JP4178875B2 - Mark position detection device, mark position detection method, overlay measurement device, and overlay measurement method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mark position detection apparatus, a mark position detection method, an overlay measurement apparatus, and an overlay measurement method for detecting the position of a test mark on a substrate, and in particular, a highly accurate manufacturing process of a semiconductor element or the like. The present invention relates to a mark position detection device suitable for position detection.
[0002]
[Prior art]
As is well known, in the manufacturing process of a semiconductor element or a liquid crystal display element, an exposure process in which a circuit pattern formed on a mask (reticle) is baked on a resist film, and a development process in which an exposed or unexposed part of the resist film is dissolved. 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 and vapor deposition (machining process) to form a circuit on a predetermined material film adjacent to the resist film. A pattern is transferred (pattern formation process).
[0003]
Next, in order to form another circuit pattern on the circuit pattern formed on the predetermined material film, the same pattern forming process is repeated. As described above, by repeatedly performing the pattern formation 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. The
[0004]
By the way, in the above manufacturing process, in order to accurately overlay circuit patterns of various material films, the mask and the substrate are aligned before the exposure process in each pattern formation process, and further after the development process. In addition, prior to the processing step, the resist pattern on the substrate is inspected for superposition to improve the product yield.
[0005]
Incidentally, the alignment between the mask and the substrate (before the exposure process) is an alignment between the circuit pattern on the mask and the circuit pattern formed on the substrate in the previous pattern formation process. This is performed using an alignment mark indicating a reference position.
Further, the inspection of the overlay state of the resist pattern on the substrate (before the processing step) is a resist pattern overlay inspection with respect to the circuit pattern (hereinafter referred to as “underlying pattern”) formed in the previous pattern formation step. Yes, it is performed using an overlay mark indicating the reference position of each of the base pattern and the resist pattern.
[0006]
The position of these alignment marks and overlay marks (generally referred to as “test marks”) is detected by positioning the test marks within the field of view of the apparatus and using an image sensor such as a CCD camera. This is performed based on the edge signal among the obtained image signals. The image signal represents a distribution related to the luminance value for each pixel on the imaging surface of the imaging element. The edge signal is a sudden change portion of the luminance value in the image signal.
[0007]
In calculating the position of the test mark from the edge signal, a known algorithm called a correlation method is used. In the correlation method, since the correlation calculation is performed using the entire waveform of the edge signal, the position of the test mark can be calculated with high reproducibility without being affected by the signal noise.
[0008]
[Problems to be solved by the invention]
However, the correlation method is an algorithm on the assumption that the waveform of the edge signal is symmetrical. For this reason, if 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 detected with high accuracy. Note that a situation where the symmetry of the waveform of the edge signal is lowered can occur even when the shape of the edge pair of the test mark is symmetrical.
[0009]
An object of the present invention is to provide a mark position detection device, a mark position detection method, an overlay measurement device, and a mark position detection device capable of accurately detecting the position of the test mark even if the waveform of the edge signal related to the edge pair of the test mark is asymmetric. Another object of the present invention is to provide an overlay measurement method.
[0010]
[Means for Solving the Problems]
The mark position detection apparatus according to claim 1, 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, An imaging means for outputting an image signal composed of a plurality of sample points, an extraction means for extracting a sudden change portion of a luminance value of the image signal as an edge signal related to the edge pair, and the test based on the edge signal Detection means for detecting the center position of the mark, and the detection means corrects 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 unit, a waveform based on the edge signal corrected by the correction unit, and a waveform obtained by folding the waveform; And it has a calculating means for calculating a location.
[0011]
The mark position detection apparatus according to claim 2, 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, An imaging means for outputting an image signal composed of a plurality of sample points, an extraction means for extracting a sudden change portion of a luminance value of the image signal as an edge signal related to the edge pair, and the test based on the edge signal Detecting means for detecting the center position of the mark, wherein the detecting means corrects the edge signal by removing one or more of the sample points included in the edge signal; The maximum correlation value is calculated in the correlation function between the waveform for calculation based on the edge signal before or after correction by the correction means and the waveform obtained by folding the waveform for calculation. A calculation means for calculating a candidate for the center position based on the maximum correlation value, and a plurality of the maximum correlation values and the candidates calculated by the calculation means using each of a plurality of different calculation waveforms. And selecting means for selecting one of the plurality of candidates having the largest corresponding maximum correlation value as the center position.
[0012]
According to a third aspect of the present invention, in the mark position detection device according to the second aspect, the detection means uses the maximum correlation calculated by the calculation means using the waveform for calculation based on the edge signal before correction. The comparator further includes a comparing unit that compares a value with a predetermined threshold value, and as a result of comparison by the comparing unit, the maximum correlation value based on the edge signal before correction is smaller than the threshold value. Sometimes, the edge signal is corrected.
[0013]
The mark position detection method according to claim 4, an illumination step of illuminating a test mark including one or more edge pairs formed on a substrate, and an image based on light from the test mark, An imaging step of outputting an image signal composed of a plurality of sample points, an extraction step of extracting a sudden change portion of the luminance value of the image signal as an edge signal related to the edge pair, and the test based on the edge signal A detection step of detecting a center position of the mark, wherein the detection step corrects 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 correction in the correction step, and a waveform obtained by folding the waveform; Position are those having a calculation step of calculating.
[0014]
The mark position detection method according to claim 5, an illumination process for illuminating a test mark including one or more edge pairs formed on a substrate, and an image based on light from the test mark, An imaging step of outputting an image signal composed of a plurality of sample points, an extraction step of extracting a sudden change portion of the luminance value of the image signal as an edge signal related to the edge pair, and the test based on the edge signal A detection step of detecting the center position of the mark, wherein the detection step corrects the edge signal by removing one or more of the sample points included in the edge signal; The maximum correlation value in the correlation function between the waveform for calculation based on the edge signal before correction or the edge signal after correction in the correction step and the waveform obtained by folding back the waveform for calculation is calculated. A calculation step of calculating the center position candidate based on the maximum correlation value; and a plurality of the maximum correlation values and the candidates calculated in the calculation step using each of a plurality of different calculation waveforms. And a selection step of selecting one of the plurality of candidates having the largest corresponding maximum correlation value as the center position.
[0015]
According to a sixth aspect of the present invention, in the mark position detection method according to the fifth aspect, the detection step uses the maximum waveform calculated in the calculation step using the waveform for calculation based on the edge signal before correction. The method further includes a comparison step of comparing a correlation value with a predetermined threshold value. In the correction step, as a result of comparison in the comparison step, the maximum correlation value based on the edge signal before correction is more than the threshold value. When it is small, the edge signal is corrected.
[0016]
According to a seventh aspect of the present invention, in the overlay measurement apparatus for inspecting the overlay state of the plurality of patterns formed on the substrate, the center position of the test mark indicating each reference position of each of the plurality of patterns is set. 4. The overlay error between the plurality of patterns based on a difference between the mark position detection device according to claim 1 or claim 2 to be detected and the respective center positions detected by the mark position detection device. Measuring means for measuring the quantity.
[0017]
The invention according to claim 8 is an overlay measurement method for inspecting an overlay state of a plurality of patterns formed on a substrate using the mark position detection method according to claim 4 or claim 5 or claim 6. The detecting step is a step of detecting a center position of each of the test marks indicating a reference position of each of the plurality of patterns, and based on the difference between the center positions detected in the detecting step, The method further includes a measuring step of measuring an overlay error amount between the plurality of patterns.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiments of the present invention correspond to claims 1 to 8.
Here, the mark position detection apparatus of the present embodiment will be described using the overlay measurement apparatus 10 shown in FIG. 1 as an example.
[0019]
As shown in FIG. 1, the overlay measurement apparatus 10 includes an inspection stage 12 that supports the wafer 11, an illumination optical system (13 to 15) that emits illumination light L <b> 1 toward the wafer 11, and an image of the wafer 11. Are formed by an imaging optical system (16, 17), a CCD image pickup device 18, and an image processing device 19.
Before specifically describing the overlay measurement apparatus 10, the wafer 11 (substrate) will be described.
[0020]
A plurality of circuit patterns (all not shown) are laminated on the surface of the wafer 11. The uppermost circuit pattern is a resist pattern transferred to a resist film. That is, the wafer 11 is in the process of forming another circuit pattern on the base pattern formed in the previous pattern forming process (after exposure / development of the resist film and before etching processing of the material film). Is in a state.
[0021]
Then, the overlay measurement apparatus 10 inspects the overlay state of the resist pattern on the underlying pattern of the wafer 11. For this reason, an overlay mark 30 (FIG. 2A) used for the inspection of the overlay state is formed on the surface of the wafer 11. FIG. 2A is a plan view of the overlay mark 30.
