JPH043987A - Method of gas injection for gas laser - Google Patents

Abstract

PURPOSE:To obtain stable and reliable laser oscillation by supplying a small amount of buffer gas to increase pressure before introduction of laser medium gas so that the pressure of the laser medium gas can be measured in a reliable measuring zone. CONSTITUTION:Buffer gas is first introduced to deviate the reference point for halogen pressure measurement from zero point so that pressure measurements can be carried out in a measuring zone where a reliable measurement of a pressure transducer 10 is expected. Therefore, a laser chamber 1 is charged at accurate partial pressures, PH and PR, of laser medium or halogen gas, having a substantial effect on laser performance, and rare gas. The method can be applied to a system that includes a low-pressure transducer 10 and a high-pressure transducer 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas injection method for a gas laser such as an excimer laser in which the partial pressure of a laser medium in a buffer gas is small.

[Conventional technology]

The gas used in excimer lasers is halogen gas (F
, etc.), rare gases (Kr, Ar, etc.), and buffer gases (He, Ne, etc.).
Buffer gas is about 2.5K, while it is low at 0 Torr.
gf/c-, and the difference between them is very large.

The partial pressure ratio of halogen gas and rare gas in such an excimer laser is deeply related to laser oscillation performance, and if this ratio goes out of order, there is a risk that the output will decrease or the discharge will be disturbed and the laser beam mode will change. Care must be taken during injection.

Therefore, in conventional excimer lasers, gas injection was performed in the following manner. Note that the pressure when the laser chamber is evacuated is Pu, and the injection pressure of halogen gas is PH.
, PR the injection pressure of rare gas.

Let the total pressure of the gas be PT.

(2) Evacuate the laser chamber to near vacuum Pu.

(2) Further inject halogen gas to PH (several 1 O Torr) based on the pressure Pu.

(2) Further inject rare gas to PR (several tens of Torr).

■Inject buffer gas and raise the total pressure PT to about 2. 5kgf/
Let it be c-.

■Performs laser oscillation.

[Problem to be solved by the invention]

In the conventional method described above, the chamber is evacuated and the halogen gas injection pressure PH and rare gas injection pressure PR are measured based on the pressure Pu at that time. needed to be measured accurately.

However, this is very difficult for the following reasons.

In other words, the linearity of the measured pressure with respect to the input pressure of the pressure quadrangle transducer used to measure gas pressure deteriorates as shown in Figure 4 near the zero point near vacuum, or it becomes offset as shown in Figure 5. There are many cases in which the 0 point is shifted due to the error. Therefore, the pressure Pu near this vacuum pressure
In the conventional method in which halogen gas and rare gas are injected based on the measurement standard, there is a problem that the halogen gas and rare gas cannot be injected at accurate pressures because the measurement standard deviates. In other words, the drawback of the conventional method is that the injection pressures PH and PR of halogen gas and rare gas, which greatly affect laser performance, are measured using the unreliable and unstable region of the pressure quadrangle transducer near vacuum pressure. It is in.

In particular, in the case of an excimer laser, the total gas pressure is 2°5 kg.
Since the f/c- is large, it is necessary to use a pressure quadrature transducer with a high withstand voltage, and in such a large full scale transducer, the amount of offset also becomes large.

Therefore, one possibility is to use a cylinder in which gases are mixed in advance, but mixed gases used for special purposes such as lasers are extremely expensive, and this poses a problem for industrial use.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a gas injection method for a gas laser that can accurately measure the gas partial pressure during gas injection.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a gas injection method for a gas laser in which a laser gas containing a laser medium gas and a buffer gas is injected into a laser chamber.
After first injecting a small amount of buffer gas, the laser medium gas is injected to a predetermined pressure, and then the buffer gas is reinjected until the total pressure reaches a required value.

[Effect]

According to the method of the present invention, the reference point for measuring the pressure of the laser medium gas is shifted to the high pressure side by injecting the buffer gas to a predetermined pressure in advance, and the highly reliable area of the pressure measuring device is used to measure the laser medium gas. Measuring gas pressure.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 shows an embodiment in which the present invention is applied to an excimer laser, in which 1 is a laser chamber, 2 is a vacuum pump, and 3 is a laser chamber.
is an exhaust valve, 4 is a cylinder filled with buffer gas,
5 is a cylinder filled with halogen gas, 6 is a cylinder filled with rare gas, 7 to 9 are gas injection valves, 10 is a pressure cadence transducer, and 20 is a pressure cadence transducer that controls the opening and closing of each valve. This is a controller that measures 10 detected pressures.

In this embodiment, the laser chamber 1 is filled with gas according to the following procedure. The gas filling operation in this embodiment will be described below with reference to the flowchart in FIG.

(2) Process of evacuating the laser chamber 1 to near-vacuum pressure Pu First, the controller 20 turns on the vacuum pump 2 (step 100) and opens the exhaust valve 3 to evacuate the laser chamber 1 (step 110). The controller 20 measures the detected pressure P of the pressure transducer 10 along with this exhaust operation, and closes the exhaust valve 3 when the detected pressure P becomes equal to or less than a predetermined pressure Pu near vacuum (
Steps 120-140).

