Multi-charged particle beam lithography method and multi-charged particle beam lithography apparatus

Abstract

The drift correction interval is not made too fine, and the correction residual caused by pattern density changes is kept to a minimum. [Solution] The multi-charged particle beam drawing method involves forming a multi-beam using a charged particle source and drawing a pattern by irradiating a substrate on a stage with the multi-beam while moving it in a first direction. In this method, the drawing area of ​​the substrate is virtually divided by a predetermined width in a second direction linearly independent of the first direction to generate a plurality of stripe regions. For each stripe region, a pattern density indicating the area ratio of the pattern is calculated. If the pattern density difference between a first stripe region and a second stripe region that are continuous in the second direction is greater than or equal to a threshold, at least one of the number of beams used to draw the first stripe region and the number of beams used to draw the second stripe region is changed.

Description

Technical Field

[0001] The present invention relates to a multi-charged particle beam drawing method and a multi-charged particle beam drawing apparatus.

Background Art

[0002] With the increasing integration of LSIs, the circuit linewidth 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. The high-precision original pattern is drawn by an electron beam drawing apparatus, and so-called electron beam lithography technology is used.

[0003] For example, there is a drawing apparatus using a multi-beam. Compared with the case of drawing with a single electron beam, by using a multi-beam, a larger number of beams can be irradiated at once, so that the throughput can be significantly improved. In a multi-beam type drawing apparatus, for example, an electron beam emitted from an electron gun is passed through a shaping aperture array substrate having a plurality of openings to form a multi-beam, and each beam is individually blanked and controlled by a blanking aperture array substrate. The beam (off-beam) blanked and deflected by the blanking aperture array substrate is shielded by a stopping aperture substrate, and the beam (on-beam) that is not deflected passes through the opening of the stopping aperture substrate and is irradiated to a desired position on the sample.

[0004] In an electron beam drawing apparatus, due to various factors, a phenomenon called beam drift may occur in which the irradiation position of the electron beam shifts with time during drawing. For example, in a multi-beam drawing apparatus, when the pattern density of the drawing pattern changes, the ratio of on-beams to off-beams changes greatly, the operating current per unit time of the blanking aperture array substrate changes, and beam drift may occur.

[0005] To cancel this beam drift, drift correction is performed. For example, in drift correction, a measurement mark formed on a mark substrate placed on the stage is scanned with the electron beam to detect the irradiation position of the electron beam and measure the amount of drift. The measured amount of drift is then used to correct the beam irradiation position.

[0006] When the amount of drift changes suddenly and significantly, the correction residual can become large depending on the drift correction interval. Therefore, one approach is to set a finer drift correction interval to reduce the correction residual. However, performing drift correction frequently reduces rendering throughput. Furthermore, there may be error factors arising from the measurement of the amount of drift. For this reason, it is necessary to avoid setting a fine drift correction interval and instead minimize the correction residual caused by pattern density changes. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2010-192666 [Patent Document 2] Japanese Patent Publication No. 2013-143441 [Patent Document 3] Japanese Patent Publication No. 2012-215636 [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention has been made in view of the above-mentioned conventional problems, and aims to provide a multi-charged particle beam lithography method and a multi-charged particle beam lithography apparatus that can suppress a decrease in lithography throughput and reduce the correction residual caused by pattern density switching. [Means for solving the problem]

[0009] A multi-charged particle beam drawing method according to one aspect of the present invention is a multi-charged particle beam drawing method that uses a charged particle source to form a multi-beam and draws a pattern by irradiating a substrate on a stage with the multi-beam while moving it in a first direction, wherein the drawing area of ​​the substrate is virtually divided by a predetermined width in a second direction linearly independent of the first direction to generate a plurality of stripe regions, a pattern density indicating the area ratio of the pattern is calculated for each stripe region, and if the pattern density difference between a first stripe region and a second stripe region that are continuous in the second direction is greater than or equal to a threshold, at least one of the number of beams used to draw the first stripe region and the number of beams used to draw the second stripe region is changed.

