JPH0695007B2 - Positioning method and exposure apparatus - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine pattern alignment method, and further to an exposure apparatus such as a semiconductor device having a submicron rule of 1 micron or less using this method. is there.

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. Conventionally, the alignment of the photomask and the LSI wafer at the time of manufacturing the LSI is performed by using the alignment mark provided on the wafer, by rotating the stage on which the wafer is mounted and biaxially translating the mark on the photomask and the wafer. It was done by overlapping the above marks, but the alignment accuracy is ±
It is about 0.3 micron, and when forming a submicron element, the alignment accuracy is poor and it is not practical. Also,
S. Austin Applied physics Letters Vol31 No.7 P.428,1977, the interferometric alignment method is used, as shown in FIG. 2 and diffracted by the grating 3 formed on the photomask 2, and the diffracted light is again diffracted by the grating 5 formed on the wafer 4 to obtain diffracted light 6, 7, 8 ...
To get This diffracted light is expressed in binary notation of the diffraction order on the photomask and the diffraction order on the wafer. Diffracted light 6 is (0,1), diffracted light 7 is (1,1), and diffracted light 8 is ( -1,2) ...
It can be represented by ... 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 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. However, in this method, the alignment between the photomask 2 and the wafer 4 is performed by the distance D between the photomask 2 and the wafer 4.
Therefore, the accuracy of the distance D is required. Further, 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 is a practical problem.

Also, for alignment of elements with submicron line width,
Although there is a method of observing secondary electrons emitted from the device, it cannot be handled in the atmosphere, so that the throughput in manufacturing LS1 becomes small, which is a practical problem.

In addition, a conventional example shown in FIG. 5 [IEEE, trans on] ED ED-26,4,1974,728, Gijs
Bouwhuis)], the laser beam is incident on the Fourier transform surface of the microlens shown by the lens system of _two L ₁ and L ₂ , and the beam is applied to the grating formed on the wafer via the lens L _2. 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 threads L ₂ and L ₁ , and interference fringes are generated in the vicinity of the reticle R.
A configuration is shown in which light passing through a grating provided on the reticle is detected by a photodetector D and the wafer W and the reticle R are aligned. In the configuration shown in FIG. 3, it is stated that the position cannot be corrected for the asymmetric lattice formed on the wafer W, and in the method of manufacturing 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 As described above, in the related art, there is a problem that fine patterns cannot be aligned in the atmosphere. Therefore, the present invention provides an alignment method and an exposure apparatus that enable accurate and easy alignment of an LSI reticle and a wafer with a simple structure in which the alignment of a fine pattern can be performed with a simple structure. Is intended.

Means for Solving Problems According to the present invention, in order to realize highly accurate alignment in a projection exposure apparatus, a first light flux among the light fluxes divided by a pair of gratings formed on a reticle surface is used. An appropriate light beam is passed through a spatial filter on the spectral plane of the lens, passes through a second lens system and a projection lens, and is projected onto a second pair of gratings provided on the substrate. From the second grating, diffracted light is diffracted and this diffracted light passes in the opposite direction through the second lens of the projection lens 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 difference in the intensity of the pair of diffracted light beams that have interfered with each other, it is possible to perform highly accurate alignment.

That is, in the alignment method of the present invention, when light having coherency is incident from two directions and the alignment of the mask pattern and the pattern on the wafer is performed by the interference of these two light fluxes, the two light flux interference fringes and the lattice on the wafer are aligned. The relative position of (1) is positioned using a mask that is shifted by half the period of the interference fringes and a positioning grid on the wafer, and a mask that is not at all offset and a positioning grid on the wafer.

The exposure apparatus of the present invention has a light source, an illumination optical system, a reticle, a first lens system, a spatial filter, a second lens system, a substrate and a stage for holding the substrate, and a detector arranged near the wafer. , A first grating is formed on the reticle surface, and the light flux is made incident on the reticle surface through an illumination optical system emitted from a light source, and the light flux is divided into wavefronts by a pair of gratings whose position detection signals differ by a half cycle. And guide the light to the first lens system, and selectively transmit a predetermined spectrum with a predetermined spatial filter provided near the spectrum surface of the first lens system.
The light flux having the spectrum is transmitted through the second lens system, and the light flux is 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. The small projection optical system and the second lens system are passed in opposite directions, and the diffracted light diffracted by the pair of gratings on the second wafer corresponding to the grating on the first retil is reduced. The projection optical system and the second lens system are allowed to pass in opposite directions, the light beams diffracted by the second pair of gratings are caused to interfere with each other, the light intensities of the interfered light beams are detected, and the difference is taken. The reticle pattern and the wafer pattern are aligned at a position where the light output becomes zero.

Operation As described above, the present invention can realize highly accurate alignment with the highest position detection sensitivity by using a pair of alignment gratings on a reticle in which the phases of two-beam interference fringes differ by a half cycle.

Example 1 Example 1 of the optical system according to the present invention is shown in FIG. light source
Light emitted from 11 (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 interference optical system, such as mercury. (Which may be a spectral light source of 1) is incident on the entrance pupil of the first lens system 15.

