JP2004128253A - Mark position detecting device and its assembling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mark position detecting device which can securely reduce error TIS caused by the device and further precisely detect the position of a detected mark, and to provide its assembling method. <P>SOLUTION: The device is equipped with illumination optical systems 13 to 19 which illuminate a detected mark 30 on a substrate 11, imaging optical systems 19 to 23 which image light L2 from the detected mark to form an image of the detected mark, a correction member 24 which is arranged on the optical axis 02 of the imaging optical systems to correct residual aberrations of the imaging optical systems, an image pickup means 25 which picks up the image of the detected mark formed through the imaging optical systems and correction member to output an image signal, and a calculating means 26 which inputs the image signal from the image pickup means to calculate the position of the detected mark. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mark position detecting device for detecting the position of a test mark on a substrate and a method for assembling the mark position, and more particularly to a mark position detecting device and a method for assembling the mark position suitable for high-accuracy position detection in a manufacturing process of a semiconductor element or the like. About.
[0002]
[Prior art]
As is well known, in a manufacturing process of a semiconductor device or a liquid crystal display device, an exposure process of printing a circuit pattern formed on a mask (reticle) on a resist film, and a development process of dissolving an exposed portion or an unexposed portion of the resist film are included. The circuit pattern (resist pattern) is transferred to the resist film through etching, and the resist pattern is used as a mask to perform etching or vapor deposition (processing step), thereby forming a circuit on a predetermined material film immediately adjacent to the resist film. The pattern is transferred (pattern forming step).
[0003]
Next, to form another circuit pattern on the circuit pattern formed on the predetermined material film, a similar pattern forming step is repeated. By repeatedly performing the pattern forming process many times, circuit patterns of various material films are stacked on a substrate (semiconductor wafer or liquid crystal substrate), and a circuit of a semiconductor element or a liquid crystal display element is formed.
[0004]
By the way, in the above-described manufacturing process, in order to accurately overlap circuit patterns of various material films, alignment of a mask and a substrate is performed before an exposure process in each pattern forming process, and further, after a developing process. In addition, prior to the processing step, the inspection of the superposition state of the resist pattern on the substrate is performed to improve the product yield.
[0005]
Incidentally, the alignment between the mask and the substrate (before the exposure step) is the alignment between the circuit pattern on the mask and the circuit pattern formed on the substrate in the immediately preceding pattern formation step. This is performed using an alignment mark indicating a reference position.
Inspection of the superposition state of the resist pattern on the substrate (before the processing step) is performed by inspecting the registration of the resist pattern with respect to the circuit pattern (hereinafter referred to as “base pattern”) formed in the immediately preceding pattern formation step. Yes, this is performed using an overlay mark indicating the reference position of each of the base pattern and the resist pattern.
[0006]
The position detection of these alignment marks and overlay marks (collectively referred to as “test marks”) is performed by illuminating the test marks and capturing an image of the test marks using an image sensor such as a CCD camera. This is performed by performing predetermined image processing on the obtained image signal.
Further, in an apparatus for detecting the position of a test mark, in order to enhance the detection accuracy, for example, a method disclosed in Patent Document 1 (hereinafter referred to as a “QZ method”) is used to provide an illumination optical system The arrangement of the optical components provided in the optical system is finely adjusted to reduce an error TIS (Tool Induced Shift) caused by the apparatus. Fine adjustment using the QZ method is usually performed at the time of assembling the apparatus. Note that the illumination optical system emits illumination light to the test mark. The imaging optical system forms an image of a test mark.
[0007]
[Patent Document 1]
JP-A-2000-77295 (pages 7 to 12)
[0008]
[Problems to be solved by the invention]
However, even if the arrangement of the illumination optical system and the imaging optical system is finely adjusted by using the above-described QZ method, even if a higher-order aberration component of the imaging optical system (for example, a fifth-order or higher Components, etc.) could not be removed. For this reason, in the conventional apparatus, it is difficult to sufficiently reduce the error TIS caused by the apparatus, and there is a limit in improving the detection accuracy.
[0009]
SUMMARY OF THE INVENTION An object of the present invention is to provide a mark position detecting device and an assembling method thereof, which can surely reduce the error TIS caused by the device and can detect the position of a test mark with higher accuracy.
[0010]
[Means for Solving the Problems]
The mark position detecting device according to claim 1, wherein an illumination optical system that illuminates the test mark on the substrate, and an image that forms light of the test mark to form an image of the test mark. An optical system, a correction member disposed on an optical axis of the imaging optical system, and correcting a residual aberration of the imaging optical system, and the test object formed via the imaging optical system and the correction member. The image processing apparatus includes: an imaging unit that captures an image of a mark and outputs an image signal; and a calculation unit that receives the image signal from the imaging unit and calculates a position of the test mark.
[0011]
According to a second aspect of the present invention, in the mark position detecting apparatus according to the first aspect, the imaging optical system relays the first optical system that forms an intermediate image of the test mark to the intermediate image. A second optical system for imaging, wherein the correction member is disposed in the second optical system.
According to a third aspect of the present invention, in the mark position detection device according to the first or second aspect, the correction member is rotatable around an optical axis of the imaging optical system and is perpendicular to the optical axis. And supporting means for supporting the inside of the apparatus so as to be shiftable.
[0012]
According to a fourth aspect of the present invention, in the mark position detecting device according to the third aspect, a generating unit configured to generate an index signal according to a residual aberration of an entire system including the imaging optical system and the correction member; Control means for controlling at least one of the rotation state and the shift state of the correction member by controlling the support means based on the index signal.
