Charged particle beam drawing method and charged particle beam drawing apparatus

Abstract

The present invention enables rapid and accurate computation of an electric charge amount in a substrate. This charged particle beam drawing method comprises: a step (S100) for virtually dividing, into mesh-like regions, a drawing region of a substrate to be subjected to drawing, and computing a pattern density that shows the arrangement proportion of a pattern in each of the mesh-like regions; a step (S102) for computing a dose amount in each of the mesh-line regions using the pattern density; a step (S104) for computing, by using an electric charge amount computation function that employs a predetermined film thickness of a resist film and the dose amount as variables, an electric charge amount from the film thickness of the resist film formed on the substrate and the computed dose amount; a step (S106) for computing a positional deviation amount of a drawing position on the basis of the computed electric charge amount; and a step (S108) for correcting the irradiation position of the charged particle beam using the positional deviation amount.

Description

[Technical field]

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

[0002] As LSIs become more highly integrated, the circuit line width required for semiconductor devices is becoming finer year by year. To form the desired circuit pattern on a semiconductor device, a method is adopted in which a high-precision original pattern (mask, or particularly one used in steppers and scanners, called a reticle) formed on quartz is reduced and transferred onto a wafer using a reduction projection exposure apparatus. The high-precision original pattern is drawn by an electron beam drawing apparatus, and so-called electron beam lithography technology is used.

[0003] When an electron beam is irradiated onto a substrate such as a mask, the irradiation position and its surroundings are charged by the electron beam irradiated in the past, causing the irradiation position to shift. Conventionally, as one of the methods for eliminating this beam irradiation position shift, a method of forming an anti-charge film (CDL: Charge Dissipation Layer) on the substrate to prevent the substrate surface from being charged is known. However, since this anti-charge film basically has acid properties, it is not compatible with a substrate coated with a chemically amplified resist. In addition, it is necessary to install new equipment to form the anti-charge film, which further increases the manufacturing cost. For this reason, it is desired to perform charging effect correction (CEC: Charging Effect Correction) without using an anti-charge film.

[0004] In conventional charge effect correction, the dependence of the charge on the amount of beam irradiation was obtained from the drawing evaluation for each substrate. Therefore, every time the resist film thickness or the concentration of the acid generator contained in the resist was changed, it was necessary to draw an evaluation pattern and evaluate the drawing result in order to estimate the amount of charge on the substrate, which was time-consuming. In addition, the downtime of the equipment was prolonged.

[0005] [Patent Document 1] JP 2002-158167 A [Patent Document 2] Japanese Patent Application Publication No. 10-027753 [Patent Document 3] Japanese Patent Application Publication No. 61-142740 [Patent Document 4] Patent No. 5480555 [Patent Document 5] Patent No. 5480496 Summary of the Invention

[0006] An object of the present invention is to provide a charged particle beam drawing method and a charged particle beam drawing apparatus that can quickly and accurately calculate the amount of charge on a substrate.

[0007] A charged particle beam lithography method according to one aspect of the present invention is a charged particle beam lithography method for irradiating a substrate on which a resist film has been formed with a charged particle beam by deflecting the charged particle beam with a deflector to draw a pattern, the method comprising the steps of: virtually dividing a drawing region of the substrate into a mesh shape and calculating a pattern density indicating an arrangement ratio of the pattern in each mesh region; calculating a dose amount for each mesh region using the pattern density; calculating an amount of charge from a film thickness of the resist film formed on the substrate and the calculated dose amount using a function for calculating an amount of charge having a predetermined film thickness and a dose amount of the resist film as variables; calculating a positional deviation amount of a drawing position from the calculated amount of charge; and correcting an irradiation position of the charged particle beam using the positional deviation amount, wherein the function for calculating the amount of charge is determined from parameters representing physical properties of the resist film, and the physical properties include at least one of a secondary electron emission probability, a dielectric constant, a resistivity during beam irradiation, a work function, and a hole remaining rate of the resist. The charge amount calculation function does not depend on the dose sensitivity of the resist film. It is something.

[0008] A charged particle beam drawing apparatus according to one aspect of the present invention is a charged particle beam drawing apparatus that deflects a charged particle beam by a deflector, and irradiates the charged particle beam onto a substrate on which a resist film has been formed to draw a pattern, the charged particle beam drawing apparatus including: an emission unit that emits the charged particle beam; a pattern density calculation unit that virtually divides a drawing region of the substrate into a mesh shape and calculates a pattern density indicating an arrangement ratio of the pattern for each mesh region; a dose amount calculation unit that calculates a dose amount indicating a dose amount for each mesh region using the pattern density; a memory unit that stores a function for calculating a charge amount using a film thickness and a dose amount of the resist film as variables; a charge amount calculation unit that calculates a charge amount from the film thickness of the resist film formed on the substrate and the dose amount calculated by the dose amount calculation unit using the function; a positional deviation calculation unit that calculates a positional deviation amount of a writing position from the charge amount; a correction unit that corrects the irradiation position of the charged particle beam using the positional deviation amount; and a writing unit that irradiates the charged particle beam at the corrected irradiation position, wherein the function for calculating the charge amount is determined from parameters that represent physical properties of the resist film, and the physical properties include at least one of a secondary electron emission probability, a dielectric constant, a resistivity during beam irradiation, a work function, and a hole remaining rate of the resist. The charge amount calculation function does not depend on the dose sensitivity of the resist film. Effects of the Invention

[0009] According to the present invention, the charge amount of a substrate can be calculated quickly and accurately. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of a drawing device according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a diagram for explaining the state of stage movement. [Diagram 3] FIG. 3a is a schematic diagram showing ionization in a resist layer, and FIG. 3b is a diagram showing an equivalent circuit simulating a resist film. [Figure 4] FIG. 4a shows the test layout used to measure the resist charging effect, and FIG. 4b is a schematic diagram of the box array. [Diagram 5]FIG. 13 is a diagram showing an example of a distribution of misalignment amounts obtained from evaluation of a test layout. [Figure 6] FIG. 13 is a diagram showing an example of a distribution of positional deviation amounts obtained from a calculation formula. [Figure 7] 7a and 7b are graphs showing the correlation of the distribution of the amount of positional deviation. [Figure 8] 8a to 8d are graphs comparing the drawing evaluation results with the function calculation results. [Figure 9] 11 is a flowchart illustrating a drawing method according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiment, a configuration using an electron beam as an example of a charged particle beam will be described. However, the charged particle beam is not limited to an electron beam, and an ion beam or the like may be used.

[0012] Fig. 1 is a schematic diagram of a drawing apparatus according to an embodiment. The drawing apparatus 100 shown in Fig. 1 includes a drawing unit W and a control unit C. The drawing apparatus 100 is an example of an electron beam drawing apparatus. The drawing unit W includes an electron lens barrel 1 and a drawing chamber 14. Inside the electron lens barrel 1, an electron gun 5, an illumination lens 7, a first aperture plate 8, a projection lens 9, a shaping deflector 10, a second aperture plate 11, an objective lens 12, an objective deflector 13, and an electrostatic lens 15 are arranged.

[0013] An XY stage 3 is placed in the drawing chamber 14. A substrate 2 to be drawn is placed on the XY stage 3. The substrate 2 includes a photomask used for exposure in semiconductor manufacturing, a semiconductor wafer for forming a semiconductor device, and the like. The photomask to be drawn includes a mask blank on which nothing has been drawn yet. For example, the substrate 2 has quartz, a chrome film provided on the quartz, and a resist layer provided on the chrome film. A mirror 4 for measuring the stage position is placed on the XY stage 3 at a position different from the position where the substrate 2 is placed.

[0014] A calibration mark M is provided on the XY stage 3 at a position different from the position where the substrate 2 is placed. For example, the mark M is a metallic cross shape, and the mark M is scanned with an electron beam, and the reflected electrons from the mark M are detected by a detector (not shown) to perform focus adjustment, position adjustment, adjustment of the deflection shape correction coefficient, and the like.

[0015] The control unit C includes control computers 110 and 120, a stage position detection unit 45, a stage control unit 46, a deflection control circuit 130, a memory 142, and storage devices 21 and 140 such as magnetic disk devices. The deflection control circuit 130 is connected to the shaping deflector 10 and the objective deflector 13.

[0016] The control computer 110 has the functions of a writing control unit 30 that controls the entire apparatus, a pattern density distribution calculation unit 32, a dose amount distribution calculation unit 34, a charge amount distribution calculation unit 36, and a position deviation amount distribution calculation unit 38. Each unit of the control computer 110 may be configured with hardware including an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device, or may be configured with software. Input data and calculation results of each unit of the control computer 110 are stored in a memory 142.

[0017] The control computer 120 has the functions of a shot data generating unit 41 and a positional deviation correcting unit 42. The shot data generating unit 41 and the positional deviation correcting unit 42 may be configured as software or hardware.

[0018] The deflection control circuit 130 has the functions of a shaping deflector control unit 43 and an objective deflector control unit 44. The shaping deflector control unit 43 and the objective deflector control unit 44 may be configured by software or hardware.

[0019] The storage device 140 stores drawing data (layout data) that defines a plurality of graphic patterns to be drawn.

[0020] Electron beam 6 emitted from electron gun 5 (emitter) illuminates the entire first aperture plate 8, which has a rectangular hole, by illumination lens 7. Here, electron beam 6 is first shaped into a rectangle. The electron beam 6 of the first aperture image having passed through first aperture plate 8 is projected onto second aperture plate 11 by projection lens 9. The position of the first aperture image on second aperture plate 11 is deflected by shaping deflector 10 controlled by shaping deflector control unit 43, making it possible to change the beam shape and dimensions (variable shaping).

[0021] The electron beam 6 of the second aperture image having passed through the second aperture plate 11 is focused by the objective lens 12, deflected by, for example, an electrostatic deflector (objective deflector 13) controlled by an objective deflector control unit 44, and irradiated onto a desired position of the substrate 2 on the movably arranged XY stage 3. The XY stage 3 is driven and controlled by a stage control unit 46. The position of the XY stage 3 is detected by a stage position detection unit 45. The stage position detection unit 45 includes, for example, a laser length measurement device that irradiates a laser onto the mirror 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 in response to the unevenness of the surface of the substrate 2 (dynamic focus).

[0022] 2 is a diagram for explaining the state of stage movement. When drawing on the substrate 2, the XY stage 3 is moved continuously in, for example, the X direction. The drawing area is virtually divided into a plurality of rectangular stripe areas (SR) by the deflectable width of the electron beam 6. The drawing process is performed in stripe area units. The movement of the XY stage 3 in the X direction is, for example, continuous movement, and at the same time, the shot position of the electron beam 6 is made to follow the stage movement. Continuous movement can shorten the drawing time.

[0023] After writing one stripe area, the XY stage 3 is stepped in the Y direction and the next stripe area is written in the X direction (reverse direction). By performing the writing operation for each stripe area in a zigzag manner, the movement time of the XY stage 3 can be shortened.

[0024] In the drawing apparatus 100, when processing layout data (drawing data), the drawing area is virtually divided into a plurality of rectangular frame areas, and data processing is performed for each frame area. When multiple exposure is not performed, the frame area and the stripe area are usually the same area. When multiple exposure is performed, the frame area and the stripe area are shifted according to the degree of multiplicity. In this way, the drawing area of ​​the substrate 2 is virtually divided into a plurality of frame areas (stripe areas) that serve as drawing unit areas, and the drawing unit W draws for each frame area (stripe area).

[0025] It is known that when an electron beam is irradiated onto the resist layer of the substrate 2, the beam irradiation position is shifted due to the resist charging effect. In this embodiment, the resist film thickness d and the dose D of the irradiated electron beam, which enable the charge amount (total charge amount per unit area = charge density) of the substrate surface to be calculated, are used. exp The function σ(d, D exp ) is calculated in advance and stored in the storage device 21. During the drawing process, this function σ(d, D exp ) based on the charge amount calculated from the charge amount, the amount of positional deviation of the electron beam on the substrate 2 is calculated, and the beam irradiation position is corrected.

[0026] Function σ(d, D exp ) will be explained.

[0027] The pattern density on the substrate is p, the backscattering coefficient is η, and the reference dose (the dose when the pattern density is 100%) is D 100 Then, the proximity effect corrected dose D exp is expressed by the following equation (1).

[0028] (1) D exp =D 100 *{(1 / 2+η) / (1 / 2+η*ρ)}

[0029] The number of electrons incident on a unit area of ​​resist is n pis expressed by the following equation (2) using the elementary charge e.

