JPH0194687A - Laser device - Google Patents

Abstract

PURPOSE:To improve reproducibility of laser beam outputs per oscillation and to obtain a required total irradiation energy with a certain iterative number of oscillations by determining an applied voltage set value while adding an output from an operation in which any error found between an output signal of a beam output setting circuit and a beam output feedback signal is corrected, to an output of a voltage setting circuit, or like means. CONSTITUTION:An applied voltage of a laser oscillator 27 is controlled by controlling the beam outputs of such laser oscillator 27 in a closed-loop system. Such an oscillator comprises a beam output setting circuit 21 generating a beam output setting signal 101 by adding single-triggered increasing signals corresponding to the beam output set value per oscillation; an operation circuit correcting any error found between a beam output feedback signal 106 and a beam output setting signal 101; a voltage setting circuit 22 determining an applied voltage to the laser oscillator 27 on the basis of the beam output set value; and an addition circuit 31 determining an applied voltage set value 104 by adding an output 102 of the voltage setting circuit 22 to an output 103 of the operation circuit 23. Further, for example, a power source 28 comprising a voltage control circuit 24, a limiter circuit 25, a voltage generation circuit 26, and a timing control circuit 30, etc., are arranged.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a laser device that corrects optical output. [Prior Art] FIG. 5 is a block diagram of a conventional laser device disclosed in, for example, Japanese Unexamined Patent Publication No. 62-69577, and FIG. 6 is a time chart showing the operation of the circuit. In Fig. 5, [1] is a pulse generator, (2) is a laser oscillation fi
, (3) is a half mirror 1 (4) that partially reflects the laser beam.
) is a diffuser plate that transmits the light partially reflected by the half mirror (3), (5) is a photoelectric conversion element that receives the laser light transmitted through the diffuser plate (4) and converts it into an electrical signal; (6
) is a sample-and-hold circuit that samples and holds the electrical signal converted by the photoelectric conversion device (L element (5), (7) is an integrator circuit that integrates the output of the sample-and-hold circuit (6), and (8) is an ilt integrator circuit. The output of (7) and the standard [a
Comparator (9) that compares the output of the E% generator (9)
is a reference voltage generator that generates a voltage corresponding to the constant output of the optical film, αO is a Nandt gate, and wholesaler is the oscillator command from the t source (described later).
2), a2 is a power supply that supplies electrical energy to the laser oscillator (2), and a2 is a delay circuit that resets the sample and hold circuit (6). When considering a stepper that performs optical lithography, conventional methods have been used such that the total optical output is constant for each step and repeat cycle.The block diagram and operation time chart of the conventional example are shown in Section 5.
As shown in FIG. The operation will be explained below. First, the energy from the stain on the power supply side is absorbed by the laser oscillator.
(2) causes the laser oscillator (2) to oscillate, and a laser beam is output. This laser light output is partially reflected by the half mirror (3) and inputted to the photoelectric conversion element (5) via the diffuser plate (4). The input light is converted into an electrical signal by a photoelectric conversion element (5), and this electrical signal is held for a certain period of time by a sample and hold circuit (6). The output signal E1 of the sample and hold circuit (6) is a pulse with a constant time interval, and the peak value thereof is a different value for each pulse corresponding to the peak value P1 of the laser output (6th pulse).
(See Figures (b) and (c)) The output signal of the 0-sample hold circuit (6) is input to an integrator (7), whose output E8 is proportional to the sum of laser output energy. The output of this integrator (7) is connected to the reference voltage remainder generator (
9) The reference level set in advance and the comparator (
Compare in 8). Output T of integrator (7)! , 8 match the reference level, the output of the comparator becomes 0.