[0013]
According to a fifth aspect of the present invention, there is provided the method of assembling the mark position detecting device according to any one of the first to fourth aspects, wherein the unprocessed mark position is set at a predetermined position on the optical axis of the imaging optical system. A measuring step of measuring the residual aberration of the imaging optical system in a state where the optical members are arranged, and taking out the optical member from the predetermined position after the measuring step, and By performing a concavo-convex processing to cancel residual aberrations of the system, a manufacturing process of manufacturing the correction member, and the correction member manufactured in the manufacturing process are disposed again at the predetermined position, and the correction member is finely adjusted. And a fine adjustment step of adjusting.
[0014]
According to a sixth aspect of the present invention, in the method of assembling the mark position detecting device according to the fifth aspect, in the fine adjustment step, the index according to the residual aberration of the entire system including the imaging optical system and the correction member is provided. On the basis of the signal, at least one of a rotation state of the correction member around the optical axis of the imaging optical system and a shift state of the correction member in a plane perpendicular to the optical axis is adjusted. is there.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
An embodiment of the present invention corresponds to claims 1 to 6.
Here, the mark position detection device of the present embodiment will be described by taking the overlay measurement device 10 shown in FIG. 1 as an example.
[0016]
As shown in FIG. 1A, the overlay measurement apparatus 10 includes an inspection stage 12 that supports a product wafer 11 (or an assembly wafer (not shown)), and a product wafer 11 (or an assembly wafer) on the inspection stage 12. ), And an imaging optical system (19 to 23) for forming an image of the product wafer 11 (or assembly wafer) illuminated by the illumination light L1. Aberration correction plate 24, CCD image pickup device 25, image processing device 26, optical device control device 27, and focus detection device (41-48) arranged on the optical axis of the imaging optical system (19-23). And a stage control device 49.
[0017]
Before specifically describing the overlay measurement apparatus 10, the product wafer 11 and the assembly wafer will be described.
On the product wafer 11 (substrate), a plurality of circuit patterns (all not shown) are laminated on the surface. The uppermost circuit pattern is a resist pattern transferred to a resist film. That is, the product wafer 11 is in the process of forming another circuit pattern on the underlying pattern formed in the previous pattern forming process (after exposure and development of the resist film and before etching of the material film). It is in the state of.
[0018]
Then, the superposition measuring device 10 inspects the superposition state of the resist pattern on the base pattern of the product wafer 11. For this reason, an overlay mark 30 (FIG. 2) used for inspection of an overlay state is formed on the surface of the product wafer 11. FIG. 2A is a plan view of the overlay mark 30, and FIG. 2B is a cross-sectional view.
[0019]
As shown in FIGS. 2A and 2B, the overlay mark 30 includes a rectangular base mark 31 and a resist mark 32 having different sizes. The base mark 31 is formed simultaneously with the base pattern and indicates a reference position of the base pattern. The resist mark 32 is formed simultaneously with the resist pattern, and indicates a reference position of the resist pattern. The base mark 31 and the registration mark 32 each correspond to a “test mark” in the claims.
[0020]
Although not shown, a material film to be processed is formed between the resist mark 32 and the resist pattern and the base mark 31 and the base pattern. After the inspection of the superposition state by the superposition measuring device 10, the resist film 32 is accurately superimposed on the base mark 31, and when the resist pattern is correctly superimposed on the base pattern, the material film It is actually processed through the pattern.
[0021]
On the other hand, a line & space mark 33 (FIGS. 3A and 3B) is formed on the assembly wafer. The line & space mark 33 has a line width of 3 μm, a pitch of 6 μm, and a step of 85 nm (about １ ／ of the measurement wavelength λ). FIG. 3A is a plan view of the line & space mark 33, and FIG. 3B is a cross-sectional view.
The line & space mark 33 is used for finely adjusting the illumination optical system (13 to 18), the imaging optical system (19 to 23), and the aberration correction plate 24 when assembling the overlay measuring apparatus 10.
[0022]
Next, the specific configuration of the overlay measurement apparatus 10 (FIG. 1) will be described.
Although not shown, the inspection stage 12 holds a product wafer 11 (or an assembling wafer) in a horizontal state and supports the same, an XY drive unit that drives the holder in the horizontal direction (XY directions), and a vertical holder. And a Z drive unit that drives in the direction (Z direction). The XY drive unit and the Z drive unit are connected to a stage control device 49 described later.
[0023]
The product wafer 11 is placed on the holder of the inspection stage 12 at the time of the overlay inspection of the product wafer 11 (inspection of the overlay state of the resist pattern on the base pattern). When assembling the overlay measuring apparatus 10, an assembly wafer is placed instead of the product wafer 11.
The illumination optical system (13 to 18) includes a light source 13, an illumination aperture stop 14, a condenser lens 15, a field stop 16, an illumination relay lens 17, and a beam splitter 18 arranged in order along the optical axis O1. . The beam splitter 18 has the reflection / transmission surface 18a inclined at approximately 45 ° with respect to the optical axis O1, and is also arranged on the optical axis O2 of the imaging optical system (19 to 23). The optical axis O1 of the illumination optical system (13 to 18) is perpendicular to the optical axis O2 of the imaging optical system (19 to 23).
