JPH0566108A - Positioning device - Google Patents

Abstract

PURPOSE:To highly precisely position a reticule and a wafer through a projecting optical system in a positioning device used in various exposing devices by correcting the convergence error in an alignment wavelength different from an exposing wavelength, and imaging a positioning mark image on the reticule onto the wafer through a correcting optical system and a lens. CONSTITUTION:A first positioning mark 5 provided on a first object 1 situated on the object surface of a projecting optical system, a second positioning mark 6 provided on a second object 2 situated on the image surface of the projecting optical system, and a light source 4 emitting a coherent alignment light of two frequencies having a wavelength different from an exposing wavelength are provided. A correcting optical system 7 for correcting the convergence error of the projecting optical system so as to perform a precise imaging onto the second object surface in conformation to a specified area where an interference fringe is formed on the first object, a spatial filtering optical system 13 for removing a speckle pattern from the light returned from the second positioning mark 6, and a light detecting means 15 for detecting a light beat signal from the light transmitted through the space filtering optical system are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment apparatus used in an exposure apparatus for transferring a pattern on a reticle onto a wafer via a projection optical system.

[0002]

2. Description of the Related Art In recent years, the density of semiconductor devices has become higher and higher, and the size of the fine pattern of each element is about 0.5 μm or less. In the exposure of such a fine pattern, in order to perform the multiple exposures required for semiconductor manufacturing, the alignment between the exposures is extremely important, and the overlay accuracy is 0.1.
μm or less is required.

A conventional positioning device is disclosed in Japanese Patent Laid-Open No. 63-63
The configuration disclosed in Japanese Patent Publication No. 78004 is known. Hereinafter, the conventional alignment device will be described with reference to the drawings.

FIG. 4 shows a conventional exposure apparatus. In FIG. 4, the coherent two-frequency alignment light emitted from the laser light source 111 is split into two light fluxes by the mirror 109b, and the split light fluxes are respectively reflected by the mirror 10.
9b, via mirror 109a, or mirror 109b
It is incident on and diffracted by a pair of first diffraction gratings 110a or 110b formed on the reticle 114 via only. Each diffracted light is transmitted through the first lens system 115a or 115
An appropriate luminous flux is obtained on the spectral plane of b, and the spatial filter 1
16a or 116b, and the second lens system 1
It passes through the projection lens 119 via 17 a or 117 b and is projected onto the second pair of diffraction gratings 121 a or 121 b provided on the wafer 118. The diffracted light 122a or 122b from the diffraction grating 121a or 121b passes through the projection lens 119 and the second lens systems 117a and 117b in the opposite direction and is guided to the photodetector 123a or 123b.

A second diffraction grating 121 on the wafer 118.
When two light fluxes are projected on a and 121b from an appropriate direction, the diffracted lights are diffracted in the overlapping direction and interfere with each other.
The pair of interfering diffracted light intensities are detected by the photodetectors 123a and 1a.
23b, the detection result is compared by the comparator 124, the wafer 118 is moved by the drive of the control system 125, and a portion where the difference between the pair of diffracted light intensities is zero is selected. The alignment with the wafer 118 becomes possible.

On the other hand, the pattern of the reticle 114 is illuminated by the projection light source 112 and the illumination optical system 113,
The projected image is formed on the wafer 118 via the projection lens 119.

[0007]

In the above-mentioned conventional configuration, the exposure light emitted from the projection light source 112 and the alignment light emitted from the laser light source 111 have substantially the same wavelength, and the projection lens 119 is the same for both. It is effective only when excellent imaging performance is exhibited. For example, in the future,
For ultraviolet light such as excimer laser, which is expected to become the mainstream of exposure light, the glass material for forming the refracting optical system is limited, so it is not possible to form an achromatic projection optical system with chromatic aberration corrected. It's extremely difficult. For this reason, the projection lens 119 is designed to be sufficiently color-corrected only at the exposure wavelength, and exhibits extremely large chromatic aberration with respect to light of other wavelengths. Therefore, it is desirable that the wavelength of the alignment light is sufficiently close to the exposure wavelength.

However, from the semiconductor manufacturing process,
It is desired that the alignment wavelength be sufficiently far from the exposure wavelength. The reason for this is that the use of high-sensitivity resists such as chemically sensitized resists may cause the exposure of the resists by alignment light, and the multi-layered resists and multi-layered resists used to supplement the imaging performance of the projection lens 119. The point is that the resist containing a dye that prevents reflection absorbs alignment light near the exposure wavelength. That is, the wavelength of the alignment light must be sufficiently distant from the exposure wavelength due to the semiconductor manufacturing process. Therefore, the configuration of the conventional example has a problem that it is difficult to perform highly accurate alignment between the reticle and the wafer.

The present invention is to solve the above-mentioned problems of the prior art, and through-the-lens
In the alignment (TTL alignment), a wavelength different from the exposure wavelength is used as the alignment light, and the first
It is an object of the present invention to provide a positioning device capable of highly accurately positioning the second object.

