Noise evaluation method for charged particle beam lithography apparatus and substrate for noise evaluation

Abstract

This invention provides a noise evaluation method and a noise evaluation substrate that enable accurate and rapid evaluation of noise generated in a charged particle beam lithography system. [Solution] The noise evaluation method for a charged particle beam writing apparatus according to this embodiment involves irradiating a charged particle beam onto a mark on a noise evaluation substrate placed on a stage that moves at a constant velocity, deflecting the charged particle beam in accordance with the movement of the stage so that the irradiation position of the charged particle beam is at a predetermined relative coordinate of the mark, detecting the amount of reflected charged particles from the mark, and performing noise evaluation based on the detection result of the amount of reflected charged particles.

Description

Technical Field

[0001] The present invention relates to a noise evaluation method for a charged particle beam drawing apparatus and a substrate for noise evaluation.

Background Art

[0002] With the high integration of LSIs, the circuit line widths required for semiconductor devices have been gradually miniaturized year by year. In order to form a desired circuit pattern on a semiconductor device, a method of reducing and transferring a high-precision original pattern formed on quartz onto a wafer using a reduction projection exposure apparatus has been adopted. For the production of a high-precision original pattern, a so-called electron beam lithography technique in which a resist is exposed by an electron beam drawing apparatus to form a pattern is used.

[0003] In an electron beam drawing apparatus, noise is generated due to characteristics of electric circuits, performance degradation of each component, mechanical vibration, etc. Noise causes beam size fluctuations and beam position fluctuations, deteriorating the drawing accuracy. Therefore, it is necessary to detect and analyze the noise and take countermeasures.

[0004] Conventionally, while moving a stage on which a substrate is placed at a constant speed, a plurality of L-shaped patterns are drawn in a row, development processing is performed to form a resist pattern, and its position and size are measured with a reticle resist registration measurement system (optical position measuring device), and the measurement results are analyzed to evaluate noise components. However, this method has a problem in that it takes time and effort because it involves drawing (exposure), development, measurement, etc.

[0005] Also, as another noise detection method, a beam is irradiated onto an edge portion of a fixed mark installed on a stage while the stage is stopped, reflected electrons are detected, and the time change of the amount of reflected electrons is analyzed by FFT (Fast Fourier Transform) to obtain the frequency of the noise. Although this method can obtain the frequency of the noise in a short time, it is difficult to accurately evaluate the noise because the environment is significantly different from the actual drawing process, such as the presence or absence of stage movement and the beam irradiation location.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-326009 [Patent Document 2] Japanese Patent Publication No. 2021-044352 [Patent Document 3] Japanese Patent Publication No. 2006-073867 [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a noise evaluation method and a noise evaluation substrate that can accurately evaluate noise generated in a charged particle beam lithography apparatus in a short amount of time. [Means for solving the problem]

[0008] A noise evaluation method for a charged particle beam writing apparatus according to one aspect of the present invention involves irradiating a charged particle beam onto a mark on a noise evaluation substrate placed on a stage that moves at a constant velocity, deflecting the charged particle beam in accordance with the movement of the stage so that the irradiation position of the charged particle beam is at a predetermined relative coordinate of the mark, detecting the amount of reflected charged particles from the mark, and performing a noise evaluation based on the detection result of the amount of reflected charged particles.

[0009] A noise evaluation substrate according to one aspect of the present invention is a noise evaluation substrate used in a noise evaluation method for a charged particle beam lithography apparatus according to one aspect of the present invention, and comprises a substrate and a plurality of marks provided on the substrate, wherein the plurality of marks are arranged in a matrix at predetermined intervals in a first direction and a second direction orthogonal to the first direction. [Effects of the Invention]

[0010] According to the present invention, noise generated in a charged particle beam lithography apparatus can be evaluated accurately in a short amount of time. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of a drawing apparatus according to an embodiment of the present invention. [Figure 2] This is a flowchart illustrating the noise evaluation method according to the same embodiment. [Figure 3] (a) is a diagram showing an example of a mark, and (b) is a diagram showing an example of a beam irradiation position relative to the mark. [Figure 4] This diagram shows a beam that follows the movement of a mark. [Figure 5] (a) is a figure showing an example of the measurement results of the amount of backscattered electrons, and (b) is a figure showing an example of the noise frequency obtained by analysis. [Figure 6] This is a plan view of a noise evaluation mask. [Figure 7] This diagram explains how to switch between measurement target marks. [Modes for carrying out the invention]

[0012] In the following embodiments, an electron beam configuration will be described as an example of a charged particle beam. However, the charged particle beam is not limited to an electron beam; it may also be a beam using charged particles such as an ion beam.