[0024]
The light source 13 emits light having a wide wavelength band (for example, white light). The illumination aperture stop 14 limits the diameter of light emitted from the light source 13 to a specific diameter. The illumination aperture stop 14 is supported so as to be shiftable in a plane perpendicular to the optical axis O1. Adjustment of the shift state of the illumination aperture stop 14 is performed by using the above-mentioned line & space mark 33 (FIG. 3) when assembling the overlay measurement apparatus 10.
[0025]
The condenser lens 15 collects light from the illumination aperture stop 14. The field stop 16 is an optical element that limits the field of view of the overlay measurement device 10, and has one slit 16a that is a rectangular opening as shown in FIG. The illumination relay lens 17 collimates the light from the slit 16 a of the field stop 16.
In the illumination optical system (13 to 18), light emitted from the light source 13 uniformly illuminates the field stop 16 via the illumination aperture stop 14 and the condenser lens 15. The light passing through the slit 16a of the field stop 16 is guided to the beam splitter 18 via the illumination relay lens 17, and is reflected by the reflection / transmission surface 18a (illumination light L1). 23) is guided on the optical axis O2.
[0026]
The imaging optical system (19 to 23) includes a first objective lens 19, a second objective lens 20, a first imaging relay lens 21, an imaging aperture stop 22, a second imaging lens 22, and a second objective lens 19 arranged in order along the optical axis O2. And an image relay lens 23. The optical axis O2 of the imaging optical system (19 to 23) is parallel to the Z direction.
[0027]
The beam splitter 18 of the illumination optical system (13 to 18) is disposed between the first objective lens 19 and the second objective lens 20, and the second objective lens 20 and the first imaging relay lens 21 A beam splitter 41 of a focus detection device (41 to 48) to be described later is disposed between them. Further, an aberration correction plate 24 described later is arranged near the imaging aperture stop 22.
[0028]
The first objective lens 19 of the imaging optical system (19 to 23) receives and condenses the illumination light L1 from the beam splitter 18 of the illumination optical system (13 to 18). As a result, the product wafer 11 (or assembly wafer) on the inspection stage 12 is vertically illuminated by the illumination light L1 transmitted through the first objective lens 19.
The incident angle range of the illumination light L1 when entering the product wafer 11 (or assembly wafer) is determined by the aperture diameter of the illumination aperture stop 14 of the illumination optical system (13 to 18). This is because the illumination aperture stop 14 is arranged on a plane conjugate with the pupil of the first objective lens 19.
[0029]
Also, since the field stop 16 and the product wafer 11 (or assembly wafer) are in a conjugate positional relationship, an area corresponding to the slit 16a of the field stop 16 on the surface of the product wafer 11 (or assembly wafer). Illuminated by the illumination light L1. That is, the image of the slit 16a is projected on the surface of the product wafer 11 (or the assembly wafer) by the action of the illumination relay lens 17 and the first objective lens 19.
[0030]
Then, reflected light L2 is generated from the area of the product wafer 11 (or assembly wafer) irradiated with the above-mentioned illumination light L1. This reflected light L2 is guided to the first objective lens 19.
The first objective lens 19 collimates the reflected light L2 from the product wafer 11 (or the assembly wafer). The reflected light L2 collimated by the first objective lens 19 passes through the beam splitter 18 and enters the second objective lens 20. The second objective lens 20 focuses the reflected light L2 from the beam splitter 18 on the primary imaging surface 10a.
[0031]
The second objective lens 20 is supported so as to be shiftable in a plane perpendicular to the optical axis O2. The adjustment of the shift state of the second objective lens 20 is performed using the above-described line & space mark 33 (FIG. 3) when assembling the overlay measurement apparatus 10.
In this way, the reflected light L2 from the product wafer 11 (or the assembly wafer) irradiated with the illumination light L1 is guided to the second objective lens 20 via the first objective lens 19 and the beam splitter 18, and An image is formed on the primary imaging surface 10a by the action of the first objective lens 19 and the second objective lens 20. The primary imaging plane 10a is a position where an intermediate image on the product wafer 11 (or assembly wafer) is formed.
[0032]
The beam splitter 41 of the focus detection devices (41 to 48) disposed downstream of the primary imaging surface 10a transmits a part (L3) of the reflected light L2 from the second objective lens 20 and transmits the remaining light L2. The part (L4) is reflected. The light L3 transmitted through the beam splitter 41 is guided to the first imaging relay lens 21 of the imaging optical system (19 to 23).
The first imaging relay lens 21 collimates the light L3 from the beam splitter 41. The imaging aperture stop 22 is arranged on a plane conjugate with the pupil of the first objective lens 19, and limits the diameter of light from the first imaging relay lens 21 to a specific diameter. The imaging aperture stop 23 is supported so as to be shiftable in a plane perpendicular to the optical axis O2.
[0033]
Adjustment of the shift state of the imaging aperture stop 23 is performed using the above-described line & space mark 33 (FIG. 3) when assembling the overlay measurement apparatus 10. The second imaging relay lens 23 transmits the light from the imaging aperture stop 22 (to be precise, the light transmitted through the aberration correction plate 24 described below) to the imaging surface (secondary imaging surface) of the CCD imaging device 25. ).
[0034]
The aberration correction plate 24 is an optical element for correcting the residual aberration of the imaging optical system (19 to 23), and is located near the imaging aperture stop 23, that is, near a plane conjugate with the pupil of the first objective lens 19. Are located.
The aberration correction plate 24 is supported so as to be shiftable in a plane perpendicular to the optical axis O2, and is supported rotatably about the optical axis O2. Adjustment of the shift state and the rotation state of the aberration correction plate 24 is performed using the above-described line & space mark 33 (FIG. 3) when assembling the overlay measurement apparatus 10.
[0035]
The residual aberration of the imaging optical systems (19 to 23) and the method of manufacturing the aberration correction plate 24 will be specifically described later when the method of assembling the overlay measurement device 10 is described.
Thus, the light from the second objective lens 20 is guided to the second imaging relay lens 23 via the beam splitter 41, the first imaging relay lens 21, the imaging aperture stop 22, and the aberration correction plate 24. The relay imaging (re-imaging) is performed on the imaging surface of the CCD imaging device 25 by the operation of the first imaging relay lens 21 and the second imaging relay lens 23.
[0036]
The CCD image sensor 25 is an area sensor in which a plurality of pixels are two-dimensionally arranged, and picks up an image (reflection image) based on the reflected light L2 from the product wafer 11 (or an assembly wafer) and converts the image signal into an image. Output to the processing device 26. The image signal represents a distribution (luminance distribution) relating to a luminance value for each pixel on the imaging surface of the CCD imaging device 25.
[0037]
As described in detail later, when the product wafer 11 is mounted on the inspection stage 12, the image processing device 26 superimposes the product wafer 11 on the basis of the luminance distribution of the image signal obtained from the CCD image sensor 25. An alignment inspection (inspection of a superposition state of a resist pattern on a base pattern) is performed.
Further, as described in detail later, when the assembly wafer is mounted on the inspection stage 12, the image processing device 26 performs the following Q based on the luminance distribution of the image signal obtained from the CCD image sensor 25. The values (see FIGS. 5B to 5E) are measured. The Q value is an index for finely adjusting the illumination optical system (13 to 18), the imaging optical system (19 to 23), and the aberration correction plate 24, and is output to the optical element control device 27 as an index signal.
[0038]
As will be described in detail later, the optical element control device 27 controls the illumination optical system (13 to 13) based on an index signal from the image processing device 26 (a Q value described later (see FIGS. 5B to 5E)). 18) Fine adjustment of the imaging optical system (19 to 23) and the aberration correction plate 24. That is, the shift state of the illumination aperture stop 14, the second objective lens 20, and the imaging aperture stop 23, and the shift state and the rotation state of the aberration correction plate 24 are adjusted as necessary.
[0039]
The focus detection devices (41 to 48) move the product wafer 11 on the inspection stage 12 with respect to the imaging surface of the CCD imaging element 25 at the time of the overlay inspection of the product wafer 11 (inspection of the overlapping state of the resist pattern with the base pattern). To detect whether or not the subject is in focus.
The focus detection devices (41 to 48) include a beam splitter 41, an AF first relay lens 42, a parallel plane plate 43, a pupil division mirror 44, an AF second relay lens 45, and a cylindrical lens which are sequentially arranged along the optical axis O3. 46, an AF system 47, and a signal processing unit 48.
[0040]
The reflection / transmission surface of the beam splitter 41 is inclined by approximately 45 ° with respect to the optical axis O3, and is also arranged on the optical axis O2 of the imaging optical system (19 to 23). The optical axis O3 is perpendicular to the optical axis O2. The AF sensor 47 is a line sensor, and a plurality of pixels are one-dimensionally arranged on an imaging surface 47a. The cylindrical lens 46 has a refractive power in a direction perpendicular to the pixel arrangement direction (direction A in the drawing) on the imaging surface 47a of the AF sensor 47.
[0041]
The light L4 (hereinafter, referred to as “AF light”) reflected by the beam splitter 41 is collimated by the AF first relay lens 42, passes through the plane parallel plate 43, and enters the pupil division mirror 44. An image of the illumination aperture stop 14 of the illumination optical system (13 to 18) is formed on the pupil division mirror 44. The parallel plane plate 43 is an optical element for adjusting the position of the image of the illumination aperture stop 14 at the center of the pupil division mirror 44, and has a mechanism capable of tilt adjustment.
[0042]
The AF light that has entered the pupil splitting mirror 44 is split there into light in two directions, and then condensed near the imaging surface 47a of the AF sensor 47 via the AF second relay lens 45 and the cylindrical lens 46. . At this time, two light source images are formed on the imaging surface 47a at positions separated along the pixel arrangement direction (A direction in the drawing).
Then, the AF sensor 47 outputs information on the image forming centers P1 and P2 (FIGS. 4A to 4C) of the two light source images formed on the imaging surface 47a to the signal processing unit 48 as detection signals. 4A, 4B, and 4C show a front focus state, a focus state, and a rear focus state of the product wafer 11 on the inspection stage 12 with respect to the CCD image sensor 25, respectively.
[0043]
As can be seen from FIGS. 4A to 4C, the image forming centers P1 and P2 of the two light source images are closer to each other in the front focus state (lower than the focus state), and are closer to the rear focus state (focus position). Above). That is, by moving the inspection stage 12 up and down in the Z direction, the inspection stage 12 approaches and separates along the pixel arrangement direction (the A direction in the drawing) of the imaging surface 47a.
[0044]
The signal processing unit 48 calculates the distance between the image forming centers P1 and P2 of the two light source images based on the detection signal from the AF sensor 47. The distance between the image forming centers P1 and P2 in the focused state is stored in the signal processing unit 48 in advance. For this reason, the signal processing unit 48 compares the calculated distance between the imaging centers P1 and P2 with the distance in the focused state, calculates the difference between the two, and sends the obtained focus position signal to the stage control device 49. Output.
[0045]
Finally, the stage control device 49 will be described.
