mixture ratio even in the excited discharge region, causing instability of the excited discharge and a decrease in laser output.

The present invention solves the above-mentioned conventional problems, and provides a discharge-excited excimer laser device having means for eliminating non-uniformity in gas mixture ratio after supplying a laser medium gas into a pressure vessel.

Means for Solving the Problems To achieve this object, the present invention provides a pressure vessel for sealing a laser medium gas, a means for supplying the laser medium gas into the pressure vessel, and an excitation discharge electrode for exciting the laser medium gas. In a three-axis orthogonal discharge-pumped excimer laser device equipped with a cross-flow fan that circulates laser medium gas within a pressure vessel during laser operation, the laser medium is disposed inside the pressure vessel in the direction of the rotational axis of the cross-flow fan. It is equipped with an axial fan for moving gas, and the rotational axis of the trickle fan is the same as the rotational axis of the crossflow fan.

Function: With this configuration, the laser medium gas can also be moved in the direction of the rotation axis of the cross-flow fan, so that the gases in the pressure vessel can be mixed smoothly and quickly. Therefore, the difference in gas mixture ratio within the excited discharge region is immediately eliminated,
A decrease in laser output due to instability of excited discharge can be avoided.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a pressure vessel of a discharge excited excimer laser device in one embodiment of the present invention. Inside the pressure vessel 1 are an excitation discharge electrode 2 and a cross flow fan 12 for gas circulation.
, an axial fan 13 is housed therein. Since the rotational axis of the axial fan 13 is the same as that of the crossflow fan 12, the structure is such that the rotational driving force of the crossflow fan 12 can be used as is. The pressure vessel 1 has a gas supply port 10 for receiving supply of clean laser medium gas from a laser medium gas supply device 9, and a gas supply port 10 for exhausting the laser medium gas degraded by repeated discharges to reduce the gas pressure in the pressure vessel 1. A gas exhaust port 11 is provided to keep the gas constant. Gas supply port 10
Since the gas exhaust ports 11 are provided at both ends of the pressure vessel 1 in the laser beam direction, the clean gas supplied into the pressure vessel 1 is not immediately exhausted.

FIG. 2 (al and fbl are a front view and a side view of a cross flow fan and an axial fan in this embodiment.

Generally, the blades of a crossflow fan are fixed by several disks, so if an axial fan is attached to the shaft of the crossflow fan, the disks for fixing the blades will become an obstacle to the gas flow in the axial direction. In this embodiment, by replacing the blade fixing disk with an axial fan and integrating two fans, a cross flow fan and an axial fan, a smooth gas flow and weight reduction were achieved. Furthermore, by integrating the two fans, the rotational driving force of the crossflow fan 12 can be directly used to drive the axial fan 13.

Since the excimer laser device uses highly corrosive halogen gas, it is generally not possible to install a motor inside the pressure vessel 1. In order to introduce the rotational driving force of the external motor into the inside of the pressure vessel 1, it is necessary to use a complicated, expensive, and unreliable driving force introduction mechanism such as a magnetic fluid seal. According to this embodiment, there is no need for a dedicated motor and driving force introduction mechanism for the axial fan 12, which is very advantageous in terms of safety, reliability, and economy.

FIG. 3 is a diagram showing the operation of the laser device of the present invention and the state of laser pulse energy. The operation of the laser device shown in FIG. 1 will be explained with reference to FIG.

During laser operation, cross flow fan 1 is operated inside pressure vessel 1.
Since the laser medium gas is circulated by the rotation of 2 and a gas flow is generated between the excitation discharge electrodes 2 and 2, a decrease in laser pulse energy due to high repetition rate of oscillation is suppressed. However, as the number of oscillations accumulates, the laser pulse energy gradually decreases due to a decrease in halogen and an increase in impurities. For a while, charging capacitor 5
By gradually increasing the charging voltage and increasing the energy input to the excitation discharge, it is possible to prevent the laser pulse energy from decreasing. However, the high-voltage power supply has a limited capacity, so if the laser medium gas deteriorates to a certain extent, it will not be able to compensate for the decrease in output. At this point, the laser medium gas supply device 9 supplies a small amount of halogen gas into the pressure vessel 1 through the gas supply port 10 . At this time, the gas exhaust port 11
The deteriorated gas is exhausted to the outside of the pressure vessel 1 to keep the gas pressure inside the pressure vessel 1 constant. The halogen gas supplied into the pressure vessel 1 is guided into the cross-flow fan 12 by the rotation of the axial fan 13 . The effect of the cross flow fan 12 and the effect of the trickle fan 13 combine to quickly diffuse the supplied halogen gas within the pressure vessel 1, so that variations in the gas mixture ratio within the pressure vessel 1 are immediately eliminated. It is possible to prevent a decrease or variation in laser pulse energy due to instability of excited discharge, which has conventionally been a problem immediately after halogen gas is supplied.

The above is an example in which halogen gas was supplied. The two fans function in the same way when partially replacing the gas in the pressure vessel 1, including the rare gas and buffer gas, or when continuously replacing the gas in small amounts during laser operation.

According to the present invention, gases can be quickly mixed not only when gas is supplied during laser operation, but also when filling the pressure vessel 1 with gas again after evacuating the interior of the pressure vessel 1.

Effects of the Invention As described above, the present invention quickly eliminates non-uniformity in the mixing ratio of the laser medium gas immediately after being supplied into the pressure vessel by providing a cross-flow fan and an axial-flow fan with their rotational axes aligned. The present invention is intended to realize a discharge-excited excimer laser device that can stabilize excited discharge.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a pressure vessel of a discharge-excited excimer laser device according to an embodiment of the present invention, and FIG.
3 is a front view and a side view of a cross flow fan and an axial fan in an embodiment of the present invention, FIG. 3 is a diagram showing the operation of the discharge excited excimer laser device of the present invention and the state of laser pulse energy, 4 is a sectional view of a pressure vessel of a conventional discharge-excited excimer laser device, and FIG. 4+bl is an overall configuration diagram of the same discharge-excited excimer laser device. Excitation discharge electrode, 9...Laser medium gas supply device (supply means), 12...Cross flow fan, 13...
...Axial flow fan. Name of agent: Patent attorney Haruaki Koba et al.28 (Figure CCI) (b) Figure

Claims (1)

[Claims] A pressure vessel that seals the laser medium gas, a means for supplying the laser medium gas into the pressure vessel, an excitation discharge electrode that excites the laser medium gas, and a cross flow that circulates the laser medium gas within the pressure vessel during laser operation. In the three-axis orthogonal discharge-excited excimer laser device, the pressure vessel is provided with an axial fan that moves the laser medium gas in the direction of the rotational axis of the cross-flow fan, and the axial flow A discharge-excited excimer laser device characterized in that the rotation axis of the fan is the same as the rotation axis of the cross flow fan.