JPS6184019A - Exposure equipment - Google Patents

Abstract

PURPOSE:To perform a precise alignment on a lattice and an interference fringe using the intensity of the diffracted beam sent from the lattice of a substrate by a method wherein, after a luminous flux is diffracted by the lattice of pitch P1 located on the surface of a reticle, the interference fringe is projected on a substrate through a lens having the focal distances of f1 and f2. CONSTITUTION:The beams of light of wavelength lambda emitted from a light source 11 are magnified and formed into paralleled beams of light, they are passed through the lattice 41 of pitch P1 on the reticle 14 of x1=f1 located in front of a lens 51. When each diffracted beam of light is image-formed on the rear focus face xsi, the coordinates xsi61=f1sintheta1, P1sintheta1=lambda of the image of the minus primary diffracted beam and the coordinate xsi0=0 of the coordinate of a zero-order image are completely isolated. A space filter 16 is arranged on the face of focus, the + or - primary diffracted beam only is passed through a lens 52 of f2, and the interference fringe of P2=lambda/2sintheta2 is formed on a wafer W. As the Fourier transformation surface of the lens 51 is placed on the focus face of the lens 52, P2=f2/f1XP1/2 is obtained. Besides, when the diffracted beam is detected by providing a lattice of PG=nP2 on the wafer, the information on light intensity which changes at the observation angle theta and the opposing position (l) of the interference fringe and the lattice can be obtained, thereby enabling to align the interference fringe and the lattice precisely based on the above-mentioned information.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 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 of a photomask and an LSI wafer during LSI manufacturing involves rotating and moving a stage on which the wafer is attached using alignment marks provided on the wafer and two axes.
When the marks on the photomask and the marks on the wafer were overlapped, the alignment accuracy was about ±0.3 microns, and when forming sub-micrometer elements, the alignment accuracy was It's bad and not practical. Also, S. Austin (Appl 1edphys
ics Letters VoL 317/;7P,
428, 1977), as shown in FIG. Then, once again, this diffracted light is
Diffracted lights 6, 7, 8, . . . are obtained by diffraction by a grating 5 formed on the wafer 4. This diffracted light is
When expressed as a binary representation of the diffraction order on the photomask and the diffraction order on the wafer, diffracted light 6 is (0,1) and diffracted light 7 is (0,1).
1,1), the diffracted light 8 can be expressed as (-1,2)... 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 that is symmetrical with respect to the incident laser beam 1, and alignment between the photomask 2 and the wafer 4 can be performed by matching the intensities of the diffracted light observed on the left and right sides. . In this method, the alignment accuracy is said to be several hundred eight.

However, in this method, since the alignment between the photomask 2 and the wafer 4 is greatly influenced by the spacing between the photomask 2 and the wafer 4, precision in the spacing is required. Furthermore, 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 spacing, which complicates the apparatus, which poses a problem in practical use.

In addition, for alignment of elements with submicron line width,
There is a method of observation based on secondary electron emission from the device, but since it cannot be handled in the atmosphere, the throughput in manufacturing LSI is reduced, which poses a practical problem.

Purpose of the Invention In view of these conventional problems, the present invention provides an apparatus that enables accurate and easy alignment of an LSI reticle and a wafer, which allows alignment of fine patterns in the atmosphere and with a simple configuration. is intended to provide.

Structure of the Invention The present invention uses a light beam emitted from a light source to achieve highly accurate alignment in a projection exposure apparatus.

A light beam diffracted by a first grating with a pitch P1 formed on the reticle surface is passed through a spatial filter as two pairs of diffracted light beams on a spectral plane of a first lens system with a focal length f1, and these two light beams are is guided to a second lens system with a focal length f2, and the interference fringes generated by the two light beams are projected onto the substrate, and there is a grating of ¥iM2 on the substrate,
The pitch PG of this second grating has the following relationship, and the alignment between this second grating and the interference fringes is determined by optical detection of the light intensity of the diffracted light diffracted from the second grating. This provides a configuration of an exposure apparatus that performs positioning by detecting with a device.

Description of examples An embodiment of the optical system according to the present invention is shown in FIG.

The 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 beam expander 12 expands the light (which may be a spectral light source such as incident on the entrance pupil.

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 do not necessarily have to be Fourier transform lenses.

A reticle 14 is placed between the illumination optical system 13 and the first Fourier transform lens 15, and the image emitted from the pattern of the reticle 14 as a secondary light source is transmitted to the first Fourier transform lens 15.
The light is once focused, and then an image of the pattern on the reticle is projected onto the semiconductor wafer W through the second Fourier transform lens 17. First Fourier transform lens 15 and g
When the focal lengths of the 2O Fourier transform lenses are made equal, the pattern on the reticle is projected at the same magnification. By making the focal lengths of the first and second Fourier transform lenses 15, 17 different, reduction projection is possible. The diffracted light (Fourier spectrum) of the pattern on the reticle is spatially distributed on the rear focal plane of the first Fourier transform lens. By filtering with , interference fringes are formed on the wafer W surface.

