JP2004205466A - Linewidth measuring apparatus, linewidth measuring method, and mask for linewidth measurement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To rapidly measure fluctuations in linewidth regardless of the number of fine patterns to be measured. <P>SOLUTION: The apparatus comprises means 13 to 17 which capture a diffraction image of a substrate comprising different shot areas, each having repetition patterns transferred thereto and a means 17 which calculates fluctuations in linewidth of the repetition patterns transferred to the different shot areas by comparing the brightness information of each part corresponding to each repetition pattern with respect to the different shot areas in the diffraction image. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a line width measuring apparatus, a line width measuring method, and a line width measuring mask for measuring a line width fluctuation of a pattern on a substrate, and particularly to a measurement of a line width fluctuation of a fine pattern in a manufacturing process of a semiconductor circuit element or the like. The present invention relates to a line width measuring apparatus, a line width measuring method, and a line width measuring mask suitable for the present invention.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a manufacturing process of a semiconductor circuit element or a liquid crystal display element, a line width fluctuation of a fine pattern formed on a surface of a semiconductor wafer or a liquid crystal substrate (generally referred to as a “substrate”) has been measured. For this measurement, a CD-SEM (Critical Dimension Scanning Electron Microscope) is generally used (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP 2001-273865 A
[0004]
[Problems to be solved by the invention]
However, the measurement by the CD-SEM is a so-called one-point measurement, and is sequentially performed for each fine pattern on the substrate. Therefore, the required time increases as the number of fine patterns to be measured increases.
[0005]
An object of the present invention is to provide a line width measurement device and a line width measurement mask capable of measuring a line width variation at high speed regardless of the number of fine patterns to be measured.
[0006]
[Means for Solving the Problems]
The line width measuring apparatus according to claim 1, wherein the image capturing unit captures a diffraction image of the substrate on which the repetitive pattern is transferred to each of the different shot areas, and the different shot areas of the diffraction image, Calculating means for calculating a line width variation of the repetitive pattern transferred to the different shot area by comparing luminance information of a portion corresponding to the repetitive pattern.
[0007]
3. The line width measuring apparatus according to claim 2, wherein the image capturing unit selectively captures diffraction images of the plurality of types of repeating patterns from a substrate on which a plurality of types of repeating patterns are transferred to different shot areas. Calculating means for calculating the line width variation of the repetitive pattern transferred to the different shot area by comparing the luminance information of the different shot areas in the diffraction image.
The line width measuring device according to claim 3 is the line width measuring device according to claim 2, wherein the image capturing unit has the same repetition direction but different repetition pitches and different design line widths. The diffraction images of the pattern are selectively captured one by one.
[0008]
The line width measuring device according to claim 4 is the line width measuring device according to claim 2, wherein the image capturing unit has the same repetition pitch and design line width but different repetition directions. The diffraction images of the pattern are selectively captured one by one.
The line width measuring device according to claim 5 is the line width measuring device according to any one of claims 1 to 4, wherein the image capturing unit is configured to determine the repetition direction and the repetition of the repetition pattern. A setting unit for setting device conditions at the time of image capture according to the pitch.
[0009]
The line width measuring device according to claim 6 is the line width measuring device according to any one of claims 1 to 5, wherein the substrate has the repeating pattern in each shot area of the substrate. Plural arrays are arranged at a pitch smaller than the imaging resolution of the image capturing means.
[0010]
8. The image capturing step of capturing a diffraction image of a substrate on which a repetitive pattern having the same repetition direction, repetition pitch, and design line width is transferred to each of different shot areas. Calculating a line width variation of the repeated pattern transferred to the different shot area by comparing luminance information of a portion corresponding to each of the repeated patterns with respect to the different shot areas of the diffraction image. It is provided with.
[0011]
9. The line width measurement method according to claim 8, wherein a plurality of types of repetition patterns are transferred to each of different shot regions, and at least two of the plurality of types of repetition patterns transferred to a certain shot region. The repetition direction, the repetition pitch, and the design line of the same shot pattern from the substrate on which the repetition pattern having the same repetition direction, repetition pitch, and design line width are also transferred to other shot regions. The width and the image capturing step of selectively capturing a diffraction image of a repetitive pattern having the same width, and comparing the luminance information of the different shot areas of the diffraction image, the image transferred to the different shot areas. And a calculating step of calculating a line width variation of the repetitive pattern.
[0012]
The line width measurement method according to claim 9 is the line width measurement method according to claim 8, wherein in the image capturing step, the plurality of lines have the same repetition direction and different repetition pitches and the design line width. The diffraction images of the different types of repetitive patterns are selectively captured one by one.
The line width measuring method according to claim 10 is the line width measuring method according to claim 8, wherein, in the image capturing step, the plurality of lines having the same repetition pitch and the designed line width and different repetition directions are used. The diffraction images of the different types of repetitive patterns are selectively captured one by one.
