JPH07105335B2 - Exposure equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus that transfers a pattern onto an object via a projection optical system.

[0002]

2. Description of the Related Art In recent years, semiconductor devices, which have been the driving force of technological innovation, are becoming more and more dense, and the fine pattern of each element is about 0.5 μm or less. In the exposure of such a fine pattern, alignment between the exposures is extremely important in order to perform multiple overlay exposures required in semiconductor manufacturing, and the overlay accuracy is 0.1 μm. The following are required: As a conventional example of such an alignment method, for example, Japanese Patent Laid-Open No. 63-63
The configuration described in Japanese Patent Publication No. 78004 is known.

A conventional exposure apparatus will be described below with reference to FIG. In FIG. 16, 1 formed on the surface of the reticle 114 in order to realize highly accurate alignment.
Of the light beams divided by the pair of first gratings 110 and 110 ′, a predetermined spectrum is selectively passed by spatial filters 116 and 116 ′ provided near the spectral planes of the first lenses 115 and 115 ′. And second
Of the second grating 1 provided on the wafer 118, passing through the lens systems 117 and 117 ′ and the projection lens 119.
Project on 21,121 '. When two light beams are projected onto the second gratings 121 and 121 'on the wafer 118 from appropriate directions, the diffracted lights are diffracted in the overlapping direction and interfere with each other. The pair of diffracted light beams 122 and 122 ′ that have interfered with each other are projected in the opposite direction to the projection lens 119 and the second lenses 117 and 11.
7 ', and the intensity of the diffracted light is detected by the photodetector 123,
It is possible to perform highly accurate alignment between the reticle 114 and the wafer 118 by moving the wafer 118 such that it is detected by 123 ′ and the difference therebetween becomes zero.

[0004]

However, in the above configuration, the exposure light and the alignment light have almost the same wavelength, and only when the projection optical system exhibits the same good imaging performance for both. There is a problem of being effective. For example, with respect to ultraviolet light such as excimer laser, which is expected to become the mainstream of exposure light in the future, the glass material for forming the refraction optical system is limited, and thus the achromatic projection optical system in which chromatic aberration is corrected Is extremely difficult to construct.
For this reason, an achromatic projection optical system with corrected chromatic aberration is designed to be sufficiently color-corrected only at the exposure wavelength, and exhibits very large chromatic aberration with respect to light of other wavelengths, and the alignment light causes the projection lens to The configuration of an alignment system that passes through becomes very difficult. Further, if the alignment light does not pass through the projection lens, the exposure position of the wafer and the position for alignment are largely separated from the device configuration in which the projection lens is arranged so as to cover the wafer. However, there is a problem that the overlay accuracy is reduced.

The present invention solves such a conventional problem, and makes it possible to reduce the size of the alignment optical system and place it in the middle of the projection lens and the object on the image plane. It is an object of the present invention to provide an exposure apparatus that can align an object with high accuracy by a system.

[0006]

In order to achieve the above object, the present invention provides a light source optical system that emits coherent alignment light and a diffracted light that is returned by irradiating the object with the alignment light. Misalignment detection optical system,
It is provided with a light receiving optical system for detecting the received diffracted light and an optical waveguide having flexibility for sequentially coupling the three optical systems.

[0007]

Therefore, according to the present invention, the position shift detecting optical system, the light source optical system, and the light receiving optical system are coupled by the flexible optical waveguide, so that the position shift detecting optical system can be downsized and mounted on the apparatus. Can be facilitated. Therefore, the misalignment detection optical system can be placed directly below the projection lens, which has an extremely limited space, and has a highly accurate alignment system that minimizes the effects of vibration and atmosphere and thermal deformation of the device. An exposure apparatus can be realized.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a basic configuration of an exposure apparatus in an embodiment of the present invention, showing one axis in the X direction of a three-axis alignment system of X, Y and θ. FIG. 2 is a schematic configuration diagram of a positional deviation detecting optical system for detecting a positional deviation of a wafer used in the first embodiment of the present invention, and FIG. 3 is a laser emitted from a laser light source similarly used in the first embodiment. It is a schematic block diagram of a light source optical system which couple | bonds light into an optical fiber. 4 is a detailed view of the laser light source shown in FIG. 3, FIG. 5 is a schematic view showing the function of the collimator lens as a spatial filter in the first embodiment, and FIG.
FIG. 3 is a schematic configuration diagram of a light receiving optical system for receiving diffracted light from the wafer used in the first embodiment.

