Charged particle beam drawing method and charged particle beam drawing apparatus

Abstract

To improve the drawing accuracy of a pattern by performing drift correction with high accuracy.SOLUTION: A charged particle beam writing method includes the steps of dividing a drawing area into a plurality of sections, obtaining a drawing irradiation amount for each of the plurality of sections, setting a position measurement irradiation amount during beam position measurement so as to generate the same amount of charged particles as the reflected charged particle amount generated during drawing with the drawing irradiation amount on the basis of the relationship between the drawing irradiation amount and the reflected charged particle amount obtained in advance for each of the plurality of sections, irradiating a mark provided on a stage for each of the plurality of sections with a charged particle beam, detecting reflected charged particles, continuously measuring a beam irradiation position corresponding to each of the plurality of sections with a set position measurement irradiation amount, calculating the drift amount for each of the sections, and drawing a pattern on the substrate using the drawing data while correcting the irradiation position of the charged particle beam for each of the plurality of sections on the basis of the drift amount.SELECTED DRAWING: Figure 1

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 every year. To form the desired circuit pattern on a semiconductor device, a method is adopted in which a high-precision original pattern (called a mask, or a reticle, especially when used in steppers and scanners) formed on quartz is reduced and transferred onto a wafer using a reduction projection exposure system. The high-precision original pattern is drawn using an electron beam drawing system, using so-called electron beam lithography technology.

[0003] In electron beam lithography systems, a phenomenon called beam drift can occur, in which the irradiation position of the electron beam shifts over time during lithography due to various factors. For example, beam drift occurs when contamination adheres to the irradiation system, such as the deflection electrodes of the lithography system, and the contamination becomes charged by scattered electrons from the substrate being lithographed. Drift correction is performed to cancel this beam drift.

[0004] In conventional drift correction, the writing process is temporarily stopped, a measurement mark placed on the stage is scanned with an electron beam to measure the irradiation position of the electron beam, the difference from the previous measurement is used as the drift correction amount, and the writing process is then resumed.After the writing process is resumed, the beam irradiation position is corrected using this drift correction amount. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-274002 [Patent Document 2] Japanese Patent Application Publication No. 3-053440 [Patent Document 3] Japanese Unexamined Patent Publication No. 63-177516 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in conventional drift measurements, the measurement results of the beam irradiation position are a combination of beam drift generated by writing and beam drift generated by the influence of reflected electrons (including secondary electrons) during measurement, which results in measurement errors and hinders improvements in the accuracy of drift correction.

[0007] An object of the present invention is to provide a charged particle beam drawing method and apparatus that can perform drift correction with high precision and improve pattern drawing precision. [Means for solving the problem]

[0008] a step of calculating a writing dose for each of the plurality of sections from the writing data; a step of setting a position measurement dose during beam position measurement based on a relationship between the writing dose and a reflected charged particle amount for each of the plurality of sections so that the amount of charged particles generated by the writing dose is equal to the amount of reflected charged particles generated during writing; a step of irradiating a mark provided on the stage with the charged particle beam for each of the plurality of sections to detect reflected charged particles, continuously measuring the beam irradiation position corresponding to each of the plurality of sections with the set position measurement dose, and calculating a drift amount for each of the plurality of sections; and a step of drawing a pattern on the substrate using the writing data while correcting the irradiation position of the charged particle beam for each of the plurality of sections based on the drift amount.

[0009] A charged particle beam drawing apparatus according to one aspect of the present invention includes: a measurement condition setting unit that reads drawing data of a drawing area of ​​a substrate placed on a stage, divides the drawing area into a plurality of sections based on the drawing data, calculates a drawing irradiation dose for each of the plurality of sections from the drawing data, and sets a position measurement irradiation dose when measuring the beam irradiation position so that an amount of charged particles generated during drawing is equal to an amount of reflected charged particles generated during drawing, based on a relationship between the drawing irradiation dose and a reflected charged particle amount that has been calculated in advance for each of the plurality of sections; a drift correction unit that irradiates a charged particle beam onto a mark provided on the stage for each of the plurality of sections to detect reflected charged particles, continuously measures the beam irradiation position corresponding to each of the plurality of sections with the set position measurement irradiation dose, and calculates an amount of drift of the charged particle beam based on the beam position fluctuation data; and a drawing unit that draws a pattern on the substrate using the drawing data while correcting the irradiation position of the charged particle beam based on the drift amount. [Effects of the Invention]