[0013]
The line width measuring method according to claim 11, wherein in the image capturing step, the repetition direction and the repetition of the repetition pattern are provided. The apparatus conditions at the time of image capture are set according to the pitch.
The line width measuring method according to claim 12 is the line width measuring method according to any one of claims 7 to 11, wherein the substrate has the repetitive pattern in each shot area of the substrate. Plural arrays are arranged at a pitch smaller than the imaging resolution of the image capturing means.
[0014]
The line width measurement mask according to claim 13, comprising a plurality of types of pattern groups including a plurality of repetition patterns having the same repetition direction, repetition pitch, and design line width, wherein the plurality of types of pattern groups are in the repetition direction. And the repetition pitch and the design line width are different.
The mask for line width measurement according to claim 14, comprising a plurality of types of pattern groups including a plurality of repetition patterns having the same repetition direction, repetition pitch, and design line width, wherein the plurality of types of pattern groups include the repetition pitch. And the design line width is the same and the repetition direction is different.
[0015]
A line width measurement mask according to claim 15 is the line width measurement mask according to claim 13 or 14, wherein the plurality of types of pattern groups have the same number density of the repeating pattern. is there.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
An embodiment of the present invention corresponds to claims 1 to 8.
As shown in FIG. 1, the line width measuring device 10 of the present embodiment includes a stage 12 for holding a substrate 11, an illumination optical system 13 for irradiating the substrate 11 on the stage 12 with illumination light L1, and an illumination light L1. The image processing unit 17 includes a light receiving optical system (14 to 16) for receiving the diffracted light L2 from the irradiated substrate 11 and an image processing unit 17.
[0018]
The line width measuring device 10 is a device for automatically measuring a line width variation of a fine pattern (described later) formed on the surface of the substrate 11 in a manufacturing process of a semiconductor circuit element or the like. The substrate 11 is a test wafer, which is in a state after exposure and development of a resist film formed on the uppermost layer and before etching of a predetermined material film immediately adjacent to the resist film.
[0019]
Before specifically describing the line width measuring apparatus 10 of the present embodiment, the substrate 11 will be described. A plurality of shot areas (not shown) are two-dimensionally arranged on the entire surface (for example, 300 mmφ) of the substrate 11. Further, in each shot area, a pattern group for line width measurement (described below) is uniformly transferred without gaps.
These pattern groups are transferred using the line width measurement mask 20 shown in FIG. 2 and an exposure device (not shown). 2A and 2B are diagrams showing a configuration of the line width measurement mask 20, FIG. 2A shows an entire image of the line width measurement mask 20, and FIG. 2B shows FIG. 2A. It is the figure which expanded the inside of broken line frame 20A.
[0020]
The pattern area of the line width measurement mask 20 is composed of a plurality of two-dimensionally arranged basic blocks 21 as shown in FIG. 2B. It consists of different types of cells 22, 23, 24, 25, 26. As shown in FIG. 2C, two cells 22, 23, 24, 25, and 26 are provided in one basic block 21, respectively.
[0021]
FIG. 3 is a diagram showing a configuration in one cell 22 of the line width measurement mask 20. As shown in FIG. 3, the cell 22 is provided with four types of repeating patterns 31, 32, 33, and. The repetition pattern 31 includes five line patterns 41, and these line patterns 41 are arranged at a constant pitch P1 along the short direction B1. The five line patterns 41 have the same design line width D1.
[0022]
The other three types of repetition patterns 32, 33, and 34 are each composed of five line patterns 42, 43, and 44, as in the repetition pattern 31 described above, and these line patterns 42, 43, and 44 have a fixed pitch. Are arranged. Each of the line patterns 42, 43, and 44 has the same design line width and pitch as the design line width D1 and the pitch P1 of the line pattern 41.
[0023]
The arrangement directions B2, B3, and B4 of the five line patterns 42, 43, and 44 are different from each other, and also different from the arrangement direction B1 of the line pattern 41. Specifically, the four types of arrangement directions B1, B2, B3, and B4 are different from each other at an angle interval of 45 degrees.
In the present specification, the design line width D1, the pitch P1, and the arrangement directions B1 to B4 of the line patterns 41 to 44 are appropriately referred to as "design line width D1, the repeat pitch P1, and the repeat directions B1 to B4 of the repeat patterns 31 to 34".
[0024]
As described above, the four types of repetition patterns 31 to 34 provided in one cell 22 have the same design line width D1 and the same repetition pitch P1 and different repetition directions B1 to B4.
Further, although not shown, cells 23 to 26 (FIG. 2C) other than the cell 22 have four types of repetition patterns having the same design line width and repetition pitch but different repetition directions, similarly to the cell 22. Is provided.
