JPH0544817B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an exposure apparatus for devices having fine patterns, particularly semiconductor devices and the like having a submicron rule of 1 micron or less.

Conventional Structure and Problems Semiconductor devices have recently become more and more densely packed, and the dimensions of the fine patterns of each element are now 1 micron or less. Conventionally, alignment between a photomask and an LSI wafer during LSI manufacturing is achieved by rotating and parallelly moving a stage on which the wafer is mounted, using alignment marks provided on the wafer, to align the marks on the photomask with the marks on the wafer. This was done by superimposing the images, but the alignment accuracy was ±
It is about 0.3 microns, and when forming submicron elements, the alignment accuracy is poor and it is not practical. Also, S. Austin (Applied physics
In the alignment method using interferometry shown by Letters Vol 311 No. 7 P. 428, 1977), as shown in Fig. 1, an incident laser beam 1 is made incident on a photomask 2, The diffracted light is diffracted by the grating 3 formed on the wafer 4, and the diffracted light is again diffracted by the grating 5 formed on the wafer 4, thereby obtaining diffracted lights 6, 7, 8, and so on. When this diffracted light is expressed as a binary representation of the diffraction order at the photomask and the diffraction order at the wafer, the diffraction light 6 is (0,
1), the diffracted light 7 is (1,1), and the diffracted light 8 is (-1,
2) It can be expressed as... This diffracted light is collected at one point by a lens and the light intensity is measured. The diffracted light has a light intensity at a position symmetrical 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 sides. The alignment accuracy of this method is said to be several hundred angstroms. but,
In this method, a photomask 2 and a wafer 4 are
Since the alignment with the photomask 2 and the wafer 4 is greatly influenced by the distance D between the photomask 2 and the wafer 4, 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 and poses a problem in practical use.

In addition, there is a method for aligning elements with submicron line widths through observation using secondary electron emission from the elements, but this method cannot be handled in the atmosphere, which reduces the throughput in manufacturing LSIs. There was a practical problem.

Purpose of the Invention In view of these conventional problems, the present invention provides a method for accurately and easily aligning an LSI reticle and a wafer, which allows fine pattern alignment to be performed in the atmosphere and with a simple configuration. The purpose is to

Structure of the Invention In order to realize highly accurate positioning in a projection exposure apparatus, the present invention provides for a first lens system having a spectral plane of ± The first-order light is passed through a spatial filter, the ±1st-order light is guided to a second lens system, and the interference fringes generated by the two light beams are projected onto the substrate. This provides a configuration of an exposure apparatus in which positioning between the second grating and the interference fringes is performed by measuring, with a photodetector, a change in the optical output of the diffracted light diffracted from the second grating.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the optical system according to the present invention is shown in FIG. Light emitted from the light source 11 (In order to obtain clearer coherence and deeper depth of focus, the configuration is assumed to be a laser beam, but the overall optical system is a white interference optical system, and a mercury lamp is used.) A spectral light source such as The light enters the entrance pupil of the lens system 15.

In the following description, in order to briefly describe the principle of the present invention, it is assumed that the reticle is illuminated by a parallel light beam, and that the first and second lens systems are Fourier transform lenses, but they are not necessarily Fourier transform lenses. It doesn't have to be.

Light source optical system 13 and first Fourier transform lens 1
A reticle 14 is arranged between the reticle 1 and the reticle 1.
The image produced using the pattern No. 4 as a secondary light source is once focused by the first Fourier transform lens, and then the image of the pattern on the reticle is projected onto the wafer 18 through the second Fourier transform lens 17. 1st
When the focal lengths of the Fourier transform lens and the second Fourier transform lens are made equal, the pattern on the reticle is projected at the same magnification. By changing the focal lengths of the first and second Fourier transform lenses, reduced projection becomes possible. On the rear focal plane of the first Fourier transform lens, the diffracted light (Fourier spectrum) of the pattern on the reticle is spatially distributed, and in the configuration example of the present invention, on this Fourier transform surface,
Interference fringes are formed on the surface of the wafer 18 by arranging a spatial filter 16 to filter the pattern formed on the reticle in the spectral plane.