[0013] Figure 1 is a conceptual diagram showing the configuration of a drawing apparatus in an embodiment. As shown in Figure 1, the drawing apparatus 1 comprises a drawing chamber 2 that houses a stage 4 supporting a substrate 5, an electron-optical lens barrel 3 that irradiates the substrate 5 on the stage 4 with an electron beam B, a control device 6 that controls each part, and a stage control circuit 9. The stage 4 is movable in the horizontal plane in the mutually orthogonal X-axis and Y-axis directions by a movement mechanism and is controlled by the stage control circuit 9.

[0014] The electron optical column 3 is provided above the drawing room 2 and connected to the inside of the drawing room 2. The electron optical column 3 forms and deflects the electron beam B by an optical system and irradiates the substrate 5 on the stage 4. The electron optical column 3 includes an electron source 21 such as an electron gun that emits the electron beam B, an illumination lens 22 that condenses the electron beam B, a first aperture 23 for beam shaping, a projection lens 24 for projection, a shaping deflector 25 for beam shaping, a second aperture 26 for beam shaping, an objective lens 27 that forms a beam focus on the substrate 5, and a sub-deflector 28 and a main deflector 29 for controlling the beam shot position with respect to the substrate 5.

[0015] In the electron optical column 3, the electron beam B is emitted from the electron source 21 and irradiated onto the first aperture 23 by the illumination lens 22. The first aperture 23 has, for example, a rectangular opening. When the electron beam B passes through the first aperture 23, the cross-sectional shape of the electron beam is shaped into a rectangle and projected onto the second aperture 26 by the projection lens 24.

[0016] The second aperture 26 has an opening for variable shaping formed therein. The shaping deflector 25 controls the shape and dimensions of the electron beam B by deflecting the projection position on the second aperture 26. The focus of the electron beam B that has passed through the second aperture 26 is aligned with and irradiated onto the substrate 5 on the stage 4 by the objective lens 27. At this time, the sub-deflector 28 and the main deflector 29 can deflect the shot position of the electron beam B with respect to the substrate 5 on the stage 4.

[0017] The drawing room 2 is provided with a detector 8 that detects secondary electrons when the substrate 5 is irradiated with the electron beam B. The detection result of the detector 8 is transmitted to the control device 6.

[0018] The control device 6 includes a drawing control unit 60, a reflected electron amount acquisition unit 61, a mark position identification unit 62, and an analysis unit 63. The functions of each part of the control device 6 may be configured by hardware such as an electric circuit, or may be configured by software such as a program that executes these functions. Alternatively, it may be configured by a combination of hardware and software. Information input and output to each part and information during calculation are stored in a memory (not shown) each time.

[0019] When performing drawing by the electron beam B, shot data for drawing is input to the drawing control unit 60. This shot data is data in which a drawing pattern defined by drawing data is divided into a plurality of stripe regions (the longitudinal direction is the X-axis direction and the short-side direction is the Y-axis direction), and each stripe region is further divided into a large number of sub-regions in a matrix shape.

[0020] When drawing a pattern on the substrate 5 (for example, a mask blank) on the stage 4, the drawing control unit 60 moves the stage 4 in the longitudinal direction (X-axis direction) of the stripe region, positions the electron beam B at each sub-region by the main deflector 29 based on the shot data, and shoots at a predetermined position in the sub-region by the sub-deflector 28 to draw a figure. After that, when the drawing of one stripe region is completed, the stage 4 is stepped in the Y-axis direction and then the drawing of the next stripe region is performed, and this is repeated to perform drawing by the electron beam B on the entire drawing region of the substrate 5.

[0021] Noise occurs in the drawing apparatus 1 due to various factors, and this noise can cause beam size fluctuations and beam position fluctuations, deteriorating the drawing accuracy. Therefore, it is necessary to detect and evaluate the noise. The noise evaluation method according to the present embodiment will be described along the flowchart shown in FIG. 2.

[0022] First, the noise evaluation mask, which will serve as the substrate 5, is transported to the drawing chamber 2 and placed on the stage 4 (step S1). For example, a mask blank is prepared having a quartz substrate, a light-shielding film such as a chromium film provided on the quartz substrate, and a resist layer provided on the chromium film. An electron beam is irradiated onto the mask blank to draw a cross-shaped pattern. The mask blank after drawing is developed, and the exposed (or unexposed) parts of the resist are dissolved and removed to form a resist pattern. This resist pattern is used as a mask to perform an etching process and process the light-shielding film. After that, the resist is peeled off to produce a noise evaluation mask having a cross mark 7 as shown in Figure 3(a).

