JP5439530B2 - Discharge excitation laser equipment for exposure - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure discharge excitation laser apparatus, and more particularly to an exposure discharge excitation capable of reducing the spatial coherence of laser light and reducing speckles (interference fringes) generated on the mask and wafer of the exposure apparatus. The present invention relates to a laser device.

In recent years, excimer lasers have been used as light sources for semiconductor exposure apparatuses. In particular, in the technology node of 60 nm or less, an ArF laser light source having a high output (40 W or more) and an ultra-narrow band (0.2 pm or less) is adopted. It is shown below.
1. Along with ensuring high dose stability and increasing throughput, higher output of 90 W or higher is required. In addition, there is a demand for extending the life of laser light sources.
2. In order to satisfy the requirements of the light source, a double chamber ArF laser has been put into practical use. The form of the double chamber type laser device is roughly classified into a MOPA (Master Oscillator Power Amplifier) method in which no resonator mirror is provided on the amplifier side and a MOPO (Master Oscillator Power Oscillator) method in which a resonator mirror is provided.
3. Interference fringes (speckles) are generated on the mask illuminated by the illumination optical device of the exposure apparatus, and the interference fringes are achieved by reducing the spatial coherence of the laser light source and devising the illumination optical device of the exposure apparatus in order to suppress exposure spots. (Speckle) has been reduced.
In view of this, there have been proposed (i) a low spatial coherence of a double chamber type laser light source and (ii) a method for eliminating speckle in an illumination optical apparatus of an exposure apparatus.

Patent Document 1 proposes a MOPO laser device that injects seed light from an oscillation stage laser (MO) into a low coherence resonator of an amplification stage laser (PO).
By adopting the MOPO method with low spatial coherence, a higher amplification efficiency and a longer pulse width are realized while maintaining the beam quality equivalent to that of the MOPA compared to the MOPA method.
FIG. 25 is a diagram showing a schematic configuration of the MOPO system described in Patent Document 1. In FIG.
The laser beam emitted from the oscillation stage laser (MO) 100 functions as a seed laser beam, and the amplification stage laser (PO) 200 has a function of amplifying the seed laser light.
An oscillation stage laser (MO) 100 and an amplification stage laser (PO) 200 have laser chambers 101 and 201, respectively, filled with a laser gas, opposed to each other and spaced apart by a predetermined distance. These electrodes (not shown) are installed, and a high voltage pulse is applied to the pair of electrodes to generate a discharge.

The oscillation stage laser 100 has a narrow band module (LNM) 300 constituted by a magnifying prism 301 and a grating (diffraction grating) 302, and a laser resonator includes an optical element in the narrow band module 300 and a front mirror 102. Configure.
A laser beam (seed laser beam) from the oscillation stage laser 100 is injected into the amplification stage laser (PO) 200 via the conversion optical system 400 including a reflection mirror and the like, amplified and output.
The amplification stage laser (PO) 200 is provided with a set of light stable resonators including a rear mirror 211 and a front mirror 212. Then, the injected seed laser beam is reflected between the front mirror 212 and the rear mirror 211 as indicated by the arrows in the figure, and the power is increased by effectively passing through the discharge part and amplifying the laser beam. Laser light is output from the mirror 212.
In the one described in Patent Document 1, the MOPO method in which the seed light from the oscillation stage laser (MO) 100 is injected into the stable resonator of the amplification stage laser (PO) 200 is adopted, and the MOPO method with low spatial coherence is adopted. By adopting, the generation of interference fringes (speckles) on the mask of the exposure apparatus has been suppressed.

Patent Document 2 discloses a technique for reducing interference fringes (speckles) by devising an illumination optical device of an exposure apparatus. In other words, in a step-and-scan exposure apparatus, the laser beam has a direction in which spatial coherence is high, and the influence of speckle is reduced by moving the mask and wafer in that direction.
FIG. 26 shows a schematic configuration of the illumination optical device.
In FIG. 26, a laser beam emitted from an excimer laser light source 300 enters an oscillating mirror 303 through an optical system 301 including a reflecting mirror and a fly-eye lens 302. The oscillating mirror 303 scans the laser beam within a predetermined angle range on the horizontal plane.
The laser beam scanned by the oscillating mirror 303 is irradiated to the rectangular illumination area 310 having a width D in the short side direction on the reticle R via the optical system 304. The pattern image in the illumination area 310 is imaged and projected into a rectangular exposure area 311 on the wafer W via the projection optical system PL.

The reticle R is scanned in the scanning direction SR with respect to the illumination area 310, the wafer W is scanned in the scanning direction SW with respect to the exposure area 311 conjugate with the illumination area 310, and the pattern of the reticle R is sequentially exposed on the wafer W. .
As described above, the device described in Patent Document 2 has a vibrating mirror disposed in front of a fly-eye lens (optical integrator) in an illumination optical system, and scans the laser light incident on the optical integrator with the vibrating mirror. Thus, exposure is performed while changing the phase of the speckle pattern generated on the mask (reticle), thereby reducing exposure spots due to speckle.

International Publication No. 2004/095661 Pamphlet JP-A-6-349701

However, in the exposure of a fine pattern with a technology node of 45 nm or less, even if the conventional double chamber laser light source and the speckle reduction method by the illumination system of the exposure apparatus are combined, the fine speckle on the mask pattern is combined. The noise is not completely erased.
For this reason, a circuit pattern is formed on the wafer by a projection lens using a mask image in which minute speckle noise of 45 nm or less is generated, which affects the formation of a resist pattern of 45 nm or less.
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to reduce the spatial coherence of laser light, and to form a resist pattern by generating speckle noise when exposing a fine pattern of 45 nm or less. It is to reduce the adverse effects on.

In the present invention, the above-mentioned problem is solved by detecting the coherence of the final output beam by the coherence monitor and controlling it to have a predetermined coherence.
That is, in the present invention, the above problem is solved as follows.
(1) A narrow-band oscillation stage laser configured to output laser light, a chamber in which a laser gas is sealed, a pair of discharge electrodes provided in the chamber, and a discharge space of the discharge electrode The laser light from the narrow-band oscillation stage laser is injected into the resonator, and a high voltage pulse is applied to the discharge electrode for discharge to amplify the laser light. An amplification stage laser configured in the above, coherence changing means arranged on the optical path of the laser beam and configured to change the spatial coherence of the laser beam, and spatial coherence of the output laser beam output from the amplification stage laser Or measuring means for measuring a parameter correlated with spatial coherence, and control means for controlling the coherence changing means based on the measurement result of the measuring means; Provided.
(2) In the above (1), the control unit is configured so that the spatial coherence of the output laser beam output from the amplification stage laser or the integrated value of the spatial coherence falls within a predetermined upper limit and lower limit range. Control the coherence changing means.
(3) In the above (1) or (2), the control means controls the coherence changing means at least while the narrow-band oscillation stage laser is outputting laser light.
(4) In any one of the above (1) to (3), the control means controls the coherence changing means so that the spatial coherence of the laser light varies based on a predetermined program.
(5) In any one of the above (1) to (4), the measuring means is an apparatus for measuring beam divergence.
(6) In any one of the above (1) to (4), the measuring means is a Young interferometer or a sharing interferometer.

In the present invention, the following effects can be obtained.
Measuring means for measuring the spatial coherence of the output laser beam to be output or a parameter correlated with the spatial coherence is provided, and based on the measurement result of the measuring means, the spatial coherence of the output laser beam is set to a predetermined upper limit and lower limit. By controlling the spatial coherence of the laser light so as to be within the range, it is possible to prevent the influence of fluctuations in the attitude angle of the optical element due to temperature drift or the like, and to keep the spatial coherence of the output light more stable.

FIG. 1 is a diagram showing a basic configuration of a laser apparatus according to the present invention. FIG. 2 is a diagram illustrating a configuration example when a beam divergence monitor is used as a coherence monitor. FIG. 3 is a diagram showing a configuration example when a Young interferometer is used as a coherence monitor. FIG. 4 is a diagram illustrating a configuration example when a sharing interferometer is used as a coherence monitor. FIG. 5 is a diagram showing a first embodiment in which low spatial coherence is realized by shifting the attitude angle of the mirror of the resonator of the amplification stage laser (PO) with respect to the optical axis. FIG. 6 is a diagram showing a second embodiment in which low spatial coherence is realized by shifting the attitude angle of the resonator mirror of the amplification stage laser (PO) with respect to the optical axis. FIG. 7 is a diagram showing a configuration example of an actuator having a mirror holder with a general biaxial gimbal mechanism for driving a rear mirror, OC, and the like. FIG. 8 is a diagram showing an embodiment in which low spatial coherence is realized by installing a wavefront adjuster in the resonator of the amplification stage laser (PO) 20. FIG. 9 is a diagram showing an example of a wavefront adjuster in which cylindrical concave and convex lenses are combined. FIG. 10 is a diagram showing a first embodiment in the case where a ring-type resonator is employed as the resonator, and the direction of light is shifted every time the ring resonator is reciprocated. FIG. 11 is a diagram showing a second embodiment in the case where a ring-type resonator is employed as the resonator and the light resonator is installed so that the direction of light is shifted every time the ring resonator is reciprocated. FIG. 12 is a diagram showing an embodiment in which a ring type resonator is employed as the resonator and the wavefront of the light of the ring resonator can be adjusted by changing the curvature of the mirror. FIG. 13 is a diagram showing an embodiment in which a ring-type resonator is employed as a resonator and a wavefront adjuster is installed in the optical path of the ring resonator. FIG. 14 is a diagram showing a configuration example of an actuator for swinging a beam angle by a PO beam steering unit. FIG. 15 is a diagram showing a configuration example of an actuator for swinging the beam angle by the MO beam steering unit. FIG. 16 is a diagram illustrating a main flow of a flowchart for realizing low coherence. FIG. 17 is a diagram showing a subroutine for driving the actuator of the resonator mirror to stabilize the spatial coherence low and the condensing state at the condensing position of the outgoing beam. FIG. 18 is a diagram showing an example of a driving subroutine of an actuator that drives a mirror of the beam steering unit and a program pattern of angle swing. FIG. 19 is a diagram illustrating a main flow in the case where the spatial coherence is feedback-controlled. FIG. 20 shows an example of a subroutine for detecting a beam parameter having a correlation with the spatial coherence of the output laser beam. FIG. 21 is a diagram showing a first embodiment of a subroutine for evaluating with a movement integrated value of spatial coherence of output laser light. FIG. 22 is a diagram showing a second embodiment of a subroutine for evaluating with a movement integrated value of spatial coherence of output laser light. FIG. 23 is a diagram illustrating an example of a subroutine for driving the actuator based on the evaluation value of the spatial coherence of the output laser beam. FIG. 24 is a diagram illustrating an example of a subroutine for performing the adjustment oscillation. FIG. 25 is a diagram showing a schematic configuration of the MOPO method described in Patent Document 1. In FIG. FIG. 26 is a diagram showing a schematic configuration of an illumination optical apparatus that reduces the influence of speckles by moving a mask and a wafer.

