Charged particle beam drawing method and charged particle beam drawing device

Abstract

Correcting positional deviations caused by charging with high precision. A charged particle beam drawing method comprises: a step of virtually dividing a drawing area of ​​the substrate into a predetermined grid size and calculating a pattern density distribution representing the configuration ratio of the pattern in each grid area; a step of calculating a dose distribution using the pattern density distribution; a step of calculating an irradiation amount distribution using the pattern density distribution and the dose distribution; a step of calculating a covered charged particle amount distribution; a step of calculating a charge amount distribution generated by direct charging and a charge amount distribution generated by cover charging; a step of calculating a positional deviation of a drawing position based on the charge amount distribution generated by the direct charging and the charge amount distribution generated by the cover charging; a step of correcting an irradiation position using the positional deviation; and a step of irradiating the charged particle beam to the corrected irradiation position so that the potential of the surface of the substrate is higher than the potential of the lower surface of the potential regulating member.

Description

Technical Field

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

[0002] With the high integration of LSIs, the circuit line widths required for semiconductor devices have been miniaturized year by year. In order to form a desired circuit pattern on a semiconductor device, the following method is adopted: using a reduction projection exposure apparatus, a high-precision original pattern (mask, or particularly an intermediate mask used in a stepper or a scanner) formed on quartz is reduced and transferred onto a wafer. The high-precision original pattern is drawn by an electron beam drawing apparatus using a so-called electron beam lithography technique.

[0003] When irradiating an electron beam onto a substrate such as a mask, the irradiation position and its surroundings are charged by the electron beam irradiated in the past, and the irradiation position is shifted. Conventionally, as one of the methods for eliminating the shift of the beam irradiation position, a method of forming a charge dissipation layer (CDL) on the substrate to prevent the charging of the substrate surface is known. However, since this charge dissipation layer basically has acidic properties, the compatibility is poor when a chemically amplified resist is coated on the substrate or the like. In addition, new equipment needs to be provided to form the charge dissipation layer, and the manufacturing cost is further increased. Therefore, it is desired to perform charging effect correction (CEC) without using a charge dissipation layer.

[0004] The charging of the substrate surface includes direct charging caused by the irradiated electron beam, covering charging (Japanese: かぶり帯電) in which electrons scattered in the drawing chamber land on the substrate, and low-energy covering charging in which low-energy secondary electrons generated by the beam irradiation onto the substrate land on the substrate. The following method has been studied: setting the electrode for dynamic focusing to a positive potential to prevent secondary electrons from returning to the substrate surface and reducing the influence of covering charging. However, if the electrode for dynamic focusing is set to a positive potential, the secondary electrons invading the column increase, which causes contamination, and the electrons are confined in the magnetic field of the magnetic lens to form a strong negative space potential, which affects the electron beam orbit. As a result, there is a problem of deteriorating the drawing accuracy.

[0005] Patent Document 1: Japanese Patent Laid-Open No. 6-232032

[0006] Patent Document 2: Japanese Patent Laid-Open No. 2000-200579

[0007] Patent Document 3: Japanese Patent Laid-Open No. 2000-182942 Summary of the Invention

[0008] An object of the present invention is to provide a charged particle beam drawing method and a charged particle beam drawing device that accurately correct a beam irradiation position deviation caused by a charging phenomenon.

[0009] The charged particle beam drawing method of one embodiment of the present invention is to deflect the charged particle beam by a deflector, focus by an objective lens, and draw a pattern on a substrate on a workbench, comprising: a process of virtually dividing the drawing area of ​​the above-mentioned substrate into a predetermined grid size, and calculating a pattern density distribution representing the configuration ratio of the above-mentioned pattern in each grid area; a process of using the above-mentioned pattern density distribution to calculate a dose distribution representing the dose of each grid area; a process of using the above-mentioned pattern density distribution and the above-mentioned dose distribution to calculate the irradiation amount distribution of the above-mentioned charged particle beam irradiated to the above-mentioned substrate; a process of calculating the distribution of the amount of covered charged particles by performing a convolution integral on the distribution function of the covered charged particles and the above-mentioned irradiation amount distribution; a process of using the above-mentioned pattern density distribution to calculate the distribution of the amount of covered charged particles; The cloth, the above-mentioned dose distribution and the above-mentioned irradiation amount distribution, calculate the charge amount distribution generated by direct charging, and use the above-mentioned covered charged particle amount distribution to calculate the charge amount distribution generated by covering charging; the process of calculating the position offset of the drawing position based on the charge amount distribution generated by the above-mentioned direct charging and the charge amount distribution generated by the above-mentioned covering charging; the process of correcting the irradiation position using the above-mentioned position offset; and the process of applying a prescribed voltage to at least either one of the above-mentioned substrate and the above-mentioned potential regulating component in a manner that makes the potential of the surface of the above-mentioned substrate higher than the potential of the lower surface of the potential regulating component arranged at a position opposite to the above-mentioned substrate to form an electric field, and irradiating the above-mentioned charged particle beam to the above-mentioned corrected irradiation position.

[0010] A charged particle beam drawing device according to one embodiment of the present invention deflects the charged particle beam by a deflector, focuses the charged particle beam by an objective lens, and draws a pattern on a substrate on a workbench, and comprises: an emitting unit for emitting the charged particle beam; a pattern density distribution calculation unit for virtually dividing the drawing area of ​​the substrate into a grid shape, and calculating a pattern density distribution representing the configuration ratio of the pattern in each grid area; a dose distribution calculation unit for calculating a dose distribution representing the dose in each grid area using the pattern density distribution; an irradiation quantity distribution calculation unit for calculating an irradiation quantity distribution of the charged particle beam emitted from the emitting unit and irradiated to the substrate using the pattern density distribution and the dose distribution; a covered charged particle quantity distribution calculation unit for calculating a covered charged particle quantity distribution by performing a convolution integral on a distribution function of the covered charged particles and the irradiation quantity distribution; a charged quantity distribution calculation unit for calculating a covered charged particle quantity distribution using the pattern density distribution, the above-mentioned The dose distribution and the irradiation amount distribution are used to calculate the charge amount distribution generated by direct charging, and the charge amount distribution generated by cover charging is calculated using the cover charged particle amount distribution; a position offset distribution calculation unit calculates the position offset of each drawing position based on the charge amount distribution generated by the direct charging and the charge amount distribution generated by the cover charging; a correction unit corrects the irradiation position using the position offset; a potential regulating component is arranged at a position opposite to the substrate and is controlled to a prescribed potential; a voltage control circuit applies a prescribed voltage to at least either one of the substrate and the potential regulating component in such a manner that the potential of the surface of the substrate is higher than the potential of the lower surface of the potential regulating component, and forms an electric field in the direction from the substrate toward the objective lens; and a drawing unit irradiates the charged particle beam to the corrected irradiation position in a state where the electric field is formed.

[0011] Effects of the Invention

[0012] According to the present invention, it is possible to correct with high precision the beam irradiation position deviation caused by the charging phenomenon. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of a drawing device according to an embodiment of the present invention.

[0014] Figure 2 This is a diagram showing a cover covering the periphery of a substrate.

[0015] Figure 3 This is a diagram illustrating how the table moves.

[0016] Figure 4a is a graph showing the drift of secondary electrons. Figure 4b This is a schematic diagram of the state where secondary electrons are pushed back by the electric field.

[0017] Figure 5This is a flowchart illustrating the method for determining the applied voltage according to this embodiment.

[0018] Figure 6 This is a diagram showing a mathematical formula that generalizes the charge amount distribution.

[0019] Figure 7a 、 7b It is a figure which shows the example of an evaluation pattern.

[0020] Figure 8a 、 8b 8c is a diagram showing the distribution of positional deviation amounts.

[0021] Figure 9 This is a graph showing the relationship between applied voltage and plotting position deviation. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the embodiments, 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 may also be an ion beam or the like.

[0023] Figure 1 This is a schematic diagram of the configuration of a drawing device according to an embodiment. Figure 1 The drawing device 100 shown includes a drawing unit W and a control unit C. The drawing device 100 is an example of an electron beam drawing device. The drawing unit W includes an electron lens barrel 1 and a drawing chamber 14. Within the electron lens barrel 1 are arranged an electron gun 5, an illumination lens 7, a first aperture 8, a projection lens 9, a shaping deflector 10, a second aperture 11, an objective lens 12, an objective lens deflector 13, an electrostatic lens 15, and a potential regulating member 16.

[0024] An XY stage 3 is located within the drawing chamber 14. A substrate 2, to be drawn, is placed on the XY stage 3. The substrate 2 includes photomasks used for exposure in semiconductor manufacturing and semiconductor wafers used to form semiconductor devices. Photomasks to be drawn also include mask blanks, which have not yet been drawn. During drawing, a resist layer exposed by an electron beam is formed on the substrate. A reflector 4 for measuring the stage position is located on the XY stage 3 at a position different from that where the substrate 2 is placed.

[0025] Furthermore, a calibration mark M is provided on the XY stage 3 at a position different from the position where the substrate 2 is disposed. For example, the mark M is in the shape of a metal cross. The mark M is scanned by an electron beam, and a detector (not shown) detects reflected electrons from the mark M to perform focus adjustment, position adjustment, and adjustment of the deflection shape correction coefficient.

[0026] The control unit C includes control computers 110 and 120, a stage position detector 45, a stage controller 46, a deflection control circuit 130, a memory 142, storage devices 21 and 140 such as magnetic disks, a voltage control circuit 150, etc. The deflection control circuit 130 is connected to the shaping deflector 10 and the objective lens deflector 13.

[0027] The voltage control circuit 150 is connected to at least one of the stage 3 and the potential regulating member 16 disposed to face the substrate. The voltage control circuit 150 can control the voltage applied to the substrate 2 placed on the stage 3.

[0028] For example, Figure 2 As shown, a conductive frame-shaped cover H is placed on the workbench 3 to maintain the substrate 2 at a predetermined potential. The cover H covers the periphery of the substrate 2, shielding it from the irradiated electron beam and the electric field generated by the side surface charging of the substrate. Pins extend from the bottom surface of the cover H and contact the substrate 2. The voltage control circuit 150 can apply a desired voltage to the substrate 2 via the cover H.

[0029] In addition, the voltage control circuit 150 can apply a desired voltage to the potential regulation component 16 configured to be opposite to the substrate. The potential regulation component 16 is a conductive component that is arranged just above the substrate 2 across a specified gap. For example, the potential regulation component 16 can also be a reflection electron prevention plate that is provided to reduce the reflected electrons from the top plate of the drawing chamber from being incident again on the substrate. In addition, the potential regulation component 16 can also be a heat shield that is used to prevent the heat generated by the excitation of the object lens from being transferred to the substrate due to radiation. Alternatively, the potential regulation component 16 can also be an electrode of the electrostatic lens of the lowest layer constituting the electron optical system, or a structural member for maintaining the electrode.

[0030] The control computer 110 includes a drawing control unit 30, a pattern density distribution calculation unit 31, a dose distribution calculation unit 32, an irradiation dose distribution calculation unit 33, a coverage electron dose distribution calculation unit 34, a charge quantity distribution calculation unit 35, a drawing elapsed time calculation unit 36, a cumulative time calculation unit 37, a position shift amount distribution calculation unit 38, and an applied voltage setting unit 39. Each component of the control computer 110 can be composed of hardware including electrical circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices, or software. Input data and calculation results of each component of the control computer 110 are stored in the memory 142.

[0031] The control computer 120 has the functions of a transmission data generating unit 41 and a position shift correcting unit 42. The transmission data generating unit 41 and the position shift correcting unit 42 may be configured by software or hardware.

[0032] The deflection control circuit 130 has the functions of the shaping deflector control unit 43 and the objective lens deflector control unit 44. The shaping deflector control unit 43 and the objective lens deflector control unit 44 may be configured by software or hardware.

[0033] The storage device 140 stores drawing data (layout data) that defines a plurality of graphic patterns to be drawn.

[0034] Electron beam 6 emitted from electron gun 5 (emitting unit) illuminates the entire first aperture 8, which has a rectangular hole, through illumination lens 7. Here, electron beam 6 is first shaped into a rectangular shape. After passing through first aperture 8, the first aperture image of electron beam 6 is projected onto second aperture 11 by projection lens 9. The position of the first aperture image on second aperture 11 is deflected by shaping deflector 10 controlled by shaping deflector control unit 43, enabling the beam shape and size to be varied (variable shaping).

[0035] The electron beam 6 of the second aperture image after passing through the second aperture 11 is focused by the objective lens 12, deflected by a deflector (objective lens deflector 13), for example, of an electrostatic type, which is controlled by the objective lens deflector control unit 44, and irradiated onto a desired position of the substrate 2 on the XY worktable 3 configured to be movable. The XY worktable 3 is driven and controlled by the worktable control unit 46. The position of the XY worktable 3 is detected by the worktable position detection unit 45. The worktable position detection unit 45 includes, for example, a laser length measuring device that irradiates a laser onto the reflector 4 and measures the position based on the interference between the incident light and the reflected light. The electrostatic lens 15 dynamically corrects the focal position of the electron beam 6 (dynamic focusing) in accordance with the concave and convex portions of the surface of the substrate 2.

[0036] Figure 3 This figure illustrates the movement of the worktable. When drawing on a substrate 2, the XY worktable 3 is continuously moved, for example, in the X direction. The drawing area is virtualy divided into a plurality of long strip regions (SR) based on the deflectable width of the electron beam 6. Drawing is performed in units of strip regions. The XY worktable 3 is continuously moved in the X direction, for example, while the emission position of the electron beam 6 also follows the movement of the worktable. Continuous movement can shorten drawing time.

[0037] After drawing a strip area, the XY table 3 is fed in steps in the Y direction to draw the next strip area in the X direction (reverse direction). By making the drawing operation of each strip area proceed in a serpentine manner, the movement time of the XY table 3 can be shortened.

[0038] When processing layout data (drawing data), the drawing area is virtually divided into multiple strip-shaped frame areas in the drawing device 100, and data processing is performed on each frame area. Without multiple exposures, the frame area and the strip area are typically the same area. With multiple exposures, the frame area and the strip area are offset depending on the degree of multiple exposures. Thus, the drawing area of ​​the substrate 2 is virtually divided into multiple frame areas (strip areas) that serve as drawing unit areas, and the drawing unit W draws on each frame area (strip area).

[0039] It is known that when an electron beam is irradiated to the resist layer of the substrate 2, the beam irradiation position is offset due to the resist charging effect. In this embodiment, in the charging effect correction, the covering electron amount distribution is calculated based on the irradiation amount distribution of the electron beam irradiated to the substrate 2 and the extended distribution of the covering electrons extending from the irradiated area of ​​the irradiated electron beam to the non-irradiated area. The irradiation amount distribution and the covering electron amount distribution are used to calculate the charge amount distribution (direct charging) of the irradiated area and the charge amount distribution (covered charging) of the non-irradiated area. Then, based on the charge amount distribution of the irradiated area and the charge amount distribution of the non-irradiated area, the position offset distribution of the electron beam on the substrate 2 is calculated to correct the beam irradiation position.

[0040] The inventors found that: Figure 4a As shown, the low-energy secondary electrons among the covering electrons that contribute to charging are deviated to a location deviated from the beam irradiation position under the influence of the leakage magnetic field and leakage electric field from the electron optical system to the drawing chamber, and then charged. Therefore, the spread distribution deviates from the irradiation area R of the electron beam, which reduces the correction effect of the beam irradiation position. Furthermore, the present inventors have found that: Figure 4b As shown, low-energy secondary electrons are actively pushed back to the irradiation area R by an electric field in the direction from the substrate 2 toward the potential regulating component 16, thereby enabling the same treatment as "direct charging" at the same position as the irradiation area R to be performed, and enabling the offset of the irradiation position of the beam to be corrected with high precision.

[0041] In this embodiment, in order to form an electric field in a direction from the substrate 2 toward the potential regulating member 16, a voltage is applied to the potential regulating member 16 and / or the substrate so that the substrate potential is higher than the potential of the lower surface of the potential regulating member 16. For example, a voltage is applied by the voltage control circuit 150 so that the substrate 2 has a positive potential or the lower surface of the potential regulating member 16 has a negative potential.

[0042] Figure 5This flowchart illustrates a method for determining the voltage applied to the potential defining member 16 and / or the substrate in this embodiment. The method includes a pattern density distribution calculation step (step S100), a dose distribution calculation step (step S102), an irradiation amount distribution calculation step (step S104), a cover electron amount distribution calculation step (step S106), a charge amount distribution calculation step (step S108), a positional offset distribution calculation step (step S110), a deflection position correction step (step S112), a drawing step (step S114), and an analysis step (step S116).

[0043] In the pattern density distribution calculation step (step S100), the pattern density distribution calculation unit 31 reads the drawing data of the evaluation pattern from the storage device 140, virtualizes the drawing area (or frame area) into a grid with a predetermined grid size (grid size), and calculates the pattern density ρ, which represents the arrangement ratio of the graphic pattern defined in the drawing data, for each grid area (the charging effect correction grid). Then, a pattern density distribution ρ(x, y) is generated for each grid area.

[0044] In the dose distribution calculation process (step S102), the dose distribution calculation unit 32 uses the pattern density distribution ρ(x, y) to calculate the dose distribution D(x, y) for each grid area. The dose calculation preferably includes a proximity effect correction based on backscattered electrons. The dose D can be defined by the following equation (1).

[0045] (1)D=D0×{(1+2×η) / (1+2×η×ρ)}

[0046] In formula (1), D0 is the reference dose and η is the backscattering rate.

[0047] The reference dose D0 and the backscattering rate η are set by the user of the drawing apparatus 100. The backscattering rate η can be set in consideration of the acceleration voltage of the electron beam 6, the resist film thickness of the substrate 2, the type of base substrate, and process conditions (eg, PEB conditions, development conditions).

[0048] In the irradiation distribution calculation process (step S104), the irradiation distribution calculation unit 33 calculates the irradiation distribution E(x, y) (also called "irradiation intensity distribution") of each grid area by multiplying each grid value of the pattern density distribution ρ(x, y) with the corresponding grid value of the dose distribution D(x, y).

[0049] In the covering electron amount distribution calculation step (step S106), the covering electron amount distribution calculation unit 34 (covering charged particle amount distribution calculation unit) calculates the covering electron amount distribution F (covering charged particle amount distribution) by performing a convolution integral on the covering electron distribution function g and the irradiation amount distribution E = ρD calculated in step S104. The covering electron distribution function g can use a Gaussian distribution, for example.

[0050] The distribution function g(x, y) and the coverage electron quantity distribution F(x, y) can be defined by the following equations, respectively.

[0051] (2) g(x, y) = (1 / πσ 2 )×exp[-{x 2 +y 2} / σ 2 ]

[0052] (3)F(x,y)=∫∫g(x,y)E(x',y')dx'dy'

[0053] In the formula (2), σ is a constant representing the influence radius of the covering electron.

[0054] In the charge amount distribution calculation step (step S108 ), the charge amount distribution calculation unit 35 calculates the charge amount distribution C(x, y) using the irradiation amount distribution E, the cover electron amount distribution F, and the charge attenuation amount with the passage of time.

[0055] First, the elapsed time t after the charged portion is drawn (irradiated) is calculated. The drawing elapsed time calculation unit 36 ​​calculates the elapsed time T1(x, y) from the drawing start time (the time when drawing of the layout start or the first frame starts) to the actual drawing time for each position on the substrate 2. For example, when the corresponding frame area (strip area) is the i-th frame area, the estimated time from the drawing start time of the drawing start position to the drawing of each position (x, y) of the previous i-1-th frame area (strip area) is calculated as the elapsed time T1(x, y).

[0056] Next, the cumulative time calculation unit 37 calculates the cumulative time T2 obtained by accumulating the drawing time required for drawing the completed drawing unit area (e.g., frame area, strip area). For example, when the currently corresponding frame area is the i-th frame area, the cumulative value is calculated by adding the time T2(1) used to draw the first frame area, the time T2(2) used to draw the second frame area, and the time T2(i) used to draw the i-th frame area. In this way, the cumulative time T2 up to the corresponding frame area can be obtained.

[0057] Here, when drawing is actually performed within the frame area currently being processed, since drawing has already been completed by the previous frame area, the portion irradiated by the electron beam 6 in the previous frame area becomes the charged portion. Therefore, the difference (T2-T1) obtained by subtracting the drawing elapsed time T1(x, y) of each position (x, y) in the previous frame area with the charged portion from the accumulated time T2 of the current frame area becomes the elapsed time t after the charged portion is drawn.

[0058] The function used to calculate the charge distribution C(x, y) includes a direct charge term, which is the contribution of the irradiated electrons, and a covered charge term, which is the contribution of the covered electrons. The direct charge term and the covered charge term each include a decay term, which is the contribution of time, and a static term, which is not the contribution of time. Each decay term uses the charge decay value (i.e., the charge amount immediately after plotting, based on the charge amount after a sufficient period of time) and the charge decay time constant.

[0059] First, assume the function C(E, F, t) for obtaining the charge distribution C(x, y). Specifically, the variable C(E, F, t) is separated into the contribution of the irradiated electrons. E (E, t) and the variable C covering the electronic contribution F (F, t). Then, separate each variable into the decay term C that contributes to the passage of time. ET (t), C FT (t) and the static term C which does not contribute to the elapsed time ES (E), C FS (F). Function C(E, F, t) is defined by the following formula (4).

[0060] (4) C(x, y) = C(E, F, t)

[0061] =C E (E, t) + C F (F, t)

[0062] =C ES (E)+C ET (t)+C FS (F)+C FT (t)

[0063] In addition, the variable C ES (E), C ET (t), C FS (F), C FT (t) is defined by the following equations (5), (6), (7), and (8).

[0064] (5)C ES (E) = d0 + d1 × ρ + d2 × D + d3 × E

[0065] (6)C ET (t) = κ E (ρ)·exp{-t / λ E (ρ)}

[0066] (7)C FS (F) = f1×F+f2×F 2 +f3×F 3

[0067] (8)C FT (t) = κ F (ρ)·exp{-t / λ F (ρ)}

[0068] Here, d0, d1, d2, d3, f1, f2, and f3 are constants.

[0069] In addition, the charge attenuation κ used in equations (6) and (8) depends on the pattern density ρ. E (ρ),κ F (ρ) can be approximated by the following equations (9) and (10), for example. Here, equations (9) and (10) are quadratic functions, but are not limited thereto and may be high-order functions or low-order functions.

[0070] (9)κ E (ρ)=κ E0 +κ E1 ρ+κ E2 ρ 2

[0071] (10)κ F (ρ)=κ F0 +κ F1 ρ+κ F2 ρ 2

[0072] Here, κ E0 , κ E1 , κ E2 , κ F0 , κ F1 , κ F2 is a constant.

[0073] Furthermore, the charge decay time constant λ used in equation (4) and dependent on the pattern density ρ is E (ρ), λ F (ρ) can be approximated by, for example, the following equations (11) and (12). Here, equations (11) and (12) are quadratic functions, but are not limited thereto and may be high-order functions or low-order functions.

[0074] (11)λ E(ρ)=λE0+λE1ρ+λE2ρ 2

[0075] (12)λ F (ρ)=λ F0 +λ F1 ρ+λ F2 ρ 2

[0076] Here, λ E0 ,λ E1 ,λ E2 ,λ F0 ,λ F1 ,λ F2 is a constant. That is, the charge distribution C(x, y) can be expressed as Figure 6 The formula shown is defined.

[0077] The coefficients of equations (2), (3), (5), (7), (9) to (12) can be obtained by fitting (approximating) the experimental results and / or simulation results. Data related to these coefficients are stored in the storage device 21.

[0078] In the positional offset distribution calculation step (step S110), the positional offset distribution calculation unit 38 (positional offset calculation unit) calculates the positional offset based on the charge amount distribution. Specifically, the positional offset distribution calculation unit 38 calculates the positional offset P of the drawing position (x, y) caused by the charge amount at each position (x, y) of the charge amount distribution C(x, y) by performing a convolution integral on the charge amount distribution calculated in step S108 and the response function r(x, y).

[0079] Assume that the charge distribution C(x, y) is converted into a response function r(x, y) of the position offset distribution P(x, y). Here, (x', y') represents the charged position represented by each position of the charge distribution C(x, y), and (x, y) represents the beam irradiation position of the corresponding frame area (for example, the i-th frame area) currently undergoing data processing. Here, the position offset of the beam can be expressed as a function of the distance from the beam irradiation position (x, y) to the charged position (x', y'), so the response function can be described as r(x-x', y-y'). The response function r(x-x', y-y') can be obtained in advance by conducting experiments in a manner consistent with the experimental results, or by numerical calculation. In the following, (x, y) represents the beam irradiation position of the corresponding frame area currently undergoing data processing.

[0080] The positional offset distribution calculation unit 38 then creates a positional offset distribution Pi(x, y) (also referred to as a positional offset map Pi(x, y)) based on the positional offset P at each position (x, y) in the frame region to be rendered. The calculated positional offset map Pi(x, y) is stored in the storage device 21 and output to the control computer 120.

[0081] On the other hand, in the control computer 120, the emission data generating unit 41 reads the depiction data from the storage device 140, performs multi-stage data conversion processing, and generates the emission data of the format inherent to the drawing device 100. The size of the graphic pattern defined in the depiction data is usually larger than the emission size that the drawing device 100 can form by a single emission. Therefore, in the drawing device 100, each graphic pattern is segmented (emission segmentation) into a plurality of emission graphics to become the size that the drawing device 100 can form by a single emission. Then, for each emission graphic, the data such as the graphic code, coordinates and size representing the type of graphic are defined as the emission data.

[0082] In the deflection position correction process (step S112) (position offset correction process), the position offset correction unit 42 uses the position offset calculated in step S110 to correct the irradiation position. Here, the emission data of each position is corrected. Specifically, each position (x, y) of the emission data is added to the correction value of the position offset shown in the correction position offset map Pi (x, y). The correction value is preferably a value that makes the positive and negative signs of the position offset shown in the position offset map Pi (x, y) opposite. Thus, in the case of irradiating the electron beam 6, the coordinates of the irradiation destination are corrected, and therefore, the deflection position deflected by the objective lens deflector 13 is corrected. The emission data is defined in the data file in a manner arranged in the order of emission.

[0083] In the drawing process (step S114), within the deflection control circuit 130, in accordance with the emission order, the shaping deflector control unit 43 calculates the deflection amount of the shaping deflector 10 for deforming the electron beam 6 for each emission pattern based on the pattern type and size defined in the emission data. In addition, the objective lens deflector control unit 44 calculates the deflection amount of the objective lens deflector 13 for deflecting to the position on the substrate 2 that irradiates the emission pattern. In other words, the objective lens deflector control unit 44 (deflection amount calculation unit) calculates the deflection amount for deflecting the electron beam to the corrected irradiation position. Then, the objective lens deflector 13 disposed in the electron lens barrel 1 deflects the electron beam according to the calculated deflection amount, thereby irradiating the electron beam to the corrected irradiation position. Thus, the drawing unit W draws the evaluation pattern at the position on the substrate 2 after the charge correction.

[0084] Figure 7a 、 7bis a diagram showing an example of an evaluation pattern. Figure 7a and Figure 7b In order to make it easier to understand, the scales are changed for representation. After drawing the first box array on a grid (81×81 grid) with a pitch L1 of 200μmm and a side length L2 of 20mm, an irradiation pad with a pattern density of 100% and a side length L3 of 10mm is drawn in the center of the test layout. Then, the second box array is drawn on the same grid as the first box array, thereby obtaining Figure 7a The test layout is shown.

[0085] like Figure 7b As shown in the enlarged image, the first cell array is, for example, a square pattern with a side length L4 of 4 μm. Furthermore, the second cell array is, for example, a frame-shaped pattern with a side length L5 of 14 μm, larger than the first cell array and hollowed out in the center. By measuring the positions of the first and second cell arrays depicted above and subtracting the position of the first cell array from the position of the second cell array, it is possible to measure positional deviations caused by the charging effect of the irradiation pad.

[0086] The evaluation pattern is drawn multiple times by swinging the voltage applied to the potential regulating member 16 and / or the substrate. Thus, multiple evaluation patterns having different electric field intensities in the direction from the substrate 2 toward the objective lens 12 (potential regulating member 16) are drawn on the substrate 2 while correcting for the charging effect.

[0087] Figure 8a The positional offset distribution obtained from the above evaluation pattern is shown. As described above, low-energy secondary electrons drift to locations offset from the beam irradiation position due to the influence of leakage magnetic and electric fields from the electron optical system to the drawing chamber, and then become charged. Consequently, the spread distribution deviates from the electron beam irradiation area R (low-energy coverage charge), reducing the correction effect of the beam irradiation position.

[0088] Figure 8b It represents the position offset distribution after correction of the charging effect of the evaluation pattern under the applied voltage V. Under the influence of the low energy coverage charge, as shown by the dotted line, it can be seen that the correction residual is generated at the end of the irradiation area. Here, in the analysis process (step S116), the low energy coverage electron charge distribution CL(L) is considered. L represents the low energy coverage electron quantity distribution. The charge quantity distribution C(x, y) can be expressed by adding CL(L) to formula (4) as follows:

[0089] (13)C(x,y)=C(E,F,t)+CL(L).

[0090] Furthermore, the low-energy covering electron amount distribution L(x, y) and the low-energy covering electron distribution function gL(x, y) can be defined by the following equations, respectively.

[0091] (14)gL(x,y)

[0092] =(1 / πσL2)×exp[-{(x-Δx) 2 +(y-Δy) 2} / σL2]

[0093] (15)L(x,y)=∫∫g(x,y)E(x',y')dx'dy'

[0094] Here, Δx and Δy are constants representing the amount of displacement of low-energy cover electrons from the beam irradiation position due to the influence of leakage magnetic fields, leakage electric fields, etc. from the electron optical system to the drawing chamber.

[0095] In addition, the variable CL(L) is defined by the following equation.

[0096] (16)CL(L)=l1×L+l2×L2+l3×L3

[0097] Here, l1, l2, and l3 are constants.

[0098] For the position offset map after the charging effect correction (refer to Figure 8b ), and further applying the additional correction amount distribution calculated based on the charge distribution represented by equations (13) to (16), it is possible to determine l1, l2, l3, Δx, and Δy with the smallest correction residual.

[0099] Figure 8c is a low energy overlay charge distribution assuming a shift in the center distribution, relative to Figure 8b Optimize l1, l2, l3, Δx, and Δy to minimize the correction residual, and add the position offset distribution after correction. Figure 9 As shown in the relationship between the applied voltage and Δx, the center distribution shift amount is calculated to be Δx = 200 μm and Δy = 0 μm.

[0100] However, the Δx calculated from the above results represents the offset of the low-energy covering electrons from the irradiation position. This value is optimized relative to the evaluation pattern described above. In actual practice, any arbitrary drawing pattern (product pattern) is not necessarily charged by a shift of Δx. Specifically, the area already charged by drawing is affected by the generated electric field, and thus becomes larger or smaller depending on the drawing pattern. Therefore, simply performing a correction for the charging effect that takes Equation (13) into account will result in a correction residual in any drawing pattern.

[0101] In this embodiment, in the analysis step (step S116), the drawing result of the evaluation pattern is analyzed to obtain the relationship between the applied voltage and the positional deviation from the designed position of the drawing pattern. Figure 9 The relationship between the voltage applied to the plate and the positional offset Δx is shown. When the applied voltage is small, secondary electrons drift due to the influence of leakage magnetic fields and become charged at positions deviating from the directly charged area. Therefore, Δx ranges from 1 mm to several hundred μm, for example.

[0102] If the applied voltage is sufficiently increased, the charged position of the secondary electrons approaches the directly charged region, and the correction residual gradually decreases. When the position offset Δx is sufficiently small (e.g., less than 1 / 10 of the charging effect correction grid size), for example, Δx = 0, the applied voltage Vset is calculated and stored as applied voltage information in the storage device 21.

[0103] In the drawing (actual drawing) of the product pattern, the drawing data of the product pattern is read from the storage device 140 and the Figure 5 The same processing is performed as in steps S100 to S112.

[0104] At this time, the offset of the distribution center of the low-energy covered charged distribution from the irradiation position is always smaller than the charging effect correction grid, and can actually be treated in the same way as the direct charged distribution. Therefore, for any drawing pattern (product pattern), the correction residual caused by the low-energy covered electrons can be eliminated.

[0105] In the above embodiment, when applying a voltage to the substrate 2 , it is preferable to apply the voltage so that the mark M also has the same potential. This can reduce the difference in focus and deflection shape between the substrate 2 and the mark M.

[0106] In addition, when the potential difference between the mark M and the substrate 2 is kept constant and the calibration difference (focusing difference, deflection shape difference, etc.) is stable, even if the mark M is not set to the same potential as the substrate 2, the difference is calculated once based on the drawing result. Thereafter, it is sufficient to feed back the difference for drawing.

[0107] During the drawing, the voltage applied to the potential regulating member 16 and / or the substrate can be made variable and used as a dynamic focusing function to adjust the focus. The adjustment range of the applied voltage is the range in which the charging tendency remains constant, for example, Figure 9 The positional deviation amount Δx in the graph shown is within a range of Δx=0, for example, equal to or less than a predetermined value (grid size for correcting the charging effect).

[0108] The displacement of the irradiation position due to the charging phenomenon is not limited to electron beam imaging devices. The present invention is applicable to charged particle beam irradiation devices that use the results of irradiating a target position with a charged particle beam, such as an electron beam, and other inspection devices that inspect patterns.

[0109] While the present invention has been described in detail using specific embodiments, it will be apparent to one skilled in the art that various modifications can be made therein without departing from the spirit and scope of the invention.

[0110] This application is based on Japanese Patent Application No. 2020-083979 filed on May 12, 2020, the entire contents of which are incorporated herein by reference.

[0111] Explanation of symbols

[0112] 1: Electron lens; 2: Substrate; 3: XY stage; 4: Reflector; 5: Electron gun; 6: Electron beam; 7: Illumination lens; 8: First aperture; 9: Projection lens; 10: Deflector; 11: Second aperture; 12: Objective lens; 13: Deflector; 14: Drawing chamber; 15: Electrostatic lens; 16: Potential setting unit; 21, 140: Storage device; 30: Drawing control unit; 31: Pattern density distribution calculation unit; 32: Dose distribution calculation unit; 33: Exposure distribution meter Calculation unit; 34: Covered electron quantity distribution calculation unit; 35: Charge quantity distribution calculation unit; 36: Drawing elapsed time calculation unit; 37: Accumulated time calculation unit; 38: Position offset quantity distribution calculation unit; 39: Applied voltage setting unit; 41: Emission data generation unit; 42: Position offset correction unit; 43: Forming deflector control unit; 44: Objective lens deflector control unit; 45: Workbench position detection unit; 46: Workbench control unit; 100: Drawing device; 150: Voltage control circuit.

Claims

1. A charged particle beam drawing method, wherein a charged particle beam is deflected by a deflector, focused by an objective lens, and a pattern is drawn on a substrate on a workbench, comprising: a step of virtually dividing the drawing area of ​​the substrate into a predetermined grid size and calculating a pattern density distribution representing an arrangement ratio of the pattern in each grid area; a step of calculating a dose distribution representing a dose for each grid area using the pattern density distribution; a step of calculating an irradiation dose distribution of the charged particle beam to be irradiated onto the substrate using the pattern density distribution and the dose distribution; a step of calculating a distribution of covered charged particles by performing a convolution integral on a distribution function of covered charged particles and the irradiation dose distribution; a step of calculating a charge amount distribution resulting from direct charging using the pattern density distribution, the dose distribution, and the irradiation amount distribution, and calculating a charge amount distribution resulting from cover charging using the cover charged particle amount distribution; a step of calculating a positional shift amount based on a charge amount distribution resulting from the direct charging and a charge amount distribution resulting from the overlay charging; a step of correcting the irradiation position using the positional deviation; and A process of forming an electric field by applying a predetermined voltage calculated in advance based on the relationship between the voltage and the position offset from the designed position of the depicted pattern to at least either one of the substrate and the potential regulating component in such a manner that the potential of the surface of the substrate is higher than the potential of the lower surface of the potential regulating component arranged at a position opposite to the substrate, and irradiating the charged particle beam to the corrected irradiation position.

2. The charged particle beam drawing method according to claim 1, wherein: The electric field is obtained in advance based on the relationship between the magnitude of the electric field and the positional shift of the distribution center of the covered charged particle amount distribution, and the positional shift of the distribution center is smaller than the predetermined grid size.

3. The charged particle beam drawing method according to claim 1, wherein: The substrate was set to a positive potential.

4. The charged particle beam drawing method according to claim 3, wherein: The mark for calibration provided on the stage was set to the same potential as that of the substrate.

5. The charged particle beam drawing method according to claim 1, wherein: The lower surface of the potential regulating member is set to a negative potential. The charged particle beam drawing method according to claim 1 , wherein: The focus adjustment of the charged particle beam is performed by controlling a voltage applied to at least one of the substrate and the potential regulating member.

7. A charged particle beam drawing device that deflects a charged particle beam using a deflector, focuses it using an objective lens, and draws a pattern on a substrate on a worktable, comprising: an emitting unit for emitting the charged particle beam; a pattern density distribution calculation unit that virtually divides the drawing area of ​​the substrate into a grid shape and calculates a pattern density distribution representing the arrangement ratio of the pattern in each grid area; a dose distribution calculation unit that calculates a dose distribution representing a dose for each grid area using the pattern density distribution; an irradiation dose distribution calculation unit that calculates an irradiation dose distribution of the charged particle beam emitted from the emission unit and irradiated onto the substrate, using the pattern density distribution and the dose distribution; a coverage charged particle amount distribution calculation unit that calculates the coverage charged particle amount distribution by performing a convolution integral on the distribution function of the coverage charged particles and the irradiation amount distribution; a charge amount distribution calculation unit that calculates a charge amount distribution caused by direct charging using the pattern density distribution, the dose distribution, and the irradiation amount distribution, and calculates a charge amount distribution caused by cover charging using the cover charged particle amount distribution; a position shift amount distribution calculation unit that calculates a position shift amount for each drawing position based on a charge amount distribution resulting from the direct charging and a charge amount distribution resulting from the overlay charging; a correction unit that corrects the irradiation position using the position offset; A potential regulating member is arranged at a position facing the substrate and is controlled to a predetermined potential; a voltage control circuit for applying a predetermined voltage, calculated in advance based on a relationship between the voltage and the positional offset from the designed position of the drawn pattern, to at least one of the substrate and the potential regulating member so that the potential of the surface of the substrate is higher than the potential of the lower surface of the potential regulating member, thereby forming an electric field in a direction from the substrate toward the objective lens; and The drawing unit irradiates the corrected irradiation position with the charged particle beam in a state where the electric field is formed.

8. The charged particle beam drawing device according to claim 7, wherein The voltage control circuit applies a positive potential to the substrate. The mark for calibration provided on the stage is set to the same potential as that of the substrate.

9. The charged particle beam drawing device according to claim 8, wherein A storage device is provided for storing, as applied voltage information, an applied voltage at which a positional shift (Δx) calculated in advance based on the relationship between the magnitude of the electric field and the positional shift of the distribution center covering the charged particle amount distribution is equal to or less than a predetermined value.

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