JP2513299B2 - Position detection device - Google Patents

Description

The present invention relates to a position detecting device, for example, in an exposure device for manufacturing a semiconductor element, on a first object plane such as a mask or a reticle (hereinafter referred to as “mask”). The present invention relates to a position detection device suitable for performing relative positioning 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 an exposure apparatus for manufacturing a semiconductor, relative alignment between a mask and a wafer has been an important factor for improving performance. Especially in the alignment of the recent exposure apparatus, in order to achieve high integration of semiconductor elements,
For example, one having a positioning accuracy of submicron or less is required.

In many position detection devices, a so-called alignment pattern for alignment is provided on the mask and the wafer surface,
Both positions are aligned using the position information obtained from them. As an alignment method at this time, for example, the deviation amount of both alignment patterns can be detected by performing image processing, or US Pat.
No. 37969, U.S. Pat. No. 4,514,858 or Japanese Patent Laid-Open No. 56-157033, a zone plate is used as an alignment pattern to irradiate the zone plate with a luminous flux, and at this time, a predetermined luminous flux emitted from the zone plate is used. This is done by detecting the position of the focal point on the surface.

In general, 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 the alignment pattern, as compared with a method using a simple alignment pattern.

FIG. 11 is a schematic view of a conventional alignment device using a zone plate.

In the figure, the parallel light flux emitted from the light source 72 passes through the half mirror 74, is condensed by the condenser lens 76 at the condensing point 78, and is then placed on the mask alignment pattern 68a on the mask 68 surface and the support 62. The wafer alignment pattern 60a on the surface of the formed wafer 60 is irradiated. These alignment patterns 68a, 60a are composed of reflective zone plates,
Condensing points are formed on a plane orthogonal to the optical axis including the converging points 78. At this time, the amount of deviation of the position of the condensing point on the plane is guided by the condensing lens 76 and the lens 80 onto the detection surface 82 to be detected.

Then, based on the output signal from the detector 82, the control circuit 84
Thus, the drive circuit 64 is driven to position the mask 68 relative to the wafer 60.

FIG. 12 shows the mask alignment pattern shown in FIG.
FIG. 68 is an explanatory diagram showing an imaging relationship of light fluxes from 68a and the wafer alignment pattern 60a.

In the figure, a part of the light beam diverging from the condensing point 78 is diffracted by the mask alignment pattern 68a, and a condensing point 78a indicating the mask position is formed in the vicinity of the condensing point 78.
The other part of the light flux passes through the mask 68 as zero-order transmitted light and is incident on the wafer alignment pattern 60a on the surface of the wafer 60 without changing the wavefront. At this time, the light beam is diffracted by the wafer alignment pattern 60a, and then again passes through the mask 68 as 0th-order transmitted light and is condensed near the condensing point 78 to form a condensing 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 converging point 78b due to the wafer alignment pattern 60a formed in this way is determined according to the deviation amount Δσ of the wafer 60 with respect to the mask 68 along the plane orthogonal to the optical axis including the converging point 78. Deviation amount Δ corresponding to Δσ
formed as σ ′.

However, in the conventional apparatus, the condensing point indicating the position of the mask and the condensing point indicating the position of the wafer exist independently, and these converging points must be detected separately to obtain the positional relationship between them. The detector tends to be complicated.

In addition, US Pat. No. 4,311,389 proposes a device for detecting the relative positional relationship between a mask and a wafer by using a physical optical element such as a Fresnel zone plate having a function of converting an incident light beam into a wavefront.

FIG. 13 is an explanatory view showing the physical optical elements provided on the mask surface and the wafer surface used in the apparatus of the publication. In the figure, reference numeral 68b is a linear Fresnel zone plate, in which linear opaque portions and transparent portions are alternately formed so as to have a condensing effect only in the x direction, and are formed on the surface of the mask 68. Reference numeral 60b denotes a diffraction grating, which is arranged on the wafer 60 in the y direction. Linear fresnel zone plate
68b condenses the incident light beam in the x direction and focuses it on the surface of the wafer 60 into a slit having a longitudinal direction in the y direction. When this slit-shaped focal point overlaps the focal point on the wafer 60, diffracted light
69 is generated, and this diffracted light is detected by a light receiving means (detector) (not shown).

The Fresnel zone plate 68b is illuminated by an illumination system (not shown), is optically scanned, and when the focal point overlaps the diffraction grating 60b, the light receiving means detects a change in light intensity based on the diffracted light from the diffraction grating. The position of the diffraction grating 68b with respect to the Fresnel zone plate 68b, that is, the relative positional relationship between the mask 68 and the wafer 60 is detected by the change in light intensity obtained by the light receiving means at this time.

In the case of this detection method, the change in the amount of light detected by the detector indicates the relative positional relationship between the mask 68 and the wafer 60. In other words, since the relative positional relationship between the mask 68 and the wafer 60 is detected by one detector, the entire apparatus is simplified.

However, this method may be used, for example, for mask 68 and wafer
When the distance g between the and is changed, the light condensed by the Fresnel zone plate 68b is no longer focused on the wafer 60. Therefore, the light intensity per unit area of the slit-shaped light flux illuminating the diffraction grating 60b is reduced, and the illumination area is increased, so that the light intensity change detected by the detector has a small contrast and the width of the change becomes large. come. Therefore, there is a problem that the detection accuracy deteriorates and it becomes difficult to detect the relative position between the mask and the wafer with high accuracy.

(Problems to be Solved by the Invention) The present invention can detect the relative positional relationship between the first object and the second object with a simple structure and with high accuracy, and can detect the detection accuracy even with respect to the interval variation. An object of the present invention is to provide a position detection device that is resistant to deterioration.

In particular, the present invention provides physical optical elements having predetermined optical properties on the first object surface and the second object surface, respectively, when detecting the relative positional deviation amount between the first object and the second object, By applying a light beam to the physical optical element from a predetermined direction, for example, when applied to an exposure apparatus for manufacturing a semiconductor element, the movement of the alignment head before and after exposure is eliminated, and a mask,
An optical system that produces almost no alignment error even if the gap between the wafers varies can be obtained, whereby the position of the center of gravity of the light amount due to the relative positional deviation between the two can be detected with high accuracy and easily. An object is to provide a position detection device.

(Means for Solving Problems) When detecting the positional relationship of the second object with respect to the first object in the predetermined direction, the position detecting device of the present invention directs the light flux from the light projecting means onto the first object surface. The light beam deflected and emitted from the first object is irradiated so as to be perpendicular to the predetermined direction, the light beam emitted from the first object is made incident on the second object, and the light beam deflected and emitted by the second object is The second of the light flux emitted from the first object
Light is received by the light receiving means arranged at a position where the incident position changes depending on the incident position on the object, and the output signal from the light receiving means is used to detect the second object relative to the first object in the predetermined direction. The feature is that the position is detected.

For example, specifically, a first physical optical element for aligning at least one direction is formed on the surface of the first object when the first object and the second object are opposed to each other for relative positioning. Forming a second physical optical element for aligning at least one direction on the second object surface, and directing the light flux from the light projecting means onto the second physical optical element surface on the second object surface. The first physical optical element on the first object plane is made to enter the first physical optical element while being incident obliquely to the line, and is deflected by the second physical optical element in a direction perpendicular to the alignment direction. That is, the relative positioning of the first object and the second object is performed by detecting the light flux emitted from the physical optical element.

The center of gravity of the light flux, which is also used in the following explanation, is the position vector of each point in the light-receiving surface multiplied by the light intensity at that point in the light-receiving surface of the light flux, and integrated over the entire light-receiving surface. It is a point where the integrated value sometimes becomes a zero vector.

(Embodiment) FIG. 1A is a schematic view of a first embodiment when the present invention is applied to an exposure apparatus for manufacturing a semiconductor element. In the present embodiment, the light beam emitted from the light source 10 is converted into a parallel light beam by the light projecting lens system 11, and is passed through the half mirror 12 as the first object 1, for example, the mask surface M, and is a kind of Fresnel zone plate. The second physical optical element 4a composed of a grating lens or the like is illuminated from an oblique direction.

The second physical optical element 4a has a condensing function and emits the reflected light in the direction normal to the wafer surface (+ Z direction) as the second object 2 to separate it from the second physical optical element 4a by a predetermined distance. A first physical optical element as a first object 1 including, for example, a grating lens provided on a mask surface.
It is incident on 3a. The first physical optical element 3a has a light condensing function. The light beam is emitted toward the alignment head 6 and passed through the half mirror 12, and then condensed on the detection surface 9 of the detector 8.

In the figure, 5 is, for example, a wafer chuck,
The wafer 2 is adsorbed. Reference numeral 6 denotes an alignment head, which houses various elements for alignment. E is an exposure area for transferring the circuit pattern on the mask onto the wafer surface.

The mask 1 and the wafer 2 are held with a gap value within a predetermined range.

Reference numeral 100 denotes an XY stage, which moves the wafer sucked by the wafer chuck 5 in the XY directions. A stage driver 101 drives the XY stage 101 in the XY directions. Reference numeral 102 denotes a CPU, which uses the XY stage 100 to align the mask 1 and the wafer 2 based on the output of the detector 8.
A command signal is sent to the stage driver 101 to move the.

Further, the XY stage 100 moves the wafer 2 to a certain position in the z direction and sets the relationship between the mask 1 and the wafer 2 at a predetermined interval.

In this embodiment, the wafer 2 is moved for alignment, but a mask chuck moving mechanism (mask stage) or the like may be similarly provided to move the mask 1.

The XY stage 100 includes a precision wafer stage driven by a piezo element and a coarse wafer stage driven by a stepping motor, the stage driver 101 includes this piezo element and a stepping motor, and the CPU 102 is a piezo element for minute movement of the wafer. In addition, a command signal is sent to the stepping motor when moving a relatively large distance.

Hereinafter, in this embodiment, for convenience, the first physical optical element 3a is a mask grating lens 3a, the second physical optical element 4a is a wafer grating lens, and the first object is a mask.
The second object is called a wafer.

As described above, in this embodiment, the alignment pattern on the surface of the wafer 2 is composed of a grating lens (a type of Fresnel zone plate) having a predetermined focal length, and the light flux for alignment obliquely incident on the surface of the wafer 2 from the alignment head 6 is formed. Is deflected in the normal direction (+ Z direction) of the surface of the wafer 2 and focused on a predetermined position (for example, Z = + 276.0 μm).

In this embodiment, the angle α at which the wafer 2 is obliquely incident is α
Is preferably 10 <α <80.

Further, the alignment pattern 3a on the mask 1 is an off-axis type grating lens having an asymmetric pattern with respect to the Y-axis, and is designed to have a focal length of 278.78 μm, for example, and reflects off the grating lens on the wafer 2 surface.
The diffracted convergent (divergent) light is guided toward the alignment head.

At this time, the alignment light beam 10a is incident on the light receiver 8 in the alignment head 6 due to the lens action of the grating lens. In the first embodiment, alignment is performed in the longitudinal direction (y direction) of the scribe line where the pattern exists.

Now, the mask 1 and the wafer 2 are deviated by Δσ in the parallel direction, the distance from the wafer 2 to the focal point of the light flux reflected by the grating lens 4a of the wafer 2 is a, and the light flux passing through the grating lens 3a of the mask 1 is If the distance to the focal point of is b, then the center of gravity deviation Δδ of the focal point on the detection surface 9 is That is, the center-of-gravity deviation amount Δδ is expanded by (b / a + 1) times.

For example, if a = 0.5 mm and b = 50 mm, the center of gravity shift amount Δδ
Is enlarged 101 times from the equation (a).

In this case, the center-of-gravity shift amount Δδ and the positional shift amount Δσ have a proportional relationship as shown in FIG. 2, for example, as is apparent from the equation (a). Assuming that the detection resolution of the luminous flux incident position of the detector 8 is 0.1 μm, the positional deviation amount Δσ is 0.001 μm.
Position resolution.

If the second object is moved based on the positional deviation amount Δσ thus obtained, the positioning of the first object and the second object can be performed with high accuracy.

In the present embodiment, the reference position on the detection surface 9 (first, second
The position of the center of gravity of the light flux when the physical optical element is not displaced is calculated as follows. First, the mask having the first physical optical element 3a is fixed at an appropriate position. Second
The wafer having the physical optical element 4a is placed at an appropriate position with respect to the mask. At this time, the light flux from the light source 10
The light beam is made incident on the physical optical element and the center of gravity of the light beam on the detection surface 9 in this state is detected. Then, in this state, for example, the pattern on the mask is transferred onto the wafer. The transferred pattern is observed with another microscope or the like, and the amount and direction of displacement are measured. The calculated shift amount and direction are the shift amount Δσ of the second physical optical element in the expression (a). Therefore, how much the position of the center of gravity of the light beam detected before the equation (a) is displaced from the reference position, that is, the amount of deviation Δδ is obtained. Therefore, the reference position is calculated back from the amount of deviation Δδ and the detected center of gravity. ing.

In addition, as a procedure for performing the alignment in the present embodiment, for example, the following method can be adopted.

As a first method, a barycenter shift signal Δδ of a light beam on the detection surface of the detector 8 with respect to a positional shift amount Δσ between two objects.
A characteristic (for example, a proportional constant) indicating the relationship with s is determined in advance, the amount of positional deviation Δσ between the two objects is obtained from the value of the center-of-gravity deviation signal Δδs, and only the amount corresponding to the amount of positional deviation Δσ at that time is obtained. The first object or the second object is moved.

As a second method, the center-of-gravity deviation signal Δδ from the detector 8 is used.
The position shift direction, that is, the direction in which the position shift amount Δσ is canceled is obtained from s, and the first object or the second object is moved in that direction until the position shift amount Δσ falls within the allowable range.

The above CPU alignment procedure is shown in FIGS. 1 (B) and 1 (C), respectively.

As described above, the alignment light beam 10a is reflected by the grating lens 4a on the wafer 2 and is transmitted and diffracted by the grating lens 3a on the mask 1, so that the deviation of the optical axis between the mask and the grating lens on the wafer is n.
It is magnified twice by the magnification of the grating lens system and enters the light receiving surface 9 in the alignment head 6. Then, the light receiver 8 detects the position of the center of gravity of the light flux.

Here, the focal length of the grating lens is set in consideration of the gap between the mask and the wafer during exposure and the magnification of the grating lens system.

For example, consider a proximity exposure system in which the exposure gap for detecting the barycentric position of the light flux on the light receiving surface 9 by expanding the amount of positional deviation between the mask and the wafer by 100 times and having the exposure gap of 30 μm.

Now, the wavelength of the alignment light flux is 0.83 μm as the light flux from the semiconductor laser. At this time, the alignment light flux passes through the projection lens system 11 in the alignment head 6 to become a parallel light flux, and passes through the wafer 2 and the grating lens system composed of two grating lenses when sequentially passing through the mask 1. Schematic diagrams of the refractive power arrangement of the system at this time are shown in FIGS.

3 shows the case where the grating lens 4a on the wafer 2 has a negative refracting power and the grating lens 3a on the mask 1 has a positive refracting power, and FIG. 4 shows the grating lens 4a on the wafer 2 has a positive refracting power. Grating lens on 1
This is the case where 3a has a negative refractive power.

Here, the negative refracting power and the positive refracting power are determined by using the diffracted light of the negative order or the diffracted light of the positive order.

In the figure, for example, the diameter of the grating lens 4a on the wafer 2 is 300 μm, the diameter of the grating lens 3a on the mask 1 is 280 μm, and the positional deviation (axial deviation) between the mask and the wafer is magnified 100 times. The center of gravity of the light flux moves on 9 and as a result, the diameter of the light flux on the light receiving surface 9 (Airly disk e ^-2 diameter); Airy disk, the light intensity at (the disk-shaped image in the middle of the spot diffraction image) Was arranged and the focal length of each element was determined so that the diameter of the region up to e ⁻² times the peak value was about 200 μm.

Next, the optical pattern shapes of the mask grating lens 3a and the wafer grating lens 4a in this embodiment will be described.

First, the grating lens 4a for a wafer is set so that a parallel light beam having a predetermined beam diameter is incident at a predetermined angle and is condensed at a predetermined position. Generally, the pattern of the grating lens 4a is an interference fringe pattern on the lens surface when a coherent light source is placed on each of the light source (object point) and the image point. As shown in FIG. 5, the coordinate system on the wafer 2 surface is determined. Here the origin is in the center of the scribe line width,
The x axis is taken in the scribe line direction, the y axis is taken in the width direction, and the z axis is taken in the direction normal to the wafer surface. A parallel light beam which is incident at an angle α with respect to the normal to the wafer surface and whose projection component is orthogonal to the scribe line direction is reflected and diffracted by the grating lens 4a, and then the position of the focal point (x ₁ , y ₁ , z ₁ ) The equation of the curve group of the grating lens that forms an image at is ysinα + P ₁ (x, y) -P ₂ = mλ / 2 (1) when the contour position of the grating is represented by x and y. Given in. Where λ is the wavelength of the alignment light beam, m
Is an integer.

The chief ray is incident at an angle α, passes through the origin on the mask surface,
Assuming that the light ray reaches the converging point (x ₁ , y ₁ , z ₁ ), the left side of the equation (1) passes through the point (x, y, 0) on the mask with respect to the optical path of the principal ray, and the point (x ₁ , It represents the difference in the optical path lengths of the rays reaching y ₁ , z ₁ ), and the right side shows that the difference is m / 2 times the wavelength.

On the other hand, the grating lens 3a on the mask is set so as to focus the spherical wave emitted from a predetermined point light source on a predetermined position (on the detection surface). The position of the point light source is represented by (x ₁ , y ₁ , z ₁ −g), where the gap between the mask and the wafer during exposure is g. It is assumed that the alignment of the mask and the wafer is performed in the x or y axis direction, and if the alignment light flux is focused at the position of the point (x ₂ , y ₂ , z ₂ ) on the detection surface when the alignment is completed, The equation of the curve group of the above grating lens is the coordinate system defined earlier. Is represented.

(2) has mask surface within z = -g, principal ray point on the origin and the mask surface on the wafer surface (0,0, -g), further points on the detection plane (x _2, y ₂ , z ₂ ) which is a ray that passes through the grating (x, y, −g) on the mask surface and the principal ray is a difference in optical path length that is an equation that satisfies an integer multiple of a half wavelength.

Generally, in a zone plate (grating lens) for a mask, two regions, that is, a region through which light rays pass (transparent portion) and a region through which light rays do not pass (light shielding portion) are alternately formed.
It is created as a 0,1 amplitude type grating element.
The zone plate for the wafer is formed, for example, as a phase grating pattern having a rectangular sectional shape. (1),
In equation (2), the contour of the grating is defined at a position that is an integral multiple of a half wavelength with respect to the principal ray, because the grating lens 3a on the mask has a line width ratio of 1: 1 between the transparent portion and the light shielding portion. It means that the grating lens 4a on the wafer has a line-to-space ratio of 1: 1 in the rectangular lattice.

The grating lens 3a on the mask is formed by transferring the grating lens pattern of the reticle previously formed by EB exposure on the induction thin film made of polyimide, for example, or the grating lens on the wafer is formed after forming the exposure pattern of the wafer on the mask. It is formed by exposure and transfer.

FIG. 6 (A) shows a grating lens 4 on the wafer surface.
a, the grating lens 3a on the mask surface is shown in FIG.
The pattern of one Example is shown.

Next, in the embodiment shown in FIG. 1A, a case where a predetermined positional deviation amount is given between the mask and the wafer will be specifically described.

First, a semiconductor laser as an alignment light source (wavelength
The light beam emitted from the 830 nm) passes through the projection lens system 11 to become a parallel light beam having a half-value width of 600 μm and enters the alignment head 6 at 40 ° with respect to the normal line of the wafer 2.

The scribe line on the mask M surface is 60 μm wide and long
A 280 μm grating lens 3a is set, and a grating lens 4a of the same size is set on the scribe line on the wafer surface. The relative displacement between the mask and the wafer is given by a piezo-driven precision wafer stage for a minute displacement amount, and a relatively large displacement amount by a stepping motor-driven coarse wafer stage. For the displacement, use a length measuring machine (resolution 0.001μm) and control temperature 23 ° c.
The measurement was carried out in a constant temperature chamber of ± 0.5 ° c. A one-dimensional CCD line sensor was used as a light receiver for detecting the position of the center of gravity of the light beam in the alignment head 6. The element array direction of the line sensor is the misregistration detection direction (alignment direction)
Matches The output of the line sensor is signal-processed so as to be standardized by the total light intensity of the light receiving area. Thus, even if the output of the alignment light source fluctuates to some extent, the measurement value output from the line sensor system accurately indicates the position of the center of gravity.

The center-of-gravity position resolution of the line sensor was 0.2 μm as a result of measurement with a semiconductor laser of 50 mW, although it depends on the power of the alignment light flux.

Grating lens for mask according to first example
In the design example of 3a and the grating lens 4a for the wafer,
The positional deviation between the mask and the wafer is magnified 100 times, and the signal light flux is set so that the center of gravity of the light flux moves on the sensor surface. Therefore, if there is a displacement of 0.01 μm between the mask and the wafer, an effective center of gravity shift of 1 μm will occur on the line sensor surface.
It can be measured with a resolution of m.

FIG. 2 shows a change in the position of the center of gravity detected by the alignment licensor when a predetermined amount of positional deviation is actually applied between the mask and the wafer. As is clear from FIG. 2, the detected position of the center of gravity has a linear relationship with the magnification of the grating lens system as a proportional constant with respect to the amount of positional deviation between the mask and the wafer. However, the linearity is not established when the amount of positional deviation exceeds a certain value (for example, about 20 μm), and nonlinearity appears.

This is because the wavefront aberration of the light beam becomes more significant as the amount of axial misalignment between the mask and the grating lens on the wafer increases, and asymmetry appears in the spot shape on the sensor.

This wavefront aberration becomes more apparent as the NA of the grating lens is larger. Therefore, when setting the grating lens in a certain area, it is desirable to reduce the NA as much as possible.

In the alignment device according to the present embodiment, the resolution of the displacement is 0.002 μm, and the displacement measuring lens ± 20 μm.
(Linear region).

In this embodiment, since the light beam is obliquely incident on the mask surface and the oblique light receiving optical path is set, the positional deviation amount between the mask and the wafer can be measured and controlled without the alignment head 6 entering the exposure area. . As a result, it is not necessary to move the alignment head 6 before and after the exposure, which improves the total throughput in the step-and-repeat exposure system by about 20%. It was also confirmed that the overlay accuracy was improved by 0.02 μm with respect to the system that moves the alignment head before and after exposure.

In this embodiment, an alignment mark is formed so that the light beam is reflected and diffracted by the grating lens for the wafer and then passes between the wafer and the mask perpendicularly to the wafer surface (mask surface), and the vertical optical path is set. Therefore, it has the feature that the alignment accuracy does not deteriorate with respect to the variation in the distance between the mask and the wafer.

Here, the fact that the light flux is perpendicular to the mask surface means that the light flux is in a plane (xz plane) perpendicular to the misregistration detection direction (y direction) and is perpendicular to the mask surface (xy plane) and includes the misregistration detection direction. It means that it is in such a plane (yz plane).

Further, parallel light having a larger cross-sectional area than the area of the mark is put on the alignment mark of the wafer, and even when the incident side of the light on the wafer is displaced due to a slight vertical movement on the wafer side, it is always parallel to the entire surface of the mask. The state in which light is incident does not change, and therefore does not change to the position of the center of gravity of the light beam traveling from the alignment mark on the wafer to the alignment mark on the mask. As a result, a positional deviation detection system is achieved that does not affect the measurement accuracy due to vertical fluctuations on the wafer side.

FIG. 7 is a schematic view of the second embodiment of the present invention. For the sake of clarity, this figure shows only the mask 1 and the vicinity of the wafer 2 in a perspective view.

In this embodiment, the alignment patterns 3a and 4a formed on the surfaces of the mask 1 and the wafer 2 are one-dimensional grating lenses. Therefore, in the second embodiment, the mask and the wafer are aligned in the width direction of the scribe lines 1a and 2a where the alignment pattern exists. Others are the same as the first embodiment.

Also in this embodiment, the alignment light beam 10a is obliquely incident from the alignment head 6 to the normal line of the wafer 2,
After being reflected by the alignment pattern 4a on the wafer 2 surface, it passes through the grating lens 3a on the mask 1 surface, and then returns to the alignment head 6 direction. Further, at this time, the optical path of the light beam that is reflected by the grating lens 4a on the wafer surface and diffracted and then enters the grating lens 3a on the mask surface is perpendicular to the mask and the wafer surface. Therefore, as in the first embodiment, even if the wafer moves up and down and the gap between the mask and the wafer changes, the grating lens on the mask
The optical path is such that the center of gravity of the alignment light beam entering 3a does not shift.

The feature of this embodiment is that the power (lens function) of the grating lenses 3a and 4a is applied only in the scribe line width direction. As a result, the pattern shape becomes simpler with the linear grating grating lens, and the EB drawing accuracy of the pattern can be improved as compared with the case of the curved grating. This is because a straight line is easily drawn in the EB exposure used for pattern drawing.

Further, even if the mask and the wafer are misaligned in the direction orthogonal to the alignment direction detected by the photodetector in the alignment head corresponding to the pattern, the light beam has no magnification sensitivity in the alignment orthogonal direction on the detection surface and has a large center of gravity. No position is located. That is, as in the second embodiment, 1
When measuring the amount of misalignment with the dimensional sensor, use a grating lens that does not work in the direction orthogonal to the alignment direction, so that the alignment direction is not affected excessively by the misalignment in the direction orthogonal to the alignment direction. It is possible to measure the position deviation of.

In the second embodiment, the incident angle of the alignment light beam, the power and pattern size of the grating lens in the alignment direction are set in the same manner as in the first embodiment.

Also, the total throughput of the exposure system (step and repeat method) is also improved by about 20%, and the overlay accuracy is 0.
It improved by 02 μm.

FIG. 8 is a schematic diagram of the third embodiment of the present invention. Similar to FIG. 7, this figure also shows only the mask and the vicinity of the wafer in a perspective view.

In this embodiment, the grating lens 3a on the mask and the grating lens 4a on the wafer both have the same power in the scribe line direction and the direction orthogonal thereto.
It is a three-dimensional grating lens.

Similar to the first and second embodiments, the alignment light beam 10a is obliquely incident from the alignment head 6 with respect to the normal line to the wafer surface 2, and the optical path between the wafer and the mask is perpendicular to the wafer surface (mask surface). The alignment pattern is set so that The alignment light flux 10a is reflected by the grating lens 4a on the surface of the wafer 2, passes through the grating lens 3a on the surface of the mask 1, returns to the alignment head 6, and is incident on the detection surface 9a of the two-dimensional sensor 8a.
Thus, the two-dimensional sensor 8a detects the position of the center of gravity of the light beam.

That is, in this embodiment, the two-dimensional sensor 8a detects the positional deviation between the mask and the wafer two-dimensionally by the magnification of the grating lens system. As described above, by using the grating lens and the two-dimensional sensor having a two-dimensional power, the two-dimensional direction and magnitude of the positional deviation between the mask and the wafer can be accurately detected at the same time. In the sensor system, signal processing is performed so as to be standardized by the total light intensity in the light receiving area, as in the first embodiment. Therefore, even if the output of the light source fluctuates to some extent, the measured value output from the sensor system accurately indicates the position of the center of gravity.

Incident angle of alignment beam, grating lens 3
As a result that the power and size of a and 4a are the same as those of the first embodiment, the position detection characteristics have the same performance as those of the first and second embodiments. However, since the signal processing of the sensor system detects the barycentric position of the two-dimensional light amount distribution, the processing time and the algorithm are slightly different.

 FIG. 9 shows a fourth embodiment of the present invention.

In this embodiment, the light beam 10a from the light source is incident on the off-axis type grating lens element 4a formed on the wafer 2 at a predetermined angle θ ₁ (for example, 15 °) with respect to the normal to the wafer surface. Of the diffracted and reflected light that has undergone the lens action of the on-wafer grating lens element 4a, the alignment signal light flux used to detect the amount of positional deviation between the mask and the wafer is detected by the photodetector 8 in the alignment head (optical pickup) 6. , So as to be perpendicular to the wafer-to-wafer positional deviation detection direction.

For example, in this embodiment, the misregistration detection direction is the scribe line direction on the mask 3 (wafer 2) (y in FIG. 9).
In the axial direction), the traveling direction of the alignment signal light flux emitted from the on-wafer grating element 4a may be perpendicular to the scribe line direction.

In this way, even if the distance between the mask 3 and the wafer 2 in the z direction changes, the alignment signal light flux 10a emitted from the on-wafer grating element 4a and incident on the on-wafer 3 grating lens element 3a is the same as that in the third embodiment. Similarly, fluctuations in the distance between the mask 3 and the wafer 2 prevent fluctuations in the position of the center of gravity of the light beam on the photodetector in the alignment head 6 in the direction of detecting the positional deviation of the grating lens system.

The difference in structure between the fourth embodiment and the third embodiment is that the optical path of the alignment signal light flux passes through the on-wafer grating lens 4a and then on the wafer surface (or mask surface) in the third embodiment. In contrast to the vertical direction, the fourth embodiment is not vertical to the wafer surface (or the mask surface), but the direction for detecting the positional deviation amount between the mask and the wafer (for example, the y direction in FIG. 9). It is only vertical to. Here, the fact that the optical path is perpendicular to the direction in which the amount of positional deviation is detected means that the optical path is in a plane (xz plane) perpendicular to the positional deviation detection direction (y direction).

On the other hand, similarly to the third embodiment, in the fourth embodiment, the traveling direction (optical path) of the alignment signal light beam 10a reflected and diffracted by the lens action of the grating lens element 4a on the wafer 2 is diffracted by the grating lens element 3a. Even after being subjected to the masking, it is still perpendicular to the direction of detecting the amount of positional deviation between the mask and the wafer. However, in implementing the present invention, the lens action of the grating lens elements 3a and 4a as shown in the second embodiment is The optical path of the received alignment signal light flux emitted from the mask 3 may not be perpendicular to the misregistration amount detection direction.

10 (A) and 10 (B) are a side view and a front view of the essential part of the fifth embodiment of the present invention. In this embodiment, the amount of positional deviation between the mask 1 as the first object and the wafer 2 as the second object in the plane of FIG.

A light beam from the light source is incident on the surface of a first off-axis type grating element (grating lens) 112 provided on the surface of the mask 1 at an angle θ ₁ with respect to the normal line of the mask 1, and a predetermined amount from the grating element 112 is entered. The diffracted light of the order is emitted from the mask 1 perpendicularly to the mask surface, and is incident on the second off-axis type grating element 113 provided on the surface of the wafer 2.

Here, an off-axis type grating element is a device that emits a light beam with an arbitrary inclination angle with respect to the normal to the plane forming the element, and guarantees characteristics for light of a specific order other than the order of specular reflection or straight transmission. Refers to an element that has been used.

In the first off-axis type grating element 112, the emitted light beam has a principal ray substantially in the normal direction of the mask 1, and has the same finite focal length in the front view as shown in FIG. As shown in FIG. 3A, the side view includes a zone plate that forms a one-dimensional image that does not collect light.

Further, the grating element 113 has a one-dimensional image formed by the mask 1 as an object point, and the emitted light flux has an inclination angle θ ₂ within the plane of the drawing of FIG. A zone plate which forms an image on the light receiver 8, and 10a indicates the received light beam. 114 is the projected light flux 111
And showing an optical pickup housing (alignment head) including the optical receiver 8. Also, in FIG.
Indicates the exposure light for transferring the pattern of the mask 1 onto the wafer 2, and the broken line conceptually indicates the inside of the optical path.
As the exposure light, ultraviolet light, X-ray or the like is used.

Here, when the wafer 2 laterally moves in the X direction, which is the position shift detection direction, the illuminance distribution on the photodetector 8 in the plane of FIG. The off-axis type grating elements 112 and 113 are set by the following method.

That is, the first off-axis type grating element 112
Is the coordinate axis shown in the figure, and the center point on the grating element 112 is the origin, Ysin θ ₁ + P ₁ (X) −P ₂ = mλ / 2 P ₁ (X) = {(X−X ₁ ) ² + Z ₁ ² } ^1/2 P ₂ = {X ₁ ² + Z ₁ ² } ^1/2 . Where λ is the wavelength of the light of the light flux 111, m
Is an arbitrary integer. P ₂ means the distance from the origin to the focal point of the grating element 112, and Z ₁ physically means the focal length of the grating element 112.

On the other hand, the second grating element 113 is similarly set. If the set distance between the mask 1 and the wafer 2 is g, the object point for the grating element 113 is (x ₁ , y, z-g)
Therefore, in the coordinate system shown above, {(X−X ₂ ) ² + Z ₂ ² } ^1/2 − {(X−X ₁ ) ² + (Z ₁ −
g) ² } ^1/2 = {X ₂ ² + Z ₂ ² } ^1/2 + Ysin θ ₂ − {X ₁ ² + Z
₁ ² } ^1/2 + mλ / 2. Here, the coordinates of the image point on the photodetector 8 when the displacement is 0 are defined as (X ₂ , Y, Z ₂ ).

Note that θ ₂ is the deflection angle in the y direction (angle with respect to the wafer surface normal).

_First , the angles θ ₁ and θ ₂ must be set so that the pickup housing 114 can be set at a position that does not reach the exposure optical path. Considering practical dimensional conditions, the difference between the angles θ ₁ and θ ₂ is 3 ° or more is required. However, increasing θ ₁ and θ ₂ reduces the pattern line width of the grating element,
It is preferable to set the angle within 30 ° practically because the difficulty level in production becomes high and the diffraction efficiency decreases and the amount of light reaching the photodetector 8 decreases, which causes a decrease in accuracy.

Further, in order to extract the signal light quantity on the light receiver 8 with a good S / N ratio, it is necessary to sufficiently separate it from the projected light beam, and the angles θ ₁ and θ ₂
It is preferable to set the difference of 3 ° or more.

The light source for creating the light flux is applicable to the characteristics of the grating element if it is monochromatic light or quasi-monochromatic light, and a laser light source, a light emitting diode or the like is used, but especially on the premise of application to a semiconductor manufacturing device, A semiconductor laser is preferable in terms of high brightness and small size.

Since the exposure area is generally a quadrangle, the above-mentioned optical pick housings are set one on each of the four sides, and the orthogonal axes are set to X and Y, and the shift amounts ΔX ₁ and Δ between the mask and wafer from each pickup are set.
By outputting X ₂ , ΔY ₁ , and ΔY ₂ , it is possible to obtain information necessary for adjusting the entire position from the known set position of the grating element. And each pickup needs a mechanism that can move to follow when the position of the grating element changes, but it does not need to be retracted during exposure, thus improving the throughput of semiconductor fabrication, improving mechanical reliability and device life. In terms of, it can be greatly improved.

In addition, in the above-mentioned embodiment, the description has been made by taking the alignment of the mask and the wafer as an example, but the same can be applied to the means for obtaining the distance information between the mask and the wafer.

That is, for example, in the above-described embodiment, when the distance between the mask and the wafer is changed, the spot diameter on the photodetector 8 changes, so that the distance between the mask and the wafer is detected by detecting the value of the spot T diameter in addition to the lateral deviation amount. It becomes possible to detect a change.

In the above first to fourth embodiments, the light source is first diffracted by the grating lens on the wafer side and then diffracted by the grating lens on the mask side, and in the fifth embodiment it is diffracted by the grating lens on the mask side. Next, the diffraction is performed by the grating lens on the wafer side, but the incident direction of the light flux in each of these embodiments may be reversed.

For example, in FIGS. 1, 7, 8, and 9, the light path from the light source 10 to the half mirror 12 through the wafer 2 and the mask 3 to the half mirror 12 may be reversed in arrow direction. In this case, the inclination of the half mirror 12 and the position of the detector 8 are changed accordingly. The same applies to the embodiment shown in FIG.

(Effect of the Invention) According to the present invention, by setting each element as described above, the relative positional relationship between the first object and the second object can be set with high accuracy.
Moreover, it is possible to achieve a position detection device in which the detection accuracy is less deteriorated even when the distance between the two changes.

In addition to this, in the embodiment described above, for example, when applied to an exposure apparatus for manufacturing a semiconductor element, a light beam is obliquely incident on the wafer surface, and an optical path emitted from the mask surface is also received from an oblique direction. By setting the alignment pattern so that the light flux between the mask and the wafer surface is perpendicular to the mask or wafer, (a) it is not necessary to move the alignment containing the alignment optical system before and after the exposure, and the exposure is performed. It is possible to improve the total throughput of the system.

(B) Since the vibration associated with the movement of the alignment head does not occur after the alignment, the overlay accuracy of the mask and the wafer can be improved.

(C) Even if the gap variation from the predetermined exposure gap between the mask and the wafer is in the order of μm, it does not substantially affect the alignment error and the variation tolerance is high.

(D) The asymmetry of the light flux on the sensor that occurs depending on the amount of positional deviation is reduced, and the linearity of the magnification sensitivity of the grating lens system is maintained for a relatively large positional deviation of about 25 μm.

Thus, it is possible to achieve a position detecting device having the features described above.

[Brief description of drawings]

1A is a schematic diagram of a first embodiment of the present invention, and FIGS. 1B and 1C are operation block diagrams of a CPU according to the present invention.
FIG. 2 is an explanatory view showing the relationship between the center-of-gravity deviation amount and the positional deviation amount in the present invention, and FIGS. 3 and 4 are schematic diagrams showing the refractive power arrangement of two grating lenses in the present invention, and FIG. Is an explanatory view showing the principle of the optical action of FIG. 1, and FIGS. 6 (A) and 6 (B) are explanatory views of an embodiment of the alignment pattern according to the present invention, FIG. 7, FIG. 8 and FIG. , FIG. 10 is a schematic view of the second, third, fourth and fifth embodiments of the present invention, and FIG.
FIG. 12 and FIG. 12 are explanatory views of a conventional alignment device using a zone plate. FIG. 13 is an explanatory diagram of a conventional mask and a physical optical element provided on a wafer. In the figure, 10 is a light source, 11 is a projection lens system, 1 is a first object, and 2 is
Is a second object, 3 is a first physical optical element, 4 is a second physical optical element, 8 is a detector, 9 is a detection surface, M is a mask, W is a wafer, 3M is a mask alignment pattern, and 4W is a wafer alignment pattern. Is.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Ryo Kuroda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yukichi Niwa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Satoshi Nose 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-1-257208 (JP, A) JP-A-63-159705 (JP , A) JP 63-159704 (JP, A) JP 1-285804 (JP, A) JP 1-209305 (JP, A) JP 1-209304 (JP, A) JP 1-207605 (JP, A) JP 64-106427 (JP, A) JP 64-63802 (JP, A) JP 64-55824 (JP, A) JP 64-55823 (JP, A) JP-A-63-139205 (JP, A) JP-A-63-95303 (JP, A) JP 62-66632 (JP, A) JP 57-191502 (JP, A) JP-B-54603 (JP, B2)

Claims (4)

(57) [Claims] 1. When detecting a positional relationship of a second object with respect to a first object in a predetermined direction, a light beam from a light projecting means is deflected and emitted from the first object onto the first object plane in the predetermined direction. To the second object of the light flux emitted from the first object, and the light flux emitted from the first object is incident on the second object and the light flux deflected and emitted by the second object is emitted to the second object. The position of the second object relative to the first object in the predetermined direction is detected by receiving light by a light receiving means arranged at a position where the incident position changes according to the incident position of A position detecting device characterized by performing. 2. A first physical optical element for aligning at least one direction on the surface of the first object when the first object and the second object are opposed to each other for relative positioning, A second physical optical element for aligning at least one direction is formed on the second object surface, and a light beam from the light projecting means is normal to the second physical optical element surface on the second object surface. With respect to the first physical optical element on the first object plane, the second physical optical element deflects the light in a direction perpendicular to the alignment direction, and makes the first physical optical element incident on the first physical surface. A position detecting device characterized in that the first object and the second object are relatively positioned by detecting a light beam emitted from an optical element. 3. A light beam, which has been subjected to a lens action by the second physical optical element, travels between the first object and the second object in a direction orthogonal to the direction of displacement detection of these objects. 3. The position according to claim 2, wherein after the light beam is made incident, the light beam from the first physical optical element is made incident and guided in the light projecting direction of the light beam from the light projecting means. Detection device. 4. The first object is composed of a semiconductor manufacturing mask, the second object is also composed of a semiconductor manufacturing wafer, and the first and second physical optical elements are scribed on the mask and the wafer. 3. The position detecting device according to claim 2, wherein the position detecting device has a lens action in the width direction of the line, and the projection component of the projected light beam on the mask surface intersects with the scribe line.