In FIG. 1, 1 is a wafer which is an object to be aligned, 2 is a light source optical system for generating alignment light, 3 is a positional deviation detection optical system for irradiating the wafer 1 with alignment light, and 4 is a wafer 1. It is a light receiving optical system that receives the alignment light having the positional deviation information. Reference numeral 5 is a reticle that is an exposure master, 6 is exposure light, 7 is a projection lens, and 8 is a projection lens.
Is the alignment light. Numerals 20 and 21 are polarization-maintaining optical fibers that are first optical fibers that connect the light source optical system 2 and the positional deviation detection optical system 3, and 28 and 29 are first optical fibers that connect the positional deviation detection optical system 3 and the light receiving optical system 4. It is a multi-mode optical fiber which is the second optical fiber, and each constitutes an optical waveguide having flexibility. The positional deviation detection optical system 3 is shown in FIG.
As shown, the first light source optics includes a first light
Through the polarization maintaining optical fibers 20 and 21 which are fibers
Is connected in the vicinity of the projection lens 7 and is substantially
It is arranged directly below the projection lens 7.

The operation of the above arrangement will be described below. The alignment optical system according to the present embodiment includes a light source optical system 2, a position shift detection optical system 3, and a light receiving optical system 4, and the three optical systems are polarization plane maintaining optical fibers 20 and 21, a multimode optical fiber 28, and Bound by 29. Further, the projection lens 7 images the pattern on the reticle 5 illuminated by the exposure light 6 onto the wafer 1. Since this image formation is usually a reduction optical system of about 5: 1, the distance between the projection lens 7 and the reticle 5 is wide, and the distance between the projection lens 7 and the wafer 1 is narrow. However, since the positional deviation detection optical system 3 in this embodiment is made extremely small, it can be placed directly below the projection lens 7.

As shown in FIG. 4, the light source optical system 2 includes a laser light source 12 for generating coherent light beams having mutually orthogonally polarized frequencies f1 and f2. In this embodiment, a Zemine laser is used which obtains two frequencies by applying a magnetic field to the laser tube.

As another example of such a light source optical system 2, there is provided an optical modulator using an ultrasonic wave propagating in one direction and a light source for generating coherent light of one frequency. An optical system can be used which, after splitting into light fluxes, uses an optical element that slightly changes the frequency of light using the Doppler effect to give a difference in frequency of two light fluxes. The frequency difference between the frequencies f1 and f2 is several tens of k
Generally, Hz to several tens of MHz can be used.

In FIG. 3, alignment light having frequencies f1 and f2 emitted from the laser light source 12 (hereinafter referred to as alignment lights f1 and f2) is polarized optical element 1.
After being divided into the f1 component and the f2 component in step 3, (λ / 2)
The light is polarized in a specific direction using the wave plates 16 and 17. As the polarization optical element 13 for division, an element using a dielectric multilayer film such as a polarization beam splitter or an element using multiple refraction such as a Wollaston prism can be used. The polarization direction is rotated by the wave plates 16 and 17, because the polarization-maintaining optical fibers 20 and 2 are rotated.
This is because the polarization direction of 1 and the polarization directions of the alignment lights f1 and f2 are aligned.

The alignment lights f1 and f2 split by the splitting polarization optical element 13 are focused on the cores of the polarization-maintaining optical fibers 20 and 21 by the condenser lenses 18 and 19, and the inside of the optical fibers 20 and 21. Will be introduced to. It is useful to insert the optical isolators 14 and 15 at appropriate places in order to prevent the reflection of the alignment light on the surfaces of the optical fibers 20 and 21 from returning to the laser tube. Further, since the polarization maintaining optical fibers 20 and 21 have extremely small core diameters, the spot of the alignment light condensed by the light source optical system 2 may be displaced, and the efficiency of coupling to the optical fibers 20 and 21 may be reduced. There is. Therefore, the light source optical system 2 is
In order to minimize the effects of thermal expansion and vibration, it is necessary to make it highly rigid and compact.

The alignment lights f1 and f2 that have entered the polarization-maintaining optical fibers 20 and 21 are guided to the positional deviation detection optical system 3 shown in FIG. 2 while maintaining their polarization directions. The alignment lights f1 and f2 emitted from the polarization-maintaining optical fibers 20 and 21 are collimator lenses 22 and
It is guided to 23 and is collimated here. The collimator lenses 22 and 23 are required to have sufficiently high wavefront accuracy of emitted light and small size. As such a lens, a gradient index lens (GRIN lens) or an aspherical lens is suitable. Collimator lens 2
Alignment lights f1 and f2 made parallel by 2, 23
Is radiated through the epi- illumination mirror 24 onto the alignment mark 25 made of a diffraction grating on the wafer 1 at an incident angle .

The incident angle θ of the alignment lights f1 and f2 on the surface of the wafer 1 is represented by the following equation (1), where P is the pitch of the diffraction grating of the alignment mark 25 on the wafer 1 and λ is the wavelength of the alignment light. It is set.