[0025]
However, comparing the repetition patterns among the cells 23 to 26, the design line width and the repetition pitch are different from each other, and the design line width D1 and the repetition pitch P1 of the repetition patterns 31 to 34 of the cell 22 are also different. The repeating directions (four types) of the repeating pattern in each of the cells 23 to 26 are the same as the repeating directions B1 to B4 in the cell 22.
[0026]
As described above, the basic block 21 including the five types of cells 22, 23, 24, 25, and 26 has 20 types of repetitions according to the combination of the design line width, the repetition pitch (five types), and the repetition direction (four types). That is, the patterns 31, 32, 33, 34,... Are provided.
[0027]
Further, since two cells 22 to 26 are provided in one basic block 21, two repetition patterns 31, 32, 33, 34,... Of 20 types are also provided.
Further, in the pattern area of the line width measurement mask 20 in which the plurality of basic blocks 21 are two-dimensionally arranged, each of the 20 types of repeating patterns 31, 32, 33, 34,. _{twenty one} , Y _{twenty one} Many are arranged at a constant pitch according to (FIG. 2C).
[0028]
In this specification, a large number of the repetitive patterns 31, 32, 33, 34,... Arranged in the pattern area of the line width measurement mask 20 are collectively referred to as "pattern groups (31), (32), (33), (33). 34),… ”. The repetitive patterns 31, 32, 33, 34,... Constituting each of the 20 types of pattern groups (31), (32), (33), (34),.
[0029]
By using the line width measurement mask 20 (FIGS. 2 and 3) configured as described above and an exposure apparatus (not shown), the resist film in each shot region of the substrate 11 sequentially has 20 types of patterns. The groups are transferred uniformly without gaps. The 20 types of pattern groups transferred to each shot area correspond to each of the pattern groups (31), (32), (33), (34),... Of the line width measurement mask 20.
[0030]
Further, since the shot areas are two-dimensionally arranged on the entire surface of the substrate 11, as a result of the transfer using the line width measuring mask 20 (FIGS. 2 and 3), the entire surface of the substrate 11 (a plurality of shot areas) is obtained. In this case, 20 types of pattern groups are transferred in the mixed state by the same number as the shot areas.
In the following description, the pattern groups (31) and (32) of the line width measurement mask 20 (FIGS. 2 and 3) are used for each of the 20 types of pattern groups transferred over the entire surface (a plurality of shot areas) of the substrate 11. ), (33), (34),..., Each of which is given a code obtained by adding a suffix “w”.
[0031]
Here, each of the 20 types of pattern groups (31w), (32w), (33w), (34w),... Transferred on the entire surface (a plurality of shot areas) of the substrate 11 will be described. For example, the pattern group (31w) is composed of a large number of repetitive patterns 31w (fine patterns) transferred to different shot areas on the entire surface of the substrate 11, and the repetition direction, repetition pitch, and design line width of the repetition pattern 31w are the same.
[0032]
However, the actual line width of the repetitive pattern 31w fluctuates according to the deviation of the exposure focus (focus). Generally, when the exposure focus deviates from an appropriate value, the line width becomes large regardless of the direction of the deviation (front focus, rear focus). That is, the actual line width of the repetitive pattern 31w becomes narrowest when the exposure focus is at an appropriate value. Such a line width variation occurs for each shot area of the substrate 11. It is considered that the repetition direction and the repetition pitch of the repetition pattern 31w do not change due to the shift of the exposure focus.
[0033]
In the case of an isolated linear pattern having an extremely large space, the line width may be largest when the exposure focus is at an appropriate value, and may be thin when the exposure focus is shifted.
In the present embodiment, for example, a pattern group (31w) is to be measured, and the line width variation of a large number of repetitive patterns 31w transferred to the entire surface of the substrate 11 is measured for each shot area using the line width measuring device 10 ( Details will be described later). Then, based on the measurement result by the line width measuring device 10, the quality of the transfer performance of the exposure device is determined.
[0034]
The other 19 types of pattern groups (32w), (33w), (34w),... Transferred on the entire surface of the substrate 11 are different shots of the entire surface of the substrate 11 similarly to the pattern group (31w). Are repeated in the repetition direction, the repetition pitch, and the design line width of the repetition patterns 32w, 33w, 34w,...
[0035]
Also, comparing the 20 types of pattern groups (31w), (32w), (33w), (34w),... Among the repeated patterns 31w, 32w, 33w, 34w,. At least one of the directions is different from one another. In the present embodiment, there are five types of design line widths and repetition pitches and four types of repetition directions in the twenty types of repetition patterns 31w, 32w, 33w, 34w,.
[0036]
Generally, the transfer performance of an exposure apparatus differs depending on the design line width of a repetitive pattern. Further, even if the design line width is the same, it differs depending on the repetition direction. Therefore, if the exposure focus deviates from an appropriate value in one shot area, different line width fluctuations occur in each of the 20 types of repetitive patterns 31w, 32w, 33w, 34w,.
