WO2004019389A1

WO2004019389A1 - Mark position detection device, mark position detection method, superimposing measurement device, and superimposing measurement method

Info

Publication number: WO2004019389A1
Application number: PCT/JP2003/010582
Authority: WO
Inventors: Hiroshi Aoki
Original assignee: Nikon Corporation
Priority date: 2002-08-22
Filing date: 2003-08-21
Publication date: 2004-03-04
Also published as: JP2004079970A; AU2003264338A1; TW200405427A; JP4178875B2

Abstract

When detecting a mark position on a substrate, it is possible to accurately detect the mark position even if a waveform of an edge signal associated with the edge pair of the mark is asymmetric. In an image processing device (19), one or more sample points contained in the edge signal are removed so as to correct the edge signal asymmetry. According to the edge signal after correction, a waveform for calculating correlation is decided, this waveform is folded, and the maximum correlation value in the correlation function with respect to the folded waveform is calculated, thereby calculating the center position of the mark.

Description

Description Mark position detecting device, mark position detecting method, overlay measuring device, and overlay measuring method

The present invention relates to a mark position detecting device for detecting the position of a test mark on a substrate, a mark position detecting method, an overlay measuring device, and an overlay measuring method. The present invention relates to a mark position detection device suitable for position detection and the like. Background 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 developing process of dissolving an exposed portion or an unexposed portion of the resist film are included. After that, the circuit pattern (resist pattern) is transferred to the resist film, and the resist pattern is used as a mask to perform etching or vapor deposition (processing step), thereby forming a predetermined pattern immediately adjacent to the resist film. The circuit pattern is transferred to the material film (pattern forming step).

Next, in order to form another circuit pattern on the circuit pattern formed on the predetermined material film, a similar pattern forming step is repeated. By repeating the pattern formation process many times in this way, circuit patterns of various material films are laminated on a substrate (semiconductor wafer or liquid crystal substrate), and the circuit of a semiconductor element or a liquid crystal display element is formed. Is formed.

By the way, in the above manufacturing process, in order to accurately overlap circuit patterns of various material films, alignment between a mask and a substrate is performed before an exposure process in each pattern forming process, and further, after a developing process. At the same time, prior to the fabrication process, we inspect the superposition of the resist patterns on the substrate to improve product yield.

Incidentally, the alignment between the mask and the substrate (before the exposure process) This is an alignment between the circuit pattern and the circuit pattern formed on the substrate in the previous pattern forming step, and is performed using an alignment mark indicating a reference position of each circuit pattern.

• Inspection of the superposition state of the resist pattern on the substrate (before the processing step) is performed by superimposing the resist pattern on the circuit pattern (hereinafter referred to as “base pattern”) formed in the previous pattern formation step. This is an alignment detection, which is performed using an overlay mark indicating a reference position of each of the base pattern and the resist pattern. To detect the position of these alignment marks and overlay marks (generally referred to as “test marks”), the test marks are positioned within the field of view of the apparatus, and are detected using an image sensor such as a CCD camera. An image of the inspection mark is taken, and the detection is performed based on an edge signal among the obtained image signals. Note that the image signal represents a distribution relating to a luminance value for each pixel on the imaging surface of the imaging element. The edge signal is a sudden change in the luminance value of the image signal.

In calculating the position of the test mark from the edge signal, a well-known algorithm called a correlation method is used. In the correlation method, since the correlation operation is performed using the entire edge signal waveform, it is hardly affected by signal noise, and the position of the test mark can be calculated with good reproducibility.

However, the correlation method is an algorithm on the assumption that the waveform of the edge signal is symmetric. For this reason, when the symmetry of the waveform of the edge signal is reduced, an error increases when calculating the position of the test mark. That is, the position of the test mark cannot be accurately detected. The symmetry of the waveform of the edge signal may be reduced even when the shape of the edge pair of the test mark is symmetrical. Disclosure of the invention

An object of the present invention is to provide a mark position detecting device, a mark position detecting method, a mark position detecting method, an overlay measuring device, which can accurately detect the position of a test mark even if the waveform of an edge signal relating to an edge pair of the test mark is asymmetric. And to provide an overlay measurement method.

The mark position detecting device of the present invention includes one or more edge pairs formed on a substrate. Illuminating means for illuminating the test mark; imaging means for capturing an image based on light from the test mark and outputting an image signal composed of a plurality of sample points; and a sudden change in the luminance value of the image signal And a detecting means for detecting a center position of the test mark based on the edge signal, wherein the detecting means comprises: A correction unit that corrects the asymmetry of the edge signal by removing one or more of the sample points included in the edge signal; a waveform based on the edge signal corrected by the correction unit; Calculating means for calculating the center position by calculating a maximum correlation value in a correlation function with a waveform obtained by folding back.

In this mark position detecting device, the waveform of the edge signal after the asymmetry has been corrected by the correcting means (that is, a symmetrical waveform) is used, so that the position of the test mark can be detected with high accuracy.

