Method for forming evaluation patterns and method for evaluating positional changes

Abstract

An evaluation pattern is formed that allows for accurate measurement of the effect of pattern density on the beam irradiation position. [Solution] A method for forming an evaluation pattern according to one aspect of the present invention comprises the steps of: irradiating a sample with a charged particle beam to draw a plurality of first patterns with different pattern densities; and drawing a plurality of second patterns with different pattern densities such that they combine with at least some of the plurality of first patterns to have equal pattern densities, thereby forming a plurality of evaluation patterns with equal pattern densities.

Description

Technical Field

[0001] The present invention relates to a method for forming an evaluation pattern and a method for evaluating positional variation.

Background Art

[0002] With the increasing integration of LSIs, the circuit line width required for semiconductor devices has been continuously miniaturized year by year. In order to form a desired circuit pattern on a semiconductor device, a method of reducing and transferring a high-precision original pattern formed on quartz onto a wafer using a reduction projection exposure apparatus is adopted. For the production of a high-precision original pattern, a so-called electron beam lithography technique, in which a resist is exposed by an electron beam drawing apparatus to form a pattern, is used.

[0003] As an electron beam drawing apparatus, for example, a multi-beam drawing apparatus that irradiates many beams at once using multi-beams to improve throughput is known. In this multi-beam drawing apparatus, for example, an electron beam emitted from an electron source is passed through an aperture member having a plurality of openings to form multi-beams, blanking control of each beam is performed, and each unshielded beam is reduced by an optical system and irradiated onto a substrate placed on a movable stage.

[0004] The multi-beam drawing apparatus irradiates a plurality of beams at once, connects the beams formed by passing through the same or different openings of the aperture member, and draws a pattern having a desired figure shape. Therefore, the shape of the entire image of the beam array irradiated on the substrate (hereinafter, may also be described as "beam array shape") appears as the connection accuracy of the drawn figure.

[0005] It is known that the beam array shape changes (rotates and scales) depending on the irradiation amount. Since the irradiation amount depends on the pattern density, it is necessary to investigate in advance how much the pattern density affects the beam array shape (the irradiation positions of a plurality of individual beams of the multi-beams), and obtain the correction amount of the irradiation amount and irradiation position during product pattern drawing.​

[0006] Conventionally, as shown in Figure 9, an evaluation pattern was drawn that included, for example, a cross-shaped position measurement pattern 81 arranged at equal intervals and a plurality of density adjustment patterns 82 arranged between the position measurement patterns 81 with different densities. After etching and developing, the position of the position measurement pattern was measured to investigate the effect of the pattern density on the beam irradiation position.

[0007] However, in such conventional evaluation patterns, the position measurement pattern 81 and the density adjustment pattern 82 are separate, and the pattern density of the position measurement pattern 81 itself cannot be changed, making it difficult to accurately estimate the effect of the pattern density on the beam irradiation position.

[0008] Furthermore, the density adjustment patterns 82 surrounding each position measurement pattern 81 have different pattern densities. The measuring instrument used to measure the position of the position measurement pattern 81 uses light, and if the surrounding conditions of the position measurement pattern are different, the effect on light reflection also changes, which can lead to a deterioration in position measurement accuracy.

[0009] The tension of the light-shielding film on the substrate changes according to the pattern density of the density adjustment pattern 82, which sometimes caused misalignment of the pattern during etching and developing processes.

[0010] Thus, with conventional evaluation patterns, it was difficult to accurately measure the effect of pattern density on the beam irradiation position. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2011-040450 [Patent Document 2] Japanese Patent Publication No. 2017-028284 [Patent Document 3] Japanese Patent Publication No. 2014-041952 [Overview of the project] [Problems that the invention aims to solve]

[0012] This invention has been made in view of the above-mentioned conventional circumstances, and aims to provide a method for forming an evaluation pattern and a method for evaluating positional variation that can accurately measure the effect of pattern density on the beam irradiation position. [Means for solving the problem]