[0037]
For this reason, the 20 types of pattern groups (31w), (32w), (33w), (34w),... Transferred onto the entire surface of the substrate 11 are measured one by one, and shot by using the line width measuring device 10. By measuring the line width variation for each area (details will be described later), it is possible to determine whether the transfer performance of the exposure apparatus is good or not from various angles.
Incidentally, each shot area of the substrate 11 has a maximum of 30 mm to 40 mm square, and a transfer portion (hereinafter, referred to as a “basic block 21 w”) corresponding to the basic block 21 (FIG. 2C) on the substrate 11 is , Longitudinal dimension (X in FIG. 2 (c)) _{twenty one} Is about 60 μm. Therefore, one shot area includes about 100 basic blocks 21w.
[0038]
Further, the 20 types of pattern groups (31w), (32w), (33w), (34w),... Transferred to the substrate 11 have design line widths (5 types) of, for example, about 100 nm to 300 nm, and a repetition pitch (5 For example, about 200 nm to 600 nm, and the repetition direction (four kinds) has an angle interval of 45 degrees.
[0039]
Next, a specific configuration of the line width measuring device 10 (FIG. 1) will be described.
The stage 12 can be tilted within a predetermined angle range around an axis parallel to the surface of the substrate 11 (perpendicular to the paper) by a tilt mechanism (not shown). The substrate 11 can be rotated about a normal direction of the substrate 11 by a rotation mechanism (not shown). On the stage 12, the substrate 11 transported by a transport device (not shown) is placed on the upper surface and fixed and held by vacuum suction.
[0040]
Here, a direction parallel to the tilt axis of the stage 12 is defined as an “X direction”. A direction parallel to a normal line (reference normal line) in a state where the stage 12 (substrate 11) is kept horizontal is referred to as a “Z direction”. Further, a direction perpendicular to the X direction and the Z direction is referred to as a “Y direction”.
The illumination optical system 13 is disposed obliquely above the stage 12. That is, the optical axis O1 of the illumination optical system 13 is inclined by a predetermined angle with respect to the reference normal line (Z direction). The illumination optical system 13 is arranged so that the optical axis O1 is orthogonal to the tilt axis (X direction) of the stage 12. Further, the illumination optical system 13 is arranged such that the rear focal position substantially matches the substrate 11 and is an optical system that is telecentric with respect to the substrate 11 side.
[0041]
The light receiving optical systems (14 to 16) are decentered optical systems each including a concave reflecting mirror 14, an imaging lens 15, and an image sensor 16. The concave reflecting mirror 14 is arranged above the stage 12. That is, the concave reflecting mirror 14 is arranged such that the optical axis O2 of the concave reflecting mirror 14 on the stage 12 side is parallel to the Z direction. In addition, the concave reflecting mirror 14 is arranged so that the front focal position substantially matches the substrate 11. For this reason, the light receiving optical systems (14 to 16) are telecentric optical systems with respect to the substrate 11 side.
[0042]
The imaging lens 15 is arranged near the pupil position of the light receiving optical system (14 to 16) so as to substantially coincide with the rear focal position of the concave reflecting mirror 14. The imaging element 16 is a CCD image sensor in which a plurality of pixels are two-dimensionally arranged, and is arranged with its imaging surface substantially coincident with the rear focal position of the imaging lens 15. For this reason, the light receiving optical systems (14 to 16) are optical systems that are telecentric with respect to the imaging element 16 side. Note that the imaging surface of the imaging element 16 is conjugate to the surface of the substrate 11.
[0043]
The illumination light L1 (wavelength λ) emitted from the illumination optical system 13 having the above configuration is substantially parallel light, and is applied to the entire surface (a plurality of shot areas) of the substrate 11 on the stage 12. Since the substrate 11 side of the illumination optical system 13 is a telecentric system, the incident angle θi of the illumination light L1 is uniform over the entire surface of the substrate 11.
.. Among the 20 types of pattern groups (31w), (32w), (33w), (34w),... Formed on the entire surface of the substrate 11, the repetition direction of the repetition patterns 31w, 32w, 33w, 34w,. Diffracted light is generated in various directions from those parallel to the tilt axis of the stage 12 (five types).
[0044]
The diffracted light L2 shown in FIG. 1 is a part of the diffracted light generated in the direction of the optical axis O2 of the light receiving optical system (14 to 16) (for example, the first-order diffracted light of the pattern group (31w)). By changing the setting of the tilt angle θt of the stage 12, diffracted light generated from a pattern group having a different repetition pitch (design line width also differs in this embodiment) can be guided to the light receiving optical system (14 to 16). .
[0045]
Here, in the shot area where the exposure focus has deviated from the appropriate value in the entire surface (a plurality of shot areas) of the substrate 11, the line width of the repetitive pattern is large (the repetition direction and the repetition pitch are unchanged). The diffraction efficiency is reduced due to the line width fluctuation, and as a result, the intensity of the diffracted light is reduced.
Then, the diffracted light L2 guided from the substrate 11 to the light receiving optical systems (14 to 16) is condensed by the action of the concave reflecting mirror 14 and the imaging lens 15, and reaches the imaging surface of the imaging element 16. The imaging device 16 captures a diffraction image formed on the imaging surface, and outputs an image signal to the image processing device 18. The concave reflecting mirror 14 and the imaging lens 15 generally correspond to an “imaging optical system” in the claims.
[0046]
In the present embodiment, the optical magnification of the concave reflecting mirror 14 and the imaging lens 15 is set such that a diffraction image of the entire surface of the substrate 11 is formed on the imaging surface of the imaging element 16. In consideration of this optical magnification, the area (imaging resolution) on the substrate 11 corresponding to one pixel of the imaging element 16 is about 250 μm square.
With respect to the imaging resolution (about 250 μm square) of the line width measuring device 10, the size of the basic block 21 w (the transfer portion of the basic block 21 of FIG. 2C to the substrate 11) is about 60 μm × 25 μm. is there. That is, the basic block 21w is sufficiently smaller than the imaging resolution. In other words, a large number of repetitive patterns 32w, 33w, 34w,... Are arranged on the substrate 11 at a pitch smaller than the imaging resolution.
[0047]
The imaging resolution includes about 40 (4 × 10) basic blocks 21w (that is, eight repetitive patterns 32w, 33w, 34w,..., Respectively). In this case, the image signal from the image sensor 16 includes the sum of the intensities of the diffracted lights L2 generated from about 40 basic blocks 21w as information of one pixel.
Further, since the substrate 11 side of the light receiving optical system (14 to 16) is a telecentric system, the traveling direction of the diffracted light L2 is uniform over the entire surface of the substrate 11, and the intensity of the diffracted light L2 incident on the image sensor 16 is also reduced. It becomes uniform for each state of the repetitive pattern (line width variation) of the substrate 11. Therefore, only the state of the repetitive pattern (line width variation) is reflected in the strength of the image signal from the image sensor 16.
[0048]
The image processing unit 17 captures a diffraction image corresponding to the entire surface of the substrate 11 based on an image signal from the image sensor 16 when measuring the line width. This diffraction image relates to one of 20 types of pattern groups (31w), (32w), (33w), (34w),... Transferred on the entire surface of the substrate 11.
The selection of the diffraction image captured by the image processing unit 17 is performed using the tilt mechanism and the rotation mechanism of the stage 12. That is, by tilting the substrate 11 by the tilt mechanism, any one of the pattern groups having different repetition pitches (the design line widths also differ in the present embodiment) can be selected. Further, by rotating the substrate 11 by the rotation mechanism, any one of the pattern groups having different repetition directions can be selected.
[0049]
The setting of the device conditions (tilt angle θt, rotation angle) by the tilt mechanism and the rotation mechanism of the stage 12 may be performed based on a recipe created in advance. The recipes are various setting conditions necessary for optimally measuring the line width variation of the 20 types of pattern groups (31w), (32w), (33w), (34w),. It is stored in the memory in advance.
[0050]
Here, a recipe relating to the tilt angle θt of the stage 12 will be described. In general, the tilt angle θt is obtained by calculation from a design value of a repetition pitch p of a pattern group to be measured using a well-known diffraction condition equation (formula (1)), and the calculation result is registered in a recipe. I have.
sin (θi−θt) −sin (θd + θt) = mλ / p (1)
Equation (1) shows the relationship among the tilt angle θt of the stage 12, the repetition pitch p of the pattern group, the wavelength λ and the incident angle θi of the illumination light L1, the diffraction angle θd of the diffracted light L2, and the diffraction order m. It is a formula which did. The reference of the tilt angle θt is a horizontal plane. The reference of the incident angle θi and the diffraction angle θd is a reference normal (Z direction) of the substrate 11.
[0051]
By referring to a recipe created and registered in advance, the tilt condition of the stage 12 and the rotation mechanism corresponding to the repetition direction, based on the tilt angle θt corresponding to the repetition pitch p of the pattern group to be measured and the rotation angle corresponding to the repetition direction. Is set, the diffraction image of the pattern group to be measured can be selectively captured.
In this way, when the diffraction images relating to one of the 20 types of pattern groups (31w), (32w), (33w), (34w),... Transferred onto the entire surface of the substrate 11 are collectively captured, image processing is performed. First, the unit 17 corrects non-uniformity of sensitivity (for example, uneven brightness of the illumination optical system 13) inherent in the line width measurement device 10. Hereinafter, a case where the pattern group (31w) is to be measured will be described as an example.
[0052]
Then, as a result of the above-described correction processing, a diffraction image reflecting only the line width variation of a large number of repeated patterns 31w constituting the pattern group (31w) is obtained (see FIG. 4). That is, in the corrected diffraction image, the line width fluctuation of the repetitive pattern 31w appears as a local luminance change. However, since the line width fluctuation occurs for each shot area, a luminance change corresponding to the line width fluctuation also appears for each shot area.
[0053]
Further, the line width variation in the shot area where the exposure focus has deviated from the appropriate value is “variation in which the line width increases”, and the diffraction efficiency decreases due to the line width variation. Is a “change that decreases the luminance”.
That is, in the diffraction image of FIG. 4, the black portion where the luminance is greatly reduced corresponds to the shot region where the exposure focus has largely deviated from the appropriate value, and the gray portion where the luminance is slightly reduced is the exposure focus which is slightly different from the appropriate value. The white area where the luminance is not reduced corresponds to the shot area where the exposure focus is at an appropriate value, corresponding to the shot area slightly shifted.
[0054]
The image processing unit 17 compares the luminance information of a portion corresponding to each shot region (hereinafter, referred to as a “shot image”) in the corrected diffraction image (see FIG. 4), and is transferred to a different shot region. Then, the line width variation of the repeated pattern 31w is calculated (calculation means).
The brightness information of the shot image is, for example, the average brightness of 3 × 3 pixels located at the center of the shot image, and is considered to be the brightness information of the portion corresponding to the large number of repetitive patterns 31w transferred to the shot area. Can be. Note that the average luminance of all pixels of the shot image may be used as “luminance information of the shot image”.
[0055]
Further, the comparison of the luminance information of the shot images includes, for example, selecting a shot image having the highest average luminance and calculating the amount of decrease in the average luminance of other shot images based on the average luminance of this shot image. Is performed by
At this time, if the amount of decrease in the average luminance is “0”, it is considered that the exposure focus on the shot area on the substrate 11 corresponding to the shot image was an appropriate value, and the repetitive pattern transferred to the shot area The line width fluctuation of 31w is considered to be “0”.
[0056]
It is considered that the larger the amount of decrease in the average luminance, the larger the exposure focus of the shot area deviates from the appropriate value, and the larger the line width variation of the repetitive pattern 31w transferred to the shot area. That is, the reduction amount of the average luminance of the shot image indicates a relative line width variation.
Here, when the shift amount (offset amount) of the exposure focus in some shot areas is known, a diffraction image relating to the entire surface of the substrate 11 is captured, and the result of calculating the average luminance of the shot image (FIG. 5) explain.
[0057]
The horizontal axis in FIG. 5 is the exposure focus offset amount (μm), and “offset amount = 0” represents an appropriate value. The vertical axis on the right side is the average luminance (gradation) of the shot image, and the lower the figure, the higher the luminance. Further, the measurement result (μm) by CD-SEM is also shown on the left vertical axis of FIG. 5 for comparison.
As can be seen from FIG. 5, the average luminance (■) of the shot image calculated by the line width measuring device 10 of the present embodiment shows a line width variation highly correlated with the measurement result (▲) by the CD-SEM. ing. When “offset amount = 0”, the average luminance (■) of the shot image is the highest, and the line width of the measurement result (▲) by the CD-SEM is the narrowest.
[0058]
Further, it can be seen that the change in the average luminance (■) of the shot image is proportional to the line width variation. For example, in the example of FIG. 5, the correlation coefficient between the line width fluctuation and the luminance change is about 20 nm / 100 gradation. In this case, the line width fluctuation can be measured with an accuracy of several nm or less for 10 gradations of the change amount of the average luminance (■) of the shot image.
Therefore, by measuring in advance the correlation coefficient (for example, 20 nm / 100 gradation) between the line width variation and the luminance change, the other diffraction image (see FIG. 4) has the other average luminance (reference) among the highest average luminance (reference). The absolute value of the line width variation can be calculated based on the amount of decrease in the average luminance of the shot image.
[0059]
In the line width measuring apparatus 10 of the present embodiment, the diffraction image of the entire surface of the substrate 11 is captured in a collective field of view, and the line width fluctuation is measured by comparing the luminance information of each shot image in the diffraction image. The line width fluctuation can be measured at high speed regardless of the number of target repetitive patterns (the number of shot areas).
In this embodiment, the basic blocks 21w of the line width measurement pattern groups (31w), (32w), (33w), (34w),... Are sufficiently smaller than the imaging resolution (about 250 μm square). Generation of moiré fringes in an image can be reliably suppressed. That is, it is possible to avoid the occurrence of pseudo-contrast other than the contrast related to the actual pattern structure. As a result, the measurement accuracy of the line width variation is improved.
[0060]
Further, a single substrate 11 (test wafer) can be used to change a plurality of (20 in this embodiment) line width fluctuations by simply changing the setting of the apparatus conditions (tilt angle θt, rotation angle) when capturing a diffraction image. Can be easily measured. Therefore, the quality of the transfer performance of the exposure apparatus can be easily determined from various angles.
