Coverage calculation method, charged particle beam lithography method, coverage calculation device, and charged particle beam lithography device

Abstract

To reduce a calculation amount and a memory use amount of a pixel covering rate in rasterization processing.SOLUTION: A covering rate calculation method emits a charged particle beam, calculates a covering rate of a pattern for each pixel region obtained by dividing a drawing region for drawing a pattern by a prescribed size, generates a plurality of first pixel regions by virtually dividing the drawing region by the first size, calculates a covering rate of a pattern of the first pixel region, generates a plurality of second pixel regions corresponding to the pixel region by virtually dividing the first pixel region by the second size smaller than the first size, selects the second pixel region that approximates the pattern shape in the first pixel region, and calculates the covering rate of the selected second pixel region on the basis of the covering rate of the pattern of the first pixel region, the number of the second pixel regions in the first pixel region, and the number of the selected second pixel regions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a coverage calculation method, a charged particle beam drawing method, a coverage calculation apparatus, and a charged particle beam drawing apparatus. [Background technology]

[0002] As LSIs become more highly integrated, the circuit line widths required for semiconductor devices are becoming finer year by year. To form the desired circuit patterns on semiconductor devices, a method is adopted in which a high-precision master pattern formed on quartz is reduced and transferred onto a wafer using a reduction projection exposure system. To produce high-precision master patterns, a technique known as electron beam lithography is used, in which a resist is exposed to light using an electron beam writing system to form the pattern.

[0003] One known electron beam lithography device is a multi-beam lithography device that uses multiple beams to irradiate multiple beams at once, improving throughput. In this multi-beam lithography device, for example, an electron beam emitted from an electron gun passes through an aperture member having multiple openings to form multiple beams, and blanking of each beam is controlled by a blanking plate. The unblocked beam is reduced in size by an optical system and irradiated onto a desired position on a mask to be lithographed.

[0004] Multi-beam lithography systems calculate the pattern coverage (area density) for each pixel (pixel) that divides the lithography area into a mesh, and adjust the irradiation dose of each beam of the multi-beam lithography system according to the coverage. The smaller the pixel size, the more accurately the pattern shape is reflected, improving resolution and lithography accuracy. However, as the pixel size decreases, the time required to calculate the coverage increases, and the memory required to store the calculation results also increases.

[0005] For example, as shown in Figures 9(a) and 9(b), if the pixel size (length of one side of a pixel) is reduced from 16 nm to 4 nm, the number of calculations for the coverage increases from 1 to 4. Also, the memory usage for storing the calculation results of the coverage increases from 2 bytes to 32 bytes. By reducing the pixel size by 1 / n (n is an integer greater than or equal to 2), the number of calculations increases by n times, and the memory usage decreases by n times. 2 It had doubled in size. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-340438 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-230689 [Patent Document 3] International Publication No. 2008 / 084543 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a coverage calculation method, a charged particle beam drawing method, a coverage calculation device, and a charged particle beam drawing device that can reduce the amount of calculation of pixel coverage and memory usage. [Means for solving the problem]

[0008] A coverage calculation method according to one embodiment of the present invention is a coverage calculation method that irradiates a charged particle beam and calculates the pattern coverage for each pixel area obtained by dividing a drawing area in which a pattern is drawn by a predetermined size, the method comprising: virtually dividing the drawing area by a first size to generate a plurality of first pixel areas; calculating the pattern coverage for the first pixel areas; virtually dividing the first pixel area by a second size smaller than the first size to generate a plurality of second pixel areas corresponding to the pixel areas; selecting a second pixel area that approximates the pattern shape within the first pixel area; and calculating the coverage for the selected second pixel area based on the pattern coverage for the first pixel area, the number of second pixel areas within the first pixel area, and the number of selected second pixel areas.

[0009] A charged particle beam writing method according to one aspect of the present invention calculates an irradiation amount for each pixel area using the coverage of the second pixel area calculated by the above-mentioned coverage calculation method, controls the charged particle beam based on the calculated irradiation amount, and writes a pattern on a substrate.

