JPH1146025A - Laser beam generating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a user to know the change of characteristics of an output laser beam in advance. SOLUTION: A fundamental laser beam emitted from a master laser section 11 is input to a slave laser section 12. The slave laser section 12 is normally controlled in its length of resonator, so that the frequency of laser beam output from a resonator matches with the frequency of the fundamental laser beam. A temporary servo stop determining section 28 decides to temporarily stop the control for the length of resonator, when the control system for the resonator length of the slave laser section 12 reaches the point near the limit point. A temporary servo stop warning section 29 outputs, prior to the control for the resonator length stopping temporarily, a warning signal S9 to temporarily stop the control of the resonator length. Moreover, the temporary servo stop warning section 29 confirms, after restart of the control for the resonator length, that the control has stabilized and outputs a control stabilizing signal S10 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light generating apparatus for generating an injection-locked laser light used for an exposure apparatus for semiconductor manufacturing, an interferometer, science and technology, measurement, wavelength conversion and the like.

[0002]

2. Description of the Related Art Conventionally, there has been known a laser light generator which outputs injection-locked laser light as a device for generating a powerful laser light having a narrow band. The injection locking refers to synchronizing the frequency of the output laser light so as to have a predetermined relationship with the frequency of the laser light injected from the outside. Injection locking includes injection seeding that generates pulsed light and injection locking that generates continuous light. A laser light generator using such injection locking is used in an exposure apparatus for semiconductor manufacturing, an interferometer, and the like.

A laser light generator using injection locking has a resonator for resonating laser light, and a basic laser light injected into the resonator and a slave laser light generated by the resonator are synchronized with each other. And outputs laser light having a predetermined characteristic. In such a laser light generating device, in order to synchronize the basic laser light and the slave laser light, a servo is applied by an actuator so as to control the cavity length with dimensional accuracy equal to or less than the wavelength of the laser light.

[0004]

Incidentally, in a laser light generator using injection locking, the resonator length may change due to disturbances such as expansion, deformation and refractive index change of the resonator due to a temperature change. At this time, in the laser light generator, the length of the resonator is controlled by performing servo control so as to keep the length of the resonator constant, but there is a mechanical or electrical limit.
Beyond this limit, the cavity length cannot be controlled. Therefore, in the laser light generator, a predetermined control limit point is provided in the control circuit, and when the limit point is reached, the control of the resonator length is temporarily stopped, and the actuator is returned to, for example, the vicinity of the neutral point and the center point. After that, it is common to return the control of the resonator length again.

The above processing makes it possible to control the cavity length again. However, during the period from when the control of the cavity length is stopped to when the control is restored and the control is stabilized, the laser beam generating apparatus is controlled. Becomes a multi-mode oscillation state or an injection impossible state, and the laser light is not output at, for example, a single frequency. In the conventional laser light generator, the user can only know that the control of the resonator length has been temporarily stopped only after the laser light having different characteristics is output from the laser light generator. Therefore, when the user knows that the control of the resonator length has been temporarily stopped, laser beams having different characteristics have already been output, and as a result, the following various problems have occurred. Was.

Here, the characteristics of the laser light having different characteristics include output, coherence (temporal coherence, spatial coherence), spatial intensity distribution, beam characteristics (size, divergence angle, beam waist position, etc.), beam stability. (Position and angle of peak and center of gravity), time characteristics (noise, pulse width and timing, output fluctuation), wavelength (absolute wavelength, wavelength distribution,
Fluctuation, extinction ratio, polarization direction, etc. In a system using a laser light generator, for example, in order to cope with output fluctuation, drive values (current, voltage, light amount) are set so that the light amount detected by a photodetector such as a photodiode becomes a constant value.
It is also possible to make the output of the light to be used constant by adopting a means such as changing the light transmission or controlling the light transmittance on the optical axis by using an acousto-optic element or an optical attenuator. However, there is a limit to the response speed of such means, and it is impossible to follow a rapid change in the light source output faster than this limit. In that case, the output fluctuation cannot be removed.For example, when a conventional laser light generator is used for an exposure apparatus for semiconductor manufacturing,
It is expected that the exposure pattern will not be transferred with the required accuracy due to the deviation of the exposure value from the target value due to excess or deficiency of the exposure value. Therefore, it is possible to adjust the exposure time according to the amount of light to cope with this, but it is possible to cope with such a problem that there is a limit to the response speed or that the speckle intensity changes to change the exposure time. Failure may occur.

[0007] In addition, since measurement of coherence usually requires a considerable amount of time, it is difficult to constantly monitor the coherence value. However, when the coherence changes, for example, in the case of a semiconductor exposure apparatus, there is a problem that the uniformity of the light amount distribution may not be maintained due to normal averaging. Such defects are also caused by changes in spatial intensity distribution, beam characteristics, beam stability, time characteristics, extinction ratio, polarization direction, and the like. In addition, there are disadvantages that the image plane position of the lens changes and the aberration changes due to the change in the wavelength. Wavelength, power,
The stability of the beam characteristics is an important factor.

In a laser beam generator using injection seeding, the length of a resonator in a Q-switched laser into which a basic laser beam is injected is usually controlled to control the frequency of a plurality of longitudinal modes of the resonator. One of the methods is to make the frequency of the single-frequency fundamental laser light match so that the Q-switched laser oscillates at a single frequency. In a laser light generator using such injection seeding, an error signal is generated based on a parameter corresponding to a difference between one frequency of the longitudinal mode of the resonator and the frequency of the basic laser light, and the error signal is generated. Servo is applied to minimize. However, in such a laser light generating device, the servo is operated so that the error signal is maintained not at the minimum value but at a minimum value larger than the minimum value, which results in an unstable state called a so-called weak seed state. In such a case, a stable single longitudinal mode laser beam cannot be obtained unless the user manually releases the servo. Also in this case, the user can only know that the laser beam is in the weak seed state only after the laser light having different characteristics is output from the laser light generator. Also,
In order to prevent the weak seed state from continuing for a long time, the user must constantly monitor the servo state, but this will reduce the practicality of using laser light and increase labor costs. There is a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and an object of the present invention is to provide a laser light generating device which enables a user or the like to know in advance the characteristic change of an output laser light. is there.

[0010]

According to the present invention, there is provided a laser beam generating apparatus for resonating a laser beam and outputting the laser beam, and a basic laser for injecting the basic laser beam into the resonator. A light injection means, and a resonator or a resonator of the resonator in the basic laser light injection means for injection-locking the laser light output from the resonator based on the basic laser light injected by the basic laser light injection means. A resonator length control means having a function of controlling the length and temporarily stopping the control of the resonator length, and a resonator before the resonator length control means temporarily stops the control of the resonator length. Notice information output means for outputting notice information indicating that the control of the head is temporarily stopped.

In this laser light generating device, the basic laser light is injected into the resonator by the basic laser light injection means, and based on the basic laser light, the basic laser light is injected by the resonator.
The injection-locked laser light is output. Further, the cavity length of the cavity is controlled by the cavity length control means in order to injection-lock the laser beam output from the cavity or the cavity in the fundamental laser beam injection means based on the fundamental laser light. . The resonator length control means has a function of temporarily stopping the control of the resonator length. Then, before the resonator length control means temporarily stops the control of the resonator length, the advance notice information output means outputs advance notice information indicating that the control of the resonator length is temporarily stopped.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a laser light generator according to a first embodiment of the present invention. The laser light generating apparatus includes a master laser unit 11 that generates and outputs a basic laser beam, and a pulse laser beam injected and seeded by the basic laser beam injected from the master laser unit 11, that is, a basic laser beam. A slave laser unit 12 that outputs a pulse laser beam having a frequency that matches the frequency. The output light of the slave laser unit 12 is supplied to a laser light utilization system 13. In addition, the laser light utilization system 1
Reference numeral 3 generally refers to a system using laser light output from a laser light generator, such as a semiconductor manufacturing exposure apparatus and an interferometer.

The laser light generator further includes a partial mirror 14 that reflects and branches a part of the output light supplied from the slave laser unit 12 to the laser light utilization system 13.
When, a photodetector 15 for detecting the light reflected by the partial mirror 14, receives the output signals S ₁ of the light detector 15, the rise time of the later-described pulse (hereinafter, referred to as BUT.) The A BUT measuring unit 16 for measuring;
A drive circuit 17 for driving an actuator described later in the slave laser unit 12 and a BUT,
6 based on the BUT signal S ₂ output from
7 is provided with a cavity length servo circuit 18 for servo-controlling the cavity length of the cavity in the slave laser section 12 and a system control circuit 19 for controlling the entire laser light generator. In addition, partial mirror 1
4 and the photodetector 15 may be built in the slave laser unit 12.

The master laser unit 11 includes a laser oscillation unit 21 that outputs a basic laser beam, and a mirror 22 that reflects the basic laser beam output from the laser oscillation unit 21 toward the slave laser unit 12 as necessary. have.
Note that an optical isolator or the like may be provided between the laser oscillation unit 21 and the multiplexing optical element 26 as needed to prevent return light.

For the slave laser section 12, for example, a Q-switch pulse laser is used. Hereinafter, a case where a Q-switch pulse laser is used as the slave laser unit 12 will be described. In this case, the slave laser unit 12 includes two resonator mirrors 23 and 24 arranged to face each other.
And a resonator that resonates and outputs laser light, a Q switch 25, a multiplexing optical element 26, and a laser medium (not shown) arranged between the resonator mirrors 23 and 24 in order from the resonator mirror 23 side. doing. Note that these arrangements are not unique, and may be changed to several different arrangements depending on the type of Q switch used and the like.

The resonator mirror 23 reflects almost all of the laser light. The resonator mirror 24 partially transmits the laser light and outputs the laser light as output light of the slave laser unit 12. The Q switch 25 is for changing the Q value of the resonator rapidly to generate pulse laser light having a large peak output. The multiplexing optical element 26 is for injecting the basic laser light from the master laser unit 11 with the laser light that resonates by the resonator of the slave laser unit 12 so as to be injected into the slave laser unit 12.

The slave laser unit 12 further has an actuator 27 that can move the resonator mirror 23 along the optical axis of the resonator in order to control the resonator length of the resonator. For example, PZT is used for the actuator 27. The actuator 27 is driven by the drive circuit 17.

The system control circuit 19 includes a servo pause determination unit 28 for temporarily stopping the servo control of the resonator length, and the servo pause determination unit 28 temporarily controls the resonator length servo control. to when the stopping is decided, before the servo control of the resonator length it is temporarily stopped, and outputs a warning signal S ₉ indicating that temporarily stops the servo control of the resonator length, after the servo control of the resonator length resumed, the control has a confirm the stable, the servo temporary stop warning unit 29 for outputting a control stable signal S _10. The notice signal S ₉ and the control stabilization signal S ₁₀ are sent to, for example, a temporary standby control unit 13 a that performs control to temporarily wait for the use of laser light using a shutter or the like in the laser light utilization system 13. . The system control circuit 19 is configured by, for example, a microcomputer.

The resonator length servo circuit 18 includes a drive circuit 17
, A position correction signal S _{3 on} which a dither signal for microvibrating the actuator 27 is superimposed is sent, and a position signal S ₄ indicating the position of the actuator 27 is received from the drive circuit 17. I have. Drive circuit 17, and drives the actuator 27 based on the position correction signal S ₃ from the cavity length servo circuit 18. The drive circuit 17, the servo pause decision unit 28 of the system control circuit 19, and sends a position signal S ₅ representing the position of the actuator 27, from the servo pause decision section 28, of the servo control start actuator position 27 is adapted to receive a return instruction signal S ₆ for instructing the return to (neutral point, etc.).

The resonator length servo circuit 18 controls the servo temporary stop decision unit 28 of the system control circuit 19 to
And sends a control state signal S ₇ representing the state of the servo control is determined from the BUT and the like, from the servo pause decision unit 28 of the system control circuit 19, a control instruction signal S ₈ for instructing start and stop of the servo control I am going to receive it. The servo pause decision unit 28 of the system control circuit 19 based on the control state signal S _7, after the servo control resumption, control and confirm that stable, the information to the servo temporary stop warning unit 29 It is supposed to be sent.

Next, the operation of the laser light generator according to this embodiment will be described. In this laser light generator, the basic laser light output from the master laser unit 11 is transmitted through the multiplexing optical element 26 to the slave laser unit 1.
2 injected. Normally, the slave laser unit 12 has a resonator length controlled such that the frequency of the laser light output from the resonator matches the frequency of the injected basic laser light or has a certain frequency difference. You.

The control of the resonator length is specifically performed as follows. First, by the BUT measurement unit 16,
BUT it is measured on the basis of the output signals S ₁ of the light detector 15. Here, the BUT will be described with reference to FIG. The BUT is the time from when a trigger signal (voltage, high frequency, etc.) for turning on the Q switch 25 is input to the Q switch 25 until the pulse laser light is generated. FIG.
In (a), (a) shows a trigger signal, and (b) shows the optical output of the pulse laser. As shown in this figure,
T ₁ the rise time of the trigger signal, when the occurrence time of the pulsed laser beam and t _2, BUT becomes t ₂ -t _1.
Normally, the BUT often has tens to hundreds of nanoseconds, the pulse width of the pulsed laser light is several nanoseconds to several tens of nanoseconds, and the jitter at the rising edge of the pulse is often several nanoseconds. The trigger signal is sent from the system control circuit 19 to the Q switch 25.
Given to. In FIG. 2, since the voltage or the high frequency applied to the Q switch 25 during the application of the trigger signal is turned on or off, the loss of the resonator is designed to be small.

If the BUT is minimized, the frequency of one of a plurality of longitudinal modes of the resonator of the slave laser unit 12 matches the frequency of the basic laser light to be injected. It is believed that it is possible to oscillate at a single frequency equal to the frequency of the light. Therefore, in the present embodiment, B
In order to minimize the UT, the servo control is performed on the resonator length with an accuracy equal to or less than the wavelength. For this purpose, the resonator length is minutely vibrated, and the increase and decrease of the BUT including the polarity is observed (synchronous detection). Adopt the method. Therefore, the resonator length servo circuit 18, the drive circuit 17, and sends the position correction signal S ₃ to the dither (Dither) signal superimposed for the actuator 27 is small vibrations. Drive circuit 17 drives the actuator 27 based on the position correction signal S ₃ from the cavity length servo circuit 18. Thereby, the resonator length vibrates minutely. The BUT measuring section 16 is provided with a photodetector 15
Monitors the trigger signal to output a BUT signal S ₂ of the output signals S ₁ and Q-switch 25 which is output from the system control circuit 19. The resonator length servo circuit 18 has a BUT
The BUT signal S ₂ output from the measurement unit 16 and the trigger signal for the Q switch 25 output from the system control circuit 19 are monitored, and the polarity of the BUT that vibrates minutely in response to the minute vibration of the resonator length is determined. The position correction signal S ₃ is generated so that the actuator 27 moves in the direction in which the BUT becomes smaller, and is output to the drive circuit 17. By such servo control, while the resonator length vibrates minutely, one of a plurality of longitudinal modes is controlled so as to approach the frequency of the injected basic laser light. Such an operation is performed until disturbance (vibration, expansion, etc.) occurs, and then the BUT is minimized. As a result, the BUT is fixed near the minimum and the slave laser unit operates at a frequency close to the frequency of the basic laser light. 12 oscillates.

FIG. 3 shows a change in the resonator mode with respect to a small change of the resonator length of the slave laser section 12 below a wavelength. Further, the resonator length is defined as a reciprocating or one round optical path length, and this is defined as L. When the length and the refractive index of each element in the resonator are L (i) and n (i), respectively.
L = 2n (1) L (1) + 2n (2) L (2) +. Assuming that the order of the resonator mode is m, the wavelength λ _m of light that should reciprocate (can oscillate) by reciprocating once inside the resonator and is in resonance is given by L = mλ _m . Among these, the wavelength λ _{m at} which laser oscillation can be performed should be in the gain wavelength range of the laser medium.
Considering the wavelength of the gain center of the oscillation line of 4.1 nm, L = 5
If it is 00 mm, the value of m is about 939,700.
Since m greatly changes with a slight error between the wavelength and L, m is not usually specified as a single value, and its representative value is defined as m ₀ , and m in the vicinity is m ± 1, m ± 2, m Described as ± 3, ...

In FIG. 3, for simplicity, ΔL ≒ λ _m0 / 2
When the actuator 27 extends by Δz, the resonator length is reduced by 2Δz. Here, FIG.
As shown in (c) and (a), at a certain moment, the resonator length L =
In both cases of L ₀ and L = L ₀ −2ΔL, the wavelength λ _{0 of} the injected basic laser light coincides with one wavelength of the resonator mode. Therefore, in either case, the slave laser unit 12 It is possible to oscillate at a single frequency at a wavelength (or frequency) substantially equal to the wavelength (or frequency) of the laser light. On the other hand, as shown in FIGS. 3B and 3D, at the resonator lengths L ₀ −ΔL and L ₀ + ΔL, the wavelengths of the resonator modes are different from the wavelengths of the basic laser light. Normally, the laser section 12 easily oscillates in a multi-mode. Therefore, first, the actuator 27
Is near the position giving the resonator length L ₀ −ΔL, the actuator 27 normally expands and contracts to the closer one of L = L ₀ and L = L ₀ −2ΔL. Thus, the servo operates so as to oscillate in a single mode using the basic laser light.

By the way, the length of the resonator often changes with time due to expansion due to temperature change, change in refractive index, deformation and the like. At this time, in the slave laser section 12, the servo works so that the optical path length of the resonator is kept constant and the frequency of the resonator mode is adjusted to the frequency of the injected basic laser light, and the actuator 27 such as PZT expands and contracts. I do. However, such controls have mechanical or electrical limitations. Beyond this limit, control becomes impossible. For this reason, a method that is often performed is to provide a control limit point, temporarily stop the control, return the actuator 27 to a position near the neutral point and the center point, and then restart the control. In this case, the oscillation frequency is made the same by changing the resonator length and the order of the resonator mode. Hereinafter, this will be described in detail.

Now, consider the case where, for example, the temperature gradually rises after the start of the laser beam generator, and the length of the resonator gradually increases due to thermal expansion. When the injection seeding (injection synchronization) servo is on,
As described above, the actuator 27 expands to keep the resonator length constant. When starting from the position of L = L ₀ shown in FIG. 3C, after a certain period of time, the actuator 27 extends and maintains L = L ₀ , while FIG.
The state of the actuator 27 shown in FIG. If the material forming the resonator further expands and the actuator 27 further expands, the resonator length is maintained at L = L ₀ , that is, the mode order m ₀ is maintained, and finally the operation of the actuator 27 is performed. Reach the limit of the range. The control system can know the limit point of the control from the voltage or the like applied to the actuator 27. Therefore, when reaching the vicinity of the limit point, the control is temporarily stopped, and the actuator 27 is contracted by an integral multiple of λ _m0 / 2. After extending the resonator length (round trip) by an integral multiple of λ _m0 , for example, returning the actuator 27 to the vicinity of the center of the movable range, control is resumed. As a result, the mode order is changed to m ₀ + M (M is an integer other than 0), and the length of one round of the resonator is shifted to L = L ₀ + 2MΔL.
Returns to the position shown in FIG. 3C, for example. Conversely, when the ambient temperature decreases and the material forming the resonator shrinks, the actuator 27 is returned to the movable range by a movement opposite to the movement described above.

The temporary stop and restart of the control as described above is specifically performed as follows. The servo pause determination unit 28 of the system control circuit 19
Monitoring the position signal S ₅ from 7, you approach to the set limit value the position signal S ₅ predetermined, optionally calculates the arrival time from the past movement history to the limit value, the arrival sufficiently before time, sends a control instruction signal S ₈ for instructing the stop of the servo control in the resonator length servo circuit 18.
Thus, the servo control is stopped. The servo control is stopped, for example, by lowering the servo gain or changing the connection of the servo loop. Servo pause decision unit 28 of the system control circuit 19, when resuming the control sends a return instruction signal S ₆ for instructing the return to the position of the actuator 27 of the servo control start (the neutral point, etc.) to the drive circuit 17 At the same time, a control instruction signal S ₈ for instructing the start of the servo control is sent to the resonator length servo circuit 18.
Thereby, the actuator 27 returns to the neutral point or the like,
Servo control is restarted.

FIGS. 4A and 4B show that the frequency of the output laser light of the master laser unit 11 and the frequency of the output laser light of the slave laser unit 12 are substantially matched by controlling the cavity length. 3 shows the frequency characteristics of the output laser light of the master laser unit 11 and the frequency characteristics of the output laser light of the slave laser unit 12 when the laser beam is present. In FIG. 4,
The vertical solid line represents the relative intensity of the output light, and the vertical broken line represents the resonator mode.

From the time when the control of the cavity length is temporarily stopped until the time when it is restarted and the control is stabilized, the slave laser section 12 is controlled.
Usually results in multi-mode oscillation or an unstable state. FIGS. 4C and 4D show the master laser unit 1 when the slave laser unit 12 is in multi-mode oscillation.
1 and the slave laser unit 12
And the frequency characteristics of the output laser light.

A user using the output laser light of the laser light generator monitors related information, such as a drive voltage signal of the actuator 27, from the output of the system to temporarily control the resonator length. In some cases, it is possible to know that the stop is near, but it is difficult to know exactly when to stop the control because the stop of the control of the resonator length is often a slow operation. . Therefore, if the user attempts to prepare for the control stop before the control stop, the user may need to wait for a considerable amount of time in some cases, increasing the downtime of the system.

On the other hand, in the present embodiment, when the servo pause determination unit 28 determines to temporarily stop the control of the resonator length, the servo pause notification unit 29 sets Before the control is temporarily stopped,
And it outputs a warning signal S ₉ indicating that temporarily stops the control of the resonator length. The timing of outputting the warning signal S _9, for example, immediately prior to temporarily stop control or use than when temporarily stopping the control's or laser-beam utilization system 1,
It is preferable that the time 3 is before the time for performing the necessary preparation. Warning signal S ₉ is in addition to the case described above, such as if suddenly close to the limit point of the control of the resonator length may be output when needed. Servo temporary stop warning unit 29, further, after resumption of the control of the resonator length, control and confirmation of stable, outputs a control stable signal S _10. The notice signal S ₉ and the control stability signal S ₁₀ are sent to, for example, the temporary standby control unit 13 a of the laser light utilization system 13. in this way,
According to this embodiment, the user or a laser-beam utilization system 13, the warning signal S _9, knowing in advance that the control of the resonator length changes the characteristics of the output laser beam are suspending can be, also, the control stability signal S _10, after resumption of the control of the resonator length, control can know that stable.

In the laser light generator, the slave laser unit 12 may be in an unstable state called a weak seed state during the servo control of the cavity length. Is not stopped, stable single longitudinal mode laser light cannot be obtained. Here, the weak seed state will be described with reference to FIG.
In FIG. 5, the horizontal axis represents the position z of the actuator 27, and the vertical axis represents the BUT. Also, in the drawing, D indicates a small vibration range of the actuator 27 based on the dither signal. With respect to the position z of the actuator 27, periodically every half wavelength of the laser beam, BUT there is minimum position z ₁ takes the smallest value. Here, as shown in FIG.
Besides minimum position z _1, when BUT exists minimum positions z ₂ to take a larger minimum value than the minimum value, the servo control of the resonator length, the position of the actuator 27 is lost remains in minimum position z ₂ May not be able to escape. At this time, the slave laser unit 12 is considered to be in a weak seed state.

In the weak seed state, the pulse jitter and frequency distribution of the output laser light are unstable and may not be used depending on the purpose of the user. That is, in the weak seed state, the wavelength (frequency) of the injected basic laser light and the wavelength (frequency) of the resonator mode are probably not sufficiently close to each other. When the pulsed laser light rises using the photons as seeds, an unstable transition may occur between a state in which the pulsed laser light has substantially the same wavelength as the basic laser light and a state in which multimode oscillation is performed without using the basic laser light. Symptoms such as unstable fixing to a wavelength slightly different from the wavelength of the basic laser light appear. In the weak seed state, the BUT is large compared to the stable state, but small compared to the state without injected light. Pulse jitter also increases due to transitions between a plurality of states. To date, no physical solution has been found to avoid the weak seed state, so once the weak seed state is reached, the servo control is temporarily stopped to exit this weak seed state, and the position of the actuator 27 is set to the minimum position. it is necessary to return to z _1.

Therefore, in the present embodiment, the servo temporary stop decision unit 28 of the system control circuit 19 receives the control state signal S ₇ representing the servo control state determined from the BUT or the like from the resonator length servo circuit 18. , based on the control state signal S _7, and detects that it is held in a weak seed state, even when it detects that it is held in a weak seed state, temporarily stops the control of the resonator length Decide to do it. The operation of stopping and restarting the control of the resonator length is similar to the case where the control of the resonator length reaches near the limit point. In the case of a weak seed state, there is no guarantee that the control will return to a normal state and be stabilized by a single stop of the control, so that the control may be stopped repeatedly.

In this embodiment, as described above, even when the control of the resonator length is once stopped in order to escape from the weak seed state, before the control is stopped, the servo temporary stop notification unit 2
Reference numeral ₉ outputs a notice signal S9 for temporarily stopping the control of the resonator length. In addition, the servo suspension notice unit 29
Furthermore, after resumption of the control of the resonator length, control and confirmation of stable, it outputs a control stable signal S _10. Thus, the user or a laser-beam utilization system 13, the warning signal S _9, it is possible to know in advance that the control of the resonator length changes the characteristics of the output laser light is temporarily stopped, also, the control stability signal S _10, after resumption of the control of the resonator length, control can know that stable.

As described above, according to the present embodiment, the user or the laser light utilization system 13 transmits the notice signal S
By _9, that the characteristics of the control of the cavity length is temporarily stop output laser light changes can be known in advance, also, the control stability signal S _10, after resumption of the control of the resonator length, You can know that the control has stabilized. Thereby, it is possible to avoid disturbance in the user and the laser light utilization system 13 due to a change in the characteristics of the laser light without notice. When the laser light utilization system 13 is a manufacturing apparatus, the yield can be improved.

Further, according to the present embodiment, the time during which the user or the laser light utilization system 13 temporarily waits for the use of the laser light using the shutter or the like can be minimized. Therefore, when the laser light utilization system 13 is a manufacturing apparatus, downtime of the manufacturing apparatus can be reduced.

Further, as shown in FIG. 1, until the temporary waiting control unit 13a of the laser-beam utilization system 13, the control stability signal S ₁₀ from the output of the warning signal S ₉ output laser beam By temporarily suspending the use of laser light in the use system 13, the laser light use system 13 can always use stable laser light of a single frequency, and the system can be automatically stabilized. . Further, with this configuration, it is not necessary for the user to constantly monitor the control state, so that the practicality of using the laser light is improved and the labor cost can be reduced.

FIG. 6 is a block diagram showing a configuration of a laser light generator according to a modification of the present embodiment. In this modification, a servo temporary stop notice signal generation circuit 30 having the same function as the servo temporary stop notice part 29 is provided outside the system control circuit 19 without providing a servo temporary stop notice part 29 in the system control circuit 19. It is provided. The servo temporary stop notice signal generating circuit 30 includes a system control circuit 1
9, an instruction signal S for instructing the generation of a notice signal and the generation of a control stabilization signal from the servo pause determination unit 28 in
Receive _11, according to the instruction signal S _11, the warning signal S
And outputs the ₉ and control stability signal S _10. The servo temporary stop warning signal generating circuit 30, the servo pause decision unit 28, and sends a report signal S ₁₂ for reporting the occurrence of generation and control stability signal warning signal. Other configurations, operations, and effects of this modification are the same as those of the embodiment shown in FIG.

In this embodiment, a laser beam having a frequency that is frequency-modulated by a certain value from the frequency of the laser beam output from the master laser unit 11 may be used as the basic laser beam. Also, a plurality of modes can be used as the basic laser light. In addition, without controlling the resonator length of the slave laser unit 12, the resonator length may be controlled by attaching an actuator to the master laser unit 11 or controlling current and temperature. In the present embodiment, the slave laser unit 1
It is also possible to provide a nonlinear optical crystal without providing a laser medium in 2 and use the slave laser unit 12 as an external resonator used for wavelength conversion.

FIG. 7 is a block diagram showing an example of the configuration of the laser light generator according to the second embodiment of the present invention. The laser light generating device according to the present embodiment outputs continuous light using injection locking. In the case of injection locking, the cavity length is also controlled. However, unlike the case of injection seeding, the method of controlling the cavity length is such that a sideband is formed on the injected light and the reflected light is synchronously detected (RWP Drever et al. "Las
er Phase and Frequency Stabilization Using an Opt
Physical Resonator ". Appl. Phys. B 31. 97-105 (1983)
Reference) has been proposed. In this embodiment, this method is used.

The laser light generator according to the present embodiment
A master laser unit 31 that generates and outputs a basic laser beam; and a continuous laser beam that is injection-locked by the basic laser beam injected from the master laser unit 31, that is, a frequency that matches the frequency of the basic laser beam. Slave laser section 32 for outputting continuous laser light, master laser section 31 and slave laser section 32
And a phase modulator 33 that modulates the phase of the basic laser light output from the master laser unit 31 to add a sideband to the basic laser light. The output light of the slave laser unit 32 is supplied to a laser light utilization system such as a semiconductor manufacturing exposure apparatus and an interferometer (not shown).

The laser light generator further includes a photodetector 34 for detecting reflected light from a later-described resonator mirror in the slave laser section 32, and a synchronous detection of an output signal of the photodetector 34 to perform basic detection. A synchronous detection unit 35 that generates a servo error signal corresponding to a difference between the frequency of the laser beam and the frequency of the resonator mode of the slave laser unit 32, a drive circuit 37 that drives an actuator described later in the slave laser unit 32, A locking control circuit that controls the phase modulator 33 and controls the drive circuit 37 based on the servo error signal output from the synchronous detector 35 to servo-control the resonator length of the resonator in the slave laser unit 32. 38,
System control circuit 3 for controlling the entire laser light generator
9 is provided.

The slave laser section 32 includes three resonator mirrors 41, 42, and 43, and a ring-shaped resonator that resonates and outputs laser light;
And a laser medium (not shown) arranged between the laser light sources 2 and 43. The resonator mirror 41 transmits part of the laser light and reflects part of the laser light. Resonator mirror 42
Transmits a part of the laser light, outputs the laser light as output light of the slave laser unit 32, and partially transmits the laser light
It is designed to reflect toward. Resonator mirror 43
Are designed to totally reflect laser light toward the resonator mirror 41.

The slave laser section 32 further has an actuator 47 that can move the resonator mirror 41 to control the resonator length of the resonator. As the actuator 47, a PZT, a voice coil motor, or the like is used. The actuator 47 is driven by the drive circuit 37.

The system control circuit 39 includes a servo pause determination section 48 for temporarily stopping the servo control of the resonator length, and the servo pause determination section 48 temporarily controls the servo control of the resonator length. to when the stopping is decided, before the servo control of the resonator length it is temporarily stopped, and outputs a warning signal S ₉ indicating that temporarily stops the servo control of the resonator length, after the servo control of the resonator length resumed, the control has a confirm the stable, the servo temporary stop warning unit 49 for outputting a control stable signal S _10. The system control circuit 39 is constituted by, for example, a microcomputer.

The locking control circuit 38 includes a driving circuit 37
, A position correction signal S ₁₃ for controlling the position of the actuator 47 is sent, and a position signal S ₄ indicating the position of the actuator 47 is received from the drive circuit 37. Drive circuit 37, and drives the actuator 47 based on the position correction signal S ₁₃ from the locking control circuit 38. Also, the driving circuit 3
7 is a servo temporary stop determination unit 4 of the system control circuit 39
Respect 8, and sends a position signal S ₅ representing the position of the actuator 47, from the servo pause decision unit 48, the return instruction signal instructing the return to the position of the servo control at the start of the actuator 47 (the neutral point, etc.) It is adapted to receive the S _6.

Further, the locking control circuit 38 controls the servo temporary stop decision unit 48 of the system control circuit 39 to
And sends a control state signal S ₇ representing the state of the servo control, a servo pause decisions of the system control circuit 39 48
From is adapted to receive a control instruction signal S ₈ for instructing start and stop of the servo control. The servo pause decision unit 48 of the system control circuit 39 based on the control state signal S _7, after the servo control resumption, control and confirm that stable, the information to the servo temporary stop warning unit 49 It is supposed to be sent.

Next, the operation of the laser light generator according to the present embodiment will be described. In this laser light generator, the basic laser light output from the master laser unit 31 is injected into the slave laser unit 32 via the phase modulator 33. Normally, the slave laser unit 32 controls the cavity length such that the frequency of the injected basic laser and the frequency of the laser beam output from the cavity match.

The control of the resonator length is specifically performed as follows. First, the reflected laser light from the resonator mirror 41 of the slave laser section 32 is detected by the photodetector 34, and the output signal of the photodetector 34 is synchronously detected by the synchronous detection section 35, and the frequency of the basic laser light and A servo error signal corresponding to a deviation from the frequency of the resonator mode of the slave laser unit 32 is generated. The locking circuit 38 controls the driving circuit 37 based on the servo error signal so that the difference between the frequency of the basic laser beam and the frequency of the resonator mode of the slave laser unit 32 is eliminated. Servo control the resonator length of the resonators inside.

In the present embodiment, similarly to the first embodiment, the control system for controlling the resonator length becomes uncontrollable when it reaches a mechanical or electrical limit.
After the control is temporarily stopped and the actuator 47 is returned to the neutral point or the like, it is necessary to catch the servo error signal and perform the servo again while scanning by a method such as search again. While the servo control is stopped, the slave laser unit 32 is in a free running state. Become.

In the present embodiment, in order to prevent the user from using the laser beam in an unstable state while the control of the cavity length is stopped, as in the first embodiment, When it is determined that the control of the resonator length is temporarily stopped by the servo temporary stop determination unit 48, the servo temporary stop notice unit 49 sets the resonance before the control of the resonator length is temporarily stopped. and it outputs a warning signal S ₉ indicating that temporarily stops the control of the vessel length. The servo suspension notice unit 49
Furthermore, after resumption of the control of the resonator length, control and confirmation of stable, it outputs a control stable signal S _10. The drive circuit 37 and the system control circuit 39 in the present embodiment
Has the same functions as the drive circuit 17 and the system control circuit 19 in the first embodiment, and the specific operation of temporarily stopping and restarting the control of the resonator length is the same as that of the first embodiment. It is.

Other configurations, operations, and effects of the present embodiment are the same as those of the first embodiment.

FIG. 8 is a block diagram showing a configuration of a laser light generator according to the third embodiment of the present invention. The laser light generating device according to the present embodiment outputs injection-locked laser light using an external resonator for wavelength conversion. Also in this embodiment, the resonator length is controlled. Here, the control method uses the same method as in the second embodiment.

The laser light generator according to the present embodiment
A master laser unit 51 that generates and outputs a basic laser beam, and is injection-locked by the basic laser beam injected from the master laser unit 51, and performs wavelength conversion on the basic laser beam to generate a predetermined frequency. A wavelength conversion resonator 52 for outputting laser light, and a mirror 7 for guiding output light from the master laser unit 51 to the wavelength conversion resonator 52
1, 72, and provided between the mirror 72 and the wavelength conversion resonator 52, and adds a sideband to the basic laser light by phase-modulating the basic laser light output from the master laser unit 31. And a phase modulator 53.
The output light of the wavelength conversion resonator 52 is supplied to a laser light utilization system such as a semiconductor manufacturing exposure apparatus or an interferometer (not shown).

The laser light generator further includes a photodetector 54 for detecting reflected light from a later-described resonator mirror in the wavelength conversion resonator 52, and a synchronous detection of an output signal of the photodetector 54. A synchronous detection unit 55 for generating a servo error signal corresponding to a shift in injection locking based on the basic laser light, a driving circuit 57 for driving an actuator described later in the resonator 52 for wavelength conversion, and a phase modulator 53. At the same time, the drive circuit 57 is controlled based on the servo error signal output from the synchronous detection unit 55 to control the wavelength conversion resonator 5.
2 includes a locking control circuit 58 for servo-controlling the resonator length of the resonators in 2, and a system control circuit 59 for controlling the entire laser light generator.

As the master laser section 51, Nd: YA
G laser devices, Nd: YVO ₄ laser devices, and so-called S lasers in which output laser beams of these laser devices are wavelength-converted.
Ti: Al ₂ O as HG laser or tunable laser
₃ , Cr: LiSAF, Cr: LiCAF, Cr: Al
An exandrite laser device or the like is used. Nd:
Nd: YAG used for the YAG laser device is a Y ₃ Al ₅ O ₁₂ crystal doped with Nd ³⁺ ions, and Nd: Y
The oscillation wavelength of the AG laser device is typically 1.0641 μm, but there are many other wavelengths such as 1.32 μm. Nd: YV
Nd: YVO ₄ used in the O ₄ laser device is a YVO ₄ crystal doped with Nd ³⁺ ions, and Nd: YVO ₄
The oscillation wavelength of the laser device is typically 1.0641 μm, but there are many others such as 1.34 μm. Here, as an example, it is assumed that an Nd: YAG laser device is used as the master laser unit 51, and the second harmonic of the master laser unit 51 is used as a basic laser beam.

The wavelength conversion resonator 52 includes four resonator mirrors 61, 62, 63, 64, and forms a loop resonator that resonates and outputs laser light, and a resonator mirror 6.
1, 62, 62 and a nonlinear optical element for wavelength conversion disposed between them. Here, as an example, it is assumed that a BBO (barium borate) 65 is used as the nonlinear optical element in the wavelength conversion resonator 52. The resonator mirror 61 at the input end and the resonator mirror 62 at the output end of the wavelength conversion resonator 52 are designed under conditions close to impedance matching (balance of the reflectance of the mirror). In the wavelength conversion resonator 52, mode matching of the input light to the wavelength conversion resonator 52 (overlap between the resonator spatial mode and the spot and wavefront of the input light) is performed. By making the optical path length an integer multiple of the wavelength (resonating), the laser light is confined in the wavelength conversion resonator 52, and if the input light is large, the power in the resonator is increased by hundreds or more, and the wavelength conversion efficiency is increased. Can be raised.

Here, as an example, the wavelength conversion resonator 5
Reference numeral 2 has a function of wavelength conversion by second harmonic generation (SHG) and outputs ultraviolet light having a wavelength of 266 nm.

The wavelength conversion resonator 52 further has an actuator 67 that can move the resonator mirror 61 to control the resonator length of the resonator. As the actuator 67, a PZT, a voice coil motor, or the like is used. The actuator 67 is driven by the drive circuit 57.

The system control circuit 59 includes a servo pause determination unit 68 for temporarily stopping the servo control of the resonator length, and the servo pause determination unit 68 temporarily controls the resonator length servo control. to when the stopping is decided, before the servo control of the resonator length it is temporarily stopped, and outputs a warning signal S ₉ indicating that temporarily stops the servo control of the resonator length, after the servo control of the resonator length resumed, the control has a confirm the stable, the servo temporary stop warning unit 69 for outputting a control stable signal S _10. The system control circuit 69 is constituted by, for example, a microcomputer.

The locking control circuit 58 includes a driving circuit 57
, A position correction signal S ₁₃ for controlling the position of the actuator 67 is sent, and a position signal S ₄ representing the position of the actuator 67 is received from the drive circuit 57. Drive circuit 57, and drives the actuator 57 based on the position correction signal S ₁₃ from the locking control circuit 58. The driving circuit 5
7 is a servo temporary stop determination unit 6 of the system control circuit 59
8, a position signal S ₅ representing the position of the actuator 67 is sent, and a return instruction signal for instructing the servo temporary stop determination unit 68 to return to the position (neutral point or the like) of the actuator 67 at the start of the servo control. It is adapted to receive the S _6.

The locking control circuit 58 controls the servo temporary stop determination unit 68 of the system control circuit 59 to
And sends a control state signal S ₇ representing the state of the servo control from the system control circuit 59 is adapted to receive a control instruction signal S ₈ for instructing start and stop of the servo control. The servo pause decision unit 68 of the system control circuit 59 based on the control state signal S _7,
After restarting the servo control, confirm that the control has stabilized,
The information is sent to a servo suspension notice unit 69.

The synchronous detector 5 according to the present embodiment
5, the drive circuit 57, the locking control circuit 58, and the system control circuit 59 have the same functions as the synchronous detection unit 35, the drive circuit 37, the locking control circuit 38, and the system control circuit 39 in the second embodiment. I have.

Next, the operation of the laser light generator according to this embodiment will be described. In this laser light generator, the basic laser light output from the master laser unit 51 is injected into the wavelength conversion resonator 52 via the phase modulator 53. Normally, the wavelength conversion resonator 52 is precisely injection-locked by the basic laser light injected from the master laser unit 51, and outputs laser light whose wavelength has been converted with respect to the basic laser light. The resonator length is controlled. The operation of controlling the resonator length is the same as in the second embodiment.

Also in this embodiment, as in the second embodiment, the control system for controlling the resonator length becomes uncontrollable when it reaches a mechanical or electrical limit.
Once the control is stopped and the actuator 67 is returned to the neutral point or the like, it is necessary to perform the servo again. However, while the servo control is stopped, the wavelength conversion resonator 5 is required.
The average value of the laser light coupled to 2 decreases, and the output laser light becomes unstable.

In the present embodiment, in order to avoid the user from using the laser beam in an unstable state while the control of the cavity length is stopped, as in the second embodiment, When it is determined that the control of the resonator length is to be temporarily stopped by the servo pause determination unit 68, the servo pause notification unit 69 sets the resonance before the control of the resonator length is temporarily stopped. and it outputs a warning signal S ₉ indicating that temporarily stops the control of the vessel length. The servo suspension notice unit 69
Furthermore, after resumption of the control of the resonator length, control and confirmation of stable, it outputs a control stable signal S _10. The specific operation of temporarily stopping and restarting the control of the resonator length is the same as in the first embodiment and the second embodiment.

In the example shown in FIG. 8, the wavelength conversion resonator 52 has the function of second harmonic generation (SHG). However, the present embodiment is not limited to this. The resonator 52 may have a function such as optical parametric oscillation (OPO), sum frequency mixing (SMF), and difference frequency generation (DFG). Other configurations, operations, and effects in the present embodiment are the same as those in the second embodiment.

In the second embodiment or the third embodiment, similarly to the modification of the first embodiment, the servo temporary stop notice units 49 and 69 are provided in the system control circuits 39 and 59. Without providing the system control circuits 39 and 5
In addition to the above, a servo temporary stop notice signal generation circuit having the same function as the servo temporary stop notice parts 49 and 69 may be provided. Alternatively, a laser beam having a frequency that is frequency-modulated by a certain value from the frequency of the laser beam output from the master laser units 31 and 51 may be used as the basic laser beam. Also, a plurality of modes can be used as the basic laser light. The slave laser unit 32 and the wavelength conversion resonator 5
2 without controlling the cavity length,
The length of the resonator may be controlled by attaching an actuator or controlling the current or temperature.

The present invention is not limited to the above embodiments. For example, the master laser unit and the slave laser unit may be provided with various laser devices in addition to those having the configurations described in the embodiments. It is possible to use.

[0073]

As described above, according to the laser light generator of any one of the first to fifth aspects, the resonator length control means temporarily stops the control of the resonator length before temporarily stopping the control of the resonator length. The provision of the notice information output means for outputting notice information indicating that the control of the length is temporarily stopped is provided, so that it is possible for the user to know in advance the characteristic change of the output laser light.

Further, according to the laser light generating device of the fifth aspect, the resonator length control means has a function of detecting that the control of the resonator length is maintained in an unstable control state, Since the control of the resonator length is temporarily stopped when it is detected that the unstable control state is maintained, it is further necessary for the user to monitor the state of the control of the resonator length. This has the effect of disappearing.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a laser light generator according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for describing a BUT.

FIG. 3 is an explanatory diagram showing a change in a resonator mode with respect to a minute change equal to or less than a wavelength in a resonator length of a slave laser unit in FIG. 1;

FIG. 4 is an explanatory diagram showing frequency characteristics of output laser light of a master laser unit and frequency characteristics of output laser light of a slave laser unit in FIG. 1;

FIG. 5 is an explanatory diagram for describing a weak seed state.

FIG. 6 is a block diagram showing a configuration of a laser light generator according to a modification of the first embodiment of the present invention.

FIG. 7 is a block diagram illustrating a configuration of a laser light generator according to a second embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration of a laser light generator according to a third embodiment of the present invention.

[Explanation of symbols]

11: Master laser unit, 12: Slave laser unit, 13
... Laser light utilization system, 15 ... Photodetector, 16 ... BU
T measuring unit, 17: drive circuit, 18: resonator length servo circuit, 19: system control circuit, 23, 24: resonator mirror, 25: Q switch, 26: multiplexing optical element, 27 ...
Actuator, 28 ... Servo pause determination unit, 29 ...
Servo stop notice section

Claims (5)

[Claims] 1. A resonator for resonating laser light and outputting laser light, basic laser light injection means for injecting basic laser light into the resonator, and injection by the basic laser light injection means. Based on the basic laser light to be performed, while controlling the resonator length of the resonator in the resonator or the basic laser light injection means to injection-lock the laser light output from the resonator,
Resonator length control means having a function of temporarily stopping control of the resonator length; and temporarily stopping control of the resonator length before the resonator length control means temporarily stops control of the resonator length. And a notice information output means for outputting notice information for stopping the laser light. 2. The laser light generator according to claim 1, further comprising a laser device including the resonator and injecting the basic laser light. 3. The laser beam generator according to claim 1, wherein said resonator is a wavelength conversion resonator. 4. The laser light generating apparatus according to claim 1, wherein said resonator length control means temporarily stops control of the resonator length when reaching a limit near a control limit point. 5. The resonator length control means has a function of detecting that the control of the resonator length is maintained in an unstable control state, and determines that the control of the resonator length is maintained in an unstable control state. 2. The laser beam generator according to claim 1, wherein control of the cavity length is temporarily stopped when the laser beam is detected.