For example, when a plurality of types of pattern groups having the same repetition direction but different repetition pitches and design line widths are to be measured, the tilt angle θt among the device conditions is changed according to the repetition pitch (the rotation angle is fixed). Only), each diffraction image can be selectively captured one by one, and measurement of line width fluctuation (determination of the transfer performance of the exposure apparatus) when the repetition direction is the same can be easily performed.
[0061]
When a plurality of types of pattern groups having the same repetition pitch and design line width but different repetition directions are to be measured, the rotation angle of the apparatus conditions is changed according to the repetition direction (the tilt angle θt is fixed). Only), each diffraction image can be selectively captured one by one, and measurement of line width variation due to the repetition direction (determination of the transfer performance of the exposure apparatus) can be easily performed.
[0062]
(Modification)
In the above-described embodiment, the line width fluctuation is measured based on the diffraction image after correcting the non-uniformity of the sensitivity (for example, the brightness unevenness of the illumination optical system 13) inherent in the line width measuring apparatus 10. However, the present invention is not limited to this. For example, when a change in luminance over a wide range due to uneven thickness of the resist film on the substrate 11 or a change in luminance over a wide range due to warpage of the substrate 11 appears in a diffraction image, It is preferable to select only shot images outside the range and measure the line width variation.
[0063]
Furthermore, in the above-described embodiment, the line width measurement of the repetitive pattern in the resist stage has been described as an example, but the present invention is not limited to this. For example, it is also possible to measure the line width of the repetitive pattern transferred to the underlying layer in a state after the etching of the material film adjacent immediately below the resist film.
In the above-described embodiment, the line width measurement is performed by capturing the diffraction image of the entire surface of the substrate 11 in a collective visual field, but the present invention is not limited to this. For example, the line width measurement may be performed by designating an arbitrary area (including one or more shot areas) in the substrate 11 which requires the line width measurement and capturing the diffraction image in a collective visual field. .
[0064]
Further, in the above-described embodiment, the setting of the apparatus conditions (tilt angle θt, rotation angle) is changed by the tilt mechanism and the rotation mechanism of the stage 12, but the present invention is not limited to this. Instead of the tilt mechanism and the rotation mechanism of the stage 12, a tilt mechanism and a rotation mechanism are provided in the illumination optical system 13 and the light receiving optical systems (14 to 16), and the device conditions (tilt angle θt, rotation angle) are similarly changed. You may.
[0065]
In the above-described embodiment, the 20 types of pattern groups (31w), (32w), (33w), (34w),... Transferred by using the line width measurement mask 20 shown in FIG. Although the line width variation was measured, the present invention is not limited to this. For example, a plurality of pattern groups transferred by a line width measurement mask including the cell 50 shown in FIG. 6 and one or more other cells (not shown) may be used as line width fluctuation measurement targets one by one.
[0066]
The cell 50 in FIG. 6 will be described. The cell 50 is provided with two types of repeating patterns 51 and 52. Each of the repeating patterns 51 and 52 is composed of eleven line patterns 53 and 54, and these line patterns 53 and 54 are arranged at a constant pitch along the short direction. The repetition patterns 51 and 52 have the same design line width and repetition pitch, and have different repetition directions (90-degree angle intervals).
[0067]
Further, the repetitive patterns 51 and 52 are designed so that the outer shape is square. In other words, when the length of the line patterns 53 and 54 is L, the number of lines is n (= 11), the repetition pitch is P2, and the design line width is D2, the design is such that L = n × (P2 + D2). I have. The repetitive patterns 51 and 52 are arranged in a staggered arrangement in the vertical and horizontal directions.
[0068]
As described above, the outer shapes of the repetitive patterns 51 and 52 are designed in a square shape, and the occupied areas of the repetitive patterns 51 and 52 are made equal, whereby the diffraction efficiency of the repetitive patterns 51 and 52 becomes uniform. As a result, comparison measurement of the repetition patterns 51 and 52 for each repetition direction becomes possible.
The interval Δ between the repetition patterns 51 and 52 is, for example, three times or more the repetition pitch (P2). By laying out the repetitive patterns 51 and 52 while securing the interval Δ at least greater than one time the repetition pitch (P2), it is possible to prevent pseudo diffraction due to interference between the repetitive patterns 51 and 52. The interval Δ may be set based on the order to be excluded from the high-order diffraction conditions.
[0069]
A plurality of pattern groups transferred by a line width measurement mask including the cell 50 shown in FIG. 6 and one or more other cells (cells having a different repetition pitch and design line width from the cell 50) are lined one by one. Even when the width variation is to be measured, the line width variation can be measured at high speed by capturing the diffraction image of the entire surface of the substrate 11 in a collective visual field and comparing the luminance information of each shot image in the diffraction image. Can be.
[0070]
【The invention's effect】
As described above, according to the present invention, line width fluctuation can be measured at high speed regardless of the number of fine patterns to be measured.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an overall configuration of a line width measuring device 10.
