Nonlinear error measurement method for stage position measurement system and charged particle beam drawing device

Abstract

Provided is a method for accurately measuring a nonlinear error component causing a length measurement error in a stage position measurement system. A nonlinear error measurement method for the stage position measurement system according to the present embodiment comprises: a step of moving a stage on which a substrate to be drawn on by a charged particle beam drawing device is placed, by a predetermined amount, and measuring a stage position before and after the movement by using a laser interferometer; a step of scanning a mark on the stage with a charged particle beam in a stop state of the stage before and after the movement of the stage, and detecting a position of the mark; and a step of calculating a positional deviation amount by comparing the position of the stage with the position of the mark. The movement of the stage by the predetermined amount, the detection of the position of the mark, and the calculation of the positional deviation amount are repeatedly performed, a plurality of the positional deviation amounts are calculated, function fitting is performed on the plurality of positional deviation amounts, and a nonlinear error in the stage position measurement system is determined on the basis of an obtained approximation function.

Description

Method for measuring nonlinear errors in stage position measurement system and charged particle beam writing apparatus

[0001] The present invention relates to a method for measuring nonlinear errors in a stage position measurement system and a charged particle beam drawing apparatus.

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

[0003] The electron beam lithography system moves a stage on which a sample is placed within a vacuum chamber, and deflects and irradiates an electron beam onto a predetermined position on the sample on the stage, thereby lithographing a pattern on the sample.

[0004] The position of the stage described above is measured by, for example, a laser interferometer, but there is a problem of nonlinear errors occurring due to the measurement method. For example, if the polarization separation of the laser is imperfect, a nonlinear error occurs at a period of 1 / 4 (or 1 / 2) of the laser wavelength. Furthermore, since such measurement errors become error components that are not caused by the deflector, the accuracy of deflection sensitivity adjustment deteriorates, affecting the drawing accuracy.

[0005] Conventionally, nonlinear error components have been determined by measuring the stage position at regular time intervals while moving the stage at a constant speed, but this method makes it difficult to accurately measure nonlinear error components due to fluctuations in the speed of the stage, which moves at a constant speed.

[0006] JP-A No. 11-238670 JP-A No. 10-160408 Special Publication No. 2005-532554

[0007] An object of the present invention is to provide a method for measuring nonlinear errors in a stage position measurement system and a charged particle beam drawing apparatus that can accurately measure nonlinear error components that cause length measurement errors.

[0008] A method for measuring nonlinear errors in a stage position measurement system according to one aspect of the present invention comprises the steps of: moving a stage on which a substrate to be drawn in a charged particle beam drawing apparatus is placed by a predetermined amount, and measuring the stage position before and after the movement using a laser interferometer; scanning a mark on the stage with a charged particle beam while the stage is stopped before and after the stage movement, and detecting the position of the mark; and comparing the position of the stage with the position of the mark to calculate a positional deviation amount, wherein the method repeatedly moves the stage by the predetermined amount, detects the position of the mark, and calculates a plurality of positional deviation amounts, performs function fitting on the plurality of positional deviation amounts, and determines the nonlinear error in the stage position measurement system based on the obtained approximation function.

[0009] According to the present invention, the nonlinear error component that causes the length measurement error can be accurately measured.

[0010] 4A and 4B are graphs showing examples of fitting of positional deviation amount data, and are a schematic diagram of an electron beam drawing apparatus according to an embodiment of the present invention.

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] 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 2 that irradiates an electron beam onto a target workpiece W (substrate) to lithograph a desired pattern, and a control unit 3 that controls the operation of the lithography unit 2.

[0013] The imaging unit 2 has a imaging chamber 2a that houses a workpiece W to be imaged, and an optical lens barrel 2b that is connected to the imaging chamber 2a. The optical lens barrel 2b is provided on the upper surface of the imaging chamber 2a and shapes and deflects the electron beam to irradiate the workpiece W in the imaging chamber 2a. The interiors of the imaging chamber 2a and the optical lens barrel 2b are depressurized and in a vacuum state.

[0014] A stage 11 is provided in the writing chamber 2a to support a sample W. The stage 11 is movable in X-axis and Y-axis directions (hereinafter simply referred to as the X-axis and Y-axis directions) that are perpendicular to each other within a horizontal plane. A sample W, such as a mask blank, is placed on the stage 11.

[0015] Furthermore, a mark M for measuring the drift amount of the electron beam is provided on the XY stage 11. The mark M has, for example, a cross shape or a dot shape, and is formed on a silicon substrate from a heavy metal such as tantalum or tungsten.

