JP2000349014A - Registration measuring device, and manufacture of semiconductor device using the device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device, which can adjust the misregistration of a mark caused by color (wavelength), according to the color dispersion property of an image pickup optical system, and can accurately measure the registration. SOLUTION: In a registration measuring device which has illumination optical systems 1-5 for illuminating the board having a first mark and a second mark at least, image pickup optical systems 6-7 for forming the image of each mark, an image pickup part for detecting the image of each mark, and a processor 9 for obtaining the quantity of misregistration between the first mark and the second mark, based on the output signal from the image pickup device, the image pickup optical system includes an adjuster 10 for adjusting the dislocation of the image of each mark caused by the color occurring at the image pickup face of the image pickup part, based on the prescribed information.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superposition apparatus and a method of manufacturing a semiconductor device having the apparatus, and more particularly to a method of projecting and exposing an electronic circuit pattern formed on a mask surface onto a wafer surface by a projection optical system. This is suitable for manufacturing a highly integrated semiconductor device by observing the state on the wafer surface, thereby performing relative positioning between the mask and the wafer.

[0002]

2. Description of the Related Art In a photolithography process for manufacturing a semiconductor device, a circuit pattern formed on a mask is projected and exposed on a wafer by a projection optical system. At this time, prior to the projection exposure, the alignment mark on the wafer is detected by observing the wafer surface using an observation device, and based on the detection result, the relative alignment between the mask and the wafer, so-called alignment is performed. It is carried out.
The alignment is performed by measuring the amount of misalignment between the resist pattern formed in the projection exposure step and the underlying pattern using an overlay measurement device. The overlay measurement device irradiates the overlay (positioning) mark with illumination light, forms reflected light from the mark on a predetermined surface via an imaging optical system, and transfers the mark image to a CCD.
An image is taken by a camera or the like, image processing is performed, and the amount of overlay displacement is measured.

[0003]

However, when the reflected light from the overlay mark has a wide wavelength spectrum, the imaging position is shifted due to the chromatic dispersion characteristic inherent in the imaging optical system. , A device-specific measurement error value, so-called T
This is one of the causes of generating an IS value (Tool Induced Shift). Also, depending on the type of photolithography process,
Even within the same wafer, the wavelength spectrum of light reflected from the overlay mark may differ between shots (exposure regions). Therefore, the TIS value may vary even within the same wafer. In this case, the reliability of the amount of misalignment of the mask and the wafer, which is fed back to the projection exposure apparatus, is reduced, and there is a problem that the exposure cannot be performed with accurate overlay and the yield is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and can adjust a displacement of an overlay mark generated by a color (wavelength) in accordance with the chromatic dispersion characteristics of an image forming optical system, thereby achieving accurate overlay. It is an object of the present invention to provide an apparatus capable of measurement and a semiconductor device manufacturing method capable of accurately aligning a mask and a wafer using the apparatus.

[0005]

In order to solve the above-mentioned problems, the present invention provides an illumination optical system for illuminating a substrate having at least a first mark and a second mark, and an image of each of the marks. An imaging optical system for forming an image, an imaging unit for detecting each mark image, and a misalignment between the first mark and the second mark based on an output signal from the imaging unit. An overlay processing apparatus having an arithmetic processing unit for determining an amount, wherein the imaging optical system adjusts a shift of each mark image due to a color on an imaging surface of the imaging unit based on predetermined information. And an overlay measurement device characterized by comprising:

In a preferred aspect of the present invention, in order to adjust a shift of the mark image generated according to each of the processing steps performed on the substrate, an adjustment value of the shift of the mark image is adjusted by each of the processing steps. A storage unit for storing the mark image based on the adjustment value of the shift of the mark image for each of the processing steps stored in the storage unit as the predetermined information. It is desirable to optically adjust the deviation.

According to the present invention, there is further provided a step of obtaining a shift amount between the first mark and the second mark by using the overlay measuring device according to claim 1 or 2, and based on the shift amount. Obtaining an offset value for performing a relative alignment between a mask having a predetermined pattern and the substrate; and performing a relative alignment between the mask and the substrate based on the offset value. Exposing the pattern of the mask to the substrate.

