JPH0367104A - Aligning device - Google Patents

Abstract

PURPOSE:To prevent the degradation in S/N by scattered light and unnecessary diffracted light by forming the outer peripheral edge part of a mark to a curved shape so as to disperse the regular reflected and scattered light from the outer peripheral edge part. CONSTITUTION:The luminous flux emitted from a light source 17 is reflected by a reflecting mirror 18 via a projecting lens system 6 and is projected to a grating lens 15 whose peripheral shape is arc-shaped from the diagonal direc tion, provided on an object 2. This lens 15 has a condensing effect and the exit light is condensed to the point of a prescribed distance from the lens 15. The luminous flux diverged from this point is made incident to a grating lens 16 provided on the object 3 disposed at a prescribed distance. This lens 16 has the condensing effect similar to the lens 15 and the exit light from the lens 16 is passed through the lens 15 and is then condensed to a detecting sur face 14 by a condenser lens 7. The S/N by the scattered light and the unneces sary diffracted light is improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an alignment device, for example, in an exposure device for manufacturing semiconductor devices, the alignment device is used to align a mask, reticle (hereinafter referred to as “mask”), or the like on a first object surface. This invention relates to an alignment device suitable for performing relative positioning (alignment) between a mask and a wafer when exposing and transferring a fine electronic circuit pattern formed on a second object surface such as a wafer. .

[Prior Art] Conventionally, in exposure apparatuses for semiconductor manufacturing, relative alignment between a mask and a wafer has been an important element for improving performance. Particularly in alignment in recent exposure apparatuses, alignment accuracy of, for example, submicron or less is required due to the high integration of semiconductor devices.

In many alignment apparatuses, so-called alignment marks for alignment are provided on the mask and wafer surfaces, and position information obtained from the marks is used to align both. As an alignment method at this time, for example, detecting the amount of deviation between both alignment patterns by performing image processing, or US Pat.
As proposed in No. 04033, etc., this is done by using a zone plate as an alignment pattern, irradiating the zone plate with a light beam, and detecting the amount of light emitted from the zone plate on a predetermined surface. .

In general, alignment methods using zone plates are
Compared to methods using simple alignment marks, this method has the advantage of being able to achieve relatively high-precision alignment without being affected by alignment mark defects.

FIG. 12 is a schematic diagram of a conventional alignment device using zone plates. FIG. 13 shows the alignment mark. A linear zone plate 15 is formed on the mask surface 2, and rectangular patterns 16 are arranged in a line shape on the wafer 3 at equal pitches. The direction in which the linear zone plate 15 has power is the alignment detection direction, and the projection beam l is directed to the zone plate 15 at an angle Φ with respect to the normal in a plane that includes the normal at the center of the mark and a line perpendicular to the alignment direction. The light is incident on the wafer surface 3 in a linear manner by the zone plate 15, and is further diffracted by the pattern 16 on the wafer 3, and a signal is generated at a certain angle determined by the pitch of another wafer pattern 16 within the incident surface. The light enters the detection system as light 19.

If the mask 2 and the wafer 3 are misaligned in the alignment direction, the amount of light diffracted by the wafer pattern 16 will change, so by detecting this, the misalignment between the mask 2 and the wafer 3 can be controlled.

[Problem that the invention is trying to solve]

However, in the above-mentioned conventional example, the pattern of the mark edge portion 12 is a straight line and is set to be almost orthogonal to the incident light, and the detection direction is near the entrance plane, so the 14th
As shown in the figure, the intensely specularly reflected scattered light and the intensely intense light of the Franhofer diffraction pattern of the unnecessary diffracted light shown in FIG. 15 exist on the detection surface of the sensor and become noise light, resulting in S/N It had the disadvantage of lowering the

Here, the specularly reflected etch scattered light is the scattered light generated by the step shape near the etch, and its light distribution characteristics are such that the edge part is the reflective surface and the distribution is centered around the reflected light rays according to the law of reflection. As a cylindrical reflecting surface with an infinitesimal radius centered on the tangent to the etch, it has the property of scattering in a direction determined by geometrical optics.

Particularly in a mask intended for X-rays, the thickness of the mask pattern is large, and the mask is strongly affected by etch scattered light.

FIG. 14 is a diagram showing the principle of edge scattering in a conventional example. When the pattern edge portion 12 is irradiated with the incident light 1, scattered light 13 is generated in the pattern etched portion 12. At this time, considering the projected optical path onto the x-7 plane (for example, the mask surface), Fig. 14 (b
), strong scattered light is concentrated in the direction of specularly reflected scattered light 13' that is specularly reflected by the etched portion 12.

In FIGS. 14(b) and 14(c), the intensity distribution of the scattered light 13 for each angle is shown by the broken line. FIG. 14(a) shows the distribution of specularly reflected scattered light 13' on the incident surface. It can be seen that there is strong scattered light at the center of the signal detection section 14.

Particularly in the case of a mask used in an X-ray exposure device, the thickness of the pattern is 0.5 μm to 1 μm, and scattered light becomes a big problem.

Next, the influence of side light of the Fraunhofer diffraction pattern of unnecessary diffracted light will be explained. Figure 12.

In the system shown in FIG. 13, if the diffraction order of the signal light 19 determined by the pitch of the diffraction grating 16 on the wafer 3 is m-th order, then m
The diffracted lights corresponding to the +1st order and the m -1st order exist relatively close to the signal light, and as shown in Figure 15, a part of the light whose intensity is concentrated in the Fraunhofer diffraction pattern due to the diffraction reaches the sensor. It will be incident on 14. mask 2
．． Due to fluctuations other than the positional deviation of the wafer 3 in the alignment direction, such as mask/wafer rotation, the amount of unnecessary light incident on the sensor 14 fluctuates, resulting in an error.

In addition, the mask pattern is usually made of metal such as Au or Ta, and has a high reflectance, and the intensity of the 0th order light reflected from the mask is strong, even though the direction of reflection is quite far from the detection system in terms of the mark emission angle. Regardless of the shape of the mask pattern (rectangular in this case), the Fraunhofer diffraction pattern has a long tail in the direction perpendicular to the two parallel sides of the mark, and a portion of it enters the detection system, resulting in S , , / N There was a problem of lowering the . (See Figure 16) [Means for Solving the Problems] The present invention specifies the direction of incident light on a mark pattern and the peripheral shape of a physical optical element, and removes specularly reflected scattered light and unnecessary diffracted light from the mark edge. The intensity concentration region of the Fraunhofer diffraction image of the order does not exist in the detection section.

As a specific example of the shape of the mark's outer periphery, as shown in FIG. This is to avoid concentrating on the direction. The smaller the curvature, the wider the spread of the scattered light, and it is preferable to cover the entire detection surface as wide as possible in order to suppress the influence of the scattered light on various fluctuations. This can be expressed using the parameters shown in FIG. 3(b) as follows.

However, l is the length of the side of the mark to be considered, and β is the angle from which the detection system is viewed from the mark.Also, by making the mark's outer circumference shape arc-shaped, intensity concentration of the Fraunhofer pattern of light due to unnecessary diffraction orders will not occur. I did it like that. Figure 5 shows the Fraunhofer pattern of a circular aperture. The intensity spreads uniformly from the center, and has already weakened to about 5/1000 of the peak at the third light intensity.

On the other hand, the mark area is usually two sides parallel to each other, such as a scribe line. 26, and it is required to effectively utilize the entire mark area from the viewpoint of eliminating the influence on the signal light end and process alignment.

If the outer circumferential shape of the mark is one circular arc, two parallel sides 25,
The area indicated by diagonal lines between 26 and the circular arc is wide as shown in FIG. 6(a), and there are many wasted areas. Therefore, it is necessary to reduce the curvature of the outer circumferential shape of the mark of interest and to effectively utilize the mark area as shown in FIGS. 6(b) and 6(c).

FIG. 7 shows the Fraunhofer diffraction pattern in the case of FIG. 6(b). There is no intensity concentration as shown in Fig. 15.

The specific curvature setting is as shown in Fig. 8, where the projection component to the axis perpendicular to the two parallel sides 25.26 of the part whose outer circumference is arcuate is d, and the following formula is satisfied. Aimed at efficient use of mark area.

〔Example〕

FIG. 1 shows a first embodiment of the present invention, which uses the same measurement system as that shown in the conventional example, and is an enlarged view of an alignment mark that reduces the effects of specularly reflected scattered light and Franhofer diffracted light from edges. shows. FIG. 1(a) shows alignment marks on the mask surface, and FIG. 1(b) shows alignment marks on the wafer surface. As shown in Figure 1 (a), the peripheral part of the linear zone plate is cut in an arc shape to disperse the scattering of the incident light due to the edges and prevent the scattered light from concentrating on the detection system. The influence of unnecessary light is also reduced. In this embodiment, the mark width in the alignment direction (AA direction) is 5.
An arcuate cut with a radius of 100 μm is made with respect to 0 μm. FIG. 2 shows a second embodiment of the present invention in which the wafer mark is also cut in an arcuate shape.

FIG. 4 shows a third embodiment of the present invention.

When arranging a first object and a second object to face each other and performing relative positioning, the first physical optical element 15 is placed on the first object plane 2, and the second physical optical element 16 is placed on the second object plane 3, respectively. The diffracted light generated when light is incident on the first physical optical element 15 is made incident on the second physical optical element 16, and the second
The first object 2 and the second object are detected by detecting the diffracted light generated on a predetermined surface by the physical optical element 16.
When performing relative positioning with the object 3, the first and second
physical optical element 15. An arcuate cut is applied to the peripheral shape of the mark so that specularly reflected etch scattered light due to the light 1 incident on the mark 16 is dispersed and so as to prevent intensity concentration of the Fraunhofer pattern of unnecessary diffraction orders.

In this embodiment, after the light beam emitted from the light source 16 is reflected by the reflecting mirror 18 via the light projection 1 lens system 6, the peripheral shape is formed by an amplitude type or phase type zone plate provided on the first object 2. irradiates the arc-shaped first physical optical element 15 (grating lens) from an oblique direction.

The first physical optical element 15 has a light focusing function and focuses the emitted light onto a point at a predetermined distance from the first physical optical element 15. The light beam diverging from the point is made incident on a second physical optical element 16 (grating lens), which is a phase type or amplitude type zone plate, etc., provided on a second object 3 placed at a predetermined distance. The second physical optical element 16 has a light condensing function like the first physical optical element 15, and after the light emitted from the second physical optical element 16 passes through the first physical optical element 15, it condenses the light. The lens 7 focuses the light onto the detection surface 14 .

That is, in this example, the diffraction image of the first physical optical element is
An enlarged image is formed using a physical optical element.

FIG. 9 is an explanatory diagram showing the basic principle of the optical system in the third embodiment shown in FIG. 4. In the figure, a first object 2 and a second object 3 whose relative positional deviations are to be evaluated are each connected to a first object such as a zone plate. Second alignment mark 15.
There are 16. The light beam 1 is made incident on the first alignment mark 15, and the emitted light is made incident on the second alignment mark 16. The emitted light 19 from the second alignment mark 16 is focused onto a detection surface 14 of a detector such as a position sensor.

At this time, a gravity center deviation amount Δδ of the amount of light occurs on the detection surface 14 in accordance with the relative positional deviation amount Δσ between the first object 2 and the second object 3.

In this embodiment, in the same figure, the detection surface 14 by the light beam 19 is
The amount of gravity shift △δ of the light amount at the top is determined, and from this the first
A relative positional deviation amount Δσ between the object 2 and the second object 3 is detected. Here, the center of gravity of the luminous flux is within the cross section of the luminous flux,
When the position vector from each point of the cross-sectional circle is multiplied by the light intensity at that point and integrated over the entire cross-section, the integral value is O.
Although this refers to a point that becomes a vector, as another example, the position of a point where the amount of light reaches a peak may be detected.

Here, the first alignment mark 15 is used as a reference, and the second alignment mark 16 is aligned with the first alignment mark 1.
If it is deviated by Δσ in the direction parallel to 5, the amount of deviation Δδ of the center of gravity of the condensing point on the detection surface 14 will be enlarged.

However, aw is positive on the incident side from the mark, bw is positive on the mark exit side, and Δδ is positive when it is in the same direction as Δσ, and negative when it is in the opposite direction.

If the second object is moved based on the positional deviation amount Δσ determined in this way, the first object and the second object can be positioned with high precision.

Note that the position of the center of gravity of the light beam on the sensor surface 14 when the positional deviation is 0, which is the reference for the positional deviation, is determined in advance by trial firing, etc., and is determined by △δ
is evaluated as the amount of deviation from that position.

Figure 10 shows 1. It is an example of a mark shape of a 2nd physical optical element. (a) shows a mask, and (b) shows a physical optical element on the wafer surface.

In this embodiment, the scribe line is 20M.

The human output light exists in a plane perpendicular to 20W, the alignment direction is parallel to the scribe line 20, the incident angle is 17.5 degrees with respect to the normal to the mark surface, and the output angle is 7 degrees, making it an oblique incidence/exit system. ing. The focal point of the first physical optical element I5 is 217 μm below the mask. 3 caps between mask and wafer
Assuming that aw==-187 μm) and bw=18700 μm from the wafer to the sensor, the moving magnification of the position of the signal light on the sensor surface is as follows.

Also, the length of the side of the mark is 7 = 90 μm, the angle β looking into the detection system = 0.7 (rad), and the radius of curvature R of the arc-shaped cut on the outer periphery of the mark is 400 μm, so the following condition is satisfied. There is.

Although an example of an alignment method using light spot position detection has been described above, the present invention is effective with any method using diffracted light.

FIG. 11 shows a fourth embodiment of the present invention, which is applied to the case where the distance between the first object 2 and the second object 3 is measured and controlled.

A first object 2 provided with a physical optical element and a second object 3 are placed facing each other, and a light beam l is incident on the physical optical element 4 on the first object 2, and is deflected in a predetermined direction by the physical optical element 4. After the light is reflected by the second object surface 3, the light is guided onto the light receiving means surface 8, and the incident position of the light on the light receiving means surface 8 is detected, thereby separating the first object 2 and the second object. When determining the distance from 3, an arc-shaped cut is made to disperse the scattered light from the mark edge and to suppress the intensity concentration of the Fraunhofer pattern of light due to unnecessary diffraction orders.

FIG. 11(a) is a schematic diagram of an optical system of an embodiment in which the present invention is applied to a device for measuring the distance between a mask and a wafer in a semiconductor manufacturing device.

In the figure, 1 is a light beam from a He-Ne laser or a semiconductor laser (not shown), 2 is a first object such as a mask, and 3 is a second object such as a wafer.
and wafer 3 are initially spaced apart by a distance d as shown in FIG. 11(a).
. are placed facing each other across the

4.5 are the first . The second physical optical elements 4 and 5 are generally composed of a diffraction grating, a zone plate, or the like. 7 is a condensing lens, the focal length of which is fs.

Reference numeral 8 denotes a light receiving means, which is arranged at the focal point of the condensing lens 7, and is composed of a line sensor, a PSD, etc., and detects the center of gravity of the incident light beam. Reference numeral 9 denotes a signal processing circuit, which uses the signal from the light receiving means 8 to determine the center of gravity position of the light beam incident on the surface of the light receiving means 8, and calculates the distance d between the mask 2 and the wafer 3 as described later. is calculated and found.

IO is an optical probe, which includes a condenser lens 7, a light receiving means 8,
It has a signal processing circuit 9 as required, and is movable relative to the mask 2 and wafer 3.

In this embodiment, the luminous flux 1 (
Wavelength λ=830 nm) is perpendicularly incident on a point A on a first Fresnel zone plate (hereinafter abbreviated as FZP) 4 surface on a mask 2 surface. And the first FZP4
The diffracted light of a predetermined order is diffracted at an angle θ1 from the wafer 3.
It is reflected at point B (C) on the surface.

Of these, the reflected light 20 is at a position P where the wafer 3 is close to the mask 2.
The reflected light 21 when the wafer is located at the wafer 3
This is the reflected light when is displaced by a distance do from the position Pl.

Next, the reflected light from the wafer 3 is made incident on a point D (E) on the second FZP 5 surface on the first object 2 surface.

The second FZP 5 has an optical function of changing the exit angle of the outgoing diffracted light depending on the incident position of the incident light beam.

Then, the diffracted light (22, 23) of a predetermined order diffracted from the second FZP 5 at an angle θ2 is guided onto the surface of the light receiving means 8 via the condenser lens 7.

At this time, the incident light flux (
The distance between the mask 2 and the wafer 3 is calculated and determined using the center of gravity position of 22, 23).

In this example, the first . Second FZP
4.5 is configured with a known pitch set in advance, and the diffraction angles θl and θ2 of the diffracted light of a predetermined order (for example, ±1st order) of the light beam incident on them are determined in advance.

If the focal length of FZP5 and condenser lens 7 is fM, f, then the wafer is d. The amount of variation S in the position of the center of gravity on the light-receiving means when the light-receiving means is deviated by the same amount is given by 8S=2.dG.-tanθ1M. This equation is used to find do and perform interval detection. Here, the first mask, wafer spacing d. is determined by another well-known distance detection means, and the center of gravity position on the light receiving means at this time is stored as a reference position. S is detected as the deviation of the center of gravity from this reference position, and d is calculated. and d. The spacing can be determined by

FIG. 11(b) shows marks 4 and 5 on the mask surface 2, and marks 4 and 5 on the incident side. The peripheral shape of both the emission side marks 5 is cut into an arc shape to disperse the etch scattered light and prevent the specularly reflected etch scattered light with concentrated intensity from reaching the detection system.

In the above embodiments of the present invention, the peripheral shape of the mark with curvature has been shown as a part of a circular arc, but it is not limited to a circular arc, but may also be a quadratic curve such as a parabola, hyperbola, or Sui circle. It can also be connected.

〔Effect of the invention〕

According to the present invention, the intensity concentration area of specularly reflected scattered light scattered from the mark edge portion and the intensity concentration area of the Franchaux pattern of unnecessary diffracted light are set so as not to exist in the detection unit, which has been a problem in the past. In addition, it has become possible to significantly improve the reduction in S/N due to scattered light and unnecessary diffracted light.

[Brief explanation of drawings]

FIG. 1 shows the shape of a physical optical element according to a first embodiment of the present invention. FIG. 2 shows the shape of a physical optical element according to a second embodiment of the present invention. FIG. 3 is a diagram showing the principle of the present invention. FIG. 4 shows a third embodiment of the present invention. Figure 5 shows a circular aperture diffraction pattern. FIG. 6 is a diagram showing the mark area. FIG. 7 is an example of a diffraction pattern according to the present invention. FIG. 8 is a diagram showing pattern peripheral shape setting according to the present invention. FIG. 9 is an optical path diagram of a third embodiment according to the present invention. FIG. 10 shows the shape of a physical optical element according to a third embodiment of the present invention. FIG. 11 shows a fourth embodiment of the present invention. Figure 12 shows a conventional example. Figure 13 shows the shape of a conventional physical optical element. FIG. 14 is a diagram showing the principle of etch scattering in a conventional example. FIGS. 15 and 16 are conventional Fraunhofer diffraction patterns of unnecessary diffracted light. l; Projection beam 2; First object (mask) 3; Second object (wafer) 4; Incident side mark 5; Output side mark 6.7; Lens 8; Detector 9; Processing system lO; Optical probe II; Mark peripheral shape 12; Mark edge portion 13: Edge scattered light 14: Detection area] 5 16 7 8 9 20° 22° 24; 25° First physical optical element Second physical optical element Light source half mirror Detection light 21; Reflected light 23: Diffracted light 1 Fu 26 Parallel 2 sides 2 illustration lol l'7 Kashi 4 / 4 Shi (0,) and (1)) To 1

Claims (3)

[Claims] (1) A light source means for irradiating a light beam onto the mark of an object having a mark for position detection consisting of a diffraction grating, and detecting the position of the object by receiving the diffracted light from the mark that receives the light beam from the light source means. 1. A positioning device comprising: a detecting means for detecting the mark, and the outer peripheral edge portion of the mark has a curved shape so as to disperse specularly reflected and scattered light from the outer peripheral edge portion of the mark. (2) A light source means for irradiating a light beam onto the mark of an object having a position detection mark made of a diffraction grating, and detecting the position of the object by receiving the diffracted light from the mark that receives the light beam from the light source means. What is claimed is: 1. A positioning device comprising a detecting means for detecting the mark, and having a mark having a curved outer circumferential shape so as to disperse unnecessary diffracted light generated from the mark. (3) A light source means for irradiating a light beam onto the mark of an object having a position detection mark made of a diffraction grating, and detecting the position of the object by receiving the diffracted light from the mark that receives the light beam from the light source means. 1. A positioning device characterized in that the mark has a curvature of 1/R expressed by the following formula on the outer peripheral shape of the mark. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ However, l is the length of the side of the mark to which curvature is to be applied, β is the angle from the mark to the detection system, and d is the projected component of the part to be curvatured onto the axis orthogonal to the mark side.