Another mark position detection device of the present invention includes: an illumination unit that illuminates a test mark including one or more edge pairs formed on a substrate; and an image based on light from the test mark. Imaging means for outputting an image signal composed of the following sample points: extracting means for extracting a sudden change in luminance value from the image signal as an edge signal relating to the edge pair; and extracting the image signal based on the edge signal. Detection means for detecting the center position of the detection mark, wherein the detection means corrects the edge signal by removing one or more of the sample points included in the edge signal. The maximum correlation in the correlation function between the correction means, a waveform for calculation based on the edge signal before correction or the edge signal after correction by the correction means, and a waveform obtained by folding the waveform for calculation. First calculating means for calculating the maximum correlation value, and selecting means for selecting the largest one of the plurality of maximum correlation values calculated by the first calculating means using each of a plurality of different calculation waveforms. Second calculating means for calculating the center position based on one maximum correlation value selected by the selecting means.

Since the mark position detection device uses a calculation waveform (ie, a symmetrical waveform) having the largest correlation function maximum correlation value among a plurality of different calculation waveforms, the position of the test mark is accurately detected. be able to.

Preferably, in the mark position detection device according to the present invention, the detection unit may be configured to perform the correction before the correction. Comparing means for comparing the maximum correlation value calculated by the first calculating means with a predetermined threshold value using the calculation waveform based on the edge signal, wherein the correcting means As a result, when the maximum correlation value based on the uncorrected edge signal is smaller than the threshold value, the edge signal is corrected.

A mark position detection method according to the present invention includes: an illumination step of illuminating a test mark including one or more edge pairs formed on a substrate; and capturing an image based on light from the test mark. An imaging step of outputting an image signal composed of sample points; an extraction step of extracting a rapidly changing portion of a luminance value from the image signal as an edge signal relating to the edge pair; and the test mark based on the edge signal. A detection step for detecting the center position of the edge signal, wherein the detecting step corrects the asymmetry of the edge signal by removing one or more of the sample points included in the edge signal. Calculating a maximum correlation value in a correlation function between a correction step, a waveform based on the edge signal after the correction in the correction step, and a waveform obtained by folding the waveform. And calculating the center position.

In this mark position detection method, the waveform of the edge signal after the asymmetry has been corrected in the correction step (that is, a symmetrical waveform) is used, so that the position of the mark to be detected can be detected accurately.

Another mark position detection method of the present invention includes: an illumination step of illuminating a test mark including one or more edge pairs formed on a substrate; capturing an image based on light from the test mark; An imaging step of outputting an image signal composed of sample points of the following; an extraction step of extracting a rapidly changing portion of a luminance value from the image signal as an edge signal relating to the edge pair; A detection step of detecting a center position of a detection mark, wherein the detection step corrects the edge signal by removing one or more sample points included in the edge signal. The maximum phase in a correlation function between a correction process, a waveform for calculation based on the edge signal before correction or the edge signal after correction in the correction process, and a waveform obtained by folding the waveform for calculation. A first calculation step of calculating a value, most magnitude among the plurality of the maximum correlation value calculated by the first calculation step with each of a plurality of different said operational waveform And a second calculating step of calculating the center position based on the one maximum correlation value selected in the selecting step.

In this mark position detection method, among a plurality of different operation waveforms, the operation waveform having the largest correlation function maximum correlation value (that is, a symmetrical waveform) is used, so that the position of the target mark is accurately detected. be able to.

Preferably, in the mark position detecting method according to the present invention, in the detecting step, the maximum correlation value calculated in the first calculating step using the calculation waveform based on the uncorrected edge signal is determined in advance. A comparison step of comparing the maximum correlation value based on the edge signal before the correction with the maximum correlation value smaller than the threshold value as a result of the comparison in the comparison step. , Correction for the edge signal.

An overlay measurement apparatus according to the present invention is an overlay measurement apparatus for inspecting an overlay state of a plurality of patterns formed on a substrate, wherein a center position of a test mark indicating a reference position of each of the plurality of patterns is determined. A mark position detecting device for detecting each of the mark positions; and a measuring means for measuring an amount of misalignment of the plurality of patterns based on a difference between the respective center positions detected by the mark position detecting device. Things.

In this overlay measurement device, since the position of each test mark can be detected with high accuracy, a highly accurate measurement result of the overlay deviation amount between a plurality of patterns can be obtained.

An overlay measurement method according to the present invention is directed to an overlay measurement method for detecting an overlay state of a plurality of patterns formed on a substrate by using the above mark position detection method. Detecting a center position of a test mark indicating a reference position of each of the patterns, and superimposing the plurality of patterns based on a difference between the respective center positions detected in the detection step. The method further includes a measuring step of measuring a shift amount.

In this overlay measurement method, since the position of each test mark can be accurately detected, a highly accurate measurement result of the overlay displacement amount between a plurality of patterns can be obtained. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing the overall configuration of the overlay measurement device 10.

FIG. 2 is a plan view (a) of the overlay mark 30 formed on the wafer 11 and diagrams (b :) to (d) illustrating images in the observation area.

FIG. 3 is a diagram showing an example of a representative waveform (a) and a waveform (b) of an edge signal in a standard overlay mark 30.