[0010]

To achieve this object, the present invention provides a diffraction grating provided on a first object located on the object plane of a projection optical system and an image plane of the projection optical system. An alignment mark provided on the second object located on the first object, a light source for emitting coherent alignment light of two frequencies having a wavelength different from the exposure wavelength, and a first area corresponding to the specific area on the first object. A correction optical system that corrects chromatic aberration of the projection optical system so that an image is properly formed on the second object plane, a spatial filtering optical system that removes a speckle pattern from light returning from the second alignment mark, and It is an alignment device provided with a photo-detecting means for detecting an optical beat signal from the light transmitted through a spatial filtering optical system.

[0011]

According to the present invention, with the above structure, the first alignment mark on the first object is placed on the second alignment mark on the second object and has a wavelength different from that of the exposure light. Frequency alignment light is used for projection, the speckle pattern is removed by the optical system for spatial filtering, the alignment light is received by the photodetector, and the optical beat signal obtained by this photodetector and the first object are detected. From the misalignment signal obtained from the phase comparison with the optical beat signal of the return light from the first alignment mark or the optical beat signal obtained from the laser,
The relative position of the first and second objects can be detected and aligned.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an alignment apparatus according to an embodiment of the present invention, and FIG. 2 is a plan view of a reticle showing a specific region within the angle of view of a projection lens used in the present invention, FIG. 3 is a polarization direction diagram showing the polarization state of laser light emitted from the laser light source used in the present invention.

In FIG. 1, 1 is a reticle of an exposure original plate which is a first object, 2 is a wafer which is a second object on which a pattern is exposed, 3 is a projection lens, 4 is a light source for alignment, Two orthogonally polarized different frequencies (f ₁ , f ₂ )
The alignment light 11 is emitted. 5 is an alignment mark which is a diffraction grating provided on the reticle 1, 6 is an alignment mark which is a diffraction grating provided on the wafer 2,
Reference numeral 7 is a correction optical system for correcting chromatic aberration, 8 is a spatial filter, 9 is a polarization optical element, 11 is alignment light which passes through a predetermined optical path and is diffracted by the alignment mark 6 which is a diffraction grating, and 13 is a spatial filter. It is an optical system for spatial filtering including 14.

In FIG. 2, 21 is an effective angle of view of the projection lens 3 with respect to the reticle 1, and 22 is a specific area for color correction.

The operation of the position adjusting device having the above-described structure will be described below. First, the projection lens 3 is arranged so as to project the image of the reticle 1 onto the wafer 2. Since the projection lens 3 is designed according to the exposure wavelength, if the alignment mark 5 on the reticle 1 emitted from the light source 4 is imaged on the wafer 2 only by the projection lens 3, chromatic aberration is too large. It is impossible. Here, the correction optical system 7 corrects the chromatic aberration of the projection lens 3 in a specific region 22 (the same annular region in FIG. 2) of the effective field angle 21 of the projection lens 3, as shown in FIG. The alignment mark 5 existing in the specific area 22 on the reticle 1 illuminated by the alignment light 11 emitted from the light source 4 is accurately projected and imaged on the wafer 2.

That is, the refractive index of the projection lens 3 for the light (λ = 248.5 nm) of the KrF excimer laser which is the actual exposure light is greatly different from the refractive index for the visible light such as the alignment light 11. Therefore, the chromatic aberration of the projection lens 3 that is optimally designed according to the excimer laser light with respect to the alignment light 11 is extremely large, and it is extremely difficult to design a correction optical system capable of performing color correction of the entire angle of view of the projection lens 3. Therefore, within the angle of view of the projection lens 3, a correction optical system 7 is used that performs color correction on a very limited area where the alignment mark 5 exists. This makes the correction optical system 7 considerably easier to design.

The alignment mark 5 on the reticle 1 is composed of a diffraction grating, is illuminated by the alignment light 11 emitted from the light source 4, and the transmitted light is divided into a large number of diffracted lights, which are then corrected to correct chromatic aberration. Only the ± first-order diffracted light is transmitted through the optical system 7 and enters the polarizing optical element 9 by the spatial filter 8. As shown in FIG. 3, the light source 4 is an optical unit that emits coherent light beams having frequencies f ₁ and f ₂ which are orthogonal to each other. As such an optical unit, a magnetic field is applied to a laser tube. A Zeeman laser that obtains two frequencies, or a device that obtains two frequencies by performing Doppler shift of laser light using an ultrasonic wave or a rotating diffraction grating that propagates in one direction can be used. Also, f ₁ and f ₂
The frequency difference is generally tens of KHz to tens of MHz.

The polarization optical element 9 transmits only _one of the two frequencies f ₁ and f ₂ of the coherent alignment light. Further, by using a polarizing plate or a combination of a polarizing beam splitter and a phase plate as the polarizing optical element 9 or using a properly designed dielectric multilayer film, the transmitted light can be circularly polarized. The alignment lights f ₁ and f ₂ transmitted through the polarization optical element 9 pass through the projection lens 3 and the wafer 2
Image. The alignment light 11 diffracted by the alignment mark 6 on the wafer 2 passes through the projection lens 3 again, is reflected by the total reflection mirror 10, and enters the spatial filtering optical system 13 including the spatial filter 14.