FIG. 1 is a diagram showing a basic configuration of a laser apparatus of the present invention.
In this figure, the laser device of the present invention can be broadly divided into an oscillation stage laser (MO) 10 that outputs a laser beam having a narrow spectral width and a seed light output from the oscillation stage laser (MO) 10. It comprises an amplification stage laser (PO: Power Oscillator) 20 for resonating.
Also, an MO beam steering unit 30 for adjusting the injection angle of seed light output from the oscillation stage laser (MO) 10 into the amplification stage laser (PO) 20, and an optical resonator of the amplification stage laser (PO) 20 A PO beam steering unit 40 for adjusting the angle of the amplified light outputted from the optical pulse and an optical pulse stretcher (OPS) 50 for extending the pulse width of the light.
Furthermore, it has a coherence monitor 60 for monitoring the coherence of the laser beam, a laser shutter 65 for blocking the laser output beam, and a coherence controller 66 for feedback control of the coherence of the laser beam.

The oscillation stage laser (MO) 10 includes an output coupling mirror (OC) 14, a laser chamber 11 in which the discharge electrode 1 a is installed, and a band narrowing module (LNM) 3 for narrowing the spectral line width.
When a high voltage is applied to the discharge electrode 1a in the laser chamber 11 and discharge is performed, laser oscillation occurs between the optical resonators of the OC14 and the LNM3, and laser light having a narrow spectral width is output from the OC14. The LNM 3 includes a prism beam expander 3a and a diffraction grating 3b arranged in a Littrow arrangement. The wavelength is selected by this module and the spectrum is narrowed. As for the discharge electrode 1a, the anode and the cathode electrode are arrange | positioned on the same plane as the paper surface. The laser beam of the oscillation stage laser (MO) 10 is output in a rectangular beam shape that is long with respect to the discharge direction.
The beam from the oscillation stage laser (MO) 10 is reflected by the two high reflection mirrors 30 a and 30 b arranged in the MO beam steering unit 30, and seed light enters the resonator of the amplification stage laser (PO) 20. Inject.
A mirror holder (not shown) of the high reflection mirror 30b incorporates an actuator for changing the attitude angle of the mirror.

The amplification stage laser (PO) 20 includes a PO laser chamber 21 and an OC 24 in which a rear mirror 25 and a discharge electrode 2a are installed. When the seed light is injected into the resonator of the amplification stage laser (PO) 20, a high voltage is applied to the discharge electrode 2a inside the chamber 21 of the amplification stage laser (PO) 20 to discharge it. As a result, the seed light resonates between the rear mirror 25 and the OC 24 and amplifies and oscillates.
By arranging the optical element of the resonator of the amplification stage laser (PO) 20 so that the direction of the laser beam output from the resonator is deviated every time the resonator is reciprocated, the OC2 The direction of the output amplified beam can be shifted, and thereby the spatial coherence of the light output from the amplification stage laser (PO) 20 can be reduced.
Similarly, by installing a wavefront adjusting mechanism for adjusting the wavefront in the resonator of the amplification stage laser (PO) 20, and changing the wavefront in one direction by the wavefront adjustment mechanism, the amplification stage laser (PO) ) The spatial coherence of the light output from 20 can be reduced.

The beam output from the amplification stage laser (PO) 20 is reflected by the two high reflection mirrors 40 a and 40 b arranged in the PO beam steering unit 40 and enters the OPS 50.
The OPS 50 includes a beam splitter 50a for branching the main beam, relay lenses 50b and 50c for delaying the branched light and forming a transfer image, and high reflection mirrors 50d-50g.
The light output from the OPS 50 passes through a coherence monitor 60 for detecting coherence, and when an abnormality occurs in the output laser light, it passes through a shutter 65 installed so as not to transmit the laser light to the exposure apparatus. Is output.
The laser coherence controller 66 sends a command value to the PO resonator optical axis controller 67 based on the detection value of the coherence monitor 60, as will be described later. The PO resonator optical axis controller 67 outputs the amplification stage laser (PO) 20. The optical element of this resonator or a wavefront adjusting mechanism (not shown) for adjusting the wavefront installed in the resonator is controlled. Further, a drive signal is sent to the mirror actuator of the MO beam steering unit 30 and the mirror of the PO beam steering unit 40, and the angles of these mirrors are controlled so that the coherence of the output laser beam becomes a desired value. .

Next, a configuration example of the coherence monitor 60 will be shown.
FIG. 2 shows a configuration example when a beam divergence monitor is used as the coherence monitor of the present invention.
FIG. 2A shows a side view of the beam divergence monitor, and FIG. 2B shows a perspective view. A part of the laser light output from the OPS 50 is introduced into the condenser lens 61b by the beam splitter 61a, and a two-dimensional CCD 61c is disposed on the focal plane of the condenser lens 61b, and its profile is measured.
The beam divergence D is calculated as follows.
D = BD / f (1)
Here, f is the focal length of the condenser lens 61b, and BD is the profile width on the condenser surface at the focal position of the condenser lens 61b. For example, the profile width BD may be calculated by the full width at a value of 1 / e ² .

Since the coherent length Xc of the spatial coherence and the laser beam divergence D are inversely proportional as shown in the following equation (2) (Document: Proceedings. SPIE Vol. 1138 Optical Microlithography and Metrology for Microcircuit 9 (198)). When the beam divergence D is calculated, the coherent length Xc of spatial coherence can be obtained from the following equation. Where λ is the wavelength.
D · Xc = 2λ (2)
Here, the coherent length Xc of the spatial coherence is a share interval (or pinhole interval) at which the interference fringe contrast becomes a predetermined amount (for example, 1 / e ² ) or less. The share interval (or pinhole interval) will be described later.
In general, when the discharge-excited excimer laser beam divergence is defined as the V direction in the same direction as the discharge direction and defined as the H direction perpendicular to the discharge, the beam divergence Dv in the V direction and the beam divergence Dh in the H direction are There is the following relationship.
Dv> Dh (3)
As an evaluation of the beam divergence, it is possible to evaluate the discharge direction V and the direction H perpendicular to the discharge.

The advantages of the coherence monitor by the above-described beam divergence monitor measurement are as follows.
(1) The configuration of the measurement system is relatively simple and can be easily configured.
(2) Laser pointing (outgoing direction) can also be measured and can be a monitoring device for pointing.
(3) The amount and direction of the attitude angle of the mirror for reducing coherence can be detected by pointing measurement, and feedback control can be performed based on the detected value.

FIG. 3 shows a configuration example when a Young interferometer is used as a coherence monitor.
3A shows an optical layout of Young's interferometer, and FIG. 3B shows a schematic diagram of interference fringes detected by the CCD.
In FIG. 3A, a part of the laser beam output from the OPS 50 is sampled by the beam splitter 62a, and the laser beam is irradiated to the double pinhole 62b having a pinhole interval of a predetermined interval X. The lights transmitted through the double pinhole 62b interfere with each other to generate interference fringes. The interference fringe profile is measured by the CCD 62c.
(B) is a schematic diagram of interference fringes detected by the CCD. The contrast C of the interference fringes is calculated by the following equation (4).

Here, Imax is the maximum value of the interference fringes, and Imin is the minimum value of the interference fringes.
The higher the contrast C of the interference fringes, the higher the spatial coherence. The lower the contrast C, the lower the spatial coherence.
When measuring the coherence in the discharge direction V and the vertical direction H of the discharge, it is possible to measure by rotating the transmission type rotary stage 62d so that the double pinholes 62b are arranged in the V direction and the H direction, respectively.
As another example, four pinholes may be provided so as to be arranged in the V direction and the H direction, and profiles in the V direction and the H direction may be detected by the CCD.
Further, it is preferable that the pinhole interval is substantially the same as the interval between the fly-eye lenses provided in the exposure apparatus (the interval between adjacent fly-eye lenses). That is, the distance between the fly-eye lenses determines the degree of interference on the exposure surface. By providing pinholes at the same interval, the degree of interference on the exposure surface can be reflected as it is.
However, this is not the case when the pitch interval of the fly-eye lens is so small that a double pinhole cannot be produced. Manufacture at a predetermined pinhole interval, measure the contrast, and calculate the relative value of the spatial coherence height. You may compare.

