JP2698389B2 - Position detection device - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to a position detecting device, for example, in an exposure apparatus for manufacturing a semiconductor device, on a first object surface such as a mask or a reticle (hereinafter, referred to as a "mask"). The present invention relates to a position detecting apparatus suitable for performing relative alignment (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. is there.

[Conventional technology]

2. Description of the Related Art Conventionally, in an exposure apparatus for manufacturing a semiconductor, relative positioning of a mask and a wafer has been an important factor for improving performance. In particular, in recent aligners in an exposure apparatus, for high integration of semiconductor elements,
For example, one having a positioning accuracy of sub-micron or less is required.

In many alignment apparatuses, a so-called alignment pattern for alignment is provided on a mask and a wafer surface, and both alignments are performed using positional information obtained from the alignment patterns. As an alignment method at this time, for example, the amount of deviation between the two alignment patterns is detected by performing image processing, or alignment is proposed as proposed in U.S. Pat. No. 4,037,969 or Japanese Patent Application Laid-Open No. 56-157033. This is performed by using a zone plate as a pattern, irradiating the zone plate with a light beam, and detecting the position of a condensing point on a predetermined surface of the light beam emitted from the zone plate.

Generally, an alignment method using a zone plate has a feature that relatively high-precision alignment can be performed without being affected by a defect in an alignment pattern, as compared with a method using a simple alignment pattern.

FIG. 6 is a schematic view of a conventional positioning device using a zone plate.

In the same figure, a parallel light beam emitted from a light source 72 passes through a half mirror 74 and is condensed at a converging point 78 by a converging lens 76, and is then placed on a mask alignment pattern 68a on a mask 68 and a support 62. The wafer alignment pattern 60a on the surface of the wafer 60 is irradiated. These alignment patterns 68a and 60a are constituted by reflection type zone plates,
Focus points are formed on planes orthogonal to the optical axis each including the focus point 78. At this time, the amount of shift of the condensing point position on the plane is detected by guiding the light onto the detection surface 82 by the condensing lenses 76 and 80.

Then, based on the output signal from the detector 82, the control circuit 84
Drives the drive circuit 64 to perform relative positioning between the mask 68 and the wafer 60.

FIG. 9 shows the mask alignment pattern shown in FIG.
FIG. 8 is an explanatory diagram showing an image forming relationship of a light beam from 68a and a wafer alignment pattern 60a.

In the figure, a part of the luminous flux diverging from the converging point 78 is diffracted from the mask alignment pattern 68a to form a converging point 78a indicating the mask position near the converging point 78.
Further, some other light beams pass through the mask 68 as zero-order transmission light and enter the wafer alignment pattern 60a on the wafer 60 without changing the wavefront. At this time, after the light beam is diffracted by the wafer alignment pattern 60a, the light beam is transmitted again through the mask 68 as zero-order transmission light, condensed in the vicinity of the converging point 78, and forms a converging point 78b representing the wafer position. In the figure, when the light beam diffracted by the wafer 60 forms a converging point, the mask 68 acts as a simple transparent state.

The position of the focal point 78b by the wafer alignment pattern 60a formed in this way is determined by the amount of the deviation along a plane orthogonal to the optical axis including the focal point 78 according to the deviation Δσ of the wafer 60 with respect to the mask 68. The deviation amount Δ of the amount corresponding to Δσ
σ '. Δσ was determined by measuring this Δσ ′ with reference to an absolute coordinate system provided on the sensor.

[Problems to be solved by the invention]

In such a method, when the wafer surface is inclined with respect to a reference surface such as a mask surface or a mask holder surface in a semiconductor exposure apparatus, and the position of a light beam incident on the sensor when the wafer surface is inclined with respect to a ground plane or the like of the exposure apparatus. Changes, resulting in an alignment error.

In general, setting an absolute coordinate system on a sensor and setting its reference origin is caused by other alignment error factors, such as inclination having a warp or deflection of a wafer surface, fluctuation of the center of gravity of a light beam due to uneven coating of a resist, alignment light source. There is a problem that it is very difficult to set the origin with high accuracy due to fluctuations in the oscillation wavelength, oscillation output, light emission angle, fluctuations in sensor characteristics, and fluctuations due to repetition of the alignment head position.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described drawbacks of the conventional example, and has as its object to provide a position detection device that can always perform highly accurate alignment without being affected by the inclination of the wafer surface.