[0023] With Stage 4 stopped, the noise evaluation mask placed on Stage 4 is scanned with electron beam B (step S2). Detector 8 detects backscattered electrons. Backscattered electron quantity acquisition unit 61 receives measurement data of the backscattered electron quantity from detector 8. Mark position identification unit 62 identifies the position of the cross mark 7 based on the change in the backscattered electron quantity accompanying the scan and the deflection amount (irradiation position) of electron beam B (step S3).

[0024] The movement of Stage 4 begins (Step S4). The Stage Control Circuit 9 controls Stage 4 to move at a constant speed at a predetermined velocity.

[0025] The electron beam B is irradiated onto the cross mark 7 (step S5). As shown in Figure 4, the deflection amount of the electron beam B is controlled to follow the cross mark 7, which moves with the stage 4, thereby deflecting the electron beam B. This maintains the irradiation position of the electron beam B on the noise evaluation mask at the same relative coordinate (it continues to irradiate the same position (relative coordinate) on the mark).

[0026] The detector 8 detects the backscattered electrons and transmits the measurement data of the amount of backscattered electrons to the control device 6 (step S6).

[0027] For each of the four locations P1 to P4 shown in Figure 3(b), beam irradiation and measurement of the amount of backscattered electrons are performed (steps S5 to S7).

[0028] Position P1 is where half of the electron beam B in the Y direction strikes the edge of the cross mark 7. The measurement results of the amount of reflected electrons when electron beam B is irradiated at position P1 show the effect of noise that shifts the beam irradiation position in the Y direction.

[0029] Position P2 is where half of the electron beam B in the X direction strikes the edge of the cross mark 7. The measurement results of the amount of backscattered electrons when electron beam B is irradiated at position P2 show the effect of noise that shifts the beam irradiation position in the X direction.

[0030] Position P3 is the location where the entire electron beam B aligns with the cross mark 7. The measurement results of the amount of reflected electrons when electron beam B is irradiated at position P3 show the influence of noise that fluctuates the beam output.

[0031] Position P4 is the position where the entire electron beam B is outside the cross mark 7. The measurement results of the amount of backscattered electrons when electron beam B is irradiated at position P4 show the effect of noise on the detection accuracy of detector 8.

[0032] For example, when electron beam B is irradiated at position P1, the amount of backscattered electrons detected by detector 8 will be as shown in Figure 5(a).

[0033] After the measurements at P1 to P4 are completed, the analysis unit 63 performs an FFT (Fast Fourier Transform) analysis on the waveform of the backscattered electron quantity at each measurement position and decomposes it into frequency components (step S8). For example, the measurement results of the backscattered electron quantity are converted into frequency data showing a power spectrum as shown in Figure 5(b).

[0034] The analysis unit 63 identifies frequencies with power above a predetermined value as noise (step S9). For example, in the example shown in Figure 5(b), it identifies noise at frequencies f1 and f2.

[0035] Based on the identified noise frequency, the noise source is estimated, and countermeasures are taken. For example, if the noise frequency suggests that the noise source is vibration of the circulating water in a water cooling system, the impact of the noise can be suppressed by changing the path through which the circulating water is routed.

[0036] By irradiating a mark formed on a noise evaluation mask with a beam and detecting the noise frequency from the amount of reflected electrons, noise can be detected in a short time. Furthermore, since the beam is irradiated onto the noise evaluation mask on stage 4 while stage 4 is moving, the environment is almost the same as during actual pattern drawing processing, allowing for accurate noise evaluation.

[0037] The frequency band of noise detectable by the above method depends on the size of the deflection region of the main deflector 29 and the movement speed of the stage 4. The size of the deflection region corresponds to the distance over which electron beam B can track Mark 7.

[0038] For example, if the deflection region is 4 μm and the stage speed is 100 mm / s, the time that electron beam B can track the moving mark 7 is 40 μs. That is, the measurement result for the amount of backscattered electrons over 40 μs can be obtained. Therefore, the lowest frequency at which noise can be detected is 25 kHz.

[0039] When the deflection region is 81 μm and the stage speed is 100 mm / s, the time that electron beam B can track the moving mark 7 is 810 μs. In other words, the measurement result for the amount of backscattered electrons over 810 μs can be obtained. Therefore, the lowest frequency at which noise can be detected is approximately 1.2 kHz.

[0040] By forming multiple cross marks 7 along the stage movement direction on the noise evaluation mask, and irradiating each of the multiple cross marks 7 with electron beam B (step S5 in Figure 2) and detecting backscattered electrons (step S6), the frequency range in which noise can be detected can be broadened by increasing the measurement data of the amount of backscattered electrons.

