JPH0548186A - Polarizing laser - Google Patents

Abstract

PURPOSE:To provide a polarizing laser device capable of obtaining stabilized laser output, calling for no sophisticated design on the side of a device which laser light and, what is more, eliminating its directional property during working. CONSTITUTION:There is installed an output control polarizing cancellation unit 13, which comprises an attenuator which attenuates laser output light 8 based on the polarizing properties and a polarizing cancellation device, on an optical axis of the laser output light 8 outside a laser resonator. A quartz board or the like, which rotates a laser output optical axis as a rotary axis, is installed to the attenuator. The laser output light 8 is monitored by an output monitor 9 and the rotation of the quartz board is controlled by a controller 11, which makes it possible to control the output without changing the operational conditions in the laser resonator. The laser output light 8 which has permeated the quartz board is turned into non-polarized light by a polarizing cancellation device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarized laser device used as a light source for exposure for fine processing of semiconductor integrated circuits.

[0002]

2. Description of the Related Art In recent years, excimer lasers have attracted attention as a high-efficiency, high-power laser in the ultraviolet region among lasers. The excimer laser is particularly expected as a light source for exposing a fine pattern of a semiconductor integrated circuit. The excimer laser uses a combination of a rare gas such as krypton or xenon as a laser medium and a halogen gas such as fluorine or chlorine to generate an oscillation line having a sufficient output for pattern exposure at some wavelengths between 353 nm and 193 nm. Obtainable. However, if the laser light is polarized,
The shape and accuracy of the pattern may differ depending on the processing direction of the pattern.

Generally, in order to control the output of a laser, a method of changing the excitation intensity for exciting the laser medium or adjusting an optical element in the resonator is adopted.

As a conventional example, the configuration described in Japanese Patent Laid-Open No. 63-9187 will be described with reference to the schematic configuration diagram shown in FIG. The laser in this conventional example is a discharge excitation type excimer laser, and the output intensity is changed by changing the output voltage of the power source to adjust the output.

In FIG. 4, 1 is a total reflection mirror which constitutes a laser resonator, and 2 is a semi-transmission mirror which constitutes a laser resonator. A laser medium 3 is provided in the optical path of the resonator. A charge / discharge excitation circuit 4 excites the laser medium 3. 5 is a high-voltage power supply that supplies power to the charge / discharge excitation circuit 4,
An optical element etalon 6 narrows the spectrum of the laser oscillated by the laser resonator. A monitor optical system 7 branches a part of the laser output light 8 oscillated from the laser resonator. Reference numeral 9 is an output monitor, which is a monitor optical system 7.
A part of the laser output light 8 branched by is monitored and a monitor signal 10 is output. Reference numeral 11 denotes a controller, which generates a feedback signal 12 for controlling the voltage of the high-voltage power supply 5 according to the monitor signal 10.

The operation of the laser device configured as described above will be described below.

A monitor optical system 7 monitors a part of a laser output light 8 oscillated from a laser resonator composed of a total reflection mirror 1 and a semi-transmission mirror 2 and narrowed in band by an optical element etalon 6 by an monitor optical system 7. To introduce. The controller 11 outputs the feedback signal 12 according to the monitor signal 10 output from the output monitor 9 to control the voltage of the high-voltage power supply 5. By changing the voltage of the high-voltage power supply 5 by the feedback signal 12, the excitation intensity for exciting the laser medium 3 can be changed, and accordingly, the amplification factor amplified when the laser light passes through the laser medium 3 changes. Therefore, the laser output can be controlled.

[0008]

However, in the configuration of the above-mentioned conventional example, when the excitation intensity for exciting the laser medium in the laser resonator is rapidly changed and the optical element is adjusted, this optical Since the operating conditions of the element are changed drastically, the thermal load on the laser medium and the optical element changes, and the abundance ratio of atoms and molecules in the steady state of the laser medium changes. The operating conditions in the laser resonator, such as generation or adsorption of impurity gas, change. As a result, it is difficult to stabilize the laser output. Also, when applying polarized light to laser processing, design an optical system that takes into consideration the optical characteristics such as the difference in the processing cross section depending on the processing direction and the difference in the reflectance of S-polarized light and P-polarized light. There was a difficulty that I had to do.

The present invention solves the above-mentioned problems of the prior art. It is possible to obtain a stable laser output by controlling the laser output without changing the conditions in the laser resonator. , The device side that uses laser light does not require a complicated design considering the polarization direction,
Moreover, it is an object of the present invention to provide a polarized laser device in which the directionality at the time of processing is eliminated so as not to cause a disadvantage to the device side that uses laser light.

[0010]

To achieve this object, the present invention provides a laser resonator, monitor means for monitoring laser output light oscillated from the laser resonator, and laser output outside the laser resonator. An attenuator that is provided on the optical axis and that is rotated about the laser output optical axis as a rotation axis and that attenuates the laser light using polarization characteristics; and the laser resonator with respect to the attenuator on the laser output optical axis. And a control means for controlling the output by rotating the attenuator according to a monitor signal from the monitor means.

As the attenuator, at least one quartz plate that makes laser output light incident at Brewster's angle is used. When this quartz plate is used, an even number of quartz plates are provided, and two quartz plates are set as a set to set the optical axis of the optical axis. It is preferable to incline in opposite directions so as to cancel the deviation.

Further, the attenuator may be composed of at least one polarization separation mirror arranged so that reflected light does not return to the laser resonator.

[0013]

According to the present invention, with the above construction, the laser output light oscillated from the laser resonator is monitored by the monitor means to output a monitor signal, and the monitor means outputs the monitor signal, and the control means causes the attenuator to rotate the laser output optical axis. As a result, the laser output light can be attenuated by utilizing the polarized light, and then the laser output light can be made into an inhomogeneous light by the depolarization element. Since the laser output light monitoring means, the attenuator, and the depolarizing element (in particular, the attenuator) are all provided outside the laser resonator, it is not necessary to drastically change the operating conditions inside the laser resonator. It is possible to control the output. Further, since the non-polarized laser light is output, it is possible to eliminate the trouble of making a complicated design in consideration of the polarization direction on the device side that uses the laser light, and moreover, when applying it to laser processing, Directionality can be eliminated.

[0014]

(Embodiment 1) A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a polarized laser device according to a first embodiment of the present invention.

In FIG. 1, 1 is a total reflection mirror which constitutes a laser resonator, and 2 is a semi-transmission mirror which constitutes a laser resonator. A laser medium 3 is provided in the optical path of the resonator. A charge / discharge excitation circuit 4 excites the laser medium 3. 5 is a high-voltage power supply that supplies power to the charge / discharge excitation circuit 4,
An optical element etalon 6 narrows the spectrum of the laser oscillated by the laser resonator. A monitor optical system 7 branches a part of the laser output light 8 oscillated from the laser resonator. Reference numeral 9 is an output monitor, which is a monitor optical system 7.
A part of the laser output light 8 branched by is monitored and a monitor signal 10 is output. Reference numeral 11 is a controller, which responds to the monitor signal 10 with a feedback signal 12
To occur. 13 is an output control depolarization unit,
It is provided on the optical axis of the laser output light 8 outside the laser resonator,
It consists of an attenuator and a depolarizer, which are controlled according to the feedback signal 12.

The polarized laser device configured as described above will be described in more detail below together with its operation.

A laser output light 8 oscillated from a laser resonator composed of a total reflection mirror 1 and a semi-transmission mirror 2 and band-narrowed by an optical element etalon 6 is output-controlled depolarization unit 13.
Through the laser beam to reach the monitor optical system 7, a part of the laser output light 8 is branched and introduced into the output monitor 9. The controller 1 according to the monitor signal 10 detected by the output monitor 9
1 outputs a feedback signal 12 to control the output control depolarization unit 13. An attenuator of the output control depolarization unit 13 rotates with the optical axis of the laser output light 8 as a rotation axis according to the feedback signal 12 together with or independently of the output control depolarization unit 13, and controls the result output. The depolarizer depolarizes the laser output light 8.

Details of the output control depolarization unit 13 will be described. FIG. 2 is a schematic perspective view showing the output control depolarization unit 13. As shown in FIG. 2, the output control depolarization unit 13 includes a pair of quartz plates 14 that are attenuators.
a and 14b, and a depolarizer 15 which is an optical element for making polarized light unpolarized. Each quartz plate 14
The laser output light 8a and the laser light 14b are arranged in a V-shape that is symmetrically inclined in the opposite direction with respect to the optical axis of the output light 8 so that the laser output light 8 is incident at the Lewster angle θb.
Is provided so as to be rotatable about the optical axis of the quartz plate 14 as a rotation axis.
It is installed on the side opposite to the laser resonator with respect to a and 14b.

Generally, of the light incident on the quartz plate at the Brewster angle θb, the P-polarized component is completely transmitted, the S-polarized component is partially transmitted, and the rest is reflected. Therefore, in the laser output light 8 after passing through the quartz plates 14a and 14b, only the S-polarized component is attenuated. Therefore, when the laser output light 8 oscillated from the laser resonator is polarized light, the output control depolarization unit 13 is rotated with the optical axis of the laser output light 8 as the rotation axis, so that the quartz plates 14a, 14 are rotated.
S polarization component of the laser output light 8 with respect to the incident surface on b, P
Since the ratio of the polarization components changes, the output can be controlled. Laser output light 8 transmitted through the quartz plates 14a and 14b
Can be made non-polarized by the depolarizer 15.

The above control is all performed outside the laser resonator and has no influence on the laser oscillation conditions, so that more stable output control can be performed as compared with the prior art. Further, by disposing the two quartz plates 14a and 14b in a V-shape that is inclined in opposite directions, the optical axis of the laser output light 8 does not shift before and after passing through the output control depolarization unit 13. is there. Furthermore, laser output light 8
After passing through the quartz plates 14a and 14b, the depolarizer 1
Since the laser output light 8 is transmitted through the laser beam 5, the laser output light 8 becomes unpolarized, and there is an advantage that the influence of the directionality of laser processing can be eliminated.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a schematic sectional view showing an output control depolarization unit used in a polarization laser device according to the second embodiment of the present invention. In the present embodiment, the configuration other than the output control depolarization unit is the same as that of the first embodiment, so the description thereof is omitted.

In FIG. 3, reference numeral 16 denotes a polarization separation mirror installed so that the laser output light 8 does not return to the laser resonator, and the optical axis of the laser output light 8 may be provided together with the output control depolarization unit 13 or alone. It is provided so that it can rotate as a rotating shaft. Reference numeral 15 is a depolarizing element for making polarized light unpolarized, and is installed on the optical axis of the laser output light 8 on the side opposite to the laser resonator with respect to the polarization separation mirror 16. The polarization separation mirror 16 is an optical element provided with a dielectric multilayer film so as to reflect only one of the S-polarized component and the P-polarized component. Therefore, the polarization separation mirror 16
In the laser output light 8 after passing through, only the polarization component 17 reflected by the polarization separation mirror 16 is attenuated. Therefore, if the oscillated laser output light 8 is polarized light, the output control depolarization unit 13 is rotated about the optical axis of the laser output light 8 as a rotation axis, so that the laser output light with respect to the incident surface to the polarization separation mirror 16 is rotated. Since the ratio of the S-polarized component and the P-polarized component of 8 changes, the output can be controlled. Polarization separation mirror 1
The laser output light 8 that has passed through 6 can be depolarized by the depolarizer 15.

The above control is all performed outside the laser resonator and has no influence on the laser oscillation condition, so that more stable output control can be performed as compared with the conventional technique. Furthermore, since the laser output light 8 passes through the polarization separation mirror 16 and then the depolarization element 15, the laser output light 8
Becomes non-polarized light, and there is also an advantage that the influence of the directionality of laser processing can be eliminated.

[0026]

As described above, according to the present invention, the laser output light oscillated from the laser resonator is monitored by the monitor means and a monitor signal is output, and the monitor signal causes the control means to operate outside the laser resonator. Since the attenuator provided on the laser output optical axis is rotated about the laser output optical axis as the rotation axis and the laser output light is attenuated by using the polarized light, the operating condition in the laser resonator is changed. You can control the output without.
Therefore, a stable output can be obtained. Also,
Since the depolarization element installed on the opposite side of the attenuator from the laser resonator on the laser output optical axis depolarizes the laser output light, the device side that uses the laser light has a complicated polarization direction. The design is unnecessary and the processing direction can be eliminated. Therefore, it is possible to prevent the device side using the laser light from being disadvantageous.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a polarization laser device according to a first embodiment of the present invention.

FIG. 2 is a schematic perspective view showing an output control depolarization unit used in the same polarized laser device.

FIG. 3 is a schematic cross-sectional view showing an output control depolarization unit used in a polarization laser device according to a second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing a conventional polarized laser device.

[Explanation of symbols]

 1 Total Reflector 2 Semi-Transparent Mirror 3 Laser Medium 4 Charge / Discharge Excitation Circuit 5 High Voltage Power Supply 6 Etalon 7 Monitor Optical System 9 Output Monitor 11 Controller 13 Output Control Depolarization Unit 14a Quartz Plate 14b Quartz Plate 15 Depolarization Element 16 Polarization Separation Mirror

Front page continuation (72) Inventor Naoya Horiuchi 3-10-1 Higashisanda, Tama-ku, Kawasaki City, Kanagawa Prefecture Matsushita Giken Co., Ltd. No. Matsushita Giken Co., Ltd. (72) Inventor Takeo Miyata 3-10-1 Higashisanda, Tama-ku, Kawasaki-shi, Kanagawa Matsushita Giken Co., Ltd.

Claims (4)

[Claims] 1. A laser resonator, monitor means for monitoring laser output light oscillated from the laser resonator, and a laser output optical axis provided outside the laser resonator, wherein the laser output optical axis is a rotation axis. And an attenuator that is rotated as attenuator to attenuate the laser light by utilizing polarization characteristics, a depolarizing element provided on the opposite side of the attenuator from the laser resonator on the laser output optical axis, and the monitor means. And a control means for controlling the output by rotating the attenuator according to a monitor signal from the polarized laser device. 2. The polarized laser device according to claim 1, wherein the attenuator is composed of at least one quartz plate which makes laser output light incident at Brewster's angle. 3. The polarized laser device according to claim 2, wherein the attenuator includes an even number of quartz plates, two of which are set as a set, and the attenuators are tilted in directions opposite to each other so as to cancel the deviation of the optical axis. 4. The polarized laser device according to claim 1, wherein the attenuator is composed of at least one polarization separation mirror arranged so as not to return the reflected light to the laser resonator.