JPH10270781A - Method and device for generating laser light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser light generating method by which stable high- intensity laser light can be generated, and a laser light generating device which can be used for the method. SOLUTION: A laser light generating device is provided with a laser light oscillating source 1 which emits laser light, a phase modulator 2 which modulates the phase of the laser light emitted from the source 1 into a plurality of frequency components, and a laser light amplifier 3 which amplifies the intensity of the phase-modulated laser light from the modulator 2 by making the laser light to make round trips several times in a gain medium. Therefore, the intensity of the laser light can be amplified by modulating the phase of the laser light into a plurality of frequency components, and making the phase- modulated laser light to make round trips several times in the gain medium.

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 capable of generating a stable and high-output laser light (for example, a semiconductor exposure apparatus for a stepper used for fine processing in manufacturing a semiconductor device, etc.). (A method and an apparatus for generating laser light to be applied).

[0002]

2. Description of the Related Art Hitherto, studies have been made to increase the output of an exposure laser light source used in the manufacture of semiconductor devices and to shorten the wavelength thereof. In the case where the wavelength of the laser light is shortened by the wavelength conversion means, in order to obtain a predetermined output, it is necessary to increase the output of the laser light which is the fundamental wave.

For example, the fifth harmonic of a neodymium: yttrium aluminum garnet (hereinafter, referred to as Nd: YAG) laser oscillating a laser beam having a wavelength of 1064 nm, that is, a laser beam having a wavelength of 213 nm has high energy conversion efficiency. In addition, the oscillation device is small and is supplied at a relatively low cost, so that it is promising as a light source for a next-generation exposure apparatus. In addition, the control of the oscillation spectrum is relatively easy, for example, by the injection locking method, and the spectrum width is narrow, so that the chromatic aberration hardly occurs.

However, at present, it is easily available.
N of high pulse frequency in commercialized form, that is, high repetition excitation (that is, many ON-OFF repetitions)
d: YAG pulse laser (so-called Q switch laser)
The output of the fundamental wave is only about several W in average output (especially 10 W or less: about 10 kW in peak output) due to the performance of the laser light oscillation source, and the fundamental wave ( In the case of the Nd: YAG laser, the wavelength is 1064 nm, and the ultraviolet light (in particular, the fifth wavelength of 213 nm) is used.
It has been difficult for the efficiency at the time of conversion to higher harmonics to exceed 10% from the viewpoint of optical loss of laser light in the wavelength conversion means and the like. In other words, in order to obtain the required ultraviolet light having an average output of 1 W or more, increasing the output of the fundamental wave has been a problem.

On the other hand, there is known a method of increasing the output of a fundamental wave by increasing the size of a laser light oscillator (especially, increasing the size of a laser medium). In this method, however, the pulse width of the output is generally increased. Becomes longer (that is, the pulse frequency becomes shorter), and its peak becomes smaller. Alternatively, there is a disadvantage that the quality of output laser light (beam quality) is deteriorated, for example, a sharp peak is hardly generated and the diffraction limit is not reduced, and one of the reasons that the conversion efficiency cannot be increased when wavelength conversion is performed. Had become.

Therefore, the size of the laser light oscillator is not increased, and the intensity of the output having the spatial and temporal characteristics required for the laser light is amplified by using a laser light amplifier provided outside the oscillator, and the required intensity is amplified. There has been proposed a method of obtaining an appropriate laser light intensity.

In this laser optical amplifier, when the input light intensity becomes high, the amplification factor becomes saturated, and the limit becomes an infinite output with an infinite input, that is, 1 (0 dB gain).
The part of the effective power given by the constant excitation power, the output of which is increased by amplification (Extracted power or Extra
cted energy (that is, gain) has the property that it increases as the input intensity increases, and that the gain can be all extracted as effective power or energy.

Therefore, in order to further increase the output with a constant pumping intensity, it is important to increase the effective input (input intensity) and extract more energy from the amplifier.

Here, as a means for obtaining a larger output using a laser light amplifier, a method of arranging a plurality of amplifiers in series on an optical path through which laser light propagates can be considered. The system becomes complicated, for example, the number of parts increases and the size of the device increases, and the manufacturing cost also increases.

Therefore, a multi-pass amplifier becomes effective.
This is to amplify the intensity of the laser light by, for example, making a single reciprocation in the medium by a reflecting mirror (for example, a retroreflector) after the input laser light has passed through the laser medium (gain medium) (2). Path structure amplifier). Generally, the laser light that has reciprocated through the gain medium is 1
An input and an output are separated by a combination of a polarization rotation unit such as a 波長 wavelength plate or a Faraday rotator and a polarization separation unit such as a polarization beam splitter.

Further, another input / output separation means (combination of the polarization rotation means and the polarization separation means) is used, and the output of the amplifier having the two-pass structure is used by using another reflection mirror (for example, a retro reflector). By inputting the signal to the gain medium, an amplifier having a four-pass structure in addition to two more paths can be obtained, and the efficiency of the amplifier (ie, amplification efficiency) can be further increased.

FIGS. 6 and 7 show an outline of a laser light generator having a laser light amplifier having a one-pass, two-pass and four-pass structure.

FIG. 6A shows a laser light generator having an amplifier having the simplest one-pass structure. In this device, the output laser light from the laser light oscillator 1 is amplified by passing through the laser light amplifier (gain medium) 3a, so that a laser light having a high output with respect to the input can be obtained.

FIG. 6B shows a laser light generator having an amplifier having a two-pass structure. In the amplifier 3b, the output laser light from the laser light oscillator 1 that has passed through the polarization separating means 6c is amplified by passing through the gain medium 4, and the amplified laser light is then changed in polarization state by the polarization rotating means 5c. Changed by the laser beam reflecting means (for example, a retroreflector) 7c and the polarization rotating means 5c once again.
And the polarization state is changed to a polarization orthogonal to the first polarization state, and is amplified again by the gain medium 4.

Since the laser light returned from the gain medium 4 has a polarization orthogonal to the input laser light, it can be separated by the polarization separation means 6. Here, the polarization rotation unit 5c specifically rotates the polarization by 90 ° by reciprocating.
Since the purpose is to rotate, a quarter-wave plate or a Faraday rotator for rotating polarized light by 45 ° is used.

Here, the mechanism for separating and amplifying laser light in the laser light amplifier having the two-pass structure shown in FIG. 6B will be described in more detail.

First, the light is emitted (oscillated) from the laser light oscillator 1.
The emitted laser light enters the laser light amplifier 3b represented by a dashed line in the figure.

The incident laser light passes through a polarization beam splitter 6c as polarization separation means,
For example, it becomes linearly polarized light of only the P component (that is, P polarized light).
The laser light having the P polarization is subjected to the first intensity amplification in the gain medium 4.

Next, the laser light having the P-polarized light having undergone the first intensity amplification is shifted in phase by, for example, π / 2 by passing through the quarter-wave plate 5c as the polarization rotating means (that is, The phase difference becomes π / 2) and the light becomes circularly polarized light (clockwise circularly polarized light). The laser light having the clockwise circularly polarized light is reflected by a reflecting mirror (for example, a retroreflector) 7c as a laser light reflecting means, and becomes a counterclockwise circularly polarized light whose rotation direction is opposite to that of the counterclockwise circularly polarized light. Since the laser beam having the polarized light again passes through the quarter-wave plate 5c, the phase difference becomes π / 2, so that the laser beam becomes the linearly polarized light having only the S component (that is, the laser beam having the S polarized light). actually,
The quarter-wave plate 5c is arranged so that its axis forms an angle of 45 degrees with the input polarization.
Have a phase difference of π / 2 in the components along the respective axes, and are circularly polarized. That is, the phases are relatively inverted.

The laser beam having the S-polarized light passes through the gain medium 4 again, and is subjected to the second intensity amplification. Since the laser beam has a different polarization state from the P-polarized light transmitted first, the polarization beam splitter 6c Is reflected (separated) by the laser light amplifier 3b.

Here, the linearly polarized light having only the P component (P-polarized light) and the linearly polarized light having only the S component (S-polarized light) are out of phase by π (that is, each polarization state is 90 °). ° different). Therefore, the polarization beam splitter 6c is a polarization separation unit for separating P-polarized light and S-polarized light (P-polarized light passes and S-polarized light is reflected). Here, the aforementioned “out of phase”
Is the polarization component of the input (for example, P-polarized light / S-polarized light, or polarized light with a horizontal polarization plane / polarized light with a vertical polarization plane) and 4
It means the phase difference between the polarization components in the direction of 5 ° (the same applies hereinafter).

Here, in the laser light amplifier having the one-pass structure shown in FIG. 6A, of the stored energy, the energy extracted by amplification is relatively small.
The amount of energy taken out can be further increased by using the laser light amplifier having the two-pass structure (B).

Therefore, in general, higher energy can be extracted under one gain medium by multi-passing the amplifier, and when the same output is to be obtained, pumping to the amplifier is generally performed. Energy (ie, energy applied to the gain medium) can be reduced.

FIG. 7A shows an example in which the number of passes is further increased. The laser light amplifier having the two-pass structure is provided with a polarization separating means 6e, a polarization rotating means 5d and a laser light reflecting means 7e. As a result, a four-pass amplifier is realized. This essentially realizes a four-pass amplifier by further double-passing the two-pass amplifier.

Hereinafter, the mechanism of separation and amplification of laser light in the laser light generator having the four-pass amplifier will be described with reference to FIG.

First, the laser beam emitted from the laser beam oscillator 1 enters a laser beam amplifier 3c shown by a dashed line in the figure. The incident laser light passes through a polarization beam splitter 6d as a first polarization separation means (the polarization state at this time is a polarization state having a vibration plane in the horizontal direction represented by a polarization state a in the figure. Hereinafter, the same applies.) Then, the light is incident on a first polarization rotating unit (here, a combination of a Faraday rotator and a half-wave plate) 5d.

The laser light incident on the first polarization rotating means 5d once changes its polarization state (polarization state b). When the laser light is emitted from the first polarization rotation means 5d, it returns to the original polarization state. The state becomes the same as (polarization state a) (polarization state c). This laser light passes through a polarization beam splitter 6e (polarization state c) as second polarization separation means, enters the gain medium 4, and undergoes first intensity amplification.

Although not shown, the gain medium 4 is supplied with predetermined energy such as light energy and electric energy from an energy supply source (for example, an external power supply) (the same applies hereinafter).

