JPS6173958A - Exposing device - Google Patents

Abstract

PURPOSE:To perform high-precision positioning between a grating formed on a reticle and a grating formed on a wafer by utilizing part of diffracted light which is decomposed through the grating on the reticle. CONSTITUTION:Light passed through an illumination optical system 13 is projected on the reticle 14 and decomposed into spectral components. When a grating is provided on the reticle 14, the spectral components are separated spatially an made incident on a projection lens 16. A proper spatial filter 15 is arranged for the grating provided on the reticle 14 and only necessary part of spectral components decomposed through the grating is passed. Light passed through a reduction projection lens 16 is image-formed and projected on the wafer 17. The grating is formed on the wafer 17 and moire fringes are formed with interference fringes formed with + or - primary order spectral light beams. The moire fringes are utilized for the positioning.

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.
This was done by overlapping the marks on the photomask and the marks on the wafer, but the accuracy of the alignment was poor.Physics Letters Vol. 317/
; 7 P, 428.

In the alignment method using interferometry shown by (1977) et al., as shown in FIG. By diffracting this diffracted light again by the grating 5 formed on the wafer 4, diffracted lights 6, 7, 8, . . . are obtained. When this diffracted light is expressed as a binary representation of the diffraction order at the photomask and the diffraction order at the wafer, diffracted light 6 is (0', 1), diffracted light 7 is (1,
1), the diffracted light 8 can be expressed as ('12)... 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
The alignment can be performed by matching the intensities of the diffracted lights observed on the left and right sides. In this method, the alignment accuracy is said to be several hundred people. However, this method requires precision in the spacing due to the error. 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 based on 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 accurate and easy alignment method for 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

Composition of the Invention The present invention provides a system in which, in order to achieve highly accurate alignment in a projection exposure apparatus, only a specific spectrum of a light beam whose wavefront has been split by a grating formed on a reticle surface is passed through a spatial filter. This light beam is guided to a lens system, and interference fringes generated by the light beam are projected onto a substrate, and alignment between a second grating provided on the substrate and the interference fringes is determined by diffracting the light beam from the second grating. This provides a configuration of an exposure apparatus that performs exposure by measuring the light intensity of diffracted light with a photodetector.

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

The light emitted from the light $11 (In order to obtain clearer coherence and deeper depth of focus, the configuration is assumed to be a laser beam, but the entire optical system is a white interference optical system. A spectral light source such as a mercury lamp may be used.) is expanded by a beam expander 12, and the illumination optical system 13 composed of a -11 meter lens condenser lens is used to convert this light into parallel light or convergent light.
is incident on the entrance pupil of 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 the lens system is a reduction projection lens, but it does not necessarily have to be a reduction projection lens.

The light that has passed through the illumination optical system 13 is then projected onto the reticle 14 and decomposed into spectral components according to the pattern formed on the reticle 14.

If a grating is provided on this reticle, the spectral components are spatially separated and incident on the reduction projection lens 16.An appropriate spatial filter 16 is placed with respect to the grating provided on the reticle 14, and the grating is In order to make the NA of the lens as small as possible, only the minimum order of spectral light, that is, the ±1st order, is allowed to pass through.

, the light passing through the reduction projection lens 16 is imaged and projected onto the Ueno lens 17. A grating is formed on the sea urchin 17, and moiré fringes are generated between the grating and the interference fringes generated by the ±1st order spectrum light. Use these moiré fringes to help with positioning.

FIG. 3(a) shows the reticle 140 circuit pattern portion 42.
FIG. 2 is a layout diagram of a grating formed on a scribe line Ls. 43 is a black part that blocks light. A- in (,)
The grating 41 formed on the scribe line Ls is shown in more detail in FIG. 3(b) as a cross section taken along the line A. Reticle 1
The light 44 incident on 4 is divided by the grating 41 on the scribe line s into each spectrum Q-order, ±1st-order, ±2nd-order, .
It is decomposed as follows. Scribe line Ls
Light outside O does not pass through the light jg@ section 43. (It is also possible to project the light into a slit shape only on the scribe line.) The light separated into each spectrum in this way is filtered through a spatial filter 51 (15 in FIG. 2) as shown in FIG.
incident on . The spatial filter has a transparent part and an opaque part 61'
In Fig. 4, the 0th order light is received by the opaque part 51'',
±1st order light is passed through the transparent part. ±2nd order and other higher order light are blocked. The light that has passed through the spatial filter 51 passes through a reduction projection lens 52 (16 in FIG. 2).

The light is incident on the wafer W (17 in FIG. 2) at a symmetrical angle θ. The incident lights 111 and 112 interfere with each other to generate interference fringes in the space in front of the wafer W. The pitch of the interference fringes at this time is twice the pitch of the grating image when the image is formed by passing the zero-order light. For example, if a grating G2 is formed on the wafer W using this grating image, this grating G
Interference fringes with a pitch twice the pitch of 2 are generated. Furthermore, the incident light is diffracted by this grating G2, and the diffracted light is 113°11
4 is emitted from the grating G2. This diffracted light 113.11
The light intensity of 4 is detected by the photodetector D1. D2, and the positional relationship of the grating with respect to the interference fringes is converted into light intensity.

The incident light 111 is decomposed into a plurality of diffracted lights by the grating G2, and two light beams among them correspond to rays 113 and 114. Furthermore, the incident light 112 is also decomposed into a plurality of diffracted beams by the grating G2, and when the grating and the interference fringes are parallel, two beams of the diffracted beams are diffracted into beams 113 and 114. This 11
Since the diffracted lights of the two incident lights 1 and 112 by the grating G2 are diffracted to the same position, the once diffracted lights interfere with each other to generate moiré fringes.

FIG. 5 shows the peaks ψ1°ψ2. ψ3.
ψ4. ψ6 was shown. A photodetector is provided at the peak position of this diffracted light to measure the intensity of the moire light.

The observed light intensity on the photodetectors D1 and D2 is 1"" uA+uB +uA-uB+uAeuB*, where uA and uB are the amplitude intensities up of the light fluxes 111 and 112, respectively, and , lJn are the conjugate complex amplitudes.

+Kx(sinθA-”1nθB)) (For fc, 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, θ□, OB is the light beams 111 and 1
12 and the perpendicular to the wafer).

Figure 5 shows the observation angle dependence of light intensity.

It is a figure when the pitch of an interference fringe is 1 micrometer, and the pitch of a grating is 2 micrometers. The sharp peak that appears in the light intensity is the light intensity! As shown in , this is limited to cases where the pitch of the grating is an integral multiple of the pitch of the interference fringes. and,
In Figure 5, when the observation angle is changed from 0 to πA, 5
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 peak of θ1 to θ5 contains positional information between the interference fringe and the grating on the wafer. The graph shows the change in light intensity I when the relative position X between the interference fringes created by the light beams 111 and 112 and the grating on the wafer is changed. The relative position X can be changed by periodically changing the light intensity 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 three beams to be exposed.

FIG. 7 shows an alignment pattern when a conventional alignment mark M and a grating G are combined. As shown in the figure, the cross-shaped 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 grating, the diffracted light from the B and turn in Figure 7 is a combination of the dark cross pattern 7 in the bright quadrilateral pattern. If the alignment is insufficient, the dark pattern of the cross will appear double as shown in FIG. 8a, and alignment is performed to match the cross pattern as shown in FIG. 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. O, 3 by this alignment method similar to the conventional one.
Approximate positioning on the micron level is possible. When this alignment is completed, as shown in Figure 8, moiré-like stripes can be observed in the quadrilateral bright pattern, and these stripes can be used to perform the alignment method of the present invention for a short time. Although an example has been described in which a 0 to 1 positioning grid is provided on the scribe line to enable highly accurate positioning, other positions may be used.

Effects of the Invention In the present invention, the positioning system between the grating formed on the reticle and the grating formed on the surface of the sea urchin is not changed drastically, and the distance between the reticle and the reduction projection lens is changed. By inserting a spatial filter into the structure, highly accurate alignment is achieved with a simple configuration.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional mask alignment example, Fig. 2 is a schematic block diagram of an optical system according to the present invention, and Fig. 3 (→ is a reticle arrangement diagram; Fig. 3 (b) is a scribe line on the reticle. FIG. 4 is a detailed partial illustration of a part of the apparatus according to the present invention, and FIG. 6 is a diagram showing diffracted light by the grating on the wafer. Fig. 7 is a diagram showing the combination of the conventional alignment mark and alignment using the grid according to the present invention; Fig. 8) is a diagram showing the position shift dependency; (b) is a diagram when the marks in FIG. 7 are almost aligned and moiré fringes are generated. 11...Light source, 13...-Illumination optical system, 14
... Reticle, 15.51 ... Spatial filter, 16°62 ... Reduction projection lens, 17
．． W...Unino, Dl, D2...Photodetector, 111,112,113°114...Light flux. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 S Figure 4 Figure 5 De, y2yJy4 Force Fishing rod Figure 6σ I/2 ノ JIh
Figure 2, Figure 7, Figure 8 (of (b+

Claims (2)

[Claims] (1) Light source, illumination optical system, reticle, spatial filter,
A first grating is formed on the reticle surface of an exposure device consisting of a lens system, a substrate, a stage for holding the substrate, and a photodetector, and a first grating is formed on the reticle surface of the exposure device, and a light beam emitted from the light source is directed to the reticle surface through the illumination optical system. The light flux is wavefront-split into spectral components by a grating, guided to the lens system, and wavefront-split into the spectral components by the predetermined spatial filter provided between the reticle and the lens system. A predetermined spectrum is selectively transmitted to project interference fringes onto the substrate, and alignment between a second grating provided on the substrate and the interference fringes is determined by diffracting the interference fringes from the second grating. An exposure apparatus characterized in that the exposure is performed by measuring the intensity of diffracted light with the photodetector. (2) Exposure according to claim 1, characterized in that of the light wavefront-split into spectral components by a grating, only the ±1st-order spectral components are passed, and interference fringes are projected onto the substrate. Device.