In the following description, the reticle is illuminated by a collimated beam and the first and second lens systems 15,15 ', 17,17' are Fourier-exchange lenses, but not necessarily, in order to briefly describe the principles of the invention. It may not be a Fourier transform lens. light source
The reticle 14 is disposed between the first Fourier transform lens 15 and 15 'and the first Fourier transform lens 15 and 15', and a pattern of a pair of first gratings 10 and 10 'formed on the reticle 14 is used as a secondary light source to form an image. The first Fourier transform lens 15, 15 'once collects the light, and then the second Fourier transform lens 17, 17' projects the image of the pattern of the reticle 14 onto the wafer 18 through the reduction projection optical system 19. Diffracted light (Fourier spectrum) of the pattern of the gratings 10 and 10 'on the reticle is spatially distributed on the rear focal plane of the first Fourier transform lens 15 and 15'. Spatial filters 16 and 16 'are arranged on the Fourier transform plane to perform filtering in the spectral plane, and the pattern of the pair of gratings 10 and 10' formed on the reticle 14 is filtered in the spectral plane so that the pattern is formed on the wafer 18 plane. Interference fringes 20 and 20 'are generated. And
Further, a reticle grid 1 formed on the semiconductor wafer 18
Second pair of gratings 2 formed at positions corresponding to 0,10 '
Diffracted lights 22 and 22 'are diffracted from 1, 21', return to the reduction projection optical system 19 and second lenses 17, 17 'in opposite directions, and are placed at the positions of the spatial filters 16, 16'. The photodetector 23,2 at the position corresponding to the alignment grid position by
You are led to 3 '. The optical signals detected by the photodetectors 23 and 23 'are input to the comparator 24, and when the optical outputs of both are equal, the reticle and the wafer are positioned.

The above is the optical system for aligning the reticle 14 and the wafer 18.On the other hand, the circuit pattern of the reticle 14 is illuminated by the projection light source 12 and the illumination optical system 13, and its projected image is passed through the reduction projection optical system 19. An image is formed on the wafer 18.

As described above, the ordinary optical system for exposing the circuit pattern is formed in this manner.

FIG. 3 is an explanatory view of the principle 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. The phase grating pattern 41 on the reticle 14 is arranged at the position z ₁ of the front focal point ₁ of the first Fourier transform lens 15.
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. 1, the spatial filter 16 is arranged on this Fourier transform plane to block the diffracted light of 0th order and ± 2nd order or more of the grating pattern 41 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 19 is omitted in FIG.

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 an interference fringe with a new pitch. To be done. Here, the pitch P ₂ of the interference fringes 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.

The the observed light intensity I on the optical detector D of Figure 6 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 Amplitude strength, u _A ^* , u _B
^* Is the conjugate complex 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, θ _A and θ _B are shown as the angles formed by the light fluxes 111 and 112 and the vertical of the wafer. ) FIG. 2 is a position detection signal observed by the photodetector obtained by the present invention. The period of the position detection signal is equal to the pitch of the interference fringes of the two light fluxes and is given by the following equation as described above.

Therefore, by using a grating on the reticle with a half phase shift of the pitch of the interference fringes, the position detection signal inverts the position detection waveform as shown in FIG. Therefore, by comparing the signals obtained from the grating whose phase is shifted by half and the grating whose phase is not shifted, and by positioning the wafer and reticle at the locations where the optical outputs of both are equal, it is possible to perform highly accurate alignment with high position detection sensitivity.

EFFECTS OF THE INVENTION As described above, according to the present invention, the pattern on the reticle can be aligned on the wafer with high accuracy through the interference fringes, and the pattern on the reticle can be exposed and formed on the wafer.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an exposure apparatus showing a basic concept of alignment according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a relationship between alignment detection signals and positioning according to the present invention, and FIG.
FIG. 4 is a principle diagram of the re-diffraction optical system according to the present invention, FIG. 4 is a principle diagram of alignment by the conventional double grating method, and FIG. 5 is alignment of a conventional reticle and a wafer by using interference fringes. It is a block diagram when it does. 11 …… Positioning light source, 12 …… Projection light source, 13 …… Illumination optical system, 14 …… Reticle, 15,17 …… First and second Fourier transform lens, 16 …… Spatial filter, 18 …… Wafer, 19
...... Reduction projection optical system, G ... Lattice, D ... Photodetector.

Claims (2)

[Claims] 1. When the light having coherency is incident from two directions and the mask pattern and the pattern on the wafer are aligned by the interference of these two light fluxes, the relative positions of the two light flux interference fringes and the grating on the wafer are A positioning method in which positioning is performed by using a mask and a positioning grid on the wafer that are shifted by half the period of the interference fringes, and a mask and a positioning grid on the wafer that are not shifted at all. 2. A reticle surface having a light source, an illumination optical system, a reticle, a first lens system, a spatial filter, a second lens system, a substrate and a stage for holding the substrate, and a detector arranged near the wafer. The first grid is formed on the top,
The light flux is made incident on the reticle surface through an illumination optical system emitted from a light source, and the light flux is wavefront-divided by a pair of gratings whose position detection signals have different half cycles, and is guided to the first lens system. A predetermined spectrum is selectively transmitted by a predetermined spatial filter provided in the vicinity of the spectrum surface of the first lens system, a light beam having the spectrum is transmitted through the second lens system, and the reduced projection optical system is used. A light flux is projected through the system onto a substrate having a second grating, and the diffracted light diffracted from the second grating is passed through the reduced projection optical system and the second lens system in the opposite direction, Diffracted light diffracted by a pair of gratings on the second wafer corresponding to the grating on the retile is passed through the reduced projection optical system and the second lens system in opposite directions,
The light beams diffracted by the second pair of gratings are caused to interfere with each other, and the light intensities of the interfered light beams are respectively detected, and the difference is taken and the light output becomes zero. An exposure apparatus characterized by matching.