(2) Step of injecting buffer gas to a predetermined pressure PB (several tens of Torr) Next, the controller 20 opens the valve 7 and injects the buffer gas from the buffer gas cylinder 4 into the laser chamber 1 (step 150). The controller 20 measures the detected pressure P of the pressure transducer 10 along with this buffer gas injection operation, and closes the valve 7 when this detected pressure P becomes equal to or higher than a predetermined pressure PB (steps 160 to 18).
0).

(2) Step of injecting halogen gas at a predetermined pressure PH (several tens of Torr) Next, the controller 20 opens the valve 8 and injects the halogen gas from the halogen gas cylinder 5 into the laser chamber 1 (step 190). The controller 20 measures the detected pressure P of the pressure transducer 10 along with this halogen gas injection operation, and this detected pressure P is the combined pressure (PB + PH) of the partial pressure PB of the buffer gas and the partial pressure PH of the halogen gas. ), the valve 8 is closed (steps 200 to 220).

(2) Step of injecting rare gas at a predetermined pressure PR (several tens of Torr) Next, the controller 20 opens the valve 9 and injects the rare gas from the rare gas cylinder 5 into the laser chamber 1 (step 230). The controller 20 measures the detected pressure P of the pressure transducer 10 along with this rare gas injection operation,
When this detection pressure P becomes equal to or higher than the combined pressure (PB + PH + PR) of the partial pressure PB of the buffer gas, the partial pressure PH of the halogen gas, and the partial pressure PR of the rare gas, the valve 9 is closed (
Steps 240-260).

■Inject buffer gas and increase total pressure PT to approximately 2゜5kgf/
Step c- Next, the controller 20 reopens the valve 7 and reinjects the buffer gas from the buffer gas cylinder 4 into the laser chamber 1 (step 270).

The controller 20 measures the detected pressure P of the pressure quadrature transducer 10 along with this buffer gas injection operation, and closes the valve 7 when this detected pressure P reaches a predetermined pressure PT (approximately 2.5 kgf/c4). (Steps 280-30
0).

(2) Laser oscillation process When the gas injection is completed as described above, the controller 20 starts laser oscillation (step 310).

As described above, in this embodiment, by first injecting buffer gas, the reference point for halogen gas pressure measurement is shifted from the 0 point, and pressure measurement is performed using a highly reliable area of the pressure quadrature transducer 10. Therefore, the laser chamber 1 can be filled with the laser medium gas, that is, the halogen gas and the rare gas, which are closely related to the laser oscillation performance, with accurate partial pressure ratios PH and PR.

Note that the present invention includes a low-pressure pressure cadence transducer 10 and a high-pressure cadence transducer 11 as shown in FIG.
It can also be applied to systems with In this case, first, switch the switching valve 15 to the low-pressure cadence transducer 10, and use this low-pressure cadence transducer 10 to adjust the partial pressures Pu5PHSPR of the buffer gas, halogen gas, and rare gas. After that, the switching valve 15 is connected to the pressure quadrangle transducer 11 for high pressure.
Switch to the side, pressure quadrangle transducer 11 for this high pressure
Total pressure PT (approximately 2.5 kgf'/cd) using
Measure. Of course, in this case, the gas injection is performed in the order shown in the flowchart of FIG. 1 above.

Further, in the above embodiment, when injecting the laser medium gas, the halogen gas is injected before the rare gas, but this order may be reversed.

Furthermore, in the above embodiment, the present invention is applied to an excimer laser that uses halogen gas and rare gas as laser medium gas, but the partial pressure of the laser medium gas is much smaller than that of the buffer gas. If available, it may be applied to other gas lasers.

〔Effect of the invention〕

As explained above, according to the present invention, when injecting laser gas, a small amount of buffer gas is first injected to raise the gas pressure to a certain extent, and then the laser medium gas is injected. The pressure of the laser medium gas can now be measured in a highly reliable measurement region, thereby stabilizing laser oscillation and increasing the reliability of laser oscillation.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an embodiment of the invention, and FIG.
FIG. 3 is a block diagram showing a configuration example in which the present invention is applied to an excimer laser, FIG. 3 is a block diagram showing a modification of FIG. 2, and FIGS. 4 and 5 are illustrations of disadvantages of the prior art. 1... Laser chamber 2... Vacuum pump 3.7.
8.9...Valve 4-6...Cylinder 10.11
...Pressure transducer 20...Controller Fig. 2 Fig. 3

Claims (2)

[Claims] (1) In the gas injection method for gas lasers in which laser gas containing laser medium gas and buffer gas is injected into the laser chamber, a small amount of buffer gas is first injected, then laser medium gas is injected to a predetermined pressure, and then the total pressure 1. A gas injection method for a gas laser, characterized in that the buffer gas is reinjected until the value reaches a required value. (2) Claim (1) wherein the gas laser is an excimer laser, and the laser medium gas is a halogen gas and a rare gas.
) gas injection method for the gas laser.