JP2002196223A - Optical detector for deviation of position - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical detector for deviation of position with which the measurement precision and an automatic focus(AF) sensitivity are improved by separating an optical system for measurement and an optical system for AF, and a stable AF precision is kept being uninfluenced by such interference condition as the thickness of a resist film. SOLUTION: A light source 1 for illumination for measurement emits a light beam for illumination for measurement of which wavelength band is 600 to 900 nm via an aperture diaphragm 10. A light source 40 for illumination for AF emits a light beam for illumination for AF of which wavelength band is 450 to 550 nm via an aperture diaphragm 41. A large illumination NA for AF is used to increase an AF sensitivity. An optimum value of an illumination NA for measurement is decided by a measurement precision or the like. The light source 40 for illumination for AF has a wide band of 450 to 550 nm, thus the variation in the AF condition is suppressed even when the thickness of the resist film is not uniform. The light source 1 for illumination for measurement has a wide rang of 600 to 900 nm, thus an appropriate contrast is available even when the difference in level of superimposing marks 20 are variable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical position shift detecting device for detecting a position shift of an interlayer mark by observing an inspection mark, for example, an overlay mark, on an inspection object such as a semiconductor wafer.

[0002]

2. Description of the Related Art In a lithography process for forming a semiconductor pattern on a wafer, a plurality of reticles having different patterns are used. First, the first layer resist on the wafer is exposed and developed with an image of a pattern transmitted through a reticle on which a pattern for one layer is formed. Next, the second-layer resist applied on the first-layer pattern is exposed and developed with an image of a pattern transmitted through the reticle on which the two-layer pattern is formed. By performing such exposure and development processing a plurality of times, a predetermined pattern is formed on the wafer.
In such a lithography process, it is necessary to form a lower layer and an upper layer pattern, for example, a first layer pattern and a second layer pattern in a correct positional relationship.

On the reticle on which the respective patterns of the upper and lower layers are formed, an overlay mark is also formed in addition to the original pattern. When the upper layer pattern is formed on the wafer on which the lower layer pattern is formed, if the lower layer pattern and the upper layer pattern are formed in a correct positional relationship,
The relative positional relationship between the upper and lower overlay marks, that is, the positional deviation, is within a predetermined error range. Each time the development of the upper layer pattern is completed, the above-described relative positional relationship is measured by the optical misalignment detecting device, and a wafer that deviates from a predetermined error range is regarded as a defective product.

A device disclosed in Japanese Patent Application Laid-Open No. 6-214150 is known as such an optical displacement detecting device. This position shift detecting device has a wavelength of 400 to
It has a measurement optical system for measuring with 600 nm broadband illumination light and an AF optical system for detecting the focus adjustment state with a single wavelength of 800 nm illumination light. By separating the measurement optical system and the AF optical system in this manner, it is possible to set the illumination NA optimal for each of the measurement system and the AF system. However, if the measurement illumination light and the AF illumination light have different wavelength ranges,
Since the aberration generated by the common optical system differs between the two optical systems depending on the wavelength, it affects the measurement accuracy. Therefore, the above-mentioned publication discloses a device in which the wavelength ranges of the illumination light for measurement and the illumination light for AF are made to substantially coincide with each other.

[0005]

However, in an apparatus in which the wavelength ranges of the measurement illumination light and the AF illumination light are made substantially the same, if each illumination light has a single wavelength, interference due to unevenness in the thickness of the resist film. There is a possibility that the AF measurement accuracy fluctuates due to the difference in the conditions.

It is an object of the present invention to improve measurement accuracy and AF sensitivity by separating a measurement optical system and an AF optical system, and to achieve a stable AF sensitivity without being affected by interference conditions such as a resist film thickness. It is an object of the present invention to provide an optical displacement detecting device capable of maintaining the above-mentioned conditions.