FIG. 3 shows a reticle used in the exposure apparatus of the present invention. FIG. 3a is a plan view of the reticle 14, and FIG. 3b is a cross-sectional view thereof. Reticle 14
The inside consists of a circuit pattern section 42 and its peripheral section 43, and positioning grid patterns 41, 41' are formed in the peripheral section 43 at the portion corresponding to the scribe line. Incident light 44 is incident on the reticle 14, and as shown in FIG.
Multiple diffracted lights are diffracted as shown below. The sheath section 43 surrounding the pattern 41 is formed of a film of chromic acid, chromium oxide, etc., and the incident light 44
is passed only inside the pattern.

In the example of FIG. 3, a phase grating is used to obtain the diffracted light, but this grating may be an amplitude grating, or may be an emilet grating when the incident light is incident diagonally.

FIG. 4 is a diagram further explaining the principle of the exposure apparatus of the present invention. Light with a wavelength λ emitted from the light source 11 is expanded by a beam expander 20, and further converted into parallel light having a predetermined spread by a collimator lens 21. A phase grating on the reticle is placed at a position x ₁ of the front focal point f ₁ of the first Fourier transform lens. The pitch P ₁ of the phase grating and the diffraction angle θ ₁ of the diffracted light have the following relationship: P ₁ sin θ _o =nλ (n=0, ±1, ±2, etc.). The light diffracted into a plurality of light beams in this manner enters the Fourier transform lens, and further forms a Fourier spectrum image corresponding to each diffracted light beam on the rear focal plane. The coordinate ξ ₆₁ corresponding to the Fourier spectrum of the first-order diffracted light is shown as ξ ₆₁ = f ₁ sin θ ₁ P ₁ sin θ ₁ = λ, and the Fourier spectrum of the 0-th order diffracted light ξ ₆₀ ξ ₆₀ = f ₁ sin θ ₀ = 0 The Fourier spectrum image is focused on the Fourier transform plane while being completely separated from the As shown in FIG. 2b, a spatial filter 16 is arranged on this Fourier transform surface, and as shown in FIG. and the spectrum of the aperture pattern (excluding the zero-order light component). This diffracted light passes through the second Fourier transform lens and is further projected onto the wafer 5. The image projected onto the wafer W approximately focuses the image of the aperture on the reticle, and the ±1st-order light components of the grating interfere with each other to form new pitch interference fringes. Here, the pitch P ₂ of the interference fringe is given by P ₂ =λ/2sinθ ₂ . At this time, since the Fourier transform surface of the first Fourier transform lens is set at the front focal plane of the second Fourier transform lens, there is a relationship of f ₁ sin θ ₁ =f ₂ sin θ ₂ =ξ ₆₁ .

Between the images passed through the first and second Fourier transform lenses, P ₂ = λ/2sinθ ₂ = f ₂ λ/2f ₁ sinθ ₁ = f ₂ /f ₁ P ₁ /2...
…(1) is the relationship. Therefore, the pitch P ₂ of the interference fringes generated on the wafer is half the pitch of the grating on the reticle when f ₁ =f ₂ . As shown in FIG. 5, from a grating G having a pitch approximately equal to the pitch _P2 of this interference fringe, light is obtained which is diffracted by the grating G which splits the wavefronts of the two light beams 111 and 112. Further, the two beams are projected onto the wafer to generate interference fringes, and by interfering with each other the lights diffracted by the gratings on the wafer W, light intensity information indicating the positional relationship between the interference fringes and the gratings is obtained. can get.

The light intensity I observed on the photodetectors D ₁ and D ₂ is I=u _A ² + u _B ² + u _A ^*・u _B + u _A・ u _B ^* However, u _A and u _B are respectively the luminous flux 111, The amplitude intensities u _A ^* , u _B ^* of 112 are conjugate complex amplitudes.

u _A ² = A ² (sin ^N δA/2/sin δA/2) ² , u _B ² = B ² (sin ^N
δB/2/sin δB/2) ² u _A ^*・u _B +u _A・u _B ^* =2・A・Bcos｜(N−1) δA−δB
/2+Kx(sinθ _A −sinθ _B )｜×sin ^N δA/2・sin ^N δB
/2/sinδA/2・sinδB/2 (where, A and B are constants, N: number of lattices, δA,
δB is the optical path difference between the lights diffracted by two adjacent gratings, x is the relative positional relationship between the interference fringes of the light beams 111 and 112 and the gratings, and θ _A and θ _B are the light beams 111 and 112, respectively. 112 and the wafer vertical.

Figure 6 shows the observation angle dependence of the light intensity I.
This is a diagram when the pitch of the interference fringes is 1 μm and the pitch of the grating is 2 μm. A sharp peak in light intensity appears only when the pitch of the grating is an integral multiple of the pitch of the interference fringes, as shown by the light intensity I. In Fig. 6, five peaks appear when the observation angle is changed from 0 to π/2, and the peak at θ ₂ includes the incident light 111, 112.
The 0th order diffracted lights of the two overlap. The peak at θ ₄ corresponds to the peak of first-order diffracted light when the interference fringes and the grating pitch are equal. Each peak of θ ₁ to _{θ 5} contains positional information between the interference fringe and the grating on the wafer.

FIG. 7 shows the results when the position of the photodetector is fixed at the position showing the peak in FIG. 6 and the relative position x between the interference fringes formed by the light beams 111 and 112 and the grating on the wafer is changed. The change in light intensity I is shown. By changing the relative position x, the light intensity is periodically changed for every pitch l of the grating, and by observing the light intensity, the relative position between the interference fringes and the grating can be indicated.

The alignment when forming an actual LSI pattern is the alignment between the pattern of the circuit element portion formed on the wafer and the interference fringes of the two beams to be exposed.

FIG. 8 shows an alignment pattern when a conventional alignment mark M and a grating G are combined. As shown in the figure, a cross-shaped alignment mark M is formed in the pattern of the grating G. When two beams of light are irradiated onto a pattern with a cross alignment mark on this grating, the diffracted light from the pattern in Figure 8 is a combination of a dark cross pattern in a bright quadrilateral pattern, and alignment is difficult. If the alignment is insufficient, the dark cross patterns will be combined as shown in Figure 9a, and if the alignment is insufficient, the dark cross patterns will look double as shown in Figure 9a. Positioning is performed to match the cross pattern as shown in b.
That is, by providing a light detection means in accordance with this cross pattern, pattern positioning can be performed in the same way as in the conventional method. Rough alignment of about 0.3 microns can be achieved by this alignment method similar to the conventional one. When the alignment is completed in this way, as shown in FIG. 9b, moire-like stripes can be observed in the quadrilateral bright pattern, and using these stripes, the alignment method of the present invention can be used for a short time. High-precision alignment can be performed.

FIG. 10 schematically shows the optical path during alignment in the second embodiment of the present invention. Reticle 1
The light diffracted by the grating 41 on the first lens 1
The light is separated into 0th order and ±1st order light and enters the light beam.
Light in the X and Y directions are decomposed in the same way. 0
The next light is blocked by the spatial filter 16, and only the ±1st-order light passes through the second lens 17,
It is projected onto a grid pattern on semiconductor wafer 18. These two ±1st-order light beams generate interference fringes at their intersection, and are further diffracted by a grating on the wafer. Some of the diffracted light travels in the opposite direction toward the lens, while others are diffracted toward the photodetector _D3 . With photodetector D ₃ ,
The interference fringes and the grating on the wafer are aligned. In addition, the light incident on the lens in the opposite direction is transmitted to the lens system 17,
The light passes through the filter 16 and the lens system 15 and is incident on the grating on the reticle 14. At this time, the first
As shown in FIG. 1, these two beams generate interference fringes again, and using the same principle as when aligning the interference fringes 120 and the grating on the wafer 18, the interference fringes 13
0 and the grating 41 on the reticle can be aligned with high precision. The grating 41 and the interference fringes 130 are aligned by reading the light intensity of the photodetector _D4 . Therefore, the grating on the wafer and the grating on the reticle can be aligned with higher precision than in the first embodiment by the interference fringes generated on the surfaces of each grating.