FIG. 4 shows a configuration example when a sharing interferometer is used as a coherence monitor.
FIG. 4A shows an optical layout of a shearing interferometer, and FIG. 4B shows the relationship between the shear amount ΔS and the contrast of interference fringes observed by the CCD.
In FIG. 4A, the sharing interferometer includes a diffraction grating 63b for diffracting light, a condensing lens 63c for condensing parallel light, and 2-hole light shielding that cuts zero-order light and transmits ± first-order light. The plate 63d is composed of a collimator lens 63e for forming an image of the diffraction grating 63b and a CCD 63f for measuring the profile of interference fringes.
A diffraction grating 63b is disposed on the front focal plane of the condenser lens 63c, and a two-hole light shielding plate 63d that transmits ± primary light is disposed on the rear focal plane. Further, the collimator lens 63e is arranged so that the position of the two-hole light shielding plate 63d that transmits ± primary light is the front focal plane of the collimator lens 63e, and the image of the diffraction grating 63b is formed on the rear focal plane of the collimator lens 63e. Forms an image. The CCD 63f is arranged at a position separated by a distance Z from the reference position of the position of the diffraction image.

A part of the laser beam output from the OPS 50 is sampled by the beam splitter 63a, and the diffraction grating 63b with a predetermined interval α is irradiated with the laser beam. The light transmitted through the diffraction grating 63b is diffracted and enters the condenser lens 63c. The light diffracted by the diffraction grating 63b is collected for each order on the focal plane of the condenser lens 63c. Here, the interval between the condensing points of ± primary light is d. The ± first-order light is transmitted through the two-hole light-shielding plate 63d, and the other orders (0th-order light, ± second-order light) are shielded. The + 1st order light and the −1st order light form an image of the diffraction grating on the rear focal plane of the collimator lens 83e through the collimator lens 63e.
In general, the equation of diffraction is expressed as follows.
mλ = a (sin α + sin β) (5)
Here, m is the order of the diffracted light, a is the groove interval of the diffraction grating, α is the incident angle (= 0) of the diffraction grating, and β is the emission angle of the diffracted light.
The diffraction angle β of the first-order light is obtained from the equation (5) as follows: β = sin ⁻¹ (λ / a) (6)
The space | interval d of +/- primary light can be calculated | required with the following formula | equation.
d = 2 tan β · f (7)

When the distance between the image of the diffraction grating 63b and the CCD 63f is Z, the shear amount ΔS is expressed by the following equation.
ΔS = (d / f) Z (8)
FIG. 4B shows the relationship between the shear amount ΔS and the interference fringe contrast C observed by the CCD 63f, and the contrast C is calculated by the above equation (4).
The contrast C at the share amount ΔS = 0 (Z = 0 when the position of the CCD 63f is on the image plane of the diffraction grating) is 1. By changing the position of the CCD 63f little by little, the interference fringes at that time are evaluated. The contrast can be calculated.
In general, the contrast of the interference fringes decreases as the share amount ΔS increases. For example, the amount of share at which the contrast becomes 1 / e ² can be used as the spatial coherence index as the spatial coherent length Xc.

As a measure of coherence, the position of the CCD 63f may be fixed so that the pitch interval of the fly-eye lens of the exposure apparatus and the shear amount ΔS substantially match, and the contrast of interference fringes may be evaluated, or the position of the CCD 63f may be scanned. Then, the relationship between the shear amount ΔS and the interference fringe contrast observed by the CCD 63f may be measured and evaluated. When measuring the coherence in the discharge direction V and the direction H perpendicular to the discharge, the transmission type rotary stage 63g is rotated so that the pitch directions of the diffraction grating 63b are aligned in the V direction and the H direction, respectively. It becomes possible by measuring.
The advantages of sharing interferometers compared to Young's interferometers are shown below.
(1) The share amount ΔS can be arbitrarily set (measurement is possible even with a share amount where a double pinhole cannot be manufactured).
(2) The coherent length Xc of spatial coherence can be measured by measuring the relationship between the share amount ΔS and the contrast C of the interference fringes.

FIG. 5 shows a first embodiment in which low spatial coherence is realized by shifting the attitude angle of the mirror of the resonator of the amplification stage laser (PO) 20 with respect to the optical axis.
FIG. 5A shows a side view of the oscillation stage laser 10 and the amplification stage laser (PO) 20 of this embodiment.
An oscillation stage laser (MO: Master Oscillator) 10 includes an MO laser chamber 11 in which an OC 14 and a discharge electrode 1a are installed, and a narrowband module (LNM) 3 for narrowing the spectral line width. When a high voltage is applied to the discharge electrode 1a in the laser chamber 11 and discharge occurs, laser oscillation occurs between the optical resonators OC14 and LNM3, and laser light having a narrow spectral width is output from the OC14.
The LNM 3 includes a prism beam expander 3a and a diffraction grating 3b arranged in a Littrow arrangement. The wavelength is selected by this module and the spectrum is narrowed. As for the discharge electrode 1a, the anode and the cathode electrode are arrange | positioned on the same plane as the paper surface. The laser beam of the oscillation stage laser (MO) 10 is output in a rectangular beam shape that is long with respect to the discharge direction. The spatial coherence of this beam is higher in the direction H perpendicular to the discharge than in the discharge direction V.

The MO beam is reflected by the two high reflection mirrors 30 a and 30 b arranged in the MO beam steering unit 30 and injects seed light into the resonator of the amplification stage laser (PO) 20.
The amplification stage laser (PO) 20 includes a PO laser chamber 21 and an OC 24 in which a rear mirror 25 and a discharge electrode 2a are installed. In synchronism with the injection of the seed light into the resonator of the amplification stage laser (PO) 20, a high voltage is applied to the discharge electrode 2a inside the chamber 21 of the amplification stage laser (PO) 20 to discharge.
As a result, the seed light resonates between the rear mirror 25 and the OC 24 and amplifies and oscillates. Here, the posture angle of the rear mirror of the resonator of the amplification stage laser (PO) 20 is arranged so that the beam emission angle is shifted depending on the number of times the amplified light is reciprocated. Further, the optical path length of the PO resonator is configured to be shorter than the temporal coherent length of the MO laser light. By doing so, beams of each round-trip number amplified by the amplification stage laser (PO) 20 do not interfere with each other.

FIG. 5B shows a top view of the amplification stage laser (PO) 20.
The MO beam having a narrow spectrum is reflected by the high reflection mirror 30b, is incident on the discharge space obliquely through the window 22a from the rear mirror 25 of the PO resonator provided with the partial reflection film, and is perpendicular to the discharge in the discharge region. Then, the light is transmitted through the end in the direction H, amplified, transmitted through the window 22b, transmitted through the OC 24 with the partially reflective film, and output as 0.5 round-trip light.
Then, the light reflected by the OC 24 transmits and amplifies the discharge region in the PO chamber 21 through the window 22b at the reflection angle α1, and reaches the rear mirror 25 through the window 22a.
The posture angle of the rear mirror 25 is set in a state where the posture angle of the mirror is shifted in the H direction (direction perpendicular to the discharge) with respect to the normal line of the OC 24. The rear mirror 25 reflects the light at a reflection angle β1, enters the discharge region again through the window 22a, passes through the discharge region, is amplified, and passes through the OC 24 through the window 22b to be output.
The reflected light is reflected at an angle α2, and is again transmitted and amplified through the window 22b through the window 22b. The reflected light is reflected at the reflection angle β2 by the rear mirror 24 through the window 22a and passes through the window 22a. After transmission amplification, the light reaches the OC 24 through the window 22b, and the transmitted light is extracted as output light, and the reflected light is returned as feedback light.
The incident / reflection angle of each mirror has a relationship of α1>β1>α2>β2>.

In this embodiment, the orientation angle of the rear mirror 25 is shifted in the H direction and the axis of the OC 24 is shifted, so that the direction of the amplified beam output from the OC 24 is shifted every reciprocation.
Thereby, the beam die beam divergence can be increased. That is, the light transmitted through the OC 24 and the light reflected and output again after reciprocating through the laser resonator are not coherent with each other. This has the same effect as shifting the position of a plurality of non-interfering light sources to increase the size of the light source. As a result, the spatial coherence of the light output from the amplification stage laser (PO) is lowered.
The rear mirror 25 in this example is coated with a partial reflection film, and operates normally within a range of 60% to 90%.

FIG. 6 shows a second embodiment in which low spatial coherence is realized by shifting the attitude angle of the resonator mirror of the amplification stage laser (PO) with respect to the optical axis.
FIG. 6 shows a top view of the amplification stage laser (PO), and a side view of the amplification stage laser (PO) is the same as FIG. Differences from FIG. 5 are as follows.
(1) A region coated with an antireflection (AR) film for transmitting all seed light is provided on the surface of the rear mirror 25 on the resonator side, and the region where the seed light resonates and reflects is high. A reflective (HR) film is coated. The other surface is coated with an AR film.
(2) A partial reflection (PR) film for functioning as the OC 25 on the surface of the OC 25 and a high reflection (HR) for highly reflecting the seed light in order to inject seed light from the OC 25 side. ) A region coated with a film is provided, and the other side is coated with an antireflection (AR) film.