[0010] A multi-charged particle beam lithography apparatus according to one aspect of the present invention is a multi-charged particle beam lithography apparatus that forms a multi-beam using a charged particle source and irradiates a substrate on a stage with the multi-beam while moving it in a first direction to draw a pattern, comprising: a calculation unit that virtually divides the drawing area of ​​the substrate in a second direction linearly independent of the first direction with a predetermined width to generate a plurality of stripe regions, and calculates a pattern density indicating the area ratio of the pattern for each stripe region; and a control unit that, when the pattern density difference between a first stripe region and a second stripe region continuous in the second direction is greater than or equal to a threshold, changes at least one of the number of beams used to draw the first stripe region and the number of beams used to draw the second stripe region. [Effects of the Invention]

[0011] According to the present invention, the change in the amount of drift when switching pattern densities can be made gradual, thereby suppressing a decrease in drawing throughput and keeping the correction residual small. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of a drawing apparatus according to an embodiment of the present invention. [Figure 2] This is a plan view of a molded aperture array substrate. [Figure 3] (a) and (b) are diagrams illustrating an example of a drawing operation. [Figure 4] This diagram illustrates the relationship between pattern density and the number of beams used for plotting. [Figure 5] This figure shows an example of how the number of beams used for drawing changes. [Figure 6] This figure shows an example of how the number of beams used for drawing changes. [Figure 7] This is a flowchart illustrating the drawing method according to the same embodiment. [Figure 8] This diagram illustrates the relationship between pattern density and the number of beams used for plotting. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below with reference to the drawings. In the embodiments, an electron beam will be described as an example of a beam. However, the beam is not limited to an electron beam; it may also be a charged particle beam such as an ion beam or a beam using laser light.

[0014] Figure 1 is a schematic diagram of a lithography apparatus according to an embodiment. As shown in Figure 1, the lithography apparatus 100 comprises a lithography unit 150 and a control unit 160. The lithography apparatus 100 is an example of a multi-charged particle beam lithography apparatus. The lithography unit 150 comprises an electron-optical lens barrel 102 and a lithography chamber 103. Inside the electron-optical lens barrel 102 are an electron gun 201, an illumination lens 202, a molded aperture array substrate 203, a blanking aperture array substrate 204, a reduction lens 205, a limiting aperture member 206, an objective lens 207, a deflector 208, and a detector 211.

[0015] In the drawing room 103, an XY stage 105 is arranged. On the XY stage 105, a substrate 101 to be drawn is arranged. A resist to be irradiated with a charged particle beam is applied on the upper surface of the substrate 101. The substrate 101 is, for example, a substrate (mask blank) processed as a mask or a semiconductor substrate (silicon wafer) processed as a semiconductor device. Further, the substrate 101 may be a mask blank on which a resist is applied and nothing is drawn yet.

[0016] On the XY stage 105, a mark 106 and a mirror 210 for stage position measurement are arranged.

[0017] The control unit 160 includes a control computer 110, a deflection control circuit 130, a detection circuit 132, a stage position detector 139, and a storage unit 140. Drawing data is input from the outside and stored in the storage unit 140.

[0018] The control computer 110 includes a data processing unit 111, a drawing control unit 112, a drift correction unit 113, an area density calculation unit 114, a determination unit 115, and a beam selection unit 116. Each part of the control computer 110 may be composed of hardware such as an electric circuit, or may be composed of software such as a program that executes these functions. Alternatively, it may be composed of a combination of hardware and software.

[0019] The stage position detector 139 irradiates a laser, receives the reflected light from the mirror 210, and detects the position of the XY stage 105 based on the principle of laser interference method.

[0020] FIG. 2 is a conceptual diagram showing the configuration of the shaping aperture array substrate 203. In the shaping aperture array substrate 203, openings 22 of m rows in the vertical (y direction) × n columns in the horizontal (x direction) (m, n ≧ 2) are formed at a predetermined arrangement pitch. Each opening 22 is formed, for example, as a rectangle with the same size and shape. Each opening 22 may be a circle with substantially the same diameter.

[0021] The electron beam 200 emitted from the electron gun 201 (emitting section) illuminates the molded aperture array substrate 203, for example, almost vertically, by the illumination lens 202. The electron beam 200 illuminates a region containing multiple apertures 22. A portion of the electron beam 200 passes through the multiple apertures 22 of the molded aperture array substrate 203, while the remaining beam is stopped by the molded aperture member. As the electron beam 200 passes through the multiple apertures 22 of the molded aperture array substrate 203, multiple electron beams (multibeams) 20a to 20e are formed.

[0022] For example, the molded aperture array substrate 203 is provided with 512 x 512 apertures 22 in the x direction and y direction, forming a multibeam consisting of 512 x 512 beams. In this case, the beam array shape (overall shape of the multibeam) is square.

[0023] The blanking aperture array substrate 204, which is the irradiation dose control unit, has beam passage holes formed in it to match the positions of each aperture 22 in the molded aperture array substrate 203. Each passage hole is fitted with a pair of electrodes (blankers). The blanking aperture array substrate 204 is also equipped with a control circuit for the blankers. The electron beam passing through each passage hole is independently controlled for each beam to either a beam-on or beam-off state by the voltage applied to the blanker. When the beam is on, the opposing electrodes of the blanker are controlled to the same potential, and the blanker does not deflect the beam. When the beam is off, the opposing electrodes of the blanker are controlled to different potentials, and the blanker deflects the beam. In this way, multiple blankers control the beam to the beam-off state by performing blanking deflection on the corresponding beam from among the multiple beams that have passed through the multiple apertures 22 in the molded aperture array substrate 203.

[0024] The multi-beams 20a to 20e that have passed through the blanking aperture array substrate 204 are reduced in size by the reduction lens 205.

[0025] When the beam is controlled to the beam-off state, it is deflected by the blanker of the blanking aperture array substrate 204 and follows a trajectory that passes outside the opening of the limiting aperture member 206, and is therefore shielded by the limiting aperture member 206. On the other hand, when the beam is controlled to the beam-on state, it is not deflected by the blanker and passes through the opening of the limiting aperture member 206. Ideally, it passes through the same point. The beam trajectory is adjusted using an alignment coil (not shown) so that this point is located within the central opening of the limiting aperture member 206. In this way, the on / off state of the beam is controlled by the blanking control of the blanking aperture array substrate 204. That is, the irradiation amount is controlled by controlling the irradiation time with the blanking aperture array substrate 204.

[0026] The limiting aperture member 206 shields each beam that has been deflected by multiple blankers 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 a multi-beam for one shot.

[0027] The multi-beams that have passed through the limiting aperture member 206 are focused by the objective lens 207 and projected onto the substrate 101 at a desired reduction ratio. The deflector 208 deflects the entire multi-beam in the same direction and irradiates it onto a desired position on the substrate 101.

[0028] When the XY stage 105 is moving continuously, the beam trajectory is tracked and controlled by the deflector 208 so that the irradiation position of the beam on the substrate 101 follows the movement of the XY stage 105. Ideally, the irradiated multi-beam 20 will be arranged on the substrate 101 at a pitch obtained by multiplying the array pitch of the multiple apertures of the molded aperture array substrate 203 by the desired reduction ratio described above. For example, the drawing device 100 performs the drawing operation using a raster scan method that irradiates shot beams in sequence, and when drawing a desired pattern, unnecessary beams are controlled to be off by blanking control.

[0029] Figure 3 is a conceptual diagram illustrating the drawing operation in the embodiment. As shown in Figure 3, the drawing area 30 of the substrate 101 is virtually divided into a plurality of stripe-shaped areas 34 with a predetermined width in the y-direction (first direction), for example. The predetermined width is, for example, the y-direction size of the beam array of a multi-beam system.

[0030] First, the XY stage 105 is moved to adjust the irradiation area 35, which can be irradiated with a single multi-beam irradiation, to the left edge of the first stripe area 34, and then the drawing begins.

[0031] When drawing the first stripe region 34, the XY stage 105 is moved in the -x direction, thereby relatively advancing the drawing in the +x direction. The XY stage 105 is moved continuously at a predetermined speed. After the drawing of the first stripe region 34 is completed, the stage position is moved in the -y direction to adjust the position of the illuminated region 35 to the right edge of the second stripe region 34, which is continuous with (and drawn consecutively with) the first stripe region 34 in the y direction. At this time, if drawing is done in one pass, the stage position is moved in the -y direction to shift the y-direction width of the stripe region 34, and if drawing is done in N passes (N is an integer of 2 or more), the stage position is moved in the -y direction to shift the y-direction width by 1 / N. Subsequently, as shown in Figure 3(b), the XY stage 105 is moved in the +x direction, thereby performing drawing toward the -x direction.

[0032] In the third stripe region 34, drawing is done in the +x direction, and in the fourth stripe region 34, drawing is done in the -x direction. Drawing time can be reduced by alternating the direction of drawing. Alternatively, each stripe region 34 could be drawn in the same direction.

[0033] Each stripe region 34 has pixels defined that are not shown, and each stripe region is drawn by exposing each pixel the same number of times using a multi-beam. When drawing each stripe region 34, the beam position is controlled by the deflector 208 in parallel with the continuous movement of the XY stage 105 in the x direction to illuminate the pixels on the substrate 101. At this time, the deflector 208 performs a deflection operation that switches the illuminated pixels between one irradiation and the next irradiation, and a continuous deflection operation that is synchronized with the stage movement so that the beam position on the substrate 101 is fixed during irradiation.

[0034] During the drawing process, the data processing unit 111 divides each stripe region 34 into a mesh of a predetermined size. The mesh size is, for example, the average size of the x and y directions of one beam of the multibeam system. The data processing unit reads the drawing data from the storage unit 140, assigns the geometric patterns defined in the drawing data to the mesh regions (pixels), and calculates the pattern area density for each mesh region.

[0035] The data processing unit 111 calculates the beam irradiation amount irradiated to each pixel by multiplying the pattern area density by the reference irradiation amount. At this time, the irradiation amount may be the value obtained by multiplying by a correction coefficient to correct for the proximity effect.

[0036] The data processing unit 111 converts the irradiation amount into irradiation time and rearranges it in the order of shots according to the drawing sequence. The irradiation time can be obtained, for example, by dividing the irradiation amount for each pixel by the beam current density. Since this process yields an irradiation time map per stripe, the unit selects the set of meshes that are irradiated in one multi-beam shot from the mesh of this map to create irradiation time array data for one shot. The drawing control unit 112 outputs the rearranged irradiation time array data to the deflection control circuit 130. The drawing control unit 112 also controls the operation of each part of the drawing unit 150, including the control of the movement speed of the XY stage 105.

[0037] The deflection control circuit 130 outputs irradiation time sequence data to the control circuit of each blanker. Based on the irradiation time sequence data, each blanker switches the corresponding beam on and off.

[0038] In the drawing device 100, drift correction is performed at predetermined timings. When performing drift correction, first, the amount of positional shift (drift) of each beam's shot position in the multibeam is measured. For example, a portion of the multibeam is grouped together and scanned at a mark 106 provided on the XY stage 105, and electrons reflected from the mark 106 are detected by the detector 211. The detection circuit 132 outputs the amount of electrons detected by the detector 211 to the control computer 110. The drift correction unit 113 acquires the scan waveform from the detected amount of electrons and calculates the position of the grouped beams based on the position of the XY stage 105. The position of the XY stage 105 is detected by the stage position detector 139.

[0039] The other beams of the multibeam system are grouped together, and their positions are calculated using a similar method. By repeating this process, the beam position can be determined for each grouped beam. The difference between the calculated beam position and the ideal position is the positional displacement.

[0040] The drift correction unit 113 determines the position correction amount from the positional displacement amount and shifts the relative position of the pattern and mesh when calculating the pattern area density as described above.

[0041] In the drawing device 100, when the pattern density of the drawing pattern changes significantly between continuous stripe regions 34 in the y direction, the ratio of on-beams to off-beams within the multi-beam changes significantly. As a result, the amount of beam irradiation to the substrate 101 (total beam current) changes rapidly, and the operating current per unit time in the control circuit of the blanking aperture array substrate 204 changes, causing beam drift.

[0042] When the pattern density of a drawing pattern changes significantly, the amount of drift also increases rapidly, and even after drift correction, the correction residual may become large. By setting a finer interval for drift correction, the correction residual can be kept small, but the drawing throughput decreases.

[0043] Therefore, in this embodiment, the drift correction interval is not made finer, and when the pattern density (pattern area density) changes significantly between the continuous stripe regions 34 in the y direction, the number of beams used for drawing is changed to suppress fluctuations in the beam irradiation amount (total beam current) to the substrate 101 and fluctuations in the operating current of the blanking aperture array substrate 204, thereby keeping the change in the amount of drift small.

[0044] For example, consider the case shown in Figure 4, where the drawing area 30 contains two regions: region R0 with an average pattern density of 20% and region R1 with an average pattern density of 40%. In region R0, the entire multi-beam beam array, i.e., 512 × 512 beams, is used for the drawing process.

[0045] When the drawing target switches from region R0 to region R1, the pattern density doubles. Therefore, in region R1, the number of beams used for drawing is halved compared to region R0. For example, a multi-beam beam array is divided into two in the x-direction, and drawing is performed using 512 x 256 beams on one half. The other half's 512 x 256 beams are left unused and the corresponding blanker is controlled to keep them permanently off.

[0046] When the pattern density changes by a factor of A, reducing the number of beams used for drawing to 1 / A keeps the beam irradiation amount (total beam current) to the substrate 101 approximately the same. This results in a nearly constant operating current per unit time in the control circuit of the blanking aperture array substrate 204, minimizing the change in drift.

[0047] As shown in Figure 4, when the x-direction size of the beam array area used for drawing is reduced, the beam irradiation area of ​​the substrate 101 becomes narrower. Therefore, considering the range within which the deflector 208 can be tracked, the movement speed of the XY stage 105 must be reduced (slowed down). If the XY stage 105 is kept at a slow speed, the drawing time will be longer. For this reason, it is preferable to gradually increase the x-direction size of the beam array area used for drawing (gradually increase the number of beams used for drawing) and gradually increase the movement speed of the XY stage 105.

[0048] For example, as shown in Figure 5, region R1 with a pattern density of 40% is divided into regions R11 to R15, and when plotting regions R11 to R15 in order, the x-direction size of the beam array region used is gradually increased. Regions R11 to R14 each consist of one or more stripe regions 34.

[0049] For example, in region R11, 512 × 256 beams are used for plotting. In region R12, which is plotted after region R11, 512 × 320 beams are used for plotting. In region R13, which is plotted after region R12, 512 × 384 beams are used for plotting. In region R14, which is plotted after region R13, 512 × 448 beams are used for plotting. In subsequent regions, such as R15, the number of beams is returned to 512 × 512, the same number as in region R0, and the entire beam array is used for plotting. In this example, the reduced number of beams is restored in four steps.

[0050] When rendering region R11, the movement speed of XY stage 105 is slower than when rendering region R0. When rendering region R12, the movement speed of XY stage 105 is faster than when rendering region R11. When rendering region R13, the movement speed of XY stage 105 is faster than when rendering region R12. When rendering region R14, the movement speed of XY stage 105 is faster than when rendering region R13. When rendering region R15, the movement speed of XY stage 105 is faster than when rendering region R14 and the same as when rendering region R0.

[0051] By gradually increasing the number of beams used for drawing, the change in the beam irradiation amount (total beam current) to the substrate 101 and the change in the operating current per unit time in the control circuit of the blanking aperture array substrate 204 becomes gradual, and the change in the amount of drift can be kept small.

[0052] On the other hand, as shown in Figure 6, when the drawing target switches from region R2 with a pattern density of 40% to region R3 with a pattern density of 20%, the pattern density is halved, so the number of beams used for drawing is doubled. In region R2, the entire beam array is used for drawing except in the vicinity of region R3, and the number of beams used for drawing is gradually reduced in the vicinity of region R3.

[0053] For example, when dividing region R2 into regions R21 to R25 and sequentially plotting regions R21 to R25, the x-direction size of the beam array region used is gradually reduced. Regions R22 to R25 each consist of one or more stripe regions 34.

[0054] In region R21, the entire beam array, consisting of 512 x 512 beams, is used for plotting. In region R22, which is plotted after region R21, 512 x 448 beams are used for plotting. In region R23, which is plotted after region R22, 512 x 384 beams are used for plotting. In region R24, which is plotted after region R23, 512 x 320 beams are used for plotting. In region R25, which is plotted after region R24, 512 x 256 beams are used for plotting. In this example, the number of beams used for plotting is reduced over four steps.

[0055] In region R3, which will be plotted after region R25, the entire beam array—512 x 512 beams—will be used for plotting, similar to region R21.

[0056] When the drawing target switches from region R25 to region R3, the pattern density is halved. Since the number of beams used for drawing is doubled, the beam irradiation amount (total beam current) to the substrate 101 remains approximately the same, the operating current per unit time in the control circuit of the blanking aperture array substrate 204 becomes almost constant, and the change in the amount of drift can be kept to a minimum.

[0057] When rendering region R22, the movement speed of XY stage 105 is slower than when rendering region R21. When rendering region R23, the movement speed of XY stage 105 is slower than when rendering region R22. When rendering region R24, the movement speed of XY stage 105 is slower than when rendering region R23. When rendering region R25, the movement speed of XY stage 105 is slower than when rendering region R24. When rendering region R3, the movement speed of XY stage 105 is faster than when rendering region R25, and the same as when rendering region R21.

[0058] Thus, when the pattern density in region R3 is smaller than that in region R2, the entire beam array can be used for plotting in areas of region R2 other than the vicinity of region R3 (region R21), and the number of beams used for plotting can be gradually reduced in the vicinity of region R3 (regions R22 to R25). This minimizes changes in the amount of drift, reduces drift correction residuals, and suppresses a decrease in plotting throughput.

[0059] Next, the drawing method according to this embodiment will be explained with reference to the flowchart shown in Figure 7.

[0060] The area density calculation unit 114 of the control computer 110 virtually divides the drawing area 30 into multiple stripe areas and calculates the pattern density, which indicates the area ratio of the pattern, for each stripe area (steps S1, S2).

[0061] The determination unit 115 determines whether or not there are any areas where the difference in pattern density between consecutive stripe regions in the y direction exceeds a threshold (step S3).

[0062] If the difference in pattern density between the k-1th stripe region (where k is an integer greater than or equal to 2) and the kth stripe region is greater than or equal to a threshold, and the pattern density of the kth stripe region is greater than that of the k-1th stripe region (step S3_Yes, S4_Yes), the beam selection unit 116 selects a beam to be used for drawing the kth and subsequent stripe regions (step S5).

[0063] The beam selection unit 116, when the pattern density of the k-th stripe region is A times the pattern density of the (k-1)-th stripe region, sets the number of beams used to draw the k-th stripe region to 1 / A times the number of beams used to draw the (k-1)-th stripe region.

[0064] For example, if the pattern density of the k-th stripe region is twice that of the (k-1)th stripe region, the number of beams used to draw the k-th stripe region will be halved compared to the number of beams used to draw the (k-1)th stripe region. If the entire multi-beam beam array (512 x 512 beams) is used to draw the (k-1)th stripe region, then 512 x 256 beams (half of the beam array in the x-direction) will be selected as the beams to draw the k-th stripe region.

[0065] Furthermore, the beam selection unit 116 selects the beams to be used for drawing the k+1th and subsequent stripe regions in order to restore the reduced number of beams to their original state. The beam selection unit 116 selects the beams to be used for drawing the k+1th and subsequent stripe regions based on a pre-set number of steps to restore the number of beams to their original state and the number of stripe regions at each step.

[0066] In the example shown in Figure 5, the number of steps required to restore the number of beams to its original state is 4. Also, in the example shown in Figure 5, the number of stripe regions in each step corresponds to the number of stripe regions contained in each of regions R11 to R14.

[0067] For example, if the number of stripe regions per step is 3, the number of beams used for drawing is increased every time three stripe regions are drawn. In other words, the beam selection unit 116 selects the beams to be used in such a way that the x-direction size of the beam array region is increased.

[0068] If the difference in pattern density between the (k-1)th stripe region and the (k)th stripe region is greater than or equal to a threshold, and the pattern density of the (k)th stripe region is smaller than that of the (k-1)th stripe region (step S3_Yes, S4_No), the beam selection unit 116 selects a beam to be used for drawing the (k)th to (k-1)th stripe region (step S6).

[0069] The beam selection unit 116, when the pattern density of the k-th stripe region is A times the pattern density of the (k-1)-th stripe region, sets the number of beams used to draw the k-th stripe region to 1 / A times the number of beams used to draw the (k-1)-th stripe region.

[0070] For example, if the pattern density of the k-th stripe region is half that of the (k-1)th stripe region, the number of beams used to draw the k-th stripe region is doubled compared to the number of beams used to draw the (k-1)th stripe region. If the entire multi-beam beam array (512 x 512 beams) is used to draw the k-th stripe region, then 512 x 256 beams (half the beam array in the x direction) are selected as the beams to draw the (k-1)th stripe region.

[0071] Furthermore, the beam selection unit 116 selects the beams to be used for drawing the kj-th to k-2-th stripe regions in order to gradually reduce the number of beams. The beam selection unit 116 selects the beams to be used for drawing the kj-th to k-2-th stripe regions based on a pre-set number of steps to reduce the number of beams to a target value and the number of stripe regions at each step. The target value for the number of beams is the number of beams to be used for drawing the k-1-th stripe region. j is determined by the number of steps and the number of stripe regions at each step.

[0072] In the example shown in Figure 6, the number of steps required to reduce the number of beams is 4. Also, in the example shown in Figure 6, the number of stripe regions in each step corresponds to the number of stripe regions contained in each of regions R22 to R25.

[0073] For example, if the number of stripe regions per step is 2, the number of beams used for drawing is reduced each time two stripe regions are drawn. In other words, the beam selection unit 116 selects the beams to be used in such a way that the x-direction size of the beam array region is reduced.

[0074] The beam selection unit 116 draws a pattern for each stripe region using the selected beam (step S7). The drawing control unit 112 controls the movement speed of the XY stage 105 according to the x-direction size of the beam array used for drawing.

[0075] Thus, in this embodiment, when the pattern density changes significantly between stripe regions, the change in the total beam current is suppressed by changing the number of beams used for drawing, thereby minimizing the change in drift and reducing the correction residual caused by pattern density switching without having to make the drift correction interval finer. Furthermore, by gradually changing the number of beams used for drawing before or after the pattern density switch, the change in drift can be made more gradual while suppressing a decrease in drawing throughput.

[0076] In the above embodiment, an example was described in which the x-direction size of the beam array is changed when changing the number of beams used for drawing, but the y-direction size of the beam array may also be changed. In this case, the height (y-direction size) of the stripe area 34 changes.

[0077] For example, consider the case shown in Figure 8(a) where the pattern density of stripe area 34a is 20% and the pattern density of stripe area 34b is 40%. When the drawing target switches from stripe area 34a to stripe area 34b, the pattern density doubles.

[0078] Therefore, in stripe region 34b, the number of beams used for drawing is halved compared to stripe region 34b. The multi-beam beam array is divided into two in the y direction, and drawing is performed using 256 x 512 beams on one half. The other 256 x 512 beams are not used and the corresponding blanker is controlled to keep them off at all times.

[0079] Using 256 × 512 beams, stripe regions 34b_1 and 34b_2 are sequentially drawn by dividing stripe region 34b into two in the y direction, as shown in Figure 8(b). Since the x-direction size of the beam array used for drawing is the same for stripe region 34a and stripe regions 34b_1 and 34b_2, the movement speed of the XY stage 105 is the same.

[0080] 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. For example, although the number of beams is changed by restricting the area in the X or Y direction, the number of beams may be changed on average within the beam array, such as by arranging the on-beams in a staggered pattern. 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]

[0081] 100 drawing device 110 Control Computer 111 Data Processing Unit 112 Drawing Control Unit 113 Drift Correction Section 114 Area density calculation section 115 Judgment section 116 Beam selection section 150 Drawing section 160 Control Unit

Claims

1. A multi-charged particle beam drawing method comprising forming a multi-beam using a charged particle source, and drawing a pattern by irradiating a substrate on a stage with the multi-beam while moving it in a first direction, The drawing area of ​​the substrate is virtually divided by a predetermined width in a second direction linearly independent of the first direction to generate a plurality of stripe areas. For each of the aforementioned stripe regions, the pattern density, which represents the area ratio of the pattern, is calculated. A multi-charged particle beam lithography method, wherein, when the pattern density difference between a first stripe region and a second stripe region continuous in the second direction is greater than or equal to a threshold, at least one of the number of beams used to draw the first stripe region and the number of beams used to draw the second stripe region is changed.

2. In order to change the number of beams used for drawing, the size of the multi-beam beam array in the first direction is changed. The multi-charged particle beam lithography method according to claim 1, wherein the movement speed of the stage is controlled based on the size of the beam array in the first direction.

3. The multi-charged particle beam lithography method according to claim 1, wherein the size of the multi-beam beam array in the second direction is changed in order to change the number of beams used for lithography.

4. The multi-charged particle beam drawing method according to claim 1, wherein, after drawing the first stripe region, the number of beams is reduced to draw the second stripe region, and after drawing the second stripe region, the number of beams is gradually increased to draw multiple stripe regions.

5. The multi-charged particle beam drawing method according to claim 1, wherein, after drawing the first stripe region, the number of beams is increased to draw the second stripe region, and multiple stripe regions are drawn while gradually decreasing the number of beams until the first stripe region is drawn.

6. A multi-charged particle beam lithography apparatus that forms multiple beams using a charged particle source and irradiates a substrate on a stage with the multiple beams while moving the substrate in a first direction to draw a pattern, A calculation unit that virtually divides the drawing area of ​​the substrate into a predetermined width in a second direction linearly independent of the first direction to generate a plurality of stripe regions, and calculates a pattern density indicating the area ratio of the pattern for each stripe region, When the pattern density difference between the first stripe region and the second stripe region, which are continuous in the second direction, is greater than or equal to a threshold, a control unit changes at least one of the number of beams used to draw the first stripe region and the number of beams used to draw the second stripe region, A multi-charged particle beam lithography system equipped with the following features.

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