Next, the laser light (polarization state d) having been subjected to the first intensity amplification is used as 1/2 as the second polarization rotating means.
The light passes through the four-wavelength plate 5e, is reflected by a reflecting mirror (retroreflector) 7d as the first laser light reflecting means, and passes through the second polarization rotating means 5e again. The polarization state is changed to e) (that is, the phase is shifted by π), the light enters the gain medium 4, and the second intensity amplification is performed.

Next, this laser beam (polarization state f) is
Since the polarization state is changed so as to be orthogonal to the first polarization state, the light is reflected without passing through the second polarization separation means (polarization beam splitter) 6e, and the optical path is separated. Then, this laser light is reflected by a reflecting mirror (retro reflector) 7e as a second laser light reflecting means, and separated again by the second polarization separating means 6e (polarization state g).
Then, the light is incident on the gain medium 4 and the third intensity amplification is performed.

Next, the laser light (the polarization state h) subjected to the third intensity amplification is subjected to the second polarization rotation in the same manner as the laser light subjected to the first amplification (the polarization state is different). The first laser light reflecting means 7d passing through the means 5e
, And again passes through the second polarization rotating means 5e, so that its polarization state is rotated by 90 ° (polarization state i).
Then, the light enters the gain medium 4 and is subjected to fourth intensity amplification.

The laser light (polarization state j) which has been subjected to the fourth intensity amplification is a polarized light having its vibration plane in the horizontal direction (ie, because the polarization state is the same as the polarization state c). ), The laser light that has passed through the second polarization separation means 6e and once passed through the first polarization rotation means 5d.
The polarization state is changed by a half-wave plate (polarization state k),
Further, the polarization state is changed by the Faraday rotator, the polarization state is changed to a polarization state orthogonal to the first polarization state (polarization state a) (polarization state 1), and the optical path is separated by the first polarization separation means 6d. Laser optical amplifier 3c of four-pass structure
Emitted from

Here, the above-mentioned polarization states a, c, d, i and j are, for example, P-polarized light (linearly polarized light having only the P component) having a vibration plane in the horizontal direction, and polarization states e, f, and
g, h, and l may be considered as S-polarized light (linearly polarized light of only S-polarized light) having its vibration plane in the vertical direction.

Next, FIG. 8 is a graph showing the relationship between the average input intensity and the average output intensity in the amplifiers having the one-pass, two-pass and four-pass structures. These are the same gain medium (gain unit) which is reciprocated one pass, two reciprocations, and two reciprocations. However, FIG. 8 shows Nd:
It is a simulation result when a YAG oscillator is used and an Nd: YAG amplifier is used as an amplifier.

According to this, as the number of times of passing through the gain medium increases, the output intensity with respect to the input intensity increases. In particular, before the amplified output shows saturation, ie,
4 when the average input intensity is 1W or less (and low input in this range)
The advantage of using a Quad-Pass is apparent.
That is, the ratio of the amplification of the output intensity is larger than the ratio when the average input intensity exceeds 1 W.

[0036]

By the way, it is needless to say that the output of an industrial laser light source (laser light generator) which requires precise control, such as a semiconductor manufacturing apparatus, needs to be stable. Absent.

Here, as described above, in the case of the amplifier having the two-pass structure (FIG. 6B), ie, the polarization rotating means 5c
Is placed between the gain medium 4 and the laser light reflecting means (retroreflector) 7c, since the polarization of the forward and backward paths is different by 90 °, it is impossible to generate a standing wave pattern in the gain medium. Absent.

However, in the case of the amplifier having the 4-pass structure, as described above, the second pass (II in FIG.
The first pass (same, III), the first pass (same, I), and the fourth pass (same, IV) have the same polarization state, and a standing wave pattern is formed in the gain medium as shown in FIG. Can occur.

In the portion corresponding to the node 51 of the standing wave 52, the excited energy is not effectively extracted, and
As shown by an arrow A in FIG. 7C, the gain changes as the standing wave pattern changes due to mechanical vibration or the like (that is, the position of the node 51 changes). In some cases, the amplified output intensity varies with time. Actually, the output fluctuates as much as 20 to 30%, which is a problem in practical use.

Since the laser light oscillator used here is a device for oscillating a single frequency for controlling the spectrum of the laser light, the laser light has a very high coherence and is generated in an amplifier having a two-pass structure. Missing output fluctuations occurred in the four-pass amplifier.

When the coherence (coherence) is high, the laser light interferes with stray light having different propagation distances such as scattered light, and noise generated based on an interference pattern generated by interfering with each other in an irregular phase relationship. , So-called speckle noise is easily generated. Such speckle noise particularly deteriorates the performance of an apparatus that requires a highly uniform illumination system, such as a semiconductor exposure apparatus used for manufacturing a semiconductor device, for example. It has been considered that application to a semiconductor exposure apparatus is hindered.

That is, in the amplifier having the four-pass structure according to the conventional technique, a standing wave is generated due to mutual interference between the forward path and the backward path of the laser light, and the intensity of the laser light serving as a stimulated emission signal is remarkably reduced. Since the energy stored in the laser light amplifier cannot be taken out, the laser light amplifier can practically be used only up to a two-pass structure, which limits the amplification factor of the laser light amplifier. As a result, the energy required to obtain the required output is increased, resulting in a decrease in the overall efficiency and a reduction in economic efficiency.

The present invention has been made in view of the above-mentioned conventional circumstances, and has as its object a method of generating a laser beam capable of generating a stable and high-intensity laser beam, and a method suitable for implementing the method. Another object of the present invention is to provide a simple laser light generator.

[0044]

The inventor of the present invention has conducted intensive studies to solve the above-mentioned problems. As a result, when amplifying the laser beam, the laser beam was previously divided into a plurality of frequency components before the amplification. By performing phase modulation, an amplifier having a multi-pass structure capable of emitting high-power laser light (for example,
It has been found that, in an amplifier having a four-pass structure, output fluctuations due to the generation of standing waves can be minimized, and stable and high-intensity (high-output) laser light can be generated.

That is, the present invention provides a laser light oscillation source for emitting laser light, phase modulation means for phase-modulating the laser light emitted from the laser light oscillation source into a plurality of frequency components, and the phase modulation means. And a laser light amplifying means for reciprocating the phase-modulated laser light a plurality of times in a gain medium and amplifying the intensity of the laser light in this order.

According to the laser light generator of the present invention, a laser light oscillation source for emitting laser light (for example, a Q-switch N for oscillating laser light having a wavelength of 1064 nm by the Q-switch method).
d: YAG laser light oscillator) and a phase in which the laser light emitted from the laser light oscillation source is phase-modulated into a plurality of frequency components by, for example, a high-frequency electric signal (that is, the spectrum of the laser light has a width). Intensity modulating means, and laser light phase-modulated by the phase modulating means is reciprocated a plurality of times (that is, 2n times: n is an integer of 2 or more) in a gain medium (or a laser medium or a gain medium) to amplify the intensity. And a so-called multi-pass laser light amplifying means in this order, for example, in a four-pass amplifier capable of emitting high-power laser light, it is possible to minimize fluctuations in the output and achieve stable operation. And high strength (high output)
Can be generated.

As described above, the problem with the conventional laser light generator having an amplifier having a four-pass structure is that, within the gain medium provided in the amplifier, laser lights having the same polarization state in the forward path and the return path interfere with each other. In combination, a standing wave is formed, the intensity of the laser light serving as a stimulated emission signal becomes zero, and energy stored inside the gain medium may not be able to be taken out. Was the cause.

On the other hand, according to the laser light generator of the present invention, the phase modulation means widens the spectrum width of the laser light output from the laser light oscillation source (laser light oscillator),
The coherence (coherence) can be reduced to an acceptable level. That is, before the laser light is introduced into the amplifier, the laser light is phase-modulated in advance to reduce its coherence (that is, coherence) to a certain extent, thereby reducing the standing wave in the gain medium. Occurrence can be prevented. Therefore, the laser light amplifier has, for example, a four-pass structure (or an eight-pass structure, or a multi-pass structure of more than eight) without causing the above-described problem of temporal fluctuation of the output intensity of about 20 to 30%. In addition, the laser light can be efficiently amplified to generate a stable and high-intensity laser light.

Further, even if a standing wave is generated in the gain medium, it can be minimized according to the degree of phase modulation in the phase modulating means. That is, by giving the laser light a certain phase (spectrum) width (blurring the laser light), the standing wave can be easily flattened.

Next, with reference to FIG. 1 (A), a schematic flow of an example of the laser light generator according to the present invention will be described.

The laser light generating apparatus according to the present invention is, for example, shown in FIG.
As shown in (A), the fundamental laser light emitted (oscillated) from the laser light oscillator 1 as the laser light oscillation source is:
A laser light amplifier for phase-modulating a plurality of frequency components with a phase modulator 2 serving as the phase modulator, and amplifying the intensity by reciprocating the laser light phase-modulated by the phase modulator 2 a plurality of times in a gain medium. (Hereinafter, the same applies).

First, as shown in (a) of the figure, the phase (particularly the spectrum) and intensity of the laser light emitted from the laser light oscillator 1 is the phase P ₁ (where P ₁ is a single frequency or extremely high). Phase in a narrow frequency band.),
The intensity T ₁ (for example, the total intensity at this time (the integral value of the intensity by the phase) and 1W).

Next, the laser beam having the phase P ₁ and the intensity T ₁ is subjected to the phase width (ie, the spectrum width of the phase P ₁ ) by the phase modulating means 2 as shown in FIG.
Is spread to become a phase P ₂ having a certain phase width. At this time, theoretically, the integral value of the phase P ₁ and the intensity T ₁ becomes equal to the integral value of the phase P ₂ and the intensity T ₂ (however, the intensity amplification in the phase modulator or the phase modulation means). Is not performed, and there is no optical loss during phase modulation). Therefore, the total intensity of the first laser beam is 1 W
Then, the total intensity at this time is also approximately 1 W.

Next, as shown in (c) of the figure, the intensity of the laser light is amplified by the laser light amplifier 3, and the phase P
₃ (however, a phase P ₃ ≒ phase P ₂ ) and a laser beam having an intensity T ₃ are generated. Here, 4 as laser light amplifier 3
When an amplifier having a path structure is used, as described above, since the laser light is phase-modulated in front of the amplifier 3, generation of a standing wave in the amplifier 3 is suppressed to minimize output fluctuation.
Alternatively, a stable and high-output amplification can be performed, and a high-intensity output with a total intensity of, for example, about 5.2 W can be obtained.

On the other hand, for example, as in the comparative example shown in FIG. 1B, the laser light emitted (oscillated) from the laser light oscillator 1 is intensity-amplified by the laser light amplifier 3 and then phase-modulated. When the phase is modulated into a plurality of frequency components by the device 2,
The object of the present invention cannot be achieved.