Θ = sin ⁻¹ (λ / P) (1)

At such an incident angle θ, the alignment light f
When 1 and f2 enter, the alignment lights f1 and f2 diffracted by the diffraction grating 25 both go upward. here,
The electric field intensities E1 and E2 of f1 and f2 are expressed by equations (2) and (3), respectively. However, ω1 and ω2 are angular velocities of f1 and f2, and φ1 and φ2 are phase delays of the optical paths 20 and 21 corresponding to the optical path length with respect to the alignment lights f1 and f2.

E1 = A1 · cos (ω1 · t + 2πx / P + φ1) (2)

E2 = A2 · cos (ω2 · t−2πx / P + φ2) (3)

Since the alignment lights f1 and f2 travel in the same direction in this way, they interfere with each other, and as a result, the beats such that the light intensity Is changes at the frequency (f1-f2) as shown in equation (4). Emits light.

Is = (E1 + E2) ² = A1 ² + A2 ² + 2A1 · A2 · cos ((ω1-ω2) t + 4πx / P + (φ1-φ2)) (4)

The beat light is introduced again into the multimode optical fiber 28 by the collimator lens 26, and the position shift amount of the wafer 1 is detected from the beat light. The reason for using the multi-mode optical fibers 28 and 29 is that the multi-mode optical fibers have a large core system and are not easily affected by misalignment when re-combining the alignment lights, and that the alignment lights f1 and f2 already interfere. This is because there is no need to hold the wavefront because they are in agreement.

By the way, the optical length of the optical fiber largely changes depending on temperature and stress. For example, if the temperature of an optical fiber of 1 m rises by 1 ° C., an optical path length variation of about 10 to 20 wavelengths is brought about. Further, when the pressure applied to the 1 m optical fiber changes by 1 Pa, the optical path length changes by 10 ⁻⁶ to 10 ⁻⁵ wavelength. This means that if there is a slight difference between the environments in which the polarization-maintaining optical fibers 20 and 21 are placed, (φ1−φ2) in the equations (2) and (3) will change and an error will occur in the positional deviation detection. You know that it will happen. Therefore, the beam sampler 30 is placed to measure this (φ1−φ2) separately, and the alignment lights f1 and f2 partially divided by the beam sampler 30 are reflected by the glass plate 31.
The diffraction grating 32 having the same pitch as that of the wafer 1 formed above is irradiated. Since the diffraction grating 32 on the glass 31 plate is fixed, beat light is generated. This beat light is expressed as in equation (5), where Ir is the light intensity.

Ir = A1 ² + A2 ² + 2A1 · A2 · cos ((ω1−ω2) t + (φ1−φ2)) (5)

This beat light is also guided into the multimode optical fiber 29 by the collimator lens 27 in the same manner as the signal light. Here, the glass plate 31 on which the diffraction grating 32 is formed
Is important to be placed at an angle to the alignment light. This is because the diffracted light is generated not only in the transmission direction but also in the reflection direction, and when the glass plate 31 is placed perpendicularly to the alignment light, the reflected diffracted light 33 mixes with the reflected diffracted light from the wafer to detect the positional deviation. This is because the accuracy may be reduced. Further, the glass plate 31 on which the diffraction grating 32 is formed can be replaced with a half mirror arranged so that the alignment lights f1 and f2 interfere with each other.

The diffraction grating 25 on the wafer 1 is variously changed depending on each process that the wafer 1 receives. Generally, it is a form in which a resist transparent to alignment light is applied on the unevenness formed of a semiconductor material, and often acts as an optical multilayer film for alignment light. Since the action of the optical multilayer film changes sensitively to the polarization direction of light, the alignment lights f1 and f2 are either P-polarized light (polarized light in the incident plane) or S-polarized light (perpendicular to the incident plane) with respect to the wafer 1. It is disadvantageous because it is easily influenced by the surface state of the wafer 1 regardless of which of the polarized light). Therefore, the optical fiber 2 is arranged so that the polarization direction is inclined at 45 ° at the exits of the polarization-maintaining optical fibers 20 and 21.
0 and 21 are fixed. By doing this, wafer 1
On the surface, the ratio of P-polarized light and S-polarized light is 5: 5, and the adverse effect caused by the state of the wafer 1 can be minimized.

Here, considering the case where the surface of the wafer 1 is roughened by an aluminum pattern or the like, speckles from the aluminum pattern are mixed in the diffracted alignment light (diffracted light) 34. FIG. 5 shows an optical pattern on the focal plane (on the surface of the multimode optical fiber 28) when the diffracted light 34 is received by the collimator lens 26. As is clear from this figure, the speckle light 36 is included in the core 35 of the multimode optical fiber 28 arranged in the central portion.
It can be seen that the alignment light 34 from which is excluded is received. Thus, it can be seen that the collimator lens 26 and the core 35 also act as a spatial filter for the alignment light 34.