[0030] (2) n p =D exp *p / e

[0031] Here, when the energy of the incident electron beam is high (e.g., 50 keV), almost all of the incident electrons themselves penetrate the resist layer and the light-shielding film layer (e.g., Cr) and accumulate in the glass layer, as shown in Figure 3a. In electron beam lithography, the light-shielding film layer is usually kept at ground potential (0V), so the electric field created by these incident electrons is shielded by the light-shielding film layer and does not contribute to the charging effect of the resist. On the other hand, when the incident electrons pass through the resist layer, they interact with the material that makes up the resist, causing ionization in the resist layer. When ionization occurs near the resist surface, some of the electrons generated by ionization fly out toward the drawing chamber and become secondary electrons, and holes are generated where the electrons were originally. In this case, the probability of secondary electron / hole pairs being generated for one incident electron (secondary electron emission probability) is α.

[0032] When ionization occurs inside the resist, the multiple electron-hole pairs that are generated are randomly oriented as shown in Figure 3a, and the electric fields they generate cancel each other out, so these charges do not contribute to resist charging. However, the carrier concentration inside the resist increases, resulting in the electron beam induced conduction phenomenon described below. Since the electron-hole pairs recombine and disappear immediately after being generated, electrical conduction occurs only during beam irradiation and disappears when the beam irradiation ends.

[0033] Number of secondary electrons generated n SE Assuming that the same number of holes are supplied to the resist surface as n p The number of holes that are generated on the resist surface when electrons are incident on the resist is n h is expressed by the following equation (3).

[0034] (3) n h =n SE =n p *α

[0035] Next, let us consider the holes that accumulate on the resist surface. When electrical conduction appears inside the resist due to the EBIC (Electron Beam Induced Conductivity) effect, the resist layer can be considered as an equivalent circuit (RC circuit) as shown in Figure 3b, and the amount of charge accumulated in the capacitor of the equivalent circuit becomes the amount of charge accumulated on the resist surface. This amount of charge Q(t) can be expressed by the general RC circuit charging equation (4). In equation (4), t is the irradiation time of the electron beam, C is the electrostatic capacitance per unit area of ​​the resist, and R is the conductivity that appears only during beam irradiation due to the EBIC effect. I is the charge supplied per unit time, and is considered to be holes supplied by secondary electrons escaping from the resist.

[0036] (4) Q(t) = RCI{1-exp(-t / RC)}

[0037] When considering the charge I per unit area, it can be expressed as the following equation (5) using the current density J of the incident electron beam.

[0038] (5) I = αJ

[0039] As mentioned above, the equivalent circuit is completed by the EBIC effect only during beam irradiation, so t in equation (4) can be replaced with the irradiation time as shown in equation (6) below.

[0040] (6) t=en p / J

[0041] Therefore, n p The total charge of holes when electrons are incident on the resist is given by the following equation (7).

[0042] (7) Q(n p )=αJRC{1-exp(-en p / JRC)}

[0043] The number of holes accumulated on the resist surface, n rh is Q(np ) by the elementary charge e. Therefore, n rh is expressed by the following equation (8): If the dielectric constant of the resist is ε, the thickness of the resist is d, and the resistivity of the resist during beam irradiation is ρ, then C=ε / d and R=ρd, and therefore these can be replaced by RC=ρε.

[0044] (8) n rh =αJRC{1-exp(-en p / JRC)} / e =αJρε{1-exp(-en p / Jρε)} / e

[0045] Among the secondary electrons generated by the irradiation of the electron beam, those with an energy level equal to or lower than the surface potential Vs of the resist are attracted back to the resist and contribute to charging. Therefore, the number of secondary electrons that accumulate on the resist surface, n rSE It is necessary to consider the following. p The secondary electrons generated when the SE In this case, the increase in the number of secondary electrons accumulated in the resist is dn rSE is expressed by the following formula (9). P(E) in formula (9) is the generation probability (spectrum) of secondary electrons with energy E, and is expressed by the following formula (10).

[0046] TIFF0007628114000001.tif91140

[0047] The surface potential Vs of the resist can be expressed by the following equation (11) using the charge amount on the resist surface and the electrostatic capacitance of the resist.

[0048] (11) Vs = e(n rh -n rSE ) / C

[0049] By substituting equation (11) into equation (9) and replacing it with C = ε / d, the following equation (12) is obtained as a differential equation.

[0050] TIFF0007628114000002.tif35140

[0051] It is known that the normalized secondary electron emission spectrum P(E) can be expressed by the following equation (13) (BL Henke, et.al., Journal of Applied Physics 48, 1852(1977); “0.1-10-keV x-ray-induced electron emissions from solids-Models and In equation (13), W is the work function of the resist.

[0052] (13) P(E)=2W 2 E / (E+W) 4

[0053] It is known that in writing that performs charging effect correction, more accurate writing is possible by taking into account the amount of charge that decays (for example, Patent Publication No. 5480555). For this reason, it is desirable to wait for a sufficient amount of time to pass after writing and to determine the amount of charge after decay. At this time, it is considered that, of the holes accumulated in the resist, those in the vicinity of the chrome film under the resist move to the chrome film and decay. For this reason, it is assumed that, regardless of the pattern density, holes at a certain distance from the chrome film move to the chrome film, decreasing the number of accumulated holes. Number of accumulated holes after decay n rh(static) can be expressed by the following formula (14): In formula (14), β is the remaining rate of holes after attenuation.

[0054] (14) n rh(static) =βn rh

[0055] It is believed that the secondary electrons are not attenuated because they accumulate on the resist surface and are far from the chromium film.

[0056] Function σ(d, D exp) is expressed by the following formula (15). This uses the above formulas (2), (8), (12), (13), and (14), and by defining the secondary electron emission probability α, the resist dielectric constant ε, the resist resistivity during beam irradiation ρ, the resist work function W, and the hole remaining rate after attenuation β as a group of parameters that represent the physical properties of the resist, the resist film thickness d and the dose D exp The secondary electron emission probability α, dielectric constant ε, resistivity ρ, work function W, and residual rate β are calculated by applying the function σ(d, D exp ) can be determined by fitting

[0057] TIFF0007628114000003.tif40142

[0058] Substrates (mask blanks) provided with the following four types of resists A to D, which have different film thicknesses or dose sensitivities, were prepared, and the relationship between the dose and the charge amount was obtained by drawing evaluation, and the function σ(d, D exp ) and the results were compared.

[0059] Resist A: Film thickness 300 nm, dose sensitivity ~ 7 μC / cm 2 Resist B: Film thickness 165 nm, dose sensitivity ~ 23 μC / cm 2 Resist C: Film thickness 80 nm, dose sensitivity ~ 60 μC / cm 2 Resist D: Film thickness 80 nm, dose sensitivity ~100 μC / cm 2

[0060] Function σ(d, D exp The parameters of are as follows: α=0.036 ρ=13.6[Ωm] β=0.65 ε=3.1*ε0 (relative dielectric constant 3.1, ε0: dielectric constant of a vacuum) W=3.0[eV]

[0061] The resist charge amount (amount of charge per unit area) during electron beam irradiation can be measured by drawing evaluation as follows, for example, in a similar manner to that disclosed in the examples of Japanese Patent Publication No. 5480555. Figure 4a shows a test layout used to measure the resist charging effect. Note that in Figure 4a, the scale is changed to make the contents of each part easier to understand.

[0062] The test layout TL shown in FIG. 4a has an irradiation pad with a pattern density p and a side length L3 of 10 mm at the center of the layout TL, and a dose D exp Immediately after drawing the irradiation pad, a first box array is drawn on a grid (81 × 81 grid) having a pitch L1 of 200 μm and a side length L2 of 20 mm. Then, after a sufficient amount of time has passed since drawing the irradiation pad (e.g., 10 minutes), a second box array is drawn on the same grid as the first box array.

[0063] As shown in an enlarged view in Fig. 4b, the first box array is, for example, a square pattern with a side length L4 of 4 µm, and the second box array is, for example, a frame-shaped pattern with a side length L5 of 14 µm, which is larger than the first box array and has a hollowed-out center.

[0064] In this way, by measuring the positions of the first and second box arrays written, distributions of positional deviations P1 and P2 from the design position due to the charging effect of the irradiation pad can be obtained. P1 is written immediately after the irradiation pad is charged, so it can be used to evaluate the charge amount immediately after irradiation, and P2 is written after a sufficient amount of time has passed since the irradiation pad is charged, so it can be used to evaluate the charge amount after it has decayed.

[0065] FIG. 5 shows an example of the distribution of the amount of positional deviation obtained by evaluating such a test layout.

[0066] Using the assumed response function r(x,y) for calculating the positional displacement from the charge distribution, the charge can be calculated from the positional displacement distribution as follows. First, the irradiation pad is uniformly charged to 1 nC / cm 2 The position shift distribution P0 when it is assumed that the electrode is charged is expressed as follows: 2 In the region other than the irradiation pad, the function C0(x, y) is calculated by convolution integral of the response function r(x, y) and a function C0(x, y) which is zero.

[0067] TIFF0007628114000004.tif57161

[0068] FIG. 6 shows the distribution of the positional deviation P0 obtained by the above formula.

[0069] The charge amount of the irradiation pad can be calculated from the slope when P0 is correlated with the measurement results P1 and P2.

[0070] Figures 7a and 7b show the irradiation pad with a pattern density of 25% and a dose of 23 μC / cm 2 This graph shows the correlation between P1 and P2 and P0 when the irradiation pad is irradiated with 1 nC / cm. As a result of linear approximation of this correlation, the slope is obtained as 1.57 and 0.75, respectively. This is because the positional deviation of P1 and P2 is 1 nC / cm when the irradiation pad is irradiated with 1 nC / cm. 2 This shows that the displacement is equivalent to that when the charged model is multiplied by 1.57 and 0.75, so the irradiation pad is 1.57 nC / cm 2 and 0.75 nC / cm 2 It is clear that it is electrically charged.

[0071] The results obtained by drawing evaluation and the function σ(d, D exp 8a to 8d show the comparison results of the calculation results by the function σ(d, D exp8a to 8d, the charge amount indicated by the marker is calculated based on the pattern density p and the dose D exp The horizontal axis is the value obtained by the above drawing evaluation with various changes in D exp *Plotted as p.

[0072] The square marker indicates the time immediately after writing, and the triangular marker indicates the time after attenuation. From this result, it can be seen that if the physical properties of the resist do not change, even if the resist thickness or sensitivity changes, the function σ(d, D exp ) was confirmed to be able to calculate the charge amount with high accuracy.

[0073] The resist is composed of a base polymer and a small amount of a dissolution inhibitor and an acid generator, and since the majority of the resist volume is occupied by the base polymer, it is considered that the physical properties of the resist related to charging during beam irradiation described in the model of this embodiment are determined only by the properties of the polymer. Therefore, the amount of charging could be calculated for four types of substrates with different sensitivities using a function determined by the same parameters. In other words, in this embodiment, unless there is a significant change in the polymer composition that changes the physical properties of the resist such as the secondary electron emission probability α, the dielectric constant ε, and the work function W, the function σ(d,D) using the same parameters can be calculated for various substrates with different sensitivities by changing the resist film thickness or the concentration of additives such as the acid generator. exp ) can be used to quickly and accurately calculate the charge.

[0074] The storage device 21 of the rendering device 100 shown in FIG. exp ) and a group of parameters indicating the physical properties of the resist formed on the substrate 2 are stored in advance.

[0075] 9 is a flowchart for explaining the writing method according to this embodiment. This method includes a pattern density distribution calculation step (step S100), a dose amount distribution calculation step (step S102), a charge amount distribution calculation step (step S104), a position deviation amount distribution calculation step (step S106), a deflection position correction step (step S108), and a writing step (step S110).

[0076] In the pattern density distribution calculation process (step S100), the pattern density distribution calculation unit 32 reads out the drawing data from the storage device 140, virtually divides the drawing area (or frame area) into a mesh shape with a predetermined dimension (grid dimension), and calculates the pattern density indicating the arrangement ratio of the figure pattern defined in the drawing data for each mesh area. Then, the pattern density distribution for each mesh area is created.

[0077] In the dose distribution calculation step (step S102), the dose distribution calculation unit 34 calculates the dose D for each mesh region using the pattern density distribution. exp Calculate the distribution of dose D exp can be calculated using the above formula (1).

[0078] In the charge distribution calculation step (step S104), the charge distribution calculation unit 36 ​​receives the function σ(d, D exp ) and the parameter set, and the function σ(d, D exp ), the film thickness d of the resist formed on the substrate 2, and the dose D calculated in step S102 exp and calculate the distribution of the charge amount for each mesh region.

[0079] In the positional deviation amount distribution calculation process (step S106), the positional deviation amount distribution calculation unit 38 (positional deviation amount calculation unit) calculates the positional deviation amount based on the charge amount distribution. Specifically, the positional deviation amount distribution calculation unit 38 calculates the positional deviation amount of the writing position caused by the charge amount at each position of the charge amount distribution by convolving the charge amount distribution calculated in step S104 with the response function r(x, y).

[0080] A response function r(x,y) that converts this charge distribution into a positional deviation distribution is assumed. Here, the charge position indicated by each position of the charge distribution is represented by (x',y'), and the beam irradiation position of the corresponding frame area currently undergoing data processing is represented by (x,y). Here, the beam position deviation can be represented as a function of the distance from the beam irradiation position (x,y) to the charge position (x',y'), so the response function can be written as r(x-x',y-y'). The response function r(x-x',y-y') can be obtained in advance by performing an experiment in advance so as to match the experimental results, or by numerical calculation. Hereinafter, (x,y) indicates the beam irradiation position of the corresponding frame area currently undergoing data processing.

[0081] Then, the positional deviation amount distribution calculation unit 38 creates a positional deviation amount distribution from the positional deviation amount of each position (x, y) to be drawn in the corresponding frame area. The created positional deviation amount distribution is stored in the storage device 21 and is also output to the control computer 120.

[0082] Meanwhile, in the control computer 120, the shot data generating unit 41 reads out the drawing data from the storage device 140, and performs multiple stages of data conversion processing to generate shot data in a format specific to the drawing device 100. The size of a figure pattern defined in the drawing data is usually larger than the shot size that the drawing device 100 can form in one shot. Therefore, in the drawing device 100, each figure pattern is divided into multiple shot figures (shot division) so that the size is such that the drawing device 100 can form in one shot. Then, for each shot figure, data such as a figure code indicating the type of figure, coordinates, and size are defined as shot data.

[0083] In the deflection position correction step (step S108) (positional deviation correction step), the positional deviation correction unit 42 corrects the irradiation position using the positional deviation amount calculated in step S106. Here, the shot data for each position is corrected. Specifically, a correction value for correcting the positional deviation amount indicated by the positional deviation amount distribution is added to each position (x, y) of the shot data. For example, it is preferable to use a value obtained by reversing the positive and negative signs of the positional deviation amount indicated by the positional deviation amount distribution as the correction value. As a result, when the electron beam 6 is irradiated, the coordinates of the irradiation destination are corrected, and the deflection position deflected by the objective deflector 13 is corrected. The shot data is defined in the data file so as to be arranged in the order of shots.

[0084] In the drawing process (step S110), in the deflection control circuit 130, the shaping deflector control unit 43 calculates the deflection amount of the shaping deflector 10 for variably shaping the electron beam 6 from the figure type and size defined in the shot data for each shot figure in the shot order. Also, the objective deflector control unit 44 calculates the deflection amount of the objective deflector 13 for deflecting the shot figure to the position on the substrate 2 to be irradiated. In other words, the objective 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 deflector 13 arranged 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. As a result, the drawing unit W draws a pattern at the charge-corrected position on the substrate 2.

[0085] In this embodiment, if the physical properties of the resist such as the secondary electron emission probability α, the dielectric constant ε, and the work function W are not changed, the same function σ(d, D exp ) can be used to quickly and accurately calculate the charge amount, which can reduce equipment downtime due to substrate changes.

[0086] For example, when a substrate with a different resist thickness is intentionally used, the resist thickness after the change is expressed as a function σ(d, D exp ) can be substituted.

[0087] If the resist thickness changes unintentionally between multiple substrates, the resist thickness is measured periodically, and the resist thickness of the currently used substrate is predicted based on the change in the resist thickness of the substrates used in the past. The predicted value is calculated by the function σ(d, D exp ) may be substituted.

[0088] When the resist has a film thickness distribution within a single substrate, the film thickness distribution is measured in advance, and the film thickness at the position where the charge amount is calculated is calculated using the function σ(d, D exp The drawing apparatus may be provided with a measuring device for measuring the film thickness of the resist.

[0089] The deviation of the irradiation position due to the charging phenomenon is not limited to the electron beam lithography apparatus, but the present invention can be applied to any charged particle beam apparatus that uses the results obtained by irradiating a targeted position with a charged particle beam, such as an inspection apparatus that inspects a pattern with a charged particle beam such as an electron beam.

[0090] In the above embodiment, in order to reduce the effect of fogging caused by electrons scattered within the drawing chamber raining down on the substrate and to make direct charging by the irradiated electron beam predominant, it is preferable to apply a positive potential to the lower surface of the objective lens 12 (objective optical system) so as not to return secondary electrons to the substrate surface.

[0091] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2020-78344, filed on April 27, 2020, the entirety of which is incorporated by reference. [Explanation of symbols]

[0092] 1 Electron Tube 2. Board 3 XY stage 4. Mirror 5. Electron Gun 6. Electron Beam 7 Lighting Lens 8 First Aperture Plate 9 Projection Lens 10 deflector 11 Second aperture plate 12 Objective Lens 13 Deflector 14 Drawing room 15 Electrostatic Lens 21,140 Storage device 30 Drawing control section 32 Pattern density distribution calculation unit 34 Dose distribution calculation section 36 Charge distribution calculation section 38 Position deviation distribution calculation unit 41 Shot data generation unit 42 Position deviation correction unit 43 Molding deflector control section 44 Objective deflector control section 45 Stage position detection unit 46 Stage Control Unit 100 drawing device

Claims

1. 1. A charged particle beam lithography method for irradiating a substrate on which a resist film is formed with a charged particle beam by deflecting the charged particle beam using a deflector, thereby lithographing a pattern, comprising: a step of virtually dividing a drawing region of the substrate into a mesh shape and calculating a pattern density indicating an arrangement ratio of the pattern for each mesh region; calculating a dose for each mesh region using the pattern density; calculating an amount of charge from a film thickness of the resist film formed on the substrate and the calculated dose amount by using a function for calculating an amount of charge, the function having a previously obtained film thickness and a dose amount of the resist film as variables; calculating a positional deviation amount of a writing position from the calculated charge amount; correcting the irradiation position of the charged particle beam using the positional deviation amount; Equipped with the function for calculating the charge amount is determined from parameters representing physical characteristics of the resist film, the physical characteristics including at least one of a secondary electron emission probability of the resist, a dielectric constant, a resistivity during beam irradiation, a work function, and a hole remaining rate; The charge amount calculation function is capable of calculating the charge amount even when the dose sensitivity of the resist film is different.

2. 2. The charged particle beam writing method according to claim 1, wherein the charge amount is calculated based on a film thickness distribution of the resist film formed on the substrate and the charge amount calculation function.

3. Periodically measure the resist film thickness. A resist film thickness of a substrate to be patterned is predicted based on a change in the resist film thickness of a substrate on which a pattern has been previously patterned; 2. The charged particle beam writing method according to claim 1, further comprising the step of calculating the charge amount based on a predicted value of the resist film thickness and the charge amount calculation function.

4. 1. A charged particle beam lithography apparatus that deflects a charged particle beam by a deflector, and irradiates a substrate on which a resist film is formed with the charged particle beam to draw a pattern, comprising: an emission section that emits the charged particle beam; a pattern density calculation unit that virtually divides a drawing area of ​​the substrate into a mesh shape and calculates a pattern density that indicates an arrangement ratio of the pattern for each mesh area; a dose calculation unit that calculates a dose indicating a dose for each mesh region using the pattern density; a storage unit that stores a function for calculating a charge amount, the function having a thickness and a dose of the resist film as variables; a charge amount calculation unit that retrieves the function from the storage unit, and calculates a charge amount from the film thickness of the resist film formed on the substrate and the dose amount calculated by the dose amount calculation unit using the function; a positional deviation amount calculation unit that calculates a positional deviation amount of a writing position from the charge amount; a correction unit that corrects an irradiation position of the charged particle beam using the positional deviation amount; a writing unit that irradiates the charged particle beam at the corrected irradiation position; Equipped with the function for calculating the charge amount is determined from parameters representing physical characteristics of the resist film, the physical characteristics including at least one of a secondary electron emission probability of the resist, a dielectric constant, a resistivity during beam irradiation, a work function, and a hole remaining rate; The function for calculating the amount of charge is capable of calculating the amount of charge even when the dose sensitivity of the resist film is different.

5. 5. The charged particle beam drawing apparatus according to claim 4, wherein the charge amount calculation unit calculates the charge amount based on a film thickness distribution of the resist film formed on the substrate and a function for calculating the charge amount.

6. 5. The charged particle beam drawing apparatus according to claim 4, wherein the charge amount calculation unit predicts a resist film thickness of a substrate to be drawn based on a change in a resist film thickness of a substrate on which a pattern has been drawn in the past, and calculates the charge amount based on the predicted resist film thickness and the charge amount calculation function.

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