JPH03248490A - Excimer laser device - Google Patents

Abstract

PURPOSE:To put the gas cooled by a gas purifying device to proper temperature so as to sent it into a chamber by taking out the gas inside a laser chamber by the gas purifying device so as to remove impurities by a low temperature trap, and also detecting the temperature of laser gas, and controlling a heater by means of the control circuit to which detection output is input. CONSTITUTION:By opening gas flow valves 6 and 7 during the oscillation of a laser, the laser gas inside a laser chamber 1 is circulated, and first of all gas impurities are removed by a liquid nitrogen trap 8. Then, the laser gas is set in the laser chamber 1, after being put to proper temperature by a heater 9 for heating. At this time, by monitoring the gas temperature by a temperature sensor 10, and controlling the heater 9 for heating by the control circuit 11 to which this output is input, the laser gas to be sent in the laser chamber 1 is controlled to be at proper temperature. That is, when laser gas temperature has risen, by decreasing the current being let flow to the heater for heating, the laser gas temperature is lowered, and when the temperature has dropped, by increasing the currents, laser gas temperature is raised.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an excimer laser, and particularly to an ArF laser of rare gas halide excimer lasers whose laser gases include argon (Ar) and fluorine (F2).

[Prior art] A rare gas halide excimer laser device uses rare gases such as krypton (Kr), xenon (Xe), and argon (Ar) as laser gases, as well as fluorine (F2) and hydrogen chloride (
It uses a mixed gas of a halogen such as HCl) and a diluent gas using helium (He) or neon (Ne), and can produce powerful ultraviolet laser light by exciting it with an electric discharge or the like.

Several types of oscillation lines can be obtained by combining rare gases and halogens, but among these, the ArF excimer laser, which is made by combining argon and fluorine, has an oscillation wavelength of 193.
Among the rare gas halide excimer lasers, it has the shortest wavelength and high photon energy, so it is expected to be used as a light source for optical lithography and optical CVD.

When excimer laser gas is excited by discharge or the like, the laser oscillation efficiency, that is, the ratio of what percentage of the injected discharge energy is converted to laser light energy, is on the order of several percent at most, and the remainder is thermal energy, It becomes a sound wave. In particular, the generation of thermal energy is large, and if left untreated, the temperature of the laser gas will rise, leading to instability of laser oscillation. Therefore, a heat exchanger is usually provided in the laser chamber, and the laser gas is cooled by flowing cooling water through the heat exchanger.

On the other hand, since excimer laser gas uses an active gas such as fluorine as a component as mentioned above, this active residue may cause impurities such as moisture attached to the structures such as the chamber electrodes that make up the laser resonator or the surfaces of the structures. reacts.

Since the light is absorbed by the impurity gas generated by this reaction, there is a problem that the laser output gradually decreases. Conventionally, the gas from the laser chamber is supplied to a gas purification device that removes impurities using a low temperature trap. Gas impurities are removed by

[Problems to be Solved by the Invention] Conventional excimer laser devices are configured as described above, and this is sufficient for excimer lasers other than ArF lasers, but in the case of ArF excimer lasers, the following There are problems like this. In other words, in the case of an ArF excimer laser, when the laser gas temperature drops below 30 to 40 C, the oscillation efficiency drops significantly and the power decreases dramatically, and as shown in Figure 3, the laser output increases depending on the chamber temperature and oscillation repetition frequency. Change. For this reason, ArF
Excimer lasers have an unstable oscillation output, and when the injection energy for discharge is small or the oscillation repetition frequency is low, there is a problem that the laser gas is supercooled and the oscillation efficiency decreases.

The present invention was devised to eliminate the drawbacks of the prior art as described above, and increases and stabilizes laser output and oscillation efficiency without being affected by temperature changes or set oscillation repetition rate. An object of the present invention is to provide an excimer laser device that can achieve the desired results.

[Means for Solving the Problems] In order to achieve the above object, an excimer laser device according to the present invention includes a laser chamber, a gas purification device to which gas from the laser chamber is supplied and removes impurities by a low-temperature trap, It has a heater that brings the gas from the gas purification device to an appropriate temperature and sends it into the chamber, and a control circuit that controls the heater according to the temperature of the laser gas.

[Operation] The excimer laser device configured as described above extracts the gas in the laser chamber using a gas purification device and removes impurities using a low-temperature trap, and also detects the temperature of the laser gas using a temperature sensor, etc., and outputs this detection output. By controlling the heater by a control circuit to which the gas is input, the gas cooled by the gas purifier is brought to an appropriate temperature and sent into the chamber.

[Example] An example will be described with reference to the drawings. In FIGS. 1 and 2, 1 indicates a laser chamber 2, a discharge electrode, and 3
is a laser reflection mirror, 4 is a laser beam extraction window, 5 is a laser beam, 6.7 is a gas flow valve, 8 is a liquid nitrogen trap,
9 is a heater, 10 is a temperature sensor, 11 is a control circuit, and a liquid nitrogen trap 8 removes impurities by cooling a pipe through which laser gas flows with liquid nitrogen.

To explain how to use this excimer laser device, a laser gas is sealed in a laser chamber 1, a voltage is applied to a discharge electrode 2, the laser gas is excited by discharge, and the emitted light is reflected by a laser reflection mirror 3 (total reflection mirror). A laser beam 5 is obtained by confining it in a resonator consisting of a laser beam extraction window 4 (partial reflection mirror) and a laser beam extraction window 4 (partial reflection mirror). Only a few percent of the injected excitation energy is converted into optical energy, and most of the rest is emitted as thermal energy. Therefore, if the discharge continues, the temperature of the laser gas will increase, resulting in instability of laser oscillation. Therefore, a heat exchanger (not shown) is provided in the laser chamber 1, and the laser gas is cooled by flowing cooling water through the heat exchanger.

Meanwhile, during laser oscillation, the laser gas in the laser chamber 1 is circulated by opening the gas flow valve 6.7;
First, gas impurities are removed using the liquid nitrogen trap 8. Thereafter, the laser gas is heated to an appropriate temperature by the heater 9 and sent into the laser chamber 1. At this time, the gas temperature in the laser chamber 1 is monitored by the temperature sensor 10,
A control circuit 11 to which the output of this temperature sensor 10 is input.
By controlling the heating heater 9, the laser gas fed into the laser chamber 1 is controlled to have an appropriate temperature. That is, when the laser gas temperature rises, the control circuit 11 lowers the laser gas temperature by decreasing the current flowing through the heating heater, and when the laser gas temperature decreases, it increases the current flowing through the heating heater 9. This increases the laser gas temperature.

In the above embodiment, a temperature sensor was installed inside the laser chamber to detect the temperature of the laser gas, but the temperature of the laser gas can be detected by installing a temperature sensor at an appropriate location in the gas circulation piping outside the laser chamber. You can also.

[Effects of the Invention] As described above, the present invention provides a heater after the gas purification device that removes impurities using a low-temperature trap, and controls the laser gas temperature at a constant level, so that it is not affected by changes in temperature or the set oscillation repetition rate. It is possible to increase and stabilize the laser output and oscillation efficiency without being affected by this.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an excimer laser device according to the present invention,
FIG. 2 is a block diagram of a control circuit of the excimer laser device shown in FIG. 1, and FIG. 3 is a data diagram for explaining the output characteristics of the conventional excimer laser device. 1... Laser chamber 2... Discharge electrode, 3... Laser reflection mirror 4...
・Laser light extraction window, 5... Laser light, 6.7
... Gas flow valve, 8 ... Liquid nitrogen trap, 9 ... Heating heater, 10 ...
・Temperature sensor, 11... Control circuit

Claims (1)

[Claims] (1) A laser chamber, a gas purification device to which the gas from the laser chamber is supplied and removes impurities using a low-temperature trap, a heater that brings the gas from the gas purification device to an appropriate temperature and sends it into the chamber, and a heater to adjust the temperature of the laser gas. An excimer laser device comprising a control circuit for controlling the heaters according to the respective conditions.