JP2789787B2 - Position detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a position detecting device, for example, in an exposure apparatus for manufacturing a semiconductor element, 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 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. .

2. Description of the Related Art Conventionally, in an exposure apparatus for manufacturing a semiconductor, relative positioning between 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 light-converging 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. 7 shows the mask alignment pattern shown in FIG.
FIG. 8 is an explanatory diagram showing an image forming relationship between light beams from a wafer alignment pattern 68 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 more diffracted on 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 '.

Conventionally, the position of the mask 68 and the wafer 60 has been adjusted by detecting the shift amount Δσ ′ at this time.

(Problems to be Solved by the Invention) In the positioning apparatus shown in FIG. 6, there is a certain amount of uncertainty in the distance g between the mask and the wafer, which causes, for example, the following problems.

Since the shift amount Δσ ′ depends on both the shift amount Δσ and the interval g, a number of sets of the shift amount Δσ and the interval g correspond to one shift amount Δσ ′. Therefore, if an attempt is made to detect a matching state at the position of the focal point 78a, if the light beam is condensed at an out-of-focus state, for example, at the position of the focal point 78b, the value of the shift amount Δσ ′ can be accurately determined. Even if it is measured, the deviation amount Δσ is not accurately determined. For this reason, only one positioning operation is required, and it is necessary to perform the operation twice, three times, and the throughput decreases.

The present invention solves an error factor generated when detecting a position between a first object such as a mask and a second object such as a wafer, and detects a position with a simple configuration capable of performing highly accurate and easy alignment. The purpose is to provide the device.

(Means for Solving the Problems) In the present invention, the relative displacement in the plane between the first object and the second object (hereinafter, also simply referred to as “displacement amount”) is determined, and at the same time, the interval is determined. It is characterized in that the position detection of the first object and the second object is obtained with high accuracy.

In particular, in the present invention, a physical optical element is provided on each of the first object plane and the second object plane, and a diffracted light beam of a predetermined order generated on a predetermined surface of a light beam incident on these physical optical elements is detected by a detecting means. When the relative position between the first object and the second object is detected by performing the first and third physical optical elements on the first object surface, the first and third physical optical elements are disposed on the second object surface. Are provided with two physical optical elements, second and fourth, respectively, and one physical optical element on the first object plane and the second physical optical element
The relative shift amount W and the relative distance g between the first object and the second object among the diffracted light beams of at least three diffracted light beams diffracted by one physical optical element on the object plane, respectively. Detecting at least two values between the diffracted beams related to both,
It is characterized in that the shift amount W and the interval g are obtained by the calculation means using the output signal from the detection means.

(Embodiment) FIG. 1 is a schematic view of a main part of a first embodiment of the present invention, and FIG. 2 is a schematic view of a main part when an optical path of each light beam in FIG. 1 is schematically developed.

In FIGS. 1 and 2, l1 denotes a semiconductor laser or LE (not shown).
This is a light beam from a D or X-ray source or the like, and is incident on physical optical elements z1 and z3, which will be described later, on the first object 1 surface such as a mask at an angle θ. Reference numeral 2 denotes a second object such as a wafer, which is opposed to the first object 1 at an interval g. W indicates a relative shift amount between the first object 1 and the second object 2. z1 and z3 are transmission-type first and third physical optical elements provided on the surface of the first object 1, respectively, and the light flux l1 is incident on the physical optical elements z1 and z3. z2 and z4 are reflection type (transmission type in FIG. 2) second and fourth physical optical elements provided on the surface of the second object 2, and these physical optical elements z1 to z4 are, for example, diffraction gratings and zone plates. Consists of

FIG. 3 shows a pattern example of the physical optical elements on the surfaces of the first object 1 and the second object 2 according to the present embodiment.

The physical optical elements z1 to z4 have a lens function, and the focal points are F1 to F4 and the focal lengths are f1 to f4.

l2 to l9 are diffracted lights of predetermined orders from the physical optical elements,
Reference numeral 3 denotes a detecting means, for example, a sensor such as a line sensor or an area sensor, which is arranged at a position separated from the first object 1 by a distance L. a1 and a2 are the optical axes of the physical optical elements z1 and z3, respectively, of which the optical axis a1 and the optical axis a2 are separated by a distance D.

Points C1 to C4 are the luminous flux barycentric positions of the diffracted lights l3, l5, l7, and l9 on the sensor 3 surface, respectively. Of these, points C1 and C2 are points away from the optical axis a1 by distances y1 and y2, respectively, and points C3 and C4 indicate positions away from the optical axis a2 by distances y3 and y4, respectively.

The luminous flux centroid is, for convenience, a point in the luminous flux cross-section where a value obtained by multiplying the position vector from each point in the cross-section by the light amount at that point is integrated over the entire cross-section to obtain a zero vector. Is shown.

Reference numeral 4 denotes a signal processing circuit as an arithmetic unit, and the sensor 3
From the information from, the luminous flux centroids of the luminous fluxes l3, l5, l7, l9 are obtained, and the displacement W between the first object 1 and the second object 2 is calculated from the distances y1 to y4, D, etc. The interval g is determined. Reference numeral 5 denotes a control circuit, which controls the first object 1 and the second object 2 in accordance with information on the displacement W and the interval g from the signal processing circuit
The position shift amount W from the object 2 and the interval g are controlled.

Reference numeral 6 denotes a stage controller, which drives a stage (not shown) on which the second object 2 is mounted in accordance with a command from the control circuit 5.

In this embodiment, the light beam l1 from the light source is incident on the physical optical elements z1 and z3 on the first object 1 surface. Among these, of the light beam l1 incident on the physical optical element z1, the first-order diffracted light l2 generated by the physical optical element z1 is incident on the physical optical element z2. Then, a first-order diffracted light 13 having a different diffraction direction is generated according to the positional deviation amount W. The diffracted light 13 passes through the physical optical element z1 as it is as the zero-order diffracted light. The diffracted light l3 is reflected on the optical axis a1 on the surface of the sensor 3.
An image is formed at a distance y1 away from. Since the distance between the sensor 3 and the first object 1 is a constant value L, the value of the distance y1 is an amount that depends on the interval g and the displacement W.

On the other hand, the light beam l1 that has passed through the physical optical element z1 as a 0th-order diffracted light without being subjected to the diffraction action enters the physical optical element z2.
Then, the first-order diffracted light 14 subjected to the first-order diffraction action by the physical optical element z2 re-enters the physical optical element z1. Then, a first-order diffracted light 15 having a different diffraction direction is generated according to the displacement W. The first-order diffracted light 15 forms an image at a distance y2 from the optical axis a1 on the surface of the sensor 3.

From the light beam l1 incident on the physical optical element z3, the physical optical element
Diffracted light beams l6 to l9 similar to the light beam l1 incident on z1 are generated. Of these, the diffracted light beams l7 and l9 form images at positions at distances y3 and y4 from the optical axis a2 on the surface of the sensor 3, respectively. Reference numeral 4 denotes a signal processing circuit as arithmetic means. First, based on information read from the sensor 3, light beam centroid positions C1, C2, C3, and C3 of the light beams l3, l5, l7, and l9.
After obtaining C4, an interval D14 between points C1 and C4 and an interval D23 between points C2 and C3 are calculated. The position shift amount W and the distance g between the first object 1 and the second object 2 are obtained using the values of the distances D14 and D23 by using the relations of the respective expressions described later.

The control circuit 5 drives the stage controller 6 in accordance with the information on the displacement W and the distance g from the signal processing circuit 4 to move the second object 2 to a predetermined position.

In this embodiment, the same effect can be obtained by using not only the first-order diffracted light but also the second-order or higher-order diffracted light.

In this embodiment, since the light source, the sensor, and the like can be configured as a single unit, the optical probe can be reduced in size, and since the optical probe does not need to be moved during exposure, the throughput is further improved. have.

Next, a method of obtaining the displacement W and the gap g between the first object 1 and the second object 2 in this embodiment will be described with reference to FIG.

In FIG. 2, the lens system that generates the diffracted light l3
Il enters the point C1 through the physical optical elements z1 and z2 functioning as a lens. At this time, the distance y1 of the diffracted light l3 to the luminous flux center C1 is the displacement W between the first object 1 and the second object 2, and the distance g.
And is generally expressed as y1 = F1 (W, g) (1).

Similarly, in the other three lens systems, the distances y2, y3, and y4 are determined by the shift amount W and the distance g, and y2 = F2 (W, g) (2) y3 = F3 (W, g) ... (3) y4 = F4 (W, g)... (4)

When the distances y1 to y4 are represented as described above, the points C1 and C3
Using the interval D13 between them and the interval D24 between the points C2 and C4, the amounts Y1 and Y2 that depend on the shift amount W and the interval g can be expressed as follows.

Y1 = y1 + y3 = D13-D = F1 + F3 = F5 (g, W) Y2 = y2 + y4 = D24-D = F2 + F4 = F6 (g, W) That is, Y1 = F5 (g, W) ... (5) Y2 = F6 (g, W) (6) In general, when there are two unknowns, the solution of the unknowns can be obtained if there are two equations including the unknowns.

That is, if two relational expressions such as A = G1 (W, g) (7) B = G2 (W, g) (8) can be prepared, the amounts of A and B are measured by measurement or the like. The values of the two unknowns W and g can be obtained by obtaining the values.

The above equation (1) is specifically expressed as W, g as follows.

y1: W = L + 2g-f1: f1-g From this Becomes The other equations (2), (3) and (4) are similarly Becomes Based on the above relational expressions, the expressions (5) and (6) are concretely expressed. Becomes In the equations (13) and (14), the interval D is the optical axis a1 and the optical axis a1.
Since the interval D13 and the interval D24 are known at the interval of a2, and the values of the intervals D13 and D24 can be specifically obtained by measurement, (13), (14)
The values of the shift amount W and the interval g can be obtained from the equations.
If the shift amount W is eliminated from the equations (13) and (14), the interval g becomes 3
The following equation is obtained, from which the shift amount W and the interval g can be easily obtained by a personal computer or the like.

In the present embodiment, the first to fourth physical optical elements z1 to z4
Are set so as to satisfy the following equation.

FIG. 4 is an explanatory diagram showing how the luminous flux centroids C1, C2, C3, and C4 of the diffracted luminous fluxes l3, l5, l7, and l9 change on the sensor 3 surface according to the shift amount W in this embodiment. It is. Diffracted light beam
Since l3, l5, l7, l9, and the like have a certain width on the sensor surface, it is difficult to accurately determine the points C1 to C4 if there are overlapping portions.

Therefore, in the present embodiment, for example, when it is desired to measure within the deviation amount W = ± 3 μm, the range in which each light beam is separated is set to the point Wo of the same point.
The characteristics between −3 and Wo + 3 are obtained in advance by simulation or the like, and are used.

That is, in this embodiment, the positions of the centers of gravity of the first and second two diffracted light beams generated on the predetermined surface via the first and second two physical optical elements and the third and fourth two physical The positions of the centers of gravity of the third and fourth diffracted light beams generated on the predetermined surface via the optical element are detected in such a manner that they are separated by more than the width of the diffracted light beams.

In this embodiment, when the displacement W between the first object and the second object is 0, the physical optical element (for example, z
1) Optical axis a1 and physical optical element on the second object (eg, z2)
Is shifted by the distance Wo, the point C1 and the point C are shifted when the displacement W between the first object and the second object is zero.
2, and the points C3 and C4 can be kept apart.

The pattern arrangement of the first to fourth physical optical elements z1 to z4 shown in FIG. 3 shows this state. When the displacement W between the first object and the second object is 0, the first and second physical optics are set. Elements z1 and z2
Are set so that the optical axes of the third and fourth physical optical elements z3 and z4 are respectively shifted by the distance Wo.

Therefore, when this pattern is used, the first object and the second object
When the object and the object are shifted by the distance Wx, the calculation may be performed by replacing the value of the shift amount W in the equations (9) to (12) with W = Wo + Wx.

In this embodiment, instead of providing two physical optical elements on the first and second object planes, four physical optical elements are provided to correspond to the diffracted light fluxes l3, l5, l7, and l9. Even if two diffracted lights are obtained, the same effect can be obtained.

However, the method of providing two physical optical elements as in this embodiment requires a smaller area than the method of providing four physical optical elements, and the amount of diffracted light is doubled when compared with the same area. There are advantages.

 Next, other embodiments of the present invention will be described in order.

(A) Second Embodiment In the first embodiment, the shift amount W and the interval g are obtained from the combination of the distances y1 and y3 and the distances y2 and y4. The distances y1 and y4, the distances y2 and y3, or the distances y1 and y2, and the distance Similarly, the shift amount W and the interval g can be obtained from the combination of y3 and y4.

When the distance between the points C1 and C4 is D14 and the distance between the points C2 and C3 is D23 when the distances y1 and y4 and the distances y2 and y3 are combined, the equations corresponding to the equations (7) and (8) are as follows. It is expressed as follows.

Similarly, when the distances y1 and y2 and the distances y3 and y4 are combined, the point C1
The distance between point C2 and point C2 is D12, and the distance between point C3 and point C4 is D34. Becomes From these equations, the shift amount W and the interval g can be obtained.

(B) Third Embodiment In the first and second embodiments, the center of gravity C1, C2,
Equations (7) and (8) corresponding to equations (7) and (8) were derived using C3 and C4 to determine the shift amount W and the interval g.
Even if three of C3 and C4 are used, equations corresponding to equations (7) and (8) can be similarly derived.

That is, the distance Dij (the distance between the points i and j) as described above.
, The following combinations are applicable.

Of these combinations, (I), (IV), (V),
The case of (VII) has a feature that the width of the sensor may be shorter by D12 or D34 than that of (II), (III), (VI), (VIII) and the first and second embodiments.

Next, specific examples of numerical values for the case (I) of the above-mentioned equations (19) and (20) will be shown. All units are μm.

g = 30, Wo = 10, L = 18627 f1 = 150.000, f2 = 120.768 f3 = 115.000, f4 = 143.885 y1 = 154.475 · W, y2 = 124.547 · W y3 = 129.669 · W, y4 = 162.560 · W W = 7 (Wo-3) Distance between light beam centroids C1 and C2: 209 Distance between light beam centroids C3 and C4: 230 (Note: Light beam width: about 210) W = 13 (Wo + 3) Distance from the optical axis a1: 2008 Distance from the optical axis a2 of the light beam centroid C3: 1685 Therefore, the required sensor width: D + 3693 + (210/2) × 2 = D + 3903 (c) Fourth Embodiment On the first object surface Instead of providing the two physical optical elements z1, z3 provided and the two physical optical elements z2, z4 provided on the second object plane independently, they are constituted by one pattern which is overlapped with each other as shown in FIG. The same effect as described above is obtained.

In this embodiment, the value of D corresponding to the distance between the optical axes a1 and a2 is zero, and if D = 0 in the first to third embodiments, all can be applied in this embodiment.

The feature of the pattern in the present embodiment is that the effect of the second object tilted in the alignment direction is less than that of the pattern in FIG. That is, when the pattern of FIG. 3 is used, when the second object is tilted, the effects of the lens systems of the first and second physical optical elements z1 and z2 and the lens systems of the third and fourth physical optical elements z3 and z4 are affected. Since they are different, a detection error occurs. On the other hand, in the present embodiment, the influence is the same, so that even if a detection error occurs, there is a feature that the detection error is extremely small as compared with the case of FIG.

(D) Fifth Embodiment In the present embodiment, a plurality of combinations of two values between the diffracted light beams regarding both the shift amount W and the interval g are detected, and the plurality of combinations are detected. Is evaluated by the evaluation means to improve the detection accuracy. As the evaluation means at this time, for example, a plurality of shift amounts W and intervals g obtained from a plurality of combinations, respectively.
It is possible to average the values of.

(E) Sixth Embodiment In actually carrying out the first to fourth embodiments, pre-alignment is performed in advance. However, as is apparent from FIG. 4, the right and left sides of the shift amount W = 0, that is, the positions of the light flux centroid positions C1 to C4 are reversed depending on the shift direction, but the state of the light flux at the positions C1 to C4 is changed. At first glance, it is not clear which side the second object is shifted with respect to the first object.

For this reason, in this embodiment, the first and second two diffracted light beams l3 and l5
Each element is set so that the distance D12 between the centroid positions C1 and C2 is different from the distance D34 between the centroid positions C3 and C4 of the third and fourth diffracted light beams l7 and l9.

Thus, after measuring the positions of the luminous flux barycenter positions C1 to C4 on the sensor 3 surface, the difference between the positions C1 and C2 and the positions C3 and C4 is calculated, and it becomes clear.

In addition, the light beams overlap near the shift amount W = 0, but when the positions C1 and C2 and the positions C3 and C4 are far apart, the state can be determined by, for example, obtaining the half width of the light beam. Becomes

Further, in the present embodiment, when four light beams are superimposed on the sensor surface, the discrimination may be performed after once changing the amount of displacement between the first object and the second object so that the first object and the second object can be discriminated.

(Effect of the Invention) According to the present invention, the displacement W between the first object and the second object is obtained.
By calculating the distance g between the first object and the second object,
It is possible to achieve a highly accurate position detection device with high throughput without misidentifying the coincidence state.

For example, the position information C1, C3 in the position detecting device of the present invention.
When the alignment is performed only from the relationship between the displacement and the shift amount W, the aforementioned constants are g = 30 μm, f1 = 150 μm, L = 18627 μm, y1 = 1
At 544.75 μm, if there is an error of 0.06 μm in the interval g, an error of 0.005 μm occurs in the shift amount W. Therefore 0.01 μm
When trying to align with the accuracy of
It is necessary that the thickness be about 0.06 μm or less. Therefore, the interval g must be set in advance by some method with an accuracy of 0.06 μm or less.

On the other hand, according to the present invention, if the interval g is set with a certain degree of accuracy in the pre-alignment, the shift amount W can be accurately obtained regardless of the value of the interval g.

For example, in a method of measuring the center of gravity of the two diffracted light beams in a state in which the diffracted light beams at the positions of the centers C1 and C2 overlap, when the light amount changes due to a change in diffraction efficiency or the like, the center of gravity moves and causes an error. According to the present invention, since the measurement is performed in a state where the diffracted light beams are sufficiently separated, the occurrence of such a detection error can be prevented.

Further, in the present invention, the physical optical element is used for both the detection of the displacement W and the interval g, thereby reducing the number of light beams and the number of physical optical elements, simplifying the detection system and reducing the size of the entire apparatus. It is trying to make it.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention, FIG. 2 is a schematic view of a main part when an optical path of each light beam of FIG. 1 is schematically developed, and FIGS. The first object 1 and the second object 1 in FIG.
FIG. 4 is an explanatory view of a physical optical element provided on the surface of the object 2; FIG. 1 is a schematic view of a conventional positioning device. In the figure, 1 is a first object, 2 is a second object, 3 is a sensor, 4 is a signal processing circuit, 5 is a control circuit, 6 is a stage controller, l1 to l9 are light beams, z1 to z4 are physical optical elements, and a1 , a2 is the optical axis of the physical optical element, W is the amount of displacement, and g is the interval.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01B 11/00-11/30 H01L 21/30 501-531,561-5 79

Claims (6)

(57) [Claims] 1. A physical optical element is provided on each of a first object surface and a second object surface, and a predetermined order diffracted light beam generated on a predetermined surface of a light beam incident on these physical optical elements is detected by a detecting means. When the relative position between the first object and the second object is detected by performing the first and third physical optical elements on the first object surface, the first and third physical optical elements are disposed on the second object surface. Are provided with two physical optical elements, second and fourth, respectively, and the detecting means includes one physical optical element on the first object surface and one physical optical element on the second object surface. At least 3 each diffracted
The first object and the second
At least two values between the diffracted light beams related to both the relative shift amount W and the relative distance g from the object are detected, and the shift amount W and the interval are calculated by the calculating means using an output signal from the detecting means. A position detecting device, wherein g is obtained. 2. The method according to claim 1, wherein the two physical optical elements on the first object plane and the two physical optical elements on the second object plane overlap each other to form one pattern. Item 4. The position detecting device according to Item 1. 3. The position of first and second two diffracted light beams generated on a predetermined surface via the first and second two physical optical elements and the third and fourth two physical optical elements. 2. The position detecting device according to claim 1, wherein the positions of the third and fourth diffracted light beams generated on the predetermined surface via the first and second light beams are detected at a distance from each other by at least the width of the diffracted light beams. 4. The detecting means detects each of a plurality of combinations of two values between the diffracted light beams relating to both the shift amount W and the interval g, and obtains the values obtained from the plurality of combinations. 4. The position detecting device according to claim 1, wherein the displacement amount W and the interval g are evaluated by an evaluation means. 5. The position detecting device according to claim 4, wherein said evaluation means averages a plurality of shift amounts W and intervals g obtained from a plurality of combinations. 6. Each element so that a position interval D12 of said first and second diffracted light beams on a predetermined surface is different from a position interval D34 of said third and fourth diffracted light beams on a predetermined surface. 4. The position detecting device according to claim 3, wherein is set.