JPH043481A - Gas laser device - Google Patents

Abstract

PURPOSE:To lengthen the lifetime of a gas laser medium inversely proportional to a discharge input by controlling the repeated frequency of laser oscillation so that the mean output of laser beams is kept constant without increasing the discharge input and supplying an airtight vessel with a specified gas component when repeated frequency reaches a fixed value or more. CONSTITUTION:When the charging voltage of the main capacitor of the discharge circuit of a discharge exciting section 3 is set at a value, where maximum oscillation efficiency is acquired, and a laser device is operated, a gas laser medium in an airtight vessel 2 is excited, and laser beams L are generated. The laser beams L generated in the airtight vessel 2 are amplified by an optical resonator, laser beams L emitted from an output mirror 5 for the optical resonator are split by a beam splitter 15 and input to an output monitor 14, and the mean output is detected. The detecting signal is compared with an optimum output set value by the comparison setting section 13 of a controller 9, and a control signal corresponding to the difference is output to an oscillation control section 11. The oscillation control section controls the repeated frequency of trigger pulses driving a power supply 4, and brings the mean output of the laser beams L emitted from the output mirror 5 close to the set value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Field of Application) The present invention relates to a gas laser device that discharge-excites a gas laser medium to output laser light.

(Prior art) Various gas laser media are used in gas laser devices, one of which is Ne (neon) and Kr (krypton).
Using a mixed gas containing F2 (fluorine) and F2 (fluorine),
KrF excimer lasers are known. When this KrF excimer laser is operated for a long time, the fluorine gas in the gas laser medium dissociates due to the collision of electrons caused by discharge, and the ratio of the three types of mixed gases deviates from the optimum value. A phenomenon occurs in which the human power (manpower) gradually declines.

In order to prevent the laser output from decreasing due to such a phenomenon, conventional measures have been taken.

In other words, the output of the laser light emitted from the gas laser device is monitored by a sensor, and as the laser oscillation efficiency decreases, the charging voltage to the main capacitor of the discharge circuit is increased to increase the laser input energy, thereby decreasing the laser output. I was trying to prevent it from happening.

On the other hand, when the charging voltage to the discharge circuit main capacitor reaches the upper limit of the power supply itself or the upper limit limited to prevent the discharge from transitioning to an arc state, fresh fluorine gas is injected. When fluorine gas is injected, the mixing ratio of the gas laser medium approaches the initial value, and the laser oscillation efficiency is restored to near the initial value, so that the charging voltage can be reduced to about the initial value. In this way, by repeatedly increasing the charging voltage and replenishing the fluorine gas, the laser output can be maintained at a predetermined value or higher.

This state is shown in FIG. In the figure, curve X shows the relationship between laser operating time and laser average output, and curve Y shows the relationship between laser operating time and charging voltage.

In the curve Y, an arrow F indicates the timing of injecting fluorine gas. Note that it is possible to extend the life of the gas laser medium by injecting fluorine gas.

However, since there is a limit to the number of times that fluorine gas injection can be effective, the longer the fluorine gas injection interval, the better.

Incidentally, the laser oscillation efficiency depends on the charging voltage as shown in FIG. 5, and the life of the gas laser medium has the property of being proportional to the reciprocal of the discharge input as shown in FIG. Therefore, changing the charging voltage in order to keep the average laser output constant leads to a decrease in oscillation efficiency from a comprehensive standpoint, resulting in a shortened lifespan of the gas laser medium.

In other words, if a decrease in output is prevented by increasing the voltage, it is only possible to sufficiently lengthen the time until the gas laser medium deteriorates and the laser output becomes uncontrollable.

(Problem to be Solved by the Invention) As described above, in conventional gas laser devices, when the output of laser light decreases, the output is increased by increasing the discharge input, which causes the gas laser medium to deteriorate. In some cases, the time until the laser output becomes uncontrollable cannot be made sufficiently long.

This invention was made based on the above circumstances, and its purpose is to make it possible to sufficiently lengthen the time until the gas laser medium deteriorates and the laser output becomes uncontrollable. An object of the present invention is to provide a gas laser device.

[Structure of the Invention] (Means and Effects for Solving the Problems) In order to solve the above problems, the present invention provides an airtight container in which a gas laser medium is sealed and is provided with excitation means for exciting the gas laser medium; a supply means for supplying a predetermined gas component of the gas laser medium into a container; an optical resonator that amplifies and oscillates a laser beam generated when the gas laser medium is excited by the excitation means; a detection means for detecting the output of the oscillated laser light; an oscillation control section for controlling the repetition frequency of the laser oscillation so that the average output of the laser light detected by the detection means is constant; The apparatus is characterized by comprising a supply control section that supplies a predetermined gas component from the supply means to the airtight container when the repetition frequency of oscillation becomes equal to or higher than a predetermined value.

According to this configuration, the average output of the laser beam can be maintained constant by changing the repetition frequency of laser oscillation, so when the discharge input is increased, the time required for the Vegas laser medium to deteriorate can be lengthened. can.