The MO beam having a narrow spectrum is reflected by the high reflection mirror 30b, passes through the AR coat area of the rear mirror 25 of the PO resonator obliquely through the window 22a, passes through the discharge area, and passes through the window 22b to transmit the high reflection film of the OC24. Reaches the coated area.
The light totally reflected by the high reflection film of the OC 24 is transmitted and amplified at the end in the H direction of the discharge region in the PO chamber 21 through the window 22b at the reflection angle α1, and the rear mirror 25 is passed through the window 22a. To the HR part. The posture angle of the rear mirror 25 is set in a state where the posture angle of the mirror is shifted in the H direction with respect to the normal line of the OC 24. The rear mirror 25 reflects the light at a reflection angle β1, and again transmits and amplifies the discharge region through the window 22a, and transmits through the window 22b and is output through the OC 24 (one round-trip light).
The reflected light is reflected at an angle α2, and is again transmitted and amplified through the window 22b through the window 22b. The reflected light is reflected by the rear mirror 25 at the reflection angle β2 through the window 22a. Then, the discharge space is transmitted and amplified through the window 22a, reaches the OC 24 through the window 22b, the transmitted light is extracted as output light (two reciprocating light), and the reflected light is returned as feedback light.
The incident / reflection angle of each mirror has a relationship of α1>β1>α2>β2>.

In this embodiment, the orientation angle of the rear mirror 25 is shifted in the H direction and the axis of the OC 24 is shifted, so that the direction of the amplified beam output from the OC 24 is shifted every reciprocation. Thereby, beam divergence can be increased.
That is, the light transmitted through the OC 24 and the light reflected and output again after reciprocating through the laser resonator are not coherent with each other. This has the same effect as shifting the position of a plurality of non-interfering light sources to increase the size of the light source. As a result, the spatial coherence of the light output from the amplification stage laser (PO) is lowered.
Compared to the embodiment of FIG. 5, the merit of the embodiment of FIG. 6 is that the seed light injection efficiency is increased and the spatial coherence is lowered with respect to the H direction. It is in the point that can be reduced.

Here, in general, in the discharge cross section of the discharge excitation excimer laser, the width of the discharge electrode in the discharge direction (V direction) is longer than the width in the direction perpendicular to the discharge (H direction). Therefore, the cross section of the laser beam is output in a rectangular shape (for example, 2 mm in the H direction and 12 mm in the V direction). Beam divergence (for example, 1 mrad in the H direction and 1.5 mrad in the V direction) Therefore, the spatial coherence in the V direction is lower than that in the H direction.
Therefore, by shifting the beam output from the OC 24 in the H direction with high spatial coherence for each direction reciprocation, spatial coherence in the H direction equivalent to the V direction can be obtained, and speckle on the mask surface of the exposure apparatus. Can be greatly reduced.
For example, assuming that the beam width and beam divergence in the H direction output from the amplification stage laser (PO) are Wpoh and Dpoh, respectively, and the beam width and beam divergence in the V direction are Wpov and Dpov, respectively, the following equation (9) By adjusting and fixing the alignment of the mirror of the PO resonator so that the above holds, speckles in the exposure apparatus can be significantly reduced.
Wpoh / Dpoh = Wpov / Dpov (9)

The merit of this method is that the speckle on the mask of the exposure apparatus can be reduced by shifting the alignment of the PO resonator with respect to the direction with high spatial coherence (that is, the direction perpendicular to the discharge (H direction)). .
Further, by adjusting and fixing the posture angle of the mirror of the PO resonator so that the relationship as expressed by the equation (9) is satisfied, the laser beam is adjusted to have the same size in the V direction and the H direction. Even if the direction of the beam expands, the spatial coherence is the same. Therefore, even if it enters the fly-eye lens of the illumination optical system of the exposure apparatus, the generation of speckle becomes very small and the directionality is lost.

The present invention is not limited to the above embodiment, and may be configured as follows, for example.
(1) Although the posture angle of the rear mirror 25 is shifted, the angle of the OC 24 may be shifted.
(2) In the embodiment of FIG. 5, a region coated with the AR film used in the embodiment of FIG. 6 and a rear mirror coated with the HR film may be installed as the rear mirror. In this case, the same operation is possible even if the seed beam injection position of the oscillation stage laser (MO) 10 is set to the AR-coated region of the region-coated rear mirror, and this region is injected into the PO resonator. . In short, any method can be used as long as the alignment of the PO resonator is shifted to change the beam direction for each round trip.
(3) In the embodiment of FIGS. 5 and 6, seed light is injected obliquely from the direction of the OC 24 so as not to overlap with the output laser light, and the alignment of the PO resonator is shifted to change the beam direction for each round trip. A method of changing may be used.
5 and FIG. 6, the resonator configuration of the rear mirror 25 of the plane mirror and the OC 24 of the plane mirror is used. However, if the resonator is a stable resonator, the resonator is configured by the rear mirror 25 and the OC 24 with curvature. The alignment of the OC 24 and the rear mirror 24 may be shifted so that the direction of the emitted laser beam is shifted every reciprocation by shifting the optical axes of the OC 24 and the rear mirror 25.

Here, a configuration example of an actuator that swings the rear mirror 25 and the like will be described.
FIG. 7 shows a configuration example of an actuator having a mirror holder with a general biaxial gimbal mechanism for driving a rear mirror, OC, and the like.
In this mirror holder with a gimbal mechanism, an L-shaped plate 72 and a plate 71 to which a mirror 70 is attached are supported at three points: a moving pin 76a of a pulse motor 73a, a moving pin 76b of a pulse motor 73b, and a fulcrum 77. These plates are fixed by tension springs 75a and 75b.
In the operation of this mirror holder, the posture angle of the plate 71 changes as the moving pins 76a and 76b of the pulse motors 73a and 73b are put in and out. Further, in this example, PZT (piezo elements) 74 a and 74 b are installed between the moving pins 76 a and 76 b and the plate 71. By applying a high voltage to the PZTs 74a and 74b, the thickness can be changed at high speed. Therefore, it is possible to drive the PZTs 74a and 74b for each pulse to swing the attitude angle of the mirror.
Further, by driving the pulse motor 73a and the pulse motor 73b, the posture angle of the biaxial mirror 70 can be changed.
In order to change the direction of the beam output from the resonator of the amplification stage laser (PO) 20 for each reciprocation, it is not necessary to control, so a micrometer is installed in place of the pulse motor and a predetermined scale is set. The position may be adjusted and fixed.
Further, the mirror adjustment mechanism is not limited to the cymbal mechanism, and any mechanism that can adjust the attitude angle of the mirror may be provided. FIG. 7 shows the case where the mirror is arranged on the plate. However, when the laser beam is transmitted like the rear mirror or the OC, the end of the mirror is attached to the plate so that the laser beam can be transmitted. To.

FIG. 8 shows an embodiment in which low spatial coherence is realized by installing a wavefront adjuster 80 in the resonator of the amplification stage laser (PO) 20.
FIG. 8A shows a side view of the oscillation stage laser (MO) 10 and the amplification stage laser (PO) 20 of the present invention.
The beam of the oscillation stage laser (MO) 10 is reflected by two high reflection mirrors 30a and 30b arranged in the MO beam steering unit 30 and is used as seed light in the resonator of the amplification stage laser (PO) 20. Injected.
The amplification stage laser (PO) 20 is composed of a rear mirror 25 (reflectance R = 60% to 90%) coated with partial reflection, a PO laser chamber 21 in which discharge electrodes are installed, a wavefront adjuster 80 and an OC 24. .
When the seed light is injected into the resonator of the amplification stage laser (PO) 20, a high voltage is applied to the discharge electrode 2a inside the chamber 21 of the amplification stage laser (PO) 20 to discharge. As a result, the seed light resonates between the rear mirror 25 and the OC 24 and amplifies and oscillates.

Here, a wavefront adjuster 80 is installed between the PO chamber 21 and the OC 24 of the resonator of the amplification stage laser (PO) 20, and the wavefront adjuster 80 can change the spatial coherence and beam divergence of the outgoing beam. . The resonator length L of the amplification stage laser (PO) is configured to be longer than the temporal coherent length lc / 2 of the MO laser light. Here, the temporal coherent length lc of the laser is expressed by the following equation.
lc = λ ² / Δλ
λ: center wavelength of laser, Δλ: spectral line width of MO.
By doing so, beams of each round-trip number amplified by the amplification stage laser (PO) 20 do not interfere with each other.
FIG. 8B shows a top view of the amplification stage laser (PO).
The MO beam having a narrow spectrum is reflected by the high reflection mirror 30b, enters the discharge region from the rear mirror 25 of the PO resonator through the window 22a, passes through the discharge region, is amplified, and is amplified through the window 22b. 80, and the wavefront changes in a cylindrical shape in a plane perpendicular to the discharge direction. Then, the light passes through the OC 24 and is output as 0.5 round trip light.
The light reflected by the OC 24 is changed again by the wavefront adjuster 80 in the plane in the H direction, and the discharge region in the PO chamber 21 is transmitted and amplified through the window 22b, and is transmitted to the rear mirror 25 through the window 22a. To reach. This light is reflected by the rear mirror 25, and is transmitted and amplified again through the window 22a. Then, the wavefront is changed in the H direction by the wavefront adjuster 80 through the window 22b and transmitted through the OC24. Is output. The reflected light is returned as feedback light and this is repeated.

