JP4789266B2 - Discharge excitation excimer laser equipment - Google Patents

Description

  The present invention relates to an improvement in output characteristics of a pulsed discharge-excited excimer laser device when using a low gas pressure.

  In a conventional excimer laser device, in order to obtain a preionization electrode for preionizing a laser gas in a laser container filled with a laser gas containing a halogen gas such as fluorine gas, and a discharge capable of oscillating laser light. And a cross-flow fan for creating a high-speed laser gas flow between the pair of main discharge electrodes.

  Laser light oscillation is obtained by performing laser excitation discharge by applying a high voltage between a pair of main discharge electrodes. The generated laser light is taken out of the laser container through two windows provided on the side wall of the laser container. When laser excitation discharge is performed, the laser gas between the pair of main discharge electrodes deteriorates in output characteristics due to deterioration and cannot oscillate repeatedly.

  For this reason, the laser gas in the laser container is circulated by the cross-flow fan to generate a laser gas flow between the pair of main discharge electrodes, and the laser gas between the pair of main discharge electrodes is exchanged for each discharge, thereby realizing stable and repetitive oscillation. Is going. The laser gas flow flows at a uniform flow rate in the longitudinal direction of the pair of main discharge electrodes.

The configuration of the conventional excimer laser device as described above is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-218432.
JP 2003-218432 A

  In the conventional excimer laser device, when the gas pressure of the laser gas is low, the variation in output power for each laser pulse is larger than in the high state, and it is difficult to obtain the required stability. was there. Increasing the rotation speed of the once-through fan increases the output power stability for each laser pulse. However, the motor that rotates the fan and the inverter that drives it become larger, resulting in problems such as higher costs and lower maintainability. .

In order to solve the above problems, a laser chamber enclosing a laser gas, a pair of main discharge electrodes arranged in the laser chamber for obtaining a discharge capable of oscillating laser light, and the pair of main discharge electrodes A discharge-excited excimer laser device comprising a cross-flow fan that creates a laser gas flow between them increases the rotational speed of the cross-flow fan as the laser gas pressure in the laser chamber decreases .

  According to the discharge-excited excimer laser device according to the embodiment of the present invention, when the gas pressure of the laser gas is low, variation in output power for each laser pulse can be reduced, and stable output can be obtained. The effect that can be obtained.

  In order to realize the present invention, it is not necessary to make the motor more sophisticated or to change the circuit configuration such as an inverter for driving the motor.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a configuration example of a discharge excitation excimer laser device according to an embodiment of the present invention. In FIG. 1, 100 is a discharge excitation excimer laser device, 101 is a laser chamber, 102 and 102 are main discharge electrodes, 103 is a cross-flow fan, 105 and 105 are windows, 104 is a rotating shaft, 112 is a motor, and 114 and 114 are bearings. , 121 are gas pressure sensors, 130 is a controller, and 131 is an inverter.

  A discharge-excited excimer laser device 100 according to the present invention obtains a preionization electrode (not shown) for preionizing a laser gas and a discharge enabling oscillation of laser light inside a laser chamber 101 in which the laser gas is sealed. A pair of main discharge electrodes 102 and 102 are arranged for this purpose. Further, a cross-flow fan 103 for creating a high-speed laser gas flow is disposed in the laser chamber 101 between the pair of main discharge electrodes 102 and 102.

  The oscillation of the laser beam is obtained by performing laser excitation discharge by applying a high voltage between the pair of main discharge electrodes 102 and 102. The generated laser light is extracted to the outside of the laser chamber 101 through windows 105 and 105 provided on the side wall of the laser chamber 101. When laser excitation discharge is performed, the laser gas between the pair of main discharge electrodes 102 and 102 deteriorates in output characteristics due to deterioration and cannot oscillate repeatedly. For this reason, the laser gas in the laser chamber 101 is circulated by the cross-flow fan 103 and the laser gas between the pair of main discharge electrodes 102 and 102 is exchanged for each discharge to perform stable and repetitive oscillation.

  The overall length of the cross-flow fan 103 is slightly longer than the length of the main discharge electrodes 102 and 102 in order to obtain a uniform wind speed over the entire length of the pair of main discharge electrodes 102 and 102. The cross-flow fan 103 is rotated to obtain a necessary and sufficient gas flow between the pair of main discharge electrodes 102 and 102.

  Cross-flow fan 103 has a rotating shaft 104 that penetrates the inside and protrudes from both ends. The rotary shaft 104 is rotatably supported by bearings 114 and 114 provided at both ends of the laser chamber 101. The motor 112 gives rotational power to the rotating shaft 104 of the once-through fan 103. A driving AC voltage is supplied to the motor 112 by an inverter 131.

  The controller 130 includes a general-purpose arithmetic unit that comprehensively controls the discharge excitation excimer laser device 100. In the present invention, at least a gas pressure sensor 121 detects a laser gas pressure detection signal related to the gas pressure of the laser chamber 101. , And plays the role of a higher-level control unit that issues a speed command signal of the motor 112 to the inverter 131.

  The gas pressure sensor 121 is provided in the laser chamber 101 and detects the pressure of the laser gas in the laser chamber 101. The inverter 131 is set so as to be able to generate a driving AC voltage for rotating the motor 112 at a desired rotational speed. In addition, the controller 130 transmits a speed command signal to the inverter 131 so as to generate a driving AC voltage for rotating the motor 112 at a desired rotational speed. In the present specification, the term rotation speed and the rotation speed may be used interchangeably.

  FIG. 2 is a diagram schematically showing the state of the laser gas flow accompanying the rotation of the cross-flow fan 103. Here, a concept for determining the rotational speed of the cross-flow fan 103 in the conventional excimer laser device will be described. In the figure, reference numeral 115 denotes a fin of the cross-flow fan 103.

  Conventionally, the fan rotation speed of the once-through fan 103 has been determined by the discharge repetition frequency and the required CR value. The CR value used at this time will be described.

  If debris or ions generated by the discharge between the main discharge electrodes 102 and 102 remain between the discharge electrodes, a discharge occurs in the portion where the debris and the like remain at the next discharge, and the entire discharge electrode The discharge at is not stable. If the discharge between the main discharge electrodes 102 and 102 is not stable, the variation in laser output increases.

  In order to avoid this, it is necessary to keep the debris and ions, which are discharge products, away from the space between the discharge electrodes as much as possible before the next discharge. Such a phenomenon is represented by a parameter called CR value. If the gas flow rate in the discharge space is v, the discharge interval time is t, and the discharge width is W, CR = vt / W. The gas flow velocity v is determined by the rotational speed of the once-through fan 103. Further, since the discharge interval time t is the reciprocal of the discharge repetition frequency, if the discharge repetition frequency and the discharge width are determined, the CR value depends on the fan rotation speed.

  Next, the relationship between deterioration of the main discharge electrodes 102 and 102 due to laser light oscillation and laser output will be described. FIG. 3A is a diagram showing the relationship between the laser gas pressure and the laser output in the excimer laser device.

In FIG. 3A, the curve of T _{0 is} a curve showing the laser gas pressure vs. laser output characteristics when the main discharge electrodes 102, 102 are new (almost unused). The laser gas pressure versus the laser output characteristic in such an excimer laser apparatus is indicated by a curve indicated by T ₀ (almost output characteristic when the electrode is not used) → T _{1 as} the main discharge electrodes 102 and 102 are deteriorated by discharge. Curve (output characteristics when T ₁ elapses after use of electrode) → T ₂ curve (output characteristics when T ₂ elapses after use of electrode) → curve indicated by T ₃ (output characteristics when T ₃ elapses after use of electrode), It will change. However, T ₁ <T ₂ <T ₃ .

In an excimer laser device, the rating of the laser output guaranteed by the device is determined. If the rated output is W ₀ , the electrode output is almost unchanged due to the change in output characteristics due to electrode deterioration due to the discharge as described above. The laser gas pressure at the time of use is set to P ₀ , the laser gas pressure at the time T ₁ after use of the electrode is set to P ₁ , the laser gas pressure at the time T ₂ after use of the electrode is set to P ₂ , The laser gas pressure when T ₃ elapses after the use of the electrode is set to P ₃ so that a rated laser output is obtained. In this way, the excimer laser apparatus is used in such a manner that the pressure in the laser chamber 101 is gradually increased from P ₀ → P ₁ → P ₂ → P _{3 according} to the elapsed use time.

  FIG. 3B is a diagram showing the relationship between the laser gas pressure and the motor rotation speed in a conventional excimer laser device.

In such a conventional excimer laser device, when the gas pressure of the laser gas is low (when the gas pressure is P ₀ ), the output power per laser pulse is higher than when the gas pressure is high (when the gas pressure is P ₃ ). There is a problem that the dispersion becomes large and it is difficult to obtain the necessary stability.

Therefore, in the discharge excitation excimer laser device of the present invention, as the laser gas pressure is set low, the rotational speed of the cross-flow fan 103 is increased (or as the laser gas pressure increases according to the actual usage form of the laser device). The rotation speed of the cross-flow fan 103 is reduced). With such a configuration, from the viewpoint of only the CR value, when the gas pressure of the laser gas is low (when the gas pressure is P ₀ ), the apparatus operates with a CR value higher than necessary. However, the inventors have now found that when the gas pressure of the laser gas is low (when the gas pressure is P ₀ ), the output power stability for each laser pulse can be obtained by operating the apparatus with a CR value higher than necessary. Obtained. In the present invention, by utilizing such knowledge, as described above, the rotational speed of the cross-flow fan 103 is increased as the laser gas pressure is set lower.

  Next, an embodiment of the present invention will be described with reference to FIG. 4A and 4B are diagrams showing the relationship between the laser gas pressure and the laser output in the excimer laser apparatus (A), and FIGS. 4B and 4C show the laser gas pressure and the rotation speed of the motor in the discharge excitation excimer laser apparatus of the present invention. It is a figure which shows the relationship.

FIG. 4 (A) is the same as FIG. 3 (A), but in the present invention, (gas pressure P ₀ ), (gas pressure P ₁ ), (gas pressure P ₂ ), (gas The rotational speed of the cross-flow fan 103 at the pressure P ₃ ) is set as shown in FIGS.