[0010] According to the present invention, drift correction can be performed with high precision, and pattern writing precision can be improved. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of an electron beam writing apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram illustrating variable shaping of an electron beam. [Figure 3] 10 is a flowchart illustrating a method for estimating fluctuations in a beam irradiation position. [Figure 4] FIG. 10 is a diagram showing an example of beam position measurement conditions. [Figure 5] FIG. 10 is a diagram illustrating an example of mark scanning. [Figure 6] FIG. 10 is a diagram showing an example of measurement results of a beam irradiation position. [Figure 7] 10 is a flowchart illustrating a drawing method. [Figure 8] FIG. 10 is a diagram showing an example of interpolation of a beam irradiation position. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the embodiment, a configuration using an electron beam as an example of a charged particle beam will be described. However, the charged particle beam is not limited to an electron beam, and an ion beam or the like may also be used.

[0013] Fig. 1 is a schematic diagram of an electron beam lithography apparatus according to an embodiment of the present invention. The lithography apparatus 1 shown in Fig. 1 is a variable-shape lithography apparatus including a lithography unit 30 that irradiates an electron beam onto a substrate 56 to be lithographed, thereby lithographing a desired pattern, and a control unit 10 that controls the operation of the lithography unit 30.

[0014] The drawing unit 30 has an electron lens barrel 32 and a drawing chamber 34. Inside the electron lens barrel 32, an electron gun 40, a blanking aperture substrate 41, a first shaping aperture substrate 42, a second shaping aperture substrate 43, a blanking deflector 44, a shaping deflector 45, an objective deflector 46, an illumination lens 47, a projection lens 48, and an objective lens 49 are arranged.

[0015] A movably arranged stage 50 is disposed within the pattern writing chamber 34. The stage 50 moves in X and Y directions that are orthogonal to each other within a horizontal plane. A substrate 56 is placed on the stage 50. The substrate 56 is, for example, an exposure mask used in manufacturing a semiconductor device, a mask blank, a semiconductor substrate (silicon wafer) on which the semiconductor device is manufactured, or the like.

[0016] A mirror 51 is provided on the stage 50 to measure the position of the stage 50 in a horizontal plane. Also provided on the stage 50 is a mark M that is used when measuring the amount of drift of the electron beam B. For example, the mark M is formed on a silicon substrate and is made of a heavy metal such as tantalum or tungsten. The shape of the mark is not particularly limited, but for example, a cross mark J as shown in FIG. 5 is formed.

[0017] A detector 52 is provided above the stage 50 to detect, as a current value, electrons reflected by the mark M when the mark M is irradiated with an electron beam B. Here, the reflected electrons are an example of reflected charged particles, and include secondary electrons. The detected current value is sent to a control computer 11, which will be described later.

[0018] The control unit 10 has a control computer 11, a stage position measurement unit 18, and storage devices 20, 22, and 24. The control computer 11 has a shot data generation unit 12, a writing control unit 13, a measurement condition setting unit 14, an irradiation position detection unit 15, and a drift correction unit 16. Input / output data of each unit of the control computer 11 and data being calculated are stored appropriately in a memory (not shown).

[0019] Each part of the control computer 11 may be configured as either hardware or software. When configured as software, a program that realizes at least some of the functions may be stored on a recording medium such as a CD-ROM, and may be read and executed by a computer having electrical circuits.

[0020] The stage position measurement unit 18 includes a laser length measuring device that measures the position of the stage 50 by making a laser beam incident on and reflected by a mirror 51 fixed on the stage 50. The stage position measurement unit 18 notifies the control computer 11 of the measured stage position.

[0021] The storage device 20 stores drawing data obtained by converting layout data in which designed graphic patterns are arranged into a format that can be input to the drawing device 1. The drawing data defines the graphic patterns to be drawn in the drawing area of ​​the substrate 56.

[0022] The shot data generation unit 12 reads the drawing data from the storage device 20 and performs multiple stages of data conversion processing to generate shot data specific to the device. The shot data defines, for example, the type of figure, the size of figure, the irradiation position, the irradiation time, etc. The drawing control unit 13 controls the drawing unit 30 based on the shot data to perform drawing processing.

[0023] The irradiation position detection unit 15 detects the beam irradiation position using the beam profile based on the current value detected by the detector 52 and the stage position (mark position) measured by the stage position measurement unit 18.

[0024] The drift correction unit 16 calculates the amount of drift from the difference between the beam irradiation position detected by the irradiation position detection unit 15 and the reference irradiation position, and determines a drift correction amount to cancel the amount of drift. The method for calculating the drift amount will be described later. The drift correction unit 16 generates correction information for the deflection amount (beam irradiation position) of the electron beam B based on the drift correction amount, and provides it to the writing control unit 13. The writing control unit 13 uses this correction information to control the writing unit 30 and correct the beam irradiation position.

[0025] 1 shows the configuration necessary for explaining the embodiment, but the drawing device 1 may also include other configurations.

[0026] Electron beam B emitted from electron gun 40 provided in electron lens barrel 32 is deflected by blanking deflector 44 as it passes through blanking aperture substrate 41 in the beam-on state, and is deflected by blanking deflector 44 so that the entire beam is shielded by blanking aperture substrate 41 in the beam-off state. The electron beam B that passes through blanking aperture substrate 41 from the beam-off state until it switches from beam-on to beam-off constitutes one electron beam shot.

[0027] The electron beam B of each shot, generated by passing through the blanking deflector 44 and the blanking aperture substrate 41, is irradiated onto the first shaping aperture substrate 42, which has a rectangular opening 42a (see FIG. 2), by the illumination lens 47. By passing through the opening 42a of the first shaping aperture substrate 42, the electron beam B is shaped into a rectangle.

[0028] The electron beam of the first aperture image that has passed through the first shaping aperture substrate 42 is projected onto the second shaping aperture substrate 43 by the projection lens 48. The position of the first aperture image on the second shaping aperture substrate 43 is controlled by the shaping deflector 45. This makes it possible to change the shape and dimensions of the electron beam that passes through the opening 43a of the second shaping aperture substrate 43 (perform variable shaping).

[0029] The electron beam that has passed through the second shaping aperture substrate 43 is focused by the objective lens 49, deflected by the objective deflector 46, and irradiated onto a desired position on a substrate 56 to be written, which is placed on an XY stage 50. At this time, the beam current amount of the electron beam irradiated onto the substrate 56 (or the mark M) can be changed by changing the size of the electron beam that passes through the opening 43a of the second shaping aperture substrate 43. Furthermore, the beam current amount may be changed by changing the beam current density and thereby changing the setting of the emission current of the electron gun 40 or the illumination lens 47.

[0030] In the drawing apparatus 1, beam drift occurs due to charging of contaminants adhering to electrodes of the objective deflector 46, etc., and therefore drift correction is required. In drift correction, the mark M is scanned with the electron beam B to detect the beam irradiation position, and the amount of deviation from the reference position is calculated as the drift amount.

[0031] The calculated drift amount includes a drift component during writing and a drift component during beam irradiation position detection due to reflected electrons (including secondary electrons) from the mark, resulting in measurement errors. Therefore, in this embodiment, before writing processing (actual writing), beam position measurements are continuously performed under conditions that simulate the amount of reflected electrons generated during actual writing, and beam drift (fluctuations in the beam irradiation position) during actual writing is estimated. Then, during actual writing, the beam irradiation position is measured at predetermined time intervals, and the drift amount is calculated by referring to the previously estimated fluctuations in the beam irradiation position during the period from when the beam irradiation position is measured until the next measurement.

[0032] A method for estimating fluctuations in the beam irradiation position during actual writing will be described with reference to the flowchart shown in FIG.

[0033] The writing data is read from the storage device 20, and the writing region of the substrate 56 to be written is virtually divided into a plurality of rectangular stripe regions extending in the x direction, each having a width that can be deflected by the objective deflector 46 (step S1). Then, a figure pattern defined in the writing data is assigned to each stripe region. The stripe division and the assignment of figure patterns may be performed by the shot data generation unit 12 or the measurement condition setting unit 14.

[0034] The measurement condition setting unit 14 divides each stripe into multiple sections (step S2). The measurement condition setting unit 14 divides one stripe into multiple sections based on the position and area density of the graphic pattern assigned to the stripe. For example, one stripe is divided into multiple micro-regions in the longitudinal direction, the area density of each micro-region is determined, and adjacent micro-regions with similar area densities are grouped together to form one section. For example, as shown in FIG. 4, one stripe is divided into ten sections #1 to #10.

[0035] The measurement condition setting unit 14 sets beam position measurement conditions that simulate the writing process (actual writing) for each section (step S3). As shown in Fig. 4, the beam position measurement conditions include a position measurement time, which is the time required to measure the beam position, and a position measurement irradiation amount, which is the beam irradiation amount during beam position measurement.

[0036] The division of the regions may be performed so that the time required to draw each region matches the time required to measure the position of each region. Here, "match" does not necessarily mean a perfect match, but rather allows for some error based on the required measurement accuracy.

[0037] The position measurement dose is set so that the amount of reflected electrons during beam position measurement (mark scanning) is the same as the amount of reflected electrons during actual writing. For example, if the reflectance of incident electrons on substrate 56 to be written is 50% of the reflectance of incident electrons on mark M, the position measurement dose is set to 50% of the dose during writing. Note that "same" does not mean that the amount of reflected electrons need to be exactly the same, and an error is allowed based on the required measurement accuracy.

[0038] The writing dose can be found from the shot data for the relevant section among the shot data generated by the shot data generating unit 12. Reflectance data indicating the reflectance of the substrate 56 and the mark is stored in the storage device 22. The measurement condition setting unit 14 reads the reflectance data from the storage device 22 and calculates the position measurement dose that makes the amount of reflected electrons the same from the writing dose and the reflectance. In the example of FIG. 4, the reflectance of the substrate 56 and the reflectance of the mark are set to be the same, and the writing dose = the position measurement dose.

[0039] The beam position measurement conditions also include parameters such as the shot time, the number of shots, the "number of lines" indicating the number of beam position measurement points on the mark corresponding to each section, and the "number of additions" indicating the number of beam position measurements. The beam position is measured for each addition, and the average of the measurement results is taken as the beam position. For example, if two beam position measurement points are set on each of the linear segments L1 to L4 extending up, down, left, and right from the center of the cross mark J shown in Figure 5, the number of lines is 8. Here, if the number of additions is set to 64, the beam position is measured eight times at eight beam position measurement points, and the average of the 64 measurement results is taken as the beam position. These parameters allow the position measurement dose and position measurement time to be adjusted to match the drawing. In addition, as mentioned above, the position measurement dose can be adjusted due to fluctuations in the beam dimension, and the position measurement time can be adjusted due to fluctuations in the settling time of beam irradiation during position measurement.

[0040] The mark is scanned with electron beam B under the measurement conditions for each section set in step S3, and the irradiation position detection unit 15 measures and detects the beam irradiation position (step S4). For example, in the example of FIG. 4, the beam position measurement corresponding to section #1 measures the beam position by scanning the mark at a first irradiation dose over a first time period at locations based on the number of lines and a number of times based on the number of additions. The beam position measurement corresponding to section #2 measures the beam irradiation position by scanning the mark at a second irradiation dose over a second time period at locations based on the number of lines and a number of times based on the number of additions. This type of beam irradiation position measurement is performed continuously in order (the same order as actual writing) for all stripes and all sections.

[0041] For example, the measurement results of the beam irradiation positions corresponding to the sections #1 to #10 in FIG. 4 are as shown in FIG.

[0042] In this way, the mark is scanned for the same time as actual writing with an irradiation dose that results in the same amount of reflected electrons as actual writing, and the beam irradiation position corresponding to each section is determined. The determined beam irradiation positions are arranged in stripe order and section order to generate beam position fluctuation data that estimates the fluctuation of the beam irradiation position during actual writing. The beam position fluctuation data is stored in the memory device 24.

[0043] Next, a method for writing a pattern while performing drift correction using beam position fluctuation data will be described with reference to the flowchart shown in FIG.

[0044] The drawing control unit 13 controls the drawing unit 30 based on the shot data to perform the pattern drawing process (step S11). When a predetermined timing for drift measurement arrives (step S12_Yes, step S13_Yes), the drawing process is interrupted, and the mark is scanned with the electron beam B to detect the beam irradiation position (step S14). Specifically, the stage 50 is moved to align the mark with the center position of the objective lens 49, the mark is scanned with the electron beam B at a predetermined beam current, and the detector 52 detects reflected electrons (including secondary electrons). The irradiation position detection unit 15 measures the beam profile from the detection result of the detector 52 and detects the beam irradiation position on the mark surface.

[0045] The drift correction unit 16 calculates the amount of deviation between the detected beam irradiation position and the reference position as the amount of drift on the mark surface. The writing control unit 13 resumes the writing process, corrects the beam irradiation position based on the calculated amount of drift, and writes the pattern.

[0046] The process of interrupting writing and measuring the beam irradiation position is performed at regular time intervals. For example, writing is interrupted and the beam irradiation position is measured every time a predetermined number of stripe regions are written. Since the beam irradiation position cannot be measured while pattern writing is in progress, the beam irradiation position during that time is interpolated using beam position fluctuation data.

[0047] The drift correction unit 16 reads the beam position fluctuation data from the storage device 24 and estimates the subsequent fluctuation of the beam irradiation position based on the beam irradiation position detected in step S14. The drift correction unit 16 calculates the amount of drift from the estimated value of the beam irradiation position and the amount of deviation from the reference position. The writing control unit 13 performs writing processing while correcting the beam irradiation position based on the calculated amount of drift (step S15).

[0048] For example, as shown in Fig. 8, consider a case where the writing process is interrupted after writing the stripe area with stripe number 132 and before writing the stripe area with stripe number 133, and the beam irradiation position is measured. After the writing process is resumed, the beam position fluctuation data is referenced and the fluctuation of the beam irradiation position during writing of the stripe area with stripe number 133 is estimated. Then, the amount of drift is calculated from the estimated beam irradiation position, and the beam irradiation position is corrected to write the pattern.

[0049] The beam irradiation position of each section defined in the beam position fluctuation data is measured under conditions that simulate the writing time and amount of reflected electrons when a pattern is actually written in that section, so that the fluctuation of the beam irradiation position during pattern writing can be accurately estimated, and the pattern can be written with high accuracy.

[0050] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined. [Explanation of symbols]

[0051] 1 Drawing device 10 Control Unit 11 Control computer 12 Shot data generation unit 13 Drawing control unit 14 Measurement condition setting section 15 Irradiation position detection unit 16 Drift correction section 20,22,24 Storage device 30 Drawing section 32 Electron Telescope 34 Drawing room 40 Electron Gun 41 Blanking aperture board 42 First shaping aperture substrate 43 Second shaping aperture substrate 44 Blanking Deflector 45 Molded deflector 46 Objective deflector 47 Lighting Lens 48 Projection Lens 49 Objective Lens 50 stages 52 detector

Claims

1. A charged particle beam lithography method for irradiating a charged particle beam onto a substrate to be lithographed, the substrate being placed on a stage, to lithograph a pattern, the method comprising the steps of: dividing the drawing area of ​​the substrate into a plurality of sections based on drawing data of the drawing area; determining a writing dose for each of the plurality of sections from the writing data; setting a position measurement dose during beam position measurement based on a relationship between the writing dose and a reflected charged particle amount obtained in advance for each of the plurality of sections so that a charged particle amount equal to a reflected charged particle amount generated during writing by the writing dose is generated; a step of irradiating a mark provided on the stage for each of the plurality of sections with a charged particle beam to detect reflected charged particles, continuously measuring beam irradiation positions corresponding to each of the plurality of sections with a set position measurement irradiation amount, and calculating a drift amount for each of the sections; writing a pattern on the substrate using the writing data while correcting an irradiation position of the charged particle beam for each of the plurality of sections based on the drift amount; A charged particle beam writing method comprising the steps of:

2. 2. The charged particle beam writing method according to claim 1, wherein the plurality of sections are divided such that a writing time for each of the plurality of sections coincides with a position measurement time during the beam position measurement.

3. 3. The charged particle beam writing method according to claim 1, wherein the position measurement time during the beam position measurement is adjusted to the writing time for each of the multiple sections, or the position measurement irradiation amount is adjusted to the amount of reflected charged particles, by varying at least one of the shot time, the number of shots, the number of beam position measurement points on the mark corresponding to each section, the number of beam position measurements, the beam dimension, and the settling time.

4. interrupting the drawing of the pattern on the substrate at a predetermined timing, irradiating the mark with the charged particle beam, and detecting the reflected charged particles to detect the beam irradiation position; 4. The charged particle beam drawing method according to claim 1, further comprising the step of calculating the drift amount based on the detected beam irradiation position and a beam irradiation position measurement result corresponding to a section during pattern drawing, after resuming drawing of the pattern.

5. a measurement condition setting unit that reads drawing data of a drawing area of ​​a substrate placed on a stage, divides the drawing area into a plurality of sections based on the drawing data, calculates a drawing irradiation amount for each of the plurality of sections from the drawing data, and sets a position measurement irradiation amount at the time of beam irradiation position measurement so that a charged particle amount equal to a reflected charged particle amount generated during drawing is generated for each of the plurality of sections based on a relationship between the drawing irradiation amount and a reflected charged particle amount obtained in advance; a drift correction unit that irradiates a charged particle beam onto a mark provided on the stage for each of the plurality of sections to detect reflected charged particles, continuously measures beam irradiation positions corresponding to each of the plurality of sections with a set position measurement irradiation amount, and calculates a drift amount of the charged particle beam based on beam position fluctuation data; a drawing unit that draws a pattern on the substrate using the drawing data while correcting an irradiation position of the charged particle beam based on the drift amount; A charged particle beam writing apparatus comprising:

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