[0016] A detector 12 is provided above the XY stage 11 to detect, as a current value, electrons reflected from the mark M when the mark M is irradiated with an electron beam. The detection result by the detector 12 is notified to a control computer 3b, which will be described later. The mark M may be formed on a mask. The mark M may also be a transmission mark, in which case the detector 12 may be provided below the mark M to detect the current value of electrons that have transmitted through the mark M.

[0017] A measurement unit 4 that measures the position of the stage 11 is provided on the outer periphery of the writing chamber 2a. The position of the stage 11 is controlled by a position control unit 35 (described later) via a drive mechanism 36 based on the measurement results by the measurement unit 4. The configuration of the measurement unit 4 will be described later.

[0018] Arranged within the optical barrel 2b are an emission section 21 such as an electron gun that emits an electron beam B, an illumination lens 22 that focuses the electron beam B, a first shaping aperture 23 for beam shaping, a projection lens 24, a shaping deflector 25, a second shaping aperture 26 for beam shaping, an objective lens 27 that focuses the beam on the sample W, and a sub-deflector 28 and a main deflector 29 for controlling the beam shot position relative to the sample W.

[0019] In the writing unit 2, an electron beam B is emitted from an emission unit 21 and irradiated onto a first shaping aperture 23 by an illumination lens 22. The first shaping aperture 23 has, for example, a rectangular opening. When the electron beam B passes through the first shaping aperture 23, the cross section of the electron beam is shaped into a rectangular shape and projected onto a second shaping aperture 26 by a projection lens 24. The projection position onto the second shaping aperture 26 can be deflected by a shaping deflector 25, and the shape and size of the electron beam B can be controlled by changing the projection position. The electron beam B that has passed through the second shaping aperture 26 is focused by an objective lens 27 onto a sample W on the stage 11 and irradiated thereon. At this time, the shot position of the electron beam B relative to the sample W on the stage 11 is deflected by a sub-deflector 28 and a main deflector 29.

[0020] The control unit 3 has a storage unit 3a that stores writing data, and a control computer 3b. The control computer 3b has a shot data generation unit 31, a writing control unit 32, a mark position detection unit 33, an error calculation unit 34, and a position control unit 35. The shot data generation unit 31, the writing control unit 32, the mark position detection unit 33, the error calculation unit 34, and the position control unit 35 may be configured by hardware such as an electric circuit, or may be configured by software such as a program that executes each function, or may be configured by a combination of both.

[0021] The shot data generating unit 31 processes the drawing data to generate shot data. The drawing control unit 32 controls each unit of the drawing unit 2.

[0022] The mark position detection unit 33 detects the position of the mark M using the detection result of the detector 12. For example, when the mark M is scanned with an electron beam, the mark position detection unit 33 detects the position of the mark M based on a change in the current value of the reflected electrons detected by the detector 12.

[0023] The error calculation unit 34 calculates the nonlinear error component of the stage position measurement in the measurement unit 4. The method of calculating the nonlinear error component will be described later.

[0024] The drawing data is data converted into a format for the drawing device 1 so that design data (layout data) created by a designer of a semiconductor integrated circuit or the like can be input to the drawing device 1, and is input from an external device to the storage unit 3a and stored therein. As the storage unit 3a, for example, a magnetic disk device or a semiconductor disk device (flash memory) can be used.

[0025] When drawing a pattern, the drawing control unit 32 moves the stage 11 in the longitudinal direction (X direction) of the stripe region, while positioning the electron beam B in each sub-region using the main deflector 29, and then shoots the electron beam B at a predetermined position in the sub-region using the sub-deflector 28 to draw a figure. After that, when drawing of one stripe region is completed, the stage 11 is moved stepwise in the Y direction and then drawing of the next stripe region is performed, and this is repeated to perform drawing with the electron beam B over the entire drawing region of the sample W. Note that during drawing, since the stage 11 moves continuously in one direction, the main deflector 29 tracks the drawing origin of the sub-region so that the drawing origin follows the movement of the stage 11.

[0026] In this way, the electron beam B is deflected by the sub-deflector 28 and the main deflector 29, and its irradiation position is determined while following the continuously moving stage 11. By continuously moving the stage 11 in the X direction and making the shot position of the electron beam B follow the movement of the stage 11, the writing time can be shortened.

[0027] The writing control unit 32 controls the sub-deflector 28, the main deflector 29, etc., i.e., controls the beam irradiation position, using the position information of the stage 11 measured by the measurement unit 4. The writing control unit 32 corrects the position data of the stage 11 (sample W) based on the nonlinear error component calculated by a method described later, and controls the writing unit 2 based on the corrected position data to write a pattern on the sample W.

[0028] Next, the configuration of the measurement unit 4 will be described. As shown in Fig. 2, the measurement unit 4 (stage position measurement system) includes a laser source 5, a laser interferometer 6, and a light receiving unit 7. For example, a helium-neon laser can be used as the laser light. For example, a photodiode can be used as the light receiving unit 7.