is opened and the trigger circuit 0]), and the υ aftershock is stopped by the oscillation stop operation of the power supply (2) (Fig. 6 (e), (f)
, see (g)). Next, when a signal is given to the external reset terminal α (A), the output of the integrator (7) will become O.Then, in the same way, the total irradiation energy control is repeatedly executed in a constant cycle. (See Figures 6(h) and (e)). delay circuit a
3 is for resetting the sample and hold circuit (6) (see FIGS. 6(d) and (c)). As described above, the laser oscillation is configured to stop when the optical output feedback level reaches a set reference level. [Problems to be solved by the invention] The conventional laser device is T/cWI! Because of this, the reproducibility of the laser light output for each oscillation is poor, and depending on the number of oscillation edge turns and fluctuations in oscillation efficiency, the optical output may vary from a few percent to more than 10 percent depending on the situation. . This fluctuation value may have a negative effect on the material being processed, and depending on the magnitude of the light output, there is a constant oscillation. There were problems such as making it difficult to set the time. This invention was made to solve the above-mentioned problems, and it improves the reproducibility of the laser light output for each oscillation, and also makes it possible to obtain the necessary total irradiation energy with a constant number of oscillations. [Means for solving the problems] The laser device according to the present invention mainly performs closed-loop control of optical output, has applied voltage control of an oscillator, and has single-shot optical output setting. an optical output setting circuit that generates an optical output setting signal by adding a gradual increase signal according to the optical output at each oscillation, an arithmetic circuit that corrects the deviation between the setting circuit and the optical output feedback signal, and The applied voltage is set by adding the output of the arithmetic circuit and the output of the voltage setting circuit in an adder circuit. [Function] The laser device of the present invention has the output obtained by correcting the deviation between the optical output setting circuit output signal and the optical output feedback signal, and the output of the voltage setting circuit that determines the voltage applied to the oscillator based on the optical output setting. The applied voltage is set to quickly suppress optical output fluctuations due to fluctuations in oscillation efficiency. [Embodiment of the Invention] An embodiment of the invention will be described below with reference to the drawings. 1st
In the figure, ■1) is an optical output setting circuit that stabilizes the optical output setting signal by adding a step-like gradual increase signal that matches the single optical output setting every oscillation, A voltage setting circuit that sets the voltage applied to the oscillator, an arithmetic circuit that corrects the output of the voltage setting circuit based on the deviation between the output of the optical output setting circuit and the output of the photodetector circuit, and the foundation performs feedback control, etc. A voltage control circuit that controls the applied voltage of the oscillator using the oscillator, (to) a limiter circuit that limits the range of the applied voltage of the ILT oscillator, and (a) generates the applied voltage of the oscillator that corresponds to the output of the limiter circuit (1). Voltage generation circuit, @ is the laser oscillator, @ is the power supply, and the handle is the laser oscillator (
A photodetection circuit that detects the optical output from the main unit) and converts it into an appropriate signal, ■ is an optical output setting circuit (goods), and a voltage control circuit (c)
, a timing control circuit for controlling the photodetection circuit at an appropriate timing, @ is an adder circuit. Next, the operation of the present invention will be explained. First, the concept of the present invention will be explained based on FIG. Figure 2 shows that there is a nearly proportional characteristic between the single light output and the applied voltage of the oscillator (IEEJ study group material: Discharge Study Group. ED-86-53~65. Japan Society of Bone Electricity, rArF, KrF, X
"Output characteristics and discharge parameters of ecl excimer laser", pages 107 to 116). This figure shows the following:

