JP4427980B2 - Mark position detection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mark position detection method for detecting the position of an overlay mark on a substrate.
[0002]
[Prior art]
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 applied to a wafer, and a development process in which an exposed or unexposed part of the resist film is dissolved Then, the circuit pattern (resist pattern) is transferred to the resist film, and the resist pattern is used as a mask to perform etching, film formation, etc. (processing step), and a predetermined material film immediately adjacent to the resist film The circuit pattern is transferred to (pattern forming step). 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 forming process many times, circuit patterns of various material films are stacked on a substrate (semiconductor wafer or liquid crystal substrate), and a semiconductor element or a liquid crystal display element is formed.
[0003]
In the above manufacturing process, in order to accurately overlay circuit patterns of various material films, the mask pattern and the pattern on the substrate are superimposed in each exposure process, and further after the development process and the processing process Prior to the above, the inspection of the overlay state of the resist pattern formed on the substrate is performed to improve the yield of the product (see, for example, Patent Document 1).
[0004]
The overlay of the mask pattern and the pattern on the substrate (before the exposure process) is the overlay of the circuit pattern on the mask and the circuit pattern formed on the substrate, and the reference position of each circuit pattern is determined. This is done using the overlay mark shown. The inspection of the overlay state of the resist pattern on the substrate (before the processing step) is an overlay inspection of the resist pattern with respect to the circuit pattern (hereinafter referred to as “underground pattern”) formed on the substrate. And an overlay mark indicating each reference position of the resist pattern.
[0005]
The position of the overlay mark is detected by positioning the overlay mark in the field of view of the apparatus, picking up an image of the overlay mark using an image sensor such as a CCD camera, and using the obtained image signal as an edge signal. Done with. 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.
[0006]
In calculating the position of the overlay 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 overlay mark can be calculated with high reproducibility without being affected by signal noise.
[0007]
[Patent Document 1]
JP-A-6-174428
[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 there is a defect in the edge part of the overlay mark and the waveform of the edge signal is disturbed, the edge position error will increase when calculating the edge position of the overlay mark, and the edge position of the overlay mark will be accurate. There is a risk that it will not be possible to decide well.
[0009]
SUMMARY An advantage of some aspects of the invention is that it provides a mark position detection method suitable for a mark position detection apparatus.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, mark position detecting means for detecting the edge position of an overlay mark having at least one or more edge positions, comprising: a plurality of image signal profiles of the overlay mark; Obtained using extraction means for extracting a plurality of edge positions, statistical processing means for calculating the degree of variation of the edge positions from the extracted plurality of edge positions, the degree of variation, and an overlay mark having no defect Comparing means for comparing with a predetermined variation threshold based on variation in edge position, and selecting means for selecting the plurality of edge positions based on the result of the comparing means, and based on the result of the selecting means Provided is a mark position detecting method characterized by calculating the edge position.
[0011]
In the mark position detection method of the present invention, it is preferable that the selection unit selects the plurality of edge positions whose degree of variation does not exceed the variation threshold.
[0012]
In the mark position detection method of the present invention, it is preferable that the selection unit selectively removes the plurality of edge positions whose degree of variation exceeds the variation threshold.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 shows a schematic configuration diagram of an overlay measurement apparatus according to the present invention. FIG. 2 is an example of an overlay mark used in the mark position detection method according to the present invention. FIG. 2A is a perspective view of the overlay mark and an example of a profile extraction position thereof, and FIG. A plan view of an example of an overlay mark and an example of a profile extraction position thereof are shown. (C) shows an example of a light quantity cross-sectional profile obtained by image processing of the overlay mark of (b). FIG. 3 is a flowchart of the mark position detection method according to the first embodiment of the present invention. FIG. 4 is a flowchart of a mark position detection method according to the second embodiment of the present invention.
[0015]
In FIG. 1, the overlay measurement apparatus 10 forms an image of the wafer 11, an inspection stage 12 that supports the wafer 11, an illumination optical system (13 to 16) that emits illumination light L <b> 1 toward the surface of the wafer 11, and the wafer 11. The imaging optical system (16, 15, 17), the CCD image sensor 18, and the image processing device 19 are included.
[0016]
The inspection stage 12 holds 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) of the wafer 11 is positioned within the field of view of the imaging optical system (16, 15, 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.
[0017]
The illumination optical system (13 to 16) includes a light source 13, an illumination lens 14, a prism 15, and an objective lens 16, and the prism 15 is disposed on the optical axis 02 between the objective lens 16 and the imaging lens 17. The The optical axis 02 of the imaging optical system (15, 16, 17) is parallel to the Z direction. The reflection / transmission surface 15 a of the prism 15 is inclined by approximately 45 degrees with respect to the optical axis 02. In the illumination optical system, the optical axis 01 from the illumination lens 14 to the reflection / transmission surface of the prism 15 is perpendicular to the optical axis 02 of the imaging optical system (15, 16, 17).
[0018]
The imaging optical system (15, 16, 17) is an optical microscope unit configured by an objective lens 16, a prism 15, and an imaging lens 17 in this order from the inspection stage side. The imaging lens 17 is an optical element that functions as a second objective lens.
[0019]
In the illumination optical system (13-16) and the imaging optical system (15, 16, 17), the light emitted from the light source 13 is guided to the prism 15 via the illumination lens 14, and the reflection / transmission surface 15a thereof. After being reflected (illumination light L1), it is 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. From the observation region of the wafer 11 irradiated with the illumination light L2, reflected light L3 is generated according to the uneven structure (overlapping mark 30) there. The reflected light L3 is collected by the objective lens 16, is transmitted through the prism 15 and is guided to the imaging lens 17, and forms an image on the imaging surface of the CCD imaging device 18 by the action of the objective lens 16 and the imaging lens 17. Is done. 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.
[0020]
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.
[0021]
The image processing device 19 captures a reflection image of the observation region (including the overlay mark 30) of the wafer 11 as an image based on the image signal from the CCD image pickup device 18, and the light amount cross section as shown in FIG. The profiles (F1 to F5) are taken out.
[0022]
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 middle of the process of forming another circuit pattern on the base pattern formed on the substrate (after exposure / development of the resist film and before etching processing of the material film).
[0023]
The overlay measurement device 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 overlay state inspection is formed on the surface of the wafer 11.
[0024]
FIG. 2A is a perspective view of the overlay mark 30. Registration mark 30 has a substantially rectangular outer Box 33, outer Box 33 and the center position is a mark substantially overlay Box-in-Box type made of the same substantially rectangular inner Box 35 Tokyo, outer Box33, One of the inner boxes 35 is a base mark and the other is a resist 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.
[0025]
The image captured by the image sensor 18 is extracted by the image processing device 19 as light amount cross-sectional profiles (F1 to F5) for each position (for example, S1 to S5). In FIG. 2B, S1 to S5 show examples of each position. In the overlay mark 30 shown in FIG. 2A, the edge positions P11 and P14 of the outer Box 33 and the edge positions P12 and P13 of the inner Box 35 are obtained, for example, from the light quantity cross-sectional profile at the position S1. Each edge position is calculated from the light quantity cross-sectional profile, and a deviation amount between the center position of the outer Box 33 and the center position of the inner Box 35 is detected. At this time, generally, the inspection stage and the measurement optical system are relatively moved in a direction perpendicular to the scanning direction, and scanning is performed at different positions in the overlay mark, and a plurality of pieces of positional information are averaged to perform dispersion. The measurement is suppressed. Note that an image may be captured by a two-dimensional area sensor (for example, a CCD), the captured result may be stored in an image memory, and averaging processing may be performed in a matrix manner based on the stored pixel data.
[0026]
As shown in FIGS. 2B and 2C, for example, the edge positions P11 and P21 are obtained from the light quantity cross-sectional profiles F1 and F2 by the positions S1 and S2 where the defect portion 37 is located at the edge position of the outer box 33 of the overlay mark 30. , Edge positions X11 and X21 corresponding to. Further, edge positions X31, X41, and X51 corresponding to the edge positions P31, P41, and P51 are obtained from the light quantity cross-sectional profiles F3, F4, and F5 at the positions S3, S4, and S5 where there is no defect, respectively. The degree of variation σa obtained by performing statistical processing using X11 to X51 (generally indicates a standard deviation), and the degree of variation σb obtained by performing statistical processing using X31 to X51 (generally, Indicates a standard deviation). Further, the average value Xa obtained by performing statistical processing using X11 to X51 has a larger deviation from the original edge position than the average value Xb obtained by performing statistical processing using X31 to X51. turn into. As described above, when the defective portion 37 is present in the overlay mark 30, performing statistical processing using the edge positions obtained from all the light quantity cross-sectional profiles (for example, F1 to F5) greatly increases the error of the edge position. There is a risk of doing.
[0027]
Note that edge positions are detected in the same manner for the other edges of the outer and inner boxes. Further, the center position shift between the outer Box and the inner Box can be detected by capturing an image in a direction (Y direction) perpendicular to the image capturing direction (X direction) described above and performing the same processing.
[0028]
In the measurement method described above, the two-dimensional image of the overlay mark is first captured, and the cross-sectional profile at each position of the image is captured. However, each position of the overlay mark is scanned and each position is scanned. A one-dimensional cross-sectional profile may be captured.
[0029]
The embodiment of the present invention proposes a mark position detection method capable of obtaining an edge position with high accuracy even when a defect is included in the overlay mark 30 as described above. The mark position detection method according to the embodiment of the present invention will be described below.
[0030]
(First embodiment)
FIG. 3 shows a flowchart of the make position detection method according to the first embodiment of the present invention. In FIG. 3, the overlay measuring apparatus 10 uses the degree of variation when the edge position is measured using the overlay mark 30 having no defect as the threshold value σin. Note that the threshold value σin may be determined from statistical calculation without being actually measured.
[0031]
After setting the threshold value σin (step 1), the edge positions (for example, X11 to X51) obtained by capturing the image of the overlay mark 30 and extracting the profiles (for example, F1 to F5) corresponding to the respective positions are obtained. Statistical processing is used to calculate the edge position variation degree σ (step 2). The calculated σ is compared with the threshold value σin (step 3).
[0032]
As a result of comparison, if the data variation degree σ is smaller than σin, it is determined that the shape of the overlay mark 30 is normal, the data is statistically processed, and the edge position is calculated (step 4). The process proceeds to the calculation process of the overlay deviation amount between the outer Box 33 and the inner Box 35.
[0033]
On the other hand, when σ is larger than σin, it is determined that there is a possibility that the edge position data includes a defective portion, and data of the degree of variation calculated in the course of statistical calculation so far (for example, edge Review the frequency distribution of positions and the respective variance values when the edge position is sequentially statistically processed), extract edge position data with a small variance value (step 5), perform statistical processing again, and perform σ and σin Are compared (return to step 3). If σ is smaller than σin in step 3, the process proceeds to step 4 and then proceeds to the calculation process of the overlay deviation amount. In selecting the edge position data described above, edge position data having a high appearance frequency may be selected from the appearance frequency distribution of the edge position.
[0034]
(Second Embodiment)
FIG. 4 shows a flowchart of the mark position detection method according to the second embodiment of the present invention. The difference between the second embodiment and the first embodiment is in step 5, and other steps are the same as those in the first embodiment, so that the same reference numerals are given and the description thereof is omitted.
[0035]
In FIG. 4, in step 5 in the second embodiment, variation degree data calculated in the course of statistical calculation (for example, the frequency distribution of edge positions and the respective variances when the edge positions are sequentially statistically processed). The edge position data having a large variance value is extracted and removed. Then, statistical processing is performed again using the edge position data after the removal, and the determination processing in step 3 is performed. When σ becomes smaller than σin, the mark shape is determined to be normal, the data is statistically processed, the edge position is calculated (step 4), and the process proceeds to the calculation processing of the overlay deviation amount between the outer Box 33 and the inner Box 35. . In the selection of the edge position data described above, edge position data with a small appearance frequency may be selected from the appearance frequency distribution of the edge positions.
[0036]
As described above, in the mark position detection method according to the present embodiment, an accurate edge position can be calculated even when the overlay mark 30 has a defect, and highly accurate overlay measurement can be performed.
[0037]
The above-described embodiment is merely an example, and is not limited to the above-described configuration and shape, and can be appropriately modified and changed within the scope of the present invention.
[0038]
【The invention's effect】
As described above, the present invention can provide a mark position detection method suitable for a mark position detection apparatus.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an overlay measurement apparatus according to the present invention.
2A is an example of an overlay mark used in the mark position detection method according to the present invention, FIG. 2A is a perspective view of the overlay mark and an example of a profile extraction position thereof, and FIG. A plan view of an example of an overlay mark and an example of a profile extraction position thereof are shown. (C) shows an example of a light quantity cross-sectional profile obtained by image processing of the overlay mark of (b).
FIG. 3 is a flowchart of a mark position detection method according to the first embodiment of the present invention.
FIG. 4 shows a flowchart of a mark position detection method according to a second embodiment of the present invention.
[Explanation of symbols]
10 overlay measurement apparatus 11 wafer 12 the inspection stage 13 light source 14 illuminating lens 15 prism 16 to objective lens 17 imaging lens 18 CCD imaging device 19 image processing device 30 the registration mark 33 outside Box
Box 35
37 Defects

Claims (3)

Mark position detection means for detecting the edge position of an overlay mark having at least one edge position,
Extracting means for extracting a plurality of edge positions from a plurality of image signal profiles of the overlay mark;
Statistical processing means for calculating a variation degree of the edge position from the extracted edge positions;
Comparing means for comparing the degree of variation with a variation threshold determined in advance based on variation in edge position determined using a defect-free overlay mark ;
Selecting means for selecting the plurality of edge positions based on the result of the comparing means;
A mark position detection method, wherein the edge position is calculated based on a result of the selection means.   The mark position detection method according to claim 1, wherein the selection unit selects the plurality of edge positions whose degree of variation does not exceed the variation threshold.   The mark position detection method according to claim 1, wherein the selection unit selectively removes the plurality of edge positions in which the degree of variation exceeds the variation threshold.

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