Next, the light receiving optical system 4 will be described with reference to FIG. In the light receiving optical system 4, the alignment light transmitted by the two multimode optical fibers 28 and 29 is introduced into photodetectors 37 and 38 such as a photomultiplier and converted into electric signals. When the relative phase difference between the two signals converted into the electric signal is detected by the phase comparator 39, the expressions (4) and (5) are changed to the expression (6), which is proportional to the positional deviation x of the wafer 1. You can get the output.

(Phase of Is) − (Phase of Ir) = 4πx / P (6)

Therefore, by moving the wafer stage 40 based on this output so that the amount of positional deviation becomes zero, the positional deviation of the wafer 1 with respect to the projection lens 7 can be eliminated.

As described above, in this embodiment, the alignment light is projected from the projection lens 7 by the optical fibers 20 and 21 from the light source optical system 2 arranged at a position apart from the exposure apparatus main body.
Is guided to the misalignment detection optical system 3 placed immediately below, and the alignment light from the misalignment detection optical system 3 is irradiated onto the alignment mark 25 of the wafer 1, and the diffracted light 34 from the wafer 1 is emitted.
Is again sent to the light receiving optical system 4 through the optical fibers 28 and 29, the beat light having the positional deviation information of the wafer 1 is converted into an electric signal by the photodetectors 37 and 38, and the positional deviation of the wafer 1 is performed by the phase comparator 39. The wafer 1 is moved with respect to the projection lens 7 by determining the amount and moving the wafer stage 40 based on the amount to control the displacement of the wafer 1 to zero.
Can be aligned with high accuracy.

Although the present invention has been described with reference to the first embodiment, the advantage of this embodiment is that the light source optical system 2 and the light receiving optical system 4 are first moved from the misregistration detection optical system 3 to the optical fiber 2.
By using 0, 21, 28, and 29 for separation, the positional deviation detection optical system 3 can be downsized, and the laser light source 12, which is a heat source, can be kept away from the delicate mechanism portion. By reducing the size of the positional deviation detecting optical system 3, the degree of freedom of arrangement of the optical system 3 in the exposure apparatus increases, and the positional deviation detecting optical system 3 is connected to the projection lens 7 and the wafer 1.
It will be possible to place it in an extremely narrow space between and. For this reason, not only is it possible to perform alignment at a position extremely close to the exposure position, but it is also possible to minimize the influence from the atmosphere, which is most likely to be a detection error in laser interferometry. Further, a diffraction grating 32 serving as a reference is installed in the positional deviation detection optical system 3 and the optical system 3 as a whole is made compact so that an optical system extremely resistant to vibration and other disturbances can be realized. it can. Further, by not transmitting the heat from the laser light source 12 to the main body of the exposure apparatus, it is possible to prevent thermal deformation of the mechanism and to ensure a stable alignment operation. Furthermore, because the alignment system is constructed using an optical fiber, which is an extremely flexible optical waveguide,
There is also an advantage that mounting on a device and adjustment of the optical axis are extremely easy, and that diversion to another device is easy.

In the first embodiment described above, the position of alignment and the exposure position are extremely close to each other (OffA).
However, in the second embodiment of the present invention described below, the configuration of an optical system for alignment (OnAxis alignment) in which the position of alignment and the exposure position are the same. Are shown in FIGS. In these figures, the reference numerals used in the description of the first embodiment above are used for similar elements.

What is important in performing the OnAxis alignment is to guide the alignment light into the exposure light beam without kicking the exposure light. In general, the difference in wavelength between the exposure light and the alignment light is used to guide the alignment light into the exposure light with a dichroic mirror or the like. However, as in this time, the positional deviation detection optical system 3
Is to be placed in a very limited space between the projection lens 7 and the wafer 1, it is impossible to use a dichroic mirror.

Therefore, in the second embodiment of the present invention, as shown in FIG.
As shown in, the coating surface 41, which is the lowermost surface of the projection lens 7 designed and manufactured exclusively for exposure light, is used as a substitute for the dichroic mirror. The coating surface 41 has a transmission efficiency of almost 100% with respect to the exposure light and is designed to have an extremely low transmission efficiency with respect to the alignment light. That is, the coating surface 41, which is the lowermost surface of the projection lens 7, is a flat surface or a surface having a large curvature,
The alignment light 8 acts as a nearly perfect reflecting surface.