[1] If the voltage is below 'VQ, no optical output can be obtained. (2) Single optical output can be controlled by controlling the applied voltage of the oscillator.0 Also, if the applied voltage of the oscillator becomes high, the It is generally known that if the discharge is too low, sufficient ionization cannot be achieved in the pre-discharge ionization method, and the discharge is disturbed, damaging the oscillator. From the above, the circuit configuration suppresses fluctuations in optical output by limiting the range of applied voltage to the oscillator to avoid damaging the oscillator, and by determining the initial applied voltage setting of the oscillator in accordance with the single optical output setting. is used. Based on the above, the operation of the embodiment shown in FIG. 1 will be explained based on the time chart of FIG. 3. In the example, an oscillation (a circuit that generates light output with a constant repetition period) is used. In the example, the case where the total irradiation energy is obtained by seven oscillations is shown. The output setting is shown as PQ in Fig. 2. At time 30 in Fig. 3, the first oscillation command is given to the timing control circuit from the outside, and the timing control circuit (1)
A voltage is supplied from the stain source (c) to the oscillator by the signal from the oscillator. At this time, the voltage setting signal (104) of the applied voltage is the output (102) of the voltage setting circuit (A) as shown in FIG.
When the value Vre f corresponding to the generated signal + the output (101) of the optical output setting circuit (2) is 0. Output of arithmetic circuit (1
03) becomes 0, and eventually becomes Vref. At time Qt2, the voltage supply to the laser oscillator ends at time Qt2, a laser oscillation H@VC oscillation signal is applied from the timing control circuit (7), and the laser oscillator oscillates. After oscillation, the photodetection circuit operates in the same manner as the conventional detection circuit. On the other hand, the output (101) d of the optical output setting circuit ■D,
A signal corresponding to the single optical output PQ is output. t3-t
At time 4, the next power supply starts. At this time, since the optical output (105) due to oscillation at time t2 was smaller than the optical output set value PO, the output (103) of the arithmetic circuit - outputs a +δ1 signal. Therefore, the voltage setting signal (104) Vi at the time t3-t4 works to increase the applied voltage of the laser oscillation iaa (Vref + δ1), and works to correct the optical output.<The second oscillation occurs at the time OtS. O At this time, the output (106) of the photodetector circuit becomes Pf. The output (1o1) of the optical output setting circuit e°C is added to the single optical output setting FQ, resulting in a value of 2PQ. Pf is 2P
The output of the arithmetic circuit (103) V was larger than Q.
It is an i-δ2 signal. Therefore, the voltage setting signal (xoa) at time t6-t7 acts to suppress the voltage applied to the laser oscillator (Vref-δ2) and corrects the optical output. From then on, it will continue to operate in the same way. FIG. 2 shows a state in which optical output was obtained without error from time point 78. At time 19, the external oscillation command is released, and the timing control circuit (7) resets the output of the light detection circuit and the light output setting circuit 3°C, making the configuration ready for the next light output control. There is. In addition, if the applied voltage range is set by a limiter circuit (c), then v1 to v2 in Figure 3.
In addition, even if there is a sudden change in the optical output, the oscillator will not be damaged or an abnormal applied voltage will occur.Also, even if the single-shot optical output setting is changed during optical output control, the spectral output setting will remain the same. Even if the 10 oscillation repetition period is changed during optical output control, which is a problem with the adding method, there is no problem because the optical output setting value is added for each oscillation. As described above, fluctuations in optical output due to fluctuations in oscillation efficiency are quickly suppressed, and damage to the oscillator due to applied voltage is not caused. In the above embodiment, the optical output circuit adds a step signal corresponding to a single optical output setting every oscillation to obtain an optical output signal. However, if the oscillation cycle (ΔT) is constant and the optical output setting value (ΔP) does not change during optical output control, input the optical output setting to the ramp function generating circuit 0υ as shown in Figure 4, and then The same effect as described above can be obtained by using a light output setting circuit that outputs a lamp output with a slope of ΔP/ΔT according to an external timing signal in accordance with the output of the detection circuit. In addition, if the total light output (P) is input to the ramp function generation circuit and the light output control period (T) is known, the slope P/T
[Effects of the Invention] As described above, according to the present invention, the applied voltage setting value is determined by adding the output of the arithmetic circuit and the output of the voltage setting circuit. This has the effect of improving the reproducibility of the optical output.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, FIG. 2 is an explanatory diagram showing the characteristics of an oscillator, FIG. 3 is a time chart showing the operation of FIG. 1, and FIG. 4 is a diagram showing another embodiment of the present invention. They are a configuration diagram (,) and an explanatory diagram (b) showing an example. Figure 5 shows the W bottom opening of a conventional laser device, and Figure 6 is a time chart showing the operation of Figure 5. , (C) is a voltage control circuit, @ is a laser oscillator, @ is a power supply, 翺 is a photodetection circuit, and c (TJ is an adder circuit).

Claims (3)

[Claims] (1) In a device in which the applied voltage of the laser oscillator is controlled by closed-loop control of the optical output of the laser oscillator, the optical output setting signal is obtained by adding a gradual increase signal corresponding to the single optical output setting value for each oscillation. A light output setting circuit that generates
an arithmetic circuit that corrects a deviation between the optical output feedback signal and the optical output setting signal; a voltage setting circuit that determines the applied voltage of the laser oscillator from the optical output setting value; A laser device including an addition circuit that determines an applied voltage setting value by adding the output of an arithmetic circuit. (2) The laser device according to claim 1, wherein the gradually increasing signal is step-like. (3) The laser device according to claim 1, wherein the gradually increasing signal has a ramp function shape.