Photomask and inspection method of the same

Abstract

To provide a photomask which can accurately and easily inspect a device pattern even if it has a curve shape, and an inspection method of the same.SOLUTION: A photomask 100 has a device region 121 formed with a device pattern, and an inspection region 122 which is provided in areas other than the device region 121 and is formed with an inspection pattern, wherein a Lissajous figure of a closed curve obtained by synthesizing displacement magnitudes x, y, which are represented by the following expressions (1) and (2), of a cycle of simple vibration in two directions perpendicular to each other is formed as an inspection pattern 122C in the inspection region 122. Expression (1): x=Acos(at). Expression (2): y=Bsin(bt+δ). In the expressions, A and B are amplitudes, a and b are frequencies, t is a time, and δ is an initial phase difference.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a photomask and an inspection method thereof. [Background technology]

[0002] Photomasks used in manufacturing semiconductors are designed by CAD so that the design of the device pattern to be formed on the semiconductor is parallel to the X-axis and Y-axis that make up the horizontal plane. However, if the device pattern is formed on the photomask with the designed design intact, the wafer will not be exposed to light in the shape of the device pattern when the semiconductor is manufactured due to the optical proximity effect, and the semiconductor cannot be obtained with the designed design.

[0003] For this reason, optical proximity correction (OPC) is performed to take the influence of optical proximity effect into consideration in advance, and to perform a simulation to determine a device pattern that can be used to expose a wafer with a designed design, thereby correcting the device pattern to be formed on the photomask in advance.

[0004] In this case, the device pattern of the photomask that can expose the wafer with the designed design is likely to be curved in many parts. On the other hand, the electron beam lithography equipment that forms the device pattern on the photomask is mainly a rectangular variable shaped beam (VSB) type, which forms the device pattern with a shape of a row of rectangles, that is, a shape of connected straight lines. Therefore, the device pattern is formed on the photomask by replacing the curves of the device pattern obtained by the OPC process with straight lines to approximate them.

[0005] In such photomasks, during manufacturing, inspection patterns consisting only of straight lines parallel to the X-axis and Y-axis, such as squares, rectangles, L-shapes, and crosses, are formed simultaneously with the formation of the device patterns in the device outside areas other than the device areas where the device patterns are formed. Then, by measuring the length of this inspection pattern with a critical dimension scanning electron microscope (CD-SEM), it becomes possible to easily inspect the dimensional accuracy of device patterns with complex shapes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-161834 A [Patent Document 2] U.S. Patent No. 9,557,655 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, the shift from the VSB method to the multi-beam (MB) method has been considered for the drawing equipment that forms the device pattern on the photomask. The MB method first rasterizes the OPC-processed device pattern and creates a lithography mask pattern in which all the patterns are converted into pixels (dots). Then, a large number of electron beams (approximately 260,000) are irradiated at once in accordance with this lithography mask pattern to draw and form the OPC-processed device pattern.

[0008] With this MB method, even if many parts of the OPC processed device pattern have curved shapes, it is easy to form the device pattern by drawing it with a lithography mask pattern that corresponds to the curved shapes, making it possible to manufacture semiconductors with higher precision device patterns.

[0009] Incidentally, when inspecting the dimensional accuracy of a photomask on which a curved device pattern is formed, the following method has been considered: In this method, the device pattern formed on the photomask is photographed by CD-SEM to extract a contour image, and the finished shape is predicted from the lithography mask pattern by a simulation model, and the contour image and the predicted shape are superimposed for inspection.

[0010] However, the contour images captured and extracted by CD-SEM are noisy and very unstable, so it is necessary to average a large number of images or calculate the true contour position using machine learning, which makes it extremely time-consuming to perform accurate inspections.

[0011] In view of the above, an object of the present invention is to provide a photomask and an inspection method thereof that can easily inspect even device patterns having curved shapes with high accuracy. [Means for solving the problem]

[0012] In order to solve the above-mentioned problems, the photomask of the present invention is a photomask having a device region in which a device pattern is formed, and an inspection region provided outside the device region in which an inspection pattern is formed, and is characterized in that a Lissajous figure of a closed curve obtained by combining the displacement amounts x and y of the period of simple harmonic motion in two mutually perpendicular directions, represented by the following equations (1) and (2), is formed in the inspection region as the inspection pattern.

[0013] x=Acos(at) (1) y = B sin(bt + δ) (2) Here, A and B are amplitudes, a and b are frequencies, t is time, and δ is the initial phase difference.

[0014] Furthermore, in the photomask of the present invention, it is preferable that, in the above-mentioned photomask, the inspection region is sized to fit within a field of view (FOV) at a measurement magnification of a critical dimension scanning electron microscope (CD-SEM) that is set based on the line width of the device pattern in the device region.

[0015] In addition, in the photomask according to the present invention, it is preferable that a plurality of the inspection regions are provided, and the inspection patterns in the plurality of the inspection regions are Lissajous figures having shapes different from one another.

[0016] Furthermore, the photomask of the present invention is preferably such that, in the above-mentioned photomask, a plurality of the inspection areas are provided, the inspection pattern in at least one of the inspection areas is the Lissajous figure, and the inspection pattern in at least one other of the inspection areas is a figure consisting of only straight lines.

[0017] On the other hand, a photomask inspection method according to the present invention for solving the above-mentioned problems is the above-mentioned photomask inspection method, characterized in that it includes an imaging step of imaging the inspection pattern in the inspection area of ​​the photomask as a bitmap image, a coordinate calculation step of determining pixel coordinates of a center position of the inspection pattern from data of the bitmap image and determining pixel coordinates of each maximum position in the X-axis direction and Y-axis direction of the inspection pattern, a reference pattern creation step of determining values ​​of A and B constituting equations (1) and (2) of the inspection pattern from the obtained pixel coordinates and creating a bitmap image of a reference pattern corresponding to the inspection pattern based on equations (1) and (2), a pattern synthesis step of superimposing the reference pattern on the inspection pattern so that pixel coordinates of a center position of data of the bitmap image of the reference pattern coincide with pixel coordinates of a center position of data of the bitmap image of the inspection pattern, and an evaluation step of comparing the superimposed reference pattern and the inspection pattern to perform evaluation.

[0018] In the photomask manufacturing method according to the present invention, in the above-mentioned photomask manufacturing method, it is preferable that the photographing step is a step of photographing an entire image of the inspection pattern collectively as a single data.

[0019] Furthermore, in the photomask manufacturing method according to the present invention, in the above-described photomask manufacturing method, it is preferable that the evaluation step includes a distance calculation step of calculating a distance between the superimposed reference pattern and the inspection pattern at specified intervals, a variation calculation step of calculating a variation in the calculated distances, and a determination step of determining that the pattern is pass when the calculated variation is within a preset range and that the pattern is fail when the calculated variation is outside the preset range.

[0020] Furthermore, in the photomask manufacturing method according to the present invention, in the above-described photomask manufacturing method, it is preferable that the distance calculation step is a step of calculating a slope of the reference pattern at each specified interval by a differential method, determining perpendicular lines to the reference pattern based on each of the calculated slopes, and calculating a distance of each of the perpendicular lines to an edge of a line of the inspection pattern.

[0021] In addition, the present invention also provides a method for manufacturing a photomask, which is characterized in that the processing conditions of the photomask are adjusted to manufacture the photomask so that the variation judged as a failure in the judgment step of the above-mentioned photomask inspection method falls within the predetermined range. Effect of the Invention

[0022] According to the photomask and the inspection method thereof of the present invention, since the Lissajous figure expressed by the above formulas (1) and (2) is formed in the inspection area as an inspection pattern, an inspection pattern and a reference pattern having a central intersection point at the origin and being line-symmetric (mirror-symmetric) about the X-axis and Y-axis can be created based on the formulas and superimposed for inspection. Therefore, even if a device pattern has a curved shape with various curvatures and directions, it can be easily inspected with high accuracy because it can be easily inspected by the inspection pattern and the reference pattern corresponding to the curved shape of the device pattern. [Brief description of the drawings]

[0023] [Figure 1] 1 is a plan view showing a schematic configuration of a main embodiment of a photomask according to the present invention. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Diagram 3] 1 is a plan view of an inspection pattern of various Lissajous figures formed in an inspection area. FIG. [Figure 4] 2 is a diagram illustrating the steps of a method for manufacturing the photomask of FIG. 1. [Diagram 5] FIG. 1 is a flow chart for explaining the procedure of a main embodiment of a photomask inspection method according to the present invention. [Figure 6] 2 is an explanatory diagram of an observation field when an inspection pattern in an inspection region of the photomask in FIG. 1 is measured by a critical dimension measuring scanning electron microscope. [Figure 7] 2 is an explanatory diagram of a reference pattern corresponding to an inspection pattern in an inspection area of ​​the photomask in FIG. 1; [Figure 8] 8 is an explanatory diagram of the inspection pattern in FIG. 6 and the reference pattern in FIG. 7 superimposed on each other. [Figure 9] FIG. 9 is an explanatory diagram of the inspection method in FIG. 8. [Figure 10] FIG. 11 is a plan view showing a schematic configuration of another embodiment of a photomask according to the present invention. [Figure 11] 11 is an extracted and enlarged view of an inspection area in which a rectangular (line) inspection pattern is formed in FIG. 10. FIG. [Figure 12] 11 is an extracted and enlarged view of an inspection area in which a square (space) inspection pattern is formed in FIG. 10. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The embodiments of the photomask and the inspection method thereof according to the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments described with reference to the drawings, and various technical matters described in each embodiment can be appropriately combined or substituted as necessary.

[0025] [Main embodiment] Main embodiments of a photomask and an inspection method thereof according to the present invention will be described with reference to FIGS.

[0026] 1 and 2, a light-shielding film 120 made of chromium or the like is provided on a substrate 110 made of glass or the like. The light-shielding film 120 is provided with a device region 121 in which a device pattern is formed, and an inspection region 122 in which an inspection pattern is formed. In the device region 121, a device pattern is formed by performing optical proximity correction (OPC) on a design to be formed on a device such as a semiconductor.

[0027] The inspection region 122 is provided in an area other than the device region 121, and a Lissajous figure of a closed curve obtained by combining the displacement amounts x and y of the period of simple harmonic motion in two mutually perpendicular directions (X-axis direction and Y-axis direction), as represented by the following equations (1) and (2), is formed as the inspection pattern.

[0028] x=Acos(at) (1) y = B sin(bt + δ) (2) Here, A and B are amplitudes, a and b are frequencies, t is time, and δ is the initial phase difference.

[0029] Here, for example, when A and B are 1, δ is 0, and a=1, b=2, the result is inspection pattern 122A of a Lissajous figure of a symmetrical closed curve having an intersection at the center as shown in FIG. 3(A). When a=3, b=2, the result is inspection pattern 122B of a Lissajous figure of a symmetrical closed curve having an intersection at the center as shown in FIG. 3(B). When a=3, b=4, the result is inspection pattern 122C of a Lissajous figure of a symmetrical closed curve having an intersection at the center as shown in FIG. 3(C). When a=5, b=4, the result is inspection pattern 122D of a Lissajous figure of a symmetrical closed curve having an intersection at the center as shown in FIG. 3(D).

[0030] In addition, since the above formula (1) expressing the displacement amount x in the X-axis direction uses cosine (cos), and the above formula (2) expressing the displacement amount y in the Y-axis direction uses sine (sin), a phase difference of π / 2 is originally generated between the X-axis direction and the Y-axis direction. Therefore, by setting the initial phase difference δ to 0 (or π) and the actual phase difference to π / 2, a Lissajous figure of a symmetrical closed curve is obtained.

[0031] On the other hand, when both the displacement amount x in the X-axis direction and the displacement amount y in the Y-axis direction are expressed using sine (sin) or cosine (cos), the X-axis direction and the Y-axis direction are in phase. Therefore, by setting the initial phase difference δ to π / 2 and the actual phase difference to π / 2, a Lissajous figure of a symmetric closed curve can be obtained.

[0032] In the above formulas (1) and (2), the values ​​of A and B and the values ​​of a and b are appropriately set according to the shape of the device pattern obtained by OPC, that is, conditions such as the curvature and direction of the curved portion.

[0033] Moreover, the inspection region 122 has a size that fits within the observation field of view (FOV) at the measurement magnification of a critical dimension scanning electron microscope (CD-SEM) that is set based on the line width of the device pattern in the device region 121. Specifically, for example, when the line width of the device pattern in the device region 121 is 60 nm, the appropriate measurement magnification of the CD-SEM is about 50,000 times (50k times), so the inspection region 122 is set to a square shape with a side length of about 2.8 to 3 μm.

[0034] Such a photomask 100 according to this embodiment can be manufactured in the same manner as in the conventional method. For example, as shown in Fig. 4, a photomask blank is manufactured by depositing chromium or the like on a substrate 110 such as glass to provide a light-shielding film 120 (see Fig. 4(A)), and then a photosensitive resin solution is uniformly applied on the light-shielding film 120 and dried to form a resist film 130 (see Fig. 4(B)).

[0035] Next, a lithography mask pattern in which the inspection pattern and the OPC-processed device pattern are all converted into pixels (dots) is drawn on the resist film 130 by irradiating with MB, and then a development process is performed to remove the MB-irradiated parts of the resist film 130 (see Figure 4(C)).

[0036] Next, the portion of the light-shielding film 120 exposed from the resist film 130 is removed by dry etching using a reactive gas or the like (see FIG. 4(D)), and then the resist film 130 is entirely removed and washed (see FIG. 4(E)). This makes it possible to obtain a photomask 100 having the light-shielding film 120 on which the device region 121 and the inspection region 122 are formed, on the substrate 110.

[0037] A method for inspecting the photomask 100 according to this embodiment manufactured in this manner will be described below with reference to FIG.

[0038] First, the manufactured photomask 100 is set in a CD-SEM (setting step S1 in FIG. 5). Next, the CD-SEM is set to a measurement magnification (e.g., 50,000 times (50k times)) corresponding to the line width (e.g., 60 nm) of the device pattern in the device region 121, and the CD-SEM is adjusted so that the inspection region 122 is located within the observation field of view (FOV). At this time, the inspection region 122 has a length (e.g., 2.8 to 3 μm) corresponding to the measurement magnification by the CD-SEM, so that the entire interior of the region fits within the FOV (adjustment step S2 in FIG. 5).

[0039] Specifically, in the above formulas (1) and (2), for example, if A and B are 1 μm, a=3, b=4, δ is 0, and the line width is 60 nm, the inspection area 122 having the inspection pattern 122C formed thereon as shown in Fig. 6 can be accommodated within the FOV. Then, by photographing the inspection area 122, the entire inspection pattern 122C in the inspection area 122 is acquired collectively as single (identical) data of a bitmap image (photographing step S3 in Fig. 5).

[0040] Next, the pixel coordinates of the center position Oc of the check pattern 122C are calculated from the obtained bitmap image data, and the pixel coordinates of each maximum position in the X-axis direction and Y-axis direction of the check pattern 122C are calculated (coordinate calculation step S4 in FIG. 5).

[0041] From the obtained pixel coordinates, the values ​​of A and B constituting the equations (1) and (2) of the test pattern 122C on the bitmap image are calculated, and a reference pattern 122Cs as shown in FIG. 7 corresponding to the test pattern 122C is created based on the equations (1) and (2) (reference pattern creation step S5 in FIG. 5).

[0042] Then, the reference pattern 122Cs is superimposed on the check pattern 122C so that the pixel coordinates of the center position Os of the bitmap image data of the created reference pattern 122Cs coincide with the pixel coordinates of the center position Oc of the bitmap image data of the check pattern 122C (pattern combining step S6 in FIG. 5). This allows a center line of the reference pattern 122Cs to be provided in the check pattern 122C, as shown in FIG.

[0043] Next, an evaluation step is performed in which the superimposed reference pattern 122Cs and the inspection pattern 122C are compared for evaluation. Specifically, the inclination of the reference pattern 122Cs at each specified interval is calculated by a differential method, and based on each calculated inclination, a perpendicular line Lv to the reference pattern 122Cs is set as shown in Fig. 9, and the distance of each perpendicular line Lv to the edge of the line of the inspection pattern 122C is calculated. As a result, the distance between the reference pattern 122Cs and the inspection pattern 122C is obtained at each specified interval (distance calculation step S7 in Fig. 5).

[0044] Then, the variation in the distance for each of the determined specified intervals is calculated (variation calculation step S8 in FIG. 5), and it is determined whether the variation is within a preset range (determination step S9 in FIG. 5). If it is within the range, it is deemed to be a pass, and if it is outside the range, it is deemed to be a fail.

[0045] In other words, the test pattern and the reference pattern are created based on a formula that can draw a closed curve that has an intersection point at the origin, is line symmetric (mirror symmetric) about the X-axis and Y-axis, and is expandable and scalable in the X-axis and Y-axis directions, i.e., a Lissajous figure, and are superimposed for inspection. This allows device patterns having curved shapes with various curvatures and directions to be easily inspected using the test pattern 122C and the reference pattern 122Cs that correspond to the curved shapes of the device patterns.

[0046] Therefore, according to the photomask 100 and the inspection method thereof according to this embodiment, even device patterns having curved shapes can be easily inspected with high accuracy.

[0047] Furthermore, since the inspection pattern 122C and the reference pattern 122Cs can be expanded or contracted in the X-axis and Y-axis directions, the entire inspection pattern 122Cs in the inspection area 122C can be accommodated within the FOV by setting the measurement magnification of the CD-SEM corresponding to the line width of the device pattern in the device area 121. This eliminates the need to divide and photograph the inspection pattern 122Cs, thereby reducing the labor required for inspection and preventing a decrease in inspection accuracy due to misalignment of the divided images.

[0048] In addition, since they are closed curves with their centers at the origin, the center position Oc of the test pattern 122C obtained by photographing and the center position Os of the reference pattern 122Cs obtained by a formula can be easily superimposed on each other by matching them on a bitmap image, which makes it easy to combine the photographed image and the formula image.

[0049] Furthermore, the processing conditions are adjusted so that the variations judged as failing in judgment step S9 are within the previously set range, i.e., by feeding back the inspection results to the manufacturing conditions, the photomask 100 can always be manufactured with high precision.

[0050] Specifically, for example, since the Lissajous figure is linearly symmetric (mirror symmetric) about the X-axis and Y-axis, the degree of eccentricity of the MB can be obtained by inspecting the symmetry of the inspection pattern 122C. The degree of eccentricity thus obtained is fed back to the angle control of the MB irradiation head of the drawing device when the next photomask is manufactured. This allows the photomask to be manufactured with high accuracy at all times.

[0051] [Other embodiments] In the above embodiment, the photomask 100 is provided with one inspection region 122 in which the inspection pattern 122C is formed, but the present invention is not limited to this. As another embodiment, for example, it is possible to appropriately provide a photomask with a plurality of inspection regions 122 in which the inspection pattern 122C is formed, or a photomask with a plurality of inspection regions 122 in which inspection patterns 122A to 122D of Lissajous figures with different shapes are formed, as necessary.

[0052] Furthermore, for example, as shown in Fig. 10, it is possible to provide not only a plurality of inspection regions 122 in which a Lissajous figure inspection pattern is formed, but also a plurality of inspection regions 123, 124 in which inspection patterns of figures (linear figures) consisting only of straight lines parallel to the X-axis and Y-axis, such as squares, rectangles, L-shapes, crosses, etc. Specifically, for example, it is possible to provide a plurality of inspection regions 123 in which a rectangular (line) inspection pattern 123A is formed as shown in Fig. 11, and a plurality of inspection regions 124 in which a square (space) inspection pattern 124A is formed as shown in Fig. 12. [Industrial Applicability]

[0053] The photomask and inspection method thereof according to the present invention can easily perform inspection with high accuracy and can therefore be used extremely beneficially in various industries. [Explanation of symbols]

[0054] 100 Photomask 110 Substrate 120 Light-shielding film 121 Device Area 122 Inspection Area 122A~122D Inspection pattern (Lissajous figure) 122Cs Reference Pattern (Lissajous Figure) 123 Inspection Area 123A Inspection Pattern (Line) 124 Inspection Area 124A Test Pattern (Space)

Claims

1. a device region having a device pattern formed thereon; an inspection area provided outside the device area and having an inspection pattern formed therein; A photomask having A Lissajous figure of a closed curve obtained by combining displacement amounts x and y of the period of simple harmonic motion in two mutually perpendicular directions, which are expressed by the following formulas (1) and (2), is formed in the inspection area as the inspection pattern. A photomask comprising: x=Acos(at) (1) y=Bsin(bt+δ) (2) where A and B are amplitudes, a and b are frequencies, t is time, and δ is an initial phase difference.

2. The inspection area has a size that fits within a field of view (FOV) at a measurement magnification of a critical dimension scanning electron microscope (CD-SEM) that is set based on the line width of the device pattern in the device area.

2. The photomask according to claim 1.

3. The inspection area is provided in plurality, The inspection patterns in the plurality of inspection regions are Lissajous figures having different shapes from each other.

2. The photomask according to claim 1.

4. The inspection area is provided in plurality, the test pattern of at least one of the test areas is the Lissajous figure; The inspection pattern in at least one of the other inspection areas is a figure consisting of straight lines only.

2. The photomask according to claim 1.

5. 2. The photomask inspection method according to claim 1, comprising: an imaging step of imaging the inspection pattern in the inspection area of ​​the photomask as a bitmap image; a coordinate calculation step of calculating pixel coordinates of a center position of the inspection pattern from the data of the bitmap image, and calculating pixel coordinates of each maximum position in the X-axis direction and the Y-axis direction of the inspection pattern; a reference pattern creating step of determining the values ​​of A and B constituting the formulas (1) and (2) of the inspection pattern from the obtained pixel coordinates, and creating a bitmap image of a reference pattern corresponding to the inspection pattern based on the formulas (1) and (2); a pattern synthesis step of superimposing the reference pattern on the test pattern so that pixel coordinates of a center position of the data of the bitmap image of the reference pattern coincide with pixel coordinates of a center position of the data of the bitmap image of the test pattern; an evaluation step of performing an evaluation by comparing the superimposed reference pattern and the inspection pattern; 13. A photomask inspection method comprising the steps of:

6. The photographing step is a step of photographing an entire image of the inspection pattern as a single data item.

6. The photomask inspection method according to claim 5.

7. The evaluation step includes: a distance calculation step of calculating a distance between the superimposed reference pattern and the inspection pattern at a specified interval; a variation calculation step of calculating a variation of the obtained distance; a judging step of judging the calculated variation as pass when it is within a preset range, and judging the calculated variation as fail when it is outside the preset range; This is the step to 6. The photomask inspection method according to claim 5.

8. The distance calculation step includes: Calculating the slope of the reference pattern at each specified interval by a differential method; determining a perpendicular line to the reference pattern based on each of the calculated inclinations; Calculating the distance of each of the perpendicular lines to an edge of a line of the inspection pattern.

8. The photomask inspection method according to claim 7.

9. 8. The photomask inspection method according to claim 7, further comprising the step of manufacturing the photomask by adjusting processing conditions of the photomask so that the variation evaluated as "rejected" in the judgment step falls within the preset range. A method for manufacturing a photomask comprising the steps of:

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