Next, the light source optical system 2 and the positional deviation detection optical system 3 in the second embodiment of the present invention will be described. The light source optical system 2 has the same configuration and function as the light source optical system 2 in the first embodiment shown in FIG. As shown in FIG. 8, the positional deviation detecting optical system is different from that of the first embodiment shown in FIG. 2 in that an imaging lens 44 is used instead of the collimator lens 26, and an image transmission optical fiber is used instead of the multimode optical fiber 28. 43, and the folding mirror 42 is arranged instead of the epi-illumination mirror 24. The imaging lens 44 is for imaging the alignment mark (diffraction grating) 42 of the wafer 1 on the surface of the image transmission optical fiber 43, and a GRIN lens or a small spherical / aspherical lens can be used. As shown in FIG. 11, the image transmission optical fiber 43 is an optical fiber in which a large number of cores are fused and integrated in one optical fiber so as to share a clad, and an image of the incident end face is directly output. Can be reproduced. Therefore, the state of the alignment mark 45 on the wafer 1 can be reproduced in the light receiving optical system 4 by the combination of the imaging lens 44 and the image transmission optical fiber 43. Further, the folding mirror 42 directs the alignment light from the displacement detection optical system 3 to the coating surface 41 of the projection lens 7 or diffracted light reflected from the alignment mark 45 on the wafer 1 and reflected by the coating surface 41. Is used again to direct the light to the misregistration detection optical system 3.

The alignment light emitted upward from the displacement detection optical system 3 by the folding mirror 42 is
It is reflected by the bottom coating surface 41 of the projection lens 7,
As a result, it enters the light flux of the exposure light 6. A two-dimensional diffraction grating 45 as shown in FIG. 10 is provided on the surface of the wafer 1. The diffraction grating 45 is a combination of an X-direction diffraction grating and a Y-direction diffraction grating, and the X-direction diffraction pattern detects a positional deviation, and the Y-direction diffraction pattern detects the obliquely incident alignment light. This is for diffracting again at the same angle in the oblique direction. For example, returning to FIG. 7, when the incident angle of the alignment light 8 with respect to the wafer 1 is α, the pitch Py in the Y direction is determined to be the following expression (7).

2Py · sin α = nλ (n = 1, 2, ...) (7)

By virtue of such a diffraction pattern in the Y direction, the alignment light 8 can be diffracted on the wafer 1 and then returned to the misregistration detection optical system 3.

Next, the light receiving optical system 4 in the second embodiment.
Will be described with reference to FIG. An image at the exit end of the image transmission optical fiber 43 is magnified by a magnifying lens 46, and an aperture 49 that is two-dimensionally driven by actuators 47 and 48 is arranged therein. This aperture 49 makes it possible for the photodetector 38 to receive the alignment light from only the alignment mark at any position through the condenser lens 50. This state is shown in FIG. It can be seen from FIG. 12 that the rightmost one of the three alignment works is selected by the aperture 49. Other old alignment marks are not received by the photodetector 38.

The advantage of having such a configuration of the light receiving optical system 4 can be explained as follows. That is, the alignment marks are gradually broken as the wafer undergoes process processing, which necessitates the use of new alignment marks one after another. In OnAxis alignment,
Since the exposure position is the alignment position immediately, this means that the position of the alignment mark 45 at the time of alignment is displaced with respect to the displacement detection optical system 3. Therefore, even if the position is changed by moving the aperture 49, only the alignment light from the latest alignment mark 45 is detected, so that high detection accuracy can be maintained even if the alignment mark is updated. FIG. 12 also shows that the old alignment mark is being removed from the visual field of the light receiving optical system 4.

The present invention has been described above using the second embodiment. However, in the second embodiment of the present invention, in addition to the advantages described in the first embodiment, alignment during exposure is also performed. It has the advantage of being possible. Therefore, the wafer 1
Is accurately aligned with the projection lens 7 when it comes to the exposure position, it is possible to configure an exposure apparatus in which overlay accuracy is not affected by the motion accuracy of the wafer stage 40. .

As described above, in the present embodiment, the alignment light is projected from the light source optical system 2 arranged at a position distant from the exposure apparatus main body by the optical fibers 20 and 21.
Is guided to the misalignment detection optical system 3 placed immediately below, and the alignment light from the misalignment detection optical system 3 is irradiated onto the alignment mark 25 of the wafer 1, and the diffracted light 34 from the wafer 1 is emitted.
Is again sent to the light receiving optical system 4 through the optical fibers 28 and 29, the beat light having the positional deviation information of the wafer 1 is converted into an electric signal by the photodetectors 37 and 38, and the positional deviation of the wafer 1 is performed by the phase comparator 39. The wafer 1 is moved with respect to the projection lens 7 by determining the amount and moving the wafer stage 40 based on the amount to control the displacement of the wafer 1 to zero.
Can be aligned with high accuracy.

Next, a third embodiment of the present invention will be described with reference to FIG. The present embodiment has the same configuration and function as the first and second embodiments except for the light source optical system, and therefore only the light source optical system will be described below.

In FIG. 13, reference numeral 51 is a laser light source for generating linearly polarized coherent light of a single frequency, 52 is an isolator, 53 and 54 are acousto-optic modulators using ultrasonic waves,
55 and 56 are 1/2 λ wavelength plates, 57 and 58 are condenser lenses, and 59 is a beam stopper. Reference numerals 20 and 21 denote polarization-maintaining optical fibers for coupling the light source optical system 2 with the above-described position shift detecting optical system 3.