FIG. 3 shows a reticle used in the exposure apparatus of the present invention. 3a is a plan view of the reticle 14, and FIG. 3 is a sectional view thereof. The reticle 14 includes a circuit pattern section 4
2 and its peripheral portion 43, and a first grating 4 for positioning is provided in a portion of the peripheral portion 43 corresponding to the scribe line.
1.41' is formed. Incident light 44 is incident on the reticle 14, and as shown in FIG. Ru.

FIG. 4 is a diagram further explaining the principle of the exposure apparatus of the present invention.

The light of wavelength λ emitted from the light source 11 is transmitted through the beam extractor 12.
The light is expanded by the collimator lens 21, and then converted into parallel light with a predetermined spread. A first grating 41 with a pitch P1 provided on the reticle 14 is placed at a position x1 of the front focal point f1 of the first Fourier transform lens 61. The pitch P1 of the first grating 41 and the diffraction angle θ1 of the diffracted light are P
1 sin θ, = nλ (n = o, ±1. ±2...
・) There is a relationship. The light diffracted into a plurality of light beams in this way enters the first Fourier transform lens 51, and furthermore, the −1st-order diffracted light forms a Fourier spectrum image corresponding to each diffracted light on the back focal plane ξ. The coordinate ξ61 corresponding to the 717 es vector is expressed as ξ61=f1S1nθ1 P1sinθ1=λ, and the Fourier spectrum of the 0th order diffracted light ξ6゜ξ
A Fourier spectrum image is formed on the Fourier transform plane in a state completely separated from s6=f1s+nθo=O.

As shown in FIG. 2, a spatial filter 16 is arranged on this Fourier transform surface, and as shown in FIG. Allows the first-order diffracted light to pass through. This diffracted light passes through the second Fourier transform lens 52 having a focal length f2, and is further projected onto the wafer W. On the wafer W, the ±1st-order light components of the first grating 41 interfere to form interference fringes with a pitch P2.

Here, the pitch P2 of the interference fringes is given by: At this time, since the Fourier transform surface of the first Fourier transform lens 51 is set on the front focal plane of the second Fourier transform lens 62, flSl[Iθ1=f2Sl
There is a relationship nθ2=ξ61.

There is a relationship between the images passed through the first and second Fourier transform lenses 51 and 52. Further, as shown in FIG. 6, a second grating G having a pitch PG that is an integral multiple of the pitch P2 of the interference fringes is provided on the Unino W. Here, the second lattice G
and the first lattice 41 have the following relationship (integer)...(2).

Here, based on equation (2), equal magnification exposure (f1=f2), 5:1a small projection exposure (fl:f2=5:1), 10:1 reduction projection exposure (f2:f1=10:1) In each case,
Examples of selection of Pl and PG are shown in the following table.

fl, f2. Selection example of Pl and PG Furthermore, as shown in FIG. 5, ±1st-order diffracted light 111.
112 and the light diffracted by the grating G is passed through the lens L1. It is sent via L2.

The observed light intensity I on photodetectors D1 and D2 is T = uA2+uB2+uA*euB+uA@uB
*However, uA and uB are the amplitude intensities of the light beams 111 and 112, respectively, and uA* and uB* are the conjugate complex amplitudes.

δA-δB uA ”B”uA”B ”2°A-Bcosl(N-1
) 2-4-Kx (sin θA-5in θB) 1 (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, I is the relative positional relationship between the interference fringes of the light beams 111 and 112 and the gratings, and θA and θB are the light beams 111 and 11
2 and the perpendicular to the wafer).

Figure 6 shows the observation angle dependence of the light intensity I.

It is a diagram when the pitch of the interference fringes is 1 μm and the pinch of the grating is 2 μm. A sharp peak appears in the light intensity 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. and,
In Figure 6, when the observation angle is changed from 0 to π, 6
There are two peaks, and the peak of θ2 has the incident light 11
1,112 zero-order diffracted lights overlap. The peak at θ4 corresponds to the peak of the first-order diffracted light when the interference fringes and the grating pitch are equal. Each of the peaks from 01 to θ5 contains positional information between the interference fringe and the grating on the wafer.

Fig. 7 shows the light when the position of the photodetector is fixed at the position showing the peak in Fig. 6 and the relative position xf between the interference fringes formed by the light beams 111 and 112 and the grating on the wafer is changed. All changes in intensity I are shown. Changes in the relative position The alignment when forming the pattern is between the pattern of the circuit element portion formed on the wafer and the interference fringes of the three 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, the cross alignment mark M is aligned with the grid G
It is formed in the pattern of When three beams of light are irradiated onto a pattern with a cross alignment mark on this grid, the diffracted light from the pattern in Figure 8 is a combination of a quadrilateral bright pattern and a cross dark pattern, and the position If the alignment is insufficient, the dark pattern of the cross will appear double as shown in FIG. That is, by using all of the light detection means in accordance with this cross pattern, pattern positioning can be performed in the same way as in the conventional method. By this alignment method similar to the conventional one, 0.3
Approximate positioning on the micron level is possible. When this alignment is completed, moiré-like stripes can be observed in the quadrilateral bright pattern, as shown in Figure 9, and □
Using these stripes, the positioning method of the present invention allows highly accurate positioning to be performed in a short time. Also, (2)
In the formula, only when N=2.4.6... is an even number, θ=
Diffracted light 140 is also emitted in the Q direction.