Further, the present invention provides a step of detecting a positioning mark formed on a substrate by a position detecting optical system, and an image forming position based on a color of the positioning mark generated by optical characteristics of the position detecting optical system. Adjusting the misalignment,
A method for manufacturing a semiconductor device, comprising: a step of aligning the substrate; and a step of exposing the pattern image of the mask to the substrate via a projection optical system.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. (First Embodiment) FIG. 1A is a diagram showing a schematic configuration of an overlay measurement apparatus according to a first embodiment. Light source 1
The illumination light flux emitted from the lens is condensed by the condenser lens 2 and illuminates the field stop 3 uniformly. The field stop 3 is shown in FIG.
As shown in (b), it has a rectangular opening S1. Next, the light beam that has passed through the field stop 3 is converted (collimated) by the illumination relay lens 4 into a substantially parallel light beam, and reflected by the half prism 5. Then, the light is condensed by the first objective lens 6 and irradiates the wafer 21 having the overlay mark 20 vertically. Here, since the field stop 3 and the wafer 21 are located at conjugate positions, an area on the wafer 21 corresponding to the shape of the opening S1 of the stop 3 is uniformly illuminated. Further, the wafer 21 is mounted on a stage 22 having a rotation mechanism, and the setting of the measurement direction can be changed by rotating the stage around the optical axis AX.

The overlay mark 2 on the illuminated wafer
The reflected light L1 from 0 is collimated by the first objective lens 6, transmitted through the half prism 5, condensed again by the second objective lens 7, and transmitted through the plane parallel plate 10 having a chromatic dispersion adjusting function. Then, the light beam L1 is
An image of the overlay mark 20 is formed on the CD 8. FIG.
(A) and (b) are overlay (resist) marks 20
FIG. 3 is a diagram showing the configuration of FIG. The arithmetic processing unit 9 performs image processing such as edge detection and calculates a difference R between the mark center position C1 of the overlay mark 20 and the base mark center position C2 as an overlay shift amount. Preferably, FIGS. 3 and 4
As shown in FIG. 4, the marks M1 to M5 of the shot areas S1 to S5 are overlapped twice in a predetermined direction (FIG. 3) and in a direction in which the wafer 21 is rotated by 180 degrees with respect to the predetermined direction (FIG. 4). It is desirable to measure the amount of misalignment. When the measurement result in a predetermined direction is R ₀ , and the measurement result in a direction rotated by 180 degrees with respect to the direction is R ₁₈₀ , the TIS of the measurement deviation amount of the present apparatus is given.
The value is obtained by the following equation.

TIS = (R ₀ + R ₁₈₀ ) / 2 Here, one of the causes of the TIS is the formation of the entire mark image due to the difference in the color (wavelength) of the light reflected from the overlay mark 20 as described above. The image position may be shifted. FIG. 5 shows a first objective lens 6, a half prism 5, and a second objective lens 7 for forming an image of the mark 21 on the CCD.
3A and 3B respectively show an image forming position IB of blue light and an image forming position IR of red light in the case where the image forming optical system having the asymmetrical chromatic dispersion characteristics. As can be seen from the figure, IB and IR are imaged at positions symmetric with respect to the axis L passing through the center C of the visual field. On the other hand, if the imaging optical system has chromatic dispersion characteristics, as shown in FIG.
The axis L corresponds to the blue light imaging position IB and the red light imaging position IR.
Is asymmetric with respect to. For this reason, the measured value of the amount of overlay deviation by the above procedure includes the TIS value unique to the measuring device. The cause of the asymmetric chromatic dispersion characteristic is a prism effect caused by the eccentricity of the optical element constituting the imaging optical system. Further, the amount of chromatic dispersion of the image forming optical system also varies from device to device.

Next, the function of the plane-parallel plate 10 for adjusting the shift of the mark image forming position due to the above-described color difference will be described.
As shown in FIG. 7, among the reflected lights from the marks traveling along the same optical path toward the imaging surface (imaging surface) S of the CCD 8, light beams having different wavelengths, for example, blue light LB (solid line) and red light LR ( (Broken line). When the two light beams LB and LR pass through the plane-parallel plate 10, as shown in FIG.
When 0 is inclined by an angle θ with respect to the optical axis AX, the light fluxes LB and LR pass through different optical paths and form images at different positions on the image plane S due to the prism effect. This is the same for the light fluxes LB ′ and LR ′ off the optical axis. As described above, the image forming position of the mark image on the CCD differs depending on the wavelength of the reflected light. The difference Δ between the image forming positions of LB and LR can be adjusted by changing the inclination angle θ of the parallel plane plate 10 by the motor MT (FIG. 1). Therefore, by adjusting the inclination angle of the plane parallel plate 10, the deviation of the imaging position due to the color can be corrected.

(Second Embodiment) FIG. 9 is a view schematically showing an overall configuration of a projection exposure apparatus provided with the above-described overlay measurement apparatus. In the illustrated projection exposure apparatus, light emitted from a light source 31 uniformly illuminates a mask 33 on which a predetermined pattern is formed, via an illumination optical system 32.

In the optical path from the light source 31 to the illumination optical system 32, one or a plurality of bending mirrors for deflecting the optical path are arranged as required. When the light source 31 and the projection exposure apparatus main body are separate bodies, an automatic tracking unit that always directs the direction of the light from the light source 31 toward the projection exposure apparatus main body, or a light beam cross-sectional shape of the light from the light source 31 is specified. An optical system such as a shaping optical system and a light amount adjusting unit for shaping to the size and shape of the above is arranged. In addition, the illumination optical system 32
For example, an optical integrator formed of a fly-eye lens or an internal reflection type integrator to form a surface light source of a predetermined size and shape, a field stop for defining the size and shape of an illumination area on the mask 33, an image of the field stop And an optical system such as a field stop imaging optical system for projecting light onto a mask. Further, an optical path between the light source 31 and the illumination optical system 32 is sealed by a casing (not shown), and a space from the light source 31 to the optical member closest to the mask in the illumination optical system 32 absorbs exposure light. The mask 33, which has been replaced with an inert gas such as helium gas or nitrogen, which is a gas having a low rate, passes through a mask holder 34 via a mask holder 34.
5 is held parallel to the XY plane. A pattern to be transferred is formed on the mask 33, and a rectangular (slit-shaped) pattern region having a long side along the Y direction and a short side along the X direction in the entire pattern region is illuminated. Is done. The mask stage 35 can be moved two-dimensionally along the mask plane (that is, the XY plane) by the action of a drive system (not shown), and its position coordinates are measured by an interferometer 37 using a mask moving mirror 36. And the position is controlled.

Light from the pattern formed on the mask 33 forms a mask pattern image on a wafer 39 as a photosensitive substrate via a projection optical system 38. The wafer 39 is
It is held on a wafer stage 41 in parallel with the XY plane via a wafer holder 40. The wafer 39 has a long side along the Y direction on the wafer 39 so as to optically correspond to a rectangular illumination area on the mask 33, and X
A pattern image is formed in a rectangular exposure area having a short side along the direction.

The wafer stage 41 can be moved two-dimensionally along the wafer surface (ie, XY plane) by the action of a drive system (not shown), and its position coordinate is an interferometer 43 using a wafer moving mirror 42. And the position is controlled.

Further, in the projection exposure apparatus shown in the drawings, the projection optical system 38 is arranged between the optical member disposed closest to the mask and the optical member disposed closest to the wafer among the optical members constituting the projection optical system 38. The inside of the projection optical system 38 is replaced with an inert gas such as helium gas or nitrogen.

Further, the illumination optical system 32 and the projection optical system 38
A mask 33 and a mask stage 35 are disposed in a narrow optical path between the mask 33 and the mask stage 35. An inert gas such as nitrogen or helium gas is provided inside a casing (not shown) that hermetically surrounds the mask 33 and the mask stage 35. Gas is filled.

A wafer 39 and a wafer stage 41 are arranged in a narrow optical path between the projection optical system 38 and the wafer 39. A casing (not shown) that hermetically surrounds the wafer 39 and the wafer stage 41 and the like. ) Is filled with an inert gas such as nitrogen or helium gas. In this way, an atmosphere in which the exposure light is hardly absorbed is formed over the entire optical path from the light source 31 to the wafer 39.