FIG. 4 is a diagram showing an example of a representative waveform (a) and a waveform (b) of an edge signal in a standard overlay mark 30.

FIG. 5 is a diagram showing an example of a representative waveform (a) and a waveform (b) of an edge signal in the superimposition mark 30 in the proximity state.

FIG. 6 is a diagram showing an example of the representative waveform (a) and the waveform (b) of the edge signal in the superimposition mark 30 in the proximity state.

FIG. 7 is a flowchart showing a procedure of position detection in the overlay measurement device 10.

FIG. 8 is a diagram illustrating a waveform example of an edge signal after the symmetry is improved.

FIG. 9 is a diagram for explaining an improvement in symmetry and an improvement in detection accuracy.

FIG. 10 is a diagram showing an overlay mark (a) having a large size difference between the frame mark and the box mark and a small overlay mark (b). BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. ° Here, the mark position detection device of the present embodiment will be described using the overlay measurement device 10 shown in FIG. 1 as an example.

As shown in FIG. 1, the overlay measurement apparatus 10 includes a detection stage 12 that supports the wafer 11 and an illumination optical system (13 to 13) that emits illumination light L1 toward the wafer 11 side. 1

5), an imaging optical system (16, 17) for forming an image of the wafer 11, a CCD image sensor 18, and an image processing device 19.

Before specifically describing the overlay measurement apparatus 10, the wafer 11 (base Plate).

On the wafer 11, a plurality of circuit patterns (all not shown) are laminated on the surface. The uppermost circuit pattern is the resist pattern transferred to the resist film. In other words, the wafer 11 is in the process of forming another circuit pattern on the underlying pattern formed in the previous pattern forming process (exposure to the resist film, etching of the material film, and etching of the material film). Before).

Then, the superposition state of the resist pattern with respect to the base pattern of the wafer 11 is inspected by the superposition measuring device 10. For this reason, on the surface of the wafer 11, an overlay mark 30 (FIG. 2 (a)) used for the inspection of the overlay state is formed. FIG. 2A is a plan view of the overlay mark 30.

The overlay mark 30 is composed of an outer frame mark 31 and an inner box mark 32, and one of the frame mark 31 and the box mark 32 is a base mark and the other is a resist mark. The base mark and the resist mark are formed simultaneously with the base pattern and the resist pattern, respectively, and indicate the reference positions of the base pattern and the resist pattern.

The frame mark 31 includes two edge pairs E 1 and, 2 in the X direction. One edge pair Ε 1 is composed of a left edge E 1 (L) and a right edge Ε 1 (R), and the other edge pair E 2 is a left edge E 2 (L) and a right edge. E 2 (R). That is, the frame mark 31 has two edges E 1 (L) and E 2 (L) on the left side and two edges E 1 (R) and E 2 (R) on the right side. The same applies to the Y direction of the frame mark 31.

The box mark 32 includes one edge pair E 3 in the X direction. The edge pair E 3 is composed of a left edge E 3 (L) and a right edge E 3 (R). That is, the box mark 32 has one edge E 3 (L) on the left side and one edge E 3 (R) on the right side. The same applies to the Y direction of the box mark 32. The frame mark 31 and the box mark 32 respectively correspond to the “test mark” in the claims.

Although not shown, a material film to be processed is formed between the resist mark and the resist pattern, and the base mark and the base pattern. When the registration mark is accurately superimposed on the underlying mark after the inspection of the overlay state by the overlay measuring device 10 and the resist pattern is accurately overlaid on the underlying pattern, It is actually processed through the resist pattern.

Next, the specific configuration of the overlay measurement apparatus 10 (FIG. 1) will be described.

The inspection stage 12 of the overlay measurement device 10 holds the wafer 11 in a horizontal state and can be moved to an arbitrary position in a horizontal plane. By moving the inspection stage 12, the observation area including the overlay mark 30 (FIG. 2 (a)) of the wafer 11 is positioned within the field of view of the imaging optical system (16, 17). The normal direction of the inspection stage 12 is the Z direction, and the mounting surface of the wafer 11 is the XY surface.

The illumination optical system (13 to 15) is composed of a light source 13, an illumination lens 14, and a prism 15, and the prism 15 is on the optical axis O2 of the imaging optical system (16, 17). Placed in The optical axis ◦2 of the imaging optical system (16, 17) is parallel to the Z direction. The reflection / transmission surface 15 a of the prism 15 is inclined at approximately 45 ° with respect to the optical axis O 2. The optical axis O l of the illumination optical system (1 3-1 5) is perpendicular to the optical axis O 2 of the imaging optical system (16, 17).

The imaging optical system (16, 17) is an optical microscope section composed of an objective lens 16 and an imaging lens 17, and the objective lens 16 is connected between the detection stage 12 and the prism 15 Placed between. The imaging lens 17 is an optical element that functions as a second objective lens, and is disposed on the opposite side of the prism 15 from the objective lens 16.