That is, as shown in FIG. 10, diffracted light is emitted in a direction perpendicular to the wafer W, undergoes a second Fourier transform, returns through the /z 52, and forms a Fourier spectrum image on the Fourier transform plane. The Fourier spectrum image is focused at the zero point where the light emitted from the light source 11 is diffracted by the first grating 41 as described above.
It overlaps with the position of the next diffracted light's IJ varnish vector ξ6°. Therefore, the 0th order diffracted light is blocked, and the diffracted light 140
A photodetector D6 is provided within the spatial filter 16 so as to detect the light intensity of .

Here, the diffracted light 140 is composed of the light beams 141 and 112 which are the light beams 111 diffracted by the grating G, and the light beams 142 which are diffracted by the grating G. If the light intensities of the light beams 111 and 112 are equal, the light beams 141 and 142 The light intensity is equal. Therefore, by detecting this diffracted light 140 with the photodetector D5, changes in the light intensity of the light beam 141 and the light beam 142 can be observed equally, so that light intensity information indicating the positional relationship between the interference fringes and the grating can be obtained. This results in more accurate alignment and improved alignment accuracy.

In this embodiment, the photodetector D6 is provided inside the spatial filter 15, but it may be placed in the vicinity of the Fourier transform surface separately from the spatial filter 15. In addition, as a third embodiment, as shown in FIG. 11, the diffracted light 140 is reflected by a reflecting mirror 150 near the Fourier transform surface, and then made incident on the photodetector D6 via the optical system. The photodetector D6 can be configured without being subject to dimensional restrictions on the Fourier transform surface.

Effects of the Invention According to the present invention, the light diffracted by the grating on the reticle can be aligned with high precision by the interference fringes generated through the first lens system, the spatial filter, and the second lens system and the grating on the reticle. can.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of alignment using the conventional double grating method, Fig. 2 is a basic conceptual diagram of alignment according to the present invention, Fig. 3 (-) is a configuration diagram of a reticle according to the present invention; 3
Figure C) is a sectional view of the alignment grating, Figure 4 is a diagram explaining the principle of the re-diffraction optical system according to the present invention, Figure 5 is a detailed view of the vicinity of the wafer according to the present invention, and Figure 6 is a diagram showing the wafer surface according to the present invention. FIG. 7 is a diagram showing the stage position dependence of the diffracted light intensity from the grating on the sea urchin according to the present invention, and FIG. 8 is a diagram showing the stage position dependence of the diffracted light intensity from the grating on the sea urchin according to the present invention. Pattern diagram, FIG. 9 is a diagram showing a pattern of a diffraction image from a positioning grating according to the present invention, FIG. 1Q is a basic configuration diagram showing a second embodiment according to the present invention, and FIG. FIG. 3 is a basic configuration diagram showing a third embodiment. 14... Reticle, 15.51... First Fourier transform lens, 16... Spatial filter, 17°62... Second Fourier transform lens, W.
...Wafer, 41.41'...First grating, Pl...Pitch of first grating, P2...
・Pitch of interference fringes, G...Second grating, Pa...
...Pitch of the second grating, Dl. D2. D3. D4. D6. D6. , , , Photodetector, 14o... Diffracted light. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 5 Figure 6 Figure 7 O group 1”/2 21 Figure 8 N Figure 9 (0-) (b) Figure 10

Claims (3)

[Claims] (1) The light flux emitted from the light source is incident on the reticle surface on which a first grating with a pitch P_1 is formed, and the light flux is
is guided to a first lens system having a focal length f_1 through a grating, and a predetermined spectrum is selectively transmitted through a predetermined spatial filter provided near the spectral plane of the first lens system to focus the spectrum. distance f_
interference fringes generated using the light flux that has passed through the second lens system are projected onto a substrate, and a second grating is provided on the substrate; The pitch P_G of this second grating is P_G=(f_2/f_1)
・(P_1/2)・N (N=1, 2, 3...integer), and the diffracted light diffracted by this second grating and the interference fringes is An exposure apparatus characterized in that the first grating and the second grating are aligned by detection with a detector. (2) The pitch of the first grating on the reticle surface is P_1, and the focal lengths of the first and second lens systems are f_1 and f_2, respectively.
Between the pitch P_G of the second grating on the substrate, P_G=(
f_2/f_1)・(P_1/2)・N(N=2, 4,
Among the generated interference fringes and the diffracted light diffracted by the second grating,
The diffracted light diffracted in a direction perpendicular to the substrate is returned through the second lens system and detected by a photodetector provided near the spectral plane. Exposure equipment. (3) The diffracted light diffracted in the direction perpendicular to the substrate is returned through the second lens system, reflected by a reflecting mirror near the spectral plane, and the diffracted light is detected by a photodetector via the optical system. An exposure apparatus according to claim 2, characterized in that: