Overlay mark and method for correcting overlay precision measurement accuracy

Abstract

The invention provides an overlay mark and a method for correcting overlay precision measurement accuracy. The overlay mark comprises a front-layer overlay mark and a current-layer overlay mark, the front layer overlay marks comprise a first pair of front layer marks arranged along a first direction, a second pair of front layer marks arranged along a second direction and a third pair of front layer marks arranged along a third direction; the current layer overlay mark comprises a first pair of current layer marks, a second pair of current layer marks and a third pair of current layer marks, and further comprises a fifth pair of current layer marks located between the first pair of current layer marks and a center mark located in the center area. According to the method, the center mark is arranged in the center area of the current-layer overlay mark, and the asymmetry of the front-layer overlay marks is obtained through the distance from the first pair of front-layer marks in the front-layer overlay marks to the center mark, so that the overlay precision compensation value containing the asymmetry is finally obtained, and the accurate overlay precision is obtained; and wafer scrapping caused by inaccurate measurement of the overlay precision is reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to an overlay marking method and a method for correcting the accuracy of overlay measurement. Background Technology

[0002] In the semiconductor integrated circuit manufacturing process, multiple photolithography steps are required. The alignment accuracy of the photolithography machine, i.e., the overlay accuracy (OVL), needs to meet certain design requirements. Current technologies typically use metrology equipment to measure the overlay marks to obtain the overlay accuracy, mainly by collecting the signal differences between the previous and current layers to calculate the overlay accuracy value.

[0003] However, while the overlay marks of the current layer are generally quite regular, the overlay marks of the previous layer may be deformed after etching, dielectric layer deposition, and chemical polishing. The asymmetry of the deformed overlay marks will affect the interpretation of the overlay accuracy signal, ultimately affecting the accuracy of the overlay accuracy measurement and causing the wafer to be scrapped.

[0004] Figure 1 It is an ideal cross-sectional view of the overprinted markings of the previous layer and the overprinted markings of the current layer. Figure 2 This is a cross-sectional view of the overprinted markings of the previous layer and the current layer. Please refer to it. Figure 1 As shown, when the overlay mark 10 and the previous overlay mark 20 are both relatively regular, the overlay accuracy can be directly measured and obtained relatively accurately. Please refer to... Figure 2 As shown, when the overlay mark 10 is relatively regular, but one of the marks in the previous overlay mark 20 is deformed, the previous overlay mark 20 becomes asymmetrical, which will lead to distorted measurement results. Summary of the Invention

[0005] The purpose of this invention is to provide an overlay marking method and a method for correcting the accuracy of overlay precision measurement, correcting the problem of overlay precision measurement distortion caused by asymmetry of overlay marking, obtaining accurate overlay precision results, and reducing wafer scrap caused by inaccurate overlay precision measurement.

[0006] To solve the above-mentioned technical problems, the present invention provides an overlay mark, including a previous layer overlay mark and a current layer overlay mark; The front layer overprinted marks include a first pair of front layer marks arranged along a first direction and centrally symmetrical with respect to the center of the front layer marks, a second pair of front layer marks arranged along a second direction and centrally symmetrical with respect to the center of the front layer marks, and a third pair of front layer marks arranged along a third direction and centrally symmetrical with respect to the center of the front layer marks. The layer overlay markings include a first pair of layer markings arranged along a first direction and centrally symmetrical with respect to the center of the layer markings, a second pair of layer markings arranged along a second direction and centrally symmetrical with respect to the center of the layer markings, and a third pair of layer markings arranged along a third direction and centrally symmetrical with respect to the center of the layer markings. The current layer overlay mark is located inside the previous layer overlay mark, and the center of the current layer mark coincides with the center of the previous layer mark in a direction perpendicular to the overlay mark; The layer overlay markings also include a fifth pair of layer markings arranged along the first direction and centrally symmetrical with respect to the center of the layer markings, and a center marking located in the central region of the layer overlay markings. The fifth pair of layer markings is located between the first pair of layer markings, and the center of the center marking coincides with the center of the layer marking.

[0007] Optionally, the first direction is perpendicular to the second direction, and the angle between the positive direction of the third direction and the positive direction of the first direction is an acute angle.

[0008] Optionally, the preceding layer overprinting marks further include a fourth pair of preceding layer marks arranged along the fourth direction and centrally symmetrical with respect to the center of the preceding layer marks; the current layer overprinting marks further include a fourth pair of current layer marks arranged along the fourth direction and centrally symmetrical with respect to the center of the current layer marks; the angle between the positive direction of the fourth direction and the positive direction of the first direction is an obtuse angle.

[0009] Optionally, the angle between the positive direction of the third direction and the positive direction of the first direction is 45 degrees, and the angle between the positive direction of the fourth direction and the positive direction of the first direction is 135 degrees.

[0010] Optionally, the marks in the previous layer overprinted marks and the marks in the current layer overprinted marks are both strip-shaped, the extension direction of the strip-shaped marks is perpendicular to the arrangement direction, and the extension direction of the center mark is the same as the extension direction of the fifth pair of current layer marks.

[0011] Optionally, the front layer overlay mark is a regular octagon, and the first pair of overlay marks, the second pair of overlay marks, the third pair of overlay marks, and the fourth pair of overlay marks also form a regular octagon.

[0012] Accordingly, the present invention also provides a method for calibrating the accuracy of overlay measurement, comprising the following steps: Create the overlay markings as described above; The distance between each pair of previous layer marks in the previous layer overlay marks is measured using a CDSEM machine, the distance between each pair of current layer marks in the current layer overlay marks is measured, the distance from each mark in the fifth pair of current layer marks to the center mark is measured, and the distance from each mark in the first pair of previous layer marks to the center mark is measured. Determine whether the difference in distance from each mark to the center mark in the fifth pair of current layer marks is greater than the accuracy of the CDSEM machine; if so, inspect and repair the CDSEM machine, and then remeasure the overlay marks. If not, the mark center of the overlay mark in the current layer is obtained based on the distance between each pair of current layer marks; The mark center of the front layer overlay mark is obtained based on the distance between each pair of front layer marks and the distance from each mark in the first pair of front layer marks to the center mark; The actual overlay accuracy OVL1 is obtained by comparing the center of the current layer overlay mark with the center of the previous layer overlay mark. The overlay accuracy OVL2 is obtained by measuring the overlay mark. The overlay accuracy compensation value Offset=OVL1-OVL2 is obtained. The measurement overlay accuracy is corrected based on the overlay accuracy compensation value Offset.

[0013] Optionally, the center of the overlay markings is M=(A3+ A4+ A5 + A6) / 8, where A3 is the distance between the first pair of overlay markings, A4 is the distance between the second pair of overlay markings, A5 is the distance between the third pair of overlay markings, and A6 is the distance between the fourth pair of overlay markings.

[0014] Optionally, the center of the front layer overprinted mark is N=N2-N1, where N1=(A7+A8+A9+A10) / 8, N2=(A11-A12) / 2, where A7 is the distance between the first pair of front layer marks, A8 is the distance between the second pair of front layer marks, A9 is the distance between the third pair of front layer marks, A10 is the distance between the fourth pair of front layer marks, A11 is the distance from one of the marks in the first pair of front layer marks to the center mark, and A12 is the distance from the other mark in the first pair of front layer marks to the center mark.

[0015] Optionally, inspecting the CDSEM machine includes checking for measurement errors and inspecting the CDSEM machine's process formulation. Repairing the CDSEM machine includes modifying the CDSEM machine's process formulation.

[0016] In summary, the overlay markings and the method for correcting the accuracy of overlay measurement provided by this invention include: the previous layer overlay markings comprising a first pair of previous layer markings arranged along a first direction and centrally symmetrical with respect to the center of the previous layer markings; a second pair of previous layer markings arranged along a second direction and centrally symmetrical with respect to the center of the previous layer markings; and a third pair of previous layer markings arranged along a third direction and centrally symmetrical with respect to the center of the previous layer markings; the current layer overlay markings comprising a first pair of current layer markings arranged along a first direction and centrally symmetrical with respect to the center of the current layer markings; and a second pair of current layer markings arranged along a second direction and centrally symmetrical with respect to the center of the current layer markings. The second pair of overlay marks and the third pair of overlay marks arranged along a third direction and centrally symmetrical with respect to the center of the overlay mark; the overlay marks are located inside the previous overlay marks, and the center of the overlay mark coincides with the center of the previous overlay mark in a direction perpendicular to the overlay mark; the overlay marks also include a fifth pair of overlay marks arranged along the first direction and centrally symmetrical with respect to the center of the overlay mark, and a center mark located in the central region of the overlay marks, the fifth pair of overlay marks being located between the first pair of overlay marks, and the center of the center mark coinciding with the center of the overlay mark. An unexpected effect of this invention is that by setting a center mark in the central region of the overlay marks, the asymmetry of the previous overlay marks is obtained by measuring the distance from the first pair of previous overlay marks to the center mark, thereby ultimately obtaining an overlay accuracy compensation value containing the asymmetry. This corrects the problem of overlay accuracy measurement distortion caused by overlay mark asymmetry, obtains accurate overlay accuracy results, and reduces wafer scrap caused by inaccurate overlay accuracy measurement. Attached Figure Description

[0017] Figure 1 It is an ideal cross-sectional view of the previous layer overlay mark and the current layer overlay mark.

[0018] Figure 2 It is an actual cross-sectional view of the overprinted marks of the previous layer and the overprinted marks of the current layer.

[0019] Figure 3 This is a top view of the overprinted mark provided in an embodiment of the present invention.

[0020] Figure 4 This is a flowchart of a method for calibrating the accuracy of overlay measurement according to an embodiment of the present invention.

[0021] Figure 5 This is a schematic diagram of the dimensions of the overlay mark in the overlay mark provided in an embodiment of the present invention.

[0022] Figure 6 This is a schematic diagram of the dimensions of the front layer overlay mark in an overlay mark according to an embodiment of the present invention.

[0023] Explanation of reference numerals in the attached figures: 10 - Overlapping mark of the same layer; 11 - First overlapping layer mark; 11a - First overlapping layer mark; 11b - Second overlapping layer mark; 12 - Second overlapping layer mark; 12a - Third overlapping layer mark; 12b - Fourth overlapping layer mark; 13 - Third overlapping layer mark; 13a - Fifth overlapping layer mark; 13b - Sixth overlapping layer mark; 14 - Fourth overlapping layer mark; 14a - Seventh overlapping layer mark; 14b - Eighth overlapping layer mark; 15 - Fifth overlapping layer mark; 15a - Ninth overlapping layer mark Note: 15b - Tenth layer mark; 16 - Center mark; 20 - Previous layer overprint mark; 21 - First pair of previous layer marks; 21a - First previous layer mark; 21b - Second previous layer mark; 22 - Second pair of previous layer marks; 22a - Third previous layer mark; 22b - Fourth previous layer mark; 23 - Third pair of previous layer marks; 23a - Fifth previous layer mark; 23b - Sixth previous layer mark; 24 - Fourth pair of previous layer marks; 24a - Seventh previous layer mark; 24b - Eighth previous layer mark. Detailed Implementation

[0024] The core idea of ​​this invention is to design an overlay mark capable of detecting asymmetry in the previous overlay mark. After the overlay mark is made, the distance between each mark is measured using a CDSEM machine to obtain the actual overlay accuracy including the asymmetry. At the same time, the overlay mark is measured to obtain the measured overlay accuracy. Based on the actual overlay accuracy and the measured overlay accuracy, an overlay accuracy compensation value is obtained, and the measured overlay accuracy is corrected based on the overlay accuracy compensation value.

[0025] Specifically, the present invention provides an overlay mark, including a front layer overlay mark and a current layer overlay mark; the front layer overlay mark includes a first pair of front layer marks arranged along a first direction and centrally symmetrical with respect to the center of the front layer mark, a second pair of front layer marks arranged along a second direction and centrally symmetrical with respect to the center of the front layer mark, and a third pair of front layer marks arranged along a third direction and centrally symmetrical with respect to the center of the front layer mark; the current layer overlay mark includes a first pair of current layer marks arranged along the first direction and centrally symmetrical with respect to the center of the current layer mark, and a third pair of current layer marks arranged along the second direction and centrally symmetrical with respect to the center of the current layer mark. The second pair of overprinted marks and the third pair of overprinted marks arranged along a third direction and centrally symmetrical with respect to the center of the overprinted mark; the overprinted mark is located inside the previous overprinted mark, and the center of the overprinted mark coincides with the center of the previous overprinted mark in a direction perpendicular to the overprinted mark; the overprinted mark also includes a fifth pair of overprinted marks arranged along the first direction and centrally symmetrical with respect to the center of the overprinted mark, and a center mark of the central region of the overprinted mark, the fifth pair of overprinted marks being located between the first pair of overprinted marks, and the center of the center mark coinciding with the center of the overprinted mark.

[0026] Accordingly, the present invention also provides a method for correcting the accuracy of overlay precision measurement, comprising: fabricating overlay marks as described above; using a CDSEM machine to measure the distance between each pair of previous layer marks in the previous layer overlay marks, measuring the distance between each pair of current layer marks in the current layer overlay marks, measuring the distance from each mark in the fifth pair of current layer marks to the sixth mark, and measuring the distance from each mark in the first pair of previous layer marks to the sixth mark; determining whether the difference in distance from each mark in the fifth pair of current layer marks to the center mark is greater than the accuracy of the CDSEM machine; if so, inspecting and repairing the CDSEM machine. Next, it is determined whether the difference in distance from each mark to the center mark in the fifth pair of current layer marks is greater than the accuracy of the CDSEM instrument; if not, the mark center of the current layer overlay mark is obtained based on the distance between each pair of current layer marks; the mark center of the previous layer overlay mark is obtained based on the distance between each pair of previous layer marks and the distance from each mark in the first pair of previous layer marks to the sixth mark; the actual overlay accuracy OVL1 is obtained based on the mark center of the current layer overlay mark and the mark center of the previous layer overlay mark, the overlay mark is measured to obtain the measured overlay accuracy OVL2, and the overlay accuracy compensation value Offset = OVL1 - OVL2 is obtained; the measured overlay accuracy is corrected based on the overlay accuracy compensation value Offset.

[0027] The unexpected effect of this invention is that a center mark is set in the central region of the current layer overlay mark, and the asymmetry of the previous layer overlay mark is obtained by the distance from the first pair of previous layer overlay marks to the center mark. Thus, an overlay accuracy compensation value containing the asymmetry is finally obtained, which can correct the problem of overlay accuracy measurement distortion caused by overlay mark asymmetry, obtain accurate overlay accuracy results, and reduce wafer scrap caused by inaccurate overlay accuracy measurement.

[0028] To make the objectives, advantages, and features of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and are not drawn to scale, and are only used to facilitate and clarify the explanation of the embodiments of this invention. Furthermore, the structures shown in the drawings are often part of the actual structures. In particular, different figures may emphasize different aspects and may sometimes use different scales.

[0029] As used herein, the singular forms “a,” “an,” and “the” include plural objects unless otherwise expressly indicated. As used herein, the term “or” is generally used to include “and / or” unless otherwise expressly indicated. As used herein, the term “a number” is generally used to include “at least one” unless otherwise expressly indicated. As used herein, the term “at least two” is generally used to include “two or more” unless otherwise expressly indicated. Furthermore, the terms “first,” “second,” and “third” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as “first,” “second,” or “third” may explicitly or implicitly include one or at least two of that feature.

[0030] Figure 3 This is a top view of an overlay mark provided in an embodiment of the present invention. Please refer to... Figure 3 As shown, the overprinting marks provided in this embodiment of the invention include a front overprinting mark 20 and a current overprinting mark 10. The front overprinting mark 20 includes a first pair of front overprinting marks 21 arranged along a first direction x1 and centrally symmetrical with respect to the center of the front overprinting mark, a second pair of front overprinting marks 22 arranged along a second direction x2 and centrally symmetrical with respect to the center of the front overprinting mark, and a third pair of front overprinting marks 23 arranged along a third direction x3 and centrally symmetrical with respect to the center of the front overprinting mark. The current overprinting mark 10 includes a first pair of current overprinting marks 11 arranged along a first direction x1 and centrally symmetrical with respect to the center of the current overprinting mark, a second pair of current overprinting marks 12 arranged along a second direction x2 and centrally symmetrical with respect to the center of the current overprinting mark, and a third pair of current overprinting marks 13 arranged along a third direction x3 and centrally symmetrical with respect to the center of the current overprinting mark.

[0031] The current layer overprint mark 10 is located inside the previous layer overprint mark 20, and the center of the current layer mark coincides with the center of the previous layer mark in a direction perpendicular to the overprint mark. Specifically, for example: the first pair of previous layer marks 21 includes a first previous layer mark 21a and a second previous layer mark 21b, which are arranged along a first direction x1 and are centrally symmetrical with respect to the center of the previous layer mark; the first pair of current layer marks 11 includes a first current layer mark 11a and a second current layer mark 11b, which are arranged along a first direction x1 and are centrally symmetrical with respect to the center of the current layer mark. In the first direction x1, for example from the negative direction to the positive direction, the second previous layer mark 21b, the second current layer mark 11b, the first current layer mark 11a, and the first previous layer mark 21a are arranged sequentially.

[0032] Similarly, the second pair of front layer marks 22 includes a third front layer mark 22a and a fourth front layer mark 22b, which are arranged along the second direction x2 and are centrally symmetrical with respect to the center of the front layer marks; the second pair of current layer marks 12 includes a third current layer mark 12a and a fourth current layer mark 12b, which are arranged along the second direction x2 and are centrally symmetrical with respect to the center of the current layer marks. In the second direction x2, for example from the negative direction to the positive direction, the fourth front layer mark 22b, the fourth current layer mark 12b, the third current layer mark 12a, and the third front layer mark 22a are arranged sequentially.

[0033] The third pair of front layer marks 23 includes a fifth front layer mark 23a and a sixth front layer mark 23b, which are arranged along a third direction x3 and are centrally symmetrical with respect to the center of the front layer marks. The third pair of current layer marks 13 includes a fifth current layer mark 13a and a sixth current layer mark 13b, which are arranged along a third direction x3 and are centrally symmetrical with respect to the center of the current layer marks. Along the third direction x3, for example from the negative direction to the positive direction, the sixth front layer mark 23b, the sixth current layer mark 13b, the fifth current layer mark 13a, and the fifth front layer mark 23a are arranged sequentially.

[0034] The layer overlay marking 10 further includes a fifth pair of layer overlay markings 15 arranged along the first direction x1 and centrally symmetrical with respect to the center of the layer overlay marking, and a center marking 16 located in the central region of the layer overlay marking. The fifth pair of layer overlay markings 15 are located between the first pair of layer overlay markings 11, and the center of the center marking 16 coincides with the center of the layer overlay marking. Please refer to... Figure 3 As shown, the layer overlay marking 10 further includes a fifth pair of layer overlay markings 15 and a center marking 16. The fifth pair of layer overlay markings 15 includes a ninth layer overlay marking 15a and a tenth layer overlay marking 15b. The ninth layer overlay marking 15a and the tenth layer overlay marking 15b are arranged along a first direction x1 and are centrally symmetrical with respect to the center of the layer overlay markings. The center marking 16 is located in the central region of the layer overlay marking 10, and the center of the center marking 16 coincides with the center of the layer overlay markings. In the first direction x1, for example from the negative direction to the positive direction, the second front layer marking 21b, the second layer overlay marking 11b, the tenth layer overlay marking 15b, the center marking 16, the ninth layer overlay marking 15a, the first layer overlay marking 11a, and the first front layer marking 21a are arranged sequentially.

[0035] In this embodiment of the invention, the overlay mark 10 of the current layer generally does not deform, and its mark center can be obtained by measuring the first pair of current layer marks 11, the second pair of current layer marks 12, and the third pair of current layer marks 13. The overlay mark 20 of the previous layer may deform, and its center in the previous layer can be obtained by measuring the first pair of previous layer marks 21, the second pair of previous layer marks 22, and the third pair of previous layer marks 23. The asymmetry of the overlay mark 20 of the previous layer can be obtained based on the distance from each of the previous layer marks 21 to the center mark 16. The mark center of the overlay mark 20 of the previous layer can be obtained based on the center of the overlay mark 20 of the previous layer and the asymmetry. Thus, an overlay accuracy compensation value containing the asymmetry is finally obtained, thereby correcting the problem of overlay accuracy measurement distortion caused by overlay mark asymmetry, obtaining accurate overlay accuracy results, and reducing wafer scrap caused by inaccurate overlay accuracy measurement.

[0036] In one embodiment of this application, the front layer overlay mark 20 is a regular hexagon, and the first pair of overlay marks 11, the second pair of overlay marks 12, and the third pair of overlay marks 13 in the current layer overlay mark 10 also form a regular hexagon. The included angles between the first direction x1, the second direction x2, and the third direction x3 are all 60 degrees.

[0037] In another embodiment of this application, the first direction x1 is perpendicular to the second direction x2, and the angle between the positive direction of the third direction x3 and the positive direction of the first direction x1 is an acute angle.

[0038] In this embodiment, the preceding layer overprinting mark 20 further includes a fourth pair of preceding layer marks 24 arranged along the fourth direction x4 and centrally symmetrical with respect to the center of the preceding layer marks; the current layer overprinting mark 10 further includes a fourth pair of current layer marks 14 arranged along the fourth direction x4 and centrally symmetrical with respect to the center of the current layer marks; the angle between the positive direction of the fourth direction x4 and the positive direction of the first direction x1 is an obtuse angle. Please refer to... Figure 3 As shown, the fourth pair of front layer marks 24 includes a seventh front layer mark 24a and an eighth front layer mark 24b, which are arranged along the fourth direction x4 and are centrally symmetrical with respect to the center of the front layer marks; the fourth pair of current layer marks 14 includes a seventh current layer mark 14a and an eighth current layer mark 14b, which are arranged along the fourth direction x4 and are centrally symmetrical with respect to the center of the front layer marks. Along the fourth direction x4, for example from the negative direction to the positive direction, the eighth front layer mark 24b, the eighth current layer mark 14b, the seventh current layer mark 14a, and the seventh front layer mark 24a are arranged sequentially.

[0039] In one embodiment of this application, the angle between the positive direction of the third direction x3 and the positive direction of the first direction x1 is 45 degrees, and the angle between the positive direction of the fourth direction x4 and the positive direction of the first direction x1 is 135 degrees. In a preferred embodiment, the front layer overlay mark 20 is a regular octagon, and the first pair of overlay marks 11, the second pair of overlay marks 12, the third pair of overlay marks 13, and the fourth pair of overlay marks 14 in the current layer overlay mark 10 also form a regular octagon.

[0040] In one embodiment of this application, the marks in the front layer overprinted marks 20 and the marks in the current layer overprinted marks 10 are both strip-shaped, with the extension direction of the strip-shaped marks perpendicular to the arrangement direction. The extension direction of the center mark 16 is the same as the extension direction of the fifth pair of current layer marks 15. For example, the first front layer mark 21a and the second front layer mark 21b in the first pair of front layer marks 21 are arranged along the first direction x1, and their extension direction is the second direction x2. The ninth current layer mark 15a and the tenth current layer mark 15b in the fifth pair of current layer marks 15 are arranged along the first direction x1, and their extension direction is the second direction x2. The extension direction of the center mark 16 is also the second direction x2.

[0041] Please continue to refer to this. Figure 3 As shown, in this embodiment, each mark has the same shape and size. For example, the length L1 of the mark is 10 μm, the width L2 is 1.08 μm, the distance L3 between the adjacent previous layer mark and the current layer mark is 1.08 μm, and the distance L4 between a pair of previous layer marks (e.g., from the left side of the second previous layer mark 21b to the right side of the first previous layer mark 21a) is 34 μm, but it is not limited to these.

[0042] In the overlay markings provided by the present invention, the front layer overlay markings 20 include a first pair of front layer markings 21 arranged along a first direction x1 and centrally symmetrical with respect to the center of the front layer markings, a second pair of front layer markings 22 arranged along a second direction x2 and centrally symmetrical with respect to the center of the front layer markings, and a third pair of front layer markings 23 arranged along a third direction x3 and centrally symmetrical with respect to the center of the front layer markings; the current layer overlay markings 10 include a first pair of current layer markings 11 arranged along a first direction x1 and centrally symmetrical with respect to the center of the current layer markings, a second pair of current layer markings 12 arranged along a second direction x2 and centrally symmetrical with respect to the center of the current layer markings, and a third pair of front layer markings 23 arranged along a third direction x3 and centrally symmetrical with respect to the center of the current layer markings. A third pair of current layer marks 13 arranged in the third direction x3 and centrally symmetrical with respect to the center of the current layer mark; the current layer overprint mark 10 is located inside the previous layer overprint mark 20, and the center of the current layer mark coincides with the center of the previous layer mark in a direction perpendicular to the overprint mark; the current layer overprint mark 10 also includes a fifth pair of current layer marks 15 arranged along the first direction x1 and centrally symmetrical with respect to the center of the current layer mark, and a center mark 16 located in the central region of the current layer overprint mark, the fifth pair of current layer marks 15 is located between the first pair of current layer marks 11, and the center of the center mark 16 coincides with the center of the current layer mark. An unexpected effect of this invention is that a center mark 16 is set in the central region of the current layer overlay mark 10, and the asymmetry of the previous layer overlay mark 20 is obtained by measuring the distance from the first pair of previous layer overlay marks 21 to the center mark 16. This results in an overlay accuracy compensation value containing the asymmetry, thereby correcting the problem of overlay accuracy measurement distortion caused by overlay mark asymmetry, obtaining accurate overlay accuracy results, and reducing wafer scrap caused by inaccurate overlay accuracy measurement.

[0043] The present invention also provides a method for calibrating the accuracy of overlay measurement. Figure 4 This is a flowchart of a method for correcting the accuracy of overlay measurement according to an embodiment of the present invention. Please refer to it. Figure 4 As shown, the method for calibrating the accuracy of overlay measurement provided in this embodiment of the invention includes the following steps: S1: Create the overlay markings as described above; S2: The distance between each pair of previous layer marks in the previous layer overlay marks is measured using a CDSEM machine, the distance between each pair of current layer marks in the current layer overlay marks is measured, the distance from each mark in the fifth pair of current layer marks to the center mark is measured, and the distance from each mark in the first pair of previous layer marks to the center mark is measured. S3: Determine whether the difference in distance from each mark to the center mark in the fifth pair of current layer marks is greater than the accuracy of the CDSEM machine; S4: If so, check the CDSEM machine and then repeat the judgment to see if the difference in distance from each mark to the center mark in the fifth pair of current layer marks is greater than the accuracy of the CDSEM machine. S5: If not, then obtain the mark center of the overlay mark in the current layer based on the distance between each pair of current layer marks; S6: Obtain the mark center of the front layer overlay mark based on the distance between each pair of front layer marks and the distance from each mark in the first pair of front layer marks to the center mark; S7: Obtain the actual overlay accuracy OVL1 based on the mark center of the current layer overlay mark and the mark center of the previous layer overlay mark, measure the overlay mark to obtain the measured overlay accuracy OVL2, and obtain the overlay accuracy compensation value Offset=OVL1-OVL2. S8: Correct the measurement overlay accuracy according to the overlay accuracy compensation value Offset.

[0044] Figure 5 This is a schematic diagram of the dimensions of the overlay mark in the current layer provided in an embodiment of the present invention. Figure 6 This is a schematic diagram showing the dimensions of the front layer overlay mark in an overlay mark according to an embodiment of the present invention. The following is in conjunction with... Figure 4 and Figure 3 , Figure 5 , Figure 6 The method for calibrating the accuracy of overlay measurement described in this embodiment will be explained in detail.

[0045] In step S1, the overlay marks as described above are made. The overlay marks are made to measure the overlay accuracy between the current layer and the previous layer. Therefore, the previous layer overlay mark 20 is made simultaneously when the previous layer is made, and the current layer overlay mark 10 is made simultaneously when the current layer is made.

[0046] In step S2, a CDSEM (characteristic size scanning electron microscope) is used to measure the distance between each pair of front layer marks in the front layer overlay marks 20, the distance between each pair of current layer marks in the current layer overlay marks 10, the distance from each mark in the fifth pair of current layer marks 15 to the center mark 16, and the distance from each mark in the first pair of front layer marks 21 to the center mark 16.

[0047] Please refer to Figure 3 and Figure 5 As shown, a CDSEM machine is used to measure the distance between each pair of overlapping markings in the overlapping marking 10 and the distance from each marking in the fifth pair of overlapping markings 15 to the center marking.

[0048] Specifically, the distance A1 from the ninth layer mark 15a to the center mark 16 and the distance A2 from the tenth layer mark 15b to the center mark 16 are measured in the fifth pair of layer marks 15. Distance A1 can be the distance between the right side of the ninth layer mark 15a and the right side of the center mark 16, and distance A2 can be the distance between the left side of the tenth layer mark 15b and the left side of the center mark 16. That is, both distance A1 and distance A2 are the width of one mark plus the distance between the two marks. Of course, distances A1 and A2 can also be simply the distance between the two marks; this invention does not limit this.

[0049] The distance A3 between the first pair of layer markers 11a and the second pair of layer markers 11 is measured; the distance A4 between the third pair of layer markers 12a and the fourth pair of layer markers 12b is measured; the distance A5 between the fifth pair of layer markers 13a and the sixth pair of layer markers 13b is measured; and the distance A6 between the seventh pair of layer markers 14a and the eighth pair of layer markers 14b is measured. In this embodiment, the distance between a pair of layer markers refers to the distance between the outer edges of the two layer markers. For example, the distance A1 between the first pair of layer markers 11 refers to the distance between the right side of the first layer marker 11a and the left side of the second layer marker 11b.

[0050] Please refer to Figure 3 and Figure 6 As shown, the distance between each pair of front layer marks in the front layer overlay mark 20 is measured, and the distance from each mark in the first pair of front layer marks 21 to the center mark 16 is measured.

[0051] Specifically, the distance A11 from the first front layer mark 21a to the center mark 16 and the distance A12 from the second front layer mark 21b to the center mark 16 are measured. Distance A11 can be the distance between the left side of the first front layer mark 21a and the right side of the center mark 16, and distance A12 can be the distance between the right side of the second front layer mark 21b and the left side of the center mark 16; that is, both distances A11 and A12 are distances between the two marks. Of course, distances A11 and A12 can also be the width of one mark plus the distance between the two marks, and this invention does not limit this. Furthermore, the distances A11 from the first front layer mark 21a to the center mark 16 and A12 from the second front layer mark 21b to the center mark 16 refer to horizontal distances, that is, the distance from the projection of the center mark 16 in the front layer to the first front layer mark 21a, and the distance from the projection of the center mark 16 in the front layer to the second front layer mark 21b.

[0052] The distance A7 between the first front layer mark 21a and the second front layer mark 21b in the first pair of front layer marks 21 is measured; the distance A8 between the third front layer mark 22a and the fourth front layer mark 22b in the second pair of front layer marks 22 is measured; the distance A9 between the fifth front layer mark 23a and the sixth front layer mark 23b in the third pair of front layer marks 23 is measured; and the distance A10 between the seventh front layer mark 24a and the eighth front layer mark 24b in the fourth pair of front layer marks 24 is measured. In this embodiment, the distance between a pair of front layer marks refers to the distance between the outer edges of the two front layer marks. For example, the distance A7 between the first pair of front layer marks 21 refers to the distance from the right side of the first front layer mark 21a to the left side of the second front layer mark 21b, but it is not limited to this.

[0053] In steps S3 and S4, it is determined whether the difference in distance from each mark in the fifth pair of layer marks 15 to the center mark 16 is greater than the accuracy of the CDSEM machine; if so, the CDSEM machine is checked, and then the determination of whether the difference in distance from each mark in the fifth pair of layer marks 15 to the center mark 16 is greater than the accuracy of the CDSEM machine is repeated.

[0054] Determine whether the difference in distance from each marker in the fifth pair of layer markers 15 to the center marker 16 is greater than the accuracy of the CDSEM instrument. Specifically, determine whether the difference between distance A1 from the ninth layer marker 15a to the center marker 16 and distance A2 from the tenth layer marker 15b to the center marker 16 is greater than the accuracy of the CDSEM instrument. When the accuracy of the CDSEM instrument is 1 nm, determine whether A1 - A2 > 1 nm.

[0055] If so, i.e., A1-A2 > 1nm, then proceed to step S4 to inspect and repair the CDSEM instrument. In one embodiment, inspecting the CDSEM instrument includes checking whether the CDSEM instrument has measurement errors and checking the CDSEM instrument's process recipe, i.e., determining whether the problem is a measurement error or a problem with the instrument itself. If it is a problem with the instrument itself, then the CDSEM instrument's process recipe needs to be modified. In other words, repairing the CDSEM instrument includes modifying the CDSEM instrument's process recipe.

[0056] If the measurement is incorrect or the process formula of the CDSEM machine is modified, continue to execute step S2, that is, remeasure the overlay marks. Specifically, use the CDSEM machine to measure the distance between each pair of previous layer marks in the previous layer overlay marks 20, measure the distance between each pair of current layer marks in the current layer overlay marks 10, measure the distance from each mark in the fifth pair of current layer marks 15 to the center mark 16, and measure the distance from each mark in the first pair of previous layer marks 21 to the center mark 16.

[0057] If not, i.e., A1-A2≤1nm, then proceed to step S5 to obtain the mark center of the overlay mark 10 of the current layer based on the distance between each pair of current layer marks. The mark center of the overlay mark 10 of the current layer is M=(A3+ A4+ A5 + A6) / 8, where A3 is the distance between the first pair of current layer marks 11, A4 is the distance between the second pair of current layer marks 12, A5 is the distance between the third pair of current layer marks 13, and A6 is the distance between the fourth pair of current layer marks 14.

[0058] In step S6, the mark center of the front layer overprinted mark 20 is obtained based on the distance between each pair of front layer marks and the distance from each mark in the first pair of front layer marks 21 to the center mark 16. The mark center of the front layer overprinted mark 20 is N=N2-N1, where N1=(A7+A8+A9+A10) / 8, N2=(A11-A12) / 2, where A7 is the distance between the first pair of front layer marks 21, A8 is the distance between the second pair of front layer marks 22, A9 is the distance between the third pair of front layer marks 23, A10 is the distance between the fourth pair of front layer marks 24, A11 is the distance from one of the marks in the first pair of front layer marks 21 (specifically the first front layer mark 21a) to the center mark 16, and A12 is the distance from the other mark in the first pair of front layer marks 21 (specifically the second front layer mark 21b) to the center mark 16. N1 is the center of the previous layer overprint mark 20 in the previous layer, and N2 is the offset of the previous layer overprint mark 20 relative to the center of the current layer overprint mark 10, that is, the asymmetry of the previous layer overprint mark 20. The mark center N = N2 - N1 of the previous layer overprint mark 20 includes the asymmetry of the previous layer overprint mark 20.

[0059] In step S7, the actual overlay accuracy OVL1 is obtained based on the center of the current layer overlay mark 10 and the center of the previous layer overlay mark 20. The measured overlay accuracy OVL2 is obtained by measuring the overlay marks, and the overlay accuracy compensation value Offset = OVL1 - OVL2 is obtained. The actual overlay accuracy OVL1 is calculated based on the measured distance, and the measured overlay accuracy OVL2 is obtained by direct measurement using a measuring device.

[0060] In step S8, the measurement overlay accuracy is corrected according to the overlay accuracy compensation value Offset.

[0061] Compensating for the asymmetry of the overlay mark 20 in the previous layer to within the measurement overlay accuracy can correct the problem of measurement distortion of overlay accuracy caused by the asymmetry of the overlay mark, obtain accurate overlay accuracy results, and thereby reduce wafer scrap caused by inaccurate overlay accuracy measurement.

[0062] The method for correcting the accuracy of overlay measurement provided by this invention first involves creating overlay marks as described above; then, a CDSEM machine is used to measure the distance between each pair of previous layer marks in the previous layer, the distance between each pair of current layer marks in the current layer, the distance from each mark in the fifth pair of current layer marks to the center mark, and the distance from each mark in the first pair of previous layer marks to the center mark; next, it is determined whether the difference in distance from each mark in the fifth pair of current layer marks to the center mark is greater than the accuracy of the CDSEM machine; if so, the CDSEM machine is then used to correct the accuracy of the measurement. The EM machine is inspected and repaired, and then the overlay marks are remeasured. If not, the mark center of the current layer overlay mark is obtained based on the distance between each pair of current layer marks. The mark center of the previous layer overlay mark is obtained based on the distance between each pair of previous layer marks and the distance from each mark in the first pair of previous layer marks to the center mark. The actual overlay accuracy OVL1 is obtained based on the mark center of the current layer overlay mark and the mark center of the previous layer overlay mark. The overlay mark is measured to obtain the measured overlay accuracy OVL2, and the overlay accuracy compensation value Offset = OVL1 - OVL2 is obtained. The measured overlay accuracy is corrected based on the overlay accuracy compensation value Offset. The unexpected effect of this invention is that a center mark is set in the central region of the current layer overlay mark, and the asymmetry of the previous layer overlay mark is obtained by the distance from the first pair of previous layer overlay marks to the center mark. Thus, an overlay accuracy compensation value containing the asymmetry is finally obtained, which can correct the problem of overlay accuracy measurement distortion caused by overlay mark asymmetry, obtain accurate overlay accuracy results, and reduce wafer scrap caused by inaccurate overlay accuracy measurement.

[0063] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A type of overprinted mark, characterized in that, Including the overprint mark of the previous layer and the overprint mark of the current layer; The front layer overprinted marks include a first pair of front layer marks arranged along a first direction and centrally symmetrical with respect to the center of the front layer marks, a second pair of front layer marks arranged along a second direction and centrally symmetrical with respect to the center of the front layer marks, and a third pair of front layer marks arranged along a third direction and centrally symmetrical with respect to the center of the front layer marks. The layer overlay markings include a first pair of layer markings arranged along a first direction and centrally symmetrical with respect to the center of the layer markings, a second pair of layer markings arranged along a second direction and centrally symmetrical with respect to the center of the layer markings, and a third pair of layer markings arranged along a third direction and centrally symmetrical with respect to the center of the layer markings. The current layer overlay mark is located inside the previous layer overlay mark, and the center of the current layer mark coincides with the center of the previous layer mark in a direction perpendicular to the overlay mark; The layer overlay markings also include a fifth pair of layer markings arranged along the first direction and centrally symmetrical with respect to the center of the layer markings, and a center marking located in the central region of the layer overlay markings. The fifth pair of layer markings is located between the first pair of layer markings, and the center of the center marking coincides with the center of the layer marking.

2. The overprinting mark according to claim 1, characterized in that, The first direction is perpendicular to the second direction, and the angle between the positive direction of the third direction and the positive direction of the first direction is an acute angle.

3. The overprinting mark according to claim 2, characterized in that, The preceding layer overprinting marks further include a fourth pair of preceding layer marks arranged along the fourth direction and centrally symmetrical with respect to the center of the preceding layer marks; the current layer overprinting marks further include a fourth pair of current layer marks arranged along the fourth direction and centrally symmetrical with respect to the center of the current layer marks; the angle between the positive direction of the fourth direction and the positive direction of the first direction is an obtuse angle.

4. The overprinting mark according to claim 3, characterized in that, The angle between the positive direction of the third direction and the positive direction of the first direction is 45 degrees, and the angle between the positive direction of the fourth direction and the positive direction of the first direction is 135 degrees.

5. The overprinting mark according to claim 4, characterized in that, The marks in the preceding layer overprinted marks and the marks in the current layer overprinted marks are both strip-shaped, with the extension direction of the strip-shaped marks perpendicular to the arrangement direction, and the extension direction of the center mark is the same as the extension direction of the fifth pair of current layer marks.

6. The overprinting mark according to claim 5, characterized in that, The front layer overlay mark is a regular octagon, and the first pair of overlay marks, the second pair of overlay marks, the third pair of overlay marks and the fourth pair of overlay marks also form a regular octagon.

7. A method for calibrating the accuracy of overlay measurement, characterized in that, Includes the following steps: To produce overlay marks as described in any one of claims 1 to 6; The distance between each pair of previous layer marks in the previous layer overlay marks is measured using a CDSEM machine, the distance between each pair of current layer marks in the current layer overlay marks is measured, the distance from each mark in the fifth pair of current layer marks to the center mark is measured, and the distance from each mark in the first pair of previous layer marks to the center mark is measured. Determine whether the difference in distance from each mark to the center mark in the fifth pair of current layer marks is greater than the accuracy of the CDSEM machine; if so, inspect and repair the CDSEM machine, and then remeasure the overlay marks. If not, the mark center of the overlay mark in the current layer is obtained based on the distance between each pair of current layer marks; The mark center of the front layer overlay mark is obtained based on the distance between each pair of front layer marks and the distance from each mark in the first pair of front layer marks to the center mark; The actual overlay accuracy OVL1 is obtained by comparing the center of the current layer overlay mark with the center of the previous layer overlay mark. The overlay accuracy OVL2 is obtained by measuring the overlay mark. The overlay accuracy compensation value Offset = OVL1 - OVL2 is obtained. The measurement overlay accuracy is corrected based on the overlay accuracy compensation value Offset.

8. The method for calibrating the accuracy of overlay measurement according to claim 7, characterized in that, The center of the overlay markings is M=(A3+ A4+ A5 + A6) / 8, where A3 is the distance between the first pair of overlay markings, A4 is the distance between the second pair of overlay markings, A5 is the distance between the third pair of overlay markings, and A6 is the distance between the fourth pair of overlay markings.

9. The method for calibrating the accuracy of overlay measurement according to claim 7, characterized in that, The center of the front layer overprinted mark is N=N2-N1, where N1=(A7+A8+A9+A10) / 8, N2=(A11-A12) / 2, where A7 is the distance between the first pair of front layer marks, A8 is the distance between the second pair of front layer marks, A9 is the distance between the third pair of front layer marks, A10 is the distance between the fourth pair of front layer marks, A11 is the distance from one of the marks in the first pair of front layer marks to the center mark, and A12 is the distance from the other mark in the first pair of front layer marks to the center mark.

10. The method for calibrating the accuracy of overlay measurement according to claim 7, characterized in that, Inspecting a CDSEM machine includes checking for measurement errors and reviewing the process formulation. Repairing a CDSEM machine involves modifying the process formulation.

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