The coherent light emitted from the light source 51 passes through the isolator 52 and the first acousto-optic modulator 5
By 3, the 0-th order diffracted light 60 which is not modulated and the 1st-order diffracted light 61 which is modulated are separated. The first-order diffracted light 61 is
The light passes through the half-wave plate 55 and is coupled to the polarization-maintaining optical fiber 20 by the condenser lens 57. The 0th-order diffracted light 60 that has not been modulated enters the second acousto-optic modulator 54 this time, and the 0th-order diffracted light 62 that has not been modulated and the 1st modulated
The 0th-order diffracted light 62 is separated into the 2nd-order diffracted light 63, the 0th-order diffracted light 62 is blocked by the beam stopper 59, and the 1st-order diffracted light 63 passes through the ½λ wavelength plate 56 and is coupled to the polarization-maintaining optical fiber 21. Here, the isolator 52 is arranged in order to eliminate the destabilization of the laser light source 51 due to the light reflected from the surface of each optical element and returning to the laser light source 51.
The ½λ wave plates 55 and 56 are inserted to match the polarization planes of the first-order diffracted lights 61 and 63 with the polarization planes of the polarization-maintaining optical fibers 20 and 21. This is as described for the light source optical system 2 in the first embodiment.

The light source optical system 2 in this embodiment differs from the light source optical system 2 in the first embodiment shown in FIG. 3 in that the laser light source 51 is changed from two frequencies to a single frequency, which is a problem in the above embodiments. There is an advantage that it is possible to completely eliminate the deterioration of the positional deviation detection accuracy due to the mixing of the two frequencies. Further, by arranging the two acousto-optic modulators 53 and 54 in series on one optical axis without splitting the coherent light, the ratio of the light rays that can be used as alignment light in the coherent light is increased. You can

That is, the light source optical system 2 in this embodiment.
May be divided into two by the beam splitter 64 and then modulated by the acousto-optic modulators 53 and 54, respectively, like the light source optical system 2 shown in FIG. The intensity ratios of the first-order diffracted lights 61 and 63 in the containers 53 and 54 to the incident light are respectively P1,
If P2 is set, the ratio of the light that can be used as the alignment light in the coherent light from the laser light source 51 is given by the following expression (8).

(P1 + P2) / 2 (8)

On the other hand, when the light source optical system 2 shown in FIG. 13 is used, the proportion of light that can be used as alignment light is
It becomes like the following formula (9).

P1 + (1-P1) · P2 (9)

Therefore, as can be seen from these two equations, by using the light source optical system 2 shown in FIG. 13, there is a gain of the amount of light represented by the following equation (10).

1/2 · (P1 + P2) −P1 · P2> 0 ... (10)

In this embodiment, a plurality of alignment devices are generally required for the exposure device, so the laser light source 51 is used.
When the intensity of the alignment light from is strong, the alignment light can be split in the middle to supply the alignment light to a plurality of alignment devices with one light source.
There is an advantage that the heat source that causes the measurement error can be reduced.

Further, the intensity of the diffracted light usually depends on the frequency given to the acousto-optic modulators 53 and 54, and in order to obtain the beat light having a high contrast, the intensities of the two alignment lights are as equal as possible. It is necessary to dispose the acousto-optic modulators 53 and 54 as described above. In the configuration shown in FIG. 14, the intensity difference of the diffracted light is the intensity difference of the alignment light as it is, but in the configuration shown in FIG. By disposing the low acousto-optic modulator 53 on the upstream side of the light source, it is possible to reduce the intensity difference of the alignment light.

The present invention has been described above using the third embodiment. However, in addition to the advantages described in the first and second embodiments, this embodiment provides a high intensity alignment light and both alignment light. Since the intensity difference can be reduced, beat light with high contrast can be obtained, and there is an advantage that the alignment accuracy can be improved. Further, there is also an advantage that the mechanical strength of the optical system can be increased by reducing the total number of elements constituting the optical system.

Next, a fourth embodiment of the present invention will be described with reference to FIG. In FIG. 15, the light source optical system 2
Is the same as the light source optical system 2 in the third embodiment shown in FIG. 13, but the light source optical system 2 shown in FIG. 14 may be used. The light receiving optical system 4 is the same as the light receiving optical system 4 in the first embodiment shown in FIG. 6, but the light receiving optical system 4 in the second embodiment shown in FIG. 8 may be used. Other configurations are the same as those of the first and second embodiments.

In FIG. 15, reference numeral 65 is a beat signal amplitude detector to which the output of the photodetector 37 in the light receiving optical system 4 is input, and 66 is a comparison / determination device which outputs a control signal so as to keep the amplitude of the beat signal constant. , 67 are acousto-optic modulators 5 on the downstream side of the light source to which the control signal from the comparison / determination device 66 is input.
It is a power supply for 4. These constitute an alignment light intensity control system 68. The beat signal amplitude detector 65 includes a photodetector 38 instead of the photodetector 37.
May be input.

As described in the first embodiment, the intensity of the alignment light emitted from the polarization-maintaining optical fibers 20 and 21 is affected by the surrounding environment, and the amplitude,
Both the phases become unstable, and the positional deviation detection accuracy in the light receiving optical system 4 deteriorates. Therefore, in this embodiment,
The beat signal detector 65 detects the amplitude of the beat signal output from the photodetector 37 of the light receiving optical system 4, and supplies power to the acousto-optic modulator 54 on the downstream side of the light source so that the amplitude becomes constant. Give feedback to the power supply 67. By applying such feedback, it is possible to eliminate the influence of environmental changes and the like that are applied to all of the light source optical system 2 to the light receiving optical system 4, and prevent the positional deviation detection accuracy from deteriorating due to fluctuations in the intensity of the beat signal. be able to.

Inside the acousto-optic modulators 53 and 54, a compression wave traveling inside the optical material is generated by an ultrasonic transducer having a single frequency.
The coherent light incident on is diffracted by the refractive index distribution due to the compressional wave. Since the compressional wave of the ultrasonic transducer is a traveling wave, the diffracted light undergoes a kind of Doppler effect and is subjected to frequency modulation by the frequency of the ultrasonic transducer. Since the diffracted light intensity is a function of the energy supplied to the ultrasonic oscillator when the frequency is constant, the diffracted light intensity can be controlled by the amount of power supplied to the ultrasonic oscillator.

As another example of controlling the amount of alignment light by applying feedback, in the light source optical system 2 shown in FIG. 14, the intensity of alignment light emitted from the polarization-maintaining optical fibers 20, 21 is measured, and each alignment is performed. Each acousto-optic modulator 53, so that the light intensity is always constant,
It is also possible to have a configuration in which the power supply for 54 is fed back.

Although the present invention has been described with reference to the fourth embodiment, the alignment light intensity control system 68 is provided in this embodiment in addition to the advantages described in the first, second and third embodiments. By providing the above, it becomes possible to eliminate the fluctuation of the alignment light intensity due to the environmental change applied to all of the light source optical system 2 to the light receiving optical system 4, and prevent the deterioration of the positional deviation detection accuracy due to the beat signal intensity fluctuation. It has the advantage that

[0064]

As described above, according to the present invention, a light source optical system for emitting coherent alignment light for aligning an object placed on the image plane of a projection lens, and this light source optical system. And a second optical fiber connected to the position deviation detection optical system via the first optical fiber and arranged in the vicinity of the projection lens, and to the position deviation detection optical system via the second optical fiber. A light receiving optical system for converting the alignment light emitted from the optical signal into an electric signal, and an alignment light intensity control system for making the amplitude of the electric signal from the light receiving optical system constant, A misalignment detection optical system irradiates a diffraction grating on an object with alignment light at a specific incident angle via a fiber, and the diffracted light from this object is guided to a light receiving optical system via a second optical fiber to transmit an electric signal. Then, the amount of displacement of the object is calculated from this electrical signal, the amplitude of the electrical signal is measured by the alignment light intensity control system, and the alignment light incident on the first optical fiber is adjusted so that the amplitude becomes constant. Since the intensity of the light is adjusted, the misalignment detection optical system can be downsized, and mounting on the device can be facilitated, and the effects of environmental changes on everything from the light source optical system to the light receiving optical system can be reduced. It is possible to remove it, and it is possible to prevent the accuracy of positional deviation detection from deteriorating due to fluctuations in the intensity of alignment light, and exposure with a highly accurate alignment system that minimizes the effects of vibration, atmospheric air, and thermal deformation of the device. The device can be realized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a basic configuration of an exposure apparatus in an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a positional deviation detection optical system that irradiates a wafer with alignment light according to the first embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of a light source optical system that generates laser light in the first embodiment.

FIG. 4 is a polarization direction diagram showing the polarization state of the laser light source in the first embodiment.

FIG. 5 is a schematic diagram showing the function of a collimator lens as a spatial filter in the first embodiment.

FIG. 6 is a schematic configuration diagram of a light receiving optical system that receives alignment light in the first embodiment.

FIG. 7 is a partially enlarged cross-sectional view showing a configuration for performing OnAxis alignment in the second embodiment of the present invention.

FIG. 8 is a schematic configuration diagram of a positional deviation detection optical system in the second embodiment.

FIG. 9 is a schematic configuration diagram of a light receiving optical system in the second embodiment.

FIG. 10 is a partial plan view of an alignment mark composed of a two-dimensional diffraction grating in the second embodiment.

FIG. 11 is a schematic sectional view of an image transmission optical fiber according to the second embodiment.

FIG. 12 is a schematic diagram for explaining a method of updating an alignment mark according to the second embodiment.

FIG. 13 is a schematic configuration diagram of a light source optical system in a third embodiment of the present invention.

FIG. 14 is a schematic configuration diagram showing a modification of the light source optical system in the third embodiment.

FIG. 15 is a schematic configuration diagram of a light source optical system, a light receiving optical system, and an alignment light intensity control system in a fourth embodiment of the present invention.

FIG. 16 is a schematic configuration diagram showing an example of a conventional exposure apparatus.

[Explanation of symbols]

1 wafer 2 light source optical system 3 misregistration detection optical system 4 light receiving optical system 5 reticle 6 exposure light 7 projection lens 8 alignment light 12 laser light source 20,21 polarization maintaining optical fiber (first optical fiber) 25,45 alignment Mark (diffraction grating) 28,29 Multimode optical fiber (second optical fiber) 32 Diffraction grating (reference for positional deviation detection) 37,38 Photodetector 39 Phase comparator 40 Wafer stage 43 Image transmission optical fiber 49 Aperture 51 Laser light source 52 Isolator 53,54 Acousto-optic modulator 55,56 Wave plate 57,58 Condensing lens 59 Beam stopper 60,62 0th-order diffracted light 61,63 1st-order diffracted light 64 Beam splitter 65 Beat signal amplitude detector 66 Comparative judgment device 67 Power source for acousto-optic modulator 68 Alignment light intensity control System

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location G03F 9/00 H (72) Inventor Keno Sato 3-10-1 Higashisanda, Tama-ku, Kawasaki-shi, Kanagawa (56) Reference JP 62-291919 (JP, A) JP 64-14918 (JP, A) JP 2-105406 (JP, A)

Claims (7)

[Claims] 1. A light source optical system for emitting coherent alignment light for aligning an object placed on an image plane of a projection lens, and a light source optical system connected to the light source optical system via a first optical fiber. Near the projection lens
A misalignment detection optical system qualitatively arranged directly below the projection lens is electrically connected to the misalignment detection optical system via a second optical fiber, and alignment light emitted from the second optical fiber is electrically generated. a light receiving optical system for converting a signal, before the amplitude of the electrical signal from the light receiving optical system so that a constant
An alignment light intensity control system for controlling the light source optical system, and the alignment light emitted from the light source optical system.
Is the first optical fiber and the positional deviation detection optical system.
The diffraction grating on the object is sequentially irradiated with a certain incident angle of incident light, and the diffracted light from the diffraction grating is irradiated to the position.
The deviation detection optical system and the second optical fiber are sequentially guided to the light receiving optical system to be converted into an electric signal, the amount of positional deviation of the object is obtained from the electric signal, and the alignment light intensity control system further performs the electric operation. An exposure apparatus which measures the amplitude of a signal and adjusts the intensity of the alignment light incident on the first optical fiber so that the amplitude becomes constant. 2. The light source optical system comprises a light source for generating coherent light of one frequency and an acousto-optic modulator which is arranged in series on the optical axis of the light source and sequentially outputs diffracted light of slightly different frequencies. The exposure apparatus according to claim 1, wherein: 3. A light source optical system includes a light source for generating coherent light of one frequency, a beam splitter for splitting the coherent light into two light beams, and two light beams split into two light beams for slightly different frequencies. An acousto-optic modulator that sequentially outputs diffracted light is provided.
The exposure apparatus described. 4. The alignment light intensity control system detects the amplitude of the electric signal converted by the light receiving optical system, and outputs a control signal so that the amplitude of the electric signal becomes constant based on the detection result. 4. The exposure apparatus according to claim 2, further comprising: means for controlling the electric power supplied to the acousto-optic modulator by the control signal. 5. The misregistration detection optical system has a misregistration detection reference therein, and prevents the misregistration detection accuracy from being deteriorated with respect to a disturbance received by the optical fiber from the surrounding environment. Item 4. The exposure apparatus according to item 4. 6. The alignment light emitted from the misregistration detection optical system onto the wafer is reflected on the lowermost coating surface of the projection lens and then onto the wafer, and the diffracted light is reflected from the wafer onto the coating surface. The exposure apparatus according to claim 4 or 5, wherein the exposure apparatus is allowed to move and then incorporated into a positional deviation detection optical system. 7. The diffraction grating is renewed by forming a magnified image of a diffraction grating on a wafer on an aperture by using one of the second optical fibers as an image transmission optical fiber and controlling the position of the aperture. 7. The exposure apparatus according to claim 6, wherein the latest one can be received.