Overlay mark, overlay error measurement method and exposure machine table

Abstract

The invention provides an overlay mark, an overlay error measuring method and an exposure machine table, the overlay mark comprises a grating pattern area and an auxiliary pattern area, the grating pattern area comprises a plurality of sub-areas, each sub-area comprises two lines with a first width and a second width, the lines with the first width and the lines with the second width are alternately arranged in sequence, and the second width is smaller than the first width; the auxiliary pattern areas are distributed around the sub-areas; the auxiliary pattern area comprises a sub-resolution line, and the width of the sub-resolution line is smaller than the second width. The overlay mark provided by the invention is provided with two lines with different widths to reflect asymmetry and meet the requirement of threading overlay, and in addition, the overlay mark provided by the invention is provided with an auxiliary line design, so that edge effect crosstalk can be avoided, the sensitivity of a mark film system can be improved, and the measurement error of threading overlay can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of overlay error measurement, and in particular to an overlay mark, an overlay error measurement method and an exposure machine. Background Art

[0002] In the process of lithography machine alignment, threading overlay (WSO) marks are usually used to measure and monitor the overlay error between the workpiece stage and the mask stage. Internationally, diffraction overlay marks (DBO) are generally used as measurement marks at the WSO level. DBO is a mark used to measure the relative position relationship between the current layer pattern and the reference layer to determine the overlay error. Among them, the micro-diffraction overlay mark (μDBO) has the characteristics of small area affected by aberration consistency image. However, in actual application, the μDBO mark with only a single line width mark pattern can only be used for the measurement of inter-layer overlay conditions. Due to the characteristics of threading overlay, the mark pattern will be split into two areas of the same mask. During the exposure process, the mark pattern exists in the same layer. The existing single line width mark cannot reflect asymmetry under this condition, so it is difficult to adapt to the measurement under this threading overlay condition. In addition, the μDBO mark is often affected by the edge effect of the mark and the crosstalk between the measured light intensity, resulting in problems such as low sensitivity of the mark film system and large measurement error. Summary of the invention

[0003] The object of the present invention is to provide an overlay mark to solve one or more problems existing in the existing μDBO mark.

[0004] In order to solve the above technical problems, the present invention provides an overlay mark, comprising: a grating pattern area and an auxiliary pattern area,

[0005] The grating pattern area includes a plurality of sub-areas, each of the sub-areas includes two types of lines having a first width and a second width, and the lines having the first width and the lines having the second width are arranged alternately in sequence, and the second width is smaller than the first width;

[0006] The auxiliary graphic area is distributed around each of the sub-areas, and the auxiliary graphic area includes sub-resolution lines, and the width of the sub-resolution lines is smaller than the second width.

[0007] Optionally, in the overlay mark, in each of the sub-areas along the arrangement direction, the first and last two lines have the second width.

[0008] Optionally, in the overlay mark, the grating graphic area includes four sub-areas, all of which are rectangular areas, and are rotated 90° in sequence around the same center so that the grating graphic area has a square outer contour and inner contour;

[0009] The auxiliary graphic area has an outer frame graphic and an inner frame graphic. The outer frame graphic is distributed around the grating graphic area and matches the shape of the outer contour. The inner frame graphic is distributed inside the grating graphic area and matches the shape of the inner contour.

[0010] Optionally, in the overlay mark, the aspect ratio of each sub-area is greater than 3:2.

[0011] Optionally, in the overlay mark, two types of lines with the first width and the second width in each of the sub-areas are alternately arranged in sequence along the length direction.

[0012] Optionally, in the overlay mark, the spacing between each sub-region and the adjacent sub-resolution line is D1, the difference between the periodic size and the line width in the auxiliary graphic region is D2, D1 is equal to D2; and the inner contour and outer contour of the grating graphic region are squares.

[0013] Optionally, in the overlay mark, a period width in the auxiliary graphic region is smaller than a period width in each of the sub-regions, and the number of periods in the auxiliary graphic region is plural.

[0014] Optionally, in the overlay mark, the ratio of the line width to the period width in the auxiliary graphic area is in the range of 2:1 to 1:4.

[0015] The present invention also provides an overlay error measurement method, comprising: using the overlay mark as described in any of the preceding items to perform overlay error measurement, and the spatial coherence coefficient of the illumination device used in the measurement is [0.71, 0.92], the polar angle ranges from 0 to 70 degrees, and the wavelength ranges from 600 to 700 nm.