Effects of the Invention According to the present invention, a pattern on a reticle can be aligned on a wafer with high precision using interference fringes.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of alignment using the conventional double grating method, Fig. 2 is a basic conceptual diagram of alignment according to the present invention, Fig. 3a is a block diagram of a reticle according to the present invention, Fig. 3 b is a cross-sectional view of the alignment grating, FIG. 4 is a diagram explaining the principle of the re-diffraction optical system according to the present invention, FIG. 5 is a detailed view of the vicinity of the wafer according to the present invention, and FIG. 6 is a grating on the wafer according to the present invention. 7 is a diagram showing the stage position dependence of the diffracted light intensity from the grating on the wafer according to the present invention. FIG. 8 is a pattern diagram of the alignment grating according to the present invention. 9a and 9b are pattern diagrams of diffraction images from the alignment grating according to the present invention, FIG. 10 is an explanatory diagram of a second embodiment of high precision alignment of a reticle and a wafer according to the present invention, and FIG. FIG. 7 is a diagram showing the positioning principle of the second embodiment. 11... Light source, 13... Optical system, 14... Reticle, 15... First lens system, 16... Spatial filter, 17... Second lens, 18... Wafer, 41, 41'... Lattice, 111, 112...
Luminous flux, 120, 130...Interference fringes, D ₁ , D ₂ , D ₄
...Photodetector.

Claims (1)

[Scope of Claims] 1. On the reticle surface of an exposure apparatus consisting of a light source, an illumination optical system, a reticle, a first lens system, a spatial filter, a second lens system, a substrate, a stage for holding the substrate, and a photodetector. , a first grating is formed, the light flux emitted from the light source is made incident on the reticle surface through the illumination optical system, the wavefront of the light flux is split by the first grating, and a first lens system is formed. At the same time, the ±1st-order light diffracted by the first grating is selectively transmitted through a predetermined spatial filter provided near the spectral plane of the first lens system. is guided to the second lens system, interference fringes generated using the light flux passing through the second lens system are projected onto the substrate, and a second grating provided on the substrate and the interference fringes are projected onto the substrate. An exposure apparatus characterized in that alignment between the second grating and the second grating is performed by measuring a change in optical output of diffracted light diffracted from the second grating using the photodetector. 2. The exposure apparatus according to claim 1, wherein the pitch of the first grating provided on the reticle and the second grating provided on the substrate is an integral multiple. 3. The first grating provided on the reticle is a grating with a constant period extending in two orthogonal directions, and the second grating provided on the substrate is also a grating with a constant period extending in two orthogonal directions. Claim 1, characterized in that the projected interference fringes extending in two directions and the grating on the substrate are aligned simultaneously.
Exposure apparatus described in Section 1. 4. 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, a first photodetector placed near the reticle, and a first photodetector placed near the wafer. A first grating is formed on the reticle surface of an exposure device including a second photodetector, and the light beam emitted from the light source is made incident on the reticle surface through the illumination optical system. The wavefront is split by a first grating and guided to a first lens system, and is diffracted by the first grating by a predetermined spatial filter provided near the spectral plane of the first lens system. selectively transmitting the ±1st-order light, guiding the ±1st-order light to the second lens system, and generating first interference fringes using the light flux that has passed through the second lens system. The second grating is projected onto a substrate, and the alignment between the second grating provided on the substrate and the first interference fringe is determined by the optical output change of the diffracted light diffracted from the second grating. This is carried out by measuring with a photodetector of
A suitable component of the light diffracted from the grating of the reticle is passed through the second lens, the spatial filter, and the first lens in reverse order, and
generating a second interference fringe near the surface of the grating, and measuring a change in the light output diffracted by the first grating with the first photodetector;
An exposure apparatus characterized in that the reticle and the wafer are aligned with high precision.