[0029] FIG. 2 illustrates the measurement unit 4 that measures the position of the stage 11 in the y direction, but does not illustrate the measurement unit that measures the position of the stage 11 in the x direction.

[0030] A laser beam emitted from a laser source 5 is split by a laser interferometer 6. One of the laser beams split by the laser interferometer 6 travels to a stage 11, is reflected by a mirror on the stage 11, and returns to the laser interferometer 6. On the other hand, the other of the split laser beams travels to a mirror (not shown) within the laser interferometer 6 and is reflected therefrom.

[0031] The laser light reflected by the mirror on the stage 11 and the laser light reflected by the mirror in the laser interferometer 6 interfere with each other in the laser interferometer 6. The interfered laser light (interference beat signal) is received by the light receiving unit 7, and interference fringes generated by the optical path difference are observed. The observation results are notified to the drawing control unit 32. In this embodiment, two-pass laser interference observation is performed in which the laser light makes two round trips between the laser interferometer 6 and the mirror on the stage 11.

[0032] The movement of the stage 11 changes the frequency of the light reflected from the stage 11, and the interference fringes also change. The drawing control unit 32 determines the position of the stage 11 from the change in the interference fringes.

[0033] The stage position measurement results using the laser interferometer 6 contain nonlinear errors. If this nonlinear error is large, it will degrade the drawing accuracy. Therefore, it is necessary to measure the nonlinear error, and if the error is large, it is necessary to adjust the laser optical axis or replace the laser head.

[0034] The method for measuring the nonlinear error will be described with reference to the flowchart shown in FIG.

[0035] The stage 11 is moved so that the mark M is positioned at a predetermined position within the beam deflection range of the main deflector 29, and the stage 11 is then stopped (step S1).

[0036] With the stage 11 stopped, the main deflector 29 deflects the beam B to scan the mark M. The detector 12 detects electrons reflected from the mark M. The mark position detection unit 33 detects the mark position using the reflected electron detection result by the detector 12 (step S2). Note that the "stopped state" includes an oscillation state that is sufficiently smaller than the period in which a nonlinear error appears, and is included in the stopped state if, for example, it is smaller than 1 / 30 of the nonlinear error period.

[0037] The stage 11 is moved a small amount and then stopped (step S3). The amount of movement of the stage 11 is controlled, for example, based on the measurement results of the measurement unit 4, which is a laser length measurement system. The amount of movement (pitch) of the stage 11 needs to be optimized depending on the performance of the device, but it should be sufficiently smaller than the period at which nonlinear errors appear. For example, if the laser wavelength λ is 632.8 nm and the nonlinear errors appear at a period of 158.2 nm, which is ¼ of the wavelength, then a pitch of 10 to 20 nm is preferable, which allows for control of the stage position and ensures a sufficient number of measurements. It is also preferable that the number of measurements be 15 or more within the measurement wavelength. The amount of movement of the stage 11 is, for example, 10 nm.

[0038] The main deflector 29 is controlled so that the beam B follows the moved mark M, and at the position after the movement, the beam B scans the mark M on the stopped stage 11. The mark position detection unit 33 detects the mark position (amount of mark movement) using the result of reflected electron detection by the detector 12 and the amount of deflection by the main deflector 29 (step S4).

[0039] The error calculation unit 34 calculates the amount of positional deviation of the stage 11 based on the result of mark position detection (step S5). For example, if the stage 11 is controlled to move 10 nm using the measurement result of the measurement unit 4, but the amount of mark movement obtained by beam scanning is 11 nm, the amount of positional deviation will be 1 nm.

[0040] The micro-movement of the stage 11, the detection of the mark position, and the calculation of the amount of misalignment are repeated until a predetermined number of data pieces of misalignment amount are acquired in each of the X and Y directions (steps S3 to S6).

[0041] The error calculation unit 34 performs fitting processing on the acquired positional deviation amount data to approximate it to a sine function with the wavelength set to ¼ of the laser wavelength λ (step S7). The amplitude of the approximation formula is calculated as the nonlinear error amount (step S8).

[0042] FIG. 4A shows an example of the measurement results when the nonlinear error is large, and FIG. 4B shows an example of the measurement results when the nonlinear error is small.

[0043] In this way, the nonlinear error can be determined by repeatedly moving and stopping the stage 11 slightly, measuring the mark position while the stage 11 is stopped, and determining an approximate function of the positional deviation. This method allows for more accurate determination of the nonlinear error component than the conventional method in which measurements are performed while moving the stage 11 at a constant speed. Note that the mark position measurement is performed for the same mark, but it is also possible to determine the positional deviation by measuring different marks whose relative positions are known in advance.