[Means for solving the problem]

The present invention newly forms a second signal light beam in addition to a first signal light beam as a means for removing an error factor when detecting a shift amount when performing alignment between a first object such as a mask and a second object such as a wafer. In addition, it is an object of the present invention to provide a position detection device that realizes highly accurate position detection by using these and can always confirm a direction of a position shift.

One embodiment of the position detecting device of the present invention for achieving the above object is a position detecting device that detects a positional relationship along a predetermined direction orthogonal to a facing direction of a first object and a second object that are opposed to each other. Light source means for emitting light in the direction of the first object or the second object, and a first light beam emitted from the light source means and diffracted by the first and second objects is made incident on a first light receiving surface. First detecting means for detecting an incident position on the first light receiving surface of the first light flux, which changes according to a change in a relative positional relationship between the first object and the second object along the predetermined direction; A second light flux emitted from the light source means and diffracted by the first and second objects is incident on a first light receiving surface, and a relative position of the first object and the second object along the predetermined direction The first light flux according to a change in the relationship Second detecting means for detecting an incident position of the second light flux changing in a direction opposite to the incident position on the first light receiving surface; and light emitted from the light source means and diffracted by the first and second objects. A third light beam is made incident on a second light receiving surface, and the third light beam changes to a first light receiving surface of the third light beam that changes according to a change in a relative positional relationship between the first object and the second object along the predetermined direction. Of detecting the incident position of light
Detecting means for causing a fourth light flux emitted from the light source means and diffracted by the first and second objects to be incident on a second light receiving surface, along the predetermined direction between the first object and the second object; The first object and the second object when the incident position of the first light beam and the second light beam coincide with each other change in a direction opposite to the incident position of the third light beam according to the change of the relative positional relationship.
When the first object and the second object have a relative positional relationship different from the relative positional relationship with the object, the third light beam and the incident position coincide with each other when the fourth light beam is incident on the second light receiving surface. A fourth detection unit for detecting a position, a positional shift amount between the first object and the second object along the predetermined direction based on a detection result of the first, second, third, and fourth detection units; Means for detecting the direction of displacement.

In an embodiment which will be specifically described later, in order to solve the above-mentioned problem, four points having different coordinate points on two planes which face substantially in parallel, such as a mask and a wafer in a semiconductor manufacturing apparatus. In the apparatus for detecting the amount of relative positional deviation based on the information of (2), two of the four positions are used to determine the amount of deviation of one direction component orthogonal to each other from the distance between two light spots formed on a one-dimensional sensor, and By inverting the polarities (that is, the directionality of the sensor signal with respect to the deviation) of the two detection portions that perform detection in the same direction, a wide measurement range and high resolution are achieved by referring to both.

〔Example〕

First, the principle and components of the detecting means used in the present invention will be described with reference to FIG. In the figure, 1 is a first object, 2 is a second object, and 5, 3 are alignment marks for obtaining the first signal light, respectively, provided on 1 and 2, respectively. Similarly, reference numerals 6 and 4 denote alignment marks for obtaining the second signal light, respectively, which are also provided on the reference numerals 1 and 2, respectively. Each of the alignment marks 3, 4, 5, and 6 has a function of a physical optical element having a one-dimensional or two-dimensional lens function. Reference numerals 7 and 8 denote the first and second alignment signal light beams, respectively. 11,12
Are first and second detection units for detecting the first and second signal light beams, respectively, and the optical distance from the object 2 is set to the same value L for convenience of explanation. Further, the distance between the object 1 and the object 2 is δ, the focal length of the alignment marks 5 and 6 is f _a1 ,
f _a2 , the relative displacement between the object 1 and the object 2 is ε,
The amounts of displacement of the first and second signal light beam centroids from the matching state at that time are denoted by S ₁ and S ₂ , respectively. The alignment light beam incident on the object 1 is a plane wave for the sake of convenience, and the signs are as shown in the figure.

Intersection of displacement S ₁ and S ₂ of the signal light beam centroid and the straight line connecting the center of the optical axis of the focus F _1, F ₂ and the alignment marks 3 and 4 of the alignment marks 5 and 6, the light receiving surface of the detector 11 and 12 Geometrically as Therefore, the displacement amounts S ₁ and S ₂ of the respective signal light beam centroids with respect to the relative displacement between the object 1 and the object 2 are equal to the optical imaging magnification of the alignment marks 3 and 4 as is clear from FIG. The opposite direction is achieved by reversing each other. Also, quantitatively The shift magnification can be defined as β ₁ = S ₁ / ε, β ₂ = S ₂ / ε. Therefore, if the shift magnification is the opposite sign, the light fluxes 7 and 8 are opposite to each other on the light receiving surfaces of the detectors 11 and 12 with respect to the shift between the object 1 and the object 2, specifically, by S ₁ and S ₂ respectively. Change.

Among them, practically L» One suitable structure condition _{| f a1 | f a1 / f} a2 <0 | f a1 |> δ | a condition of> δ | f _a2. That is, the distance L to the detection unit is increased with respect to the focal lengths f _a1 and f _{a2 of} the alignment marks 5 and 6, the interval δ between the objects 1 and 2 is reduced, and one of the alignment marks is a convex lens and the other is a concave lens. The configuration is as follows.

The upper side of FIG. 1 and condensed light beam incident light beam by the alignment marks 5 so as to irradiate light beam to alignment marks 3 before reaching the focal point F _1, further imaged on a first detecting section 11 so The focal length f _b1 of the alignment mark 3 is the lens formula It is determined to satisfy The lower side of FIG. 1 as well as in terms of the incident side of the incident light beam by the alignment mark 6 F ₂
Change to a more divergent luminous flux, which is
The focal length f _b2 of the alignment mark 4 to be imaged on the second detection unit 12 via It is determined to satisfy Under the above configuration conditions, the imaging magnification of the alignment mark 3 and the alignment mark 5 with respect to the converged image is clearly a positive magnification from the figure, and the movement ε of the object 2
The direction of the light spot displacement amount S ₁ of the detection unit 11 becomes reversed, the deviation magnification beta _1, as defined above, of the negative. Similarly imaging magnification of the alignment marks 4 for the point image (virtual image) of the alignment mark 6 is negative, the direction of the light spot displacement amount S ₂ of the detector 12 and the movement of the object 2 epsilon in the same direction, the deviation magnification β ₂ is positive.
Accordingly, the signal beam shifts S ₁ and S ₂ of the systems of the alignment marks 5 and 3 and the systems of the systems 6 and 4 are opposite to each other with respect to the relative shift ε between the object 1 and the object 2.

That is, considering the state in which the object 1 is spatially fixed and the object 2 is displaced to the lower side in the drawing in the arrangement of FIG. When it is displaced to, it becomes narrow. This is schematically shown in FIG. (A)-(b) are objects 1 and 2
FIG. 6 is a light amount distribution on the detection unit in each state when the relative shift amount ε is monotonously changed. Here, the light amount distribution in the coincidence state between the object 1 and the object 2 is represented by (c).

 Next, a specific embodiment will be described.

FIG. 3A is a configuration diagram of a position detecting device according to a first embodiment of the present invention, and FIG. 3B is a schematic diagram of the principal part. Members similar to those in FIG. 1 are denoted by the same reference numerals.

In the figure, reference numeral 1 denotes a first object, for example, a mask. Reference numeral 2 denotes a second object, for example, a wafer to be aligned with the mask 1. Each of the alignment marks 3, 4 and 5, 6 is composed of a one-dimensional or two-dimensional grating lens such as a Fresnel zone plate, and is provided on scribe lines 10 and 9 on the mask 1 surface and the wafer 2 surface, respectively. ing. 7
Is a first light beam, 8 is a second light beam, these light beams (signal light beams) 7, 8 are emitted from a light source 13, collimated to a predetermined beam diameter by a lens system 14, and the optical path is bent by a mirror 15. I have.

In this embodiment, as the type of light source a semiconductor laser, H _e -N _e laser, or a light source for emitting a coherent light beam, such as A _r laser, a light source or the like that emits non-coherent light beam such as a light emitting diode. First detector in FIG.
In this figure, 11 and the second detection unit 12 are one sensor (photoelectric conversion element) 22 and receive the light beams 7 and 8, for example, one-dimensional.
It consists of CCD etc.

In this embodiment, the light beams 7 and 8 are incident on the alignment marks 5 and 6 on the mask 1 at a predetermined angle, then transmitted and diffracted, further reflected and diffracted on the alignment marks 3 and 4 on the wafer 2 surface, and received. The light is condensed by the lens 21 and is incident on the light receiving surface of the sensor 22. Then, the signal processing device 23 receiving the signal from the sensor 22 detects the position of the center of gravity in the sensor surface of the alignment light beam incident on the sensor surface with the sensor 22,
Using the output signal from the sensor 22, the signal processor 23 detects the positional deviation of the mask 1 and the wafer 2.

Here, the center of gravity of the luminous flux is defined as a point in the luminous flux cross section at which the integral value becomes a zero vector when the value obtained by multiplying the position vector from each point in the cross section by the light intensity at that point is integrated over the entire cross section. However, as another example, the position of a point where the light intensity reaches a peak may be detected.

 Next, alignments 3, 4, 5, and 6 will be described.

Each of the alignment marks 3, 4, 5, and 6 is composed of a Fresnel zone plate (or a grating lens) having a different value of the focal length. The dimensions of these marks are 50 to 300 μm in the direction of the scribe lines 9 and 10 and 20 to 100 μm in the scribe line width direction (y direction), respectively, which are practically appropriate.

In this embodiment, the light beams 7 and 8 are both
At an incident angle of about 17.5 ° with respect to the surface of the mask 1 so that the projected component is orthogonal to the scribe line direction (x direction).

The alignment light beams 7 and 8 incident on the mask 1 at these predetermined angles become convergent or divergent light under the action of the grating lenses 5 and 6, respectively, and the chief ray from the mask 1 with respect to the normal line of the mask 1 At a predetermined angle.

The light beams 7 and 8 transmitted and diffracted through the alignment marks 5 and 6 respectively have a light condensing point and a divergence origin at predetermined points vertically below and vertically above the wafer surface 2. At this time, the focal lengths of the alignment marks 5 and 6 are 214.426-156.57 μm, respectively.
It is. The distance between the mask 1 and the wafer 2 is 30 μm. The first signal light beam 7 is transmitted and diffracted by the alignment mark 5, receives a concave lens effect on the alignment mark 3 on the wafer 2 surface, and is condensed on one point on the sensor 22 surface. At this time, the light beam on the surface of the sensor 22 is in a state where the amount of change in the incident position of the light beam corresponds to the amount of displacement of the alignment marks 5 and 3 in the x direction, that is, the amount of axial displacement, and the amount is enlarged. Incident. As a result, a change in the position of the center of gravity of the incident light beam is detected by the sensor 22.

The second signal light beam 8 is transmitted and diffracted by the alignment mark 6, and is reflected and diffracted by the alignment mark 4 on the surface of the wafer 2 so that the spot position at the image forming point is moved in a direction different from that of the first signal light beam. Focus on one point on 22 surfaces. Similarly to the light beam 7, the amount of change in the incident position of the light beam 8 corresponds to the amount of axis deviation and is in an enlarged state.

At this time, assuming that the position of the light receiving surface of the sensor 22 where the light fluxes 7 and 8 converge is 18.657 mm from the wafer surface or a position equivalent thereto through the light receiving lens 21, each shift magnification (= variation amount of incident position) The absolute value of (/ axis shift amount) is 100 times and the direction can be set in the opposite direction. As a result, when the mask 1 and the wafer 2 are shifted by 0.005 μm in the x direction, the distance between the centers of gravity of the two light beams, that is, the spot distance, changes by 1 μm. By detecting the spot interval, the positional deviation between the mask 1 and the wafer 2 is detected. At this time, the spot diameter of the sensor surface can be set to about 200 μm, assuming that the effective diameter of the alignment mark as a lens is about 200 μm and that a 0.8 μm band semiconductor laser is used as a light source. It is possible to determine this using

It is appropriate to set the interval between the two spots in the coincident state as shown in (C) to, for example, about 1.5 to 2.5 mm.

As an effect of setting the configuration in which the two signal light beams are displaced in the opposite directions as in the present invention, even if the setting accuracy of the interval δ between the object 1 and the object 2 is relaxed, it is necessary to calculate the displacement amount. The point is that each of the shift magnifications β ₁ and β ₂ has a compensation relationship with each other in the two optical paths. That is, in the aforementioned lens parameters, the distance δ between the object 1 and the object 2 is set to 30 μm.
Taking as an example the case where it is expanded to 33 μm, β ₁ is −100
From -100 to +101.684, and? ₂ from +100 to +98.64. Therefore, the total magnification used when obtaining the displacement amount |
β ₁ | + | β ₂ | changed from 200 to 200.148,
The ratio can be reduced to a magnification change of 0.0741%. this is,
For each signal having a change of 1.68% and 1.53% respectively, it is suppressed to about 1/20,
This has the effect of directly enlarging the detection lens or improving the detection accuracy when applied to a system in which the interval setting is difficult.

Another result is that the error caused by the tilt of the objects 2 and 3 is compensated in principle.

In this embodiment, the wafer surface 2 is 1 m in the xz plane of FIG.
Assuming a rad inclination, the first signal light beam 7 moves on the sensor 22 by about 37.3 μm. On the other hand, the second signal light beam 8 also has a symmetry plane parallel to the yz plane with the signal light beam 7 and passes through an optical path having the same optical path length. I'm trying to wake up. By doing this, in the sensor system, if signal processing is performed so as to output the difference between the signals of the effective center of gravity position from each sensor,
The output signal from the sensor system does not change even if the wafer is tilted in the yz plane.

On the other hand, when the wafer is tilted in the yz plane, two signal beams
Both 7 and 8 move the center of gravity in the width direction orthogonal to the longitudinal direction of the sensor, but this is the direction orthogonal to the direction of movement of the center of gravity of the light beam due to displacement detected on the sensor. It does not result in an effective alignment error.

Furthermore, an alignment head incorporating an alignment light source, a projection lens system and a sensor, etc.
When the position changes with respect to the wafer system, the position changes one to one. For example, if the head is moved in the 5 μm y direction with respect to the mask, the signal light beam 7 is 5 μm on the sensor 11.
m, which causes an effective movement of the center of gravity,
Also causes the center of gravity to move by 5 μm on the sensor 22 exactly equally.

Therefore, the final output from the sensor system, that is, the difference signal between the center-of-gravity position output of the first signal light beam and the center-of-gravity position output of the second signal light beam does not change at all.

Further, it can be seen that a change in the position in the z-axis direction does not result in an essential alignment error even without two light beams.

In this apparatus, the alignment marks 3, 4, 5, and 6 are provided at four points P ₁ , P ₂ , P ₃ , and P ₄ on the scribe line 1a surrounding the pattern of the square circuit portion, and the four points are provided. A light beam is projected onto this mark at a position corresponding to the above, and the above-described optical systems for detecting the light beam from the mark are set, respectively, and a two-dimensional lateral displacement and rotation are obtained as a positional displacement amount between the mask and the wafer. The arrangement of the marks at this time is shown in FIG. When the present apparatus is used in a semiconductor exposure apparatus, exposure is performed after correcting this.

At this time, generally, the wafer 2 is provided with an orientation flat 2a, and the rotation component is used to reduce the maximum error 3a.
Since the correction can easily be made to about 0 ″, the parallel-lateral shift component is mainly the shift component.

By the way, as is apparent from FIG. 2, when the relative shift amount is detected with two spot intervals, the behavior is symmetrical with respect to the state of (e). A certain (g) cannot be discriminated from this one piece of information.

However, the detection of this position and P _1, in the P ₁ and the circuit pattern corresponding same direction detecting Tsukasa Nikki at point P ₂ Metropolitan in I narrow and a system obtained by polarity inversion of each of the detector, both It is possible to determine the true value by referring to the spot deviation detection value. That is, with respect to the direction of displacement of between objects 1 and 2, for example, in a system provided in the P ₁ spread two Supotsuto spacing, in a system provided with the corresponding side P ₂ 2
The relationship is set such that the interval between two spots is narrowed so that the deviation amount is in a certain section. This can be achieved simply by the form in which the 6,4 optical path of the optical beam path and below the upper of 5,3 upside down in FIG. 1 the alignment mark P _2. FIG. 4 shows the resulting spot behavior of the detection unit in correspondence with FIG. State of it from the output of the detection system provided in P ₁ is a shift state of the as shown in FIG. 2 (c) and (g) are indistinguishable, the output of the detection system provided on P ₂ is (c) ' the closer to, P ₁ is found to be in the state of (c), 4
When FIG. (G) 'output that occurs when a large Supotsuto intervals on the sensor surface as the can determined that a P ₁ is (g). When this is graphed, it can be shown in FIG. The detection value of the detection system and the detection system each Supotsuto distance P ₂ of the P ₁ corresponds to a shift amount of 2 values alone, do not know any. At this time, if the polarities of the two detection systems are reversed, only one corresponding shift amount is obtained from the outputs from the two detection systems. Specifically, two different shift amounts estimated from the spot intervals obtained from the respective detections are output for each of the detection systems, and the difference between the four combinations is obtained. What is necessary is just to perform the process which judges the combination of the minimum output value as a true value. FIG. 6 shows the flow of this calculation.

Naturally, a similar system is provided at two other points P ₃ and P ₄ for detection in the direction orthogonal to the direction in which P ₁ and P _{2 control} detection, and the true amount of deviation is calculated at a total of four points. Object 1 and object 2
Is completed. According to the detection result, the mask 1 and the wafer 2 are aligned by a well-known alignment mechanism.

〔The invention's effect〕

As described above, according to the present invention, an apparatus suitable for a semiconductor manufacturing apparatus for measuring a positional shift amount between a mask and a wafer is realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing the detection principle of the present invention, FIG. 2 is a diagram showing the behavior of a sensor signal in the detection principle of the present invention, and FIG. 3A is a configuration diagram of a position detecting device according to an embodiment of the present invention. FIG. 3B is a schematic view of a main part of the device, FIG. 4 is a diagram showing a behavior of a signal of a sensor of the device, FIG. 5 is a correlation diagram of a position shift-spot interval in the device, and FIG. FIG. 7 is a flow chart of the signal processing of the apparatus, FIG. 7 is a layout diagram of alignment marks on a mask and a wafer, and FIGS. 8 and 9 are explanatory views of a conventional example. In the figure, 1 ... mask 2 ... wafer 3,4,5,6 ... alignment mark 13 ... light source 22 ... sensor 23 ... signal processing device.

Claims (1)

(57) [Claims] 1. A position detecting device for detecting a positional relationship along a predetermined direction orthogonal to an opposing direction between a first object and a second object disposed opposite to each other, wherein the position detecting device detects a positional relationship between the first object and the second object. Light source means for emitting light, and a first light flux emitted from the light source means and diffracted by the first object and the second object is incident on a first light receiving surface, and the first object and the second object A first detecting unit configured to detect an incident position on the first light receiving surface of the first light flux that changes according to a change in a relative positional relationship along a predetermined direction;
Detecting means for causing a second light flux emitted from the light source means and diffracted by the first object and the second object to be incident on a first light receiving surface, along the predetermined direction between the first object and the second object. A second detecting unit that detects an incident position on the first light receiving surface of the second light beam that changes in a direction opposite to an incident position of the first light beam according to a change in the relative positional relationship. A third light beam emitted and diffracted by the first object and the second object is made incident on a second light receiving surface, and according to a change in a relative positional relationship between the first object and the second object along the predetermined direction. Detecting means for detecting an incident position of the third light flux changing on the first light receiving surface, and a fourth light flux emitted from the light source means and diffracted by the first and second objects. The first object and the second object are incident on a light receiving surface. Changes in the direction opposite to the incident position of the third light beam according to the change in the relative positional relationship along the predetermined direction with the third light beam, and when the incident positions of the first light beam and the second light beam coincide with each other, When the first object and the second object are in a relative positional relationship different from the relative positional relationship between one object and the second object, the third light beam and the incident position coincide with each other when the first object and the second object are present. (2) Fourth detecting means for detecting the position of incidence on the light receiving surface; and in the predetermined direction between the first object and the second object based on the detection results of the first, second, third, and fourth detecting means. Means for detecting the amount of displacement and the direction of displacement along the position.