[0016] The present invention further provides an exposure machine for forming the overlay mark as described in any of the preceding items, wherein the exposure accuracy of the exposure machine is 193 nm, and the thickness of the photoresist film is 100-300 nm.

[0017] In summary, the overlay mark, overlay error measurement method and exposure machine provided by the present invention have the following beneficial effects compared with the prior art:

[0018] (1) Due to the characteristics of WSO threading overlay, the mark pattern will be split into two areas of the same mask, which will be reflected in the same photoresist layer during the exposure process. This process can assist the lithography machine in calibrating the overlay accuracy. Since the pattern exists in the same layer, it must be asymmetric with a combination of CD values ​​of different sizes. According to the simulation scanning results, the present invention determines two specific CD values ​​for the threading overlay μDBO mark, which has better performance than the traditional design;

[0019] (2) The threading overlay mark provided by the present invention has an auxiliary line design, which can avoid edge effect crosstalk, thereby improving the sensitivity of the marked film system and reducing the measurement error of threading overlay.

[0020] (3) Furthermore, the present invention can place thin lines with small CD at the edge of the mark within the grating graphic area. In this design, the number of thin lines = the number of thick lines + 1, which is different from the conventional design in which the number of two CD lines is equal. According to simulation results, this design can effectively suppress the measurement field uniformity problem caused by the inner edge effect of the mark under the specific condition of threading and overlaying. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A distribution diagram of each area of ​​the overlay mark provided in an embodiment of the present invention;

[0022] Figure 2 A schematic diagram of the structure of an overlay mark provided by an embodiment of the present invention;

[0023] Figure 3 A schematic diagram of the structure of another overlay mark provided by an embodiment of the present invention;

[0024] Figure 4 It is a simulated light intensity diagram of the existing mark under several measurement modes;

[0025] Figure 5 Simulated light intensity diagrams of the markers provided by the embodiment of the present invention under several measurement modes;

[0026] The descriptions of the reference numerals are as follows:

[0027] 100a-first graphic area; 100b-second graphic area; 100c-third graphic area; 100d-fourth graphic area;

[0028] 200a-outer frame graphic; 200b-inner frame graphic;

[0029] 101-thick lines; 102-thin lines. DETAILED DESCRIPTION

[0030] In order to make the purpose, advantages and features of the present invention clearer, the present invention is described in detail in conjunction with 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 conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In addition, the structure shown in the drawings is often a part of the actual structure. In particular, the emphasis of each drawing is different, and sometimes different proportions are used. It should also be understood that, unless otherwise specified or indicated, the terms "first", "second", "third", etc. in the specification are only used to distinguish the various components, elements, steps, etc. in the specification, and are not used to represent the logical relationship or sequential relationship between the various components, elements, steps, etc.

[0031] See also Figure 1 An embodiment of the present invention provides an overlay mark, wherein the overlay mark includes a grating pattern area and an auxiliary pattern area. Figure 1 In the figure, the light grey area indicates the grating pattern area, the dark grey area indicates the auxiliary pattern area, and the other black area is the non-pattern area. Figure 1 As shown in , only the positions of the grating pattern area, the auxiliary pattern area and the non-pattern area are distinguished, which does not mean that the structure of the overlay mark provided by the embodiment of the present invention is like this.

[0032] The grating pattern area includes a plurality of sub-areas, each of which includes two lines having a first width and a second width, and the lines having the first width and the lines having the second width are arranged alternately in sequence, and the second width is smaller than the first width, that is, see Figure 2 and Figure 3 , each of the sub-areas includes thick lines 101 and thin lines 102, and the thick lines 101 and the thin lines 102 are arranged alternately in sequence. It should be noted that, Figure 2 and Figure 3 In the figure, black represents the photoresist retention area, white represents the base area where the photoresist is removed, that is, the line area, and the adjacent thick lines 101 and thin lines 102 are separated by the photoresist retention area, that is, the black area in the figure; please refer to Figure 1 The auxiliary graphic area is distributed around each of the sub-areas and preferably has an integrated design. Here, the "integrated design" can be understood as that the various parts of the auxiliary graphic area are connected into a whole. The auxiliary graphic area includes a sub-resolution line 201, and the width of the sub-resolution line 201 is less than the second width.

[0033] The overlay mark provided in the embodiment of the present invention has two lines of different widths to reflect asymmetry and meet the needs of threading overlay. In addition, the overlay mark provided in the embodiment of the present invention has an auxiliary line design to avoid edge effect crosstalk, thereby improving the sensitivity of the marking film system and reducing the measurement error of threading overlay. In the present embodiment, preferably, the grating graphic area includes four sub-areas, and the four sub-areas are all rectangular areas, and are rotated 90° in sequence around the same center so that the grating graphic area has a square outer contour and inner contour. It can be understood that in some other embodiments, there may be no restrictions on the relative positional relationship between the multiple sub-areas of the grating graphic area and the number of the sub-areas. It is only necessary to provide auxiliary lines between adjacent sub-areas and on the periphery of each sub-area, and the area where the auxiliary lines are preferably located presents an integrated design.

[0034] Specifically, if Figure 1 As shown, the four sub-areas are respectively the first graphic area 100a, the second graphic area 100b, the third graphic area 100c and the fourth graphic area 100d, and the first graphic area 100a, the second graphic area 100b, the third graphic area 100c and the fourth graphic area 100d respectively overlap with the adjacent graphic areas after the center is rotated 90°. For example, the first graphic area 100a overlaps with the second graphic area 100b after the center is rotated 90° clockwise, and overlaps with the fourth graphic area 100d after the center is rotated 90° counterclockwise. It can also be understood that each adjacent two sub-areas are distributed in an L shape, and the four sub-areas constitute two L shapes that are symmetrically distributed at the center, so that the whole has a square outer contour and inner contour. Preferably, the aspect ratio of each sub-area is greater than 3:2, for example, the aspect ratio of each sub-area is 2:1, so that the four sub-areas are arranged in sequence by rotating 90°.

[0035] Since the auxiliary graphic area is distributed around each of the sub-areas and is designed in an integrated manner, when the grating graphic area includes four sub-areas, and the four sub-areas are arranged in sequence in a 90° rotation, the grating graphic area has an outer frame graphic 200a and an inner frame graphic 200b, the outer frame graphic 200a is distributed around the grating graphic area and matches the shape of the outer contour, that is, the outer frame graphic 200a is also a square, and the inner frame graphic 200b is distributed on the inner side of the grating graphic area and matches the shape of the inner contour, that is, the inner frame graphic 200b is also a square. The auxiliary graphic area can realize edge compensation in two vertical directions at the same time, so the influence of the edge effect of the inner side of the grating graphic area in two directions can be suppressed at the same time.

[0036] Since two adjacent sub-regions overlap with the other sub-region after one of the sub-regions rotates 90°, the lines of the two adjacent sub-regions have perpendicular arrangement directions. Specifically, Figure 2 and Figure 3 As shown in , the first graphic area 100a and the third graphic area 100c have the same arrangement direction, and the two lines with different widths are arranged alternately in the first direction, and each line extends in the second direction; the second graphic area 100b and the fourth graphic area 100d have the same arrangement direction, and the two lines with different widths are arranged alternately in the second direction, and each line extends in the first direction, and the second direction is perpendicular to the first direction. Preferably, the two lines with different widths in each sub-area are arranged alternately in the length direction, that is, the length directions of the first graphic area 100a and the third graphic area 100c are both in the first direction, and the length directions of the second graphic area 100b and the fourth graphic area 100d are both in the second direction.

[0037] The two types of lines with different widths in each sub-area are designed to be arranged alternately in the length direction, which can meet the working requirements of threading and engraving. Even if the patterns exist in the same layer, the asymmetry of the patterns can be reflected by the combination of lines with different width values.

[0038] In this embodiment, no specific restrictions are imposed on the length and width of each sub-region, as well as the width, number of periods and period width of each line in each sub-region. It is only necessary that after the four sub-regions are rotated 90° in sequence, the overall area does not exceed the maximum area limit of the mark.

[0039] Preferably, for each of the sub-areas, along the arrangement direction, the first and last two lines of each of the sub-areas have the second width. Figure 2 and Figure 3 As shown, in each of the sub-areas, along the arrangement direction, the first and last are thin lines 102, and the number of thin lines 102 is one more than the number of thick lines 101. Different from the usual design in which the number of two CD lines is equal, according to the simulation results, this design can effectively suppress the measurement field uniformity problem caused by the inner edge effect of the mark in the specific case of threading and overlaying.

[0040] In addition, in order to ensure the effect of suppressing the edge effect, in this embodiment, the auxiliary graphic area is designed as follows: the period width in the auxiliary graphic area is smaller than the period width in each of the sub-areas, and the number of periods in the auxiliary graphic area is plural, and the ratio of the line width to the period width in the auxiliary graphic area is in the range of 2:1 to 1:4.

[0041] In addition, in order to meet the integration of the overall pattern, preferably, the spacing between each sub-region and the adjacent sub-resolution line is D1, the difference between the period size and the line width in the auxiliary graphic region is D2, and D1 is equal to D2; and the inner and outer contours of the grating graphic region are squares, that is, correspondingly, the inner frame graphic 200b and the outer frame graphic 200a of the auxiliary graphic region are also squares. When the overall pattern is integrated, the influence of light from different directions on the measurement results can be reduced.

[0042] As a specific example, Figure 2 The specific characteristic values ​​of the overlay marks shown are shown in Table 1. In each sub-area of ​​the grating graphic area, the width of the thin line is CD1=150nm, and there are 13 thin lines, the width of the thick line is CD2=300nm, and there are 12 thick lines, the period width Pitch=800nm, the length of each sub-area Length=5675nm, the distance between the thin line and the thick line SP=175nm, and the ratio of the width to the length of each sub-area W:L=1:2; in the auxiliary graphic area, the width CD of the sub-resolution line is 100nm, the period width Pitch=200nm, that is, the distance between two sub-resolution lines, and the distance between the auxiliary graphic area and the adjacent sub-resolution line is 200nm.

[0043] Table 1

[0044] Raster Graphics Area Auxiliary graphics area 13CD1, CD1=150nm 2CD, CD=100nm 12CD1,CD2=300nm Pitch=200nm Pitch=800nm Length=5675nm SP=175nm W:L=1:2

[0045] As another specific example, Figure 3 The specific characteristic values ​​of the overlay marks shown are shown in Table 2. In each sub-area of ​​the grating graphic area, the width of the thin line is CD1=170nm, and there are 13 thin lines, the width of the thick line is CD2=230nm, and there are 12 thick lines, the period width Pitch=800nm, the length of each sub-area is Length=5630nm, the distance between the thin line and the thick line is SP=200nm, and the ratio of the width to the length of each sub-area is W:L=1:2; in the auxiliary graphic area, the width CD of the sub-resolution line is 100nm, the period width Pitch=200nm, that is, the distance between two sub-resolution lines, and the distance between the auxiliary graphic area and the adjacent sub-resolution line is 200nm.

[0046] Table 2

[0047] Raster Graphics Area Auxiliary graphics area 13CD1, CD1=170nm 2CD, CD=100nm 12CD2, CD2=230nm Pitch=200nm Pitch=800nm Length=5630nm SP=200nm W:L=1:2

[0048] An embodiment of the present invention also provides an overlay error measurement method, comprising: using the overlay mark as described in this embodiment to measure the overlay error, and the spatial coherence coefficient (Sigma) of the illumination device used in the measurement is [0.71, 0.92], that is, Sigma in = 0.71, Sigma out = 0.92, the open angle (Open angle) has a value range of 0 to 70 degrees, and the wavelength (Wavelength) has a value range of 600 to 700 nm.

[0049] The embodiment of the present invention further provides an exposure machine for forming the overlay mark as described in this embodiment. The exposure accuracy of the exposure machine is 193nm, the thickness of the photoresist film is 100-300nm, and the mask can be a weak phase-shift mask.

[0050] Under the above-mentioned specific exposure machine and overlay error measurement method, the marks shown in Table 1 were jointly simulated using self-made lithography simulation software and general lithography simulation software, and the output results are shown in Table 3.

[0051] Table 3

[0052]

[0053]

[0054] Under the above-mentioned specific exposure machine and overlay error measurement method, the marks shown in Table 2 were jointly simulated using self-made lithography simulation software and general lithography simulation software, and the output results are shown in Table 4.

[0055] Table 4

[0056]

[0057] The currently used μDBO marker has an experimental film sensitivity (SS) of 0.0444 at a wavelength of 650nm, and the SS simulation data under the same conditions is 0.0487, with a measurement error (Err) of 10.1%. As can be seen from Table 3, the marker shown in Table 1 has an SS of 0.0690 under the optimized configuration, an increase of about 55%, and an Err of 1.3%. As can be seen from Table 4, the marker shown in Table 2 has an SS of 0.098 under the optimized configuration. It can be seen that the two overlay markers in the above examples perform better in terms of measurement linearity and marker accuracy than the traditional design.

[0058] Figure 4 The simulated light intensity diagram of the existing marker in several measurement modes is shown below. Figure 5The simulated light intensity diagrams of the marker provided in this embodiment under several measurement modes are shown in FIG. By comparison, it can be seen that the uniformity of light intensity distribution on the surface of the marker provided in this embodiment is significantly improved, which also proves that the marker provided in this embodiment can improve the measurement performance.

[0059] It should be noted that although the data shown in Table 3 and Table 4 are measured under the above-mentioned specific exposure machine and overlay error measurement method, it is understood that the above-mentioned exposure machine and overlay error measurement method are only preferred implementation modes and do not constitute a limitation on the overlay mark provided by the embodiment of the present invention. In some other embodiments, the overlay mark can be formed by an exposure machine with other settings, and the overlay error measurement method under other lighting conditions can be used for measurement, which will not be repeated here. It should also be noted that the overlay mark provided by the embodiment of the present invention is required to solve the technical problems existing in the μDBO mark, but it can be understood that the overlay mark provided by the present invention is not only applicable to the design of the μDBO mark, but also applicable to other overlay marks.

[0060] In summary, in the overlay mark, overlay error measurement method and exposure machine provided by the embodiments of the present invention, the overlay mark includes: a grating graphic area and an auxiliary graphic area, the grating graphic area includes a plurality of sub-areas, each of the sub-areas includes two lines with a first width and a second width, respectively, and the lines with the first width and the lines with the second width are arranged alternately in sequence, and the second width is smaller than the first width; the auxiliary graphic area is distributed around each of the sub-areas; the auxiliary graphic area includes sub-resolution lines, and the width of the sub-resolution lines is smaller than the second width. The overlay mark provided by the present invention has two lines of different widths to reflect asymmetry and meet the requirements of threading overlay. In addition, the overlay mark provided by the present invention has an auxiliary line design, which can avoid edge effect crosstalk, thereby improving the sensitivity of the mark film system and reducing the measurement error of threading overlay.

[0061] In addition, it should be recognized that although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belongs to the scope of protection of the technical solution of the present invention.

Claims

1. An overlay mark, characterized in that: include: Raster graphics area and auxiliary graphics area, The grating pattern area includes a plurality of sub-areas, each of the sub-areas includes two types of lines having a first width and a second width, and the lines having the first width and the lines having the second width are arranged alternately in sequence, and the second width is smaller than the first width; The auxiliary graphic area is distributed around each of the sub-areas, and the auxiliary graphic area includes sub-resolution lines, and the width of the sub-resolution lines is smaller than the second width.

2. The overlay mark according to claim 1, characterized in that: In each of the sub-areas along the arrangement direction, the first and last two lines have the second width.

3. The overlay mark according to claim 1, characterized in that: The grating graphic area includes four sub-areas, all of which are rectangular areas and are rotated 90° in sequence around the same center so that the grating graphic area has a square outer contour and inner contour. The auxiliary graphic area has an outer frame graphic and an inner frame graphic, the outer frame graphic is distributed around the grating graphic area and matches the shape of the outer contour, and the inner frame graphic is distributed on the inner side of the grating graphic area and matches the shape of the inner contour.

4. The overlay mark according to claim 3, characterized in that: The aspect ratio of each sub-region is greater than 3:

2.

5. The overlay mark according to claim 3, characterized in that: The two types of lines with the first width and the second width in each of the sub-areas are alternately arranged in sequence along the length direction.

6. The overlay mark according to claim 3, characterized in that: The spacing between each sub-region and the adjacent sub-resolution line is D1, the difference between the periodic size and the line width in the auxiliary graphic region is D2, D1 is equal to D2; and the inner contour and outer contour of the grating graphic region are squares.

7. The overlay mark according to claim 1, characterized in that: The period width in the auxiliary graphic region is smaller than the period width in each of the sub-regions, and the number of periods in the auxiliary graphic region is plural.

8. The overlay mark according to claim 8, characterized in that: The ratio of the line width to the period width in the auxiliary graphic area is in the range of 2:1 to 1:

4.

9. A method for measuring overlay error, characterized in that: include: The overlay error is measured using the overlay mark as described in any one of claims 1 to 8, and the spatial coherence coefficient of the illumination device used in the measurement is [0.71, 0.92], the polar angle ranges from 0 to 70 degrees, and the wavelength ranges from 600 to 700 nm.

10. An exposure machine for forming the overlay mark according to any one of claims 1 to 8, characterized in that: The exposure accuracy of the exposure machine is 193nm, and the thickness of the photoresist film is 100-300nm.

Images