[0007]

The present invention will be described with reference to FIG. 1 showing one embodiment. (1) An optical displacement detecting apparatus according to the first aspect of the invention inspects a measurement illumination light source 1 for emitting measurement illumination light in a first wavelength band, and a measurement illumination light from the measurement illumination light source 1. A measurement illumination optical system for irradiating the target mark 20, a measurement imaging optical system for forming an illuminated reflected light from the inspection target mark 20 on the measurement photoelectric conversion element 8, and a measurement photoelectric conversion element 8 , An AF illumination light source that emits AF illumination light in a second wavelength band different from the first wavelength band, based on a detection signal from the device. 40 and the AF illumination light source 40
A that irradiates the AF target illumination light with the AF illumination light from
An illumination optical system for F, and an AF for forming an image of the reflected light from the illuminated inspection target mark 20 on the AF photoelectric conversion element 34
Adjustment state detecting device 3 that detects the focus adjustment state of the AF imaging optical system with respect to the inspection target mark 20 based on the detection signal from the AF imaging optical system and the AF photoelectric conversion element 34.
5 is provided. (2) The optical displacement detection apparatus according to claim 2 is the optical displacement detection apparatus according to claim 1, wherein the measurement imaging optical system and the AF imaging optical system are commonly used.
And at least a difference between aberrations generated in a common optical system of the two optical systems due to a difference between wavelengths of the measurement and AF illumination light is compared with a measurement imaging optical system of the AF imaging optical system. It is characterized in that compensation is performed by optical systems 30, 32, and 33 that are not common. (3) The optical displacement detection apparatus according to claim 3 is the optical displacement detection apparatus according to claim 1 or 2, wherein the illumination NA of the measurement illumination optical system and the illumination NA of the AF illumination optical system are different.
Are set to different values. (4) The optical displacement detection device according to claim 4 is the optical displacement detection device according to any one of claims 1 to 3, wherein the wavelength band of the illumination light for measurement (for example, 600 to 900).
nm) to the wavelength band of the illumination light for AF (for example, 450 to 5).
50 nm). (5) The optical displacement detecting apparatus according to claim 5 is the optical displacement detecting apparatus according to any one of claims 1 to 4, wherein the ratio between the shortest wavelength and the longest wavelength of the measurement illumination light and the AF illumination light is determined. 1.2 to 1.7.

In the section of the means for solving the above problems, the invention has been described with reference to the embodiments, but the invention is not limited to the embodiments.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical displacement detecting apparatus according to the present invention will be described with reference to FIG. As described above, in a lithography process of semiconductor manufacturing, it is necessary to form a lower layer and an upper layer pattern, for example, a first layer pattern and a second layer pattern in a correct positional relationship. Therefore, an overlay mark is formed in addition to the circuit patterns of the upper and lower layers. When the upper layer pattern is formed on the wafer on which the lower layer pattern is formed, the position shift of the overlay mark of the lower layer pattern and the upper layer pattern is measured,
If the relative positional relationship between the upper and lower overlay marks, that is, the positional deviation is within a predetermined error range, the mark is transported as a non-defective product to the next process. The optical displacement detecting device of FIG. 1 measures this displacement.

FIG. 1 is a diagram schematically showing the configuration of an optical displacement detecting apparatus according to a first embodiment of the present invention.
In FIG. 1, the Z-axis is set in parallel with the optical axis AX of the optical displacement detection device, the X-axis is set in a direction perpendicular to the paper surface of FIG. 1, and the Y-axis is set in directions perpendicular to the Z-axis and X-axis. ing.

The wafer 21 is supported on a Z stage 22 through a wafer holder (not shown) substantially parallel to the XY plane. The Z stage 22 is driven by the stage control system 36 along the optical axis AX. The Z stage 22 is supported on an XY stage (not shown). The XY stage is also two-dimensionally driven by the stage control system 36 in an XY plane perpendicular to the optical axis AX.

The optical displacement detecting apparatus shown in FIG. 1 is a broadband measuring illumination light AL having a wavelength of 600 nm to 900 nm.
Is provided. The illumination light emitted from the light source 1 is restricted by the illumination aperture stop 10 and then enters the condenser lens 2. The measurement illumination light AL that has passed through the condenser lens 2 is once collected, and then enters the illumination relay lens 4 via the illumination field stop 3. The illumination relay lens 4 has a cross-sectional shape S as shown in FIG.
An illumination light beam having 1 enters. The illumination light for measurement AL converted into parallel light by the illumination relay lens 4 passes through the dichroic mirror 45 and is reflected downward by the beam splitter 5. The measurement illumination light AL reflected downward is collected by the first objective lens 6 and illuminates the overlay mark 20 formed on the wafer 21.

As described above, the light source 1, the illumination aperture stop 10,
The condenser lens 2, the illumination field stop 3, the illumination relay lens 4, the dichroic mirror 45, the beam splitter 5, and the first objective lens 6
The illumination optical system for measurement for irradiating illumination light to the illumination device is constituted.