[0010] A coverage calculation device according to one aspect of the present invention is a coverage calculation device that irradiates a charged particle beam and calculates the pattern coverage for each pixel area obtained by dividing a drawing area in which a pattern is drawn by a predetermined size, and has a rasterization unit that virtually divides the drawing area by a first size to generate a plurality of first pixel areas, calculates the pattern coverage for the first pixel areas, virtually divides the first pixel area by a second size smaller than the first size to generate a plurality of second pixel areas corresponding to the pixel areas, and selects the second pixels that approximate the pattern shape within the first pixel area, and calculates the coverage of the selected second pixel areas based on the pattern coverage of the first pixel area, the number of second pixel areas within the first pixel area, and the number of selected second pixel areas.

[0011] A charged particle beam drawing apparatus according to one embodiment of the present invention comprises a dose map creation unit that calculates the irradiation dose for each pixel region using the coverage of the second pixel region calculated by the coverage calculation device and creates a dose map that defines the irradiation dose for each pixel region, an irradiation time calculation unit that calculates the irradiation time for each pixel region based on the dose map, and a drawing control unit that controls the irradiation dose of the charged particle beam based on the calculated irradiation time. [Effects of the Invention]

[0012] According to the present invention, the amount of calculation of pixel coverage and memory usage can be reduced. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of a multi-charged particle beam writing apparatus according to an embodiment of the present invention; [Figure 2] 10A and 10B are diagrams illustrating an example of the configuration of an aperture member. [Figure 3] FIG. 10 is a diagram illustrating an example of a drawing operation. [Figure 4] 10A and 10B are diagrams illustrating an example of a multi-beam irradiation area and a pixel to be written. [Figure 5] 10 is a flowchart illustrating a drawing method according to the embodiment. [Figure 6] 1A is a diagram showing the coverage rate of a first pixel, FIG. 1B is a diagram showing second pixels obtained by dividing the first pixel, and FIG. 1C is a diagram showing inside / outside determination information of the second pixel. [Figure 7] FIG. 10 is a diagram showing the coverage of a second pixel. [Figure 8] FIG. 1(a) is a diagram showing the position of the center of gravity of the pattern in the first pixel, and (b) to (d) are diagrams for explaining a method for selecting the second pixel. [Figure 9] 10(a) and 10(b) are diagrams illustrating the number of calculations of the coverage rate according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiment, a configuration using an electron beam as an example of a charged particle beam will be described. However, the charged particle beam is not limited to an electron beam, and an ion beam or the like may also be used.

[0015] 1 is a schematic diagram of a lithography system using a coverage calculation device according to an embodiment. As shown in FIG. 1, the lithography system 100 includes a lithography unit 150 and a control unit 160. The lithography system 100 is an example of a multi-charged particle beam lithography system.

[0016] The drawing unit 150 includes an electron lens barrel 102 and a drawing chamber 103. Inside the electron lens barrel 102, an electron gun 201, an illumination lens 202, an aperture member 203, a blanking plate 204, a reduction lens 205, a limiting aperture member 206, an objective lens 207, and a deflector 208 are arranged.

[0017] A continuously movable XY stage 105 is disposed within the patterning chamber 103. A substrate 101, which is the target of patterning during patterning, is disposed on the XY stage 105. The substrate 101 includes an exposure mask used in manufacturing a semiconductor device, or a semiconductor substrate (silicon wafer) on which a semiconductor device is manufactured. The substrate 101 also includes a mask blank coated with resist and on which nothing is yet to be patterned. A mirror 210 for measuring the position of the XY stage 105 is also disposed on the XY stage 105.

[0018] The control unit 160 has a control computer 110, a memory 112, a deflection control circuit 130, a stage position detector 139, and storage devices 140 and 142 such as magnetic disk drives. These are connected to each other via a bus. Drawing data is input from the outside and stored in the storage device 140.

