Non-linear error measurement method of stage position measurement system

Abstract

To surely measure a non-linear error component that becomes a factor of a measurement error.SOLUTION: A non-linear error measurement method of a stage position measurement system by a present embodiment, comprises: a step of moving a stage onto which a drawing object substrate of an electric charging particle beam drawing device is mounted at a predetermined amount, and measuring a stage position after and before the movement by using a laser interferometer; a step of scanning a mark on the stage in a stop state of each stage after and before the movement of the stage with the electric charging beam, and detecting a position of the mark; and a step of comparing the position of the stage with the position of the mark, and calculating a position deviation amount. The predetermined amount movement of the stage, a detection of position of the mark, and a calculation of a position deviation amount are repeatedly performed to calculates a plurality of position deviation amounts. A function fitting is performed to the plurality of position deviation amounts, and a non-linear error in the stage position measurement system is calculated on the basis of an approximate to be obtained.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for measuring a nonlinear error in a stage position measurement system. [Background technology]

[0002] As LSIs become more highly integrated, the circuit line width of semiconductor devices becomes 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 (a mask, or a mask used in steppers and scanners in particular is 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] 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 of the sample on the stage, thereby lithographing a pattern on the sample.

[0004] The position of the above-mentioned stage 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 incomplete, a nonlinear error occurs at a period of 1 / 4 (or 1 / 2) of the laser wavelength. And since such a measurement error becomes an error component that is not caused by the deflector, the deflection sensitivity adjustment accuracy deteriorates, affecting the drawing accuracy.

[0005] Conventionally, the nonlinear error components were obtained by measuring the stage position at regular time intervals while moving the stage at a constant speed. However, with this method, it was difficult to accurately measure the nonlinear error components due to speed fluctuations of the stage, which moves at a constant speed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 11-238670 [Patent Document 2] Japanese Patent Application Publication No. 10-160408 [Patent Document 3] Special Publication No. 2005-532554 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a nonlinear error measuring method for a stage position measurement system that can accurately measure nonlinear error components that cause length measurement errors. [Means for solving the problem]

[0008] A nonlinear error measurement method for 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 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 a positional deviation amount, repeatedly moving the stage by the predetermined amount, detecting the position of the mark, and calculating the positional deviation amount, calculating a plurality of the positional deviation amounts, performing function fitting on the plurality of positional deviation amounts, and determining the nonlinear error in the stage position measurement system based on the obtained approximation function. Effect of the Invention

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

[0010] [Figure 1] 1 is a schematic diagram of an electron beam writing apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of a stage position measurement system. [Diagram 3] 11 is a flowchart illustrating a method for measuring a nonlinear error. [Figure 4] 4A and 4B are graphs showing examples of fitting of positional deviation amount data. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0012] 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 shaping type lithography apparatus including a lithography unit 2 that irradiates an electron beam onto a substrate W to be lithographed 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 insides 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 in 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 electrons reflected from the mark M as a current value when the mark M is irradiated with an electron beam. The detection result by the detector 12 is notified to a control computer 3b described later. The mark M may be formed on a mask. Also, the mark M may 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 driving mechanism 36 based on the measurement result by the measurement unit 4. The configuration of the measurement unit 4 will be described later.

[0018] Within the optical barrel 2b, there are arranged an emission section 21 such as an electron gun that emits electron beam B, an illumination lens 22 that focuses 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 with respect to the sample W.

[0019] In the drawing unit 2, the electron beam B is emitted from the emission unit 21 and irradiated onto the first shaping aperture 23 by the 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-sectional shape of the electron beam is shaped into a rectangular shape, and the electron beam is projected onto the second shaping aperture 26 by the projection lens 24. The projection position onto the second shaping aperture 26 can be deflected by the shaping deflector 25, and the shape and dimensions 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 on the sample W on the stage 11 by the objective lens 27 and irradiated. At this time, the shot position of the electron beam B with respect to the sample W on the stage 11 is deflected by the sub-deflector 28 and the main deflector 29.

[0020] The control unit 3 has a storage unit 3a that stores drawing data, and a control computer 3b. The control computer 3b has a shot data generation unit 31, a drawing 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 drawing control unit 32, the mark position detection unit 33, the error calculation unit 34, and the position control unit 35 may be configured with hardware such as an electric circuit, or may be configured with software such as a program that executes each function, or may be configured with 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 a 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 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 in a stepwise manner in the Y direction and then the next stripe region is drawn, and this is repeated to perform drawing with the electron beam B over the entire drawing region of the sample W. Note that since the stage 11 moves continuously in one direction during drawing, 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 tracking 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 track the movement of the stage 11, the writing time can be shortened.

[0027] The writing control unit 32 uses the position information of the stage 11 measured by the measurement unit 4 to control the sub deflector 28, the main deflector 29, etc., that is, to control the beam irradiation position.

[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, and omits the illustration of the measurement unit that measures the position of the stage 11 in the x direction.

[0030] The laser light emitted from the laser source 5 is split by the laser interferometer 6. One of the laser lights split by the laser interferometer 6 travels to the 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 lights travels to and is reflected by a mirror (not shown) in the laser interferometer 6.

[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 interfering 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 result is notified to the drawing control unit 32. In this embodiment, a two-pass type 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 reflected light 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 result using the laser interferometer 6 contains a nonlinear error. If this nonlinear error is large, it will deteriorate 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 located at a predetermined position within the beam deflection range of the main deflector 29, and the stage 11 is 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 the reflected electrons from the mark M. The mark position detector 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 it is smaller than 1 / 30 of the nonlinear error period, for example.

[0037] The stage 11 is moved by a small amount and stopped (step S3). The amount of movement of the stage 11 is controlled based on the measurement results of the measurement unit 4, which is, for example, a laser length measurement system. The amount of movement (pitch) of the stage 11 must be optimized depending on the performance of the device, but it is assumed to be sufficiently smaller than the period at which nonlinear errors appear. For example, when 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, the stage position can be controlled, and it is preferable that the pitch is 10 to 20 nm, which allows a sufficient number of measurements to be obtained. It is also preferable that the number of measurements is 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 mark M on the stopped stage 11 is scanned. The mark position detection unit 33 detects the mark position (mark movement amount) using the reflected electron detection result by the detector 12 and the deflection amount 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 the mark position detection (step S5). For example, if the measurement result of the measurement unit 4 is used to control the stage 11 to move by 10 nm, 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 pieces of misalignment data 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 being ¼ of the laser wavelength λ (step S7). The amplitude of the approximation formula is calculated as the amount of nonlinear error (step S8).

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

[0043] In this way, the nonlinear error can be obtained by repeatedly moving and stopping the stage 11 slightly, measuring the mark positions while the stage 11 is stopped, and finding an approximation function of the positional deviation. This makes it possible to find the nonlinear error component more accurately than with the conventional method of measuring 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 find the positional deviation by measuring different marks whose relative positions are known in advance.

[0044] In the above embodiment, a 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, and the phase makes one revolution when the stage 11 moves by λ / 4, so the period of the nonlinear error is λ / 4. When a 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 equal to or greater than 1), approximation to a sine function (trigonometric function) of wavelength λ / 2n is sufficient. In this case, a Fourier transform may be used. A combination of sine functions (trigonometric functions) may also be used. The fitting function is not limited to a sine function (trigonometric function), and may be a polynomial.

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

[0046] The present invention is not limited to the above-described embodiment, and the components can be modified and embodied in the implementation stage 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. [Explanation of symbols]

[0047] 1 Drawing device 2. Drawing section 2a drawing room 2b Optical barrel 3. Control Unit 3a Storage section 3b Control computer 4. Side of the scale 5 Laser Source 6 Laser interferometer 7 Light receiving section 11 Stage

Claims

1. a step of moving a stage of a charged particle beam drawing apparatus, on which a drawing target substrate is placed, by a predetermined amount, and measuring the stage position before and after the movement using a laser interferometer; a step of 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 a position of the mark; a step of calculating a positional deviation amount by comparing a position of the stage with a position of the mark; Equipped with 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 repeated to calculate a plurality of the positional deviation amounts; A method for measuring a nonlinear error in a stage position measurement system, comprising: performing function fitting on the plurality of positional deviation amounts; and determining a nonlinear error in the stage position measurement system 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. When the laser interferometer measures the position of the stage by 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, 3. The method for measuring a nonlinear error in a stage position measurement system according to claim 2, wherein a wavelength of the sine function is fitted as 1 / 2n of the wavelength of the laser light.

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

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