The rear mirror 25 in this example is coated with a partial reflection film, and operates normally within a range of 60% to 90%.
By combining an uneven cylindrical lens as a wavefront adjuster, the wavefront in the H direction can be adjusted without changing the wavefront in the V direction.
In this example, the wavefront adjuster 80 is installed between the OC 24 and the PO chamber 21 of the amplification stage laser (PO), but the present invention is not limited to this, and may be installed between the rear mirror 25 and the PO chamber 21. .
Further, a wavefront may be adjusted by installing a deformable mirror that can freely change the curvature of the rear mirror 25 or the OC 24.

FIG. 9 shows an embodiment of a wavefront adjuster that combines cylindrical concave and convex lenses.
9A and 9B show a top view and a side view of the wavefront adjuster, respectively.
The cylindrical concave lens 80 a is fixed on a uniaxial automatic stage 81 that moves in the optical axis direction, and the cylindrical convex lens 80 b is fixed on a plate 84. The single-axis automatic stage 81 is provided with a pulse motor 85 and a PZT 86. When moving at a high speed and small, the PZT 86 can be moved for each pulse.
When it is moved largely, the stage 81 can be moved greatly by the pulse motor 85. Such an automatic stage 81 is necessary when the spatial coherence is adjusted to a desired range required by the exposure apparatus.

In FIG. 10, a ring resonator is used as the resonator of the amplification stage laser (PO) 20, and the orientation angle of at least one mirror deviates the direction of the light output from the OC 25 each time the ring resonator is reciprocated. The 1st Example at the time of installing in this way is shown.
FIGS. 10A and 10B show a top view and a side view of the oscillation stage laser (MO) 10 and the amplification stage laser (PO) 20, respectively.
As shown in FIG. 10B, on the output side of the chamber 21 of the amplification stage laser (PO) 20, an OC 24 that partially reflects at 45 degrees incidence and a high reflection mirror 31 a that highly reflects at 45 degrees correspond to each other. It is arranged so that the angle of the surface is 90 degrees. Further, on the rear side of the PO chamber 21, two high-reflection mirrors 31b and 31c that are highly reflective at 45 ° incidence are provided so that the angle between the surfaces is slightly smaller than 90 °. Has been placed.
The mirror surfaces of the OC 24 and the high reflection mirrors 31a, 31b and 31c are installed in parallel to the discharge surfaces of the electrodes. That is, the optical axis of the ring resonator of the amplification stage laser (PO) 20 is disposed so as to include a plane perpendicular to the discharge surface. Further, the intersection of the mirror surface of the OC 24 and the high reflection mirror 31a and the intersection of the mirror surfaces of the high reflection mirrors 31b and 31c are arranged to coincide with each other.

The MO beam is incident on the end of the OC 24 of the amplification stage laser (PO) 20 at an incident angle of 45 degrees by the high reflection mirror 30c. A part of this beam passes through the OC 24 and enters and reflects the highly reflective mirror 31a at 45 degrees. The seed light passes through the window 22a and enters the laser chamber 21. The seed light passes through the discharge electrode 2a with a substantially parallel optical axis and passes through the chamber 21 without being amplified.
Further, the seed light is incident on and reflected by the high reflection mirror 31b at 45 degrees, and is reflected by the high reflection mirror 31c at an angle slightly smaller than 45 degrees. In the case of incident / reflected at 45 degrees, the angle of β is 90 degrees, and the light advances as shown by the dotted arrow in the figure and returns to the position where it coincides with the injection position at OC.
On the other hand, in the present invention, the reflection angle of the high reflection mirror 31c is made slightly smaller than 45 degrees to transmit and amplify the discharge space, and enters the OC 24 at a position moved from the injection position as shown in FIG. The light transmitted through the OC 24 is output as output laser light (amplified light by one round trip).

  On the other hand, the reflected light from the OC 24 is returned to the laser chamber 21 by the total reflection mirror 31a again with an optical axis slightly inclined with respect to the first round-trip PASS, and is transmitted through the chamber 21 without being amplified. Incident on 31b and 31c. Then, the light is returned to the laser chamber 21 again, and is transmitted through the discharge space and amplified by the optical axis translated by a predetermined distance with respect to the first round-trip PASS. The amplified light moves at a constant rate with respect to the first round trip, the beam is incident on the OC 24 again, the reflected light is output as a laser beam, the transmitted light resonates in the resonator again, and the third round trip is also performed. Similarly, the optical path tilts and resonates each time it reciprocates. As a result, the direction of the beam output from the OC 24 changes every round trip.

  In this embodiment, the direction of the amplified beam output from the OC 24 is shifted every reciprocation by shifting the attitude angle of the ring resonator in the H direction. Thereby, the beam divergence can be increased as in the case of the Fabry-Perot resonator. That is, the resonator length L of the amplification stage laser (PO) 20 is configured to be longer than the temporal coherent length lc / 2 of the MO laser light. For this reason, the light that has passed through the OC 24 and the light that has been reflected and output again through the laser resonator are not coherent. This has the same effect as shifting the position of a plurality of non-interfering light sources to increase the size of the light source. As a result, the spatial coherence of the light output from the amplification stage laser (PO) 20 is lowered.

As described above, the MO laser light is injected into the ring resonator of the amplification stage laser (PO) 20, and the injected light is injected at the injection position for each round trip of the amplification stage laser (PO) 20 laser. In addition to the advantages of the embodiment of FIG. 5, there are the following advantages by arranging an optical resonator that reciprocates while moving in a substantially vertical direction (H direction) with respect to the surface and is amplified for each reciprocation.
(1) The injection efficiency is higher than the injection method from the rear surface of the rear mirror as in the embodiment of FIG.
(2) Since the beam of the laser beam inside the ring resonator moves and the beam width widens every time it is reciprocated, the energy density of the laser beam in the optical element (OC, laser window, and high reflection mirror) of the ring resonator of the PO laser is reduced. Is done. Therefore, the lifetime of the optical element of the amplification stage laser (PO) is extended.

Further, in this embodiment, the position of the beam for each round trip is moved by reflecting the angle of the high reflection mirror 31c within a plane perpendicular to the discharge direction at an angle greater than 45 degrees. Without being limited to this embodiment, at least one of the mirrors constituting the ring resonator is shifted from the incident / reflective angle (here 45 degrees) of the other mirrors, so The beam position on the OC may be moved so that the beam emitted from the OC 24 is shifted in the H direction for each round trip.
Furthermore, in this embodiment, an example of a ring resonator composed of a plane mirror has been shown. However, the present invention is not limited to this example, and a ring resonator composed of a mirror with a curvature constituting a stable resonator. Similarly, the same effect can be obtained by shifting the attitude angle of the mirror with curvature in the plane perpendicular to the discharge direction so that the direction of the laser beam output from the OC is shifted every time the resonator is reciprocated. Can do.

In FIG. 11, a ring-type resonator is employed as the resonator of the amplification stage laser (PO) 20, and the orientation angle of at least one mirror is determined so that the direction of light output from the OC 24 each time the ring resonator is reciprocated. A second embodiment in the case of installation so as to deviate will be shown.
Differences from the embodiment of FIG. 10 are as follows.
(1) A ring resonator of the type that amplifies through the discharge space in both the forward path and the return path is employed as the ring resonator.
(2) Intersection of the surfaces of the high reflection mirrors 31b and 31c, where A is the distance between the intersection of the surface of the OC 24 and the high reflection mirror 31a and the center of the optical axis of the laser (a line perpendicular to the discharge direction and passing through the center of the discharge region). And the distance between the centers of the optical axes of the lasers is B, and the sizes of A and B are approximately equal.
Also in this embodiment, the surfaces of the OC 24 and the high reflection mirrors 31a, 31b and 31c are installed in parallel to the surface in the discharge direction, and the light of the ring resonator travels in a plane perpendicular to the surface in the discharge direction.

The operation of this resonator will be described below.
The MO beam is incident on the end of the OC 24 of the amplification stage laser (PO) 20 at β1 = 45 degrees by the high reflection mirror 30c. It passes through the OC 24 coated with a 45 degree partial reflection (PR) film, enters the high reflection mirror 31a at an incident angle α1 (an angle several mrad smaller than 45 degrees), passes through the window 22a, and passes through the amplification stage laser (PO). ) Inclined into the discharge space of the laser chamber 21 of 20, and a voltage is applied to the discharge electrode 2a in synchronization with the seed light to discharge.
Then, the seed light transmitted through the discharge space is amplified, transmitted through the window 22b, and is incident and reflected on the high reflection mirror 31c at an incident angle α2 (= α1).

  Then, the light is incident and reflected on the high reflection mirror 31b at an incident angle β2 at an angle slightly smaller than 45 degrees, is transmitted through the window 22b along the optical axis parallel to the longitudinal direction of the discharge electrode, and is led to the discharge space where the discharge is performed again. Amplified. Then, the beam moves in a plane perpendicular to the plane in the discharge direction from the injection portion, enters the OC 24, partially transmits, and becomes laser output light (one reciprocating light). Light that is incident on the reflection mirror 31a, is similarly transmitted through the discharge space with the optical axis shifted from the first round-trip PASS, and is again shifted from the discharge space by the high-reflection mirrors 31b and 31c with respect to the first round-trip PASS. Transmitted by the axis, moved relative to the first reciprocation, the beam again enters the PR part (partial reflection region) of the OC 24, the transmitted light is output as laser light, and the reflected light resonates again in the resonator, Similarly, in the third round trip, each time the round trip is made, the optical path is shifted and the oscillation is amplified. As a result, the direction of the beam output from the OC 24 changes every round trip.

In this embodiment, by shifting the attitude angle of the ring resonator in the H direction, the direction of the amplified beam output from the OC 24 is shifted every reciprocation. Thereby, the beam divergence can be increased as in the case of the Fabry-Perot resonator. That is, the resonator length L of the amplification stage laser (PO) 20 is configured to be longer than the temporal coherent length lc / 2 of the MO laser light. For this reason, the light that has passed through the OC 24 and the light that has been reflected and output again through the laser resonator are not coherent. This has the same effect as shifting the position of a plurality of non-interfering light sources to increase the size of the light source. As a result, the spatial coherence of the light output from the amplification stage laser (PO) 20 is lowered.
As described above, the MO laser light is injected into the ring resonator of the amplification stage laser (PO) 20, and the injection position of the injected light with respect to the discharge surface of the amplification stage laser (PO) 20 is reciprocated. In addition to the merit of the embodiment of FIG. 10 by arranging an optical resonator that amplifies for each round-trip while moving in a substantially vertical direction (H direction), the amplification efficiency increases because the amplification is performed in the forward path and the backward path. There are benefits.

Further, in this embodiment, the position of the beam for each round trip is moved by reflecting the angle of the high reflection mirror 31c within a plane perpendicular to the discharge direction at a reflection angle smaller than 45 degrees. Without being limited to this embodiment, at least one of the mirrors constituting the ring resonator is shifted from the incident / reflective angle (here 45 degrees) of the other mirrors, so The position of the beam on the OC may be moved so that the beam emitted from the OC2 is shifted in the H direction every round trip.
Furthermore, in this embodiment, an example of a ring resonator composed of a plane mirror has been shown. However, the present invention is not limited to this example, and a ring resonator composed of a mirror with a curvature constituting a stable resonator. Similarly, the same effect can be obtained by shifting the attitude angle of the mirror with curvature in the plane perpendicular to the discharge direction so that the direction of the laser beam output from the OC is shifted every time the resonator is reciprocated. Can do.

FIG. 12 shows an implementation in which a ring-type resonator is adopted as the resonator of the amplification stage laser (PO) 20 and the wavefront of the light of the ring resonator can be adjusted by changing the curvature of at least one mirror. An example is shown.
The operation of this resonator will be described below.
The MO beam is incident at 45 degrees on the end of the OC 24 of the amplification stage laser (PO) 20 by the high reflection mirror 30c. Transmits through the OC24 coated with a partial reflection (PR) film that partially reflects at 45 degrees incident, enters the high reflection mirror 31a at an incident angle α (an angle smaller by several mrad than 45 degrees), passes through the window 22a, and is amplified. The laser is incident on the discharge space of the laser chamber 21 of the stage laser (PO) 20 in an inclined manner, and a voltage is applied to the discharge electrode 2a in synchronization with the seed light to discharge. The seed light that has passed through the discharge space is amplified, passes through the window 22b, and is reflected by the highly reflective mirror 31c at an incident angle α. Then, the light is incident on and reflected by the high reflection mirror 31b at an incident angle of 45 degrees.

A plurality of retractable actuators 32 are attached to the back surface of the high reflection mirror 31b. A mirror surface having an arbitrary curvature can be formed by controlling these actuators 32. This mirror is called a deformable mirror. With this deformable mirror, the wavefront can be changed in a plane perpendicular to the discharge direction. The light reflected by the deformable mirror is guided to the discharge space where it is discharged again through the window 22b and amplified. The beam then enters the OC 24 and partially transmits to become laser output light (one reciprocating light). A part of the beam is reflected and returned as feedback light into the ring resonator.
In this embodiment, as described above, the spatial coherence and beam divergence of the outgoing beam change by adjusting the wavefront in a plane perpendicular to the discharge direction by the deformable mirror of the ring resonator.

As described above, the MO laser beam is injected into the ring resonator of the amplification stage laser (PO) 20, and the mirror constituting the ring resonator is made a deformable mirror capable of adjusting the wavefront, whereby the embodiment of FIG. In addition to the following advantages:
(1) Since the injection is performed from the OC 24, the injection efficiency is increased.
(2) Since amplification is performed in the forward path and the multiple paths, the amplification efficiency is increased.
(3) Since it is a reflection type wavefront adjuster, no extra elements are required in the ring resonator, and the efficiency is high.
In this embodiment, the highly reflective mirror 31b is a deformable mirror. However, the present invention is not limited to this, and any of the highly reflective mirrors constituting the ring resonator may be a deformable mirror.

FIG. 13 shows an embodiment in which a ring type resonator is employed as the resonator of the amplification stage laser (PO), and a wavefront adjuster is installed in the optical path of the ring resonator.
The operation of this resonator will be described below.
The MO beam is incident at 45 degrees on the end of the OC 24 of the amplification stage laser (PO) 20 by the high reflection mirror 30c. Transmits through the OC24 coated with a partial reflection (PR) film that partially reflects at 45 degrees incident, enters the high reflection mirror 31a at an incident angle α (an angle smaller by several mrad than 45 degrees), passes through the window 22a, and is amplified. The laser is incident on the discharge space of the laser chamber 21 of the stage laser (PO) 20 in an inclined manner, and a voltage is applied to the discharge electrode 2a in synchronization with the seed light to discharge. Then, the seed light transmitted through the discharge space is amplified, passes through the window 22b, and is reflected by the high reflection mirror 31c at an incident angle α. Then, the light is incident on and reflected by the high reflection mirror 31b at an incident angle of 45 degrees.

This reflected light is incident on a wavefront adjuster 80 formed of a cylindrical concave / convex lens. An actuator is attached to the wavefront adjuster 80 so that the cylindrical lens can move in the optical axis direction. By controlling these actuators, a wavefront having an arbitrary curvature can be formed.
The wavefront adjuster 80 can change the wavefront in a plane perpendicular to the discharge direction. The light transmitted through the wavefront adjuster 80 is guided to the discharge space where it is discharged again through the window 22b and is amplified. The beam then enters the OC 24 and partially transmits to become laser output light (one reciprocating light). A part of the beam is reflected and returned as feedback light into the ring resonator.

In this embodiment, the wavefront adjuster 80 provided in the ring resonator adjusts the wavefront in a plane perpendicular to the discharge direction to change the spatial coherence and beam divergence of the outgoing beam.
As described above, the MO laser beam is injected into the ring resonator of the amplification stage laser (PO) 20, and the wavefront adjuster 80 capable of adjusting the wavefront is provided in the optical path of the ring resonator. In addition to the following advantages:
(1) Since injection is performed from the OC 24, the injection efficiency is increased.
(2) Since amplification is performed in the forward path and the multiple paths, the amplification efficiency is increased.
In this embodiment, the wavefront adjuster 80 is installed between the optical path of the high reflection mirror 31b and the laser chamber 21. However, the present invention is not limited to this and can be installed anywhere in the optical path of the ring resonator. Good.

In the above, the case where the attitude angle of the mirror of the resonator is shifted with respect to the optical axis or the low spatial coherence is achieved by using the wavefront adjuster has been described. However, as described above, the mirror of the MO beam steering unit 30 By controlling the angle of the mirror of the PO beam steering unit 40, the coherence of the output laser beam can be reduced.
Hereinafter, an embodiment will be described in which low coherence is achieved by swinging the angles of these mirrors.

FIG. 14 shows a configuration example of an actuator for swinging the beam angle by the PO beam steering unit.
FIG. 14A is a diagram illustrating an example in which a beam is shaken by changing the attitude angle of the mirror in the PO beam steering unit.
When the laser beam output from the amplification stage laser (PO) 20 is reflected by the high reflection mirror 41a and further guided to the OPS 50 by the high reflection mirror 41b, the gimbal is used as the mirror holder 44 of the high reflection mirror 41b as shown in FIG. Using a holder with a mechanism, the attitude angle of the mirror is changed for each pulse. The mirror holder mechanism 44 may be the same as that shown in FIG.
The beam is preferably oscillated in a direction perpendicular to the laser discharge (H direction). However, as described above, the position angle of the mirror of the resonator is shifted, or the wavefront adjuster is used. When changing the beam, it is desirable to oscillate the beam in the direction in which the laser beam output from the resonator is shifted or in the direction orthogonal to the direction in which the wavefront is changed by the mirror in the PO beam steering unit.

FIG. 14B is a diagram illustrating an example in which the beam emission angle is changed by arranging a wedge substrate in the optical path and changing the incident angle to the wedge substrate.
The laser beam output from the amplification stage laser (PO) 20 is reflected by the high reflection mirror 41a, is incident and refracted on the wedge substrate 45a to change the direction of the beam, and is further guided to the OPS 50 by the high reflection mirror 41b. Yes. Here, the wedge substrate 45a is fixed to the automatic rotation stage 45b so that the incident angle on the substrate can be changed.
The automatic rotation stage 45b is provided with a PZT 42b at the tip of the moving pin of the pulse motor 42a. The automatic rotation stage 45b is in contact with a plate 42d fixed to the rotation stage 45b, and a pin of a plunger screw 42c is provided on the back side of the plate 42d. It is in contact. When the coarse rotation is performed, the rotation of the rotation stage 45b is controlled by moving the pin of the pulse motor. When finely rotating at high speed, the rotation can be controlled by being driven by the PZT 42b.
FIG. 14C is a diagram showing a configuration example in the case where the direction of the laser beam is changed by rotating the wedge substrate 47a about the incident optical axis, and FIG. It is the figure seen from.
The wedge substrate 47a is installed on a transmission type rotary stage 47b, and the gear 46a is rotated by rotating the gear 46b with the pulse motor 42a. A wedge substrate 47a is fixed on the gear 46a, and the beam can be swung in such a manner that the direction of the laser beam rotates on the circumference. For example, if the number of exposure pulses of the exposure apparatus is N pulses, it is possible to reduce coherence in all directions by controlling the rotation speed so that the wedge substrate 47a rotates once during the N pulses.
Even in the configurations shown in (b) and (c) above, it is desirable to oscillate the beam in the direction in which the laser beam output from the resonator deviates or in the direction orthogonal to the direction in which the wavefront is changed.

FIG. 15 shows a configuration example of an actuator for swinging the beam angle by the MO beam steering unit.
The configuration of the beam steering unit is functionally the same as the embodiment of FIG.
FIG. 15A shows an example in which the attitude angle of the mirror in the MO beam steering unit is swung.
When the laser beam output from the oscillation stage laser (MO) 10 is reflected by the high reflection mirror 31a and further guided to the amplification stage laser (PO) 20 by the high reflection mirror 31b, the gimbal is used as the mirror holder 34 of the high reflection mirror 31b. A holder with a mechanism is used, and the attitude angle of the mirror 31b is changed for each pulse. The mirror holder mechanism 34 may be the same as that shown in FIG.
The beam is preferably oscillated in a direction perpendicular to the laser discharge (H direction). However, as described above, the position angle of the mirror of the resonator is shifted, or the wavefront adjuster is used. When changing the laser beam, it is desirable to oscillate the beam in the direction in which the laser beam output from the resonator deviates or in the direction orthogonal to the direction in which the wavefront is changed.

FIG. 15B shows an example in which a wedge substrate 35a is disposed in the optical path, and the incident angle on the wedge substrate 35a is changed to change the beam emission angle.
The laser beam output from the oscillation stage laser (MO) 10 is reflected by the high reflection mirror 31a, incident and refracted on the wedge substrate 35a to change the direction of the beam, and further the amplification stage laser (PO) 20 by the high reflection mirror 31b. It is the composition which leads to. Here, the wedge substrate 35a is fixed to the automatic rotation stage 35b so that the incident angle on the substrate can be changed. The rotary stage 35b is provided with a PZT 32b at the tip of the moving pin of the pulse motor 32a. The rotary stage 35b is in contact with a plate 32d fixed to the rotary stage 35b, and a pin of a plunger screw 32c is applied to the back side of the plate 32d. It is touched. When performing coarse rotation, the rotation stage 35b is controlled to rotate by moving the pin of the pulse motor. When finely rotating at high speed, the rotation can be controlled by being driven by the PZT 32b.

FIG. 15C shows an example in which the direction of the laser beam is changed by rotating the wedge substrate about the incident optical axis.
The wedge substrate 37a is installed on a transmissive rotary stage 37b, and the gear 36a is rotated by rotating the gear 36b with the pulse motor 32a. A wedge substrate 37a is fixed on the gear 36a, and the beam can be swung in such a manner that the direction of the laser beam rotates on the circumference. For example, if the number of exposure pulses of the exposure apparatus is N pulses, the coherence can be reduced in all directions by controlling the rotation speed so that the wedge substrate 37a rotates once during the N pulses.

Next, a control example for reducing the coherence shown in the above embodiment will be described.
First, a case where the laser beam angle is changed according to a predetermined program for each pulse without detecting the spatial coherence index value or the spatial coherence will be described.
FIG. 16 shows a main flow of a flowchart for driving the actuator to realize low coherence.
In the start of the control for reducing the spatial coherence, first, in step 101, it is detected whether or not the laser has oscillated. In this case, it may be determined that laser oscillation has occurred by receiving a light emission trigger signal from the exposure apparatus without detecting actual light emission.
When the laser emission is detected, the process proceeds to the next step 102, and the subroutine for driving the actuator for lowering the spatial coherence is entered.
In this subroutine, for example, the attitude angle of the mirror of the resonator is driven to reduce the spatial coherence.

FIG. 17A shows a subroutine for driving the actuator of the mirror of the resonator in order to stabilize the spatial coherence low.
In this subroutine, the mirror of the PO resonator is mirrored as in the embodiments shown in FIGS. 5 and 6 so that the direction of the outgoing beam from the amplification stage laser (PO) 20 deviates every reciprocation. Fixed control of equal posture angle. Alternatively, as in the embodiments of FIGS. 15 and 16, the wavefront of light in the PO resonator may be controlled and fixed.
FIG. 17B shows the shape of the beam at the condensing position in the embodiment of FIG. The converging image of the output beam from the amplification stage laser (PO) 20 is 0.5 reciprocating light (B), 2.5 reciprocating light (C), and 3.5 reciprocating light (0.5) (A). In D), the condensed image of the outgoing beam is shifted in the H direction. In this case, the beam divergence in the H direction is about four times, and the spatial coherence in the H direction is reduced.
The advantage of this embodiment is that, for example, the spatial coherence can be lowered only by fixing to a desired fixed value as described above without changing the attitude angle of the mirror for each pulse. However, within the range of the allowable angle of the beam to the exposure apparatus, the spatial coherence can be further reduced by changing the attitude angle of the mirror or the like.

FIG. 18A shows a driving subroutine for an actuator that drives the mirrors of the PO and MO beam steering units in order to realize low coherence.
In this subroutine, first, in step 201, a beam swing program pattern is called.
Then, the process proceeds to step 202, and the direction of the laser beam emitted from the MO or PO beam steering unit is changed so that the program pattern called in step 201 is obtained. Then, the process returns to the main routine.
FIG. 18B shows an example of a program pattern for beam angle swing.
This beam angle swing pattern is represented by a beam pointing (index of beam direction), and the point represents one pulse.
When measuring the pointing of the beam, as shown in FIG. 2, it can be measured by collecting the sample light with a condenser lens and placing a CCD camera on the focal plane of the condenser lens. By calculating the center of gravity of the condensing profile measured by the CCD camera, the pointing or direction of the beam can be measured.

The positions of the points in this figure represent, for example, the barycentric position of the focused beam for each pulse, the V direction being the laser discharge direction, and the H direction being the direction perpendicular to the discharge. Here, the case of oscillating the beam in the H direction is shown, but as described above, it is possible to change the direction in which the laser beam output from the resonator deviates or in the direction orthogonal to the direction in which the wavefront is changed. desirable.
The angle of the mirror and the angle of the wedge substrate are changed so that the beam emission angle is condensed at a point as shown in the figure for each pulse. For example, if the exposure integrated pulse number in the exposure apparatus is 24 pulses, the beam swing cycle is 24 pulses, and the 25th pulse returns to the start point. Thereby, efficient spatial coherence can be achieved.
Here, the pointing angle is changed within the beam allowable angle of the exposure apparatus. What is necessary is just to make the period of the change of pointing coincide with the exposure integrated pulse number of the exposure apparatus.

Specific examples are shown below.
(i) is a pattern in which the beam pointing is linearly changed at a predetermined interval from the start point to the end point in the H direction, and is returned to the first pointing after 25 pulses are oscillated.
(ii) is a pattern in which the beam pointing is changed at a predetermined interval from the start point to the end point so that the line connecting the beam pointing becomes a rectangular shape, and is returned to the start point pointing after 25 pulses are oscillated.
(iii) is a pattern in which the beam pointing is changed at a predetermined interval so that the line connecting the beam pointing becomes a circle, and is returned to the initial pointing every 25 pulse oscillations. As an example of forming such a pattern, it can be carried out by rotating the wedge substrate around the optical axis as in the embodiment of FIGS. 14 (c) and 15 (c).
(iv) is a pattern in which the beam pointing is changed at a predetermined interval so that the line connecting the beam pointing becomes an ellipse, and is returned to the first pointing every 25 pulse oscillations.
In the above embodiments (ii), (iii), and (iv), since the distance from the start point to the end point is small, the angle swing can be performed smoothly.
As long as the line connecting the pointing for each pulse is drawn with a single stroke, the exposure pattern of any exposure apparatus can be exposed with the same low spatial coherence beam.

Next, a case where feedback control of spatial coherence is performed using the coherence monitor will be described.
FIG. 19 shows a main flow in the case of feedback control of spatial coherence.
The control of the low spatial coherence control is started by first entering the adjustment oscillation subroutine of step 400. In this routine, the shutter 65 (see FIG. 1) at the exit of the laser is closed, adjustment oscillation is performed to control the spatial coherence until the spatial coherence is OK with respect to the required specification of the exposure apparatus, and exposure is performed when the OK is achieved. A preparation OK signal is transmitted to the exposure apparatus, and the shutter 65 at the exit opening is opened.
Then, the actual exposure mode is entered, and it is detected in step 401 whether the laser has oscillated. If oscillation is detected, the process proceeds to step 402, and a parameter having a correlation with the spatial coherence of the output laser beam is detected.
Specifically, a beam condensing profile, a Young's interferometer, or an interference fringe profile generated by a sharing interferometer. This detection profile proceeds to step 403, and enters a subroutine for evaluating with the movement integrated value (or integrated value) of spatial coherence.