[0013] A method for forming an evaluation pattern according to one aspect of the present invention comprises the steps of: irradiating a sample with a charged particle beam to draw a plurality of first patterns with different pattern densities; and drawing a plurality of second patterns with different pattern densities such that, when combined with at least some of the plurality of first patterns, their respective pattern densities become equal, thereby forming a plurality of evaluation patterns with equal pattern densities. [Effects of the Invention]

[0014] According to the present invention, an evaluation pattern can be formed that allows for the accurate measurement of the effect of pattern density on the beam irradiation position. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram of a drawing apparatus according to an embodiment of the present invention. [Figure 2] This is a schematic diagram of the aperture member. [Figure 3] This is a conceptual diagram illustrating an example of drawing operation. [Figure 4] Figures 4a to 4c illustrate a method for measuring pattern density-dependent beam irradiation position variations. [Figure 5] This is a diagram illustrating how to plot evaluation patterns. [Figure 6] This is a diagram illustrating how to plot evaluation patterns. [Figure 7] This is a diagram illustrating how to plot evaluation patterns. [Figure 8] This is a diagram for explaining a method of drawing an evaluation pattern and a measurement method. [Figure 9] This is a diagram for explaining a method of drawing an evaluation pattern according to a comparative example.

Embodiments for Carrying out the Invention

[0016] Hereinafter, in the embodiments, as an example of a charged particle beam, a configuration using an electron beam will be described. However, the charged particle beam is not limited to an electron beam, and a beam using charged particles such as an ion beam may also be used.

[0017] FIG. 1 is a conceptual diagram showing the configuration of a drawing apparatus in an embodiment. In FIG. 1, the drawing apparatus 100 includes a drawing unit 150 and a control unit 160. The drawing apparatus 100 is an example of a multi-charged particle beam drawing apparatus. The drawing unit 150 includes an electron column 102 and a drawing chamber 103.

[0018] In the electron column 102, an electron source 201, an illumination lens 202, a shaping aperture array substrate 203, a blanking aperture array substrate 204, a reduction lens 205, a limiting aperture member 206, an objective lens 207, deflectors 208 and 209 are arranged.

[0019] In the drawing chamber 103, an XY stage 105 is arranged. On the XY stage 105, a sample 101 such as a mask which becomes a drawing target substrate at the time of drawing is arranged. The sample 101 is, for example, an exposure mask when manufacturing a semiconductor device, a semiconductor substrate (silicon wafer) on which a semiconductor device is manufactured, a mask blank, etc. On the XY stage 105, further, a mirror 210 for measuring the position of the XY stage 105 is arranged.

[0020] The control unit 160 has a control computer 110, a deflection control circuit 130, a stage position detector 139, and a storage device 140 such as a magnetic disk device. Drawing data is stored in the storage device 140 (storage unit).

[0021] The control computer 110 contains a drawing data processing unit 112 and a drawing control unit 114. The functions of the drawing data processing unit 112 and the drawing control unit 114 may be configured as hardware such as electrical circuits, or as software such as programs that execute these functions. Alternatively, they may be configured as a combination of hardware and software. Information input to and output from the drawing data processing unit 112 and the drawing control unit 114, as well as information being calculated, are stored in a memory (not shown) each time.

[0022] Figure 2 is a conceptual diagram showing the configuration of the molded aperture array substrate 203. The molded aperture array substrate 203 has m rows (vertical, y direction) × n rows (horizontal, x direction) (m, n ≥ 2) of apertures 22 formed in a matrix at a predetermined arrangement pitch. For example, 512 × 512 apertures 22 are formed in the vertical and horizontal (x, y directions). Each aperture 22 is formed, for example, as a rectangle or circle of the same dimensions and shape. A multi-beam 20 is formed when a portion of the electron beam 200 passes through each of these multiple apertures 22.

[0023] The blanking aperture array substrate 204 has through holes (openings) for the passage of each individual beam of the multibeam, at positions corresponding to each aperture 22 of the molded aperture array substrate 203 shown in Figure 2. Near each through hole, a pair of electrodes for blanking deflection (blankers: blanking deflectors) is placed on either side of the corresponding through hole.

[0024] Figure 3 is a conceptual diagram illustrating an example of the drawing operation. As shown in Figure 3, the drawing area 30 of the sample 101 is virtually divided into multiple stripe-shaped areas 32 with a predetermined width in the y-direction, for example. Each stripe area 32 becomes a drawing unit area. First, the XY stage 105 is moved to adjust the position so that the irradiation area 34 that can be irradiated with a single multi-beam 20 is located at the left end of the first stripe area 32, or further to the left, and drawing is started.

[0025] When drawing the first stripe area 32, the drawing progresses relatively towards the +x direction by moving the XY stage 105, for example, in the -x direction. The XY stage 105 moves continuously at a predetermined speed. After the drawing of the first stripe area 32 is completed, the stage position is moved in the -y direction to adjust the illumination area 34 so that it is positioned relatively in the +y direction at the right edge of the second stripe area 32, or even further to the right. Then, the XY stage 105 is moved, for example, in the +x direction, and drawing is performed similarly toward the -x direction.

[0026] Drawing time can be shortened by alternating directions while drawing, such as drawing in the +x direction in the third stripe region 32 and in the -x direction in the fourth stripe region 32. However, it is not limited to alternating directions; drawing can also be done in the same direction when drawing each stripe region 32. In a single shot, multiple shot patterns, up to the same number as the apertures 22, are formed at once by the multi-beam formed by passing through each aperture 22 of the molded aperture array substrate 203.

[0027] The drawing data processing unit 112 reads drawing data from the storage device 140 and performs multiple stages of data conversion processing to generate shot data. The shot data defines whether or not each irradiation area is irradiated when the drawing surface of the sample 101 is divided into multiple grid-like irradiation areas by, for example, the beam size, and the irradiation time.

[0028] Tracking control using beam deflection is initiated so that the drawing positions of each individual beam of the multi-beam 20 are grouped together and follow the movement of the XY stage 105. Specifically, the stage position detector 139 measures the position of the XY stage 105 by irradiating the mirror 210 with a laser and receiving the reflected light from the mirror 210. The measured position of the XY stage 105 is output to the control computer 110. The drawing control unit 114 outputs a control signal to the deflection control circuit 130 based on the shot data and stage position information.

[0029] Within the deflection control circuit 130, deflection amount data (tracking deflection data) is calculated to deflect the beam in accordance with the movement of the XY stage 105. The tracking deflection data, which is a digital signal, is converted into an analog signal and applied to the deflector 208 as a tracking deflection voltage.

[0030] The drawing unit 150 performs tracking control and illuminates each beam at the drawing position of each beam with the corresponding ON beam from the multi-beam 20 for the corresponding drawing time within the preset maximum drawing time. Specifically, it operates as follows.

[0031] The electron beam 200 emitted from the electron source 201 (emission unit) illuminates the entire molded aperture array substrate 203 almost vertically through the illumination lens 202. A portion of the electron beam 200 passes through a plurality of apertures 22 provided in the molded aperture array substrate 203, thereby forming multiple electron beams (multibeams) 20, for example, rectangular in shape. The multibeams 20 pass through their respective blankers in the blanking aperture array substrate 204. Each blanker deflects each beam of the multibeams 20 as it passes through, so that the beam is ON only for a calculated drawing time (illumination time), and OFF otherwise (performing blanking deflection).

[0032] The multi-beam 20 that has passed through the blanking aperture array substrate 204 is reduced by the reduction lens 205 and moves toward the central opening formed in the limiting aperture member 206. Here, the individual beams that have been deflected by the blanker of the blanking aperture array substrate 204 to be beam-off are moved away from the central opening of the limiting aperture member 206 (blanking aperture member) and are shielded by the limiting aperture member 206. On the other hand, the individual beams that have not been deflected by the blanker of the blanking aperture array substrate 204 pass through the central opening of the limiting aperture member 206. Blanking control is performed by turning the individual blanking mechanism ON / OFF, and the ON / OFF is controlled for each individual beam.

[0033] In this way, the limiting aperture member 206 shields the individual beams that have been deflected by the individual blanking mechanism to the beam-off state. Then, the beam that has passed through the limiting aperture member 206, formed from the time the beam is turned ON until it is turned OFF, forms one shot of the beam.

[0034] The multi-beams 20 that have passed through the limiting aperture member 206 are focused by the objective lens 207 to form a pattern image with a desired reduction ratio, and are then deflected in the same direction by the deflector 209 and irradiated onto the respective drawing positions (irradiation positions) on the sample 101 for each beam.

[0035] The multi-beams 20 irradiated at once are ideally arranged at a pitch obtained by multiplying the array pitch of multiple apertures in the molded aperture array substrate 203 by the desired reduction ratio described above. The drawing device 100 irradiates a large number of individual beams at once, connecting the individual beams to fill the beam pitch and thereby drawing a pattern of the desired geometric shape. Therefore, the beam array shape has a significant impact on the drawing accuracy. The beam array shape (irradiation positions of multiple individual beams) changes depending on the irradiation amount. Since the irradiation amount changes with the pattern density, it is necessary to measure the effect of the pattern density on the beam irradiation position and correct the beam irradiation position and the irradiation amount of the individual beams.

[0036] This paper describes a method for measuring beam irradiation position variations that are dependent on pattern density.

[0037] First, multiple position measurement patterns P1 and a first density adjustment pattern P2a, as shown in Figure 4a, are drawn on the sample 101.

[0038] The position measurement pattern P1 is, for example, a cross shape.

[0039] The first density adjustment pattern P2a is placed in the region between the position measurement patterns P1. For example, the first density adjustment pattern P2a is placed in a rectangular region enclosed by four position measurement patterns P1. The pattern shape of the first density adjustment pattern P2a is not particularly limited and may be a line and space pattern or a contact hole pattern. The pattern density of the first density adjustment pattern P2a differs from region to region. For example, the pattern density may decrease towards the right side of Figure 4a.

[0040] After drawing the position measurement pattern P1 and the first density adjustment pattern P2a over the entire drawing area or a predetermined area of ​​the sample 101, a second density adjustment pattern P2b is drawn as shown in Figure 4b. The second density adjustment pattern P2b is positioned so as to overlap the placement area of ​​the first density adjustment pattern P2a.

[0041] The second density adjustment pattern P2b has different pattern densities in each region, and the pattern density change is the reverse of that of the first density adjustment pattern P2a. For example, the pattern density is made higher towards the right in Figure 4b.

[0042] By superimposing the first density adjustment pattern P2a and the second density adjustment pattern P2b, a pattern P2 with the same pattern density is formed in each region, as shown in Figure 4c.

[0043] After drawing an evaluation pattern consisting of a position measurement pattern P1, a first density adjustment pattern P2a, and a second density adjustment pattern P2b, development and etching are performed, and the position of the position measurement pattern P1 is measured using a position measuring instrument (not shown).

[0044] The position measurement pattern P1 is drawn together with the first density adjustment pattern P2a, and therefore is drawn in a position affected by the pattern density. On the other hand, during position measurement, all patterns P2 have the same pattern density, and the conditions around the position measurement pattern P1 are the same. Since the influence of pattern P2 on the reflection of the light used for position measurement is also the same, the position of the position measurement pattern P1 can be measured with high accuracy.

[0045] Thus, according to this embodiment, pattern density-dependent beam irradiation position variations can be accurately measured.

[0046] Using Figure 5, a method for drawing an evaluation pattern to measure pattern density-dependent beam irradiation position variation according to another embodiment will be explained.

[0047] First, multiple position measurement patterns P11a to P11d are drawn on the sample 101. The position measurement patterns P11a to P11d are dot patterns with different pattern densities. In the example shown in Figure 5, the pattern density is P11a <P11b<P11c<P11dとなっている。

[0048] After drawing the position measurement patterns P11a to P11d, the density adjustment patterns P12a to P12c are drawn. The density adjustment patterns P12a to P12c are grid-like and are arranged to surround the position measurement patterns P11a to P11c.

[0049] The density adjustment patterns P12a to P12c have different pattern densities. In the example shown in Figure 5, the pattern densities are P12a > P12b > P12c.

[0050] By combining position measurement pattern P11a and density adjustment pattern P12a, a dot pattern P13 can be obtained. A dot pattern P13 with the same pattern density can also be obtained by combining position measurement pattern P11b and density adjustment pattern P12b. Furthermore, a dot pattern P13 with the same pattern density can also be obtained by combining position measurement pattern P11c and density adjustment pattern P12c.

[0051] Furthermore, in this example, since the position measurement pattern P11d has the same pattern density as the dot pattern P13, there is no need to combine it with a density adjustment pattern.

[0052] After drawing multiple dot patterns P13 (evaluation patterns) consisting of position measurement patterns P11a to P11d and density adjustment patterns P12a to P12c, development and etching processes are performed, and the positions of the dots (pattern edges) of the dot patterns P13 are measured using a position measuring instrument (not shown).

[0053] The position measurement patterns P11a to P11d each have different pattern densities and are drawn at positions affected by the pattern density. On the other hand, when measuring the position of a dot, the pattern edges of the dot pattern P13 are P11a to P11d, so the results for positions affected by the pattern densities of P12a to P12c are not observed, and only the results for positions affected by the pattern densities of P11a to P11d are measured. All dot patterns P13 have the same pattern density, and the conditions around the dots are the same. Therefore, beam irradiation position variations dependent on pattern density can be accurately measured.

[0054] Using Figure 6, a method for drawing an evaluation pattern to measure pattern density-dependent beam irradiation position variation according to another embodiment will be explained.

[0055] First, position measurement patterns P21a and P21b are drawn on sample 101. Position measurement patterns P21a and P21b are line-and-space patterns with different line widths. By controlling the line width of the line-and-space patterns, the pattern density can be arbitrarily changed. Position measurement patterns P21a and P21b are patterns with different pattern densities.

[0056] After drawing the position measurement patterns P21a and P21b, the density adjustment patterns P22a and P22b are drawn. The density adjustment patterns P22a and P22b are line and space patterns, with the line sections 61a and 61b positioned between the two line sections 60a and 60b of the position measurement patterns P21a and P21b.

[0057] Specifically, one line section 61a of the density adjustment pattern P22a is positioned between two line sections 60a of the position measurement pattern P21a, forming a single line section. The distance between the two line sections 60a is equal to the line width of line section 61a.

[0058] Similarly, one line section 61b of the density adjustment pattern P22b is positioned between the two line sections 60b of the position measurement pattern P21b, forming a single line section. The distance between the two line sections 60b is equal to the line width of line section 61b.

[0059] By combining position measurement pattern P21a and density adjustment pattern P22a, a line and space pattern P23 is obtained. By combining position measurement pattern P21b and density adjustment pattern P22b, a line and space pattern P23 with the same pattern density is obtained. For example, by combining position measurement pattern P21a and density adjustment pattern P22a, a line and space pattern with a pattern density of 50% is drawn, and by combining position measurement pattern P21b and density adjustment pattern P22b, a line and space pattern with a pattern density of 50% is drawn.

[0060] After drawing multiple line-and-space patterns P23 (evaluation patterns) consisting of position measurement patterns P21a, P21b and density adjustment patterns P22a, P22b, development and etching are performed, and the position of the pattern edges of the formed line-and-space patterns P23 is measured with a position measuring instrument (not shown).

[0061] Position measurement patterns P21a and P21b have different pattern densities and are drawn at positions affected by the pattern density. On the other hand, when measuring the position of a pattern edge, the pattern edges of the dot pattern P23 are P21a and P21b, so the results for positions affected by the pattern density of P22a and P22b are not observed, and only the results for positions affected by the pattern density of P21a and P21b are measured. All line-and-space patterns P23 have the same pattern density and the surrounding conditions are the same. Therefore, beam irradiation position variations dependent on pattern density can be accurately measured.

[0062] In the example shown in Figure 6, a case was described in which position measurement patterns P21a and P21b, which target pattern edges for measurement, are drawn in the first pass, and a density adjustment pattern is drawn in the second pass. However, the position measurement pattern and the density adjustment pattern may be drawn in the first and second passes respectively. A method for drawing such evaluation patterns will be explained using Figure 7.

[0063] First, a position measurement pattern P31a and a density adjustment pattern P32b are drawn on the sample 101. Both the position measurement pattern P31a and the density adjustment pattern P32b are line and space patterns.

[0064] After drawing the position measurement pattern P31a and the density adjustment pattern P32b, the density adjustment pattern P32a and the position measurement pattern P31b are drawn. The density adjustment pattern P32a and the position measurement pattern P31b are line and space patterns. The pattern density of the position measurement pattern P31b is different from that of the position measurement pattern P31a.

[0065] One line portion 72a of the density adjustment pattern P32a is positioned between the two line portions 71a of the position measurement pattern P31a. Also, one line portion 72b of the density adjustment pattern P32b is positioned between the two line portions 71b of the position measurement pattern P31b.

[0066] By combining the position measurement pattern P31a and the density adjustment pattern P32a, a line and space pattern P33 can be obtained. By combining the density adjustment pattern P32b and the position measurement pattern P31b, a line and space pattern P33 with the same pattern density can be obtained.

[0067] By measuring the edge position of the line portion of the line-and-space pattern P33, it is possible to simultaneously measure the beam irradiation position affected by the pattern density of the position measurement pattern P31a and the beam irradiation position affected by the pattern density of the position measurement pattern P31b.

[0068] In the above embodiment, an example was described in which the position measurement pattern and the density adjustment pattern are drawn in two separate steps (two passes), but they may also be drawn in three or more steps. The goal is to combine multiple drawing patterns so that a pattern with the same shape (same pattern density) is ultimately formed.

[0069] Multiple patterns with different densities can be prepared and combined as appropriate to form multiple evaluation patterns with the same pattern density. By changing the measurement points of the evaluation patterns, it may be possible to measure the edge positions of line sections affected by multiple densities.

[0070] For example, six different patterns P41 to P46 with varying densities, as shown in Figure 8, are prepared. By drawing patterns P41, P43, and P44 in sequence and combining them, an evaluation pattern with a 50% pattern density can be obtained. Similarly, by drawing patterns P42 and P43 in sequence and combining them, an evaluation pattern with a 50% pattern density can be obtained. Pattern P46 alone is an evaluation pattern with a 50% pattern density.

[0071] As shown in Figure 8, the evaluation pattern allows for the measurement of the edge position of the line section affected by six different densities.

[0072] Although the above embodiment describes a lithography system using a multi-beam system, it can also be applied to a lithography system using a single beam.

[0073] It should be noted that the present invention is not limited to the embodiments described above, and the components can be modified and implemented in practice without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiments. Moreover, components from different embodiments may be appropriately combined. [Explanation of Symbols]

[0074] 20 Multibeam 100 Drawing device 101 samples 102 Electronic Microscope Tube 103 Drawing room 110 Control Computer 150 Drawing section 160 Control Unit 200 electron beam 201 Electron source 202 Illumination Lens 203 Molded aperture array substrate 204 Blanking Aperture Array Substrate

Claims

1. A step of irradiating a sample with a charged particle beam to draw multiple first patterns with different pattern densities, A step of drawing multiple second patterns with different pattern densities such that their respective pattern densities become equal when combined with at least some of the above-mentioned multiple first patterns, thereby forming multiple evaluation patterns with equal pattern densities, A method for forming an evaluation pattern comprising the following features.

2. A method for forming an evaluation pattern according to claim 1, comprising the steps of drawing a plurality of first patterns and drawing a plurality of position measurement patterns for performing position measurement, wherein each of the plurality of position measurement patterns is arranged between each of the plurality of first patterns.

3. Each of the aforementioned multiple first patterns is grid-like, The method for forming an evaluation pattern according to claim 1, wherein each of the plurality of second patterns is a grid-like pattern surrounding the grid-like first pattern.

4. The plurality of first patterns and the plurality of second patterns are each line patterns. A method for forming an evaluation pattern according to claim 1, wherein one of the multiple first patterns is provided between any of the multiple second patterns.

5. The method for forming an evaluation pattern according to claim 1, wherein the plurality of first patterns or the plurality of second patterns are drawn separately for each of the different pattern densities.

6. A method for evaluating positional variation, comprising measuring positional variation dependent on pattern density using an evaluation pattern described in any one of claims 1 to 5.

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