JP7619123B2 - Charged particle beam drawing method and charged particle beam drawing apparatus - Google Patents

Description

The present invention relates to a charged particle beam drawing method and a charged particle beam drawing device.

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 (a mask, or a reticle, particularly one used in steppers and scanners) formed on quartz is reduced and transferred onto a wafer using a reduction projection exposure device. The high-precision original pattern is drawn by an electron beam drawing device, and so-called electron beam lithography technology is used.

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 of the lithography system, such as the deflection electrodes, and the contamination becomes charged by scattered electrons from the substrate being lithographed. Drift correction is performed to cancel this beam drift.

In conventional drift correction, the drawing process is temporarily stopped, a measurement mark placed on the stage is scanned with an electron beam to measure the electron beam irradiation position, the difference from the previous measurement value is used as the drift correction amount, and the drawing process is resumed. After the drawing process is resumed, the beam irradiation position is corrected using this drift correction amount.

Japanese Patent Application Publication No. 8-274002 Japanese Patent Application Publication No. 3-053440 Japanese Patent Application Publication No. 177516/1983

However, in conventional drift measurements, the measurement results of the beam irradiation position are a mixture of beam drift caused by drawing and beam drift caused by the influence of reflected electrons (including secondary electrons) during measurement, resulting in measurement errors and hindering improvements in the accuracy of drift correction.

The present invention aims to provide a charged particle beam drawing method and a charged particle beam drawing apparatus that can perform drift correction with high accuracy and improve pattern drawing accuracy.

The charged particle beam writing method according to one aspect of the present invention is a charged particle beam writing method for writing a pattern by irradiating a charged particle beam on a substrate to be written placed on a stage, and includes the steps of: dividing the writing area of the substrate into a plurality of sections based on writing data of the writing area; calculating 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 the relationship between the writing dose and the reflected charged particle amount determined in advance for each of the plurality of sections so that the same amount of charged particles as the amount of reflected charged particles generated during writing is generated by the writing dose; irradiating a charged particle beam onto a mark provided on the stage 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 the drift amount for each of the sections; and writing 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.

The 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 amount for each of the plurality of sections from the drawing data, and sets a position measurement irradiation amount when measuring the beam irradiation position so that a charged particle amount equal to the reflected charged particle amount generated during drawing is generated for each of the plurality of sections based on the relationship between the drawing irradiation amount and the reflected charged particle amount previously calculated; 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 amount, and calculates the drift amount 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.

According to the present invention, drift correction can be performed with high precision, improving the pattern drawing accuracy.

1 is a schematic diagram of an electron beam writing apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating variable shaping of an electron beam. 11 is a flowchart illustrating a method for estimating a fluctuation in a beam irradiation position. FIG. 11 is a diagram showing an example of beam position measurement conditions. FIG. 13 is a diagram illustrating an example of a mark scan. FIG. 13 is a diagram showing an example of a measurement result of a beam irradiation position. 11 is a flowchart illustrating a drawing method. FIG. 13 is a diagram showing an example of interpolation of a beam irradiation position.

Embodiments of the present invention will be described below with reference to the drawings. In the embodiments, a configuration using an electron beam will be described as an example of a charged particle beam. However, the charged particle beam is not limited to an electron beam, and may be an ion beam, etc.

Figure 1 is a schematic diagram of an electron beam drawing apparatus according to an embodiment of the present invention. The drawing apparatus 1 shown in Figure 1 is a variable-shape drawing apparatus that includes a drawing unit 30 that irradiates an electron beam onto a substrate 56 to be drawn to draw a desired pattern, and a control unit 10 that controls the operation of the drawing unit 30.

The drawing section 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.

A movably arranged stage 50 is disposed within the drawing chamber 34. The stage 50 moves in mutually orthogonal X and Y directions 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, etc.

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 a mark formed on a silicon substrate and 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.