(Example) An example of the present invention will be described below with reference to FIG. Figure 1 shows K as a gas laser device according to this invention.
An rF excimer laser device is shown, and this laser device is equipped with an airtight container 2. A discharge excitation section 3 serving as excitation means is provided within the airtight container 2. This discharge excitation section 3 has a main electrode and a preliminary ionization electrode (both not shown), and a power source 4 is connected to these. When electrical energy is supplied from the power source 4 to the discharge excitation section 3, the discharge excitation section 3 is first pre-ionized by the pre-ionization electrode. Then, when the preliminary ionization progresses sufficiently, a main discharge occurs between the main electrodes, thereby exciting the gas laser medium circulating in the discharge excitation section 3 as will be described later, and generating laser light.

An output mirror 5 is arranged at one end in the axial direction of the discharge excitation section 3, and a high reflection mirror 6, which forms an optical resonator with the output mirror 5, is arranged at the other end. therefore,
The laser light generated in the discharge excitation section 3 is transmitted to the output mirror 5.
After being repeatedly reflected and amplified between the output mirror 6 and the high reflection mirror 6, it is oscillated from the output mirror 5.

A gas supply device 7 is connected to the airtight container 2 via first to third supply lines 8a to 8C. In other words,
The gas supply device 7 is provided with a neon gas supply source, a krypton gas supply source, and a fluorine gas supply source (not shown). These supply sources are connected to the airtight container 2 via the respective supply lines 8a to 8C, so that neon gas, krypton gas, and fluorine gas can be supplied from each supply source to the airtight container 2 at a predetermined ratio. It has become.

A power supply 4 connected to the discharge excitation section 3 and each gas supply source of the gas supply device 7 are controlled by a control device 9. This control device 9 includes an oscillation control section 11 and a gas supply control section 1.
2 and a comparison setting section 13. Oscillation control section 11
The gas supply control section 12 outputs drive signals to the power source 4 and the gas supply device 7, respectively, in response to control signals from the comparison setting section 13. That is, the oscillation control section 11 controls the repetition frequency of the trigger pulse applied to the power source 4, and the gas supply control section 12 controls the injection of fluorine gas into the airtight container 2.

A signal from an output monitor 14 that detects the average output of the laser beam oscillated from the output mirror 5 is input to the comparison setting section 13. A portion of the laser light oscillated from the output mirror 5 is split by a beam splitter 15 and input to the output monitor 14 . Thereby, the output monitor 14 detects the average output of the laser beam.

The average output of the laser beam detected by the output monitor 13 is compared with the setting value set in the comparison setting section 13, and based on the comparison, the power source 4 and the gas supply device 7 are connected to the oscillation control section 11. It is controlled by the gas supply control section 12 as described later.

Next, the operation of the KrF excimer laser device having the above configuration will be explained. First, the control device 9 sets the charging voltage of the discharge circuit main capacitor of the discharge excitation section 3 to 33 KV, which is the value at which the maximum oscillation efficiency can be obtained in the graph shown in FIG. When the KrF excimer laser device is operated in this state and electrical energy is supplied to the discharge excitation section 3, the discharge excitation section 3 is pre-ionized and a main discharge is generated, thereby exciting the gas laser medium in the airtight container 2. Laser light is generated. Laser light generated in the airtight container 2 is amplified by the optical resonator and oscillated from the output mirror 5.

A portion of the laser beam oscillated from the output mirror 5 is split by a beam splitter 15 and input to an output monitor 14, and the average output of the laser beam is detected by the output monitor 14. This detection signal is input to the comparison setting section 13 of the control device 9.

The optimum output of the laser light emitted from the KrF excimer laser device is set in the comparison setting section 13, and the set value is compared with the average output of the laser light detected by the output monitor 14. If there is a difference between the set value and the average output, a control signal corresponding to the difference is output from the comparison setting section 13 to the oscillation control section 11. As a result, the repetition frequency of the trigger pulse that drives the power source 4 is controlled by the oscillation control unit 11 so that the average output of the laser light oscillated from the output mirror 5 approaches the set value.

In other words, if the average output of the laser light detected by the output monitor 14 is lower than the set value, or if this is input from the comparison setting section 13 to the oscillation control section 11, this oscillation control section 11 will change the repetition frequency of the trigger pulse. conversely, if the average output of the laser light is higher than the set value,
The repetition frequency of the trigger pulse is reduced and the average output is controlled to approach the set value.

When a KrF laser device is operated for a long time, the repetition frequency is gradually increased to compensate for the decrease in oscillation efficiency due to deterioration of the gas laser medium. Then, when the repetition frequency of the trigger pulse reaches the upper limit value, this is inputted from the comparison setting section 13 to the gas supply control section 12,
A drive signal is output from the gas supply control section 12 to the gas supply device 7. In response to this drive signal, fluorine gas is injected into the closed container 2 from the fluorine gas supply source through the supply line 8C. As a result, the mixing ratio of the gas laser medium approaches the initial value, so even if the repetition frequency of the trigger pulse is lowered, a predetermined average output can be obtained.

In this way, the charging voltage applied to the discharge circuit main capacitor of the discharge excitation section 3 is fixed at a value that provides the maximum oscillation efficiency,
By increasing the repetition frequency of the trigger pulse to obtain a predetermined average output, the total power input to the gas laser medium can be reduced compared to the conventional method of increasing the charging voltage to maintain a predetermined average output. The lifespan of a gas laser medium is proportional to the reciprocal of the discharge power, so the less the total power input to the gas laser medium, the longer the time it takes for the gas laser medium to deteriorate and become unable to control the laser output. I can do it. In other words, it is possible to extend the life of the gas laser medium.

Experiments have shown that when the repetition frequency of the trigger pulse is controlled to maintain a predetermined average output, the gas laser medium deteriorates and control becomes impossible compared to the conventional method of increasing the charging voltage to maintain a predetermined average output. It was confirmed that the time required for

FIG. 2 shows the relationship between laser operating time, laser output, and laser repetition frequency according to the present invention. Curve A in the figure
Curve B shows the relationship between laser operation time and laser repetition frequency, and curve B shows the relationship between laser operation time and laser output. That is, the laser output is kept constant by increasing the laser repetition frequency over time. It is also shown that if fluorine gas is injected as shown by arrow F in the figure when the laser repetition frequency reaches the upper limit, the laser output can be kept constant even if the laser repetition frequency is lowered.

In addition, the curve C shown by the broken line in the same figure is the conventional laser output,
It can be seen that the lifespan is shorter than that of this invention.

FIG. 3 shows another embodiment of the invention. In this embodiment, a charging voltage control section 21 is provided in the control device 9, and the charging voltage control section 21 controls the power source 4 to select the charging voltage supplied to the discharge excitation section 3.

That is, in the above embodiment, the charging voltage was fixed at a predetermined value, but in reality, when the oscillation repetition frequency changes, the charging voltage at which the maximum oscillation efficiency is obtained also changes slightly. For example, when the oscillation repetition frequency is 200Hz, it is 30KV, and when the oscillation repetition frequency is 150Hz, it is 30.5KV, 100Hz.
In each case, 31 KV is the charging voltage at which the maximum oscillation efficiency is obtained. Therefore, by providing the charging voltage control section 21 in the control device 9 and controlling the charging voltage according to changes in the oscillation repetition frequency, it is possible to lengthen the time until the oscillation repetition frequency reaches the upper limit value. The life of the medium can be made even longer than in the above embodiment.

In the embodiment shown in FIG. 3, parts that are the same as those in the embodiment shown in FIG. 1 are given the same symbols and their explanations will be omitted.

Note that this invention can be modified in various ways without changing the gist thereof. For example, the gas laser device of this invention has a K
The present invention is not limited to rF excimer lasers, but can also be applied to gas laser devices that use halogen gases other than fluorine gas, such as hydrogen chloride (H(1)).

[Effects of the Invention] As described above, this invention controls the repetition frequency of laser oscillation so that the average output of laser light is constant, and when the repetition frequency of laser oscillation exceeds a predetermined value, The specified gas components were supplied. In other words, since the average output of the laser beam can be maintained constant without increasing the discharge input to the discharge excitation unit as in the conventional case, the life of the gas laser medium, which is proportional to the reciprocal of the discharge input, can be extended.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a KrF laser device showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of the relationship between laser operating time, laser average output, and laser repetition frequency, showing the control method of this invention. FIG. 3 is a schematic configuration diagram of a KrF gas laser device showing another embodiment of the present invention, FIG. 4 is an explanatory diagram of the relationship between laser operating time, laser average output, and charging voltage, showing a conventional control method, and FIG. 5 is a graph of the relationship between the charging voltage and the oscillation efficiency, and FIG. 6 is a graph of the relationship between the reciprocal of the discharge input and the life of the gas laser medium. 2... Airtight container, 3... Discharge excitation part (excitation means),
5... Output mirror (optical resonator), 6... High reflection mirror (optical resonator) 11... Oscillation control section, 12... Gas supply control section, 14... Output monitor (detection means) ). Applicant's agent Patent attorney Takehiko Suzue 1 shot Sekiyo (Kondai Lepe Unhoun Q ear (h) Figure 2

Claims (1)

[Claims] an airtight container in which a gas laser medium is sealed and provided with excitation means for exciting the gas laser medium; a supply means for supplying a predetermined gas component of the gas laser medium to the airtight container; and a gas laser medium excited by the excitation means. an optical resonator that amplifies and oscillates the laser light generated by the optical resonator, a detection means that detects the output of the laser light emitted from this optical resonator, and an average output of the laser light detected by the detection means. an oscillation control unit that controls a repetition frequency of laser oscillation to be constant; and an oscillation control unit that supplies the predetermined gas component from the supply means to the airtight container when the repetition frequency of the laser oscillation by the oscillation control unit reaches a predetermined value or more. A gas laser device characterized by comprising a supply control section for supplying the gas.