JPH03255689A - Excimer laser oscillator - Google Patents

Abstract

PURPOSE:To clearly define the time when laser gas is replaced by a method wherein a photodetector which monitors the spectral intensity of emitted light, a photodetector which monitors the optical output of a laser, and a control circuit used for the supply of halogen gas comparing the electrical signals with each other obtained from the photodetectors concerned are provided inside an oscillator. CONSTITUTION:A part of laser rays branched off through a beam splitter 8 is incident on a laser monitor 9. A window 12 transmits only a discharge light, the transmitted light is selected by a band-pass filter and made to impinge on a photodetector 14. The signals of the laser output monitor 9 and the photodetector 14 are inputted into a control circuit 10, and when both the laser output and the intensity of discharge light decrease to a certain value or below at the same time, the control circuit 10 transmits a signal to a halogen gas feeder 11 and halogen gas is fed into a laser chamber. By monitoring a discharge light, it is defined whether the cause of the deterioration of a laser in output lies on the decrease of halogen gas or others, and laser gas can be decreased in consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to excimer laser oscillators, and more particularly to a method for determining when to replace gas in an excimer laser.

[Conventional technology]

Conventionally, this type of excimer laser oscillator uses rare gas (X
es or Kr) and halogen gas (H (1° or F2
), and He was used as the buffer gas.

Laser oscillation light is obtained by electric discharge in a gas to which a gas such as Ne is added. The halogen gas in the mixed gas is highly reactive and may be adsorbed to the inner wall of the laser chamber or cause chemical reactions with other constituent substances due to plasma during discharge, resulting in a gradual decrease in concentration and a decrease in laser output. Therefore, in order to obtain stable laser output over a long period of time, halogen gas is regularly replenished.

[Problem to be solved by the invention]

In the conventional excimer laser oscillator described above, the timing of halogen gas replenishment is determined when the laser output drops below a certain value. However, the cause of the decrease in laser output is not only a decrease in the concentration of halogen gas, but also a malfunction of the laser oscillator's resonator and dirt on mirrors, etc., so even if halogen gas is replenished, the laser output will not recover. There are drawbacks.

[Means to solve the problem]

The excimer laser oscillator of the present invention has a light receiving element that monitors the emission spectrum intensity of the discharge inside the oscillator, a light receiving element that monitors the laser light output, and compares the electrical signals from these elements and replenishes the nitrogen gas. It has a control circuit for driving the halogen gas supply device.

The present invention measures the decrease in the concentration of chlorogen gas by monitoring the spectral light in the gas discharge, so it is possible to eliminate factors that reduce the laser output due to resonator alignment, etc., compared to the case where only the laser light output is monitored. It has characteristics.

〔Example〕

FIG. 1(a) is a block diagram of one practical example of the present invention, and FIG. 1(b) is a cross-sectional view of a laser chamber. 1 is a laser chamber in which a mixed gas is sealed. 2.3 is a discharge electrode to which a higher voltage than the power source 4 is applied, and a discharge is obtained between the electrodes 2.3. 5 and 6 are mirrors constituting a resonator of a laser oscillator, 5 is a total reflection mirror, and 6 is a partial transmission mirror. Reference numeral 7 denotes an optical axis through which laser light is output, and a portion of the laser light split by the beam splitter 8 enters a laser monitor 9. Reference numeral 12 denotes a window that allows the discharge light to pass through, and is oriented in a direction perpendicular to the optical axis of the laser light, allowing only the discharge light to pass through. The transmitted light is filtered through 13 bandpass filters, and the wavelength is 248 nm for KrF excimer, XeCl;! 308 for excimer
Light in the vicinity of nm is selected and enters the light receiving element 14. Signals from a laser output monitor 9 and a light receiving element 14 are input to a control circuit 10. The control circuit 10 controls the control circuit 11 when the laser output and discharge light intensity simultaneously decrease below a certain value.
A signal is sent to the halogen gas supply device to supply halogen gas into the laser chamber, but if the discharge light intensity does not change even if the laser output decreases, halogen gas is not replenished.

FIG. 2 is a configuration diagram of a second embodiment of the present invention. Figure 1 Window 1
Since the optical fiber 20 is used instead of the optical fiber 20, there is an advantage that the structure for installing the window is simplified. The rest is the same as the previous embodiment.

〔Effect of the invention〕

As explained above, the present invention clarifies whether the cause of the decrease in laser output is due to a decrease in gas or some other cause by monitoring the discharge light, and reduces the amount of gas consumption. There are effects that can be reduced.

[Brief explanation of drawings]

FIG. 1(a) is a block diagram of the present invention, and FIG. 1(b) is a sectional view of a laser chamber portion. FIG. 2 is a block diagram of a second embodiment of the present invention. 1... Laser chamber, 2, 3... Electrode, 4... Power supply, 5... Total reflection mirror, 6
...Partially transmitting mirror, 7...Optical axis, 8...
...Beam splitter-9...Laser output monitor, 10...Control circuit, 11...
Halogen gas supply device, 12...Li2...
・・Bandpass filter 14・・・Photodetector, 20・・・Optical fiber

Claims (1)

[Claims] In an excimer laser oscillator that uses rare gas and halogen gas as laser media and is excited by pulsed discharge, we compared the light receiving element that converts the light emitted by the discharge into an electrical signal, the detector that monitors the laser light output, and those signals. , an excimer laser oscillator comprising a control circuit for driving a halogen gas supply device.