Above the stage 50, a detector 52 is provided which detects, as a current value, electrons reflected by the mark M when the mark M is irradiated with the 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 the control computer 11, which will be described later.

The control unit 10 has a control computer 11, a stage position measurement unit 18, and storage devices 20, 22, 24. The control computer 11 has a shot data generation unit 12, a drawing 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 during calculation are appropriately stored in a memory (not shown).

Each part of the control computer 11 may be configured as hardware or software. If 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 read and executed by a computer having electrical circuits.

The stage position measurement unit 18 includes a laser length measuring device that measures the position of the stage 50 by irradiating and reflecting laser light on a mirror 51 fixed on the stage 50. The stage position measurement unit 18 notifies the control computer 11 of the measured stage position.

The storage device 20 stores drawing data that is the layout data in which the designed graphic patterns are arranged, converted 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 board 56.

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

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.

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 the drift correction amount to cancel the amount of drift. The method of 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 drawing control unit 13. The drawing control unit 13 uses this correction information to control the drawing unit 30 and correct the beam irradiation position.

Figure 1 shows the configuration necessary for explaining the embodiment. The drawing device 1 may also include other configurations.

When the electron beam B emitted from the electron gun 40 provided in the electron lens barrel 32 passes through the blanking deflector 44, it is deflected by the blanking deflector 44 so that in the beam-on state, it passes through the blanking aperture substrate 41, and in the beam-off state, the entire beam is blocked by the blanking aperture substrate 41. When the beam goes from the beam-off state to the beam-on state, the electron beam B that passes through the blanking aperture substrate 41 before it goes to beam-off constitutes one electron beam shot.

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

The electron beam of the first aperture image that passes 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 passing through the opening 43a of the second shaping aperture substrate 43 (perform variable shaping).

The electron beam that passes through the second shaping aperture substrate 43 is focused by the objective lens 49, deflected by the objective deflector 46, and irradiated at the desired position on the substrate 56 to be drawn, which is placed on the XY stage 50. At this time, the beam current amount of the electron beam irradiated to the substrate 56 (or the mark M) can be changed by changing the dimensions of the electron beam passing through the opening 43a of the second shaping aperture substrate 43. In addition, the beam current amount can be changed by changing the beam current density and thereby changing the settings of the emission current of the electron gun 40 and the illumination lens 47.

In the drawing device 1, beam drift occurs due to charges of contamination adhering to electrodes of the objective deflector 46 and the like, so drift correction is necessary. 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.

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

The method for estimating the fluctuation of the beam irradiation position during actual drawing is explained using the flowchart shown in Figure 3.

The drawing data is read from the storage device 20, and the drawing area of the substrate 56 to be drawn is virtually divided into a number of rectangular stripe areas extending in the x direction with a width that can be deflected by the objective deflector 46 (step S1). Then, a graphic pattern defined in the drawing data is assigned to each stripe area. The stripe division and assignment of the graphic pattern may be performed by the shot data generation unit 12 or the measurement condition setting unit 14.

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 many micro-areas in the longitudinal direction, the area density of each micro-area is calculated, and adjacent micro-areas with similar area density are grouped together to form one section. For example, as shown in FIG. 4, one stripe is divided into ten sections #1 to #10.

The measurement condition setting unit 14 sets beam position measurement conditions that simulate the drawing process (actual drawing) 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 when the beam position is measured.

The partitions may be divided so that the time required to draw each partition matches the time required to measure the position of each partition. Here, "match" does not have to match perfectly, and some error is allowed based on the required measurement accuracy.

The position measurement dose is set so that the amount of reflected electrons when measuring the beam position (when scanning the mark) is the same as the amount of reflected electrons when actually drawing. For example, if the reflectance of incident electrons on the substrate 56 to be drawn is 50% of the reflectance of incident electrons on the mark M, the position measurement dose is set to 50% of the dose when drawing. Note that "same" does not mean that the amount of reflected electrons needs to be strictly equal, and some error is allowed based on the required measurement accuracy.