After the speckle pattern (speckle noise) caused by the surface state of the wafer 2 is cut by the spatial filtering optical system 13 including the spatial filter 14, the diffracted light 12 is formed on the photodetector 15. Image. Alignment light directed onto the optical detector 15, by placing a polarizing plate or the like on the way in which case the polarization state of the linearly polarized light, as it is the case of circular polarization, the frequency f ₁ and f interfere with each other A beat equal to the difference of ₂ is produced. This beat signal has information on the amount of positional deviation of the wafer 2 in the phase of the sine wave, and another detector (not shown) for detecting a beat signal that does not include information on the amount of positional deviation is used. Measuring the output of the two photodetectors with a phase difference detector (eg, phase meter)
If the measurement is performed by, the amount of positional deviation of the wafer 2 with respect to the reticle 1 can be accurately known.

Further, the cover 17 is provided with the light source 4 and the projection lens 3.
The alignment light 1 caused by the fluctuation of air is provided by covering the optical path of the alignment light 11 between
It is possible to prevent the detection accuracy from deteriorating due to the phase fluctuation of 1.

As described above, according to this embodiment, the alignment mark 5 on the reticle 1 placed at a specific position is illuminated with the alignment light 11 having two frequencies different from the exposure wavelength, and the alignment mark 5 is illuminated. For the ± 1st-order diffracted light diffracted by 5, only _one of the two frequency components f ₁ and f ₂ of the alignment light 11 is transmitted, and the alignment mark on the wafer 2 is adjusted by the correction optical system 7 and the projection lens 3. After spatially filtering the light that has been projected onto 6 and re-diffracted, the photodetector 1
5, the beat signal is detected, and the phase information of the beat signal is checked to find the positional deviation of the wafer 2 with respect to the reticle 1. Based on this positional deviation detection amount, the wafer 2 is detected.
The reticle 1 can be operated to eliminate the positional deviation, and accurate alignment can be performed.

[0023]

As described above, according to the present invention, the first alignment mark on the first object is placed on the second alignment mark on the second object, and the wavelength is different from that of the exposure light. After using the two-frequency alignment light to remove the speckle pattern with the spatial filtering optical system, the photodetector receives the alignment light, and the optical beat signal obtained by the photodetector and the first The relative position of the first and second objects from the position shift signal obtained by phase comparison with the optical beat signal of the return light from the first alignment mark on the object or the optical beat signal obtained from the laser So that it can be aligned with the
In the lens alignment, it is possible to perform highly accurate alignment of the first and second objects by using a wavelength different from the exposure wavelength as the alignment light.

[Brief description of drawings]

FIG. 1 is a front view of a positioning device according to an embodiment of the present invention.

FIG. 2 is a plan view of a reticle showing a specific area within an angle of view of a projection lens which performs color correction used in a positioning device according to an embodiment of the present invention.

FIG. 3 is a perspective view showing a polarization state of laser light emitted from a laser light source used in the alignment apparatus in one embodiment of the present invention.

FIG. 4 is a front view of a conventional alignment device.

[Explanation of symbols]

 1 Reticle 2 Wafer 3 Projection Lens 4 Light Source 5 Alignment Mark 6 Alignment Mark 7 Correction Optical System 8 Spatial Filter 9 Polarizing Optical Element 10 Total Reflection Mirror 11 Alignment Light 12 Reflected Diffracted Light 13 Spatial Filtering Optical System 14 Spatial Filter 15 Light Detector 16 Illumination optical system 17 Cover

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takeo Sato 3-10-1 Higashisanda, Tama-ku, Kawasaki City, Kanagawa Matsushita Giken Co., Ltd. (72) Shinichiro Aoki 3-chome, Higashisanda, Tama-ku, Kawasaki City, Kanagawa Prefecture No. 10 No. 1 Matsushita Giken Co., Ltd.

Claims (4)

[Claims] 1. A diffraction grating provided on a first object located on the object plane of the projection optical system, and an alignment mark provided on a second object located on the image plane of the projection optical system, A light source that emits coherent alignment light of two frequencies having a wavelength different from the exposure wavelength, and the projection optical system for correctly forming an image on the second object surface corresponding to a specific area on the first object. A correction optical system that corrects chromatic aberration, a spatial filtering optical system that removes a speckle pattern from light returning from the second alignment mark, and an optical beat signal is detected from light that has passed through the spatial filtering optical system. Positioning device provided with a light detecting means for. 2. The alignment device according to claim 1, wherein the alignment mark on the second object is a diffraction grating. 3. A first object, a chromatic aberration correction optical system, a projection lens, a second object, a projection lens, a spatial filtering optical system, and a light detection means are sequentially provided on a path through which coherent light passes. The alignment device according to claim 1 or 2, characterized in that: 4. A light source for emitting alignment light, a first object, and a first one of paths through which coherent light passes.
The alignment device according to claim 1, further comprising a cover that covers a path between the object and the projection lens.