JPH07101665B2 - Exposure equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus such as an apparatus having a fine pattern, particularly a semiconductor apparatus having a submicron rule of 1 micron or less.

2. Description of the Related Art Semiconductor devices have been densified more and more recently, and the size of the fine pattern of each element is less than 1 micron. In the conventional alignment of the photomask and the LSI wafer during LSI manufacturing, the alignment mark provided on the wafer is used to rotate the stage on which the wafer is mounted and move it in two axes in parallel. Although it was done by overlapping the marks of, the alignment accuracy is ± 0.
It is about 3 microns, and when forming sub-micron elements, the alignment accuracy is poor and it is not practical. Also, S.
Austin 〔Applied physics Letters
Physics Letters) Vol 31 No.7p.428, 1977] et al., The alignment method using the interferometry causes the incident laser beam 1 to enter the photomask 2 as shown in FIG. Diffract with the grating 3 formed above,
By diffracting the diffracted light again by the grating 5 formed on the wafer 4, diffracted light 6, 7, 8 ... Is obtained. When this diffracted light is represented by a binary representation of the diffraction order on the photomask and the diffraction order on the wafer, the diffracted light 6 is (0,
1), diffracted light 7 can be represented by (1,1), and diffracted light 8 can be represented by (-1,2) .... The diffracted light is collected by a lens at one point and the light intensity is measured. The diffracted light has a light intensity at a position symmetrical with respect to the incident laser beam 1, and the photomask 2
The wafer 4 and the wafer 4 can be aligned by matching the intensities of the diffracted light observed on the left and right. With this method, the alignment accuracy is said to be several hundred Å. But,
In this method, the alignment between the photomask 2 and the wafer 4 is greatly affected by the distance D between the photomask 2 and the wafer 4, and thus the accuracy of the distance D is required. Also,
It is necessary to bring the photomask 2 and the wafer 4 close to each other and align them while maintaining the accuracy of the distance D, which complicates the apparatus, which causes a problem in practical use.

Also, for alignment of elements with submicron line width,
There is a method by observation by secondary electron emission from the device, but since it cannot be handled in the atmosphere, there was a problem in practical use because the slew butt in manufacturing LSI was small.

In addition, the conventional example shown in FIG.
IEEE, trans on ED ED-26,4,1974,723,
Gijs Bouwhuis], the laser beam is incident on the Fourier transform surface of the microlens shown by the _two L ₁ and L ₂ lens systems, and the beam is directed to the grating formed on the wafer via the lens L _2. 1 is illuminated, and only the ± 1st-order light diffracted from the grating by the spatial filter SF is incident on the reticle R through the lens systems L ₂ and L ₁ , and interference fringes are generated in the vicinity of the reticle R and provided on the reticle. The light passing through the grating is detected by the photodetector D.
The configuration is shown in which the wafer W and the reticle R are aligned by being detected by. In the configuration of FIG. 4, it is postulated that the position cannot be corrected for the asymmetrical grating formed on the wafer W, and in the manufacturing method of the alignment mark, it cannot be realized in all steps and marks. It is possible and not enough for practical use.

Problems to be Solved by the Invention In view of such problems in the related art, the present invention enables accurate and easy positioning of an LSI reticle and a wafer that can perform alignment of a fine pattern in the atmosphere and with a simple configuration. The purpose is an aligner that enables alignment.

Means for Solving Problems According to the present invention, in order to realize highly accurate alignment in a projection exposure apparatus, among the light fluxes that are wavefront-divided by an alignment grating, an appropriate light flux is present on the spectral plane of the first lens. Through a spatial filter to a second lens system,
The light is passed through the projection lens and projected onto the second grating provided on the substrate. From the second grating, diffracted light is diffracted, and this diffracted light passes through the second lens of the projection lens in the opposite direction and is guided to the photodetector. When the two light beams are projected from the appropriate direction on the second grating on the substrate, the diffracted lights are diffracted in the overlapping direction and interfere with each other. By detecting the light intensity of the interfered diffracted light, highly accurate alignment can be realized.

By combining the positioning optical system and the projection lens, it is possible to separate the optical system for reducing and projecting the reticle image and the optical system for performing highly accurate positioning, which is used for positioning when projecting the reticle image. Since exposure can be performed without attaching or detaching the spatial filter, the mirror, etc., more accurate alignment can be realized.

Embodiment An embodiment of the optical system according to the present invention is shown in FIG. Light source 11
Light emitted from (In this figure, in order to obtain clearer coherence and a deeper depth of focus, the laser light is assumed, but the entire optical system is a white optical system and the spectrum of mercury lamps, etc. Light source) may be incident on the entrance pupil of the first lens system 15.

In the following description, in order to briefly describe the principle of the present invention, the reticle is illuminated by a parallel light beam, and the first and second lens systems 15 and 17 are Fourier transform lenses, but they are necessarily Fourier transform lenses. It does not have to be a lens. Light source 11 and first
The alignment grating 24 is disposed between the second Fourier transform lens 15 and the second Fourier transform lens 17, and the alignment grating 24 is used as a secondary light source. A pattern image of the lattice is projected onto a wafer (semiconductor substrate) 18 through a reduction projection optical system 19. The diffracted light (Fourier spectrum) of the alignment grating pattern is spatially distributed on the rear focal plane of the first Fourier transform lens 15. In the present invention, the spatial filter 16 is arranged on this Fourier transform plane. Wafer 18 by spectrally filtering the alignment grating pattern 24 in the spectral plane.
Interference fringes 20 are generated on the surface. Diffracted light 22 is diffracted from the second grating 21 formed on the semiconductor wafer 18, returns in the reverse direction through the reduction projection optical system 19 and the second lens 17, and is a mirror arranged at the position of the spatial filter 16. By photo detector 23
Be guided to. The above is the position detection system of the alignment mark on the wafer, but the alignment procedure of the pattern of the reticle and the wafer is performed by the fixed target mark 27 on the stage 26 precisely controlled by the laser length measuring machine 25 and the reticle. The reticle is aligned with the stage coordinates by observing the fixed target mark 28 of FIG. Next, after aligning about 0.5 μm by the conventional global alignment method using a cross mark or the like, the second grating 21 on the wafer is moved to the position of the interference fringe 20 by the laser length measuring machine. Then, the stage is slightly moved to cause interference fringes.
The alignment between 20 and the second grating 21 is performed. After that, the stage is moved to the coordinate position to be exposed, which is calculated from the alignment position of the interference fringe 20 and the second grating 21 on the wafer, by the laser length measuring machine, and the exposure is performed. In the embodiment of the present invention, the first and second Fourier transform lenses 15 and 17 and the spatial filter 16 are used to form the interference fringe 20. However, as shown in FIG. 20 may be formed and positioning between the interference fringe 20 and the grating 21 on the wafer 18 may be performed.

FIG. 3 is a principle explanatory view of the exposure apparatus of the present invention. The light of wavelength λ emitted from the light source 11 illuminates the grating 41 on the reticle. Position x of front focal point ₁ of the first Fourier transform lens 15
₁ to place the phase grating pattern 41 on the reticle 14. The pitch P ₁ of the phase grating pattern 41 and the diffraction angle θ ₁ of the diffracted light have a relationship of P ₁ sin θ _n = nλ (n = 0, ± 1, ± 2, ...). The light diffracted into a plurality of light beams in this way enters the Fourier transform lens 15, and further forms a Fourier spectrum image corresponding to each diffracted light on the rear focal plane. The coordinates ξ ₆₁ corresponding to the Fourier spectrum of the first-order diffracted light are shown by ξ ₆₁ = ₁ sinθ ₁ P ₁ sinθ ₁ = λ, and the Fourier spectrum of the 0th-order diffracted light ξ ₆₀ ξ ₆₀ = ₁ sinθ ₀ = 0 A Fourier spectrum image is formed on the Fourier transform plane in a completely separated state. As shown in FIG. 3, the spatial filter 18 is arranged on this Fourier transform plane, and as shown in FIG. The spectrum of the folding light and the aperture pattern (excluding the 0th-order light component) is passed. This diffracted light is the second
It passes through the Fourier transform lens 17 and is further projected onto the wafer 18W.

However, the reduction projection lens system is omitted in FIGS. 3 and 4. The image projected on the wafer W roughly connects the images of the openings (pattern 41) on the reticle, and the ± first-order light components of the grating pattern 41 interfere with each other to form interference fringes with a new pitch. To be done. Where the interference fringe pitch P
₂ is Given in. At this time, since the Fourier transform plane of the first Fourier transform lens 15 is set on the front focal plane of the second Fourier transform lens 17, there is a relation of ₁ sin θ ₁ = ₂ sin θ ₂ = ξ ₆₁ .

The first and second Fourier transform lenses 15 and 17, and between the images passing through the reduction projection optical system with the reduction ratio m, Have a relationship. Therefore, when ₁ = ₂ , the pitch P _{2 of the} interference fringes generated on the wafer W is half the pitch of the projected image of the grating pattern 41 on the reticle. A second grating G is formed on the wafer W by the projected image of the grating 41, and when the lights of the light fluxes 111 and 112 are applied to the grating G, the lights diffracted by the grating G for wavefront division are generated. can get. Further, when the two light beams 111 and 112 are simultaneously irradiated onto the wafer W, interference fringes are generated, and further, in this case, the lights diffracted by the grating G on the wafer W interfere with each other, and the interfered lights are detected by the photodetector D. The light intensity information indicating the positional relationship between the interference fringes and the grating G is obtained.

Light intensity I observed on the fourth diagram of the optical detector D is ^{_{I = u A 2 + u B}} 2 + u A * · u B + u A · u B * However, u _A, u _B each light beam 111, 112 Vibration strength u _A ^* , u
_B ^* is the complex conjugate amplitude.

(Where A and B are constants, N is the number of gratings, δA and δB are the optical path differences between the lights diffracted by two adjacent gratings, and x is the luminous flux.
The relative positional relationship between the interference fringes of 111 and the light flux 112 and the grating, and θ _A and θ _B are shown as angles formed by the light fluxes 111 and 112 and the vertical line of the wafer.

EFFECTS OF THE INVENTION According to the present invention, it is possible to detect the alignment mark on the wafer with high precision through the interference fringes. As a result, the reticle and the pattern on the wafer can be precisely aligned and exposed. Furthermore, since the projection optical system and the alignment optical system are configured as different optical paths, different wavelength alignment can be performed. Further, it becomes possible to perform exposure without attaching or detaching the spatial filter or the mirror system, so that an exposure apparatus with high alignment accuracy can be constructed.

[Brief description of drawings]

1 and 2 are the basic front view of the alignment in the exposure apparatus of one embodiment of the present invention, FIG. 3 is the principle diagram of the re-diffraction optical system according to the present invention, and FIG. 4 is the present invention. FIG. 5 is a detailed view of the vicinity of the wafer, FIG. 5 is a principle view of alignment by the conventional double lattice method, and FIG. 6 is a configuration diagram when aligning the conventional reticle and the wafer by using interference fringes. 11 …… Light source, 12 …… Projection light source, 13 …… Illumination optical system, 14
...... Reticle, 15,17 …… First and second Fourier transform lenses, 16 …… Spatial filter, 18 …… Wafer, G …… Grating, D …… Photodetector, 24 …… Alignment grating, 25 ...... Laser length measuring machine, 27 …… Fixed target on stage, 28 ……
Fixed target on reticle.

Claims (2)

[Claims] 1. An exposure apparatus having an exposure light source, an illumination optical system, a reduction projection exposure optical system, a substrate, and a stage whose position is precisely measured by a laser length measuring machine, further comprising a light source, a wavefront splitting element, a reticle and a first stage. 1 lens system, spatial filter,
A second lens system, an alignment optical system having a photodetector, and a light flux emitted from the light source is incident on the wavefront splitting element through an illumination optical system to split the light flux into wavefronts, and the first lens The two light beams of the order ± N (N is an integer) are selectively transmitted by a predetermined spatial filter provided in the vicinity of the Fourier transform surface of the first lens system while guiding the two light beams to the system. 2 lens system,
Further, the two light fluxes are projected onto the substrate having the second grating through the reduction projection optical system, and the diffracted light diffracted from the second grating passes through the reduction projection optical system and the second lens system in the opposite direction. On the basis of the change in the optical output of the light diffracted and interfered by the second grating measured by the photodetector and the stage position measured by the laser interference system, the second grating position on the substrate is determined. An exposure apparatus, wherein the reticle pattern and the pattern on the wafer are aligned by measuring. 2. An exposure apparatus having an exposure light source, an illumination optical system, a reduction projection exposure optical system, a substrate, and a stage whose position is precisely measured by a laser length measuring machine, further comprising a light source, a wavefront division element, a spatial filter, A positioning optical system having a photodetector is provided, and a light flux emitted from the light source is incident on the wavefront splitting element through an illumination optical system to split the light flux into wavefronts, and the spatial filter causes ± N (N is an integer). The following two light fluxes are selectively transmitted, the two light fluxes are projected on the substrate having the second grating through the reduction projection optical system, and the diffracted light diffracted from the second grating is reduced by the reduction projection optical system. , A change in light output measured by the photodetector of light that has passed through the second lens system in the opposite direction and is diffracted and interfered by the second grating, and a stage position measured by a laser interference system. Exposure apparatus characterized by aligning a pattern on the reticle pattern and the wafer by measuring the second grid positions on the substrate have not a group.