[0041] For example, the noise evaluation mask has a grid pattern 70, as shown in Figure 6, in which cross marks 7 are arranged in a matrix at equal intervals along the X and Y axes, and adjacent cross marks 7 are connected. In other words, multiple line patterns extending in the X axis direction at predetermined intervals and multiple line patterns extending in the Y axis direction at predetermined intervals are orthogonal, and the intersection points are cross marks 7.

[0042] As shown in Figure 7, when Stage 4 moves in the +X direction, the cross marks on the measurement target are sequentially switched in the -X direction while tracking them as marks 7_1, 7_2, 7_3, etc., so that the irradiation position of electron beam B on the noise evaluation mask is maintained at the same relative coordinates for each cross mark. Similarly, detector 8 detects backscattered electrons and acquires measurement data of the amount of backscattered electrons. The more cross marks on the measurement target there are, the more measurement data of the amount of backscattered electrons there is, and the wider the frequency band in which noise can be detected (the lower the lowest frequency in which noise can be detected).

[0043] The processes in steps S4 to S7 of the flowchart in Figure 2 may be performed at multiple different stage speeds, and the analysis may be performed for each stage speed to calculate the noise frequency. This can improve the accuracy of noise frequency identification.

[0044] In the above embodiment, an example was described in which a cross mark formed on a light-shielding film provided on a quartz substrate was used as a noise evaluation mask. However, a metal film such as tungsten may be deposited on the light-shielding film, and the metal film may be processed into a cross-shaped mark to be used as a noise evaluation mask. Furthermore, the mask is not limited to a cross mark; a line and space or an L-shaped mark may also be used. In addition, the substrate used for noise evaluation is not limited to a mask; any substrate subject to drawing processing, including wafers, can be used.

[0045] Although the above embodiment described an example of a single-beam lithography system, it is also applicable to a multi-beam lithography system.

[0046] In the above embodiment, a two-stage deflection configuration having a main deflector 29 and a sub-deflector 28 was described, but a three-stage deflection configuration with an additional sub-sub-deflector may also be provided.

[0047] It should be noted that the present invention is not limited to the embodiments described above, and the components can be modified and implemented in practice without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiments. Moreover, components from different embodiments may be appropriately combined. [Explanation of Symbols]

[0048] 1 Drawing device 4 stages 5 circuit boards 6 Control device 7 Cross mark 8 detectors 21 Electron source 28 Sub deflector 29 Main deflector

Claims

1. A charged particle beam is irradiated onto a mark on a noise evaluation substrate placed on a stage moving at a constant velocity. The charged particle beam is deflected in accordance with the movement of the stage so that the irradiation position of the charged particle beam is at a predetermined relative coordinate of the mark. The amount of reflected charged particles from the aforementioned mark is detected, A noise evaluation method for a charged particle beam lithography apparatus, which performs noise evaluation based on the detection results of the amount of reflected charged particles.

2. A noise evaluation method for a charged particle beam lithography apparatus according to claim 1, comprising converting the detection result of the amount of reflected charged particles into frequency data and identifying the noise frequency from the frequency data.

3. A noise evaluation method for a charged particle beam lithography apparatus according to claim 1 or 2, wherein a plurality of marks are formed on the noise evaluation substrate along the stage movement direction, and the amount of reflected charged particles is detected by sequentially switching the marks to be irradiated so that the irradiation position of the charged particle beam is at the predetermined relative coordinates of the marks to be irradiated.

4. A noise evaluation method for a charged particle beam lithography apparatus according to claim 2, comprising moving the stage at a constant velocity at multiple different speeds and detecting the amount of reflected charged particles at each movement speed.

5. At least one of the following is obtained: a first detection result for the amount of reflected charged particles when the charged particle beam is irradiated so that only a portion of the charged particle beam hits the edge portion of the mark; a second detection result for the amount of reflected charged particles when the charged particle beam is irradiated so that the entire charged particle beam hits the mark; and a third detection result for the amount of reflected charged particles when the charged particle beam is irradiated so that the charged particle beam does not hit the mark. A noise evaluation method for a charged particle beam lithography apparatus according to claim 2, comprising converting at least one of the detection results of the first reflected charged particle amount, the detection results of the second reflected charged particle amount, and the detection results of the third reflected charged particle amount into frequency data to identify the noise frequency.

6. A noise evaluation substrate used in the noise evaluation method for a charged particle beam lithography apparatus described in claim 3, A noise evaluation substrate having a substrate and a plurality of marks provided on the substrate, wherein the plurality of marks are arranged in a matrix at predetermined intervals in a first direction and a second direction orthogonal to the first direction.

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