JP2006337631A - Inspection method and method for manufacturing liquid crystal display apparatus using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection method for quantitatively measuring the accuracy of a seam of patterns and improving the accuracy of a seam of patterns, and to provide a method for manufacturing a liquid crystal display apparatus using the above method. <P>SOLUTION: The inspection method aims to inspect the accuracy of a seam of patterns by different exposures in a process of forming predetermined patterns by dividing a substrate into a plurality of regions and separately exposing. The method includes: in an overlap region where a first region and a second region overlap in a plurality of regions, a step of measuring a first distance between a first pattern element relating to the exposure of the first region and a second pattern element disposed approximately parallel to the first pattern element and relating to the exposure of the first region; a step of measuring a second distance between a third pattern element to be connected to the first pattern element relating to the exposure of the second region, and the second pattern element; and a step of obtaining the difference between the first distance and the second distance and quantifying and measuring the accuracy of the seam. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inspection method and a manufacturing method of a liquid crystal display device using the same, and in particular, a seam when a predetermined pattern is formed by dividing a substrate into a plurality of regions and separately exposing the substrate. The present invention relates to an inspection method and a manufacturing method of a liquid crystal display device using the same.

  In general, a liquid crystal display device using a TFT (Thin Film Transistor) has a TFT formed on one substrate using a photolithography. In photoengraving, a predetermined pattern is patterned on a substrate by an exposure apparatus. However, when the substrate is enlarged, it is difficult to perform batch exposure with a single mask. Therefore, as the substrate becomes larger, it is necessary to divide the substrate into a plurality of regions and perform exposure using a plurality of masks to form a predetermined pattern.

  However, when exposure is performed by dividing the substrate into a plurality of regions, a seam between patterns formed in each region becomes a problem. In other words, due to machine differences in the exposure apparatus and manufacturing errors of the mask itself, the pattern misalignment direction between shots at the time of exposure is different, and a pattern misalignment may occur at the overlapping portion of regions.

  The misalignment of the joint changes the transistor characteristics when the TFT is formed on the substrate. If the change in the transistor characteristics is large, the difference from the normal transistor characteristics becomes large, which is recognized by the human eye as display unevenness. This display unevenness is also called shot unevenness and may be a defective panel.

  In order to reduce display unevenness due to seam misalignment, Patent Document 1 and Patent Document 2 disclose measures using human visibility. In Patent Document 1 and Patent Document 2, an overlapping area is formed in which one area to be exposed and the other area overlap each other, and in the overlapping area, a portion exposed when one area is exposed and the other area are exposed. In this case, a portion to be exposed is arbitrarily provided. Note that the portion exposed when one region is exposed becomes a non-exposed portion when the other region is exposed. Conversely, a portion exposed when the other region is exposed becomes a non-exposed portion when one region is exposed.

  In Patent Document 1 and Patent Document 2, by arbitrarily mixing a portion exposed when exposing one region and a portion exposed when exposing the other region in the overlapping region, The other area is not joined in a straight line, but it becomes difficult for a person to visually recognize display unevenness due to a gap in the joint.

JP 2003-315831 A Republished patent WO95 / 16276

  However, even if the methods shown in Patent Document 1 and Patent Document 2 are used, display unevenness may occur due to the fact that the overlay accuracy of each layer formed on the substrate is more severe, the difference in exposure apparatus, or the manufacturing error of the mask. There was a problem recognized by the eyes.

  In particular, in the case of the first step of photolithography in which the first layer is patterned on the substrate, no reference (alignment mark) is provided on the substrate for alignment of the region to be exposed. For this reason, the exposure area is aligned based on the relative position between the mask alignment mark formed on the mask to be exposed and the alignment mark on the stage that supports the substrate. In the second and subsequent steps, alignment of the region to be exposed can be performed using the alignment mark formed by the pattern in the first step.

  Therefore, the alignment accuracy of each area to be exposed in the second and subsequent steps is affected by the alignment mark in the first step. That is, if the alignment accuracy in the first step is poor, the accuracy of the pattern seam is deteriorated, and even when Patent Document 1 or Patent Document 2 is used, display unevenness may be visually recognized.