As described above, the field of view (illumination area) on the mask 33 and the projection area (exposure area) on the wafer 39 defined by the projection optical system 38 have a rectangular shape having short sides along the X direction. It is. Therefore, the mask 33 and the wafer 39 are formed by using a drive system and interferometers (37, 43).
While controlling the position of the mask stage 3 along the short side direction of the rectangular exposure region and the illumination region, that is, in the X direction.
5 and the wafer stage 41, and thus the mask 33 and the wafer 39 are synchronously moved (scanned),
A mask pattern is scanned and exposed on the wafer 39 in a region having a width equal to the long side of the exposure region and a length corresponding to the scanning amount (movement amount) of the wafer 39.

An alignment optical system AL for performing relative positioning between the mask 33 and the wafer 39 is provided near the projection optical system 38. The configuration of the alignment optical system AL is substantially the same as the configuration of the overlay measurement apparatus described in the first embodiment, and thus the description is omitted.

When the pattern formed on the mask 33 is projected and exposed on the wafer 39 using the above-described projection exposure apparatus, the mask is exchanged with another mask having a different pattern by a mask transfer device (not shown), and the wafer is exposed on the wafer. Exposure is performed by sequentially superimposing different patterns. Therefore, the alignment optical system AL calculates, for example, the amount of misalignment between the base pattern formed by the first exposure and the resist pattern (overlay mark) formed by the second exposure, and calculates the amount of misalignment. Find the offset value. Then, based on the offset value, the mask stage 3
After performing relative alignment between the mask 33 and the wafer 39 by moving the wafer stage 5 and the wafer stage 41, the pattern on the mask 33 is exposed onto the wafer 39 via the projection optical system 38.

Next, a procedure for adjusting the plane-parallel plate 10 in the alignment optical system AL in the projection exposure apparatus will be described. As shown in FIG. 3, when there are overlay marks M1 to M5 having different shot areas in the same wafer,
When the spectrum of the reflected light is different for each mark due to a difference in the film thickness of each mark or the like, the degree of influence on the TIS value of each mark M1 to M5 may be different due to the chromatic dispersion characteristics of the imaging optical system. . Therefore, in a certain kind of lithography process, the TIS value of each mark may be greatly different even within the same wafer.

In this case, the TIS value is measured for each shot area using a sample wafer having different color information (the image forming position of the mark by the color) for each shot area in the wafer, and its variation (variance σ) is measured. It is desirable that the inclination angle θ of the plane-parallel plate 10 be determined in advance so that the angle θ becomes minimum. For example, FIG. 10A is a diagram of a characteristic curve showing a relationship between a tilt angle θ (horizontal axis) and a variance σ (vertical axis) in a certain processing step. At the angle θ ₀ , the variance σ of the TIS value is minimized. On the other hand, FIG. 10B shows a characteristic curve of the relationship between the tilt angle θ and the TIS dispersion value σ in another processing step of the same sample wafer. FIGS. 10A and 10B
As is clear from FIG. 7, the shape of the characteristic curve differs depending on the difference in the processing steps, for example, the first exposure step and the second exposure step. For this reason, the inclination angle θ ₀ at which the TIS variance value becomes minimum is measured as an adjustment value in advance for each processing step using a sample wafer, stored in the memory M (FIG. 9), and the actual test wafer is measured. In this case, the shift of the mark image is optically adjusted by tilting the parallel plate 10 by the motor MT so that the optimum tilt angle θ ₀ stored for each processing step is obtained. By such a procedure, it is possible to easily adjust the deviation of the image forming position of the mark image due to the color.

In the present embodiment, the angle of the plane parallel plate 10 is changed for each processing step. However, when it is desired to reduce the measurement time, or when the optimum value θ ₀ of the inclination angle is required in a plurality of processing steps. For example, when it is substantially constant, a plurality of processing steps may be performed with the parallel plane plate 10 set at one angle θ ₀ .

Further, the present invention is not limited to what is described in the claims, but can also have the following configurations. (A) an illumination optical system for illuminating a substrate having at least a first mark and a second mark, an imaging optical system for forming an image of each mark, and detecting each mark image An alignment unit having an imaging unit for calculating the amount of misalignment between the first mark and the second mark based on an output signal from the imaging unit. An alignment apparatus, wherein the optical system includes an adjustment unit that adjusts a shift of each mark image due to a color on an imaging surface of the imaging unit based on predetermined information.

(B) An illumination optical system for illuminating a mask on which a predetermined pattern is formed, an alignment apparatus according to (A) for detecting a positioning mark formed on a substrate, and the alignment apparatus. A drive unit for performing relative positioning between the substrate and the mask based on the obtained overlay deviation amount, and a projection optical system for projecting and exposing a pattern of the mask onto the substrate. A projection exposure apparatus.

As described above, the present invention can take various forms.

[0029]

As described above, according to the overlay measuring apparatus of the present invention, the amount of chromatic dispersion of the optical system can be adjusted to an optimal value, and the difference in the wavelength of the light reflected from the overlay mark can be reduced. The resulting image position shift of the entire mark image can be prevented. As a result, the occurrence of measurement errors unique to the apparatus can be reduced, and the overlay displacement amount can be measured with higher accuracy. Further, according to the semiconductor device manufacturing method of the present invention, since the mask and the wafer can be relatively accurately superimposed and projected and exposed, it is possible to improve the yield in manufacturing device elements.

[Brief description of the drawings]

FIG. 1A is a diagram illustrating a configuration of an overlay measuring apparatus according to a first embodiment of the present invention, and FIG. 1B is a diagram illustrating a configuration of a field stop.

FIGS. 2A and 2B are diagrams showing a configuration of an overlay mark.

FIG. 3 is a diagram showing a wafer at the time of measurement in the 0-degree direction.

FIG. 4 is a diagram showing a wafer at the time of 180-degree measurement.

FIG. 5 is a diagram showing a deviation of an image forming position depending on a wavelength when there is no chromatic dispersion.

FIG. 6 is a diagram illustrating a deviation of an image forming position depending on a wavelength when there is chromatic dispersion.

FIG. 7 is a diagram showing optical paths of blue and red light beams when the plane-parallel plate is not inclined.

FIG. 8 is a diagram illustrating optical paths of blue and red light beams when the parallel plane plate is inclined.

FIG. 9 is a diagram illustrating a schematic configuration of a projection exposure apparatus according to a second embodiment.

FIGS. 10A and 10B are curves showing characteristics of the inclination angle when the processing steps are different.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light source 2 condenser lens 3 field stop 4 illumination relay lens 5 half prism 6 first objective lens 7 second objective lens 8 image sensor CCD 9 arithmetic processing unit 10 parallel plane plate 20 overlay mark 21, 39 wafer 22 stage 31 light source 32 Illumination optical system 33 Mask 34 Mask holder 35 Mask stage 36 Mask moving mirror 37 Interferometer 38 Projection optical system 40 Wafer holder 41 Wafer stage 42 Wafer moving mirror 43 Interferometer AL Alignment optical system M Memory

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (4)

[Claims] An illumination optical system for illuminating a substrate having at least a first mark and a second mark; an imaging optical system for forming an image of each mark; In an overlay measurement apparatus having an imaging unit for detecting, and an arithmetic processing unit for calculating an overlay deviation amount between the first mark and the second mark based on an output signal from the imaging unit. An overlay measurement apparatus, wherein the imaging optical system includes an adjustment unit that adjusts a shift of each mark image due to a color on an imaging surface of the imaging unit based on predetermined information. 2. A storage unit for storing an adjustment value of a shift of the mark image for each of the processing steps in order to adjust a shift of the mark image generated according to each of the processing steps performed on the substrate. The adjustment unit optically adjusts the shift of the mark image based on the adjustment value of the shift of the mark image for each of the processing steps stored in the storage unit as the predetermined information. An overlay measuring device characterized by performing the following. 3. A step of obtaining a shift amount between the first mark and the second mark using the overlay measuring device according to claim 1 or 2, and a predetermined pattern based on the shift amount. Obtaining an offset value for performing relative alignment between the mask and the substrate having: a step of performing relative alignment between the mask and the substrate based on the offset value; Exposing a pattern to the substrate. 4. A step of detecting an alignment mark formed on a substrate by a position detection optical system, and adjusting a shift of an image formation position due to a color of the alignment mark caused by an optical characteristic of the position detection optical system. Performing a positioning of the substrate, and exposing the pattern of the mask to the substrate via a projection optical system.