The overlay mark 30 includes an outer frame mark 31 and an inner box mark 32. One of the frame mark 31 and the box mark 32 is a base mark and the other is a registration mark. The ground mark and the resist mark are formed simultaneously with the ground pattern and the resist pattern, respectively, and indicate the reference positions of the ground pattern and the resist pattern.
[0022]
The frame mark 31 includes two edge pairs E1 and E2 in the X direction. One edge pair E1 includes a left edge E1 (L) and a right edge E1 (R), and the other edge pair E2 includes a left edge E2 (L) and a right edge E2 (R). It consists of That is, the frame mark 31 has two edges E1 (L) and E2 (L) on the left side and two edges E1 (R) and E2 (R) on the right side. The same applies to the Y direction of the frame mark 31.
[0023]
The box mark 32 includes one edge pair E3 with respect to the X direction. The edge pair E3 includes a left edge E3 (L) and a right edge E3 (R). That is, the box mark 32 has one edge E3 (L) on the left side and one edge E3 (R) on the right side. The same applies to the Y direction of the box mark 32. Each of the frame mark 31 and the box mark 32 corresponds to a “test mark” in the claims.
[0024]
Although not shown, a material film to be processed is formed between the resist marks and resist pattern and the base mark and base pattern. This material film is formed when the registration mark is accurately superimposed on the ground mark and the resist pattern is accurately superimposed on the ground pattern after the overlay measurement by the overlay measuring apparatus 10. It is actually processed through.
[0025]
Next, a specific configuration of the overlay measurement apparatus 10 (FIG. 1) will be described.
The inspection stage 12 of the overlay measuring apparatus 10 can hold the wafer 11 in a horizontal state and can move to an arbitrary position within a horizontal plane. By moving the inspection stage 12, the observation region including the overlay mark 30 (FIG. 2A) on the wafer 11 is positioned in 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 plane.
[0026]
The illumination optical system (13 to 15) includes a light source 13, an illumination lens 14, and a prism 15, and the prism 15 is disposed on the optical axis O2 of the imaging optical system (16, 17). The optical axis O2 of the imaging optical system (16, 17) is parallel to the Z direction. The reflection / transmission surface 15a of the prism 15 is inclined by approximately 45 ° with respect to the optical axis O2. The optical axis O1 of the illumination optical system (13 to 15) is perpendicular to the optical axis O2 of the imaging optical system (16, 17).
[0027]
The imaging optical system (16, 17) is an optical microscope unit composed of the objective lens 16 and the imaging lens 17, and the objective lens 16 is disposed between the inspection stage 12 and the prism 15. The imaging lens 17 is an optical element that functions as a second objective lens, and is disposed on the opposite side of the objective lens 16 with the prism 15 interposed therebetween.
In the illumination optical system (13-15) 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 reflected by the reflection / transmission surface 15a. (Illumination light L1) is then guided to the objective lens 16 side. Then, after passing through the objective lens 16 (illumination light L <b> 2), it enters the wafer 11 on the inspection stage 12. At this time, the observation area of the wafer 11 is illuminated substantially vertically by the illumination light L2.
[0028]
Then, reflected light L3 is generated from the observation region of the wafer 11 irradiated with the illumination light L2 in accordance with the uneven structure (overlapping mark 30) there. The reflected light L3 is guided to the imaging lens 17 through the objective lens 16 and the prism 15, and is imaged on the imaging surface of the CCD imaging device 18 by the action of the objective lens 16 and the imaging lens 17. At this time, an enlarged image (reflected image) based on the reflected light L3 is formed on the imaging surface of the CCD image sensor 18.
[0029]
The CCD image pickup device 18 is an area sensor in which a plurality of pixels are two-dimensionally arranged, picks up a reflected image on the image pickup 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) related to the luminance value for each pixel on the imaging surface of the CCD imaging device 18.
The illumination optical system (13 to 15) and the objective lens 16 correspond to “illumination means” in the claims. The imaging optical system (16, 17) and the CCD image pickup device 18 correspond to “image pickup means” in the claims. The image processing device 19 corresponds to “extraction means” and “detection means” in the claims.
[0030]
Based on the image signal from the CCD image sensor 18, the image processing device 19 captures a reflected image of the observation region (including the overlay mark 30) of the wafer 11 as an image. Here, in the image of the observation area of the wafer 11, as shown in FIG. 2B, three edge images F1 (L), F2 (L), and F3 (L) appear on the left side in the X direction. On the right side, three edge images F1 (R), F2 (R), and F3 (R) appear.
[0031]
Among these, the inner two edge images F3 (L) and F3 (R) are images corresponding to the edges E3 (L) and E3 (R) of the concavo-convex structure of the box mark 32 shown in FIG. is there. The remaining four edge images F1 (L), F2 (L), F1 (R), F2 (R) are the edges E1 (L), E2 (L), E1 (R) of the concavo-convex structure of the frame mark 31. , E2 (R).
For this reason, the image processing apparatus 19 relates to the box mark 32 among the six edge images F1 (L), F2 (L),... (FIG. 2B) appearing in the image of the observation region of the wafer 11. Based on the edge images F3 (L), F3 (R), the center position C2 of the box mark 32 in the X direction is detected, and the edge images F1 (L), F2 (L), F1 (R) related to the frame mark 31 are detected. , F2 (R), the center position C1 of the frame mark 31 in the X direction is detected.
[0032]
The procedure for detecting the center positions C1 and C2 in the X direction will be described in detail later. In the image of the observation area of the wafer 11, edge images of the frame mark 31 and the box mark 32 appear in the Y direction in the same manner. The center positions in the frame mark 31 and box mark 32Y directions can also be detected by the same procedure as in the X direction. For this reason, only the description about the “X direction” will be described below, and the description about the “Y direction” will be omitted.
[0033]
Here, pre-processing for detecting the center positions C1 and C2 will be described. Prior to the detection of the center positions C1 and C2, the image processing device 19 integrates the image signals taken from the CCD image sensor 18 (projection processing). That is, the image signals are integrated along a 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 processing is referred to as “representative waveform”.
[0034]
For example, as shown by a dotted line in FIG. 2B, all the edge images F1 (L), F2 (L), F3 (L), F1 (R), F2 (R) appearing in the image of the observation region. , F3 (R) is 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 shown in FIGS. It becomes such a shape.
3 to 6, the horizontal axis represents the position of each sample point (pixel) of the representative waveform, and the vertical axis represents the luminance value. In FIG. 3A to FIG. 6A, the vicinity of the bottom where the luminance value of the representative waveform is minimized is the edge images F1 (L), F2 (L), F3 (L), F1 (R), F2 ( R) and F3 (R).
[0035]
3 and 4A are examples of representative waveforms in a standard overlay mark 30 having a large size difference between the frame mark 31 and the box mark 32 as shown in FIG. 10A. Yes, FIG. 3A relates to the case where the shift between the center positions C1 and C2 of the frame mark 31 and the box mark 32 is small, and FIG. 4A relates to the case where the shift between the center positions C1 and C2 is large.
[0036]
FIGS. 5A and 6B are examples of representative waveforms in the overlay mark 30 having a small size difference between the frame mark 31 and the box mark 32 as shown in FIG. FIG. 6A relates to the case where the shift between the center positions C1 and C2 of the frame mark 31 and the box mark 32 is small, and FIG. 6A relates to the case where the shift between the center positions C1 and C2 is large.
[0037]
As can be seen by comparing FIG. 3A to FIG. 6A, in FIG. 3A to FIG. 5A, the edge images F2 (L) and F2 (R) resulting from the frame mark 31 and the box mark 32 are displayed. Since the resulting edge images F3 (L) and F3 (R) are sufficiently separated, the luminance values of the boundary portions 40 (L) and (R) corresponding to the frame waveform 31 and the box mark 32 in the representative waveform. Is kept at a constant value A.
[0038]
On the other hand, in FIG. 6A, edge images F2 (L) and F2 (R) caused by the frame mark 31 and edge images F3 (L) and F3 (R) caused by the box mark 32 are obtained. Although they are separated to some extent on the left side in the figure, they are very close on the right side in the figure.
Therefore, in the representative waveform, the left boundary portion 41 (L) corresponding to the space between the frame mark 31 and the box mark 32 has a constant luminance value A, and the right boundary portion 41 (R) has a luminance value. The value is a value B smaller than a certain value A. That is, the left-right balance (symmetry) is broken. This is an influence of proximity between the frame mark 31 and the box mark 32.
[0039]
Since the actual position detection is performed separately for the frame mark 31 and the box mark 32, the projection process for generating the representative waveform as described above (see FIG. 3A to FIG. 6A) is shown in FIG. This is performed by setting ranges 34 and 35 indicated by dotted lines in 2 (c) and (d), respectively.
A range 34 in FIG. 2C is a range including two edge images F3 (L) and F3 (R) related to the box mark 32 appearing in the image of the observation region. It is set when detecting the position C2. 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 detection of the center position C2.
[0040]
A range 35 in FIG. 2 (d) 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. Is set when detecting the center position C1 of the. Then, a representative waveform (not shown) is generated by integration of the image signals within this range 35, and the obtained representative waveform is used for detecting the center position C1.
[0041]
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.
When this position is detected, an observation region including the overlay mark 30 (FIG. 2A) of the wafer 11 is positioned in the field of view of the overlay measurement apparatus 10. A reflected image of the overlay mark 30 is formed on the imaging surface of the CCD image sensor 18. Therefore, the image processing device 19 can capture the reflected image of the overlay mark 30 as an image (see FIG. 2C) based on the image signal from the CCD image sensor 18.
[0042]
Next, the image processing device 19 sets a range 34 including two edge images F3 (L) and F3 (R) related to the box mark 32 as indicated by a dotted line in FIG. A representative waveform (not shown, see FIGS. 3 to 6A) is generated by integrating the image signals in the Y direction within this range 34 (step S1 in FIG. 7). The setting of the range 34 is performed manually or automatically.
[0043]
Next, based on the representative waveform generated in step S1, the image processing device 19 extracts a sudden change portion of the luminance value from the image signal as an edge signal (step S2). The edge signal is a signal related to the edge pair E3 of the box mark 32 (FIG. 2A). The extraction of the edge signal is automatically performed, for example, according to the following procedures (1) to (6).
[0044]
(1) Find two bottom points at which the luminance value of the representative waveform related to the box mark 32 is minimized.
(2) The change of the luminance value is traced from the left bottom point to the left, and the sample point S1 (see (a) of FIGS. 3 to 6) where the luminance value is maximum is found. The luminance value of the sample point S1 is a constant value A in any of FIGS.
[0045]
(3) The change of the luminance value is traced from the left bottom point to the right, and the sample point S3 (see (a) of FIGS. 3 to 6) having the maximum luminance value is found.
(4) The change of the luminance value is traced from the right bottom point to the right, and the sample point S2 (see (a) of FIGS. 3 to 6) where the luminance value is maximum is found. The luminance value of the sample point S2 is a constant value A in FIGS. 3 to 5A, but becomes a value B smaller than the value A in FIG.
[0046]
(5) The change of the luminance value is traced from the bottom point on the right side to the left, and the sample point S3 (see (a) in FIGS. 3 to 6) where the luminance value is maximum is found. In this embodiment, the sample point S3 is the same as the sample point obtained in (3).
(6) Extract from the sample point S1 to the sample point S2 (that is, the sudden change portion of the luminance value) as an edge signal.
[0047]
As a result, the waveform 42 of the extracted edge signal has a shape as shown in FIG. As can be seen by comparing (b) in FIGS. 3 to 6, the luminance values at the left end and the right end of the waveform 42 are the same value A in FIGS. 3 to 5 (b). For this reason, the waveform 42 of FIGS. 3-5 is symmetrical. On the other hand, in FIG. 6B, the luminance values at the left end and the right end of the waveform 42 become different values A and B due to the proximity of the frame mark 31 and the box mark 32. For this reason, the waveform 42 in FIG. 6B is asymmetrical.
[0048]
In the image processing device 19, based on the waveform 42 of the edge signal extracted in step S <b> 2 (see FIGS. 3 to 6B), the center position C <b> 2 of the box mark 32 is followed according to the procedure after step S <b> 3 in FIG. 7. Is detected. Even if the waveform 42 of the edge signal is left-right symmetric as shown in FIGS. 3 to 5B or left-right asymmetric as shown in FIG. It can be detected.
[0049]
Now, the procedure after step S3 in FIG. 7 will be described. The image processing device 19 first determines a calculation waveform (step S3). In the current processing (first time), the waveform 42 of the edge signal extracted in step S2 is a 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). The correlation function represents the relationship between the offset amount between the folded waveform and the original waveform 42 and the correlation value at that time. In this case, the correlation value takes a value of “0 to 1”.
[0050]
Then, the image processing device 19 obtains the maximum correlation value in the correlation function calculated in step S5, and selects the offset amount Δ corresponding to this maximum correlation value (step S6). Since the process this time is the first time (step S7 is Y), the process of step S8 is performed next. That is, the magnitude correlation 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.
[0051]
As a result of the comparison, when the maximum correlation value obtained in step S6 is larger than a threshold value (for example, 0.95) (N in step S8), the image processing apparatus 19 has the original waveform 42 symmetrical (see FIGS. 3 to 5). (b)), and the process of step S14 is performed. That is, the center position C2 (= 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.
[0052]
On the other hand, as a result of the comparison in step S8, when the maximum correlation value obtained in step S6 is smaller than a threshold (for example, 0.95) (step S8 is Y), the image processing apparatus 19 has the original waveform 42 left and right. It is determined that it is asymmetric (see FIG. 6B), and the process of step S9 is performed. That is, the candidate (= temporary center position + Δ / 2) of the center position C2 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.
[0053]
And the data table which shows the relationship between the candidate of the center position C2 calculated by step S9 and the maximum correlation value calculated | required by step S6 is created (step S10). When the calculation of the candidate for the center position C2 as described above is repeatedly executed (N in Step S11), the image processing device 19 returns to Step S3 after performing the processing in the next Step S12.
[0054]
In step S12, one or more sample points are removed from the edge signal extracted in step S2 (the asymmetric waveform 42 in FIG. 6B), and the edge signal is corrected. At this time, the removal position and the number of removal of sample points are arbitrary. For example, it may be possible to remove one sample point located at the left end or the right end of the edge signal (the asymmetrical waveform 42 in FIG. 6B).
[0055]
When the edge signal correction process in step S12 ends, the image processing device 19 returns to the process in step S3 and executes the second process (S3 to S11). This time (second time), in the process of step S3, the waveform of the edge signal after the correction in step S12 is the waveform for calculation.
Then, steps S4 to S6 are executed using the waveform for calculation (the waveform of the corrected edge signal) to obtain the maximum correlation value in the correlation function, and the offset amount Δ corresponding to the maximum correlation value is selected. Since this process is the second time (N in step S7), the process proceeds to step S9 without executing the process in step S8, and a new candidate for the center position C2 of the box mark 32 is calculated. Then, the relationship between this new candidate and the maximum correlation value obtained in step S6 is added to the data table (step S10).
[0056]
In this way, when the candidate of the center position C2 of the box mark 32 is repeatedly calculated, a plurality of sample points can be obtained by changing the sample point removal position and the number of removals every time the process of step S12 (edge signal correction process) is performed. Candidates for the center position C2 with different calculation waveforms can be calculated one after another. The sample point to be removed may be designated by an operator or automatically set by the apparatus.
[0057]
When the calculation of the candidate for the center position C2 ends (step S11 is Y), the image processing device 19 proceeds to the next step S13. At this time, in the image processing device 19, a data table indicating the relationship between a plurality of candidates for the center position C2 and the maximum correlation value is completed.
For this reason, the image processing device 19 refers to the data table and selects one of a plurality of candidates for the center position C2 (step S13). That is, a candidate corresponding to one of the maximum correlation values having the largest value (maximum value of the maximum correlation value) is searched for, and this candidate is selected as “center position C2”. This is because as the maximum correlation value is larger, the left / right symmetry of the calculation waveform is higher, and a highly accurate detection result can be obtained.
[0058]
For example, when the waveform of the edge signal (edge signal before correction) extracted in step S2 has a left-right asymmetry like the waveform 42 shown in FIG. 6B, “center position C2” is set in step S13. The candidate to be selected is when the waveform 43 shown in FIG.
This waveform 43 is obtained by removing four sample points on the left end side and one sample point on the right end side from the sample points of the waveform 42 (FIG. 6B). It has a symmetrical waveform. The maximum correlation value in the waveform 43 is “0.97” as shown in FIG. 9, and is “0.32” compared with the maximum correlation value “0.65” in the waveform 42 of the edge signal before correction. You can see that it has only improved.
[0059]
This is because even if the waveform 42 (FIG. 6B) of the edge signal (edge signal before correction) extracted in step S2 is asymmetrical, the waveform used for correlation calculation is eliminated by removing sample points. This means that the center position C2 can be accurately calculated using the symmetrical waveform 43 (FIG. 8).
For this reason, a deviation (about 19 nm in FIG. 9) between the center position C2 calculated using the corrected left-right symmetric waveform 43 and the center position C2 calculated using the left-right asymmetric waveform 42 before correction is obtained. This represents the improvement in detection accuracy. That is, by removing the sample point, the measurement error of the center position of the inner mark can be reduced by about 19 nm.
[0060]
Similarly, the center position C1 of the frame mark 31 can be detected with high accuracy. For example, when the waveform of the edge signal (edge signal before correction) extracted in step S2 has left-right asymmetry like the waveforms 44 and 45 shown in FIG. 6B, “center position C2” is determined in step S13. The candidate selected as “” is when the waveforms 46 and 47 shown in FIG.
[0061]
Of these, the waveform 46 is obtained by removing four sample points on the right end from the sample points of the waveform 44 (FIG. 6B), and the waveform 47 is the waveform 45 (FIG. 6B). Among the sample points, one sample point on the left end side is removed. As a result, the waveforms 46 and 47 are symmetrical waveforms as can be seen from FIG. As shown in FIG. 9, the maximum correlation value in the waveforms 46 and 47 is “0.98”. Compared with the maximum correlation value “0.82” in the waveforms 44 and 45 of the edge signal before correction, It can be seen that the improvement is 0.16 ".
[0062]
This is because even if the waveforms 44 and 45 (FIG. 6B) of the edge signal (edge signal before correction) extracted in step S2 are left-right asymmetric, the waveform symmetry is eliminated by removing the sample points. This means that the center position C1 can be accurately calculated using the symmetrical waveforms 46 and 47 (FIG. 8).
[0063]
Therefore, the difference between the center position C1 calculated using the corrected left and right symmetrical waveforms 46 and 47 and the candidate of the center position C1 calculated using the left and right asymmetric waveforms 44 and 45 before correction (in FIG. 9). (About 13 nm) represents an improvement in detection accuracy. In other words, the measurement error could be reduced by about 13 nm by removing the sample points.
Subsequently, the image processing apparatus 19 performs an overlay inspection of the wafer 11 (inspection of the overlay state of the resist pattern with respect to the base pattern). That is, the overlay deviation amount R (FIG. 2A) is calculated based on the difference between the center positions C1 and C2 of the frame mark 31 and the box mark 32. The overlay deviation amount R is expressed as a two-dimensional vector on the surface of the wafer 11.
[0064]
In the present embodiment, as described above, since the center positions C1 and C2 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 overlay deviation amount R is improved by about 32 nm by removing the sample points. That is, the measurement error could be reduced by about 32 nm.
[0065]
In this 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, the frame mark is hardly affected by the signal noise. 31, center positions C1 and C2 of the box mark 32 can be calculated with good reproducibility. Also, the overlay deviation amount R can be calculated with good reproducibility.
[0066]
Note that the number of sample points removed in the edge signal correction process (S12) is preferably minimized. This is because as the number of sample points to be removed increases, the range of the waveform for calculation becomes narrower (the number of sample points decreases) and is more susceptible to signal noise.
In the above-described embodiment, after the first correlation calculation, in step S8, the maximum correlation value is compared with a predetermined threshold (for example, 0.95), and the sample point is determined only when the maximum correlation value is smaller. Although removed, the sample points may be removed in all cases regardless of the maximum correlation value obtained in the first correlation calculation. This corresponds to omitting the processing of steps S7, S8, and S14 in the flowchart of FIG.
[0067]
Furthermore, in the above-described embodiment, the image processing device 19 in the overlay measurement apparatus 10 performs the removal of the edge signal sample points, the detection of the center positions C1 and C2, etc., but is connected to the overlay measurement apparatus 10. Even when an external computer is used, the same effect can be obtained.
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 also be applied to an apparatus (an alignment system of an exposure apparatus) that aligns the mask and the wafer 11 before an exposure process in which a circuit pattern formed on the mask is printed on a resist film. In this case, the position of the alignment mark formed on the wafer 11 can be detected with high accuracy. The present invention can also be applied to an apparatus that detects an optical displacement between a single test mark and a camera reference position.
[0068]
【The invention's effect】
As described above, according to the present invention, the position of the test mark can be detected with high accuracy even if the waveform of the edge signal related to the edge pair of the test mark is asymmetric.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of an overlay measurement apparatus 10;
2A is a plan view of an overlay mark 30 formed on a wafer 11, and FIGS. 2B to 2D are views for explaining images of an 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 illustrating an example of a representative waveform (a) and a waveform (b) of an edge signal in a standard overlay mark 30. FIG.
FIG. 5 is a diagram showing an example of a representative waveform (a) and an edge signal waveform (b) in the overlay mark 30 in the proximity state.
FIG. 6 is a diagram showing an example of a representative waveform (a) and an edge signal waveform (b) in the overlay mark 30 in the proximity state.