In the illumination optical system (13 to 15) and the imaging optical system (16, 17), the light emitted from the light source 13 is guided to the prism 15 via the illumination lens 14, and After being reflected by the reflection transmitting surface 15a (illumination light L1), it is guided to the objective lens 16 side. After passing through the objective lens 16 (illumination light L 2), the light enters the wafer 11 on the inspection stage 12. At this time, the observation area of the wafer 11 is almost vertically illuminated by the illumination light L2.

Then, from the observation area of the wafer 11 irradiated with the illumination light L2, reflected light L3 is generated according to the uneven structure (overlap mark 30) there. The reflected light L 3 is guided to the imaging lens 17 via the objective lens 16 and the prism 15, and the imaging surface of the CCD imaging device 18 is operated by the action of the objective lens 16 and the imaging lens 17. Image on top Is done. At this time, an enlarged image (reflection image) based on the reflected light L3 is formed on the imaging surface of the CCD imaging device 18.

The CCD image sensor 18 is an area sensor in which a plurality of pixels are two-dimensionally arranged, captures a reflection image on an imaging surface, and outputs an image signal to the image processing device 19. The image signal is composed of a plurality of sample points, and represents a distribution (luminance distribution) relating to the luminance value of each pixel on the imaging surface of the CCD imaging device 18.

The above-mentioned illumination optical system (13 to 15) and the objective lens 16 correspond to the “illuminating means” in the claims. The imaging optical system (16, 17) and the CCD imaging device 18 correspond to the "imaging means" in the claims. The image processing device 19 corresponds to “extraction means” and “detection means” in the claims.

The image processing device 19 captures, as an image, a reflection image of the observation area (including the overlay mark 30) of the wafer 11 based on the image signal from the CCD image sensor 18. Here, as shown in FIG. 2 (b), the image of the observation region of the wafer 11 includes three edge images F 1 (L), F 2 (L), F 3 (L) appears, and three edge images F 1 (R), F 2 (R), and F 3 (R) appear on the right side.

Of these, the inner two edge images F 3 (L) and F 3 (R) correspond to the edges E 3 (L) and E 3 (R) of the concavo-convex structure of the box mark 32 shown in FIG. The corresponding image. The remaining four edge images F 1 (L), F 2 (L), F 1 (R), and F 2 (R) are the edges E 1 (L), E 2 ( L), E1 (R), and E2 (R).

For this reason, the image processing apparatus 19 outputs the box image of the six edge images F 1 (L), F 2 (L),... (FIG. 2 (b)) appearing in the image of the observation area of the wafer 11. Based on the edge images F 3 (L) and F 3 (R) related to the mark 3 2, the center position C 2 of the box mark 32 in the X direction is detected, and the edge image F 1 (L) related to the frame mark 31 is detected. , F 2 (L), F 1 (R), and F 2 (R), the center position C 1 of the frame mark 31 in the X direction is detected.

The procedure for detecting the center positions C1, C2 in the X direction will be described later in detail. In the image of the observation area of the wafer 11, the edge images of the frame mark 31 and the box mark 32 appear in the Y direction in the same manner. Frame mark 31, box mark 3 2 The center position in the Y direction can also be detected in the same procedure as in the X direction. Therefore, in the following, only the description about “X direction” is given, and the description about “Y direction” is omitted. I do.

Here, the pre-processing for detecting the center positions C 1 and C 2 will be described. Prior to detecting the center positions C 1 and C 2, the image processing device 19 integrates the image signals captured from the CCD image sensor 18 (projection processing). That is, the image signals are integrated along the direction (Y direction) perpendicular to the detection direction (X direction) of the center positions C1 and C2. This is a process for reducing signal noise. The waveform of the integrated image signal generated by the projection process is called a “representative waveform”.

For example, as shown by the dotted line in Fig. 2 (b), all edge images F 1 (L), F 2 (L), F 3 (L), F 1 (R) appearing in the image of the observation area , F 2 (R), and F 3 (R) are set, and when the image signal is integrated in the Y direction within this range 33, the representative waveform of the obtained image signal is To (a) of FIG.

The horizontal axis in FIGS. 3 to 6 represents the position of each sample point (pixel) of the representative waveform, and the vertical axis represents the luminance value. In Fig. 3 to Fig. 6 (a), the vicinity of the poton where the luminance value of the representative waveform is minimal is the edge images F1 (L), F2 (L), F3 (L), F1 (R ), F 2 (R) and F 3 (R).

3 (a) and FIG. 4 (a) show a standard superposition mark 30 having a large size difference between the frame mark 31 and the box mark 32 as shown in FIG. 10 (a). Fig. 3 (a) shows an example of a representative waveform. Fig. 4 (a) shows the center positions C1, C2 when the deviation between the center positions C1, C2 of the frame mark 31 and the box mark 32 is small. This relates to the case where the deviation is large.

FIGS. 5A and 6A are both examples of representative waveforms at the superposition mark 30 having a small size difference between the frame mark 31 and the potas mark 32 as shown in FIG. 10B. Fig. 5 (a) shows the case where the deviation between the center positions C1 and C2 of the frame mark 31 and the box mark 3 2 is small, and Fig. 6 (a) shows the case where the deviation between the center positions C1 and C2 is large. Related.