[0019] The control computer 110 has a rasterization unit 50, a dose map creation unit 52, an irradiation time calculation unit 54, and a drawing control unit 60. These functions may be configured as hardware such as an electric circuit, or may be configured as software. When configured as software, a program that realizes at least some of the functions may be stored in a recording medium and read and executed by a computer having a CPU. The recording medium that stores the program is not limited to removable media such as magnetic disks and optical disks, but may also be fixed recording media such as hard disk drives and memories. Information such as calculation results in the control computer 110 is stored in the memory 112 each time. The processing of the coverage calculation device according to this embodiment is performed by the rasterization unit 50 and the dose map creation unit 52.

[0020] Fig. 2 is a conceptual diagram showing an example of the configuration of the aperture member 203. In Fig. 2, a plurality of openings 22 are formed in the aperture member 203 in a matrix at a predetermined arrangement pitch in both the vertical and horizontal directions. For example, 512 x 512 rows of openings 22 are formed in the vertical and horizontal directions (x and y directions). Each opening 22 is formed as a rectangle of the same dimensions. The openings 22 may also be circular.

[0021] A portion of the electron beam 200 passes through each of the plurality of apertures 22, thereby forming multiple beams 20a-e. Here, an example is shown in which the apertures 22 are arranged in two or more rows both vertically and horizontally (x and y directions), but this is not limiting. For example, there may be multiple rows in either the vertical or horizontal direction (x and y directions) and only one row in the other.

[0022] The blanking plate 204 has passage holes (openings) for passing through each of the multi-beams at positions corresponding to the openings 22 of the aperture member 203 shown in Fig. 2. A pair of electrodes for blanking deflection (blankers: blanking deflectors) is arranged across each passage hole. A deflection voltage based on a control signal from the deflection control circuit 130 is applied to one of the two electrodes, and the other is grounded.

[0023] The electron beams 20a-e passing through the respective passage holes are deflected independently by the blankers, and blanking control is performed. In this manner, the blankers perform blanking deflection of the corresponding beams among the multi-beams that have passed through the multiple openings 22 of the aperture member 203.

[0024] 3 is a conceptual diagram illustrating an example of a writing operation. As shown in Fig. 3, a writing region 30 on a substrate 101 is virtually divided into a plurality of rectangular stripe regions 32 with a predetermined width in the y direction, for example.

[0025] First, the XY stage 105 is moved and adjusted so that the irradiation area 34 that can be irradiated with one irradiation of the multi-beam 20 is positioned at the left end of the first stripe area 32 or further to the left, and then writing begins. When writing the first stripe area 32, the XY stage 105 is moved, for example, in the -x direction, so that writing progresses relatively in the x direction. The XY stage 105 is moved, for example, continuously, at a predetermined speed.

[0026] After completing the drawing of the first stripe region 32, the stage position is moved in the -y direction, and the irradiation region 34 is adjusted so that it is positioned relatively in the y direction at the right end of the second stripe region 32 or at a position further to the right. Then, by moving the XY stage 105, for example, in the x direction, drawing is performed in the same manner in the -x direction.

[0027] The writing time can be reduced by alternately changing the direction of writing, such as writing in the x direction in the third stripe region 32 and writing in the -x direction in the fourth stripe region 32. However, writing is not limited to alternately changing the direction of writing, and writing may proceed in the same direction when writing each stripe region 32. In one shot, a maximum of multiple shot patterns equal in number to the number of openings 22 are formed at once by the multi-beams formed by passing through each opening 22 in the aperture member 203.

[0028] FIG. 4 is a diagram showing an example of a multi-beam irradiation area and a pixel to be written. In FIG. 4, a stripe area 32 is divided into a plurality of mesh areas 40 in a mesh shape, for example, based on the beam size of the multi-beam. Each mesh area 40 becomes a writing pixel area (writing position). The example of FIG. 4 shows a case where the writing area of ​​the substrate 101 is divided into a plurality of stripe areas 32, for example, in the y direction, with a width smaller than the size (shot size) of an irradiation area 34 that can be irradiated with a single irradiation of the multi-beams 20a to 20e. Note that the width of the stripe areas 32 is not limited thereto, and may be, for example, n times the size of the irradiation area 34 (n is an integer greater than or equal to 1).

[0029] A plurality of pixels 24 (beam drawing positions) that can be irradiated by one irradiation of the multi-beams 20a-e are shown within the irradiation area 34. In other words, the pitch between adjacent pixels 24 is the pitch between each of the multiple beams. In the example of FIG. 4, one sub-pitch area 26 is formed by a square area that is surrounded by four adjacent pixels 24 and includes one of the four pixels 24. FIG. 4 shows a case where each sub-pitch area 26 is formed by 4×4 pixels.

[0030] In FIG. 4, the size of the drawing pixel area is used as the beam size, but the smaller the size of the drawing pixel area, the more accurately the pattern shape is reflected, and the higher the resolution and drawing accuracy.

[0031] Next, the operation of the drawing unit 150 will be described. An electron beam 200 emitted from an electron gun 201 (emitting unit) is illuminated almost perpendicularly onto the entire aperture member 203 by an illumination lens 202. The electron beam 200 passes through each of a plurality of openings 22 in the aperture member 203, thereby forming a plurality of electron beams (multi-beams) 20a-e, each having, for example, a rectangular shape. The multi-beams 20a-e pass through corresponding blankers in a blanking plate 204. Each blanker individually deflects the passing electron beam 20 so that the beam is ON only during a calculated drawing time (irradiation time) and OFF at other times (performs blanking deflection).

[0032] The multi-beams 20a-e that have passed through the blanking plate 204 are reduced by the reduction lens 205 and proceed toward the central opening formed in the limiting aperture member 206. The electron beams that have been deflected by the blanker of the blanking plate 204 to turn the beam OFF move out of position from the central opening of the limiting aperture member 206 (blanking aperture member) and are blocked by the limiting aperture member 206. On the other hand, the electron beams that have not been deflected by the blanker of the blanking plate 204 (deflected to turn the beam ON) pass through the central opening of the limiting aperture member 206.

[0033] The beams formed from when the beam is turned ON until when the beam is turned OFF and that pass through the limiting aperture member 206 form one shot of beam. The multi-beams that have passed through the limiting aperture member 206 are focused by the objective lens 207 to form a pattern image with the desired reduction ratio, and the individual beams (the entire multi-beams 20) are deflected together in the same direction by the deflector 208, and are irradiated onto the respective drawing positions (irradiation positions) on the substrate 101.

[0034] When the XY stage 105 is moving continuously, the deflector 208 performs tracking control so that the beam drawing position (irradiation position) follows the movement of the XY stage 105. A laser is emitted from the stage position detector 139 toward a mirror 210 on the XY stage 105, and the position of the XY stage 105 is measured using the reflected light. Ideally, the multiple beams irradiated at one time are aligned at a pitch obtained by multiplying the arrangement pitch of the multiple openings in the aperture member 203 by the desired reduction ratio described above.

[0035] The drawing apparatus 100 irradiates the drawing position with multiple beams that become shot beams while sequentially shifting the drawing position while following the movement of the XY stage 105 during each tracking operation.

[0036] FIG. 5 is a flowchart illustrating a drawing method according to an embodiment.

[0037] The rasterizing unit 50 reads the drawing data from the storage device 140 and calculates, for each first pixel region, the pattern coverage within that first pixel region (hereinafter referred to as coverage) (step S1). The first pixel region is obtained by virtually dividing the drawing region (e.g., stripe region 32) into a mesh shape with a first size M1. The first size M1 is, for example, the size of one beam (individual beam) of a multi-beam. The coverage of the first pixel region is stored in the memory 112.

[0038] Next, the rasterization unit 50 virtually divides each first pixel region into a plurality of second pixel regions in a mesh pattern with a second size M2 smaller than the first size M1. The second pixel regions correspond to the rendering pixel regions. Hereinafter, the first pixel region, second pixel region, and rendering pixel region will be referred to as the first pixel, second pixel, and rendering pixel, respectively. For each second pixel, the rasterization unit 50 checks whether the center of the second pixel is included in the pattern, and determines that a second pixel whose center is included in the pattern is a second pixel located inside the pattern (step S2). The center of a second pixel being included in the pattern means that the center of the second pixel is located on the pattern. The group of second pixels located inside the pattern approximates the pattern shape.

[0039] A second pixel whose center is not included in the pattern is determined as a second pixel located outside the pattern. For each second pixel, inside / outside determination information determining whether it is located inside or outside the pattern is stored in memory 112.

[0040] For example, in step S1, the coverage rate for each first pixel is calculated as shown in Fig. 6(a) The coverage rate A of the first pixel is stored in the memory 112 with, for example, 16-bit precision.

[0041] 6(b), in step S2, a first pixel of a first size M1 is virtually divided into second pixels of a second size M2. In this example, the second size M2 is set to 1 / 4 of the length of one side of the first size M1 (M1 / M2=4), and the first pixel is virtually divided into 16 second pixels.

[0042] Then, it is checked whether the centers of the second pixels are included in the pattern. In the example shown in Figure 6(b), the centers of the four second pixels in the bottom row and the centers of the three second pixels in the second row from the bottom and the first to third from the right are included in the pattern, so these seven second pixels are determined to be located inside the pattern. The centers of the one second pixel in the second row from the bottom and the first from the left, the four second pixels in the first row from the top, and the four second pixels in the second row from the top are not included in the pattern, so these nine second pixels are determined to be located outside the pattern.

[0043] For each second pixel, 1-bit inside / outside determination information, which is set to "1" if the pixel is located inside the pattern and "0" if the pixel is located outside the pattern, is stored in memory 112. For example, as shown in FIG. 6(c), 16-bit inside / outside determination information is stored in memory 112 for 16 second pixels obtained by virtually dividing a first pixel.

[0044] Next, the dose map creation unit 52 virtually divides the writing region (e.g., the stripe region 32) into a plurality of proximity mesh regions (mesh regions for calculating proximity effect correction) in a mesh shape with a predetermined size. The size of the proximity mesh region is preferably set to about 1 / 10 of the range of influence of the proximity effect, for example, about 1 μm. The dose map creation unit 52 reads the writing data from the storage device 140 and calculates, for each proximity mesh region, the coverage ρ of the pattern to be placed in the proximity mesh region.

[0045] Next, the dose map creation unit 52 calculates a proximity effect correction irradiation coefficient Dp(x) for correcting the proximity effect for each proximity mesh region. The proximity effect correction irradiation coefficient Dp(x) can be defined by a threshold model for proximity effect correction similar to the conventional method, using the backscattering coefficient η, the dose threshold Dth of the threshold model, the coverage ρ, and the distribution function g(x).

[0046] Next, the dose map creation unit 52 calculates, for each drawing pixel (second pixel), an incident irradiation amount D (dose amount) for irradiating the drawing pixel. The incident irradiation amount D may be calculated, for example, as a value obtained by multiplying a preset reference irradiation amount Dbase by a proximity effect correction irradiation coefficient Dp and a coverage ratio ρ' of the drawing pixel.

[0047] The reference dose Dbase can be defined as, for example, Dth / (1 / 2+η).

[0048] When calculating the coverage ρ' of the drawing pixel, the dose map creation unit 52 reads out the coverage A and inside / outside determination information of the first pixel including the drawing pixel from the memory 112. The dose map creation unit 52 calculates the coverage A of the first pixel, the number N of drawing pixels in the first pixel whose inside / outside determination information is "1", and IN Using the size M1 of the first pixel and the size M2 of the drawing pixel, the coverage ρ' of the drawing pixel whose inside / outside determination information is "1" is calculated from the following formula (1): (M1 / M2) in the following formula (1). 2 represents the number of pixels to be drawn within the first pixel.

[0049] ρ´=(A / N IN )×(M1 / M2) 2 ···(1)

[0050] The dose map creating unit 52 sets the coverage ρ′ to 0 for the drawing pixel (second pixel) whose inside / outside determination information is “0”.

