TW202531296A - Deflection position adjustment method of charged particle beam and charged particle beam drawing method - Google Patents

Abstract

The present invention accurately adjusts the deflection sensitivity of a deflector to improve drawing accuracy. The method for adjusting the deflection position of a charged particle beam includes: in a charged particle beam drawing device, using a laser interferometer to measure the position of a worktable on which a substrate to be drawn is placed at a predetermined interval; using the worktable position measurement results based on the laser interferometer to move the worktable a predetermined amount while simultaneously scanning a mark on the worktable with a charged particle beam to detect the position of the mark; obtaining nonlinear error information about the position of the mark based on the laser interferometer; using the nonlinear error information to obtain multiple position offsets based on the measured position of the worktable and the detected position of the mark; and adjusting the deflection position of the charged particle beam based on the multiple position offsets obtained.

Description

Deflection position adjustment method for charged particle beam drawing and charged particle beam drawing method

The present invention relates to a method for adjusting the deflection position of a charged particle beam and a method for depicting a charged particle beam.

With the increasing integration of large-scale integration (LSI) circuits, the circuit widths of semiconductor devices are becoming increasingly smaller year by year. To form the desired circuit patterns on semiconductor devices, a method is employed: a high-precision original pattern (also called a mask, or, in the case of steppers or scanners, a reticle) formed on quartz is transferred to a wafer using a reduced projection exposure system. This high-precision original pattern is then mapped using an electron beam lithography system, employing a technique known as electron beam lithography.

The electron beam imaging device moves a stage on which a sample is placed within a vacuum chamber. Simultaneously, a deflector deflects the electron beam and directs it to a specific location on the sample, creating a pattern on the sample.

To ensure that the electron beam accurately irradiates the specified location on the sample, the deflector's deflection sensitivity is adjusted before pattern drawing, and the beam deflection position is corrected (compensated). For example, the beam scans a mark on the stage, and the beam position is detected based on the reflected electrons from the mark. The beam position error is calculated based on the deviation from the stage position. The stage is moved in the x- and y-directions at specified intervals, and the beam position error is calculated simultaneously at multiple locations, resulting in a matrix-like position error distribution, as shown in Figure 5A. The position error distribution is approximated by a polynomial, and the error of the beam irradiation position is calculated based on the approximation. The deflection amount of the deflector is adjusted to compensate for the calculated error, thereby allowing the beam to be irradiated with the desired position accuracy as shown in FIG5B.

In this type of deflection sensitivity adjustment, beam position error is calculated using the stage position as a reference, necessitating accurate stage position measurement. While laser interferometry is used to measure the stage position, there is a problem with nonlinear errors arising from the measurement method. For example, if the laser's polarization separation is incomplete, nonlinear errors occur within a period of 1/4 (or 1/2) the laser wavelength. Furthermore, this length measurement error is not an error component caused by the deflector, thus degrading the accuracy of deflection sensitivity adjustment, hindering the achievement of the target accuracy for deflection sensitivity adjustment or the evaluation of deflector degradation. [Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent Application Publication No. 2012-173218 Patent Document 2: Japanese Patent Application Publication No. 10-160408 Patent Document 3: Japanese Patent Application Publication No. 2012-015227

[The problem that the invention aims to solve]

The present invention aims to provide a method for adjusting the deflection position of a charged particle beam and a charged particle beam drawing method that can precisely adjust the deflection sensitivity of a deflector to improve drawing accuracy. [Means for Solving the Problem]

A method for adjusting the deflection position of a charged particle beam according to one aspect of the present invention includes: in a charged particle beam imaging device, using a laser interferometer to measure the position of a stage on which a substrate to be imaged is placed at a predetermined interval; using the stage position measurement results obtained by the laser interferometer to move the stage a predetermined amount while simultaneously scanning a mark on the stage with a charged particle beam to detect the position of the mark; obtaining nonlinear error information about the position of the mark based on the laser interferometer; using the nonlinear error information to obtain a plurality of position offsets based on the measured position of the stage and the detected position of the mark; and adjusting the deflection position of the charged particle beam based on the obtained plurality of position offsets. [Effects of the Invention]

According to the present invention, the deflection sensitivity of the deflector can be adjusted with high precision to improve the drawing accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Figure 1 is a schematic diagram of an electron beam imaging device according to an embodiment of the present invention. The imaging device 1 shown in Figure 1 includes a imaging unit 2 for irradiating a substrate W, the imaging target, with an electron beam to create a desired pattern, and a control unit 3 for controlling the operation of the imaging unit 2. The imaging device 1 is a deformable imaging device.

The imaging unit 2 comprises an imaging chamber 2a, which houses a sample W to be imaged, and an optical barrel 2b connected to the imaging chamber 2a. The optical barrel 2b, mounted on the upper surface of the imaging chamber 2a, shapes and deflects the electron beam, irradiating the sample W within the imaging chamber 2a. The interiors of the imaging chamber 2a and the optical barrel 2b are depressurized to a vacuum state.

A worktable 11 is installed in the drawing room 2a to support a sample W. The worktable 11 is movable along mutually orthogonal X-axis and Y-axis directions (hereinafter referred to as the X and Y directions) in a horizontal plane. Samples W, such as mask blanks, are placed on the worktable 11.

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

A detector 12 is installed above the XY stage 11. When the mark M is irradiated with an electron beam, the detector 12 detects the reflected electrons from the mark M as a current value. The detection results obtained by the detector 12 are transmitted and input to the control computer 3b described below. The mark M can also be formed on a mask. Alternatively, the mark M can be a transparent mark. In this case, the detector 12 can be installed below the mark M to detect the current value of the electrons that have passed through the mark M.

A measuring unit 4 is installed on the periphery of the drawing chamber 2a to measure the position of the worktable 11. Based on the measurement results obtained by the measuring unit 4, the position of the worktable 11 is controlled by a position control unit 35 (described later) via a drive mechanism 36. The structure of the measuring unit 4 will be described later.

Arranged within the optical barrel 2b are: an emission unit 21, such as an electron gun, that emits the 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 emission position relative to the sample W.

In the imaging unit 2, an electron beam B is emitted from the output portion 21 and passes through the illumination lens 22 to irradiate the first shaping aperture 23. The first shaping aperture 23 has, for example, a rectangular opening. As the electron beam B passes through the first shaping aperture 23, its cross-section is shaped into a rectangular shape and projected onto the second shaping aperture 26 by the projection lens 24. The projection position on the second shaping aperture 26 can be deflected by a shaping deflector 25. By changing the projection position, the shape and size of the electron beam B can be controlled. The electron beam B that has passed through the second shaping aperture 26 is irradiated so that its focus is aligned with the sample W on the worktable 11 via the objective lens 27. At this time, the emission position of the electron beam B relative to the sample W on the stage 11 is deflected by the sub-deflector 28 and the main deflector 29 .

The control unit 3 includes a storage unit 3a for storing drawing data and a control computer 3b. The control computer 3b includes a transmission data generation unit 31, a drawing control unit 32, a marker position detection unit 33, an error calculation unit 34, and a position control unit 35. The transmission data generation unit 31, the drawing control unit 32, the marker position detection unit 33, the error calculation unit 34, and the position control unit 35 can be composed of hardware such as circuits, software such as programs that execute their functions, or a combination of both.

The transmission data generating unit 31 processes the drawing data to generate the transmission data. The drawing control unit 32 controls each unit of the drawing unit 2.

The mark position detection unit 33 detects the mark position (beam irradiation position) using the detection results of the detector 12. For example, when the mark M is scanned with an electron beam, the mark position is detected based on the change in the current value of the reflected electrons detected by the detector 12.

The error calculation unit 34 calculates the error of the beam irradiation position based on the difference between the stage position and the mark position detected by beam scanning.

Drawing data is created by a semiconductor integrated circuit designer or the like. This data is converted into a format suitable for use with the drawing device 1 so that it can be input to the drawing device 1. This data is then input from an external device to the storage unit 3a and stored there. For example, a magnetic disk drive or semiconductor disk drive (flash memory) can be used as the storage unit 3a.

When drawing a pattern, the drawing control unit 32 moves the stage 11 along the length (X-direction) of the stripe area. Simultaneously, the main deflector 29 positions the electron beam B at each sub-area, and the sub-deflector 28 emits the electron beam B to a specified position within the sub-area to draw the pattern. After completing the drawing of one stripe area, the stage 11 is moved in steps along the Y-direction to draw the next stripe area. This process is repeated until the entire drawing area of the sample W is drawn with the electron beam B. Furthermore, since the stage 11 moves continuously in one direction during the drawing process, the main deflector 29 tracks the drawing origin of the sub-area so that the drawing origin follows the movement of the stage 11.

In this way, electron beam B is deflected by the auxiliary 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 having the emission position of electron beam B track the movement of the stage 11, the drawing time can be shortened.

The drawing control unit 32 controls the sub-deflector 28 , the main deflector 29 , and the like, that is, controls the beam irradiation position, and controls the position of the stage 11 using the position information of the stage 11 measured by the measuring unit 4 .

Next, the structure of the measurement unit 4 will be described. As shown in Figure 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 source. For example, a photodiode can be used as the light receiving unit 7.

In FIG. 2 , the measuring unit 4 that measures the position of the stage 11 in the y direction is shown, and the measuring unit that measures the position of the stage 11 in the x direction is omitted.

Laser light (wavelength λ) emitted from laser source 5 is split by laser interferometer 6. One of the split laser beams travels toward stage 11, is reflected by a mirror on stage 11, and returns to laser interferometer 6. Meanwhile, the other split laser beam travels toward and is reflected by a mirror (not shown) within laser interferometer 6.

Laser interferometer 6 interferes with laser light reflected by the mirror on stage 11 and by the mirror within it. The interfering laser light (interference difference frequency signal) is received by light receiver 7, where the interference pattern generated by the optical path difference is observed. The observation results are communicated to the image processing control unit 32. In this embodiment, double-pass laser interferometry is performed, in which light travels back and forth twice between laser interferometer 6 and the mirror on stage 11.

The movement of the stage 11 changes the frequency of the reflected light from the stage 11, and the interference pattern also changes. The drawing control unit 32 grasps the position of the stage 11 based on the change in the interference pattern.

To accurately irradiate the sample W with the beam, the electron beam imaging system adjusts the deflection sensitivity of the deflectors (main deflector 29 and sub-deflector 28) before the imaging process. For example, the deflection sensitivity adjustment involves scanning the beam across a mark M on the stage 11. The beam position is detected based on the reflected electrons from the mark M, and the beam position error is calculated based on the deviation from the stage position. The stage 11 is moved in the x- and y-directions at predetermined intervals, and the beam position error is calculated at multiple locations, resulting in a matrix-like position error distribution, as shown in Figure 5A. A polynomial approximation is performed on the position error distribution, and the error of the beam irradiation position is calculated based on the approximation. The calculated error is corrected, thereby adjusting the deflection sensitivity of the deflector to achieve the deflection area shape shown in Figure 5B.

However, the stage position measurement results obtained using the laser interferometer 6 contain nonlinear errors. For example, as described above, in the case of double-pass laser interferometry, in which laser light travels back and forth twice between the laser interferometer 6 and the reflective mirror on the stage 11, the phase rotates once for every λ/4 movement of the stage 11, resulting in a nonlinear error with a period of λ/4.

Conventional deflection sensitivity adjustment sets the interval (pitch P) between mark position measurement points without taking nonlinear errors into consideration. Consequently, as shown in Figure 3, the phase of the nonlinear errors at each measurement point varies, and the amount of nonlinear error included in the mark position measurement results varies.

If scattered nonlinear errors are present at each measurement point, it is impossible to correct them using a polynomial approximation, hindering the achievement of target accuracy for deflection sensitivity adjustment or the evaluation of deflector degradation.

Therefore, in this embodiment, the deflection sensitivity is adjusted after obtaining nonlinear error information around the mark position measurement point in advance. This deflection sensitivity adjustment method is explained with reference to the flowchart shown in FIG6.

The worktable 11 is moved at a constant speed around the mark position measurement point (step S101). During this time, the measurement unit 4 continuously measures the worktable position at high speed (step S102), acquiring nonlinear error information around the mark position measurement point (step S103). This nonlinear error information is stored in the storage unit 3a.

While the deflection sensitivity of the main deflector 29 is being adjusted, the stage 11 is moved so that the mark M is located at the measurement start position within the beam deflection range of the main deflector 29 (step S104). The movement amount of the stage 11 is controlled using the measurement results of the measuring unit 4, which is a laser length measurement system.

With the stage 11 stopped, the main deflector 29 deflects the beam B to scan the mark M (step S105). The detector 12 detects the reflected electrons from the mark M. The mark position detector 33 detects the mark position based on the reflected electron detection results obtained by the detector 12 and the deflection amount of the main deflector 29 (step S106). The error calculator 34 scans the mark M with the beam, using the mark position based on the stage position measured by the measurement unit 4 as a reference, and calculates the offset in the detected mark position (the error in the beam irradiation position) (step S107).

Based on the nonlinear error information obtained in step S103, the nonlinear error at the mark position measurement point is estimated (step S108). The beam irradiation position error (due to the offset in the deflection position of the main deflector 29) is corrected by subtracting the nonlinear error estimated in step S108 from the beam irradiation position error calculated in step S107 (step S109).

The stage 11 is moved in the x- and/or y-directions at a predetermined pitch P, and the beam irradiation position error is obtained at each position (step S110_No, step S111). By obtaining the beam irradiation position error at a plurality of predetermined locations (step S110_Yes), a grid-like position error distribution is obtained, as shown in FIG5A. This position error distribution (deflection area shape) is then subjected to a polynomial approximation (step S112).

Substitute the design drawing position into the polynomial and calculate the offset from the design drawing position. By irradiating the beam to the position obtained by subtracting the calculated offset from the design drawing position, the pattern can be drawn at the design location. Figure 5B shows the shape of the deflection area after offset correction.

By performing this deflection sensitivity adjustment, the effects of nonlinear errors can be prevented. This embodiment uses a polynomial approximation to correct errors in the beam irradiation position, enabling precise adjustment of the deflector's deflection sensitivity to improve rendering accuracy. However, the method is not limited to polynomial approximation; other functions or mappings can also be used for approximation.

If the worktable 11 has high-resolution stop position accuracy, steps S101 to S103 in Figure 6 can be omitted. The deflection sensitivity can be adjusted by setting the interval (pitch P) between the mark position measurement points to an integer multiple of the nonlinear error period (λ/4). For example, if the laser wavelength λ is 632.8 nm, the nonlinear error period is 158.2 nm, and the interval (pitch P) between the mark position measurement points is set to 90.174 μm (=158.2 nm × 570).

As a result, as shown in FIG4 , the phases of the nonlinear errors at the respective measurement points are aligned, and the mark position measurement results contain the same amount of nonlinear error.

This deflection sensitivity adjustment method is described with reference to the flowchart shown in FIG7 .

For example, when adjusting the deflection sensitivity of the main deflector 29, the stage 11 is first 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 then stopped (step S201). The movement amount of the stage 11 is controlled using the measurement results of the measuring unit 4, which is a laser length measurement system.

With the stage 11 stopped, the main deflector 29 deflects the beam B to scan the mark M (step S202). The detector 12 detects the reflected electrons from the mark M. The mark position detector 33 detects the mark position based on the reflected electron detection result obtained by the detector 12 and the deflection amount of the main deflector 29 (step S203). The error calculator 34 scans the mark M with the beam, using the mark position based on the stage position measured by the measurement unit 4 as a reference, and calculates the offset in the detected mark position (the error in the beam irradiation position) (step S204).

The stage 11 is moved in the x- and y-directions at predetermined intervals (integer multiples of the nonlinear error period (λ/4)). The beam irradiation position error (the offset based on the deflection position of the main deflector 29) is calculated at each position (step S205_No, steps S201 to S204). By obtaining beam irradiation position errors at a plurality of predetermined locations (step S205_Yes), a grid-like position error distribution is obtained, as shown in Figure 5A. This position error distribution (deflection area shape) is approximated using a polynomial (step S206). The designed drawing position is substituted into the polynomial, and the offset from the designed drawing position is calculated. By irradiating the beam to a position where the calculated offset is subtracted from the design drawing position, the pattern can be drawn at the design position. Figure 5B shows the shape of the deflection area after the offset is corrected.

By setting the interval (pitch P) between mark position measurement points to an integral multiple of the nonlinear error period (λ/4), the variation in the nonlinear error amount included in the mark position measurement results at each measurement point is suppressed, allowing for precise adjustment of the deflector's deflection sensitivity and improving plotting accuracy.

In the above embodiment, double-pass laser interferometry is performed, in which laser light reciprocates twice between the laser interferometer 6 and the reflective mirror on the stage 11. Therefore, the nonlinear error period is λ/4. In single-pass laser interferometry, in which laser light reciprocates once between the laser interferometer 6 and the reflective mirror on the stage 11, the nonlinear error period is λ/2. Therefore, the interval (pitch P) between the mark position measurement points can be set to an integer multiple of λ/2.

The deflection position adjustment method allows for precise adjustment of the deflection sensitivity of the deflector, thereby improving drawing accuracy. Furthermore, the so-called deflection position adjustment involves adjusting the deflection sensitivity coefficient based on position offset information, and deflection position correction can be performed based on the coefficient.

In the above embodiment, the imaging device irradiates electron beams, but the imaging device may also irradiate other charged particle beams such as ion beams. In addition, the imaging device may also be a multi-beam imaging device.

While the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications may be made without departing from the intent and scope of the present invention. This application is based on Japanese Patent Application No. 2024-004690, filed on January 16, 2024, the entire contents of which are incorporated herein by reference.

1: Drawing device 2: Drawing unit 2a: Drawing chamber 2b: Optical lens 3: Control unit 3a: Storage unit 3b: Control computer 4: Measurement unit 5: Laser source 6: Laser interferometer 7: Light receiving unit 11: Worktable 12: Detector 21: Output unit 22: Illumination lens 23: First shaping aperture 24: Projection lens 25: Shaping deflector 26: Second shaping aperture 27: Objective lens 28: Sub-deflector 29: Main deflector 31: Emission data generation unit 32: Drawing control unit 33: Mark position detection unit 34: Error calculation unit 35: Position control unit 36: Drive mechanism B: Electron beam M: Marker P: Pitch S101, S102, S103, S104, S105, S106, S107, S108, S109, S110, S111, S112, S201, S202, S203, S204, S205, S206: Steps W: Sample x, y: Directions

Figure 1 is a schematic diagram of an electron beam imaging device according to an embodiment of the present invention. Figure 2 is a schematic diagram of a stage position measurement system. Figure 3 is a diagram showing an example of the phase of the nonlinear error at each measurement point. Figure 4 is a diagram showing an example of the phase of the nonlinear error at each measurement point. Figures 5A and 5B are diagrams showing examples of the distribution of beam irradiation positions. Figure 6 is a flowchart illustrating a deflection sensitivity adjustment method. Figure 7 is a flowchart illustrating a deflection sensitivity adjustment method.

1: Drawing device

2: Drawing Department

2a: Drawing Room

2b: Optical lens barrel

3: Control Department

3a: Storage

3b: Control Computer

4: Measurement Department

11: Workbench

12: Detector

21: Exit part

22: Illumination lens

23: First forming aperture

24: Projection lens

25: Shaped Deflector

26: Second forming aperture

27:Objective lens

28: Auxiliary deflector

29: Main deflector

31: Transmission Data Generation Unit

32: Drawing control unit

33: Marking position detection unit

34: Error calculation unit

35: Position Control Unit

36: Drive mechanism

B: Electron beam

M:Mark

W: Sample

Claims (5)

A method for adjusting the deflection position of a charged particle beam comprises: In a charged particle beam imaging device, using a laser interferometer to measure the position of a stage on which a substrate to be imaged is placed at a predetermined interval; Using the stage position measurement results from the laser interferometer, the stage is moved a predetermined amount while simultaneously scanning a mark on the stage with a charged particle beam to detect the position of the mark; Acquiring nonlinear error information about the position of the mark from the laser interferometer; Using the nonlinear error information, the method obtains a plurality of position offsets based on the measured stage position and the detected position of the mark; And Adjusting the deflection position of the charged particle beam based on the plurality of position offsets obtained. The method for adjusting the deflection position of a charged particle beam as described in claim 1, wherein the nonlinear error information includes a nonlinear error of the mark position previously determined by continuously measuring the position of the stage while moving the stage at a constant speed, and the position offset is obtained by correcting the obtained mark position using the nonlinear error. The method for adjusting the deflection position of a charged particle beam as described in claim 1, wherein the nonlinear error information includes a period of the nonlinear error obtained by moving the stage a predetermined amount and measuring the position of a mark on the stage while the stage is stationary, and the position offset is obtained by synchronizing the predetermined interval with the period of the nonlinear error. The method for adjusting the deflection position of a charged particle beam as described in claim 1 adjusts the deflection position by polynomial approximation. A charged particle beam drawing method is provided, wherein a deflection position of the charged particle beam is adjusted by the deflection position adjustment method of the charged particle beam as described in claim 1 to draw a pattern.