As can be seen by comparing FIG. 3A to FIG. 6A, in FIG. 3A to FIG. 5A, the edge images F 2 (L) and F 2 (R) caused by the frame mark 31 and the box Since the edge images F 3 (L) and F 3 (R) caused by the mark 32 are sufficiently separated from each other, the boundary portion 40 (corresponding between the frame mark 31 and the box mark 32 in the representative waveform). The luminance values of (L) and (R) It is kept at the fixed value A.

On the other hand, in FIG. 6A, the edge images F 2 (L) and F 2 (R) due to the frame mark 31 and the edge images F 3 (L) and F 3 due to the box mark 32 are shown. (R) and the force S are separated to some extent on the left side of the figure, but are very close on the right side of the figure.

Therefore, in the representative waveform, the left boundary portion 4 1 (L) corresponding to between the frame mark 3 1 and the box mark 3 2 has a constant luminance value A, and the right boundary portion 41 (R ) Is a value B whose brightness value is smaller than a constant value A. In other words, the balance between left and right (symmetry) is broken. This is due to the proximity of the frame mark 3 1 and the box mark 3 2.

Since the actual position detection is performed separately for the frame mark 31 and the box mark 32, the projection processing for generating the representative waveform as described above (see (a) in FIGS. 3 to 6) is performed as shown in FIG. 2 (c) and (d) are implemented by setting ranges 34 and 35 indicated by dotted lines, respectively.

The range 34 in FIG. 2 (c) is a range including two edge images F 3 (L) and F 3 (R) related to the box mark 32 appearing in the image of the observation region. Set when detecting the center position C2 of mark 32. Then, a representative waveform (not shown) is generated by integrating the image signals within this range 34, and the obtained representative waveform is used for detecting the center position C 2.

The range 35 in FIG. 2D is a range including four edge images F 1 (L), F 2 (L), F 1 (R), and F 2 (R) related to the frame mark 31. This is set when the center position C 1 of the frame mark 31 is detected. Then, a representative waveform (not shown) is generated by integrating the image signals within this range 35, and the obtained representative waveform is used for detecting the center position C1.

Next, a procedure for detecting the center positions C1 and C2 of the frame mark 31 and the box mark 32 in the overlay measurement apparatus 10 will be specifically described with reference to the flowchart of FIG. Here, detection of the center position C2 of the box mark 32 will be described as an example.

At the time of this position detection, an observation area including the overlay mark 30 (FIG. 2 (a)) of the wafer 11 is positioned in the field of view of the overlay measurement device 10. And CCD imaging On the imaging surface of the element 18, a reflection image of the overlay mark 30 is formed. Therefore, the image processing device 19 can capture the reflection image of the superposition mark 30 as an image (see FIG. 2 (c)) based on the image signal from the CCD image sensor 18.

Next, as shown by the dotted line in FIG. 2 (c), the image processing device 19 sets a range including two edge images F 3 (L) and F 3 (R) related to the box mark 32. Then, a representative waveform (not shown, see (a) in FIGS. 3 to 6) is generated by integrating the image signals in the Y direction within this range 34 (step S1 in FIG. 7). Setting range 34 can be done manually or automatically. '

Then, the image processing device 19 extracts a portion where the luminance value changes abruptly from the image signal as an edge signal based on the representative waveform generated in step S1 (step S2). The edge signal is a signal related to the edge pair E 3 of the box mark 32 (FIG. 2 (a)). The extraction of the edge signal is automatically performed according to, for example, the following procedures (1) to (6).

(1) Find the two bottom points where the luminance value of the representative waveform related to the box mark 32 is minimum.

(2) Track the change in the luminance value from the bottom point on the left to the left, and find the sample point S1 (see (a) in Figs. 3 to 6) where the luminance value is the maximum. The brightness value of the sample point S1 has a constant value A in any of FIGS.

(3) Track the change in the brightness value from the bottom point on the left to the right, and find the sample point S3 (see (a) in Figs. 3 to 6) where the brightness value is the maximum.

(4) Track the change in the luminance value from the bottom point on the right to the right, and find the sample point S2 (see (a) in Figs. 3 to 6) where the luminance value is the maximum. The brightness value of the sample point S2 has a constant value A in FIGS. 3 to 5 (a), but has a value B which is smaller than the value A in FIG.

(5) Track the change in the luminance value from the bottom point on the right to the left, and find the sample point S3 (see (a) in Figs. 3 to 6) where the luminance value is the maximum. In the present embodiment, the sample point S3 is the same as the sample point obtained in (3).

(6) From the sample point S1 to the sample point S2 (that is, the part where the luminance value suddenly changes) Extracted as the edge signal.

As a result, the waveform 42 of the extracted edge signal has a shape as shown in (b) of FIGS. As can be seen from a comparison of FIGS. 3 to 6B, in FIGS. 3 to 5B, the luminance value at the left end and the right end of the waveform 42 both have the same value A. Therefore, the waveforms 42 in FIGS. 3 to 5B are symmetrical. In contrast, in Fig. 6 (b), the waveform

The luminance values at the left end and the right end of 4 2 have different values Α and で due to the proximity of the frame mark 3 1 and the box mark 3 2. For this reason, the waveform 42 in FIG. 6 (b) is bilaterally asymmetric.

In the image processing device 19, based on the waveform 42 of the edge signal extracted in step S2 (see (b) of FIGS. 3 to 6), the box mark 3 The center position C 2 of 2 is detected. This procedure is equally accurate whether the edge signal waveform 42 is symmetrical as shown in (b) of Figs. 3 to 5 or asymmetrical as shown in (b) of Fig. 6. It can perform position detection.

Now, the procedure after step S3 in FIG. 7 will be described. First, the image processing device 19 determines a waveform for calculation (step S3). In the processing of this time (the first time), the waveform 42 of the edge signal extracted in step S2 is used as the calculation waveform. Then, the image processing device 19 sets a temporary center position of the waveform 42 (step S4).

Next, the image processing device 19 folds the waveform 42 at the temporary center position, and calculates a correlation function between the obtained folded waveform and the original waveform 42 (step S5). In other words, a correlation function is calculated using a well-known algorithm called a correlation method while relatively offsetting the folded waveform and the original waveform 42. The correlation function indicates the relationship between the offset amount between the folded waveform and the original waveform 42 and the correlation value at that time. The correlation value takes a value from “0 to 1”.

Then, the image processing apparatus 19 obtains the maximum correlation value in the correlation function calculated in step S5, and selects the offset amount Δ corresponding to the maximum correlation value (step S6). Because this is the first time (Yes in step S7),

5 Perform the processing of 8. That is, a magnitude comparison between the maximum correlation value obtained in step S6 and a predetermined threshold value (for example, 0.95) is performed. The maximum correlation value is an index indicating the left-right symmetry of the calculation waveform. As a result of the comparison, if the maximum correlation value obtained in step S6 is larger than a threshold value (for example, 0.95) (step S8 is No), the image processing apparatus 19 determines that the original waveform 42 is symmetrical (see FIG. 3). (See (b) of FIG. 5), and the process of step S14 is performed. That is, the center position C 2 (= temporary center position + Δ / 2) of the box mark 32 is calculated based on the offset amount Δ selected in step S6 and the temporary center position set in step S4.

On the other hand, as a result of the comparison in step S8, if the maximum correlation value obtained in step S6 is smaller than the threshold value (for example, 0.95) (step S8 is Yes), the image processing device 19 outputs the original waveform 42 Is determined to be left-right asymmetric (see FIG. 6 (b)), and the process of step S9 is performed. That is, based on the offset amount Δ selected in step S6 and the provisional center position set in step S4, a candidate for the center position C2 of the box mark 32 (= provisional center position + Δ / 2 ) Is calculated.

Then, a data table indicating the relationship between the candidate for the center position C2 calculated in step S9 and the maximum correlation value obtained in step S6 is created (step S10). If the image processing device 19 repeatedly executes the above-described calculation of the candidate for the center position C2 (No in step S11), the image processing device 19 performs the processing in the next step S12,

Return to S3.

In step S12, one or more sample points are removed from the edge signal extracted in step S2 (the left-right asymmetrical waveform 42 in FIG. 6B), and the edge signal is corrected. At this time, the position and number of sample points to be removed are arbitrary. For example, it is conceivable to remove one sample point located at the left end or right end of the edge signal (asymmetrical waveform 42 in Fig. 6 (b)).

When the edge signal correction processing in step S12 is completed, the image processing apparatus 19 returns to the processing in step S3 and executes the second processing (S3 to S1'1). This time (second time), in the process of step S3, the waveform of the edge signal after the correction in step S12 becomes the waveform for calculation.

Then, steps S4 to S6 are executed using the waveform for calculation (the waveform of the edge signal after correction), and the maximum correlation value in the correlation function is obtained, and the offset amount Δ corresponding to the maximum correlation value is selected. I do. Because this is the second time, If the step S7 is No), the process proceeds to the step S9 without executing the processing of the step S8, and a new candidate of the center position C2 of the box mark 32 is calculated. Then, the relationship between the new candidate and the maximum correlation value obtained in step S6 is added to the data table (step S10).

In this way, when repeatedly calculating the candidate for the center position C 2 of the box mark 3 2, each time the processing of step S 12 (edge signal correction processing) is performed, the removal position and the removal number of the sample point are determined. If it is changed, candidates for the center position C 2 based on a plurality of different calculation waveforms can be calculated one after another. The sample point to be removed may be specified by the operator or automatically set by the apparatus.

After finishing the calculation of the candidate for the center position C2 (step S11 force SYes), the image processing device 19 proceeds to the next step S13. At this time, a data table indicating the relationship between the plurality of candidates for the center position C2 and the maximum correlation value has been completed in the image processing device 19.

Therefore, the image processing device 19 selects one of the plurality of candidates for the center position C2 with reference to the data table (step S13). That is, a candidate corresponding to one having the largest value among the plurality of maximum correlation values (the maximum value of the maximum correlation values) is searched for, and this candidate is selected as the "center position C2". This is because the greater the maximum correlation value, the higher the left-right symmetry of the operation waveform and the more accurate the detection result. For example, if the waveform of the edge signal (the edge signal before correction) extracted in step S2 has a left-right asymmetry like the waveform 42 shown in FIG. 6B, the “center position” is determined in step S13. The candidate selected as C 2 "is a case where the waveform 43 shown in FIG. 8 is used as the calculation waveform.

This waveform 43 is obtained by removing the four sample points on the left end and one sample point on the right end of the sample points of the waveform 42 (Fig. 6 (b)), as can be seen from Fig. 8. Symmetrical waveform. The maximum correlation value in this waveform 43 is “0.97” as shown in FIG. 9, which is improved by “0.3 2” compared to the maximum correlation value “0.65” in the waveform 42 of the edge signal before correction. You can see that.

This is because even if the waveform 42 (Fig. 6 (b)) of the edge signal (the edge signal before correction) extracted in step S2 is asymmetric, it is possible to remove the sample points and perform the correlation operation. This means that the symmetry of the waveform used in the calculation is improved, and the center position C2 can be calculated with high accuracy using the symmetrical waveform 43 (Fig. 8).

Therefore, the difference between the center position C2 calculated using the corrected left-right symmetrical waveform 43 and the candidate of the center position C2 calculated using the left-right asymmetrical waveform 42 before the correction (approximately 19 nm) represents the improvement in detection accuracy. In other words, by removing the sample points, the measurement error of the center position of the inner mark could be reduced by about 19 nm.

Similarly, the center position C 1 of the frame mark 31 can be detected with high accuracy. For example, if the waveform of the edge signal (the edge signal before correction) extracted in step S2 has left-right asymmetry like the waveforms 44 and 45 shown in FIG. The candidate selected as the center position C2 "is a case where the waveforms 46 and 47 shown in FIG.

Of these, waveform 46 is obtained by removing the four sample points on the right end from the sample points of waveform 44 (Fig. 6 (b)), and waveform 47 is the waveform 45 (Fig. 6 (b)). One of the sample points on the left side is removed. As a result, the waveforms 46 and 47 are left-right symmetrical waveforms as can be seen from FIG. The maximum correlation value of these waveforms 46 and 47 is “0.98” as shown in FIG. 9. Compared to the maximum correlation value “0.82” of the edge signal waveforms 44 and 45 before correction, “0.16” It can be seen that only improved.

This is because even if the waveforms 44 and 45 (Fig. 6 (b)) of the edge signal (edge signal before correction) extracted in step S2 are asymmetrical, the sample points are removed to remove the symmetrical waveform. This means that the center position C1 can be calculated accurately using the symmetrical waveforms 46 and 47 (Fig. 8).

For this reason, the difference between the center position C 1 calculated using the left-right symmetric waveforms 46 and 47 after correction and the candidate of the center position C 1 calculated using the left-right asymmetric waveforms 44 and 45 before correction (see FIG. In Fig. 9, about 13 nm) indicates the improvement in detection accuracy. In other words, removing the sample points reduced the measurement error by about 13 nm.

Subsequently, the image processing apparatus 19 performs an overlay inspection of the wafer 11 (inspection of an overlay state of the resist pattern with respect to the underlying pattern). That is, Based on the difference between the center positions C 1 and C 2 of the memory mark 31 and the box mark 32, an overlay displacement amount R (FIG. 2 (a)) is calculated. The overlay displacement amount R is expressed as a two-dimensional vector of the surface of the wafer 11.

In the present embodiment, as described above, since the center positions C 1 and C 2 of the frame mark 31 and the box mark 32 are both detected with high accuracy, the overlay deviation amount R can also be detected with high accuracy. . In the example of Fig. 9, the removal of the sample points improved the overlay displacement R by about 32 nm. In other words, the measurement error was reduced by about 32 nm.

In the present embodiment, since the correlation calculation (calculation of the correlation function between the calculation waveform and the folded waveform) is performed using the entire calculation waveform determined in step S3, it is hardly affected by signal noise. The center positions C 1 and C 2 of the frame mark 31 and the box mark 32 can be calculated with good reproducibility. In addition, the overlay deviation R can be calculated with good reproducibility.

It is preferable that the number of removed sample points in the edge signal correction processing (S12) be minimized. The reason for this is that the greater the number of sample points removed, the narrower the range of the operation waveform (the smaller the number of sample points), and the more likely it is to be affected by signal noise.

In the above-described embodiment, after the first correlation calculation, in step S8, the magnitude of the maximum correlation value is compared with a predetermined threshold (for example, 0.95), and only when the maximum correlation value is smaller, Although the sample points have been removed, the sample points may be removed in all cases, regardless of the maximum correlation value obtained in the first correlation operation. This corresponds to omitting the processing of steps S7, S8 and S14 in the flowchart of FIG.

Furthermore, in the above-described embodiment, the image processing device 19 in the overlay measurement device 10 removes the sample points of the edge signal and detects the center positions C 1 and C 2. The same effect can be obtained even when an external computer connected to 10 is used.

Further, in the above embodiment, the overlay measurement apparatus 10 has been described as an example, but the present invention is not limited to this. For example, before the exposure step in which the circuit pattern formed on the mask is printed on the resist film, alignment between the mask and the wafer 11 is performed. It can also be applied to equipment (alignment system of exposure equipment). In this case, the position of the alignment mark formed on the wafer 11 can be accurately detected. The present invention is also applicable to a device that detects an optical displacement between a single test mark and a reference position of a camera. Industrial potential

ADVANTAGE OF THE INVENTION According to this invention, even if the waveform of the edge signal regarding the edge pair of a test mark is asymmetrical, the position of a test mark can be detected accurately.

Claims

The scope of the claims

(1) illuminating means for illuminating a test mark including one or more edge pairs formed on a substrate;

Imaging means for capturing an image based on light from the test mark and outputting an image signal composed of a plurality of sample points;

Extracting means for extracting a rapidly changing portion of the luminance value from the image signal as an edge signal relating to the edge pair, and detecting means for detecting a center position of the test mark based on the edge signal.

The detecting means,

Correction means for correcting the asymmetry of the edge signal by removing one or more of the sample points included in the edge signal,

Calculating means for calculating the center position by calculating a maximum correlation value in a correlation function between a waveform based on the wedge signal corrected by the correction means and a waveform obtained by folding the waveform;

A mark position detecting device characterized by the above-mentioned.

(2) illuminating means for illuminating a test mark including at least one edge pair formed on a substrate;

Extracting means for extracting a rapidly changing portion of the luminance value from the image signal as an edge signal related to the edge pair;

Detecting means for detecting a center position of the test mark based on the edge signal,

The detecting means,

Correcting means for correcting the edge signal by removing one or more of the sample points included in the edge signal;

Based on the edge signal before correction by the correction means or the edge signal after correction. First calculating means for calculating a maximum correlation value in a correlation function between a calculation waveform and a waveform obtained by folding the calculation waveform;

Selecting means for selecting the largest one of the plurality of maximum correlation values calculated by the first calculating means using each of the plurality of different calculation waveforms;

Second calculating means for calculating the center position based on one maximum correlation value selected by the selecting means.

A mark position detecting device characterized by the above-mentioned.

(3) In the mark position detecting device according to claim 2,

The detection unit further includes a comparison unit that compares the maximum correlation value calculated by the first calculation unit with a predetermined threshold using the calculation waveform based on the uncorrected edge signal,

The correction means corrects the edge signal when the maximum correlation value based on the edge signal before correction is smaller than the threshold value as a result of the comparison by the comparison means.

A mark position detecting device characterized by the above-mentioned.

(4) an illumination step of illuminating a test mark including at least one edge pair formed on the substrate;

An imaging step of capturing an image based on light from the test mark and outputting an image signal including a plurality of sample points;

An extracting step of extracting a rapidly changing portion of the luminance value from the image signal as an edge signal related to the edge pair;

A detection step of detecting a center position of the test mark based on the edge signal,

The detecting step includes:

Correcting one or more of the sample points included in the edge signal to correct the asymmetry of the edge signal;

A calculating step of calculating the center position by calculating a maximum correlation value in a correlation function between a waveform based on the edge signal after the correction in the correction step and a waveform obtained by folding the waveform. Have And a mark position detecting method.

(5) an illumination step of illuminating a test mark including one or more edge pairs formed on the substrate;

The detecting step includes:

Correcting the edge signal by removing one or more of the sample points included in the edge signal,

A first calculating step of calculating a maximum correlation value in a correlation function between a waveform for calculation based on the wedge signal before correction or the wedge signal after correction in the correction step and a waveform obtained by folding the waveform for calculation. A selecting step of selecting the largest one of the plurality of maximum correlation values calculated in the first calculating step using each of a plurality of different calculation waveforms;

A second calculating step of calculating the center position based on one maximum correlation value selected in the selecting step.

And a mark position detecting method.

(6) In the mark position detecting method according to claim 5,

The detection step further includes a comparison step of comparing the maximum correlation value calculated in the first calculation step with a predetermined threshold value using the calculation waveform based on the uncorrected edge signal. And

In the correction step, when the maximum correlation value based on the edge signal before correction is smaller than the threshold value as a result of the comparison in the comparison step, the edge signal is corrected.

And a mark position detecting method.

(7) Overlay for inspecting the overlaid state of a plurality of patterns formed on the substrate In the measuring device

The mark position detecting device according to claim 1, wherein the mark position detecting device detects a center position of a test mark indicating a reference position of each of the plurality of patterns. Measuring means for measuring an amount of misalignment of the plurality of patterns based on a difference between the respective center positions.

(8) An overlay measurement method for inspecting an overlay state of a plurality of patterns formed on a substrate by using the mark position detection method according to claim 4 or claim 5 or claim 6,

The detecting step includes detecting a center position of a test mark indicating a reference position of each of the plurality of patterns.

A measuring step of measuring an amount of misalignment between the plurality of patterns based on a difference between the respective center positions detected in the detecting step.

An overlay measurement method, characterized in that: