Method of forming diffraction-based lle overlay measurement marks and overlay measurement method

Abstract

The application provides a forming method and a measurement method of a diffraction-based LLE overlay measurement mark, and the forming method comprises the following steps: providing a substrate, and a photoresist layer is formed on the substrate; forming a plurality of first grooves in the photoresist layer; and forming a plurality of second grooves in the remaining photoresist layer. The forming method and the measurement method of the diffraction-based LLE overlay measurement mark provided by the application are characterized in that, after the first grooves are formed, the first grooves are virtually filled, and then the second grooves are formed, so as to avoid the design rule that prohibits performing two same processes continuously on the same film layer, and a grating structure comprising the first grooves and the second grooves is formed in the photoresist layer, so as to perform DBO measurement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor, and in particular to a forming method of a diffraction-based LLE overlay measurement mark and an overlay measurement method. BACKGROUND

[0002] Traditional overlay is measured by using image-based overlay (IBO) measurement technology. As the CD size of lithography pattern enters 28nm and below process nodes, due to the limitation of imaging resolution limit, the traditional IBO measurement technology has gradually failed to meet the requirements of overlay measurement of new process nodes, and diffraction-based overlay (DBO) measurement technology is gradually becoming an important supplement to overlay measurement.

[0003] DBO measurement technology originates from the method of using scattering and diffraction for optical measurement. The overlay error is determined by directly measuring the diffraction light of the overlay mark. The measurement speed is fast, the sampling area is small, and many error terms of the traditional measurement method are basically eliminated, such as positioning error, focal plane error, aberration factor and mechanical vibration, etc.

[0004] DBO is mainly divided into two categories. One is model-based DBO technology, and the other is experience-based DBO technology. The technology calculates the theoretical diffraction spectrum by strictly modeling the CD, sidewall angle (SWA), height and overlay parameters of the overlay mark, compares the measured value with the theoretical value, and extracts the overlay parameters. The main advantage of this technology is that in principle, only one mark can measure the overlay value in one direction, so the cost of the mark is lower.

[0005] However, the current DBO measurement technology still has defects, so it is necessary to provide a more reliable and effective technical solution. SUMMARY

[0006] The present application provides a forming method of a diffraction-based LLE overlay measurement mark and an overlay measurement method, which can measure the overlay using LLE process.

[0007] One aspect of the present application provides a forming method of a diffraction-based LLE overlay measurement mark, comprising: providing a substrate, the substrate being formed with a photoresist layer; forming a plurality of first grooves in the photoresist layer; forming a plurality of second grooves in the remaining photoresist layer, the remaining photoresist layer being divided into a first photoresist layer and a second photoresist layer.

[0008] In some embodiments of the present application, the width of the second groove is different from that of the first groove.

[0009] In some embodiments of the present application, the second photoresist layer has a different width than the first photoresist layer.

[0010] Another aspect of the present application also provides a diffraction-based LLE overlay measurement method, comprising: providing a substrate having a photoresist layer formed thereon; forming a plurality of first grooves in the photoresist layer; forming a plurality of second grooves having an offset value d in the remaining photoresist layer; illuminating one side of the substrate having the first grooves and the second grooves formed thereon with a light beam; obtaining a light intensity of diffraction light emitted to one side and denoted as I L , obtaining a light intensity of diffraction light emitted to the other side and denoted as I R ; and obtaining an overlay accuracy OV according to the offset value d and the light intensities I L and I R .

[0011] In some embodiments of the present application, the second grooves have a different width than the first grooves.

[0012] In some embodiments of the present application, a formula for obtaining the overlay accuracy OV according to the offset value d and the light intensities I L and I R includes: (I R -I L ) +d = K(OV + d); (I R -I L ) -d = K(OV - d).

[0013] In some embodiments of the present application, the offset value d is 15 nm to 25 nm.

[0014] In some embodiments of the present application, the measurement method further comprises: calculating a difference between the accuracy OV and a preset reference value.

[0015] In some embodiments of the present application, the difference is less than or equal to zero, and the overlay is aligned.

[0016] In some embodiments of the present application, the difference is greater than zero, and the overlay is misaligned.

[0017] In some embodiments of the present application, the reference value is 2 nm to 12 nm.

[0018] The diffraction-based LLE overlay measurement mark forming method and the overlay measurement method of the present application form the first grooves, virtually fill the first grooves, and then form the second grooves, thereby avoiding the design rule that prohibits performing two same processes in succession in the same film layer, and forming a grating structure including the first grooves and the second grooves in the photoresist layer for performing DBO measurement. BRIEF DESCRIPTION OF DRAWINGS

[0019] The following drawings set forth particular applications of the present application in detail. Like numbers in different drawings represent similar components. Those skilled in the art will appreciate that the embodiments herein are non-limiting, exemplary embodiments, and the drawings are for purposes of illustration and description only and are not intended as an exhaustive description of the scope of the present application, as other embodiments can accomplish the same purpose. It is to be understood that the drawings are not to scale. In which:

[0020] Figures 1 to 3 Schematic diagram of steps in a method of forming a diffraction-based LLE overlay measurement mark according to some embodiments of the present application;

[0021] Figures 4 to 6 Schematic diagram of steps in a method of forming a diffraction-based LLE overlay measurement mark according to some embodiments of the present application;

[0022] Figures 7 to 8 Schematic diagram of a diffraction-based LLE overlay measurement method according to some embodiments of the present application. DETAILED DESCRIPTION

[0023] The following description provides specific details for the purpose of providing a thorough understanding of certain implementations of the present application. Those of ordinary skill in the art will realize that the implementations of the present application can be practiced without many of the details listed herein. Those skilled in the art will further appreciate that they can readily employ the principles described herein for applications other than those explicitly described and that the scope of the application is

[0024] The technical solutions of the present application will be described in detail below in conjunction with the embodiments and drawings.

[0025] DBO measurement techniques are gradually replacing IBO measurement techniques as the primary measurement method for overlay accuracy. However, current DBO measurement techniques do not have a solution for LLE (litho, litho, etch) processes in double patterning technology, although they can cover most cases. This is because current DBO design rules prohibit two identical process steps in a same film layer in succession, so two exposures in a photoresist layer in succession to form a mark for measurement are not possible.

[0026] To address the aforementioned issues, this application provides a method for forming LLE overlay measurement marks based on diffraction and an overlay measurement method. After forming a first trench in the photoresist layer through a first exposure, the first trench is virtually filled, and then a second exposure is performed to form a second trench. This avoids the design rule that prohibits performing the same process twice consecutively on the same film layer, and forms a grating structure including the first trench and the second trench in the photoresist layer for DBO measurement.

[0027] Figures 1 to 3 This is a schematic diagram of each step in the method for forming diffraction-based LLE overlay measurement marks as described in some embodiments of this application.

[0028] Embodiments of this application provide a method for forming LLE overlay measurement marks based on diffraction, including: referencing Figure 1 A substrate 100 is provided, on which a photoresist layer 110 is formed; Reference Figure 2 A plurality of first trenches 120 are formed in the photoresist layer 110; a virtual filling layer is formed in the plurality of first trenches 120; reference Figure 3 A plurality of second trenches 130 are formed in the remaining photoresist layer 110; the virtual fill layer is removed.

[0029] The following is in conjunction with the appendix Figure 1 To be continued Figure 3 The method for forming LLE overlay measurement marks based on diffraction described in the embodiments of this application will be described in detail.

[0030] refer to Figure 1 A substrate 100 is provided, on which a photoresist layer 110 is formed. The substrate 100 is consistent with the actual semiconductor structure to be subjected to the LLE process.

[0031] In some embodiments of this application, an anti-reflection layer may be formed between the substrate 100 and the photoresist layer 110. The anti-reflection layer can improve the effect of subsequent exposure processes and obtain exposure patterns with better shapes.

[0032] In some embodiments of this application, the process of forming the photoresist layer 110 on the substrate 100 includes a spin coating process.

[0033] refer to Figure 2 A plurality of first trenches 120 are formed in the photoresist layer 110.

[0034] In some embodiments of this application, the method for forming the plurality of first trenches 120 is, for example, to perform an exposure process on the photoresist layer using a mask that defines the positions of the plurality of first trenches 120.

[0035] Continue to refer to Figure 2A dummy fill layer is formed in the first trenches 120. It is noted that since it is a dummy fill layer, the first trenches 120 are not actually filled, and remain the same as the structure shown in FIG. 1A, and no change has occurred. Figure 2

[0036] Since the current DBO design rule prohibits two identical process steps in the same film layer in succession, after the first exposure process to form the first trenches 120, a second exposure process to form the second trenches 130 cannot be performed in succession. The technical solution of the present application, after the first exposure process to form the first trenches 120, designs a dummy fill process to fill the first trenches, and then performs a second exposure process to form the second trenches 130, thus avoiding the design rule of prohibiting two identical process steps in the same film layer in succession. A grating structure including the first trenches 120 and the second trenches 130 is formed in the photoresist layer 110, and is used for DBO measurement.

[0037] In some embodiments of the present application, other suitable dummy steps can also be used, as long as the design rule of prohibiting two identical process steps in the same film layer in succession is avoided.

[0038] Referring to FIG. 1C, Figure 3 A second trench 130 is formed in the remaining photoresist layer 110.

[0039] In some embodiments of the present application, the method of forming the second trenches 130 is, for example, an exposure process on the photoresist layer using a mask defining the positions of the second trenches 130. In some embodiments of the present application, the width of the second trenches 130 is different from that of the first trenches 120. In some embodiments of the present application, the width ratio of the first trenches 120 to the second trenches 130 is 1:(1.3-2). In some embodiments of the present application, the width ratio of the first trenches 120 to the second trenches 130 is 1:(1.4-1.8). In some embodiments of the present application, the width ratio of the first trenches 120 to the second trenches 130 is 1:(1.5-1.6).

[0040] ​For the first trench 120 and the second trench 130 in the same film layer, since they are both unfilled trenches and cannot be distinguished in material, the best way to distinguish the first trench 120 and the second trench 130 is size. If the first trench 120 and the second trench 130 have the same size, the measuring machine cannot distinguish the first trench 120 and the second trench 130. Therefore, the first trench 120 and the second trench 130 cannot have the same size, and specifically, since the height (i.e., the size in the vertical direction) of the first trench 120 and the second trench 130 cannot be changed, the width (i.e., the size in the horizontal direction) of the first trench 120 and the second trench 130 cannot be the same.

[0041] With reference to the above description of the first embodiment, the second embodiment of the present application is described as follows. Figure 3 The virtual filling layer is removed. Although the first trenches 120 are virtually filled and the virtual filling layer does not actually exist, in order to maintain logical self-consistency in the process flow, a step of removing the virtual filling layer is needed. In some embodiments of the present application, other suitable virtual steps can also be used as long as the design rule of prohibiting two same processes in the same film layer in succession is avoided.

[0042] Figures 4 to 6 The schematic diagram of each step in the method for forming a diffraction-based LLE overlay measurement mark according to another embodiment of the present application.

[0043] Another embodiment of the present application further provides a method for forming a diffraction-based LLE overlay measurement mark, comprising: Figure 4 providing a substrate 400 on which a photoresist layer 410 is formed; forming a plurality of first trenches 420 in the photoresist layer 410; forming a virtual filling layer in the plurality of first trenches 420; Figure 5 forming a plurality of second trenches 430 in the remaining photoresist layer 410, which is divided into a first photoresist layer 411 and a second photoresist layer 412; and removing the virtual filling layer. Figure 6 forming a plurality of second trenches 430 in the remaining photoresist layer 410, which is divided into a first photoresist layer 411 and a second photoresist layer 412; and removing the virtual filling layer.

[0044] The method for forming a diffraction-based LLE overlay measurement mark according to another embodiment of the present application is described in detail below with reference to the accompanying drawings. Figure 4 to Figure 6 The method for forming a diffraction-based LLE overlay measurement mark according to another embodiment of the present application is described in detail below with reference to the accompanying drawings. Figures 4 to 6 The similar parts in the embodiments shown in Figures 1 to 3 The similar parts in the embodiments shown in

[0045] With reference to the above description of the first embodiment, the second embodiment of the present application is described as follows. Figure 4A substrate 400 is provided, on which a photoresist layer 410 is formed. The substrate 400 is consistent with the real semiconductor structure that needs to be processed by LLE.

[0046] Referring to Figure 5 A plurality of first trenches 420 are formed in the photoresist layer 410.

[0047] Continuing to refer to Figure 5 A dummy fill layer is formed in the plurality of first trenches 420. It should be noted that the plurality of first trenches 420 are not filled in the actual structure, and the structure remains the same as shown in FIG. 4A, and no change occurs. Figure 5 The structure remains the same as shown in FIG. 4A, and no change occurs.

[0048] Referring to Figure 6 A plurality of second trenches 430 are formed in the remaining photoresist layer 410, which is divided into a first photoresist layer 411 and a second photoresist layer 412.

[0049] In some embodiments of the present application, the width of the second photoresist layer 412 is different from that of the first photoresist layer 411. In some embodiments of the present application, the width ratio of the first photoresist layer 411 and the second photoresist layer 412 is 1:(1.3-2). In some embodiments of the present application, the width ratio of the first photoresist layer 411 and the second photoresist layer 412 is 1:(1.4-1.8). In some embodiments of the present application, the width ratio of the first photoresist layer 411 and the second photoresist layer 412 is 1:(1.5-1.6).

[0050] The first photoresist layer 411 and the second photoresist layer 412 are the same layer of photoresist and cannot be distinguished in terms of material, so the best way to distinguish the first photoresist layer 411 and the second photoresist layer 412 is size. If the first photoresist layer 411 and the second photoresist layer 412 are the same size, the measuring machine cannot distinguish the first photoresist layer 411 and the second photoresist layer 412. Therefore, the first photoresist layer 411 and the second photoresist layer 412 cannot be the same size, and specifically, since the height (i.e., the size in the vertical direction) of the first photoresist layer 411 and the second photoresist layer 412 cannot be changed, the width (i.e., the size in the horizontal direction) of the first photoresist layer 411 and the second photoresist layer 412 cannot be the same.

[0051] Continuing to refer to Figure 6 The dummy fill layer is removed. Although the plurality of first trenches 420 are virtually filled, the dummy fill layer does not actually exist, but in order to maintain logical self-consistency in the process flow, a step of removing the dummy fill layer needs to be designed.

[0052] The forming method of the diffraction-based LLE overlay measurement mark in the present application forms the first groove, then virtually fills the first groove, and then forms the second groove, avoiding the design rule of prohibiting two same processes in the same film layer, to form a grating structure including the first groove and the second groove in the photoresist layer for DBO measurement.

[0053] The embodiment of the present application also provides a diffraction-based LLE overlay measurement method, including: providing a substrate, the substrate being provided with a photoresist layer; forming a plurality of first grooves in the photoresist layer; forming a virtual filling layer in the plurality of first grooves; forming a plurality of second grooves with an offset value d in the remaining photoresist layer; removing the virtual filling layer; irradiating one side of the substrate provided with the first groove and the second groove with a light beam; obtaining the light intensity of the diffraction light irradiated to one side and recording it as I L , obtaining the light intensity of the diffraction light irradiated to the other side and recording it as I R ; and obtaining an overlay accuracy OV according to the offset value d and the light intensities I L and I R .

[0054] In some embodiments of the present application, the widths of the first groove 120 and the second groove 130 are different. In some embodiments of the present application, the width ratio of the first groove 120 and the second groove 130 is 1:(1.3-2). In some embodiments of the present application, the width ratio of the first groove 120 and the second groove 130 is 1:(1.4-1.8). In some embodiments of the present application, the width ratio of the first groove 120 and the second groove 130 is 1:(1.5-1.6).

[0055] In some embodiments of the present application, the formula for obtaining the overlay accuracy OV according to the offset value d and the light intensities I L and I R includes: (I R -I L ) +d =K(OV+d); (I R -I L ) -d =K(OV-d). In some embodiments of the present application, the plurality of second grooves are offset to one side, and in other embodiments of the present application, the plurality of second grooves are offset to the other side, and two offset values d and two light intensities I L and I R can be obtained in turn. The two offset values d and the two light intensities I L and I RThe values of OV and K can be calculated by substituting the above two formulas into a binary linear equation set. The OV is overlay accuracy, and the K is a slope of a linear relationship between the intensity difference of the diffraction light and the overlay accuracy within a certain range.

[0056] In some embodiments of the present application, the offset value d is 10-30 nm, for example, 16 nm, 18 nm, 20 nm, 22 nm, or 24 nm, etc. The corresponding offset value is designed according to the core size of the overlay mark.

[0057] In some embodiments of the present application, the measurement method further comprises calculating a difference between the accuracy OV and a preset reference value. The reference value is a reference data for judging whether the overlay is aligned, which is calculated in advance according to the core size of the overlay mark and the exposure process, etc.

[0058] In some embodiments of the present application, the difference is less than or equal to zero, i.e., the accuracy OV is less than the reference value, and the overlay is aligned. It should be noted that the alignment does not mean complete alignment, but the deviation is within an acceptable range.

[0059] In some embodiments of the present application, the difference is greater than zero, i.e., the accuracy OV is greater than the reference value, and the overlay is not aligned. Similarly, the misalignment means that the deviation is not within an acceptable range.

[0060] In some embodiments of the present application, the reference value is 2-12 nm. The reference value is related to the core size of the overlay mark. For example, when the core size of the overlay mark is a 14 nm process, the reference value can be 6 nm; when the core size of the overlay mark is a 28 nm process, the reference value can be 12 nm; and when the core size of the overlay mark is a 7 nm process, the reference value can be 3 nm.

[0061] Figures 7 to 8 A schematic diagram of the diffraction-based LLE overlay measurement method according to some embodiments of the present application is shown in FIG. 1. The diffraction-based LLE overlay measurement method according to some embodiments of the present application will be described in detail below. Figure 7 and Figure 8 The diffraction-based LLE overlay measurement method according to some embodiments of the present application will be described in detail.

[0062] It should be noted that, since the forming method of the diffraction-based LLE overlay measurement mark has been described in detail in the foregoing, it will not be described again here, and the formed diffraction-based LLE overlay measurement mark is directly provided.

[0063] Reference is made to Figure 7As shown, a diffraction-based LLE overlay measurement mark includes: a substrate 200; a photoresist layer 210 located on the substrate; a plurality of first trenches 220 and a plurality of second trenches 230, the plurality of first trenches 220 and the plurality of second trenches 230 being staggered in the photoresist layer 210 and penetrating the photoresist layer 210. The plurality of second trenches 230 are offset to one side (left side of the figure) relative to a standard position (i.e., the position represented by the dashed line in the figure) by an offset value of d.

[0064] A beam of light is used to illuminate one side of the substrate where the first and second trenches are formed; the intensity of the diffracted light incident on one side (the left side in the figure) is obtained and denoted as I. L1 The intensity of the diffracted light incident on the other side (the right side of the figure) is obtained and denoted as I. R1 It should be noted that the diagram only illustrates a light path for ease of explanation; in reality, the light shines on the entire substrate surface.

[0065] The offset value d and the light intensity I L1 and I R1 Substituting into the above formula (I) R -I L ) +d =K(OV+d) yields formula (1): (I R1 -I L1 ) +d =K(OV+d).

[0066] refer to Figure 8 As shown, a diffraction-based LLE overlay measurement mark includes: a substrate 300; a photoresist layer 310 located on the substrate; a plurality of first trenches 320 and a plurality of second trenches 330, the plurality of first trenches 320 and the plurality of second trenches 330 being staggered in the photoresist layer 310 and penetrating the photoresist layer 310. The offset value d of the plurality of second trenches 330 relative to the standard position (i.e., the position represented by the dashed line in the figure) to the other side (the right side of the figure) is a certain value.

[0067] A beam of light is used to illuminate one side of the substrate where the first and second trenches are formed; the intensity of the diffracted light incident on one side (the left side in the figure) is obtained and denoted as I. L2 The intensity of the diffracted light incident on the other side (the right side of the figure) is obtained and denoted as I. R2 It should be noted that the diagram only illustrates a light path for ease of explanation; in reality, the light shines on the entire substrate surface.

[0068] The offset value d and the light intensity I L2 and I R2 Substituting into the above formula (I) R -I L )-d = K(OV - d) Equation (2) is obtained from Equation (1). R2 -I L2 ) -d = K(OV - d).

[0069] The formula (1) and the formula (2) are combined to form a binary linear equation group, and the value of the overlay accuracy OV can be calculated. The difference between the accuracy OV and the preset reference value can be calculated to know whether the overlay is accurate.

[0070] The LLE overlay measurement method based on diffraction described in the present application virtually fills the first trench after forming the first trench, and then forms the second trench, avoiding the design rule of prohibiting two same processes in the same film layer in succession, to form a grating structure including the first trench and the second trench in the photoresist layer for performing DBO measurement.

[0071] In summary, after reading the content of the present application, those skilled in the art can understand that the foregoing content of the application can be presented only in an exemplary manner and can not be limiting. Although not explicitly stated herein, those skilled in the art can understand that the present application is intended to encompass various reasonable changes, improvements and modifications to the embodiments. These changes, improvements and modifications are within the spirit and scope of the exemplary embodiments of the present application.

[0072] It should be understood that the term "and / or" used in the embodiments of the present application includes any or all combinations of one or more associated listed items. It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there can be an intermediate element.

[0073] Similarly, it should be understood that when an element such as a layer, a region or a substrate is referred to as being "on" another element, it can be directly on the other element, or there can be an intermediate element. In contrast, the term "directly" means that there is no intermediate element. It should also be understood that the terms "comprise", "comprising", "include", or "including", when used in the present document, indicate the presence of the recited features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0074] It will also be appreciated that, although terms such as first, second, third, etc. can be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. Thus, a first element in some embodiments could be called a second element in other embodiments without departing from the teachings of the present application. The same reference numerals or same reference designators denote the same elements throughout the specification.

[0075] Furthermore, the present application description describes exemplary embodiments by reference to idealized illustrative cross-sectional and / or plan and / or elevation views. Consequently, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and / or tolerances, are to be expected. Therefore, exemplary embodiments should not be construed as limited to the precise shapes and regions shown herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an etched region illustrated as a rectangle will, typically, have rounded or curved features. Consequently, the regions illustrated in the figures are schematic and not drawn to scale. The same reference numerals or same reference designators denote the same elements throughout the specification.

Claims

1. A method of forming diffraction-based LLE overlay measurement marks, characterized in that, The method comprises: providing a substrate, wherein a photoresist layer is formed on the substrate; forming a plurality of first grooves in the photoresist layer; forming a dummy fill layer in the plurality of first grooves, wherein the dummy fill layer does not exist in an actual structure; forming a plurality of second grooves in the remaining photoresist layer, wherein the remaining photoresist layer is divided into a first photoresist layer and a second photoresist layer by the plurality of second grooves, and the second grooves have different widths from the first grooves; removing the dummy fill layer.

2. The formation process of claim 1 wherein, The second photoresist layer has a different width from the first photoresist layer.

3. A diffraction-based LLE overlay measurement method, characterized in that, The method comprises: forming a diffraction-based LLE overlay measurement mark by using the method for forming a diffraction-based LLE overlay measurement mark according to any one of claims 1 to 2, wherein the plurality of second grooves have an offset d, and the offset d is an offset value of the plurality of second grooves relative to a standard position; illuminating one side of the substrate, on which the first grooves and the second grooves are formed, by using a light beam; The light intensity of the diffracted light directed to one side is acquired and denoted as I L The light intensity of the diffracted light directed to the other side is acquired and denoted as I R ; According to the offset value d and the light intensity I L and I R Obtaining overlay accuracy OV.

4. The measurement method of claim 3, wherein, The second grooves have different widths from the first grooves.

5. The measurement method of claim 3, wherein, According to the offset value d and the light intensity I L and I R The formula for obtaining overlay accuracy OV includes: (I R -I L )+d=K(OV+d); (I R -I L )-d=K(OV-d), wherein K is the slope of the linear relationship between the light intensity difference of the diffracted light and the overlay accuracy within a certain range.

6. The measurement method of claim 3, wherein, The offset value d is 15 nanometers to 25 nanometers.

7. The measurement method according to claim 3, characterized by, The method further comprises: calculating a difference between the accuracy OV and a reference value.

8. The method of measuring of claim 7, wherein, When the difference is less than or equal to zero, the overlay is aligned.

9. The measurement method of claim 7, wherein, When the difference is greater than zero, the overlay is misaligned.

10. The measurement method of claim 7, wherein, The reference value is 2 nanometers to 12 nanometers.

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