The stage control device 49 controls the XY drive unit of the inspection stage 12 to align the holder (the product wafer 11) in the XY direction during the overlay inspection of the product wafer 11 (inspection of the overlay state of the resist pattern with respect to the base pattern). The overlay mark 30 (FIG. 2) on the product wafer 11 is moved and positioned in the field of view of the overlay measurement apparatus 10.
[0046]
Then, the Z drive unit of the inspection stage 12 is controlled based on the focus position signals from the focus detection devices (41 to 48), and the holder (product wafer 11) is moved up and down in the Z direction. As a result, the product wafer 11 can be focused on the CCD image sensor 25 (automatic focusing).
Further, when assembling the overlay measurement device 10, the stage control device 49 controls the XY drive unit of the inspection stage 12 to move the holder (assembly wafer) in the XY directions, and to set the line and space on the assembly wafer. The mark 33 (FIG. 3) is positioned within the field of view of the overlay measurement device 10. Then, the Z drive unit of the inspection stage 12 is controlled to move the holder (assembly wafer) up and down in the Z direction within a predetermined range.
[0047]
The above-described illumination optical system (13 to 18) and the first objective lens 19 correspond to an “illumination optical system” in the claims. The imaging optical systems (19 to 23) correspond to “imaging optical systems”. Among the imaging optical systems (19 to 23), the first objective lens 19 and the second objective lens 20 correspond to a “first optical system”. The first imaging relay lens 21 and the second imaging relay lens 23 correspond to a “second optical system”.
[0048]
The aberration correction plate 24 corresponds to a “correction member” in the claims. The CCD imaging device 25 corresponds to “imaging means”. The image processing device 26 corresponds to “calculating means” and “generating means” in the claims. The optical element control device 27 corresponds to “control means” in the claims.
Next, a method of assembling the overlay measurement device 10 will be described.
[0049]
In the present embodiment, in order to accurately detect the center position C1 of the base mark 31 and the center position C2 of the registration mark 32 in FIG. 2 at the time of the overlay inspection of the product wafer 11, it is disclosed in JP-A-2000-77295. The overlay measurement apparatus 10 is assembled using the QZ method. That is, fine adjustment of the illumination optical system (13 to 18), the imaging optical system (19 to 23), and the aberration correction plate 24 is performed.
[0050]
Incidentally, at the time of assembling the overlay measuring apparatus 10, an assembling wafer having the line & space mark 33 (FIG. 3) is placed on the holder of the inspection stage 12. In the vicinity of the imaging aperture stop 23 of the imaging optical system (19 to 23), an unprocessed aberration correction plate 24 (hereinafter, referred to as “parallel plane plate 24”) is arranged. The parallel plane plate 24 is an optical member made of quartz glass.
[0051]
When the line & space mark 33 (FIG. 3) of the wafer for assembly is positioned in the field of view of the overlay measuring device 10, the line & space mark 33 is illuminated by the illumination light L1 and the CCD image sensor 25 An image of the line & space mark 33 is formed on the imaging surface.
At this time, an image signal corresponding to the light intensity (brightness) of the image of the line & space mark 33 is output from the CCD image pickup device 25 to the image processing device 26 as shown in FIG. For this reason, the image processing device 26 measures the focus characteristic of the Q value as shown in FIG. 5B based on the luminance distribution of the image signal shown in FIG.
[0052]
That is, a plurality of edges appearing in the image signal (FIG. 5A) are extracted, a signal intensity difference ΔI between the left edge 36 and the right edge 37 is calculated, and the obtained signal intensity difference ΔI is converted into an arbitrary signal. The Q value represented by the following equation (1) is calculated by normalizing with the intensity I. The Q value represents the asymmetry between the left edge 36 and the right edge 37.
Q value = ΔI / I ₀ × 100 (%)… (1)
Further, such calculation of the Q value is performed every time the stage controller 49 moves the holder (assembly wafer) of the inspection stage 12 in the Z direction. As a result, it is possible to obtain a focus characteristic curve of the Q value as shown in FIG. The focus characteristic of the Q value is output to the optical element control device 27 as an index signal when finely adjusting the illumination optical system (13 to 18), the imaging optical system (19 to 23), and the aberration correction plate 24.
[0053]
Note that, in a state where the respective components (particularly, optical elements) of the overlay measurement apparatus 10 are merely arranged according to mechanical design values, the relative positional relationship between the respective components is largely shifted. Then, the focus characteristic curve of the Q value at this time greatly deviates from a predetermined standard value (for example, a state showing 0 regardless of the Z position) as shown in FIG. 5B.
[0054]
Here, in the focus characteristic curve of the Q value (FIG. 5B), the parallel shift component α shown in FIG. 5C is a component that fluctuates due to the shift adjustment of the illumination aperture stop 14. 5D is a component that fluctuates due to shift adjustment of the imaging aperture stop 23. Further, the tilt component γ shown in FIG. 5E is a component that fluctuates due to the shift adjustment of the second objective lens 20.
[0055]
The shift adjustment of the illumination aperture stop 14 corresponds to the correction of the inclination (illumination telecentric) of the principal ray of the illumination light L1. The shift adjustment of the imaging aperture stop 23 and the second objective lens 20 correspond to the correction of the eccentricity of the reflected light L2 and the correction of the eccentric coma in the imaging optical system (19 to 23), respectively.
Therefore, the optical element control device 27 first adjusts the shift of the illumination aperture stop 14, the imaging aperture stop 23, and the second objective lens 20 using the focus characteristic curve of the Q value (FIG. 5B) as an index. Perform (QZ method).
[0056]
The order of the adjustment is desirably the imaging aperture stop 23 → the second objective lens 20 → the illumination aperture stop 14. This is because the adjustment sensitivity of the imaging aperture stop 23 is the most sensitive, and when the unevenness component β (FIG. 5D) is large in the focus characteristic curve of the Q value, the adjustment amount of the second objective lens 20 is accurately determined. Because it is difficult.
Incidentally, even if the three adjustment elements (the second objective lens 20, the imaging aperture stop 23, and the illumination aperture stop 14) are sequentially shifted and adjusted, the focus characteristic curve of the Q value (see FIG. 5B) is determined in advance. It is difficult to converge to the specified value (for example, a state indicating 0 regardless of the Z position).
[0057]
That is, even if the three adjustment elements (20, 23, 14) are shift-adjusted, a third-order or higher undulation component remains in the focus characteristic curve of the Q value as shown in FIG. . This undulation component indicates that high-order aberration components (for example, fifth-order or higher coma components by the Zernike aberration expression method) of the imaging optical system (19 to 23) have not been removed yet and remain. I have.
[0058]
Therefore, in the method of assembling the overlay measurement device 10 of the present embodiment, first, the shift adjustment of the three adjustment elements (20, 23, 14) is performed to obtain the parallel shift component α (FIG. 5) from the focus characteristic curve of the Q value. (C)), the unevenness component β (FIG. 5D) and the inclination component γ (FIG. 5E) are all removed.
That is, only the undulation component (FIG. 6A) remains in the focus characteristic curve of the Q value. If the state of FIG. 6A does not converge in one adjustment cycle, it is desirable to repeat the same adjustment cycle. Thereby, low-order aberration components of the imaging optical system (19 to 23) can be removed.
[0059]
Then, using an interferometer (not shown) prepared outside the overlay measurement apparatus 10, the residual aberration of the imaging optical system (19 to 23), that is, a higher-order aberration component (for example, Zernike aberration expression) 5th or higher order coma aberration component). As is well known, the measurement of the aberration of the imaging optical system (19 to 23) by the interferometer is the measurement of the transmitted wavefront aberration.
[0060]
At this time, not only the imaging optical system (19 to 23) but also other optical elements (beam splitters 18, 41 and the plane-parallel plate 24) arranged on the optical axis O2 are included in the imaging optical system. The residual aberration of the system (19 to 23) is measured. Therefore, it is necessary to move these optical elements to the interferometer while maintaining the relative positional relationship between the imaging optical systems (19 to 23), the beam splitters 18 and 41, and the parallel plane plate 24.
[0061]
When the aberration measurement by the interferometer is completed, the parallel plane plate 24 (unprocessed aberration correction plate 24) is taken out from the optical axis O2 of the imaging optical system (19 to 23). And uneven processing is performed. The processing surface of the parallel plane plate 24 may be only one surface or both surfaces.
[0062]
The depth (amount of processing) of the concavo-convex processing corresponds to the phase difference that cancels out the residual aberration of the imaging optical system (19 to 23). (2) It can be calculated by a computer based on the wavelength of the light used for the aberration measurement and (3) the refractive index of the material (quartz glass) of the parallel flat plate 24.
As a method of processing the unevenness on the parallel plane plate 24, for example, a plasma processing method disclosed in Japanese Patent Application Laid-Open No. 9-63791 can be used. This plasma processing is performed by a plasma processing machine using a radical reaction. Here, a procedure for performing the concavo-convex processing on the parallel flat plate 24 by plasma processing using a radical reaction will be briefly described.
[0063]
First, under high pressure, a plasma is generated from a processing electrode provided near the parallel flat plate 24 as a workpiece. A reaction gas having a high electronegativity such as halogen is supplied to the plasma. As a result, the reaction gas is dissociated into radicals having high reactivity.
Then, the radicals are reacted with the surface of the plane-parallel plate 24, and the products generated by the reaction are continuously vaporized, whereby the plane-parallel plate 24 is processed. As the reaction gas, a gas having a property of reacting with the parallel flat plate 24 and evaporating the product is selected and used.
In this processing method, plasma is generated under a high pressure, so that a radical having a higher concentration than before can be generated. Therefore, there is an effect that a high processing speed comparable to mechanical processing can be obtained.
[0064]
In addition, since it is under a high pressure, localized plasma can be generated only at a portion where the electric field intensity around the processing electrode is high. As a result, the processing region can be limited to the vicinity of the processing electrode, and an effect of achieving processing with extremely high spatial resolution depending on the processing electrode shape can be obtained.
[0065]
Furthermore, in the mechanical processing, since physical phenomena such as plastic deformation and brittle fracture are used, the surface of the parallel flat plate 24 is damaged by the processing. On the other hand, in the plasma processing, since the processing proceeds chemically, there is obtained an effect that no defect or thermally altered layer is formed on the surface of the parallel flat plate 24 and no distortion occurs.
In this way, by the above-described plasma processing, the concave and convex processing for canceling the residual aberration of the imaging optical system (19 to 23) is performed on the parallel flat plate 24, and the fabrication of the aberration correction plate 24 is completed. Then, the processed parallel flat plate 24 is used as the aberration correction plate 24.
[0066]
Next, the aberration correction plate 24 manufactured by the plasma processing is returned to the original position. That is, the aberration correction plate 24 is disposed again near the imaging aperture stop 23 of the imaging optical system (19 to 23). In addition, while maintaining the relative positional relationship between the aberration correction plate 24, the imaging optical systems (19 to 23), and the beam splitters 18 and 41, these optical elements are placed in the overlay measuring device 10. .
[0067]
In this state, it is considered that the residual aberration of the imaging optical system (19 to 23) has been corrected to some extent, but it is not yet an optimal state. Therefore, at the end of the assembling process of the overlay measurement apparatus 10, fine adjustment of the aberration correction plate 24 is performed using the same QZ method as described above. At this time, the index signal corresponding to the residual aberration of the entire system including the imaging optical systems (19 to 23) and the aberration correction plate 24 is provided to the optical element control device 27 by the focus characteristic of the Q value (FIG. 6A). Reference).
[0068]
For this reason, the optical element control device 27 adjusts the shift and / or rotation of the aberration correction plate 24 using the focus characteristic of the Q value according to the residual aberration of the entire system (19 to 24) as an index, and adjusts the Q value. The swell component shown in FIG. 6A is removed from the focus characteristics. As a result, as shown in FIG. 6B, the focus characteristic curve of the Q value can be made to converge to a predetermined standard value (for example, a state showing 0 regardless of the Z position).
[0069]
When the fine adjustment of the aberration correction plate 24 is completed, the assembling process of the overlay measurement apparatus 10 ends. At this time, the residual aberration of the imaging optical system (19 to 23) is almost completely corrected by the aberration correction plate 24 (see FIG. 6B), and the relative positional relationship of each component of the overlay measurement apparatus 10 is obtained. The optimal state can be ensured. That is, it is possible to obtain a low-aberration optical system (19 to 24) from which a high-order aberration component (for example, a fifth-order or higher-order coma aberration component by the Zernike aberration expression method) is removed.
[0070]
Then, in this optimum state, the overlay inspection of the product wafer 11 (the inspection of the overlay state of the resist pattern with respect to the underlying pattern) is performed. At the time of overlay inspection, the product wafer 11 is placed on the inspection stage 12, and the overlay mark 30 (FIG. 2) on the product wafer 11 is positioned in the visual field of the overlay measuring device 10.
[0071]
Then, the overlay mark 30 is illuminated by the illumination light L1, and an image of the overlay mark 30 is formed favorably on the imaging surface of the CCD image sensor 25 via the low-aberration optical system (19 to 24). You. At this time, the CCD imaging device 25 captures an image of the overlay mark 30 and outputs an image signal corresponding to the light intensity of the image to the image processing device 26.
[0072]
When an image signal relating to the image of the overlay mark 30 (FIG. 2) is input from the CCD image pickup device 25, the image processing device 26 extracts a plurality of edges appearing in the image, and extracts the center position C1 of the base mark 31 and the registration position. The center position C2 of the mark 32 is calculated. An edge is a point where the intensity of an image signal changes rapidly.
Further, when inspecting the superposition state of the resist pattern with respect to the base pattern of the product wafer 11, the image processing apparatus 26 detects the misalignment based on the difference between the center position C1 of the base mark 31 and the center position C2 of the registration mark 32. Calculate the quantity R. The overlay displacement amount R is expressed as a two-dimensional vector of the surface of the product wafer 11.
[0073]
In the overlay measurement apparatus 10 of the present embodiment, at the time of assembly, the residual aberration of the imaging optical system (19 to 23) is corrected by the aberration correction plate 24, and a higher-order aberration component (for example, fifth or higher order by Zernike aberration expression method) Coma aberration component) is also removed.
Therefore, the error TIS caused by the apparatus can be reliably reduced, and the center position C1 of the base mark 31 and the center position C2 of the registration mark 32 can be detected with high accuracy. As a result, the overlay deviation amount R can be measured with high accuracy.
[0074]
Therefore, according to the overlay measuring apparatus 10 of the present embodiment, the overlay state of the product wafer 11 can be inspected with high accuracy, and the product yield can be further improved.
Further, in the overlay measurement apparatus 10 of the present embodiment, since the fine adjustment of the aberration correction plate 24 using the QZ method is performed in a state where the aberration correction plate 24 is incorporated in the overlay measurement apparatus 10, the relative positional relationship between the components is ensured. To an optimal state.
[0075]
(Modification)
In the above-described embodiment, the fine adjustment (position adjustment) of the aberration correction plate 24 is performed using the QZ method, but the present invention is not limited to this. For example, the interferometer used for measuring the residual aberration of the imaging optical system (19 to 23) measures the transmission while measuring the residual aberration of the entire system including the imaging optical system (19 to 23) and the aberration correction plate 24. Fine adjustment of the aberration correction plate 24 may be performed so that the wavefront aberration becomes zero.
[0076]
In the above-described embodiment, the residual aberration of the imaging optical systems (19 to 23) is measured using an interferometer (not shown) provided outside the overlay measurement apparatus 10. In the state where (19 to 23) are incorporated in the overlay measurement device 10, direct measurement can also be performed. In this case, in order to dispose the interferometer, it is necessary to retract at least the inspection stage 12 and the CCD image sensor 25.
[0077]
Further, in the above-described embodiment, the aberration correction plate 24 is manufactured by using the plasma processing method based on the radical reaction, but the present invention is not limited to this. Any other processing method may be used. However, when the plasma processing method using the radical reaction is used, at least one surface of the aberration correction plate 24 may be a highly accurate uneven surface corresponding to the residual aberration of the imaging optical system (19 to 23). It is preferable because it is possible.
[0078]
In the above-described embodiment, the aberration correction plate 24 is arranged in the relay optical system (21 to 23) on the optical axis O2 of the imaging optical system (19 to 23). May be arranged in the optical system (19, 20) at the preceding stage (for example, the pupil plane of the first objective lens 19).
However, if the first objective lens 19 is to be arranged on the pupil plane, the space and mechanism of the aberration correction plate 24 must be taken into consideration when designing the first objective lens 19, and the load is large. Therefore, it is preferable to dispose the aberration correction plate 24 in the relay optical system (21 to 23) as in the present embodiment.
[0079]
Further, in the above-described embodiment, the illumination aperture stop 14, the second objective lens 20, the imaging aperture stop 23, and the aberration correction plate 24 are finely adjusted when assembling the overlay measurement apparatus 10, but the overlay of the product wafer 11 is adjusted. Similar fine adjustment may be performed immediately before the inspection. The means for supporting the aberration correction plate 24 so as to be shiftable and rotatable may be incorporated as a component of the overlay measurement apparatus 10 or may be an external mechanism.
[0080]
In the above-described embodiment, the optical element control device 27 automatically performs fine adjustment of the illumination optical system (13 to 18), the imaging optical system (19 to 23), and the aberration correction plate 24. Although the center positions C1 and C2 of the base mark 31 and the registration mark 32 of the registration mark 30 and the registration deviation amount R have been detected, the present invention can also be applied to an apparatus that performs manual adjustment and position detection. . In this case, the optical element control device 27 of the overlay measurement device 10 is omitted.
[0081]
Furthermore, in the above-described embodiment, the overlay measurement apparatus 10 has been described as an example, but the present invention is not limited to this. For example, the present invention can be applied to an apparatus (alignment system of an exposure apparatus) for performing alignment between a mask and a product wafer 11 before an exposure step of printing a circuit pattern formed on a mask onto a resist film. In this case, the position of the alignment mark formed on the product wafer 11 can be accurately detected. Further, the present invention can be applied to an apparatus for detecting an optical displacement between a single mark and a reference position of a camera.
[0082]
【The invention's effect】
As described above, according to the present invention, the error TIS caused by the apparatus can be reliably reduced, and the position of the test mark can be detected with higher accuracy.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an overall configuration of an overlay measurement apparatus 10. FIG.
FIG. 2 is a plan view (a) and a cross-sectional view (b) of an overlay mark 30 formed on a product wafer 11;
FIG. 3 is a plan view (a) and a cross-sectional view (b) of a line & space mark 33 formed on a wafer to be assembled.
FIG. 4 is a diagram illustrating an automatic focusing mechanism of the overlay measurement apparatus 10.
FIG. 5 is a diagram illustrating a method of finely adjusting the optical system (14, 20, 22) by the QZ method.
FIG. 6 is a diagram illustrating a fine adjustment method of the aberration correction plate 24 by the QZ method.
[Explanation of symbols]
10 Overlay measuring device
11 Product wafer
12 Inspection stage
13 Light source
14 Illumination aperture stop
15 Condenser lens
16 Field stop
17 Lighting relay lens
18 Beam splitter
19 1st objective lens
20 Second objective lens
21 1st imaging relay lens
22 Imaging aperture stop
23 Second imaging relay lens
24 Aberration correction plate
25 CCD image sensor
26 Image processing device
27 Optical element controller
30 overlay mark
33 Line & Space Mark
49 Stage control device

Claims (6)

An illumination optical system that illuminates the test mark on the substrate;
An imaging optical system that forms an image of the test mark by imaging light from the test mark;
A correction member that is arranged on the optical axis of the imaging optical system and corrects a residual aberration of the imaging optical system;
An imaging unit configured to capture an image of the test mark formed via the imaging optical system and the correction member, and output an image signal;
A mark position detecting device, comprising: a calculating unit that receives the image signal from the imaging unit and calculates a position of the test mark. The mark position detecting device according to claim 1,
The imaging optical system has a first optical system that forms an intermediate image of the test mark, and a second optical system that relay-images the intermediate image,
The mark position detecting device, wherein the correction member is disposed in the second optical system. The mark position detecting device according to claim 1 or 2,
A mark position detection device, comprising: a support unit that supports the correction member so as to be rotatable about an optical axis of the imaging optical system and to be shiftable in a plane perpendicular to the optical axis. The mark position detecting device according to claim 3,
Generating means for generating an index signal according to the residual aberration of the entire system including the imaging optical system and the correction member,
A mark position detecting device comprising: a control unit that controls at least one of a rotation state and a shift state of the correction member by controlling the support unit based on the index signal. A method for assembling the mark position detecting device according to any one of claims 1 to 4,
In a state where an unprocessed optical member is arranged at a predetermined position on the optical axis of the imaging optical system, a measurement step of measuring residual aberration of the imaging optical system,
A manufacturing process of manufacturing the correction member by removing the optical member from the predetermined position after the measurement process and performing unevenness processing on the optical member so as to cancel residual aberration of the imaging optical system; When,
A fine adjustment step of repositioning the correction member manufactured in the manufacturing step at the predetermined position and finely adjusting the correction member. The method for assembling a mark position detecting device according to claim 5,
In the fine adjustment step, based on an index signal corresponding to a residual aberration of the entire system including the imaging optical system and the correction member, the rotational state of the correction member about the optical axis of the imaging optical system, Adjusting the shift state of the correction member in a plane perpendicular to the optical axis.

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