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

Abstract

This suppresses changes in the number of on-beams and improves drawing accuracy. [Solution] In the multi-charged particle beam drawing method according to this embodiment, the irradiation time for each shot of each beam of the multi-charged particle beam is calculated, and based on the calculated irradiation time, the on / off status of each beam in each irradiation step in a shot cycle consisting of multiple irradiation steps is set, for each shot of the multi-charged particle beam, the number of beams to be set to on in the longest irradiation step with the longest irradiation time among the multiple irradiation steps is extracted, and based on the extracted number of beams, it is determined whether or not to change the shot cycle, and based on the determination, the beams with irradiation times corresponding to the multiple irradiation steps are sequentially irradiated onto a substrate placed on a stage, while performing tracking control so that the irradiation area of ​​the multi-charged particle beam follows the movement of the stage, in order to draw a pattern.

Description

[Technical Field]

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

[0002] With the increasing integration of LSIs, the circuit line widths required for semiconductor devices are becoming smaller year by year. To form the desired circuit patterns on semiconductor devices, a method is employed in which a high-precision original pattern formed on silica is reduced and transferred onto a wafer using a reduction projection exposure system. The high-precision original pattern is drawn using an electron beam lithography system, and so-called electron beam lithography technology is employed.

[0003] Multibeam lithography systems can significantly improve throughput compared to single-beam systems because they can irradiate many beams at once. In a multibeam lithography system using a blanking aperture array substrate (blanking plate), for example, an electron beam emitted from a single electron gun is passed through a molded aperture array substrate with multiple apertures to form multiple beams. A blanking aperture array substrate is positioned downstream of the molded aperture array substrate. The blanking aperture array substrate has electrode pairs for individually deflecting the beams, with apertures for beam passage formed between the electrode pairs. By fixing one electrode of the electrode pair (blanker) at ground potential and switching the other electrode between ground potential and other potentials, blanking deflection of the passing electron beam is performed. The optical tube of the multibeam lithography system is configured so that the electron beam deflected by the blanker is shielded and turned off, while the undeflected electron beam is irradiated onto the sample as an on-beam.

[0004] When performing lithography using a multi-beam system, it is possible to use a large total beam current for exposure. However, increasing the current can lead to a degradation of lithography accuracy due to the Coulomb effect. For example, repulsive forces between electrons can cause misalignment of the beam position on the sample surface and focus errors. The magnitude of the Coulomb effect depends on the on-beam current, that is, the number of on-beams that are controlled to be "on" by the blanking aperture array substrate and reach the sample surface.

[0005] When the number of on-beams changes significantly, the effect of the Coulomb effect also changes considerably, leading to large beam position fluctuations and a deterioration in drawing accuracy. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-72151 [Patent Document 2] Japanese Patent Application Publication No. 11-3845 [Patent Document 3] Japanese Patent Publication No. 2015-109323 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] 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 changes in the number of on-beams and improve lithography accuracy. [Means for solving the problem]

[0008] A multi-charged particle beam drawing method according to one aspect of the present invention involves calculating the irradiation time for each shot of each beam of the multi-charged particle beam, setting the on / off status of each beam in each irradiation step of a shot cycle composed of multiple irradiation steps based on the calculated irradiation time, extracting the number of beams to be turned on in the longest irradiation step with the longest irradiation time among the multiple irradiation steps for each shot of the multi-charged particle beam, determining whether or not to change the shot cycle based on the extracted number of beams, and, based on the determination, sequentially irradiating a substrate placed on a stage with beams corresponding to the irradiation times of the multiple irradiation steps while performing tracking control so that the irradiation area of ​​the multi-charged particle beam follows the movement of the stage, thereby drawing a pattern.

[0009] A multi-charged particle beam drawing apparatus according to one aspect of the present invention comprises: a generation unit that calculates the irradiation time for each shot of each beam of the multi-charged particle beam, and generates irradiation time control data by setting the on / off status of each beam in each irradiation step in a shot cycle composed of multiple irradiation steps based on the calculated irradiation time; a determination unit that extracts the number of beams to be turned on in the longest irradiation step, which has the longest irradiation time among the multiple irradiation steps, for each shot of the multi-charged particle beam, and determines whether or not to change the shot cycle based on the extracted number of beams; and a drawing unit that, based on the determination, sequentially irradiates a substrate with beams corresponding to the irradiation times of the multiple irradiation steps to draw a pattern. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress changes in the number of on-beams and improve drawing accuracy. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a drawing apparatus according to an embodiment of the present invention. [Figure 2]It is a plan view of a shaping aperture array substrate. [Figure 3] It is a diagram for explaining an example of a drawing operation. [Figure 4] It is a diagram showing an example of an irradiation area of a multi-beam and a pixel to be drawn. [Figure 5] It is a diagram for explaining an example of a multi-beam drawing method. [Figure 6] It is a schematic configuration diagram of a blanking aperture array substrate. [Figure 7] It is a configuration diagram of an input / output circuit and a cell array circuit. [Figure 8] It is a schematic configuration diagram of an individual blanking mechanism. [Figure 9] It is a diagram showing an example of an irradiation step within one shot cycle. [Figure 10] It is a diagram showing an example of beam on timing. [Figure 11] It is a diagram showing an example of adding the longest irradiation step. [Figure 12] It is a diagram showing an example of splitting an on beam. [Figure 13] It is a diagram showing an example of skipping the longest irradiation step. [Figure 14] It is a flowchart for explaining a drawing method. [Figure 15] It is a diagram showing an example of correcting irradiation time control data. <00​​​​​​​​​​​​​​​​​ 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 tube 102 and a lithography chamber 103. Inside the electron-optical tube 102 are an electron source 201, an illumination lens 202, a molded aperture array substrate 203, a blanking aperture array substrate 204, a reduction lens 205, a batch blanking deflector 210, a limiting aperture member 206, an objective lens 207, and a deflector 208, etc. Also inside the electron-optical tube 102 is a focus correction lens (not shown) that dynamically corrects the beam focus during lithography.

[0014] An XY stage 105 is placed inside the drawing chamber 103. The substrate 101 to be drawn is placed on the XY stage 105. A resist to be exposed by an electron beam is coated on the upper surface of the substrate 101. The substrate 101 is, for example, a substrate processed as an exposure mask used in the manufacture of semiconductor devices (mask blanks) or a semiconductor substrate processed as a semiconductor device (silicon wafer). A mirror 107 for measuring the stage position is also placed on the XY stage 105.

[0015] The control unit 160 includes a control computer 110, a deflection control circuit 130, a lens control circuit 132, a stage control unit 134, a stage position detector 139, and memory units 140 and 142. The memory unit 140 receives and stores drawing data from an external source. The drawing data typically defines information for multiple graphic patterns to be drawn. Specifically, each graphic pattern has a defined graphic code, coordinates, and size. The memory unit 142 stores irradiation time control data, which will be described later.

[0016] The control computer 110 includes a generation unit 111, a determination unit 112, a correction unit 113, a drawing control unit 114, and a stage speed setting unit 115. Each part of the control computer 110 may be composed of hardware such as electrical circuits, or it may be composed of software such as programs that execute these functions on the control computer 110. Alternatively, it may be composed of a combination of hardware and software.

[0017] The stage position detector 139 emits a laser beam, receives the reflected light from the mirror 107, and detects the position of the XY stage 105 using the principle of laser interferometry.

[0018] Figure 2 is a conceptual diagram showing the configuration of the molded aperture array substrate 203. As shown in Figure 2, the molded aperture array substrate 203 has a plurality of openings 203a formed along the longitudinal direction (y direction) and transverse direction (x direction) at a predetermined arrangement pitch. Each opening 203a is formed, for example, as a rectangle or circle with the same (approximately the same) dimensions and shape.

[0019] 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. The electron beam 200 illuminates a region containing multiple apertures 203a. A portion of the electron beam 200 passes through the multiple apertures 203a of the molded aperture array substrate 203, while the remaining beam is stopped by the molded aperture array substrate 203. As the electron beam 200 passes through the multiple apertures 203a, a multi-beam is formed containing multiple individual beams 20a to 20e.

[0020] The blanking aperture array substrate 204 has beam passage holes formed in it, corresponding to the positions of each aperture 203a in the molded aperture array substrate 203. A blanker 50 (see Figure 8), consisting of a pair of electrodes 51 and 52, is placed in each passage hole. By grounding one electrode 52 to maintain ground potential and switching the other electrode 51 to ground potential or a potential other than ground potential, the deflection of the beam passing through the passage hole is switched on and off, thereby controlling blanking.

[0021] When the beam is on, the opposing electrodes 51 and 52 of the blanker 50 are controlled to the same potential, and the blanker 50 does not deflect the beam. When the beam is off, the opposing electrodes 51 and 52 of the blanker 50 are controlled to different potentials, and the blanker 50 deflects the beam. Multiple blankers 50 can control the beam to the off state by performing blanking deflection on their respective beams from among the multi-beams that have passed through multiple apertures 203a of the molded aperture array substrate 203.

[0022] The multi-beams that have passed through the blanking aperture array substrate 204 are reduced by the reduction lens 205 and travel toward the central opening formed in the limiting aperture member 206.

[0023] Here, the beam controlled to the beam-off state is deflected by the blanker 50 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, the beam controlled to the beam-on state is not deflected by the blanker 50 and passes through the opening of the limiting aperture member 206. In this way, the beam can be individually controlled on / off by turning the deflection of the blanker 50 on / off.

[0024] Furthermore, the unified blanking deflector 210 allows for the blanking deflection of the entire multi-beam system simultaneously.

[0025] 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 a desired reduction ratio. Each beam (the entire multi-beam) that has passed through the limiting aperture member 206 is deflected in the same direction by the deflector 208 and irradiated onto a desired position on the substrate 101.

[0026] When the XY stage 105 is moving continuously, the deflector 208 controls the beam irradiation position on the substrate 101 to follow the movement of the XY stage 105, at least while the beam is irradiating the substrate 101.

[0027] For example, the drawing process is carried out using the following drawing algorithm. As shown in Figure 3, the drawing area 60 of the substrate 101 is virtually divided into multiple stripe-shaped areas 62 with a predetermined width in the y direction, for example. For example, the XY stage 105 is moved to adjust the position of the irradiation area 64 that can be irradiated with a single multi-beam irradiation at the left end of the first stripe area 62, and the drawing is started. By moving the XY stage 105 in the -x direction, the drawing can be advanced relatively in the +x direction.

[0028] After the first stripe area 62 has been drawn, the stage position is moved in the -y direction to adjust the illuminated area to be located at the right edge of the second stripe area 22, and drawing begins. Then, by moving the XY stage 105, for example, in the +x direction, drawing is performed in the -x direction.

[0029] Drawing time can be reduced by alternating directions while drawing, such as drawing in the +x direction for the third stripe area 62 and in the -x direction for the fourth stripe area 62. However, it is not limited to alternating directions; drawing can also be done in the same direction for each stripe area 62.

[0030] Figure 4 shows an example of a multi-beam irradiation area and a pixel to be drawn. In Figure 4, the stripe area 62 is divided into multiple mesh areas, for example, by the beam sizes of the individual beams that make up the multi-beam. Each mesh area becomes a pixel to be drawn 70 (unit irradiation area, or drawing position). The size of the pixel to be drawn 70 is not limited to the beam size, and may be composed of any size unrelated to the beam size. For example, it may be composed of a size of 1 / m (where m is an integer of 1 or more) of the beam size.

[0031] In the example shown in Figure 4, the drawing area of ​​the substrate 101 is divided, for example, in the y-direction into multiple stripe areas 62 with a width essentially the same as the size of the irradiation area 64 (drawing field) that can be irradiated with a single multi-beam irradiation. Note that the width of the stripe areas 62 is not limited to this.

[0032] The example in Figure 4 shows the case of an 8x8 multi-beam system. Within the illumination area 64, there are multiple pixels 74 (beam drawing positions) that can be illuminated in a single multi-beam shot (64 in this example). The pitch between adjacent pixels 74 is the pitch between each beam of the multi-beam system. In the example in Figure 4, a square area enclosed by four adjacent pixels 74 and containing one of the four pixels 74 constitutes one grid 76. In the example in Figure 4, each grid 76 consists of 4x4 pixels.

[0033] Figure 5 illustrates an example of a multi-beam plotting method using a continuous movement method. In Figure 5, the grid drawn by the first stage of eight beams in the y direction is shown among the multi-beams that plot the stripe region 62 shown in Figure 4.

[0034] In the example in Figure 5, for example, four pixels are drawn (exposed) while the XY stage 105 moves a distance of 8 beam pitches (8p). While the four pixels are drawn (exposed), the deflector 208 deflects the entire multi-beam simultaneously so that the illumination area 64 does not shift relative to the substrate 101 due to the movement of the XY stage 105. This causes the illumination area 64 to follow the movement of the XY stage 105. In other words, tracking control is performed. In the example in Figure 5, one tracking cycle is performed by drawing (exposing) four pixels while moving a distance of 8 beam pitches.

[0035] If the drawing time (maximum exposure time) for each pixel is T, then between time t=0 and t=T, the first beam shot illuminates, for example, the first pixel from the left in the bottom row of the grid of interest. Between time t=0 and t=T, the XY stage 105 moves in the -x direction by, for example, two beam pitches (2p). During this time, the tracking operation continues. In Figure 5, beams #1 to #8 illuminate each grid at t=0. For the grid after t=T, only the illumination position of beam #1 is shown for convenience of explanation. Also, pixels that have already been beam-illuminated are indicated by diagonal lines.

[0036] At time t=T, while continuing beam deflection for tracking control, the multi-beam system is deflected collectively, separately from the beam deflection for tracking control. This shifts the drawing position of each beam. In the example in Figure 5, the drawing target pixel is shifted from the bottom row and first pixel from the left of the grid of interest to the second row from the bottom and first pixel from the left. During this time, the XY stage 105 is moving, so the tracking operation continues.

[0037] Between times t=T and t=2T, the second beam shot is directed to the second-to-last pixel from the left in the grid of interest. Between times t=T and t=2T, the XY stage 105 moves in the -x direction by two beam pitches. Tracking continues during this time.

[0038] At time t=2T, the deflector 208 performs a simultaneous multi-beam deflection, shifting the pixel to be drawn from the second-to-last pixel from the bottom and first-to-last pixel of the grid of interest to the third-to-last pixel from the bottom and first-to-last pixel of the grid of interest. During this time, the XY stage 105 continues to move, so the tracking operation continues.

[0039] Between times t=2T and t=3T, the third beam shot is applied to the third pixel from the bottom and the first pixel from the left in the grid of interest. Between times t=2T and t=3T, the XY stage 105 moves in the -x direction by, for example, two beam pitches. Tracking continues during this time.

[0040] At time t=3T, the deflector 208 performs a simultaneous multi-beam deflection, shifting the target pixel from the third row from the bottom and the first pixel from the left in the grid of interest to the fourth row from the bottom and the first pixel from the left. During this time, the XY stage 105 continues to move, so the tracking operation continues.

[0041] Between times t=3T and t=4T, the fourth beam shot is applied to the fourth pixel from the bottom and the first pixel from the left in the grid of interest. Between times t=3T and t=4T, the XY stage 105 moves in the -x direction by, for example, two beam pitches. During this time, the tracking operation continues. As a result, the drawing of the first row of pixels from the left in the grid of interest is completed.

[0042] In the example in Figure 5, after illuminating each beam corresponding to its drawing position after shifting three times from the initial shot position, the tracking position is returned to the tracking start position by resetting the beam deflection for tracking control. In other words, the tracking position is returned in the opposite direction to the stage movement direction. In the example in Figure 5, at time t=4T, tracking of the grid of interest is released, and the beam is swung back to the grid of interest that has shifted by 8 beam pitch units in the x direction. Note that although beam #1 was described in the example in Figure 5, drawing is performed similarly for the other beams on their respective grids.

[0043] Since the drawing of the first pixel row from the left in each grid has been completed, after a tracking reset, in the next tracking cycle, the deflector 208 first deflects (shifts) the beam so that it aligns the drawing position with the first row from the bottom and the second pixel from the left in each grid.

[0044] Between times t=4T and t=8T, the second pixel row from the left of the grid of interest is drawn. At time t=8T, the trunking of the grid of interest is released, and the beam is swung back to the grid of interest which has been shifted by 8 beam pitch units in the x direction.

[0045] Since the drawing of the first and second pixel rows from the left in each grid has been completed, after a tracking reset, in the next tracking cycle, the deflector 208 first deflects (shifts) the beam so that it aligns the drawing position with the first row from the bottom and the third pixel from the left in each grid.

[0046] Between times t=8T and t=12T, the third pixel row from the left of the grid of interest is drawn. At time t=12T, the trunking of the grid of interest is released, and the beam is swung back to the grid of interest which has been shifted by 8 beam pitch units in the x direction.

[0047] Since the drawing of the first to third pixel rows from the left in each grid has been completed, after a tracking reset, in the next tracking cycle, the deflector 208 first deflects (shifts) the beam so that it aligns the drawing position with the first row from the bottom and the fourth pixel from the left in each grid.

[0048] As described above, during the same tracking cycle, the deflector 208 controls the irradiation area 64 so that its relative position to the substrate 101 remains the same, and each shot is performed while shifting it one pixel at a time. After the completion of one tracking cycle, the tracking position of the irradiation area 64 is returned to its original position, and the position of the first shot is adjusted to a position shifted by one pixel. Then, while performing the next tracking control, each shot is performed while shifting it one pixel at a time.

[0049] By repeating this process, a pattern is drawn.

[0050] Next, the blanking aperture array substrate 204, which performs blanking control for each beam of the multi-beam system, will be described. As shown in Figure 6, the blanking aperture array substrate 204 includes an input / output circuit 31 (31a, 31b) and a cell array circuit 34. The input / output circuit 31 receives control signals from the deflection control circuit 130.

[0051] A cell array circuit 34 is provided in the center of the blanking aperture array substrate 204, and two input / output circuits 31a and 31b are provided on either side of the cell array circuit 34. Data path D of the control signal from the deflection control circuit 130 to the blanking aperture array substrate 204 L , D R It is divided into two systems.

[0052] As shown in Figure 7, the cell array circuit 34 is provided with multiple cells that constitute individual blanking mechanisms 40. Each individual blanking mechanism 40 corresponds to one blanker 50. The input / output circuit 31 converts the control signal received from the deflection control circuit 130 into a beam on / off signal and then outputs it to the cell array circuit 34. For example, the input / output circuit 31a outputs a beam on / off signal to the individual blanking mechanism 40 located on one half of the cell array circuit 34, and the input / output circuit 31b outputs a beam on / off signal to the individual blanking mechanism 40 located on the other half.

[0053] The input / output circuit 31 is equipped with multiple selectors 320 (demultiplexers). The selectors 320 receive irradiation time control data that defines the irradiation time for each beam shot via the amplifier 310, and output beam on / off signals from the corresponding output lines. Multiple individual blanking mechanisms 40 are connected in series to each output line.

[0054] For example, the selector 320 has eight output lines, row 1 to row 8, and 256 individual blanking mechanisms 40 are connected to each output line. By arranging 64 selectors 320 in input / output circuits 31a and 31b, beam on / off signals can be transferred to 512 × 512 individual blanking mechanisms 40 in the cell array circuit 34.

[0055] The arrangement of the individual blanking mechanisms 40 in which input / output circuits 31a output beam on / off signals and input / output circuits 31b output beam on / off signals is not limited to that shown in Figure 7. For example, the output lines from input / output circuits 31a and 31b may be arranged alternately. Alternatively, the individual blanking mechanisms 40 in which input / output circuits 31a output beam on / off signals and the individual blanking mechanisms 40 in which input / output circuits 31b output beam on / off signals may be arranged alternately.

[0056] As shown in Figure 8, the individual blanking mechanism 40 includes a shift register 41, a pre-buffer 42, a buffer 43, a data register 44, a NAND circuit 45, and an amplifier 46. The shift register 41 transfers the data output from the shift register of the preceding cell to the shift register of the succeeding cell according to the clock signal (SHIFT).

[0057] The prebuffer 42 stores the beam on / off signal for the cell, which is output from the shift register 41 according to the clock signal (LOAD1).

[0058] Buffer 43 captures and holds the output value of prebuffer 42 according to the clock signal (LOAD2).

[0059] The data register 44 captures and holds the output value of buffer 43 according to the clock signal (LOAD3).

[0060] The NAND circuit 45 receives the output signal from the data register 44 and the shot enable signal (SHOT_ENABLE). The output signal from the NAND circuit 45 is then supplied to the electrode 51 of the blanker 50 via the amplifier 46 (driver amplifier).

[0061] When both the output signal of the data register 44 and the shot enable signal are High, the output of the NAND circuit 45 becomes Low, electrodes 51 and 52 are at the same potential, and the blanker 50 does not deflect the beam, so the beam turns on. When at least one of the output signal of the data register 44 and the shot enable signal is Low, the output of the NAND circuit 45 becomes High, electrodes 51 and 52 are at different potentials, the blanker 50 deflects the beam, and the beam turns off.

[0062] The shot enable signal is input to the NAND circuit 45 of all individual blanking mechanisms 40, and by setting the shot enable signal to Low, all beams can be turned off.

[0063] When the shot enable signal is maintained at High, the beam is switched on / off by the output of data register 44. That is, when the irradiation time control data is 1 (High), the beam on / off signal becomes an ON signal, and when the irradiation time control data is 0 (Low), the beam on / off signal becomes an OFF signal.

[0064] In multibeam lithography, each beam is turned on for a desired duration within a single shot cycle, and off for the remaining time. For example, the gradation value N is calculated by dividing the irradiation time by the quantization unit Δ. The quantization unit Δ can be set in various ways, but can be defined as, for example, 1 ns. The irradiation time control data is obtained by converting the gradation value N into a binary value with n digits.

[0065] For example, if N=50, then 50=2 5 +2 4 +2 1 Therefore, when converted to a 6-digit binary value, the irradiation time control data becomes '110010'. Similarly, if N=30, the irradiation time control data becomes '011110'.

[0066] The first digit (least significant bit) of the irradiation time control data indicates an irradiation time of 1Δ. The second digit of the irradiation time control data indicates an irradiation time of 2Δ. The third digit of the irradiation time control data indicates an irradiation time of 4Δ. The fourth digit of the irradiation time control data indicates an irradiation time of 8Δ. The fifth digit of the irradiation time control data indicates an irradiation time of 16Δ. The sixth digit (most significant bit) of the irradiation time control data indicates an irradiation time of 32Δ.

[0067] One shot cycle is divided into irradiation steps equal to the number of digits (bits) in the irradiation time control data, and each irradiation step has an irradiation time corresponding to the number of digits. For example, if irradiation is performed in order from the largest number of digits, and Δ = 1 ns, then as shown in Figure 9, the first irradiation step will be 32 ns. The second irradiation step will be 16 ns. The third irradiation step will be 8 ns. The fourth irradiation step will be 4 ns. The fifth irradiation step will be 2 ns. The sixth irradiation step will be 1 ns.

[0068] When N=50, the irradiation time control data is '110010', and as shown in Figure 10, the beam is turned on during the 1st (32ns), 2nd (16ns), and 5th (2ns) irradiation steps, and turned off during the 3rd, 4th, and 6th irradiation steps.

[0069] You may irradiate in order from the smallest number of digits (from the irradiation step with the shortest irradiation time).

[0070] As illustrated by this example, in multi-beam lithography, one shot cycle is divided into multiple irradiation steps, and the beam is switched on and off in each irradiation step to achieve the desired irradiation time. For example, the irradiation times of the multiple irradiation steps differ from each other and are proportional to a power of two.

[0071] In multibeam lithography, if the number of on-beams changes significantly between shots, the effect of the Coulomb effect also changes significantly, which can degrade the accuracy of the lithography.

[0072] Therefore, in this embodiment, we focus on the irradiation step with the longest irradiation time in each shot cycle (longest irradiation step). If the number of on-beams in the longest irradiation step exceeds the first threshold Th1, the on-beams are divided into two groups, an additional longest irradiation step is added, and one longest irradiation step irradiates the on-beams of one group, while the other longest irradiation step irradiates the on-beams of the other group. This keeps the number of on-beams in the longest irradiation step within a certain range and suppresses changes in the number of on-beams between shots.

[0073] When the longest irradiation step is performed twice, as shown in Figure 11, the number of irradiation steps included in one shot cycle increases by one, and therefore the irradiation time control data also increases by one bit. The most significant bit and the second bit from the top correspond to the on / off state in the longest irradiation step. In the example shown in Figure 11, the 7th digit (most significant bit) and the 6th digit (second bit from the top) of the irradiation time control data indicate the irradiation time of 32Δ. When Δ=1ns, 32Δ is 32ns.

[0074] The first threshold Th1 is not particularly limited, but for example, it can be 50% of the total number of beams in a multi-beam system. As shown in Figure 12, if 51% of the total number of beams are turned on in the longest irradiation step, the 51% of beams are divided into 26% and 25%, and 26% of the beams are turned on in the first longest irradiation step, and 25% of the beams are turned on in the second longest irradiation step.

[0075] If 75% of the total number of beams are turned on in the longest irradiation step, the 75% of beams are divided into 38% and 37%, and the 38% beams are turned on in the first longest irradiation step, and the 37% beams are turned on in the second longest irradiation step.

[0076] If 100% of the beams are turned on during the longest irradiation step, the 100% of beams are divided into two groups of 50% and 50%, with 50% of the beams turned on during the first longest irradiation step and the remaining 50% of the beams turned on during the second longest irradiation step.

[0077] Also, in this embodiment, paying attention to the number of on-beam in the longest irradiation step in each of the plurality of shots included in one tracking cycle, when the number of on-beam is less than the second threshold Th2 (Th2 < Th1), the irradiation of this longest irradiation step is not performed (skipped) during the same tracking cycle. The skipped irradiation is stacked in the memory 144, and after the tracking reset, a tracking cycle is added, and in the additional tracking cycle, the irradiation of the longest irradiation step where the number of on-beam is less than the second threshold Th2 is executed.

[0078] When the longest irradiation step is not performed, as shown in FIG. 13, since the number of irradiation steps included in one shot cycle is reduced by one, the irradiation time control data is also reduced by one bit.

[0079] The second threshold Th2 is not particularly limited, but for example, it can be set to 25% of the total number of all beams in the multi-beam. For example, when 20% of the total number of all beams is on in the longest irradiation step, the irradiation of this longest irradiation step is not performed during the same tracking cycle, but is executed in the additional tracking cycle.

[0080] In the additional tracking cycle, since the number of on-beam is small and the influence of the Coulomb effect is different when the number of on-beam is between Th2 and Th1, beam adjustment is performed using an optical system such as a focus correction lens so that the beam position fluctuation and the like are the same as when the number of on-beam is between Th2 and Th1. For example, in the additional tracking cycle, focus correction is performed using a focus correction lens so that the same beam position fluctuation occurs when 38% of the total number of all beams is on.

[0081] Next, the processing of each part of the control computer 110 will be described according to the flowchart shown in FIG. 14.

[0082] The generation unit 111 virtually divides the drawing area of the substrate 101 into a plurality of mesh areas. The size of the mesh area is, for example, about the same size as one beam, and each mesh area becomes a pixel (unit irradiation area). The generation unit 111 reads the drawing data from the storage unit 140, and calculates the pattern area density ρ of each pixel using the pattern defined in the drawing data.

[0083] The generation unit 111 multiplies the reference irradiation amount by the pattern area density ρ and a correction coefficient for correcting proximity effects and the like, and calculates the irradiation amount of the beam irradiated to each pixel. The generation unit 111 divides the irradiation amount by the current density to calculate the irradiation time.

[0084] The generation unit 111 distributes the irradiation time to a plurality of irradiation steps and generates irradiation time control data (shot data) (step S1). For example, the generation unit 111 divides the irradiation time by the quantization unit to calculate a gradation value (integerized irradiation time). In the case of the example shown in FIG. 9, the generation unit 111 obtains a column of ON / OFF flags corresponding to the sequence (2 5 , 2 4 , 2 3 , 2 2 , 2 1 , 2 0 ) as the irradiation time control data, and sets the ON / OFF of the beam in each irradiation step.

[0085] The determination unit 112 extracts the number of ON beams of the most significant bit (longest irradiation step) of the irradiation time control data corresponding to each beam of the multi-beam for each shot (step S2). Based on the extracted number of ON beams, the determination unit 112 determines whether to change the shot cycle as follows. When the number of ON beams is greater than the first threshold Th1 (step S3_Yes), the determination unit 112 divides the beams for which the longest irradiation step is ON into two groups, a first group and a second group (step S4). The number of beams in the two groups is (substantially) the same.

[0086] The correction unit 113 corrects the irradiation time control data and increases it by 1 bit, and assigns the upper two bits (the most significant bit and the second bit from the top) to the longest irradiation step (step S5). For example, the correction unit 113 sets the most significant bit to '1' and the second bit from the top to '0' for the first group of beams. The correction unit 113 sets the most significant bit to '0' and the second bit from the top to '1' for the second group of beams.

[0087] If the number of on-beams is less than the first threshold Th1 and less than the second threshold Th2 (steps S3_No, S6_Yes), the correction unit 113 corrects the irradiation time control data so that the most significant bit corresponding to the longest irradiation step is assigned in an additional tracking cycle rather than in the same tracking cycle (step S7). If the number of on-beams is less than the first threshold Th1 and greater than or equal to the second threshold Th2 (steps S3_No, S6_No), the irradiation time control data is left unchanged.

[0088] Figure 15A shows an example of irradiation time control data before correction by the correction unit 113, and Figure 15B shows an example of irradiation time control data after correction. One tracking cycle is from SF start to SF end. In the example shown in Figure 15A, 10 shots (Shot 1 to 10) are performed in one tracking cycle. That is, 10 pixels are exposed in one tracking cycle. Also, one shot (one shot cycle) includes 6 irradiation steps (DivShot 1 to 6).

[0089] For example, in Shot 1 with the longest irradiation step, DivShot 6, 75% of the entire multibeam is turned on. In Shot 6 with the longest irradiation step, DivShot 6, 13% of the entire multibeam is turned on.

[0090] In the example shown in Figure 15A, the number of on-beams in the longest irradiation step DivShot6 of Shot1 and Shot4 is greater than the first threshold Th1 (e.g., 50%). Therefore, the on-beams are divided into two groups, and as shown in Figure 15B, one bit is added to the corrected irradiation time data for Shot1 and Shot4, and the upper two bits are assigned to the longest irradiation steps (DivShot6-1, 6-2). This shows that in the longest irradiation step DivShot6-1 of Shot1, 38% of the entire multi-beam is turned on, and in DivShot6-2, 37% of the entire multi-beam is turned on.

[0091] Similarly, in Shot 4's longest irradiation step, DivShot 6-1, 50% of the entire multibeam is turned on, and in DivShot 6-2, the remaining 50% is turned on.

[0092] In the example shown in Figure 15A, the number of on-beams in the longest irradiation step DivShot6 of Shot5 and Shot6 is less than the second threshold Th2 (e.g., 25%). Therefore, as shown in Figure 15B, the most significant bit of Shot5 and Shot6 is skipped, and a tracking cycle is added to correct the irradiation time control data so that the irradiation steps corresponding to the skipped most significant bit are executed in the additional tracking cycle (SFX start to SFX end).

[0093] The drawing control unit 114 transfers the corrected irradiation time control data to the deflection control circuit 130. The deflection control circuit 130 uses the irradiation time control data to switch each beam of the multibeam on and off, controls the exposure time for each pixel of the substrate 101, and draws the pattern (step S9).

[0094] During pattern drawing, Shot1 and Shot4 perform the longest irradiation step twice. Shot5 and Shot6 skip the longest irradiation step. The skipped irradiation is stacked in memory 144 and executed in an additional tracking cycle. The pixels exposed are the same for DivShot1-5 of Shot5 and DivShot6 of Shot5 in the additional tracking cycle.

[0095] The lens control circuit 132 controls the focus correction lens to correct the focus of the multibeam when a tracking reset is performed and an additional tracking cycle begins. Furthermore, when the additional tracking cycle ends and a tracking reset is performed, the lens control circuit 132 controls the focus correction lens to return the focus of the multibeam to its original state.

[0096] Thus, according to this embodiment, since the change in the number of on-beams can be suppressed, the change in the effect of the Coulomb effect is reduced, beam position fluctuations are suppressed, and drawing accuracy can be improved.

[0097] In the above embodiment, the XY stage 105 moves at a constant reference speed, and if the longest irradiation step increases by two irradiations, and the drawing takes longer, it may exceed the upper limit of the deflection amount by the deflector 208, making tracking impossible.

[0098] Therefore, as shown in Figure 16, the speed of the XY stage 105 may be reduced each time the longest irradiation step (two irradiations) is performed a predetermined number of times. The stage speed setting unit 115 transmits the stage speed setting value to the stage control unit 134. The stage control unit 134 decelerates the XY stage 105 based on the received setting value. The speed may be accelerated or decelerated in steps, or it may be accelerated or decelerated gradually so that the speed changes linearly, in a sine curve, or in a curved manner.

[0099] Furthermore, if the number of on-beams is less than the second threshold Th2 and the longest irradiation step (most significant bit) in the shot cycle is skipped, the XY stage 105 may be accelerated to increase the stage speed, as shown in Figure 17, within a range that does not exceed the reference speed. For example, the XY stage 105 may be accelerated when performing a tracking reset and starting an additional tracking cycle.

[0100] In the additional tracking cycle, since only the irradiation for the longest irradiation step with the fewest on-beams is performed, the XY stage 105 may be accelerated and moved at a speed exceeding the reference speed, as shown in Figure 18.

[0101] In the above embodiment, when the number of on-beams in the longest irradiation step is greater than the first threshold Th1, an example was described in which the on-beams are divided (classified) into a first group and a second group, the longest irradiation step is performed twice, the on-beams of the first group are irradiated in one longest irradiation step, and the on-beams of the second group are irradiated in the other longest irradiation step. However, the on-beams may be divided into 3 or more M groups, and the longest irradiation step may be performed M times.

[0102] Furthermore, in the above embodiment, after generating the drawing data, the correction unit 113 modified the shot cycle (added / skipped the longest irradiation step) and added tracking cycles, and the stage control unit 134 controlled the stage speed based on the results. However, when generating the drawing data, irradiation time control data and a stage speed profile based on the number of on-beams in the longest irradiation step may also be generated.

[0103] 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]

[0104] 40 Individual blanking mechanism 50 Blanka 100 Drawing device 110 Control Computer 111 Generation part 112 Judgment section 113 Correction section 114 Drawing Control Unit 115 Stage Speed ​​Setting Section

Claims

1. The irradiation time for each shot of each beam in the multi-charged particle beam is calculated, Based on the calculated irradiation time, the on / off status of each beam in each irradiation step of a shot cycle consisting of multiple irradiation steps is set. For each shot of the multi-charged particle beam, the number of beams to be turned on in the longest irradiation step, which has the longest irradiation time among the multiple irradiation steps, is extracted. Based on the number of beams extracted, a decision is made as to whether or not to change the shot cycle. A multi-charged particle beam drawing method, in which, based on the above determination, a substrate placed on a stage is sequentially irradiated with beams of irradiation times corresponding to the multiple irradiation steps, while performing tracking control so that the irradiation area of ​​the multi-charged particle beam follows the movement of the stage, thereby drawing a pattern.

2. The multi-charged particle beam lithography method according to claim 1, wherein if the number of extracted beams is greater than a first threshold, the beams to be turned on in the longest irradiation step are divided into a first group and a second group, the longest irradiation step is added to the shot cycle, the beams of the first group are turned on in one of the longest irradiation steps, and the beams of the second group are turned on in the other longest irradiation step.

3. The multi-charged particle beam lithography method according to claim 1 or 2, wherein if the number of extracted beams is less than a second threshold, the longest irradiation step in the shot cycle is skipped, the tracking control is reset, and then a beam with an irradiation time corresponding to the skipped longest irradiation step is irradiated onto the substrate.

4. The multi-charged particle beam lithography method according to claim 3, wherein the focus correction of the multi-beam is performed when the tracking control is reset.

5. The multi-charged particle beam lithography method according to claim 1, wherein the stage is accelerated or decelerated during or after the tracking control is reset.

6. The multi-charged particle beam lithography method according to claim 5, wherein the stage is decelerated before performing the shot in which the longest irradiation step is added, and the stage is accelerated after the longest irradiation step is completed.

7. A generation unit calculates the irradiation time for each beam of a multi-charged particle beam for each shot, and based on the calculated irradiation time, sets the on / off state of each beam in each irradiation step in a shot cycle consisting of multiple irradiation steps to generate irradiation time control data. For each shot of the multi-charged particle beam, a determination unit extracts the number of beams that are set to be turned on in the longest irradiation step, which has the longest irradiation time among the multiple irradiation steps, and determines whether or not to change the shot cycle based on the extracted number of beams. Based on the above determination, a drawing unit sequentially irradiates the substrate with beams for irradiation times corresponding to the plurality of irradiation steps to draw a pattern, A multi-charged particle beam lithography system equipped with the following features.

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