The reflected light from the overlay mark 20 with respect to the measurement illumination light AL enters the beam splitter 5 via the first objective lens 6. The light transmitted upward in the drawing by the beam splitter 5 forms an image of an overlay mark on the primary image forming plane by the second objective lens 7. The light flux of this image passes through the dichroic mirror 14 and enters the CCD 8 via the first imaging relay lens system 12 and the second imaging relay lens system 13. First imaging relay lens system 12
And in the parallel optical path of the second imaging relay lens system 13,
An imaging aperture stop 11 is provided. The output signal from the CCD 8 is input to the image processing circuit 9, and the displacement of the overlay mark 20 is calculated.

As described above, the first objective lens 6, the beam splitter 5, the second objective lens 7, the first imaging relay lens system 12, the dichroic mirror 14, the second imaging relay lens system 13, and the imaging aperture stop. Numeral 11 constitutes a measurement imaging optical system for forming a mark image based on reflected light from an overlay mark with respect to illumination light.

The optical displacement detection apparatus shown in FIG. 1 is a broadband illumination light AF having a wavelength of 450 nm to 550 nm.
The light source 40 for supplying L is provided. The illumination light emitted from the light source 40 is restricted by the illumination aperture stop 41 and then enters the condenser lens 42. Condenser lens 42
After passing through the illumination light AFL, the light is once collected, and then enters the AF illumination relay lens 44 via the illumination field stop 43. An illumination light beam having a cross-sectional shape S2 as shown in FIG. AF
Illumination light AF converted into parallel light by the illumination relay lens 44
L is reflected by the dichroic mirror 45 and the beam splitter 5, condensed by the first objective lens 6, and illuminates the overlay mark 20 formed on the wafer 21.

As described above, the light source 40 and the illumination aperture stop 4
1. A condenser lens 42, an illumination field stop 43, an illumination relay lens 44, a dichroic mirror 45, a beam splitter 5, and a first objective lens 6 are AF illumination optics for irradiating the overlay mark 20 with AF illumination light AFL. Make up the system.

The reflected light from the overlay mark 20 with respect to the AF illumination light AFL enters the beam splitter 5 via the first objective lens 6. The light transmitted upward in the drawing by the beam splitter 5 forms an image of the overlay mark 20 on the primary image forming plane by the second objective lens 7. This image is reflected laterally by the dichroic mirror 14 and the AF first
The light enters the pupil division mirror 31 from the imaging relay lens system 30. The pupil splitting mirror 31 receives the overlapping mark 20
Is divided into a pair of images. In FIG. 1, the light flux L of a pair of images is shown.
21 and L2r. The luminous fluxes L21 and L2r of the divided mark image are passed through an AF second imaging relay lens system 32 and a cylindrical lens 33 to an AF CCD 34.
Incident on. The cylindrical lens 33 is shown in FIG.
As can be seen from FIG. 2, the light-emitting element is arranged so as to have a refractive power in the non-measurement direction (X-axis direction) and no refractive power in the measurement direction (Y-axis direction). A pair of mark images are formed on the AF CCD 34 at predetermined intervals.

At this time, as shown in FIGS. 2A to 2C, the distance L between the pair of mark images changes according to the front focus state, the focus state, and the rear focus state. The AF signal processing circuit 35
The interval L is calculated based on the output signal from the AF CCD. Then, a comparison is made between the previously stored interval Lr in the in-focus state and the calculated interval L, and the difference between the two is input to the stage control unit 36 as focal position information. The stage control unit 36 moves the position of the Z-axis stage 22 in the Z-axis direction based on the input focal position information, thereby transferring the image of the overlay mark 20 to the CCD 3.
4 forms an image in the focused state shown in FIG.

The advantages of such an AF detection system using two light beams are that, by setting the length of the slit S1 in the non-measurement direction to be long, the effect of averaging the reflection unevenness in the slit S2 and the slit S2 by pupil division. And the effect of reducing the influence of the image other than the measurement mark in the inside.

As described above, the first objective lens 6, the beam splitter 5, the second objective lens 7, the dichroic mirror 14, the AF first imaging relay lens system 30, the pupil division mirror 31, and the AF second imaging relay lens system The AF lens 32 and the cylindrical lens 33 constitute an AF imaging optical system for detecting a focus adjustment state based on reflected light from the overlay mark 20 with respect to AF illumination light.