  As a specific example, a gate pattern is formed on a substrate by a first step of photoengraving (hereinafter also simply referred to as a first step), and silicon is etched by a second step of photoengraving (hereinafter also simply referred to as a second step). The source pattern and the drain pattern are respectively patterned by a third step of photoengraving (hereinafter also simply referred to as a third step). By performing the first to third steps, a transistor is formed over the substrate.

  In the first step, since there is no alignment mark on the substrate as described above, the accuracy of the pattern seam may be deteriorated due to a difference in the exposure apparatus, a mask manufacturing error, or the like. If the accuracy of the seam of the pattern formed in the first process is poor, the pattern of the second process and the pattern of the third process are also affected, and the silicon etching pattern overlaps with the end of the source pattern or the drain pattern. Leakage is likely to occur at the location.

  When the liquid crystal panel as described above is displayed, a leak occurs at the joint portion of the pattern, causing variation in the charge characteristics of the pixels, resulting in a display defect called a flicker phenomenon.

  In addition, when there are a plurality of exposure apparatuses capable of patterning the pattern in the first step, the accuracy of the pattern seam is different even if exposure is performed under the same condition setting due to machine differences between the exposure apparatuses. It will be different between. When patterning the pattern of the second process on the substrate patterned with the pattern of the first process, if the accuracy of the pattern seam in the first process varies between exposure apparatuses, the accuracy of the pattern seam in the second process is increased. It becomes difficult to adjust.

  Specifically, when patterning the pattern of the second step, it is necessary to confirm with which exposure apparatus the pattern of the first step is patterned, and to set the exposure conditions of the second step according to the confirmation result. As a result, there was a problem that productivity was lowered.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an inspection method capable of quantitatively measuring the accuracy of pattern seams and improving the accuracy of pattern seams, and a method of manufacturing a liquid crystal display device using the same. To do.

  The solution according to the present invention is an inspection method for inspecting the accuracy of pattern seams by different exposures when a predetermined pattern is formed by dividing a substrate into a plurality of regions and separately exposing the substrate. In the overlapping region where the first region and the second region in the region overlap, the first pattern element related to the exposure of the first region and the second pattern related to the exposure of the first region arranged substantially parallel to the first pattern element A step of measuring a first distance from the element, and a step of measuring a second distance between the third pattern element joined to the first pattern element related to the exposure of the second area and the second pattern element in the overlapping area And determining the difference between the first distance and the second distance and quantifying and measuring the accuracy of the seam.

  Since the inspection method according to the present invention includes a step of obtaining the difference between the first distance and the second distance and quantifying and measuring the accuracy of the seam, the accuracy of the seam of the pattern can be managed quantitatively. This has the effect of improving the accuracy of the seam.

(Embodiment 1)
When a predetermined pattern is formed by dividing the substrate into a plurality of regions and separately exposing, in this embodiment, in particular, two regions are provided as shown in FIG. And exposing to form a pattern on the substrate. In FIG. 1A, a region 1 indicated by a thin line on the left side and a region 2 indicated by a thick line on the right side are shown. When the regions 1 and 2 are exposed on the substrate, the overlapping regions 3 where the regions 1 and 2 overlap as shown in FIG. Exposure to provide. Either exposure from the area 1 or exposure from the area 2 may be performed. Although not shown, the overlapping region 3 is exposed when the region 1 is exposed, but is exposed when the region 2 is exposed, and is exposed when the region 2 is exposed. When the region 1 is exposed, the region that is not exposed is mixed.

  A pattern formed by exposing the two regions 1 and 2 separately as shown in FIG. 1B is shown in FIG. In FIG. 2, predetermined patterns of the gate wiring 4, the capacitor wiring 5, the silicon layer 6, the source wiring 7, and the drain electrode 8 are respectively formed in the area 1 excluding the overlapping area 3, the area 2 excluding the overlapping area 3, and the overlapping area 3. Is schematically illustrated. These patterns are patterned in each step of photolithography as described in the problem to be solved by the invention. Specifically, the gate wiring 4 and the capacitor wiring 5 are patterned in the first step of photolithography, the silicon layer 6 is patterned in the second step of photolithography, and the source wiring 7 and the drain electrode in the third step of photolithography. 8 is patterned.

  As described in the background art, the pattern of the first step of photolithography is important for the accuracy of the pattern seam in the overlapping region 3. Therefore, in this embodiment, an inspection method for quantitatively inspecting the accuracy of the seam in the pattern of the first step will be described. FIG. 3 shows a view of the substrate when only the gate wiring 4 and the capacitor wiring 5 are patterned in the first step.

  The overlapping region 3 shown in FIG. 3 includes a region 3A inside the broken line and a region 3B outside the broken line. The area 3A is an area that is exposed when the area 1 is exposed, and the area 3B is an area that is exposed when the area 2 is exposed. Note that the region 3A exposed when the region 1 is exposed is a non-exposed portion when the region 2 is exposed, and the region 3B exposed when the region 2 is exposed is when the region 1 is exposed. Is an unexposed part.

  Therefore, in the overlapping region 3 shown in FIG. 3, the gate wiring 4 and the capacitor wiring 5 patterned by the exposure of the region 1 and the gate wiring 4 and the capacitor wiring 5 patterned by the exposure of the region 2 are joined together. Will exist. The jointed portion (seam 9) has a shape in which the pattern is recessed inward in a triangular shape as shown in FIG. Therefore, the joint 9 can be visually confirmed using a microscope or the like. Note that, depending on the state of the seam 9, the pattern may not have a shape that is recessed inward in a triangular shape, but may have a shape that has a step.

  An enlarged view of the overlapping region 3 is shown in FIG. FIG. 4A shows the gate wiring 4 and the capacitor wiring 5 patterned in the first step of photoengraving. An area below the broken line (hereinafter also simply referred to as area 3A) is an area. It is a region 3A that is exposed when 1 is exposed and a non-exposed portion when the region 2 is exposed. On the other hand, the region above the broken line (hereinafter simply referred to as region 3B) is a region 3B that is exposed when the region 2 is exposed, and is a non-exposed portion when the region 1 is exposed.

  That is, the left side portion of the broken line of the gate line 4 and the capacitor line 5 are patterned by the exposure of the region 1, and the right side portion of the broken line of the gate line 4 is patterned by the exposure of the region 2. Note that the present invention is not limited to the above case, and the right side portion of the broken line of the gate wiring 4 is patterned by the exposure of the region 1, and the left side portion of the broken line of the gate wiring 4 and the capacitor wiring 5 are patterned by the exposure of the region 2. But it ’s okay.

  Next, in the present embodiment, the distance between the gate wiring 4 and the capacitor wiring 5 is measured on both sides with the joint 9 (the boundary between the region 3A and the region 3B) of the gate wiring 4 as a boundary. That is, as shown in FIG. 4A, the distance 10 to the gate line 4 in the region 3A with respect to the capacitor line 5 and the distance 11 to the gate line 4 in the region 3B with respect to the capacitor line 5 are measured. Here, the distance between the gate line 4 and the capacitor line 5 to be measured is the shortest distance from the gate line 4 to the part of the capacitor line 5 provided substantially parallel to the gate line 4.

  Next, by calculating the difference between the measured distance 10 and distance 11, the accuracy of the joint of the pattern (gate wiring 4) can be quantified. This is because the measured distance 10 is measured based on the gate wiring 4 and the capacitor wiring 5 patterned together in the region 3A, while the measured distance 11 is patterned in the region 3B. Since the distance is measured based on the gate wiring 4 and the capacitor wiring 5 patterned in the region 3A, the accuracy of the joint can be quantified by obtaining the difference between the two.

  In the example shown in FIG. 4A, there is almost no difference between the distance 10 and the distance 11, but as shown in FIG. 4B, when the joint 9 of the gate wiring 4 has a shape like a step, the distance 10 And the distance 11 increases. FIG. 4B shows an example in which the distance 10 is larger than the distance 11, but the reverse may occur depending on the state of the seam 9.

  As shown in FIG. 4B, when the difference between the distance 10 and the distance 11 is large and the difference is a predetermined value or more, the exposure apparatus is corrected. Here, the predetermined value is a target value obtained from the design, past production data, or the like. If the predetermined value is equal to or higher than the target value, there is a high possibility that defects such as display unevenness will occur.