[0044] In the above embodiment, two-pass laser interference observation is performed in which the laser light makes two round trips between the laser interferometer 6 and the mirror on the stage 11. Since the phase makes one revolution when the stage 11 moves λ / 4, the period of the nonlinear error is λ / 4. When one-pass laser interference observation is performed in which the laser light makes one round trip between the laser interferometer 6 and the mirror on the stage 11, the period of the nonlinear error is λ / 2. In the fitting process for the positional deviation amount data, in the case of n passes (n is an integer greater than or equal to 1), approximation to a sine function (trigonometric function) of wavelength λ / 2n is sufficient. In this case, a Fourier transform may be used. Alternatively, a combination of sine functions (trigonometric functions) may be used. The fitting function is not limited to a sine function (trigonometric function) and may be a polynomial.

[0045] In the above embodiment, a drawing apparatus that irradiates an electron beam has been described, but the drawing apparatus may also irradiate other charged particle beams such as an ion beam. Also, the drawing apparatus may be a multi-beam drawing apparatus.

[0046] Although the present invention has been described in detail using 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 present invention. This application is based on Japanese Patent Application No. 2023-118487, filed on July 20, 2023, and is incorporated by reference in its entirety.

[0047] REFERENCE SIGNS LIST 1 Drawing device 2 Drawing section 2a Drawing chamber 2b Optical lens barrel 3 Control section 3a Storage section 3b Control computer 4 Meter section 5 Laser source 6 Laser interferometer 7 Light receiving section 11 Stage

Claims

1. A method for measuring nonlinear errors in a stage position measurement system, comprising the steps of: moving a stage on which a substrate to be drawn by a charged particle beam drawing device is placed by a predetermined amount, and measuring the stage position before and after the movement using a laser interferometer; scanning a mark on the stage with a charged particle beam while the stage is stopped before and after the movement of the stage, and detecting the position of the mark; and comparing the position of the stage with the position of the mark to calculate the amount of positional deviation, wherein the movement of the stage by the predetermined amount, the detection of the position of the mark, and the calculation of the amount of positional deviation are repeated to calculate a plurality of the amount of positional deviation, and a function fitting is performed on the plurality of amount of positional deviation, and a nonlinear error in the stage position measurement system is obtained based on the obtained approximation function.

2. The method for measuring a nonlinear error in a stage position measurement system according to claim 1, wherein a sine function or a composite function including the sine function is used for the function fitting.

3. A method for measuring nonlinear errors in a stage position measurement system as described in claim 2, wherein when the laser interferometer measures the position of the stage using a laser beam that makes n round trips (n is an integer equal to or greater than 1) between the laser interferometer and the stage, the wavelength of the sine function is fitted as 1 / 2n of the wavelength of the laser beam.

4. The method for measuring a nonlinear error in a stage position measurement system according to claim 1, wherein the predetermined amount is shorter than the wavelength of the approximation function.

5. A method for measuring a nonlinear error in a stage position measurement system according to claim 1, wherein the stopped state of the stage includes a vibration state with a vibration amplitude less than 1 / 30 of the wavelength of the approximation function.

6. A charged particle beam drawing apparatus comprising: a movable stage on which a substrate to be drawn is placed; a drawing unit which draws a pattern on the substrate using a charged particle beam; a position control unit which controls a position of the stage; a stage position measurement system which measures the position of the stage using a laser interferometer; a mark position detection unit which scans a mark on the stage with the charged particle beam and detects the position of the mark; an error calculation unit which compares a position of the stage with a position of the mark to calculate an amount of positional deviation and uses the amount of positional deviation to determine a nonlinear error in the stage position measurement system; and a drawing control unit which controls a beam irradiation position by the drawing unit based on the nonlinear error, wherein the position control unit repeatedly moves the stage by a predetermined amount, the stage position measurement system measures the stage position before and after the movement, and the mark position detection unit detects the position of the mark when the stage is stopped before and after moving the stage, respectively, and the error calculation unit calculates a plurality of the amount of positional deviation, performs function fitting on the plurality of amount of positional deviation, and determines the nonlinear error based on the obtained approximation function.

7. The charged particle beam drawing apparatus according to claim 6, wherein the error calculation section uses a sine function or a composite function including the sine function for the function fitting.

8. The charged particle beam drawing device according to claim 7, wherein the laser interferometer measures the position of the stage using a laser beam that makes n round trips (n is an integer equal to or greater than 1) between the laser interferometer and the stage, and the error calculation unit fits the wavelength of the sine function as 1 / 2n of the wavelength of the laser beam.

9. The charged particle beam drawing apparatus according to claim 6, wherein the predetermined amount is shorter than the wavelength of the approximation function.

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