In the subroutine that evaluates the movement coherence of the spatial coherence or the integrated value, the condensing profile or the interference fringe profile is integrated to evaluate the spatial coherence.
In step 404, based on the evaluation value of the spatial coherence of the output laser light, a subroutine for controlling an actuator that drives the attitude angle of a resonator mirror, for example, is executed, and the process returns to the start.
Here, the number of moving accumulated pulses and the number of pulses that measure the accumulated value are the same as the number of accumulated pulses that the resist is actually exposed by the exposure device, so that spatial coherence can be specified at any position on any wafer. Generation can be suppressed with good uniformity.

FIG. 20 shows a subroutine example for detecting a beam parameter having a correlation with the spatial coherence of the output laser beam.
In FIG. 20A, as shown in FIG. 2, the output beam is condensed by a condensing lens, a CCD is arranged on the focal plane of the condensing lens, and the condensing profile at this focal plane is measured. An example of the case will be described.
First, in step 411, the light collection profile Pn is detected. Specifically, the light intensity at each pixel of the CCD is detected.
Next, the process proceeds to step 412 to store the light collection profile Pn. Specifically, light intensity data at each pixel of the CCD is stored.
FIG. 20B shows an embodiment in which interference fringes generated by Young's interferometer or shearing interferometer are detected by a CCD as shown in FIGS.
First, in step 421, an interference fringe pattern Fn is detected. Specifically, the light intensity at each pixel of the CCD is detected.
Next, the process proceeds to step 412 to store the interference fringe pattern Fn. Specifically, light intensity data at each pixel of the CCD is stored. Then, the process returns to the main routine.
Here, n indicates the order of pulses.

FIG. 21 shows a first embodiment of a subroutine for evaluating with the movement integrated value of the spatial coherence of the output laser beam.
This embodiment shows a case where the profile of the output laser light at the focal plane of the condenser lens is detected as a spatial coherence detector. The following example is an example in which the integrated movement value is evaluated. The number of samples is k.
First, in step 431, the movement integrated value SP _n−1 of the previous light collection profile, the light collection profile P _nk before the movement integrated pulse number k, and the current light collection profile P _n are called from the storage device.
In the next step 432, by the following equation, it calculates a transfer accumulated value SP _n of the condenser profile of this accumulated sample number k.
SP _n = SP _n-1 −P _nk + P _n

Next, the process proceeds to step 433, where the beam divergence width D _n is calculated from the integrated movement value SP _n of the light condensing profile by the equation (1) (D = BD / f) described in FIG.
Then, a difference ΔD between the target beam divergence value D _t and the actual beam divergence D _n is calculated.
In the next step 435, it is determined whether the difference ΔD from the target value of the beam divergence is within an allowable range with respect to the required specification of the exposure apparatus. If it is within the allowable range, the process returns to the main routine. On the other hand, if it is not within the allowable range, the process proceeds to step 436 to notify the exposure apparatus of the spatial coherence or the beam emission angle abnormality, and jump to the adjustment oscillation subroutine.

FIG. 22 shows a second embodiment of the subroutine for evaluating with the movement integrated value of the spatial coherence of the output laser beam.
This embodiment shows a case where an interference fringe profile is detected by a Young interferometer or a shearing interferometer as a detector of spatial coherence. The following example is an example in which the integrated movement value is evaluated. The number of samples is k.
First, in step 441, the movement accumulated value SF _n-1 of the interference fringe profile up to the previous time, the interference fringe profile F _nk before the movement accumulated pulse number k, and the current interference fringe profile F _n are called from the storage device.
In the next step 442, calculating a running integration value SF _n condensing profile of this accumulated sample number k by the following equation.
SFn = SF _n−1 −F _n−1 + F _n

Next, the process proceeds to step 443, _{where the} contrast C _n (visibility: visibility) is calculated from the movement integrated value SF _n of the interference fringe profile by the equation (4) described in FIG. In step 444, a difference ΔC between the target contrast value C _t and the actual contrast C _n is calculated.
In the next step 445, with respect to the required specifications of the difference ΔC is the exposure apparatus between the target value C _t of the contrast, it is determined whether the entered tolerance. If it is within the allowable range, the process returns to the main routine. On the other hand, if it is not within the allowable range, the process shifts to step 446 to notify the exposure apparatus of the spatial coherence and jump to the adjustment oscillation subroutine.

FIG. 23 shows an embodiment of a subroutine for driving the actuator based on the evaluation value of the spatial coherence of the output laser beam.
FIG. 23A shows an example in which the beam divergence of the output laser light is evaluated and controlled as a spatial coherence detector.
In step 451, an actuator for stabilizing the spatial coherence to the target value is driven based on the difference ΔD from the beam divergence target value.
As a specific example of this actuator, a control value is transmitted to an actuator that controls the beam emission angle from the beam steering unit of the amplification stage laser (PO) 20 or the oscillation stage laser (MO) 10. Further, the attitude angle of the mirror of the resonator is controlled so that the output beam divergence becomes a target value.

  FIG. 23B shows an example in which the contrast of the interference fringes of the output laser light is evaluated and controlled. In step 452, an actuator for stabilizing the spatial coherence to the target value is driven based on the difference ΔC from the target value of the contrast of the interference fringes. As a specific example of this actuator, a control value is transmitted to an actuator that controls the beam emission angle from the beam steering unit of the amplification stage laser (PO) 20 or the oscillation stage laser (MO) 10. Further, the attitude angle of the mirror of the resonator is controlled so that the output beam divergence becomes a target value.

FIG. 24 shows an example of a subroutine for adjusting oscillation of the present invention.
In the adjustment oscillation subroutine, the laser exit shutter 65 (see FIG. 1) is closed, and adjustment oscillation is performed to control the spatial coherence until the spatial coherence is OK with respect to the required specification of the exposure apparatus. An exposure preparation OK signal is transmitted to the exposure apparatus, and the shutter 65 at the exit opening is opened.
This will be described below with reference to flowcharts.
First, in step 461, the laser emission port 65 is closed so that the laser beam is not transmitted from the laser to the exposure apparatus, and an exposure preparation NG signal is sent to the exposure apparatus.
Then, as in the main routine, it is detected in step 462 whether the laser has oscillated. If oscillation is detected, the process proceeds to step 463, and a parameter having a correlation with the spatial coherence of the output laser beam is detected. Specifically, a beam condensing profile, a Young's interferometer, or an interference fringe profile generated by a sharing interferometer.

Next, the routine proceeds to step 464, where the subroutine for evaluating with the movement integrated value or integrated value of the spatial coherence based on this detection profile is entered.
In this subroutine, the light collection profile or interference fringe profile is integrated to evaluate the spatial coherence.
In step 465, based on the evaluation value of the spatial coherence of the output laser light, a subroutine for controlling an actuator that drives the attitude angle of, for example, a mirror is executed.
In step 466, it is determined whether the evaluation value of the spatial coherence is within the allowable range of the required specification of the exposure apparatus. If it is not within the allowable range, the routine proceeds to step 462 and this routine is repeated.
If the allowable range is entered, the process proceeds to step 467, where the shutter 65 for the emitted light is opened, an exposure preparation OK signal is transmitted to the exposure apparatus, and the process returns to the main routine.

10 Oscillation stage laser (MO)
11 chamber 20 amplification stage laser (PO)
21 Chamber 30 MO beam steering unit 40 PO beam steering unit 50 Optical pulse stretcher (OPS)
60 Coherence Monitor 65 Shutter 66 Laser Coherence Controller 67 PO Resonator Optical Axis Controller 80 Wavefront Tuner

Claims (5)

A narrowband oscillation stage laser configured to output laser light;
Laser light from the narrow-band oscillation stage laser, including a chamber in which a laser gas is sealed, a pair of discharge electrodes provided in the chamber, and a resonator disposed so as to sandwich a discharge space of the discharge electrode An amplification stage laser configured to amplify the laser light by injecting into the resonator, applying a high voltage pulse to the discharge electrode to cause discharge.
Coherence changing means arranged on the optical path of the laser light and configured to change the spatial coherence of the laser light;
Measuring means for measuring a spatial coherence of output laser light output from the amplification stage laser or a parameter correlated with the spatial coherence;
Control means for controlling the coherence changing means based on the measurement result of the measuring means ,
The control means controls the coherence changing means so that the spatial coherence of the laser beam varies based on a predetermined program,
The predetermined program is such that a line connecting the beam pointing is formed into a rectangular shape, a line connecting the beam pointing is formed into a substantially circular shape, or a line connecting the beam pointing is formed. An exposure-excitation laser apparatus for exposure , wherein the beam pointing is changed so as to be substantially elliptical . The control unit controls the coherence changing means so that the spatial coherence of the output laser beam output from the amplification stage laser or the integrated value of the spatial coherence falls within a predetermined upper limit and lower limit range. The discharge excitation laser apparatus for exposure according to claim 1, wherein the discharge excitation laser apparatus is for exposure. The exposure discharge excitation laser apparatus according to claim 1, wherein the control unit controls the coherence changing unit at least while the narrow-band oscillation stage laser is outputting a laser beam. The discharge excitation laser apparatus for exposure according to any one of claims 1 to 3 , wherein the measuring means is an apparatus that measures beam divergence. The discharge excitation laser apparatus for exposure according to any one of claims 1 to 3 , wherein the measuring means is a Young's interferometer or a shearing interferometer.

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