FIG. 2 is a schematic diagram illustrating a configuration of a line width measurement mask 20;
FIG. 3 is a schematic diagram showing a configuration of one cell 22 of the line width measurement mask 20;
FIG. 4 is a diagram showing an example of a diffraction image of the entire substrate 11;
FIG. 5 is a diagram illustrating an example of a measurement result when an exposure focus shift amount (offset amount) is known.
FIG. 6 is a schematic diagram showing a configuration of a cell 50 according to a modification.
[Explanation of symbols]
10 Line width measuring device
11 Substrate
12 stages
13 Illumination optical system
14 Concave reflector
15 Imaging lens
16 Image sensor
17 Image processing unit
20 Mask for line width measurement
21 Basic Block
22, 23, 24, 25, 26, 50 cells
31, 32, 33, 34, 51, 52 repeating pattern
41, 42, 43, 44, 53, 54 line pattern

Claims (15)

Image capturing means for capturing a diffraction image of the substrate on which the pattern is repeatedly transferred to each of the different shot areas,
Calculating means for calculating a line width variation of the repeated pattern transferred to the different shot area by comparing luminance information of a portion corresponding to each of the repeated patterns with respect to the different shot areas of the diffraction image. A line width measuring device comprising: From a substrate on which a plurality of types of repetitive patterns are transferred to different shot regions, image capturing means for selectively capturing diffraction images of the plurality of types of repetitive patterns,
Calculating a line width variation of the repetitive pattern transferred to the different shot area by comparing luminance information of the different shot areas of the diffraction image. Measuring device. The line width measuring device according to claim 2,
A line width measuring apparatus, wherein the image capturing means selectively captures, one by one, the diffraction images of the plurality of types of repeating patterns having the same repetition direction and different repetition pitches and design line widths. The line width measuring device according to claim 2,
A line width measuring apparatus, wherein the image capturing means selectively captures, one by one, the diffraction images of the plurality of types of repeating patterns having the same repetition pitch and design line width and different repetition directions. In the line width measuring device according to any one of claims 1 to 4,
A line width measuring apparatus, characterized in that the image capturing means has a setting section for setting device conditions at the time of image capturing according to the repetition direction and the repetition pitch of the repetition pattern. The line width measuring device according to any one of claims 1 to 5,
A line width measuring apparatus, wherein the substrate has a plurality of the repetitive patterns arranged at a pitch smaller than an imaging resolution of the image capturing means in each shot area of the substrate. An image capturing step of capturing a diffraction image of a substrate on which a repetitive pattern having the same repetition direction, repetition pitch and design line width is transferred to each of the different shot areas,
A calculating step of calculating a line width variation of the repeating pattern transferred to the different shot area by comparing luminance information of a portion corresponding to each of the repeating patterns with respect to the different shot areas of the diffraction image. A line width measuring method characterized by comprising: A plurality of types of repetition patterns are transferred to each of different shot areas, and at least two types of repetition patterns among the plurality of types of repetition patterns transferred to a certain shot area, a repetition direction, a repetition pitch, and a design line. From the substrate on which the repeated pattern having the same width is transferred to another shot area, a diffraction image of the repeated pattern having the same repetition direction, repetition pitch and design line width of each of the different shot areas is obtained. An image capturing step for selectively capturing;
Calculating a line width variation of the repetitive pattern transferred to the different shot area by comparing luminance information of the different shot areas of the diffraction image. Measurement method. The line width measuring method according to claim 8,
In the image capturing step, the diffraction images of the plurality of types of repeating patterns having the same repetition direction and the different repetition pitch and the design line width are selectively captured one by one. Method. The line width measuring method according to claim 8,
Wherein said image capturing step selectively captures, one by one, the diffraction images of the plurality of types of repeating patterns having the same repetition pitch and the design line width and different repetition directions. Method. In the line width measuring method according to any one of claims 7 to 10,
In the image capturing step, a device condition at the time of image capturing is set according to the repetition direction and the repetition pitch of the repetition pattern. In the line width measuring method according to any one of claims 7 to 11,
The method according to claim 1, wherein a plurality of the repetitive patterns are arranged at a pitch smaller than an imaging resolution of the image capturing unit in each shot area of the substrate. A plurality of pattern groups consisting of a plurality of repetition patterns having the same repetition direction, repetition pitch, and design line width are provided,
A line width measurement mask, wherein the plurality of types of pattern groups have the same repetition direction and the repetition pitch and the design line width are different. A plurality of pattern groups consisting of a plurality of repetition patterns having the same repetition direction, repetition pitch, and design line width are provided,
A line width measurement mask, wherein the plurality of types of pattern groups have the same repetition pitch and the designed line width and different repetition directions. The line width measuring mask according to claim 13 or 14,
The plurality of types of pattern groups have the same number density of the repetitive patterns, a line width measurement mask.

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