Here, as shown in (d) of the figure, the phase and intensity of the laser light emitted from the laser light oscillator 1 are assumed to be a phase P ₄ and an intensity T ₄ . For comparison with the laser light generator according to the present invention, for example, the total intensity (integral value of intensity) at this time is set to 1 W, the phase P ₄ = phase P ₁ , and the intensity T ₄ = intensity T ₁ .

Next, as shown at (e) in the figure, the laser light is amplified in intensity by the laser light amplifier 3 to generate a laser light having a phase P ₅ and an intensity T ₅ . here,
When a two-pass amplifier is used as the laser light amplifier 3, the total intensity can be reduced to about 3.8W.

As described above, if a laser light amplifier having a four-pass structure is used, a standing wave is generated, causing an output fluctuation of about 20 to 30%. For example, a semiconductor exposure apparatus as a stepper It is difficult to actually use it. Therefore, the laser light amplifier 3 must have a two-pass structure at most.

Next, as shown in (f) in the figure, the width of the phase P ₅ (that is, the spectrum width) is expanded by the phase modulator 2, and the phase P ₆ (P ₆₎ having a certain phase width is obtained.
= P ₃ ). At this time, as described above, since the integrated value of the total intensity does not change, if the total intensity of the laser light at the previous stage is 3.8 W, the total intensity at this time is only approximately 3.8 W.

As described above, according to the laser light generator according to the present invention shown in FIG. 1A, an amplifier having a multi-pass structure of four or more passes can be used, so that a high-intensity laser light is In addition, even if such an amplifier is used, generation of a standing wave can be prevented, so that stable and high-intensity laser light can be generated. That is, higher energy can be extracted under the same amplifier (gain medium), and when the purpose is to obtain the same output, the energy supplied to the amplifier (gain medium) can be reduced. .

By the way, the present inventor has disclosed in Japanese Patent Application No. 7-320.
No. 557 (hereinafter referred to as the prior invention) has already proposed to widen the spectrum width of the chromatic aberration by the phase modulation means to an acceptable level and to reduce the coherence to some extent in order to remove speckle noise. doing.

On the other hand, the present invention is to improve the efficiency of the laser light amplifier without deteriorating the intensity stability of the obtained laser light.

The broadening of the spectrum by the phase modulating means used in the present invention can make use of the features of the phase modulating means for a semiconductor exposure apparatus shown in the prior application. That is, the laser light is phase-modulated and then amplified by the laser light amplifier, and the output laser light emitted from this amplifier is
It can be used as a fundamental wave for generating ultraviolet light such as the fifth harmonic without any additional phase modulation means. In this case as well, similarly to the prior application, the phase modulation means of the present invention can sufficiently prevent the occurrence of speckle noise. On the other hand, when a single frequency laser beam is amplified and then phase modulated as shown in FIG. 1B, it is difficult to increase the output of the laser beam even if speckle noise is suppressed.

The present invention also relates to a laser light generating method for modulating the phase of a laser light into a plurality of frequency components and reciprocating the phase-modulated laser light a plurality of times in a gain medium to amplify the intensity. is there.

According to the laser light generation method of the present invention, the laser light is phase-modulated into a plurality of frequency components (that is, decomposed into a plurality of spectra), and the phase-modulated laser light is reciprocated a plurality of times in the gain medium. To amplify the intensity, for example,
In an amplifier having a four-pass structure capable of emitting high-output laser light, fluctuations in output can be minimized, and stable and high-intensity (high-output) laser light can be generated.

The above-described laser light generating apparatus of the present invention is an apparatus capable of performing the laser light generating method of the present invention with good reproducibility.

[0067]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the laser light generating method of the present invention and the laser light generating device of the present invention (hereinafter sometimes simply referred to as "the present invention"), an electric signal (hereinafter, simply referred to as "the present invention") comprising a plurality of frequency components is provided. In particular, the phase modulation can be performed by a high-frequency electric signal.

Examples of the phase modulator for performing the phase modulation include an electro-optic effect (E / O) modulator utilizing a change in the refractive index due to the application of an electric field, and an acoustic modulator utilizing the relationship between acoustic waves and light waves in a medium. Optical effect (A / O) modulator, etc.
Known modulators can be used.

The purpose of the above-mentioned phase modulation is to reduce the coherence in order to widen the spectrum width of the laser beam and prevent the generation of a standing wave in the amplifier at the next stage. In the process of the phase modulation, the spectrum width of the laser beam itself does not widen, but only the whole spectrum is widened by separating a single spectrum into many spectra. As described above, since the width of the entire spectrum is widened, the coherence of the laser light is reduced (that is, the coherent length of the laser light is reduced).

Further, according to the present invention, a laser light amplifier having a four-pass structure can be used as the laser light amplifying means.

That is, in the laser light amplifying means, after the laser light from the phase modulating means passes through the first polarization separating means, it is incident on the first polarization rotating means and its polarization direction is rotated. Further, after the laser light has passed through the second polarization separation means, the laser light has passed through the gain medium to perform first intensity amplification, and then the laser light having undergone the first intensity amplification has passed through the second polarization separation means. And the polarization direction of the laser light is rotated, reflected by the first laser light reflecting means provided on the optical path of the laser light, and then again incident on the second polarization rotating means. The polarization direction is rotated, and a second intensity amplification is performed by passing through the gain medium. Next, the laser light subjected to the second intensity amplification is separated by the second polarization separation unit. This Second provided on an optical path of the laser beam
After being reflected by the laser light reflecting means, the light is again separated by the second polarization separating means, and passes through the gain medium to perform a third intensity amplification, and then the third intensity amplification is performed. The laser light is incident on the second polarization rotating means and its polarization direction is rotated. After being reflected by the first laser light reflecting means, the laser light is incident on the second polarization rotating means and its polarization is changed. A fourth intensity amplification is performed by rotating the direction and passing through the gain medium, and then the laser light having been subjected to the fourth intensity amplification passes through the second polarization separation unit, and the fourth intensity amplification is performed. After being incident on the first polarization rotation unit and having its polarization direction rotated, is separated and emitted by the first polarization separation unit;
Thus, the laser light amplifying means can be configured.

FIGS. 2 and 3 show an example of an apparatus capable of performing such amplification. 2 and 3 (A)
FIG. 2 is a schematic diagram of a main part of a laser light generator having a four-pass laser light amplifier.

First, as shown in FIG. 2, a laser light generator having an amplifier having a four-pass structure according to the present invention comprises a laser light oscillation source 1, a phase modulator 2, and a laser light amplifier 3A. . Further, in this laser light generating device, the laser light amplifier 3A includes polarization splitting means 6A and 6B
, Polarization rotating means 5A and 5B, and laser beam reflecting means 7
A and 7B and a gain medium 4.

In this apparatus, a laser beam a emitted (oscillated) from a laser beam oscillation source 1 is phase-modulated into a plurality of frequency components by a phase modulating means 2, and a laser beam b thus phase-modulated is converted into a laser beam b. The light enters the optical amplifier 3A and passes through the gain medium 4 four times (ie, two round trips) while passing through each device disposed on the optical path through which the laser light propagates, in the amplifier 3A, and is thus amplified. Laser light c is transmitted to the amplifier 3A
It is configured to emit light from

Next, referring to FIGS. 3A and 3B, a description will be given of a laser light amplification mechanism according to the present invention.

FIG. 3A shows the laser beam generator shown in FIG. 2 more specifically. FIG.
FIG. 3B schematically shows the polarization state of the laser light in the laser light generator shown in FIG. FIG.
The laser light of FIG. 3A corresponds to the polarization state of FIG. 3B, and the polarization state of the laser light a of FIG. 3A corresponds to the polarization state a of FIG. Similarly, the laser light b corresponds to the polarization state b, the laser light c corresponds to the polarization state c, the laser light d corresponds to the polarization state d,... However, the polarization state shown in FIG. 3B is not limited to this.

First, a laser beam a emitted (oscillated) from a laser beam oscillator 1 as a laser beam oscillation source enters a phase modulator 2 and is phase-modulated into a plurality of frequency components. The phase-modulated laser beam a ₁ has a wider spectrum width than the first laser beam a (however, each spectrum width itself does not widen, but is divided into a large number of spectra, so that the total width of the entire spectrum is increased). Spread): the same applies hereinafter).

Next, the laser beam a ₁ from the phase modulator 2 is applied to the polarization beam splitter 1 as the first polarization separation means.
After passing through 1A and passing through a Faraday rotator 12 as first polarization rotating means, the polarization state of the laser beam b changes. The laser beam c has the same polarization state as that of the laser beam c. Further, after the laser light c passes through the polarization beam splitter 11B as the second polarization splitting means and then passes through the gain medium 4, first, the first intensity amplification (I) is performed.

However, the polarization state of the laser light a (and the laser light a ₁ ) need not be a specific state (for example, linearly polarized light). For example, the first polarization splitting means (polarization beam splitter) If 11A is used as a polarization splitting means for passing only a specific polarization state, the laser beam passing through the polarization separation means is converted into a laser having a specific polarization state (for example, linearly polarized light having a vibration plane in a horizontal direction). It can be light.

Next, the laser light d having been subjected to the first intensity amplification is applied to a quarter-wave plate 14 as a second polarization rotating means.
And its polarization direction is rotated (laser light d ₁ ),
After being reflected by the retro-reflector 15A as the first laser light reflecting means provided on the optical path of the laser light (laser light d ₂ ), it is again incident on the quarter-wave plate 14 and its polarization direction is rotated. Then, the second intensity amplification (II) is performed by passing through the gain medium 4 (laser light e).

Next, the laser light f subjected to the second intensity amplification has a polarization state different from that of the laser light c (the polarization direction differs from the laser light c by 90 °), so that the laser light f is separated by the polarization beam splitter 11B. is, after being reflected by the retro-reflector 15B as a second laser beam reflecting means provided on the laser beam f ₁ of the optical path (laser beam f _2), are again separated by the polarization beam splitter 11B gain By entering the medium 4 (laser light g), third intensity amplification (III) is performed.

Next, the laser light h subjected to the third intensity amplification is incident on the quarter-wave plate 14, the polarization direction thereof is rotated (laser light h ₁ ), and reflected by the retroreflector 15A. After that (laser light h ₂ ), the light is again incident on the 波長 wavelength plate 14 and its polarization direction is rotated (laser light i), and passes through the gain medium 4, whereby the fourth intensity amplification (IV) is performed. Done.

[0083] Then, the laser beam j fourth intensity amplification was performed is different (polarization directions are different 90 °) is its polarization state is a laser beam f and laser beam f _2, passes through the polarization beam splitter 11B Then, after entering the half-wave plate 13 and rotating its polarization direction (laser light k), the polarization direction is further rotated by the Faraday rotator 12 (laser light 1). This laser beam l
Since its polarization state is different from the laser beam a (polarization direction different 90 °), is separated by the polarization beam splitter 11A, the laser optical amplifier 3B from the output laser beam l ₁
And emitted.

Here, as described above, according to the present invention, the phase modulator 2 widens the spectrum width of the coherent laser beam emitted from the laser beam oscillator 1 to increase the coherence to some extent (the chromatic aberration is reduced). (To an acceptable level), the polarization state during the first intensity amplification (I), the polarization state during the fourth intensity amplification (IV), and the second intensity amplification (I
Although the polarization state at the time of I) and the polarization state at the time of the third intensity amplification (III) are the same, generation of a standing wave in the gain medium 4 can be prevented, and laser light output can be prevented. The amplifier has a four-pass structure (or an eight-pass structure, or a multi-pass structure more than that), and efficiently amplifies the laser light to generate a stable and high-intensity laser light. Can be.

Even if a standing wave is generated in the gain medium 4, it can be minimized according to the degree of phase modulation in the phase modulator 2. That is, by giving a certain phase (spectrum) width to the laser light (blurring the laser light), the standing wave can be easily flattened (that is, no nodes of the standing wave are generated). .

Next, the operation of the polarization separating means, the polarization rotating means, and the laser beam reflecting means used in the above-described four-pass amplifier will be described.

The polarized light separating means (the above-described first and second polarized light separating means) is means for separating the transmitted (transmitted) laser light and the reflected laser light according to the polarization state of the laser light. In the present invention, for example, a polarization beam splitter that can separate P-polarized light and S-polarized light that are linearly polarized light can be used [however, P-polarized light and S-polarized light have polarization directions (oscillation planes) of 90 degrees with each other. ° differing (ie, out of phase by π / 2). As the polarizing beam splitter, a prism or the like provided with a multilayer film can be used.

Also, the polarization rotating means (the above-described first and second polarization
Means for rotating the polarization direction of the laser beam (or non-rotation depending on the polarization state).
The polarization rotating means includes a Faraday rotator,
波長 wavelength plate (λ / 2 plate) and 波長 wavelength plate (λ / 4 plate)
Etc. can be used.

For example, the half-wave plate is a birefringent crystal plate whose thickness is determined so as to generate a half-wavelength optical path difference between linearly polarized light beams vibrating in the perpendicular direction to each other. If the light is linearly polarized laser light, its direction rotates (for example, P-polarized light becomes S-polarized light), and if the incident laser light is circularly polarized, its direction is reversed (for example, clockwise circularly polarized light). Becomes counterclockwise circularly polarized light). Also,
A quarter-wave plate means that, for example, if the incident laser light is linearly polarized, the emitted laser light is circularly polarized (or elliptical) when the phase difference between two waves having orthogonal vibration planes is π / 2. (Polarized light). When the P-polarized light passes, it becomes clockwise circularly polarized light, and when the left-handed circularly polarized light passes, it becomes S-polarized light.

However, the P-polarized light becomes the S-polarized light in the half-wave plate only when the axis of the wave plate has an angle of 45 degrees with respect to the incident polarized light. Instead of being unconditionally changed by 90 degrees, the polarization can be changed symmetrically to the axis of the wave plate. Therefore, when polarized light parallel / perpendicular to the axis enters, the polarized light does not change. Similarly, for the quarter-wave plate, the direction of the axis of the wave plate is important. The Faraday rotator utilizes the Faraday effect. The rotation angle of the plane of polarization changes depending on the strength of the applied magnetic field and the length of the substance. It was done. On the outward path, for example, the light propagating in the same direction as the magnetic field has its polarization plane
Light rotates by 5 degrees, and light propagating in the opposite direction to the magnetic field on the return path rotates counterclockwise, which is opposite to the forward path, and is rotated 90 degrees by reciprocation. Also, regarding this Faraday rotator,
The most different point from the quarter wavelength plate is that the polarization plane of the laser beam can be rotated 90 degrees by reciprocation regardless of the polarization plane of the input.

The laser light reflecting means (the first and second laser light reflecting means) is a reflecting means provided on an optical path (optical axis) through which the laser light propagates in order to reflect the laser light. Yes, for example, a reflector, retroreflector, etc. can be used. In general, when the laser light is reflected by the reflection means, the phase shifts by π. For example, clockwise circularly polarized light becomes leftward circularly polarized light, and leftwardly circularly polarized light becomes clockwise circularly polarized light.

Further, in the laser light generating apparatus having the four-pass amplifier shown in FIGS. 2 and 3 according to the present invention, the distance between the gain medium and the second laser light reflecting means (retro reflector) is set. Is desirably configured so as to be longer than half the coherent length (coherence distance) of the laser light determined by the phase modulation means.

The broadening of the spectrum of the laser beam by the phase modulation means described above is characterized in that the coherent distance (coherent length) can be controlled by freely setting the spectrum width.

Therefore, in the present invention, considering that the main purpose is not to generate a standing wave in the gain medium provided in the laser light amplifier, the second embodiment shown in FIGS. If the distance between the reflector (retroreflector) as the laser beam reflecting means and the gain medium is longer than half of the coherent length designed in advance, the coherence is sufficiently reduced. No standing wave is generated, and the problem of fluctuation in output intensity can be further reduced.

As described above, the second laser light reflecting means (reflector, retroreflector) is set to have a length equal to half the coherent length of the fundamental laser light oscillated from the laser light oscillation source (laser light oscillator). If the distance is set to be longer, the coherence of the laser beam can be further reduced. That is, by adjusting the arrangement of the second laser light reflecting means, the coherence (coherence) can be further reduced (that is, the generation of a standing wave can be prevented). In addition, under these conditions, practical imaging performance of laser light can be maintained.

In the present invention, the laser light oscillation source may be a solid-state laser oscillation source that oscillates a pulse wave by a Q-switch method or a solid-state laser oscillation source that oscillates a continuous wave.

Generally, a laser light oscillation source generates a CW laser (Continuous Wave) which generates a continuous output of a constant amplitude from its output waveform.
continuous wave laser) and a pulse laser that generates an intermittent pulse waveform output. In the present invention,
Among pulse lasers, it is desirable to use a Q-switched laser because a pulse output having a large peak output and a narrow time width (giant pulse) can be obtained.

In the present invention, it is desirable that the average input intensity of the laser light incident on the laser light amplifying means be 1 W or less.

As shown in FIG. 8, as the structure of the laser light amplifier is increased to one pass, two passes, and four passes,
The average output intensity (output power) obtained with respect to the average input intensity (input power) increases. In particular, when the average input intensity is 1 W or less, the structure of the laser
The amplification factor when increasing the number of passes to four passes is large, and there is a great advantage in using a laser light generator having an amplifier having a four-pass structure. The same applies to four or more paths (for example, an amplifier having an eight-path structure).

Further, in the present invention, the laser medium of the laser light oscillation source is neodymium: yttrium-vanadate (hereinafter sometimes referred to as Nd: YVO ₄ ), and the laser light amplifying means is provided. The gain medium having neodymium: yttrium aluminum
Garnet (hereinafter sometimes referred to as Nd: YAG) is preferable.

Further, in the present invention, the laser medium of the laser light oscillation source and the gain medium of the laser light amplifying means are neodymium: yttrium aluminum garnet (Nd: YAG), neodymium: yttrium vanadate (Nd). : YVO ₄ ), neodymium-doped glass, and one kind of laser medium selected from the group consisting of neodymium: yttrium lanthanum fluoride.

Further, in the above-mentioned laser medium and gain medium, it is preferable that the laser medium of the laser light oscillation source and the gain medium of the laser light amplifying means have the same composition.

In the present invention, erbium (Er) is used instead of neodymium (Nd).
One kind of atom selected from the group consisting of praseodymium (Pr: Praseodymium), ytterbium (Yb: Ytterbium), thulium (Tm), holmium (Ho) and chromium (II) can also be used as the dopant.

Next, the selection of the material of the laser medium (gain medium) used for the laser light oscillator (oscillator) and the laser light amplifier (amplifier) according to the present invention will be described.

In general, a laser oscillator oscillates a laser beam having a specific wavelength determined by the material of the laser medium. For example, 1064 nm for Nd: YAG laser
(There are other oscillation wavelengths, but this is the most commonly used and the strongest spectrum.) This is determined by the properties of the laser medium and at other wavelengths (unless there is a transition at that wavelength).
Laser amplification (stimulated emission of light) does not occur. Although this oscillation wavelength is small, there is a spread in its gain. For example, in the case of a 1064 nm oscillation line of an Nd: YAG laser, the spread of the gain (spectral width) is about 140 GHz in frequency, which is less than 1 nm in terms of wavelength.

Laser oscillation is a phenomenon that occurs when laser amplification is fed back in a resonator. Since both laser oscillation and laser amplification are phenomena caused by stimulated emission of light, the oscillation wavelength of a laser oscillator (ie, a wavelength having a gain). And the gain wavelength of the laser amplifier must be the same, or the distance between them must be within the spread of the gain of the amplifier.

Therefore, as described above, it is desirable to use the same material (medium) for the laser medium of the oscillator and the gain medium of the amplifier.

In general, the center wavelength of laser light obtained by a solid-state laser slightly shifts (100
It is common that GHz does not move. ), The temperature of the oscillator and the temperature of the amplifier (controlling the gain center wavelength) can be controlled so that the gain becomes highest for controlling the oscillation wavelength.

However, some combinations of the above-mentioned materials (combinations of the materials of the laser medium and the gain medium) are close to each other in gain wavelength, although the materials are different. For example, the above-described Nd: YAG and Nd: YVO
₄ is an example thereof, both have a gain at 1064 nm, and these can amplify each other.

When used as a laser light oscillator, especially in the case of pumping a semiconductor laser, Nd: YVO ₄ provides more efficient oscillation. This is considered to be due to the good absorption efficiency of the excitation light. When Nd: YVO ₄ is used as a laser medium, when a Q-switch pulse is generated, the laser upper-level life may be short, and a short pulse tends to be easily obtained. In the case of a short pulse, the spire output becomes higher even with the same average output, so that the efficiency is improved when nonlinear wavelength conversion is performed.

Next, the Nd: YVO ₄ oscillator-Nd: YV
Combination of O ₄ amplifier and Nd: YVO ₄ oscillator-N
d: Compare with the combination of YAG amplifier. In this case, if the center wavelengths of the gains are sufficiently overlapped, N
Since d: YAG has a longer laser upper level lifetime, the efficiency of the amplifier may be improved. If an amplifier excited by a continuous wave is used for repeated pulse amplification, how much energy can be stored in the medium by being continuously excited between one pulse and the next pulse? Is the point of efficient laser amplification. If the upper level lifetime of the laser is shorter than the pulse repetition interval, even if excited, a part of the energy (the shorter the upper level lifetime is, the more energy) is non-stimulated emission (spontaneous emission). Is lost from the gain medium before the next pulse arrives, and the energy used for pumping is less effectively used for laser amplification.

The pulse repetition frequency actually used is:
Usually, it is about 7 kHz to 10 kHz, and the pulse interval is 1
00 to 150 μs. Here, Nd: YAG
Has an upper level lifetime (sometimes referred to as fluorescence lifetime) of about 2
Considering that the upper level lifetime of 30 μs and Nd: YVO ₄ is about 90 μs, it can be seen that the Nd: YAG amplifier is advantageous.

Further, in the present invention, it is preferable to have a wavelength conversion means for converting the wavelength of the laser light whose intensity has been amplified by the laser light amplification means.

In the present invention, the laser light emitted from the laser light amplifying means (laser light amplifier) can be used as it is, but the wavelength is converted by the wavelength converting means using the laser light as a fundamental wave. It is also possible. In particular, when the wavelength of the fundamental wave laser light is changed using the wavelength converting means, as described above, the conversion efficiency at the time of wavelength conversion of the fundamental wave laser light is small (at most 1).
(Approximately 0%), and by applying the present invention and increasing the intensity of the fundamental laser light in advance, the laser light after wavelength conversion can be made to have a desired intensity. Further, the present invention can be applied to various kinds of light modulation such as phase conversion in addition to wavelength conversion.

In particular, a harmonic component of laser light can be obtained by the wavelength conversion means. For example, a laser beam having a wavelength of 1064 nm oscillated from an Nd: YAG laser as a laser beam oscillation source is used as a fundamental wave, and a laser beam having a wavelength of 213 nm, which is the fifth harmonic of this laser beam,
It is possible to obtain a stable and high output.

FIG. 4 shows a semiconductor exposure apparatus to which the laser light generating method and the laser light generating apparatus of the present invention are applied.
This will be described with reference to FIG.

As shown in FIG. 4, this semiconductor exposure apparatus has a wavelength of 1064 nm as a laser light source (oscillator), for example, a pulse laser light source that oscillates in a longitudinal single mode.
Nd using Nd: YAG that oscillates in the vertical single mode by the Q-switch method by injection technology or the like.
YAG Q-switched laser device 1 ′, phase modulator 2 for phase-modulating the laser light from Nd: YAG Q-switched laser device 1 ′ into a plurality of frequency components, and the above-described four-pass as laser light amplifier 3 A laser light generator 10 comprising an amplifier having a structure, and lithium borate (LBO: LiB
₃ O ₅ ) and β-barium borate (β-BBO: β-Ba
B ₂ O ₄ ) or the like, undergoes phase modulation by the phase modulator 2 and is amplified by the amplifier 3. ), A uniform illuminator 23 having an action of causing an optical path difference, and a projector 27 for projecting a laser beam from the uniform illuminator 23 onto a substrate in a predetermined pattern. ing.

Although not shown, the phase modulator 2 includes:
A high frequency signal generator for generating a high frequency and a high frequency amplifier for amplifying the high frequency generated by the high frequency signal generator and outputting the amplified high frequency to the phase modulator 2 may be connected.

Nd: YAG Q-switched laser device 1 '
1064 nm laser light (hereinafter, referred to as fundamental wave laser light) emitted from the laser beam enters the phase modulator 2. A voltage signal including a plurality of frequency components from a high-frequency signal generator (not shown) may be configured to be sent to a high-frequency amplifier, amplified, and applied to the phase modulator 2.

In the phase modulator 2, the fundamental laser light is subjected to phase modulation in accordance with an electric signal (particularly, a high-frequency electric signal) generated by the phase modulator 2, as described later. By this phase modulation, the entire spectrum width of the fundamental laser light having a wavelength of 1064 nm is widened. Then, the laser light whose overall spectrum width has been expanded by receiving this phase modulation is sent to the laser light amplifier 3. next,
The laser light whose intensity has been amplified by the amplifying means as described above is sent to the wavelength conversion device 8 (the description of the operation of the amplifier 3 is omitted here).

The wavelength converter 8 has a plurality of nonlinear optical crystals. Next, the operation of extracting the fifth harmonic from the fundamental laser light in the wavelength converter 8 will be briefly described.

First, the laser light emitted from the laser light amplifier 3 passes through a lithium borate crystal plate (hereinafter referred to as LBO) 30 which is a nonlinear optical crystal. On this occasion,
A laser beam having a wavelength of 532 nm, which is the second harmonic, is generated. The laser beam emitted from the LBO 30 has a wavelength of 10
It includes both 64 nm and 532 nm.

Next, the laser light emitted from the LBO 30 is incident on the color separation mirror 33a, the laser light having a wavelength of 1064 nm is transmitted, the laser light having a wavelength of 532 nm is reflected, and the optical axis is bent by 90 °. Separated.

The separated laser light having a wavelength of 532 nm is further reflected by the total reflection mirror 33b and transmitted through a β-barium borate crystal plate (hereinafter referred to as β-BBO) 31, which is a nonlinear optical crystal. Wavelength 266 which is the fourth harmonic
nm laser light is generated. The laser light having the wavelength of 266 nm is reflected by the total reflection mirror 33c and the color separation mirror 33d, and is guided to the β-BBO32.

On the other hand, the laser beam having a wavelength of 1064 nm transmitted through the color separation mirror 33a is transmitted through the color separation mirror 33d and guided to the β-BBO32.

In this β-BBO 32, the wavelength 106
Based on the 4 nm laser light and the 266 nm laser light, sum frequency mixing described later is performed, and 213 nm ultraviolet laser light, which is the fifth harmonic of the fundamental laser light, is generated.
The laser light having the wavelength of 213 nm is emitted from the wavelength conversion device 8. At this time, the spectrum width (Δf _5W ) of the ultraviolet laser light after wavelength conversion is equal to the spectrum width (Δf _5W ) before conversion.
f _w ) (Δf _5W = 5Δf _w ). In addition to the laser light having a wavelength of 213 nm, the emitted laser light has a wavelength of 1064 nm or a wavelength 53 of the second harmonic.
Laser light of various wavelength components such as 2 nm laser light is included.

Here, the sum frequency mixing will be described.

When a laser beam is incident on a nonlinear optical crystal such as LBO or β-BBO, nonlinear polarization not proportional to the magnitude of the electric field of the laser beam applied from the outside is generated. If this non-linear polarization occurs in the second-order nonlinear susceptibility is not zero, for example, the frequency f _a, the two light f _b are incident simultaneously, nonlinear polarization frequency f _c = f _a + f _b are excited in the crystal You. The light of frequency f _c is emitted by the polarization. This is the principle of sum frequency mixing, where wavelengths λ _a ,
The wavelength λ _{c of the} sum frequency emitted when the laser light of λ _b is incident has a relationship of 1 / λ _c = 1 / λ _a + 1 / λ _b (Formula (A)). That is, the laser beam having a wavelength of 1064 nm and the laser beam having a wavelength of 266 nm are sum-frequency mixed according to the above equation (A), and become an ultraviolet laser beam (fifth harmonic) having a wavelength of 213 nm. The nonlinear optical crystal for sum frequency mixing is
The laser beam is processed so as to propagate in the direction in which the generation efficiency of the sum frequency is maximized.

Next, the prism 21 separates the laser light including the 213 nm wavelength laser light emitted from the wavelength converter 8 into each wavelength component, and passes only the 213 nm laser light through the slit 22 to the uniform illumination device. Send to 23.

The uniform illuminator 23 has a wavelength 21
It has the function of separating the ultraviolet laser light of 3 nm, generating an optical path difference, and synthesizing again, and the laser light subjected to this action becomes spatially uniform light with no occurrence of speckle noise. Next, the laser light is emitted to the projection device 27.

The projection device 27 includes a reticle 24, a projection lens 25, and a semiconductor wafer 26. Reticle 24
Is a so-called photoresist on which a pattern to be projected on the semiconductor wafer 26 is processed. Projection lens 25
Transmits the laser beam transmitted through the reticle 24 to the semiconductor wafer 2
6 is a lens for reducing projection. A resist is applied to the semiconductor wafer 26, and the pattern processed on the reticle 24 is transferred to the semiconductor device side by the photosensitive action of the resist.

First, the coherent length required for the semiconductor exposure apparatus according to the present invention will be described. The desirable coherent length is determined from the allowable range of chromatic aberration and the conditions under which speckle noise can be removed.

Generally, laser light having a short coherent length has a wide spectral width and low monochromaticity. In this case, chromatic aberration is likely to occur. In particular, when the projection lens 25 is formed using a single glass material, the effect of achromatizing the lens, that is, the effect of correcting chromatic aberration cannot be obtained. Therefore, in order to realize sufficient imaging performance, a coherent length of 80 mm or more is required in consideration of a practical NA value (numerical aperture) and magnification of the lens.

When the projection lens 25 is formed by using a plurality of types of glass materials to perform achromatism, the condition of the spectral width becomes loose. For example, when a practical glass material is used with a projection lens having an NA of 0.6 or more, sufficient imaging performance can be realized if the coherent length is 30 mm or more.

In order to remove speckle noise,
A shorter coherent length is advantageous, and practically 18
A coherent length of 0 mm or less is desirable.

As described above, when a projection lens is formed using a single glass material, the coherent length is desirably 80 mm or more and 180 mm or less, and when a projection lens is formed using a plurality of types of glass materials. The coherent length is desirably 30 mm or more and 80 mm or less.

In general, the projection lens 25, which is a projection optical system used in a semiconductor exposure apparatus, has an extremely high resolving power and minimizes various distortions in the image plane. The resolution is defined by the numerical aperture NA on the side of the semiconductor wafer 26 as a photosensitive substrate of the projection optical system to be used and the center wavelength (also related to the wavelength width) of the exposure illumination light to be used. When using a projection optical system having an NA of 0.65 under light, the difference between whether the projection optical system is composed of only a refractive optical element or a combination of a refractive optical element and a reflective optical element, Or, even if there is a difference between the exposure of the static method and the exposure of the scanning method, it is expected that a resolution of about 0.1 to 0.2 μm in line width can be obtained.

In order to obtain such performance, it is necessary to obtain a sufficient transmittance at a center wavelength of 213 nm while keeping the axial chromatic aberration and the lateral chromatic aberration both sufficiently small while keeping the practical exposure field size uniform. When designing a projection optical system using only quartz (SiO ₂ ) as a lens material (that is, a projection lens made of a single glass material), the coherent length of an ultraviolet laser beam applied to a reticle during projection exposure is about 126.
mm (corresponding to about 0.35 pm when expressed as the full width at half maximum of the spectrum as the wavelength width). In addition, when a plurality of quartz lenses and several fluorite (CaF ₂ ) lenses are combined (that is, a projection lens made of a plurality of types of glass materials) and slight chromatic aberration correction is performed, the coherent length of the ultraviolet laser light becomes Approx. 45 mm (approx.
m).

These numerical examples are based on the numerical aperture NA of the projection optical system.
However, the projection optical system varies depending on the exposure field size, the projection magnification, the chromatic aberration correction amount, and the like.
Although the upper limit is limited according to the coherence reduction performance of
About 80 mm or more is required as the coherent length of the ultraviolet laser light. In a projection optical system formed of a combination of a lens element or a refraction element and a reflection element made of a plurality of glass materials, although the lower limit is limited according to the degree of chromatic aberration correction, the coherent length of the ultraviolet laser light is about 80.
mm or less is considered appropriate.

Next, the power spectrum of ultraviolet light for realizing the above-described coherent length will be described.

Here, when the laser light generating apparatus of the present invention is put to practical use as a light source of the projection apparatus 27, in order to reduce speckle, it is necessary to sufficiently eliminate coherence with an optical path difference longer than the coherent length. Is desirable. Also, the sharpness V
Since (τ) and the power spectrum S (f) have a Fourier transform relationship, when the power spectrum has a Lorentz distribution, the sharpness decreases exponentially. That is, the coherence at the optical path difference longer than the coherent length can be almost ignored. For example, the full width at half maximum of the spectrum is Δf = 4G
If the light source is a Lorentz-type spectrum of Hz, coherence can be almost ignored at a distance of coherent length L _C = about 75 mm or more. In addition, the aforementioned 30 mm
To satisfy the condition of coherent length of <L _C <180 mm, the full width at half maximum of the spectrum is 2 GHz <Δf <10 GHz.
Is required.

Further, as described above, in phase modulation, one spectrum is simply separated into a plurality of spectra, and the width of each spectrum is not widened. It is impossible to get.

Accordingly, the spectrum that is the most ideal that can be realized has a shape in which many narrow-band spectra form an envelope of a Lorentzian distribution with a spectral line width of, for example, Δf = 4 GHz as a whole.

In the present invention, the Nd: YAG Q
As the switch laser device 1 ', a transform-limited Q switch pulse laser can be used. This Q-switch pulse laser has a pulse width of about 10 ns after wavelength conversion to 213 nm. By multiplying this pulse width by the speed of light,
The length L _P of one pulse (L _P ≒ 3 m) is calculated.
Also, in the interference phenomenon of two light beams having an optical path difference _{equal to} or greater than LP, interference occurs between different pulses, so that coherence is not exhibited.
In the present invention, even if the coherence appears again due to the optical path difference of 3 m, 6 m,.
Since the length of each pulse is about 3 m, the coherence with an optical path difference of 3 m or more eventually disappears.

Therefore, by expanding the spectrum width to, for example, 4 GHz using the phase modulation according to the present invention,
It is quite possible to achieve a coherent length L _C = 75 mm. Further, each spectrum interval is set to 100M.
By making the frequency as high as about Hz, the distance at which the coherence is reproduced can be sufficiently increased to about 3 m. Further, since the pulse width of the Q-switched laser light is about 10 ns, there is no coherence with an optical path difference of 3 m or more. From the above,
Coherence in the coherence length L _c above it can be seen negligible.

Next, a description will be given of a method of generating a spectrum that is densely distributed over a wide frequency width, for example, Δf = 4 GHz, for example, at a frequency interval f _S = 100 MHz, using the phase modulation means according to the present invention.

In the present invention, the above-mentioned spectrum can be phase-modulated by combining two means. One is means for performing phase modulation on the fundamental laser light before wavelength conversion, and the other is means for performing phase modulation at a plurality of frequencies.

First, the effect of performing phase modulation on the fundamental laser light will be described.

As described above, it is extremely difficult to generate a spectrum over a wide band whose spectral line width is 4 GHz, for example, by simply performing phase modulation directly on the ultraviolet laser light.

[0150] For example, when the phase modulation in represented by a phase modulation function [Phi (t) by _{Φ (t) = m sin2πf m} t ··· (1), newly generated spectrum of about 2m book, spectrum subjected to the phase modulation spreads the frequency width of approximately Δf = 2mf _m. Therefore, to achieve a Δf = 2mf _m = 4GHz, for example when the phase-modulated by f _m = 200 MHz,
A modulation amplitude of m = 10 is required, and a fairly high voltage must be applied to the phase modulator.

Further, the number of electro-optic crystals that allow ultraviolet laser light to pass therethrough is limited. For example, potassium dihydrogen phosphate (K
H ₂ PO ₄ ), ammonium dihydrogen phosphate (NH ₄ H ₂₎
Only crystals having a small electro-optical effect, such as PO ₄ ) and β-barium borate (β-BBO), can be used. Therefore, in order to realize a modulation amplitude of m = 10, it is generally necessary to apply a voltage having an amplitude of 5 kV or more to the phase modulation device, and it is difficult to realize this modulation amplitude. Further, a high frequency, for example, in the case of phase modulation at f _m = 1GHz, _m = is enough 2 about, but in this case since the high-frequency and voltage of a large amplitude is required, realization of a phase modulation is difficult.

Therefore, it is difficult to widen the line width of the spectrum modulated over a wide band of 4 GHz simply by directly phase-modulating the ultraviolet laser light as described above, because a high voltage is required.

Therefore, wavelength 1 before wavelength conversion and intensity amplification is used.
The above-mentioned problem can be solved by performing phase modulation on the fundamental laser light of 064 nm. The effects include the following two effects.

First, by performing wavelength conversion of the fundamental laser light and generating the fifth harmonic, the spectrum width can be broadened approximately five times. This is because, when the phase modulation is performed with the amplitude m in the fundamental laser light, the fifth harmonic corresponds to the phase modulation with the amplitude 5 m.

Second, potassium titanate phosphate (KT)
iOPO ₄ : KTP), potassium titanate arsenate (KTi)
OAsO ₄ ), rubidium arsenate titanate (RbTiOA)
sO ₄ ), cesium titanate arsenate (CsTiOAs)
Crystals having a relatively high electro-optic constant, such as O ₄ ), lithium niobate (LiNbO ₃ ), and lithium tantalate (LiTaO ₃ ), can be used as the electro-optic crystal.

For example, in comparison with β-BBO, KTiOP
O ₄ shows an electro-optic modulation efficiency of 20 times or more. Therefore, the voltage to be applied is as follows when using crystals of the same size.
It is less than 1/20.

By the above two effects, by phase-modulating the fundamental laser light having a wavelength of, for example, 1064 nm before the wavelength conversion (that is, before the intensity amplification), the fifth harmonic having a wavelength of 213 nm can be obtained at a lower voltage. It is possible to increase the spectral width of the wave. For example, when the spectrum width of the fifth harmonic is increased up to 4 GHz, the fundamental laser light may be expanded to a spectrum width of 800 MHz.
This can be realized, for example, by phase-modulating the fundamental laser light at a modulation frequency f _m = 200 MHz and a modulation index m = 2. In addition, this modulation index is such that the material of the phase modulator 2 is KTP (potassium titanate phosphate: the same applies hereinafter), the length of the portion where the laser beam passes through the crystal is 60 mm, and the distance between the electrodes is 1 mm. This can be realized by applying an electric signal having an amplitude of about 50 V and a frequency of 200 MHz to the phase modulator 2.

Next, the effect of performing phase modulation at a plurality of frequencies will be described.

First, when phase modulation is performed at a single frequency, the intensity of each divided spectrum is proportional to the square of the Bessel function, so that the shape of the entire spectrum is limited. Further, assuming that the distance at which the coherence is reproduced is L _S , in order to keep this L _S away, each frequency interval f _S
In order to reduce the value and broaden the spectrum, a large modulation index m is required. For example, f _S = 100 MH
When the spectrum width is increased to z in the entire spectrum width Δf = 800 MHz, the modulation index becomes about m = 4, and in the example of the phase modulator using KTP described above, a high voltage _Vpp = 100 V applied between the electrodes. Is required,
Further, the shape of the spectrum at that time is greatly deviated from the Lorentz type.

Therefore, in the present invention, the above problem can be solved by performing phase modulation at a plurality of frequencies simultaneously. Further, it is possible to reduce the frequency interval f _S and sufficiently widen the spectrum width, and to realize a spectrum shape close to a Lorentzian shape.

Here, when phase modulation is performed simultaneously at a plurality of frequencies, as described above, the spectrum generated by the phase modulation of a certain frequency component is further divided by another frequency component to generate many spectral lines. I do. For example, the frequency band f _m1 = 200 MHz, the modulation index m ₁ =
Phase modulation is performed at about 2.0, and the frequency band f _m2 =
When phase modulation is performed at 97 MHz and a modulation index m ₂ = 1.4, a spectrum having an interval f _S between individual spectra of 97 MHz and an overall spectrum width Δf of 800 MHz is obtained. Here, f _S = 97 MHz is set in order to sufficiently increase the least common multiple of the two frequencies so that the generated spectra do not overlap and cancel each other.

Thus, it can be seen that the same effect can be obtained with a half phase modulation index as compared with the case where the spectrum width is increased to Δf = 800 MHz only at the frequency of 100 MHz. Furthermore, by applying signals of many frequency components with appropriate amplitudes, it is possible to make the shape of the spectrum closer to the Lorentz type.

As a method of performing phase modulation at a plurality of frequencies, there are a method of arranging a plurality of phase modulation devices in series and applying voltages of different frequencies to each other, and a method of applying a plurality of frequencies to one phase modulation device. There is a method of applying a signal having a component.

When the above two methods are combined, the fundamental laser light is phase-modulated at a plurality of frequencies, so that it is possible to oscillate densely at a low voltage over a wide spectrum width. Further, when the phase-modulated fundamental laser light is converted into the fifth harmonic, the spectrum width can be broadened approximately five times. Further, by optimizing the phase modulation index of each frequency component, the envelope of the spectrum of the fifth harmonic can be approximated to an optimal Lorentzian shape. Therefore, by generating such a spectrum, the coherent length can be reduced to about 75 mm.

The materials used for the phase modulator include:
As described above, it can be used for all electro-optic crystals that transmit near-infrared light.

[0166] For example, KTP will be described as an example. K
A value of 20 J / cm ² has been reported as the threshold value of damage to the laser medium by the Q-switched pulse laser in TP. On the other hand, the pulse intensity of the Q-switch Nd: YAG laser oscillator used as a light source of the above-described semiconductor exposure apparatus using ultraviolet light is about 1 mJ. Assuming a beam diameter of 0.3 mm, the power density is 1.4 J / cm ^2.
Therefore, at this power density, the damage threshold of the laser medium is approximately one-fifteenth, and damage to the laser medium is prevented.

At this time, the clear aperture of the phase modulator (the effective diameter of the coating, etc.) is set to 1
If it is set to 1 mm × 1 mm, no diffraction loss occurs. The phase modulation index m is expressed by the following equation (2) using the electro-optic modulation constant r of KTP, the refractive index n of KTP, the used wavelength λ, the distance d between the electrodes, the length L of the crystal, and the applied voltage V.

M = (πrn ³ / λ) × (L / d) × V (2)

Here, the equation (2) shows that the wavelength λ = 1064n
m, electro-optic modulation index r = 35 pm / V, refractive index n =
By substituting 1.83 and the distance d between the electrodes d = 1 mm, the length L of the crystal is set to 60 mm (when processing is difficult, two crystals having a length of 30 mm may be arranged in series). 5
A phase modulation index of m = 2 can be realized with an applied voltage of about 0V.

In addition, KTP has the advantage that it does not show deliquescence and is chemically stable.

FIG. 5 shows a specific configuration example of the phase modulator using the KTP having the above-described size.

In the phase modulator of FIG. 5, a pair of KTPs 40a and 40b, which are electro-optical crystal elements, are arranged at predetermined positions on a mount 41. Here, b
Taking the axis in the longitudinal direction of the KTPs 40a and 40b, taking the c-axis perpendicular to the b-axis and perpendicular to the KTP installation surface, and taking the a-axis perpendicular to the b-axis and the c-axis, A pair of surfaces formed on each of the KTPs 40a and 40b are arranged such that one of the surfaces parallel to the a-c plane formed by the a and c axes faces each other.

A voltage signal from the voltage amplifier 43 is connected to one of the electrodes formed on a pair of surfaces parallel to the a-b plane formed by the a and b axes of both KTPs 40a and 40b. Applied via 44, the other electrode is grounded. Further, the voltage generator 42 generates the above phase modulation frequency, and outputs the generated voltage signal to the voltage amplifier 43. The voltage amplifier 43 can amplify and output the voltage signal generated by the voltage generator 42.

In the phase modulator shown in FIG.
Rather than using one crystal whose longitudinal direction t ₂ is t ₂ = 60 mm as KTP, two crystals each having a longitudinal direction of 30 mm are used in series in consideration of easiness of processing. I have. Further, the surface 45 perpendicular to the longitudinal direction has a square with _one side t ₁ being t ₁ = 1 mm.

According to FIG. 5, for example, the fundamental laser beam is incident in the direction of arrow A in the figure from a surface 45 whose one side t ₁ is 1 mm and faces outward. The incident fundamental laser light undergoes phase modulation at the phase modulation frequency output from the voltage generator 42 inside the KTPs 40a and 40b. The laser light that has undergone this phase modulation is
Outward from the surface 46 in the opposite direction to the surface 45 (arrow B in the figure)
Direction).

As described above, by the phase modulation of the fundamental wave and the phase modulation at a plurality of frequencies, a highly coherent Q switch Nd:
The coherent length of the fifth harmonic of the YAG laser can be reduced to about 30 to 180 mm, which is desirable for a semiconductor exposure apparatus.

As a result, the Q switch Nd: YAG laser which is small in size, consumes little energy, has no toxicity, and is easy to operate and hold can be applied to the application of a semiconductor exposure apparatus using ultraviolet laser light. Further, a phase modulation device using a crystal such as KTP or a KTP derivative can be used as the phase modulation means.

According to the semiconductor exposure apparatus shown in FIG. 4, Q is used as a light source for emitting a laser beam used in a uniform illumination device.
A laser light generator 10 including a switch laser light source 1 ', a phase modulator 2, and a laser light amplifier 3 can be used.

Further, in the laser light generator 10, the Q composed of Nd: YAG and oscillating in the longitudinal single mode is used.
After using the switch laser light source as a fundamental laser light source, the phase modulator 2 performs phase modulation on the fundamental laser light with a plurality of frequency components, and further performs high-power amplification with the amplifier 3. The output laser light can be wavelength-converted to the fifth harmonic (ultraviolet laser light) by the wavelength conversion means. Note that the laser light generator of the present invention refers to the laser light generator 10 of FIG. 4 in a narrow sense, and also includes the wavelength converter 8 and the like in a broad sense.

As described above, by applying a sine wave having a relatively low amplitude at the time of phase modulation, the spectrum width can be sufficiently widened, the coherence can be sufficiently reduced, and the uniformity with the laser light generator can be obtained. Speckle noise can be removed by combination with a lighting device. As described above, the generation of a standing wave, which is the main object of the present invention, can of course be prevented.

The speckle noise (interference noise) is
The degree of sno definition (visibility) also differs depending on the configuration of the uniform illumination device 23. For example, as an optical system for making the irradiation area on the reticle 24 used for the ultraviolet laser light for exposure rectangular or slit-shaped, and making the intensity distribution uniform within the irradiation area less than several percent, conventionally, A secondary light source surface in which a large number of secondary light sources (point light sources) are distributed in a plane can be created by the fly-eye lens integrator. Here, the fly-eye lens is
A plurality of lenses smaller than the beam diameter are arranged in parallel and two-dimensionally, and are used to make illumination intensity uniform.

In this case, depending on the coherent length of the ultraviolet laser light incident on an optical integrator (means for equalizing the light intensity) typified by a fly-eye lens, a large number of secondary light sources may be generated. Light traveling from point light sources approaching within a specific interval may interfere with each other. Due to this interference, one-dimensional or two-dimensional interference fringes corresponding to the arrangement direction of a large number of secondary light sources formed by the optical integrator may appear on the reticle 24 or the semiconductor wafer 26. The sharpness of the interference fringes depends on the coherent length of the ultraviolet laser light.

Such interference fringes are sometimes distinguished from speckle noise, which is an original random interference phenomenon due to its periodicity, but the difference is that both are interference phenomena in a broad sense. However, when the coherent length of the laser beam is extremely large, both the random speckle pattern and the periodic interference fringes have large visibility (clearness)
First, the visibility of the random speckle pattern falls below the allowable value and disappears with the decrease in coherent length, and the visibility of periodic interference fringes also falls below the allowable value by further reducing the coherent length. Can be done.

Considering the performance of an actual semiconductor exposure apparatus, even when the interference fringes have a contrast of about several percent, image quality may be deteriorated when the circuit pattern of the reticle 24 is transferred to the semiconductor wafer 26. In this case, for example, the incident angle of the ultraviolet laser light incident on the optical integrator is minutely changed by a vibrating mirror or the like together with the pulse oscillation, and a phase difference (optical path length difference) is provided between a large number of secondary light sources, so that the A method of displacing the interference fringes on the semiconductor wafer in the pitch direction over an integral multiple of 周期 cycle to uniformly uniform the exposure amount distribution on the semiconductor wafer may be used.

As a method of reducing interference fringes generated on a semiconductor wafer by using an optical integrator, a circular diffuser (such as a lemon skin) for transmitting and diffusing an ultraviolet laser beam in a random direction ahead of the optical integrator is used. And a method of rotating it at a high speed during the exposure operation. Also in this case, the exposure amount distribution on the semiconductor wafer is averaged by superimposing and integrating a large number of interference fringes generated in random directions for each of the plurality of pulse lights.

In the exposure apparatus, the illumination unevenness on the semiconductor wafer is finally made uniform, that is, the target exposure amount is ± 1% at any point in one shot area on the semiconductor wafer. Since it is important that the uniform illuminating device 23 is provided with a dynamic coherence reducing device such as the vibrating mirror or the circular diffuser in the uniform illuminating device 23, the interference noise in the dynamic coherence reducing device is used. The coherent length of the ultraviolet laser light is determined in consideration of the reduction performance of the ultraviolet laser.

As a matter of course, the uniform illumination device 23 divides the ultraviolet laser beam from the wavelength conversion device 8 into a plurality of light beams, and gives a different optical path length difference (phase difference) between the divided light beams. The static coherence reduction device that reduces coherence by combining the light beams into one light beam may be used in combination with the dynamic coherence reduction device.

In this case, the coherent length of the ultraviolet laser light from the wavelength conversion device 8 is considerably large (for example, 500
(up to about mm). As described above, the fact that a coherent length of a large value is allowed means that the high-frequency signal generator 42
This means that the substantial frequency spectrum (distribution width of a plurality of frequencies) of the high-frequency signal for phase modulation made by the above can be reduced, and there is an advantage that the configuration of the high-frequency signal generator 42 is simplified.

[0189]

According to the laser light generating apparatus of the present invention, a laser light oscillating source for emitting laser light and a laser light emitted from the laser light oscillating source are converted into a plurality of frequency components by, for example, a high-frequency electric signal. Phase modulation (ie,
A phase modulating means for giving a width to the spectrum of the laser light, and a laser light phase-modulated by the phase modulating means is reciprocated a plurality of times (that is, 2n times) in a gain medium (or a laser medium or a gain medium): However, a multi-path laser light amplifying means for amplifying the intensity by multiplying the intensity by n is an integer of 2 or more) is provided in this order. , The generation of a standing wave in the gain medium can be prevented, the output fluctuation can be minimized, and a stable and high-intensity (high-output) laser beam can be generated. It is also possible to reduce speckle noise.

Further, according to the laser light generation method of the present invention, the laser light is phase-modulated into a plurality of frequency components (that is, decomposed into a plurality of spectra), and the phase-modulated laser light is divided into a plurality of components in a gain medium. Because it reciprocates twice to amplify the intensity,
For example, in an amplifier having a four-pass structure capable of emitting high-power laser light, fluctuations in output can be minimized, and stable and high-intensity (high-power) laser light can be generated.

[Brief description of the drawings]

FIG. 1 is a schematic flowchart (A) of a laser light generator according to the present invention and a schematic flowchart (B) of a laser light generator according to a comparative example.

FIG. 2 is a schematic flowchart of a main part of a laser light generator having a four-pass amplifier according to the present invention.

FIG. 3 is a schematic diagram (A) of a main part of a laser light generator having an amplifier having a four-pass structure, and a schematic diagram (B) showing a polarization state of laser light propagating through the laser light generator.

FIG. 4 is a schematic flowchart of a semiconductor exposure apparatus to which the present invention is applied.

FIG. 5 is a schematic perspective view of a phase modulator as a phase modulation means that can be used in the present invention.

FIG. 6 is a schematic flow diagram (A) of a main part of a laser light generator having a one-pass structure based on the prior art, and is a schematic flow diagram (B) of a main part of a laser light generator having a two-pass structure;

FIG. 7 is a schematic flow diagram of a main part of the laser light generating device having a four-pass structure (A), a schematic diagram showing the polarization state of laser light propagating through the laser light amplifier (B), and the inside of a gain medium of the amplifier; FIG. 4C is a schematic diagram (C) showing the generation of a standing wave at the point (a).

FIG. 8 is a graph showing a change in output intensity depending on an input intensity when using a laser optical amplifier having a one-pass structure, a two-pass structure, and a four-pass structure.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser light oscillation source (oscillator), 2 ... Phase modulation means (phase modulator), 3, 3A, 3B, 3C, 3a, 3b, 3c
... Laser amplifier, 4 ... Gain medium, 5A, 5B, 5C ...
Polarization rotation means, 6a, 6B, 6C, 6d, 6e: polarization separation means, 7A, 7B, 7C, 7d, 7e: laser light reflection means, 8: wavelength conversion device, 10: laser light generation device, 1
1A, 11B, 11a, 11b, 11c: polarizing beam splitter, 12, 12a, 12b: Faraday rotator, 13, 13a, 13b: 1/2 wavelength plate, 14: 1
/ 4 wavelength plate, 15A, 15B, 15a, 15b, 15c
... retroreflector, 21 ... prism, 22 ... slit, 23 ... uniform illumination device, 24 ... reticle, 25 ... lens, 26 ... semiconductor wafer, 27 ... projection device, 30 ... lithium borate (LBO) crystal plate, 31, 32 ... Β-barium borate crystal plate (β-BBO), 33a, 33d... Color separation mirror, 33b, 33c... Total reflection mirror, 40a, 4
0b: Potassium titanate phosphate plate (KTP), 41: Mount, 42: Voltage generator, 43: Voltage amplifier, 44:
Connector, 45, 46 ... surface, 51 ... node, 52 ... standing wave

Claims (30)

[Claims] 1. A laser light oscillation source for emitting laser light, phase modulation means for phase modulating the laser light emitted from the laser light oscillation source into a plurality of frequency components, and phase modulated by the phase modulation means. And a laser light amplifying means for amplifying the intensity by reciprocating the laser light a plurality of times in the gain medium in this order. 2. The laser light generator according to claim 1, wherein the phase modulation is performed by an electric signal including a plurality of frequency components. 3. The laser light amplifying means, wherein the laser light from the phase modulating means passes through a first polarization separating means, and then enters a first polarization rotating means to rotate its polarization direction; Further, after the laser light has passed through the second polarization separation means, the laser light has passed through the gain medium to perform first intensity amplification. Next, the laser light having undergone the first intensity amplification has passed through the second polarization separation means. Incident on the polarization rotation means, and its polarization direction is rotated,
After being reflected by the first laser light reflecting means provided on the optical path of the laser light, the laser light is again incident on the second polarization rotating means and its polarization direction is rotated, and passes through the gain medium. Then, the second intensity-amplified laser light is then separated by the second polarization splitting means, and the second laser provided on the optical path of the laser light. After being reflected by the light reflecting means, the laser is again separated by the second polarization separating means and passed through the gain medium to perform a third intensity amplification, and then the laser which has been subjected to the third intensity amplification The light is incident on the second polarization rotating means and its polarization direction is rotated. After being reflected by the first laser light reflecting means, the light is incident on the second polarization rotating means and its polarization direction is changed. Rotated Then, a fourth intensity amplification is performed by passing through the gain medium, and then, the laser light having been subjected to the fourth intensity amplification passes through the second polarization separating means, and the first polarization rotation is performed. 2. The laser beam generating apparatus according to claim 1, wherein said laser beam generator is configured to be incident on said unit, to rotate its polarization direction, and then to be separated and emitted by said first polarization separation unit. 4. The laser light generating apparatus according to claim 3, wherein said first polarization splitting means and said second polarization splitting means comprise a polarization beam splitter. 5. The laser beam generator according to claim 3, wherein said first polarization rotation means comprises a Faraday rotator and a half-wave plate, and said second polarization rotation means comprises a quarter-wave plate. . 6. The laser light generator according to claim 3, wherein said first laser light reflecting means and said second laser light reflecting means comprise reflecting mirrors. 7. A configuration in which a distance between the gain medium and the second laser light reflecting means is longer than a half of a coherent length of the laser light determined by the phase modulation means. 4. The laser light generator according to claim 3, wherein: 8. The solid-state laser oscillation source, wherein the laser beam oscillation source oscillates a pulse wave by a Q-switch method, or
2. A solid-state laser oscillation source for oscillating a continuous wave.
The laser light generator described in 1 above. 9. The laser light generator according to claim 3, wherein an average input intensity of the laser light incident on the laser light amplifying means is 1 W or less. 10. The laser medium of the laser light oscillation source comprises neodymium: yttrium vanadate, and the gain medium of the laser light amplification means comprises neodymium: yttrium aluminum garnet. Item 2. The laser light generator according to Item 1. 11. The laser medium of the laser light oscillation source and the gain medium of the laser light amplifying means are neodymium: yttrium aluminum garnet, neodymium: yttrium vanadate, neodymium-doped glass, neodymium: yttrium lanthanum fluoride. The laser light generator according to claim 1, comprising one kind of laser medium selected from the group consisting of: 12. The laser light generator according to claim 11, wherein a laser medium of the laser light oscillation source and a gain medium of the laser light amplifying unit have the same composition. 13. An erbium instead of neodymium,
The laser beam generator according to claim 11, wherein one kind of atom selected from the group consisting of praseodymium, ytterbium, thulium, holmium, and chromium is used as a dopant. 14. The laser light generator according to claim 1, further comprising a wavelength converter for converting a wavelength of the laser light whose intensity has been amplified by said laser light amplifier. 15. The laser light generator according to claim 14, wherein a harmonic component of the laser light is obtained by said wavelength converting means. 16. A laser light generating method, wherein a laser light is phase-modulated into a plurality of frequency components, and the phase-modulated laser light is reciprocated a plurality of times in a gain medium to amplify the intensity. 17. The laser light generation method according to claim 16, wherein the laser light is phase-modulated by an electric signal including a plurality of frequency components. 18. When the laser light is reciprocated a plurality of times in a gain medium to amplify the intensity, the phase-modulated laser light is passed through a first polarization separation means, and then a first polarization rotation means is provided. And the laser beam is rotated in the direction of polarization. Further, after passing the laser beam through the second polarization separation means, the laser beam is passed through the gain medium to perform first intensity amplification. After the laser light having been subjected to the intensity amplification is incident on the second polarization rotating means, the polarization direction is rotated, and the laser light is reflected by the first laser light reflecting means provided on the optical path of the laser light. Then, the laser light is again incident on the second polarization rotating means to rotate its polarization direction, and is passed through the gain medium to perform second intensity amplification. Next, the laser light having been subjected to the second intensity amplification And the second After being separated by the polarized light separating means and reflected by the second laser light reflecting means provided on the optical path of the laser light, it is separated again by the second polarized light separating means,
A third intensity amplification is performed by passing through the gain medium. Then, the laser light having been subjected to the third intensity amplification is incident on the second polarization rotating means to rotate its polarization direction, After being reflected by the first laser light reflecting means, the light is incident on the second polarization rotating means, rotated in the polarization direction, and passed through the gain medium to perform fourth intensity amplification. The laser light having undergone the fourth intensity amplification is passed through the second polarization splitting means, is incident on the first polarization rotating means, rotates the polarization direction thereof, and then rotates the first polarized light. The light is separated and emitted by the polarized light separating means.
The method for generating laser light described in 1. 19. The first polarization splitting means and the second polarization splitting means.
19. The laser beam generation method according to claim 18, wherein said polarization separation means is a polarization beam splitter. 20. The laser beam generating method according to claim 18, wherein said first polarization rotating means is a Faraday rotator and a half-wave plate, and said second polarization rotating means is a quarter-wave plate. 21. The laser light generating method according to claim 18, wherein said first laser light reflecting means and said second laser light reflecting means are reflecting mirrors. 22. The distance between the gain medium and the second laser light reflecting means, the distance being longer than half the coherent length of the laser light determined by the phase modulation means. The method for generating laser light described in 1. 23. The laser light for phase-modulating a plurality of frequency components from a solid-state laser oscillation source that oscillates a pulse wave by a Q-switch method or a solid-state laser oscillation source that oscillates a continuous wave. Item 18. The laser light generation method according to Item 16. 24. The laser beam generation method according to claim 18, wherein the average input intensity of the laser beam when the laser beam is reciprocated a plurality of times in the gain medium to amplify the intensity is 1 W or less. 25. A laser beam for phase-modulating a plurality of frequency components from a laser beam oscillation source, wherein a laser medium of the laser beam oscillation source is neodymium: yttrium-vanadate, and the gain is 17. The laser beam generation method according to claim 16, wherein the medium is neodymium: yttrium aluminum garnet. 26. The laser light for phase-modulating a plurality of frequency components from a laser light oscillation source, and the laser medium of the laser light oscillation source and the gain medium are:
Neodymium: Yttrium Aluminum Garnet,
17. The method for generating a laser beam according to claim 16, wherein the laser beam is one kind of laser medium selected from the group consisting of neodymium: yttrium-vanadate, neodymium-doped glass, and neodymium: yttrium-lanthanum-fluoride. 27. The laser beam generating method according to claim 26, wherein the laser medium of the laser beam oscillation source and the gain medium of the laser beam amplifying unit are media having the same composition. 28. Erbium in place of neodymium,
27. The laser beam generating method according to claim 26, wherein one kind of atom selected from the group consisting of praseodymium, ytterbium, thulium, holmium, and chromium is used as a dopant. 29. The laser beam generating method according to claim 16, wherein the wavelength of the laser beam after the intensity amplification by reciprocating a plurality of times in the gain medium is wavelength-converted by a wavelength conversion unit. 30. The laser light generating method according to claim 29, wherein a harmonic component of the laser light is obtained by the wavelength converting means.