[0051] In the example shown in FIGS. 6(a) to 6(c), when the coverage rate A of the first pixel is set to 0.4, the coverage rates ρ′ of the 16 drawing pixels within the first pixel are as shown in FIG.

[0052] In this way, the dose map generating unit 52 calculates the incident dose D(x) for each drawing pixel, corrected for the proximity effect, based on the layout of a plurality of figure patterns defined in the drawing data.

[0053] Then, the dose map creating unit 52 creates a dose map that defines the incident irradiation amount D for each drawing pixel in stripe units (step S3). The created dose map is stored in the storage device 142, for example.

[0054] The irradiation time calculation unit 54 refers to the latest dose map and calculates the irradiation time t corresponding to the irradiation dose D for each drawing pixel (step S4). The irradiation time t is calculated by dividing the irradiation dose D by the current density. The irradiation time t for each drawing pixel is calculated as a value within the maximum irradiation time that can be irradiated with one shot of the multi-beam 20. The irradiation time data is stored in the storage device 142.

[0055] In the writing process (step S5), the writing control unit 60 rearranges the irradiation time data in shot order according to the writing sequence. Then, the irradiation time data is transferred to the deflection control circuit 130 in shot order. The deflection control circuit 130 outputs a blanking control signal to the blanking plate 204 in shot order, and outputs a deflection control signal to the deflector 208 in shot order. The writing unit 150 writes a pattern on the substrate 101 using multiple beams with an irradiation amount calculated for each writing pixel.

[0056] 9(b), 32 bytes of memory are required to store the calculation results of the coverage of 16 pixels. In this embodiment, however, it is sufficient to store the coverage of the first pixel (16 bits) and the inside / outside determination information of 16 second pixels (16 bits), thereby reducing the memory usage to 4 bytes. In addition, the number of times coverage is calculated can be reduced, thereby reducing the amount of calculation.

[0057] In the above embodiment, the center of the second pixel obtained by virtually dividing the first pixel is checked to see if it is inside or outside the pattern, and the second pixel whose pixel center is inside the pattern is selected as the second pixel that approximates the pattern shape. However, the second pixel that approximates the pattern shape may also be selected taking into account the position of the center of gravity of the pattern at the first pixel.

[0058] For example, as shown in FIG. 8(a), the rasterizing unit 50 calculates the coverage A of the first pixel and also finds the center of gravity CG of the pattern at the first pixel.

[0059] Next, as shown in Fig. 8(b), the rasterizing unit 50 selects the side closest to the center of gravity CG from among the four sides H1 to H4 of the first pixel of the rectangle. In the example shown in Fig. 8(b), the side H1 on the bottom side in the drawing is closest to the center of gravity CG.

[0060] Next, the rasterizing unit 50 selects a plurality of second pixels (second pixel group) that approximate the pattern shape within the first pixel. For example, the rasterizing unit 50 selects k columns of second pixel groups parallel to the side H1, starting from the side H1 closest to the center of gravity CG of the pattern toward the side H3 opposite to the side H1. k is calculated from the following formula (2) using the coverage rate A of the first pixel, the size M1 of the first pixel, and the size M2 of the second pixel.

[0061] k=ceil(A×(M1 / M2)) (2)

[0062] For example, if A=0.4 and the first pixel is virtually divided into 16 second pixels (M1 / M2=4), then k=2, and as shown in Figure 8(c), two rows of second pixels from side H1 to side H3, i.e., the bottom two rows, are selected.

[0063] As shown in FIG. 8(d), for each second pixel, one bit of selection information, which is “1” if selected and “0” if not selected, is stored in memory 112 together with the coverage rate A of the first pixel.

[0064] The dose map creating unit 52 calculates the coverage A of the first pixel, the number N of the drawing pixels (second pixels) having the selection information "1", SEL Using the size M1 of the first pixel and the size M2 of the drawing pixel, the coverage ρ' of the drawing pixel with selection information "1" is calculated from the following equation (3).

[0065] ρ´=(A / N SEL )×(M1 / M2) 2 ···(3)

[0066] The dose map creating unit 52 sets the coverage ρ′ of the drawing pixel (second pixel) having the selection information “0” to 0.

[0067] In this way, by selecting a group of second pixels that approximate the pattern shape based on the center of gravity position of the pattern at the first pixel and assigning a coverage rate to this selected second pixel, the amount of calculation for pixel coverage rate and memory usage can be reduced, as in the above embodiment.

[0068] In the above embodiment, a multi-beam lithography system has been described as an example of a charged particle beam system to which the coverage calculation device is applied, but the device can also be applied to a single-beam lithography system. The coverage calculation device can also be applied to an inspection system, in addition to lithography systems. The inspection system compares the coverage of the second pixel calculated from the lithography data by the coverage calculation method according to the above embodiment with the coverage of the second pixel based on the measurement results of a pattern actually lithographed on a target substrate using the lithography data, and inspects whether they match.

[0069] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined. [Explanation of symbols]

[0070] 50 Rasterization section 52 Dose Map Creation Department 54 Irradiation time calculation unit 60 Drawing control unit 100 Drawing device 110 Control computer

Claims

1. A method for calculating a pattern coverage rate for each pixel area obtained by dividing a pattern drawing area into a predetermined size by irradiating a charged particle beam, the method comprising: virtually dividing the drawing area by a first size to generate a plurality of first pixel areas; Calculating a pattern coverage of the first pixel region; virtually dividing the first pixel region by a second size smaller than the first size to generate a plurality of second pixel regions corresponding to the pixel region; selecting the second pixel area that approximates the pattern shape in the first pixel area; A coverage calculation method for calculating the coverage of the selected second pixel region based on the pattern coverage of the first pixel region, the number of the second pixel regions in the first pixel region, and the number of the selected second pixel regions.

2. The method of calculating a coverage rate according to claim 1 , wherein a second pixel region having a center inside the pattern is selected from the plurality of second pixel regions as a second pixel region that approximates the pattern shape.

3. Detecting a centroid of a pattern within the first pixel region; selecting a first side closest to the center of gravity from among four sides of the rectangular first pixel region; selecting k columns (k is an integer equal to or greater than 1) of second pixel regions parallel to the first side from the first side toward a second side opposite the first side as second pixel regions approximating the pattern shape; The method of claim 1 , wherein k is a value based on the coverage of the first pixel region, the first size, and the second size.

4. calculating an irradiation amount for each of the pixel regions using the coverage of the second pixel region calculated by the coverage calculation method according to any one of claims 1 to 3; A charged particle beam writing method for writing a pattern on a substrate by controlling a charged particle beam based on the calculated dose.

5. A coverage calculation device that calculates a pattern coverage for each pixel area obtained by dividing a pattern drawing area into a predetermined size by irradiating the area with a charged particle beam, the device comprising: a rasterization unit that virtually divides the drawing area by a first size to generate a plurality of first pixel areas, calculates a pattern coverage rate of the first pixel areas, virtually divides the first pixel area by a second size smaller than the first size to generate a plurality of second pixel areas corresponding to the pixel areas, and selects the second pixels that approximate a pattern shape in the first pixel area; A coverage calculation device that calculates the coverage of the selected second pixel region based on the pattern coverage of the first pixel region, the number of second pixel regions in the first pixel region, and the number of selected second pixel regions.

6. The coverage calculation device according to claim 5 , wherein the rasterization unit selects, from among the plurality of second pixel regions, a second pixel region whose center is inside the pattern as the second pixel region that approximates the pattern shape.

7. A dose map creation unit that calculates the irradiation amount for each pixel area using the coverage of the second pixel area calculated by the coverage calculation device described in claim 5 and creates a dose map that defines the irradiation amount for each pixel area; an irradiation time calculation unit that calculates an irradiation time for each pixel region based on the dose map; a writing control unit that controls an irradiation amount of the charged particle beam based on the calculated irradiation time; A charged particle beam writing apparatus comprising:

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