FIG. 7 is a flowchart showing a position detection procedure in the overlay measurement apparatus 10;
FIG. 8 is a diagram illustrating an example of a waveform of an edge signal after improving symmetry.
FIG. 9 is a diagram for explaining improvement in symmetry and improvement in detection accuracy.
FIG. 10 is a diagram showing an overlay mark (a) with a large size difference between a frame mark and a box mark and a small overlay mark (b).
[Explanation of symbols]
10 Overlay measuring device
11 Wafer
12 Inspection stage
13 Light source
14 Lighting lens
15 Prism
16 Objective lens
17 Imaging lens
18 CCD image sensor
19 Image processing device
30 Overlay mark

Claims (8)

Illuminating means for illuminating a test mark including one or more edge pairs formed on the substrate;
An 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;
Extraction means for extracting a sudden change portion of the luminance value of 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 detection means includes
Correction means for correcting 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 edge signal corrected by the correction means and a waveform obtained by folding the waveform. A mark position detecting device as a feature. Illuminating means for illuminating a test mark including one or more edge pairs formed on the substrate;
An 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;
Extraction means for extracting a sudden change portion of the luminance value of 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 detection means includes
Correction means for correcting the edge signal by removing one or more of the sample points included in the edge signal;
A maximum correlation value in a correlation function between a waveform for calculation based on an edge signal before correction by the correction means or an edge signal after correction and a waveform obtained by folding the calculation waveform is calculated, and based on the maximum correlation value Calculating means for calculating the candidate for the center position;
The plurality of maximum correlation values calculated by the calculation means using each of a plurality of different calculation waveforms and the candidate are referred to, and one of the plurality of candidates having the largest corresponding maximum correlation value And a selection means for selecting the center position as the center position. In the mark position detection apparatus according to claim 2,
The detection means further includes comparison means for comparing the maximum correlation value calculated by the calculation means with a predetermined threshold value using the waveform for calculation based on the edge signal before correction.
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. Detection device. Illuminating a test mark including one or more edge pairs formed on the substrate;
An imaging step of capturing an image based on light from the test mark and outputting an image signal composed of a plurality of sample points;
An extraction step of extracting a sudden change portion of the luminance value of 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 detection step includes
A correction step of correcting asymmetry of the edge signal by removing one or more of the sample points included in the edge signal;
A calculation step of calculating the center position by calculating a maximum correlation value in a correlation function between a waveform based on the corrected edge signal in the correction step and a waveform obtained by folding the waveform. Characteristic mark position detection method. Illuminating a test mark including one or more edge pairs formed on the substrate;
An imaging step of capturing an image based on light from the test mark and outputting an image signal composed of a plurality of sample points;
An extraction step of extracting a sudden change portion of the luminance value of 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 detection step includes
A correction step of correcting the edge signal by removing one or more of the sample points included in the edge signal;
A maximum correlation value in a correlation function between a waveform for calculation based on the edge signal before correction or the edge signal after correction in the correction step and a waveform obtained by folding back the waveform for calculation is calculated, and based on the maximum correlation value Calculating a candidate for the center position;
The plurality of maximum correlation values calculated in the calculation step using each of a plurality of different calculation waveforms and the candidate are referred to, and the corresponding maximum correlation value is the largest among the plurality of candidates 1 And a selection step of selecting one as the center position. In the mark position detection method according to claim 5,
The detection step further includes a comparison step of comparing the maximum correlation value calculated in the calculation step with a predetermined threshold value using the calculation waveform based on the edge signal before correction.
In the correction step, the mark position is corrected when the maximum correlation value based on the edge signal before the correction is smaller than the threshold value as a result of the comparison in the comparison step. Detection method. In the overlay measurement apparatus for inspecting the overlay state of a plurality of patterns formed on the substrate,
The mark position detection device according to claim 1, wherein the mark position detection device detects a center position of a test mark indicating a reference position of each of the plurality of patterns.
An overlay measurement apparatus comprising: a measuring unit that measures an overlay deviation amount between the plurality of patterns based on a difference between the respective center positions detected by the mark position detection apparatus. In the overlay measurement method for inspecting the overlay state of a plurality of patterns formed on a substrate using the mark position detection method according to claim 4 or claim 5 or claim 6,
The detection step is a step of detecting a center position of a test mark indicating a reference position of each of the plurality of patterns,
An overlay measurement method, further comprising a measurement step of measuring an overlay deviation amount between the plurality of patterns based on a difference between the respective center positions detected in the detection step.

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