FIGS. 3A to 3C are views showing an example of the upper and lower overlay marks 20L and 20U. (A),
(B) shows the positional deviation between the upper overlay mark 20U and the lower overlay mark 20L, which are the center lines CLU and C of the two.
It is indicated by the amount R of deviation from LL. In some cases, a transparent film having a predetermined thickness is formed on the base surface. Which of the overlay marks 20U and 20L is focused by the AF imaging optical system is appropriately determined according to the shape and thickness of the overlay mark.

As shown in FIG. 4, for example, the overlay shift amount R is detected for each of the overlay marks of the first to fifth shots SR1 to SR5. Here, FIG.
4B shows a state where the wafer is rotated by 180 degrees with respect to FIG. 4A. In this embodiment, FIGS.
In the two directions (b), that is, the 0-degree direction and the 180-degree direction, the positional deviation of the first to fifth shots SR1 to SR5 is detected. Then, according to the following equation (1), the measurement error T
Calculate IS. TIS = (R0 + R180) / 2 (1) R0 is the amount of displacement in the 0-degree direction shown in FIG. 4A, and R180 is the amount of displacement in the 1800-degree direction shown in FIG. 4B.

In the misalignment detecting device configured as described above, the AF illumination light is a wide band light having a wavelength of 450 to 550 nm. As described in the section of the related art, when the AF illumination light has a single wavelength, the AF accuracy fluctuates due to a difference in interference conditions due to unevenness in the thickness of the resist. Therefore, the illumination light for AF is made to be light of a broadband wavelength, and the difference in interference conditions due to unevenness in the thickness of the resist is dispersed by the light of the wideband wavelength, thereby suppressing a change in AF accuracy.

The wavelength of the illumination light for measurement is set to a wavelength of 600 to
The light was a broadband light of 900 nm. For example, if the step of the overlay mark (inspection target mark) is 600 nm, which is equal to the shortest wavelength side of the measurement illumination light, the single wavelength 600
In nm, the step cannot be detected. However, the wavelength 600
Even if a single wavelength is used between nm and 900 nm, a sufficient contrast for image processing can be obtained. Using such a principle,
The longest wavelength of the illumination light for measurement was set to 1.5 times the shortest wavelength so that the contrast was appropriately increased even if the level difference of the superimposed mark was various values.

In other words, in the position shift detecting apparatus of this embodiment, light of a wide band wavelength is used for each of the two illumination lights for measurement and AF.

The longest wavelength of the AF illumination light is 1.2 times the shortest wavelength. The wavelength of the illumination light for measurement is 600 to 90
The illumination light for AF is not limited to 0 nm, and is 450 to 550 n.
The wavelength is not limited to m. It is preferable that the ratio between the shortest wavelength and the longest wavelength of the illumination light for measurement and the illumination light for AF is 1.2 to 1.7. Further, the wavelength range of the AF illumination light was made smaller than the wavelength range of the measurement illumination light.

As described above, the illumination light for measurement has a wavelength of 60.
0 to 900 nm, AF illumination light of wavelength 450 to 550 n
Since the light is m, the aberrations generated by the optical system commonly used by the measurement optical system and the AF optical system, that is, the aberrations generated by the objective lens 6 and the relay lens 7 are different between the two optical systems.
Therefore, of the AF optical system, the influence of the aberration caused by the wavelength difference is optically removed by the AF first imaging relay lens system 30, the AF second imaging relay lens system 32, and the cylindrical lens 33. Note that C for AF
When the signal processing circuit 35 calculates the focus adjustment information based on the signal from the CD 34, the influence of this aberration may be removed by a correction calculation.

Further, in the misalignment detecting device configured as described above, the illumination optical system for measurement and the illumination optical system for AF are separated as shown in FIG. Each of the aperture stops 10 and the aperture stop 41 of the AF illumination optical system have different sizes. That is, the measurement illumination NA and the AF illumination NA are set to different values. The operation and effect of adopting such a configuration will be described.

The diameter of the aperture stop 10 of the illumination optical system for measurement is
It is determined by the optimum condition required from the desired resolution of the measuring optical system. On the other hand, the AF sensitivity is equivalent to the change rate of the interval between the pair of light beams L21 and L2r (see the following equation (2)), and the diameter (illumination NA) of the aperture stop 41 of the AF illumination optical system is increased. It gets bigger. AF sensitivity = ΔL / ΔZ (2) where ΔL is the amount of change in the interval between the pair of light beams L21 and L2r ΔZ is the unit movement amount of the Z stage

In the embodiment shown in FIG. 1, the AF field stop 4
The diameter of the AF aperture stop 41 is increased in order to reduce the measurement error due to the pattern around the overlay mark existing in the area 3. In this embodiment, since the AF illumination optical system is independent of the measurement illumination optical system, the illumination NA
Even if is increased so that the sensitivity of AF (automatic focus adjustment) becomes a desired value, the measurement accuracy is not affected. In the present embodiment, the AF illumination NA is the measurement illumination N
It is larger than A.

In the above description, an example of the apparatus for detecting a position shift of an overlay mark in a semiconductor element manufacturing process has been described. However, the present invention is applicable to various other misalignment detecting devices.

[0033]

According to the present invention, the following effects can be obtained. (1) Since the measurement illumination optical system and the AF illumination optical system are separated, the measurement illumination optical system is set to the illumination NA determined by the measurement accuracy, and the AF illumination optical system has a high AF sensitivity. Thus, the illumination NA can be increased. That is, both illumination NAs can be set to optimal conditions. (2) Since the AF illumination light is light of a broadband wavelength, AF light can be applied regardless of the situation of the measurement target, for example, the thickness of the resist film.
The sensitivity does not change. (3) Since the illumination light for measurement is light of a broadband wavelength, steps at various heights can be imaged with an appropriate contrast. (4) Since the wavelength bands of the AF illumination light and the measurement illumination light are different, different aberrations occur in the optical systems commonly used by both optical systems due to the wavelength difference. But A
Among the F imaging optical systems, an optical system that is not common to the measurement imaging optical system can remove the influence of the AF sensitivity due to the aberration difference.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment of an optical displacement detection apparatus according to the present invention.

FIG. 2 is a diagram illustrating two-beam AF by pupil division;

FIG. 3 is a diagram illustrating a wafer overlay mark.

FIG. 4 is a diagram schematically showing an example of the arrangement of wafer overlay marks on a wafer;

[Explanation of symbols]

1, 40: light source 2: condenser lens 4, 12, 13: relay lens 6: objective lens 8: measurement CCD 9, 35: signal processing system 10: illumination system aperture stop 11: imaging system aperture stop 20: overlay Mark 21: Wafer 22: Z stage 30, 32: Imaging relay lens 33: Cylindrical lens 34: AF CCD 36: Stage control system 41: AF aperture stop

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA20 BB27 CC19 DD04 DD09 EE08 FF04 FF42 GG13 GG23 GG24 HH13 JJ03 JJ09 JJ26 LL04 LL08 LL20 LL28 LL30 LL46 PP12 QQ28 2H051 AA10 BA72 CB06 FA03 CB06 FA03 CB06 FC03 FC04

Claims (5)

[Claims] An illumination light source for measurement for emitting illumination light for measurement in a first wavelength band, an illumination optical system for measurement for irradiating illumination light for measurement from the illumination light source for measurement to a mark to be inspected, and illumination. A measurement imaging optical system for forming an image of the reflected light from the inspection target mark on the measurement photoelectric conversion element, and a displacement of the inspection target mark based on a detection signal from the measurement photoelectric conversion element. , An AF illumination light source that emits AF illumination light in a second wavelength band different from the first wavelength band, and an AF illumination light from the AF illumination light source. An AF illumination optical system for irradiating the target mark, an AF imaging optical system for imaging reflected light from the inspection target mark on the AF photoelectric conversion element, and an AF imaging optical system Based on the detection signal, Optical positional deviation detecting device, characterized in that it comprises a focusing state detecting device for detecting a focusing state with respect to the inspection target mark F imaging optical system. 2. The optical displacement detection apparatus according to claim 1, wherein the measurement imaging optical system and the AF imaging optical system have an optical system commonly used, and at least the measurement and AF are used. The difference in aberrations generated in the common optical system of both optical systems due to the difference in the wavelength of the illumination light for
An optical displacement detection device, wherein the compensation is performed by an optical system that is not common to the measurement imaging optical system among the AF imaging optical systems. 3. The optical displacement detecting apparatus according to claim 1, wherein the illumination NA of the measurement illumination optical system and the illumination NA of the AF illumination optical system have different values. Position shift detection device. 4. The optical displacement detection apparatus according to claim 1, wherein a wavelength band of the measurement illumination light is set to a longer wavelength side than a wavelength band of the AF illumination light. Optical position shift detecting device. 5. The optical displacement detection apparatus according to claim 1, wherein a ratio between a shortest wavelength and a longest wavelength of the measurement illumination light and the AF illumination light is 1.2 to 1.7. An optical misalignment detection device characterized in that: