JPS62162379A - Pulse laser - Google Patents

Abstract

PURPOSE:To control energy of laser with high precision, by monitoring pulse light by means of a detector so that a shutter or power supply is controlled when an output integrated value attains a predetermined value. CONSTITUTION:Pulse light from a chamber 1 passes through a shutter 2 and is divided by a divider 3 so that a part of the light enters into a detector 4. The detector 4 photoelectrically converts each pulse and a controller 5 integrates the voltage value, so that when an integrated value attains a value corresponding to a predetermined laser output, a signal is outputted from a comparator 5B. The shutter is closed by this signal. According to this output controlling method, the controllability is determined by a ratio that the last one pulse light which operates the comparator 5B bears to the total energy. Therefore, errors caused by this method are smaller than those by a conventional method of controlling individual pulses and output can be controlled correctly. A laser power supply section may be controlled instead of the shutter.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to pulsed lasers such as excimer lasers.

(Background of the invention) Excimer lasers are being considered for various applications as light sources that can obtain high output in the ultraviolet region. Since it is a pulsed laser, the output of each pulsed light has an error of several percent even under good conditions, resulting in a lack of stability.

For this reason, it is not possible to obtain the integrated value of the laser output simply by counting the number of pulses, and it is difficult to make the integrated value of the laser output match a preset value. There was a problem that reproducible results could not be obtained during processing.

(Object of the Invention) In order to solve such problems, an object of the present invention is to provide a pulse laser that can accurately obtain a predetermined integrated value.

(Summary of the Invention) In order to achieve the above object, the pulsed laser according to the present invention includes a photodetector that monitors the output of pulsed light, integrates the output monitored by this photodetector, and calculates the integrated value in advance. It is characterized by comprising a controller that outputs a control signal for controlling the shutter, the power source of the laser, etc. when the set predetermined value is reached.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

First, FIG. 1 is a schematic diagram showing a first embodiment in which a pulse laser according to the present invention is applied to an excimer laser. In the figure, reference numeral 1 denotes a chamber constituting a laser body, which is equipped with a full mirror, a partially transmitting mirror, electrodes, etc., and is filled with a predetermined laser medium such as an inert gas or halogen molecules.

A beam splitter 3 is disposed on the optical axis of the laser beam emitted from the chamber 1 via a shutter 2 such as a mechanical shutter or an optical deflection shutter for blocking the laser beam. The beam splitter 3 is for separating and extracting a part of the laser beam, and the separated laser beam is made incident on the photodetector 4.

The photodetector 4 is a photoelectric converter that converts the intensity of the incident pulsed light into a voltage according to the light intensity, and is composed of a photodiode or the like. Here, since the oscillation output of the laser beam has a correlation (for example, a proportional relationship) with the light intensity, the voltage obtained from the photodetector 4 is also related to the output of each pulsed light.

The voltage thus output from the photodetector 4 is applied to the controller 5 at the next stage. The configuration of this controller 5 will be explained with reference to FIG. 2. The controller 5 is an amplifier A such as an operational amplifier.

an integrator 5A consisting of a resistor Ri and a capacitor Cf;
It is composed of a comparator 5B. The output terminal of the photodetector 4 is connected to the input terminal 5C, and the integrator 5
The output terminal of the comparator 5B is connected to the non-inverting input terminal of the comparator 5B, the reference voltage Vref is applied to the inverting input terminal of the comparator 5B, and the output terminal of the comparator 5B is connected to the shutter 2. That is, this controller 5 integrates the output voltage of the photodetector 4 over a certain period of time, and sets the integrated value to a predetermined reference voltage Vref corresponding to the target total laser light output.
When it reaches this level, a signal at the rHJ level is output to the shutter 2.

The controller 5 converts the output voltage of the photodetector 4 into a number of pulse signals corresponding to the output voltage using an A/D converter such as a Vf converter, counts these pulse signals, and calculates a predetermined value. It is also possible to construct it by a digital circuit that obtains a signal to the shutter 2 when the number reaches the number.

Referring again to FIG. 1, a power source 6 is connected to the chamber 1 for causing discharge excitation by high voltage pulses. The configuration of this power supply unit 6 will be explained based on FIG. 3 together with the electric circuit inside the chamber 1. In the same figure, T
H is a thyratron as a switching element, and a high DC voltage of about 20 kV to 30 kV is applied between its plate and cathode. Also, this Thyratron TH
Capacitor C0, stray capacitance, and electrodes 1a and lb in chamber 1 are connected in series between the plate and cathode of It is connected. Note that the connection point between the capacitor C0 and the floating capacitance btL is grounded via a resistor R.

In this embodiment, a thyratron TH is used as the switching element, but a semiconductor switching element such as a thyristor may be used instead.

Next, this operation will be explained. First, the operation from discharge excitation to laser oscillation begins with capacitor C in Figure 3.
1 is charged with a DC high voltage through a resistor R1 with the polarity shown. Next, when a trigger signal is applied to the grid of Thyratron TH, Thyratron TH is turned on and the load stored in capacitor C is transferred to Thyratron TH,
Pulse discharge is performed through the path of capacitor C21, pre-ionization electrode P1, and stray capacitance. At this time, the pre-ionization state PI becomes short-circuited due to arc discharge, and electrons generated by ultraviolet rays due to arc discharge are transferred to electrode 1. Charge between a and lb
r+'A and enters a pre-ionization state. At the same time capacitor C
Due to the vibration phenomenon of the L-C series circuit consisting of the capacitor C2 and the stray capacitance, the capacitor C1
A high voltage up to twice that of the current voltage is generated.

Such a high voltage of capacitor C2 is connected to pre-ionization electrode I'I
A voltage is applied between the electrodes 1a and lb through the electrodes 1a and 1b.
The area between b is discharged and transitions to pulsed laser oscillation.

The pulsed light emitted from the chamber 1 passes through the shutter 2 and a part of it is incident on the photodetector 4 by the beam splitter 3. The photodetector 4 converts each pulsed light into a voltage, and the primary stage controller 5 integrates this voltage value, and when it reaches a value corresponding to a predetermined laser output, outputs a signal from the comparator 5B. Mechanical means for operating a relay (not shown) or the like by this signal;
Alternatively, the shutter 2 may be closed using an optical deflection means to stop irradiating the object with laser light.

The controllability of the output in this embodiment is controlled by the comparator 5B.
Since it is determined by the ratio of the energy of the last one pulsed light that operates to the whole, there is less error than when controlling the energy of each individual pulsed light, and the output can be controlled accurately.

Next, FIGS. 4 and 5 show a second embodiment of the present invention. In this embodiment, feedback is applied to the power supply unit 6 in order to further improve the controllability of the laser output.

That is, as shown in FIG. 5, in the controller 5', a comparator is provided with a reference voltage Vref' that is smaller by a value corresponding to the energy of approximately one pulsed light than the reference voltage Vref applied to the comparator 5B, for example. 5B' is provided. Then, when the output voltage of the integrator 5A exceeds this reference voltage Vref',
The comparator 58' detects that the target value is almost reached by the two pulsed lights, and the comparator 58'
By adding the output signal of B' to the power supply section 6 and changing the value of the DC high voltage applied to the capacitor C, the capacitance of the capacitor C, or the timing of the trigger signal of the switching element TH, the last one The energy of the pulsed light is adjusted to reduce the deviation between the integrated output value and the target value.

In this case, the number of pulses is counted and the comparator 5B'
If the average value of the energy due to one pulse is calculated when the output of

Note that this embodiment is similar to the first embodiment in that the shutter 2 is closed by the output signal of the other comparator 5B.

In addition, in this configuration, the output signal of the comparator 5B is added to the power supply section 6 without providing the comparator 5B'.
It is also possible to stop laser oscillation by cutting off the power when the integrated voltage value reaches a predetermined value. In this case, needless to say, the shutter 2 becomes unnecessary.

Note that each of the above embodiments is a case where the present invention is applied to a discharge-excited excimer laser, but the present invention is also applicable to an electron beam-excited excimer laser, a nitrogen laser other than an excimer laser, It can also be applied to various pulsed lasers such as YAG lasers.

(Effects of the Invention) As described above, according to the present invention, since the photodetector monitors the output of the pulsed laser beam and includes a controller that integrates the output, the integrated value can be accurately adjusted to a predetermined value. Can be matched.

Therefore, it is possible to give reproducibility to the integrated value of the laser output, and if this pulsed laser is applied to, for example, an ultraviolet exposure device, exposure can be performed under the same conditions, which is preferable.

Furthermore, in the present invention, since the output of the laser beam can be controlled, there is no need to apply an excessive load to the power supply section, so the high voltage components of the power supply section can be used under more moderate conditions. As a result, the life of these high-voltage components can be extended.

[Brief explanation of drawings]

1 to 3 show a first embodiment of the present invention, in which FIG. 1 is a schematic diagram of the overall configuration, FIG. 2 is a configuration diagram of the controller, and FIG. 3 is a circuit diagram of the power supply section and the chamber. figure,
4 and 5 show a second embodiment of the present invention, in which FIG. 4 is a schematic diagram of the overall configuration, and FIG. 5 is a diagram of the configuration of the controller. 1... Chamber 1a, lb... Electrode 2...
Shutter 3... Beam splitter 4... Photodetector 5.5'... Controller 5A... Integrator 5B, 5B'... Comparator 5C... Input terminal 6... Power supply section A...Amplifier Ri, R1...
・Resistance Cf, C□, C2...Capacitor L...
Suspended volume xi TH... Thyratron PI... Pre-ionization electrode Applicant: Nippon Kogaku Kogyo Co., Ltd. Representative Patent Attorney Fuyuki Nagai Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (3)

[Claims] (1) A photodetector that monitors the output of pulsed light, and a control signal that integrates the output monitored by this photodetector and controls the output of the pulsed light when the integrated value reaches a predetermined value. A pulse laser characterized by being equipped with a controller that outputs. (2) The pulsed laser according to claim 1, wherein a shutter through which the pulsed light passes is closed in response to a control signal from a controller. (3) The pulsed laser according to claim 1, wherein a power supply section of the laser is controlled by a control signal from a controller.