The writing dose can be found from the shot data for the 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 results in the same amount of reflected electrons 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 equal, and the writing dose = position measurement dose.

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 times the beam position is measured. The beam position is measured for the number of additions, and the average value of the measurement results is set as the beam position. For example, when two beam position measurement points are set on each of the straight line sections L1 to L4 extending up, down, left, and right from the center of the cross mark J shown in FIG. 5, the number of lines is 8. Here, if the number of additions is 64, the beam position is measured eight times at each of the eight beam position measurement points, and the average value of the 64 measurement results is set as the beam position. These parameters allow the position measurement dose and position measurement time to be matched with the drawing. In addition, as described above, the position measurement dose can be adjusted by the fluctuation in the beam dimension, and the position measurement time can be adjusted by the fluctuation in the settling time during beam irradiation during position measurement.

The mark is scanned with the 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 location based on the number of lines and a number of times based on the number of additions over a first time period with a first irradiation amount. The beam position measurement corresponding to section #2 measures the beam irradiation position by scanning the mark at a location based on the number of lines and a number of times based on the number of additions over a second time period with a second irradiation amount. Such beam irradiation position measurements are performed continuously in order (the same order as the actual drawing) for all stripes and all sections.

For example, the measurement results for the beam irradiation positions corresponding to sections #1 to #10 in Figure 4 are as shown in Figure 6.

In this way, the mark is scanned for the same time as in actual drawing, with an irradiation amount that results in the same amount of reflected electrons as in actual drawing, and the beam irradiation position corresponding to each section is obtained. The obtained beam irradiation positions are arranged in stripe order and section order, and beam position fluctuation data is generated that estimates the fluctuation of the beam irradiation position during actual drawing. The beam position fluctuation data is stored in the storage device 24.

Next, a method for drawing a pattern while performing drift correction using beam position fluctuation data will be explained with reference to the flowchart shown in Figure 7.

The drawing control unit 13 controls the drawing unit 30 based on the shot data to perform the pattern drawing process (step S11). When the timing for a predetermined 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 with a predetermined beam current, and the detector 52 detects the 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.

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 drawing control unit 13 resumes the drawing process, corrects the beam irradiation position based on the calculated amount of drift, and draws the pattern.

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

The drift correction unit 16 reads out 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 deviation amount from the reference position. The drawing control unit 13 performs drawing processing while correcting the beam irradiation position based on the calculated drift amount (step S15).

For example, as shown in FIG. 8, consider a case where after drawing the stripe area of stripe number 132, the drawing process is interrupted before drawing the stripe area of stripe number 133, and the beam irradiation position is measured. After the drawing process is resumed, the beam position fluctuation data is referenced and the fluctuation of the beam irradiation position while drawing the stripe area of 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 draw the pattern.

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 actually writing a pattern in this section. This makes it possible to accurately estimate the fluctuation of the beam irradiation position while writing the pattern, and to write the pattern with high precision.

The present invention is not limited to the above-described embodiment as it is, and in the implementation stage, the components can be modified and embodied without departing from the gist of the invention. In addition, various inventions can be formed by appropriately combining the multiple components disclosed in the above-described embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, components from different embodiments may be appropriately combined.

REFERENCE SIGNS LIST 1 Writing apparatus 10 Control unit 11 Control computer 12 Shot data generation unit 13 Writing control unit 14 Measurement condition setting unit 15 Irradiation position detection unit 16 Drift correction unit 20, 22, 24 Storage device 30 Writing unit 32 Electron lens barrel 34 Writing chamber 40 Electron gun 41 Blanking aperture substrate 42 First shaping aperture substrate 43 Second shaping aperture substrate 44 Blanking deflector 45 Shaping deflector 46 Objective deflector 47 Illumination lens 48 Projection lens 49 Objective lens 50 Stage 52 Detector

Claims (5)

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. 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. 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. 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. 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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