  FIG. 5 is a flowchart showing a method for manufacturing a liquid crystal display device used in the first step of photolithography for patterning the first layer on the substrate. First, in step 1, patterning is performed based on the set exposure conditions. In step 2, the accuracy of the seam is quantified and measured for the pattern patterned in step 1 (in the example of FIGS. 4A and 4B, the gate wiring 4 and the capacitor wiring 5) using the inspection method described above. . Specifically, in the example of FIGS. 4A and 4B, in the overlapping region 3, the distance 10 between the gate wiring 4 formed at the time of exposure of the region 1 and the capacitor wiring 5 arranged substantially parallel to the gate wiring 4. And the distance 11 between the capacitance wiring 5 and the gate wiring 4 in the area 3B that is formed at the time of exposure of the area 2 and is joined to the gate wiring 4 in the area 3A, and the difference between the distance 10 and the distance 11 is measured. Measure and quantify seam accuracy. The smaller the measured difference, the higher the seam accuracy, and the larger the measured difference, the lower the seam accuracy.

  In step 3, it is determined whether or not the difference measured in step 2 (specifically, the difference between distance 10 and distance 11) is equal to or greater than a predetermined value. In step 3, if the measured difference (joint accuracy value) is greater than or equal to a predetermined value, the process proceeds to step 4. If the measured difference is smaller than the predetermined value, the process proceeds to step 5.

  In step 4, the exposure conditions of the exposure apparatus are corrected so that the measured difference becomes smaller than a predetermined value. The exposure conditions to be corrected include, for example, adjusting the positions of the areas 1 and 2 to be exposed. On the other hand, if the measured difference is smaller than the predetermined value, the production of the first process of photoengraving is started in step 5.

  As described above, the inspection method according to the present embodiment can quantify the accuracy of the seam by measuring the distances 10 and 11 between the patterns on both sides of the seam 9 and taking the difference. Further, by quantifying the accuracy of the seam, it is possible to manage the accuracy of the seam and improve the accuracy of the seam.

  In addition, since the liquid crystal display device manufacturing method according to the present embodiment corrects the exposure apparatus in the production preparation stage using an inspection method for quantifying the seam accuracy, the seam accuracy is improved and the seam accuracy is improved. Display defects (for example, shot unevenness and the like) due to badness can be reduced. Specifically, if the seam accuracy is low as shown in FIG. 4B in the first step of photoengraving, the seam accuracy is still as shown in FIG. 7 even if the second and third steps are performed thereafter. It will be affected by the first step. For this reason, as shown in FIG. 7, the end of the silicon layer 6 may overlap with the end of the gate wiring 4 to cause display defects. However, in the present embodiment, since the exposure apparatus is corrected as described above, the accuracy of the seam is increased as shown in FIG. 4A in the first step of photolithography, and then the second and third steps are performed. Even if the process is performed, the accuracy of the seam is increased as shown in FIG. 6, so that display defects can be reduced.

(Embodiment 2)
In this embodiment, an inspection method different from the inspection method described in Embodiment 1 is described. Also in this embodiment, the substrate is divided into a plurality of regions and separately exposed to form a predetermined pattern. For this reason, as shown in FIG. 1A, a predetermined pattern is patterned on the substrate in the areas 1 and 2 separately. However, the region 1 and the region 2 are not formed in a pattern in the entire region, but are formed only in a part of the region (hereinafter also referred to as a pixel portion), and the rest are non-patterned portions where no pattern is formed. is there. Note that the pixel portion constitutes a part of a predetermined pattern formed on the substrate.

  Specifically, a mask used for the region 1 and the region 2 is shown in FIG. The mask shown in FIG. 8 is provided with a mask pattern for exposing the pixel portion 12 at the center. In the mask shown in FIG. 8, measurement patterns 14 and 15 are provided in the vicinity of the pixel portion 12 of the non-patterning portion 13.

  In FIG. 8, the mask pattern of the measurement pattern 14 provided on the lower side of the region 1 is a large square measurement pattern 14a on the outside and a small square measurement pattern 14b on the inside. The mask pattern of the measurement pattern 15 provided on the upper side of the region 2 is a small square measurement pattern 15a on the outside and a large square measurement pattern 15b on the inside. By exposing with the mask patterns of the measurement patterns 14a and 15b, a square pattern can be formed on the substrate. On the other hand, a rectangular extraction pattern can be formed on the substrate by exposing with the mask patterns of the measurement patterns 14b and 15a.

  In FIG. 8, the measurement patterns 14 and 15 are also provided on the upper side of the region 1 and on the lower side of the region 2, but this overlaps another region on the upper side of the region 1 or further on the lower side of the region 2. It is used when matching.

  By using the two masks shown in FIG. 8 to expose the pattern on the substrate, the measurement patterns 14 and 15 are patterned on the substrate. FIG. 9 shows a schematic view of a substrate on which the measurement patterns 14 and 15 are patterned. In FIG. 9, the region 1 and the region 2 form an overlap region 3, and the measurement pattern 14 and the measurement pattern 15 overlap in the overlap region 3. Specifically, the extraction pattern of the measurement pattern 15a is formed in the square measurement pattern 14a, and the extraction pattern of the measurement pattern 14b is formed in the square measurement pattern 15b.

  In the present embodiment, the accuracy of the seam is quantified by forming the measurement pattern 14 and the measurement pattern 15 so as to overlap each other and measuring the position of the measurement pattern 15 with respect to the measurement pattern 14. Specifically, FIG. 10A shows an enlarged view of the measurement pattern 14 b and the measurement pattern 15 b provided on both sides of the pixel unit 12. In FIG. 10A, the horizontal distance 16 from the edge of the measurement pattern 14b to the edge of the measurement pattern 15b is indicated by a thin line arrow, and the vertical distance from the edge of the measurement pattern 14b to the edge of the measurement pattern 15b. The direction distance 17 is indicated by a thick arrow.

  In FIG. 10A, since the distances 16 and 17 on both sides of the pixel portion 12 are equal to each other, it can be quantitatively understood that the seam accuracy is high. On the other hand, when the distances 16 and 17 on both sides of the pixel portion 12 are different from each other as shown in FIG. As a specific quantification method, for example, the distance 17 from the upper end side of the measurement pattern 14b on the left side of the pixel unit 12 to the upper end side of the measurement pattern 15b and the measurement pattern from the upper end side of the measurement pattern 14b on the right side of the pixel unit 12 A method of obtaining a difference from the distance 17 to the upper end side of 15b can be considered. The inspection method for quantifying the accuracy of the seam in this way can also be applied to the flowchart shown in FIG. That is, the inspection method according to the present embodiment can be used in place of the inspection method of Step 2 shown in FIG.

  Next, FIG. 11 shows a schematic view when the substrate is divided into four regions and a predetermined pattern is patterned using different masks in the respective regions. In FIG. 11, an overlapping region 25 is formed in which the regions 21, 22, 23, and 24 overlap each other. In FIG. 11, measurement patterns 26 and 27 are formed in the vicinity of the pixel portion 12 in each region.

  FIG. 12 shows a mask for exposing the pattern as shown in FIG. 11 on the substrate. The mask of the region 21 shown in FIG. 12 is provided with a mask pattern that forms the measurement pattern 26 near the upper side and the left side of the pixel unit 12. By exposing the mask pattern, a large square measurement pattern 26 can be formed on the substrate. The mask of the region 22 shown in FIG. 12 is provided with a mask pattern that forms a measurement pattern 27 near the upper side and the right side of the pixel unit 12. By exposing the mask pattern, a small rectangular extraction pattern (measurement pattern 27) can be formed on the substrate.

  Similarly, the mask of the region 23 shown in FIG. 12 is provided with a mask pattern for forming the measurement pattern 27 on the lower side and the left side of the pixel portion 12. The mask of the region 23 shown in FIG. 12 is provided with a mask pattern that forms a measurement pattern 26 near the lower side and the right side of the pixel unit 12.

  Then, the pattern is exposed on the substrate using the four masks shown in FIG. As a result of patterning, the pattern of FIG. 11 is obtained, and the position of the measurement pattern 27 with respect to the measurement pattern 26 is measured as shown in FIGS. As a result, the accuracy of the seam can be quantified. By applying this method to the flowchart shown in FIG. 5, the accuracy of the seam can be improved.

  As shown in FIG. 11, when exposure is performed separately in four areas, the measurement patterns 26 and 27 are placed on one diagonal line of the pixel unit 12 because the two sides of one area overlap with other areas. Can only be placed. If the measurement patterns 26 and 27 are provided at the four corners of the pixel unit 12, the measurement patterns 26 and 27 are patterned in adjacent regions.

  However, when the measurement patterns 26 and 27 are arranged only on one diagonal line of the pixel unit 12, less information is obtained regarding the accuracy of the seam than when the measurement patterns 26 and 27 are provided at the four corners of the pixel unit 12. There may be cases where sufficient correction cannot be made. In that case, the above method may be applied after analyzing the pattern in the pixel portion 12 and removing the rotation component of each region in advance.

  As described above, in the inspection method according to the present embodiment, the measurement patterns 14, 15, 26, and 27 are provided in the vicinity of a part of the predetermined pattern (pixel portion 12), and the measurement pattern 15 for the measurement patterns 14 and 26 is provided. , 27 can be quantified, the seam accuracy can be quantified, the seam accuracy can be managed, and the seam accuracy can be improved.

It is a figure which shows the area | region to expose which concerns on Embodiment 1 of this invention. It is a top view which shows the liquid crystal display device which concerns on Embodiment 1 of this invention. It is a top view which shows the board | substrate which patterned the gate wiring and capacitor wiring which concern on Embodiment 1 of this invention. It is a top view which shows the joint in the overlap area | region which concerns on Embodiment 1 of this invention. It is a figure explaining the manufacturing method of the liquid crystal display device which concerns on Embodiment 1 of this invention. It is a top view for demonstrating an effect in the liquid crystal display device which concerns on Embodiment 1 of this invention. It is a top view for demonstrating an effect in the liquid crystal display device which concerns on Embodiment 1 of this invention. It is a top view which shows the mask used for the liquid crystal display device which concerns on Embodiment 2 of this invention. It is a top view which shows the measurement pattern of the liquid crystal display device which concerns on Embodiment 2 of this invention. It is a top view explaining the measurement pattern of the liquid crystal display device which concerns on Embodiment 2 of this invention. It is a top view which shows the measurement pattern of another liquid crystal display device which concerns on Embodiment 2 of this invention. It is a top view which shows the mask used for another liquid crystal display device which concerns on Embodiment 2 of this invention.

Explanation of symbols

1, 2, 21, 22, 23, 24 region, 3, 25 overlap region, 4 gate wiring, 5 capacitance wiring, 6 silicon layer, 7 source wiring, 8 drain electrode, 9 joint, 10, 11 distance, 12 pixel portion , 13 Non-patterning part, 14, 15, 26, 27 Measurement pattern, 16, 17 Distance.

Claims (3)

In the case where a predetermined pattern is formed by dividing a substrate into a plurality of regions and separately exposing, an inspection method for inspecting the accuracy of a pattern seam by different exposure,
In the overlapping region where the first region and the second region of the plurality of regions overlap, the first pattern element related to the exposure of the first region and the first region disposed substantially parallel to the first pattern element Measuring a first distance from a second pattern element related to exposure;
Measuring a second distance between the third pattern element joined to the first pattern element related to the exposure of the second area and the second pattern element in the overlapping area;
An inspection method comprising a step of obtaining a difference between the first distance and the second distance and quantifying and measuring the accuracy of the seam. In the case where a predetermined pattern is formed by dividing a substrate into a plurality of regions and separately exposing, an inspection method for inspecting the accuracy of a pattern seam by different exposure,
Providing a first measurement pattern related to exposure of the first region outside the predetermined pattern in an overlapping region where the first region and the second region in the plurality of regions overlap;
Providing a second measurement pattern related to exposure of the second region outside the predetermined pattern in the overlapping region;
And a step of quantifying and measuring the accuracy of the seam by measuring the position of the second measurement pattern with respect to the first measurement pattern. A method of manufacturing a liquid crystal display device including a step of forming a predetermined pattern by dividing a substrate into a plurality of regions and separately exposing the substrate,
(A) forming the predetermined pattern on the first layer on the substrate;
(B) quantifying and measuring the accuracy of the seam using the inspection method according to claim 1 or claim 2;
(C) determining whether the measured accuracy value of the seam is equal to or greater than a predetermined value;
(D) When it is determined in the step (c) that the accuracy value of the seam is equal to or greater than a predetermined value, the exposure positions of the first area and the second area are corrected, and the new substrate is Performing steps (a) and (b);
(E) A method of manufacturing a liquid crystal display device comprising a step of starting production based on a set condition when the accuracy value of the seam is smaller than a predetermined value in the step (b).

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