In FIG. 4B, the rotational speed of the cross-flow fan 103 at (gas pressure P ₀ ) is set to R _a [rpm], and (gas pressure P ₁ ), (gas pressure P ₂ ), (gas pressure P The rotational speed of the cross-flow fan 103 in ₃ ) was set to R ₃ [rpm]. By setting in this way, in the present invention, when the gas pressure of the laser gas is low, the output power variation for each laser pulse can be reduced and a stable output can be obtained.

4C is the gas pressure P ₀ ), the rotational speed of the cross-flow fan 103 is set as R _a [rpm], and (gas pressure P ₁ ) → (gas pressure P ₂ ) → (gas pressure as P ₃₎ and to set, in which the rotational speed of the cross-flow fan 103 so as to gradually decrease to R ₃ [rpm]. Even with such a setting, the same effect as described above can be obtained.

  As shown in FIGS. 4 (B) and 4 (C), the profile of the gas pressure versus the rotational speed is shown to increase the rotational speed of the cross-flow fan 103 as the laser gas pressure is set low. The present invention is not limited to these gas pressure versus rotational speed profiles.

In order to perform the setting as described above, in the discharge excitation excimer laser device of the present invention, the laser gas pressure is detected by the gas pressure sensor 121 in the laser chamber 101. The laser gas pressure detection signal output from the gas pressure sensor 121 is input to the controller 130. The controller 130 discriminates the gas pressure in the laser chamber 101 based on the input laser gas pressure detection signal, and generates an AC voltage for driving in the inverter 131 for rotating the motor 112 at a predetermined rotational speed accordingly. A speed command signal to be transmitted is transmitted. That is, in the example of FIG. 4A, when a gas pressure between (gas pressure P ₀ ) and (gas pressure P ₁ ) is detected, the controller 130 causes the motor 112 to rotate at a rotational speed R _a. From [rpm], a speed command signal such as the rotational speed R ₃ [rpm] is input to the inverter 131.

In the example of FIG. 4B, the controller 130 controls the motor 112 to rotate at a rotational speed R _a [rpm in response to detection of a change from (gas pressure P ₀ ) to (gas pressure P ₃ ). ], A speed command signal that gradually decreases to the rotational speed R ₃ [rpm] is input to the inverter 131.

  According to the discharge-excited excimer laser device of the present invention described above, when the gas pressure of the laser gas is low, it is possible to reduce variations in output power for each laser pulse, and stable output without increasing the size of the motor and inverter. The effect that can be obtained can be obtained.

  In the present invention, the rotation speed of the cross-flow fan 103 is increased as the laser gas pressure is set lower. The output of the motor 112 is defined by (rotation speed) × (torque). When the gas pressure is low, the required torque at the time of rotation is small, and therefore the number of rotations can be increased accordingly. Therefore, it is not necessary to increase the specifications of the motor 112 as compared with the conventional case.

This will be described with reference to FIGS. 4D and 4E. As shown in FIG. 4D, the torque required to maintain the rotation speeds R _a and R ₃ increases with the increase in the laser gas pressure. Since the motor output is rotational speed × required torque, a limit curve (broken line) of the motor output shown in FIG. 4 (E) can be drawn. Rotational speed curve of the rotational speed R _a, R _3, FIG. 4 (C) described above is set in the output range indicated by the limit curve as shown in FIG. 4 (E).

It is sectional drawing which shows the structural example of the discharge excitation excimer laser apparatus which concerns on embodiment of this invention. FIG. 6 is a diagram schematically showing a state of a laser gas flow accompanying the rotation of the cross-flow fan 103. (A) It is a figure which shows the relationship between the laser gas pressure in an excimer laser apparatus, and a laser output, (B) It is a figure which shows the relationship between the laser gas pressure in the conventional excimer laser apparatus, and the rotation speed of a motor. (A) It is a figure which shows the relationship between the laser gas pressure in an excimer laser apparatus, and a laser output, (B), (C) The figure which shows the relationship between the laser gas pressure and the rotation speed of a motor in the discharge excitation excimer laser apparatus of this invention It is. (D) It is a figure which shows the relationship between a laser gas pressure and the required torque of a motor, (E) It is a figure which shows a motor output limit superimposed on what shows the relationship between a laser gas pressure and the rotation speed of a motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Discharge excitation excimer laser apparatus, 101 ... Laser chamber, 102, 102 ... Main discharge electrode, 103 ... Cross-flow fan, 105, 105 ... Window, 104 ... Rotating shaft, 112 ... Motor, 114, 114 ... Bearing, 115 ... Fin, 121 ... Gas pressure sensor, 130 ... Controller, 131 ... Inverter

Claims (1)

A laser chamber enclosing a laser gas;
A pair of main discharge electrodes disposed in the laser chamber for obtaining a discharge capable of oscillating laser light;
In a discharge excitation excimer laser device comprising a cross-flow fan that creates a laser gas flow between the pair of main discharge electrodes,
A discharge-excited excimer laser device characterized in that the rotational speed of the cross-flow fan is increased as the laser gas pressure in the laser chamber is lower .

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