Optical device and charged particle beam device

Abstract

Provided are an optical device (100) capable of irradiating a sample (101) with measurement light (110) and state change light (120) from a single passage hole (130), and a charged particle beam device. The optical device (100) comprises a measurement light source (111) that emits the measurement light (110), which is light with which the sample (101) is irradiated and which is used to measure the height of the sample (101), the passage hole (130) that is disposed between the measurement light source (111) and the sample (101) and through which the measurement light (110) passes, a state change light source (121) that emits the state change light (120), which is light with which the sample (101) is irradiated and which changes the state of the sample, and a control unit (150) that controls each unit, the optical device (100) being characterized by additionally comprising a beam combiner (131) that guides the state change light (120) to the passage hole (130).

Description

Optical device and charged particle beam device

[0001] The present invention relates to an optical device that irradiates a sample with measurement light, which is light used for measuring the height of the sample, and state change light, which is light that changes the state of the sample, and a charged particle beam device including the optical device.

[0002] A charged particle beam device is a device that detects secondary electrons and reflected electrons generated in a sample irradiated with a charged particle beam such as an electron beam, and acquires an observation image of the sample based on a detection signal. For focusing the charged particle beam necessary for improving the image quality of the observation image, it is important to accurately measure the height of the sample.

[0003] Patent Document 1 discloses that a two-dimensional slit image is generated by detecting the reflected light of two-dimensional slit light projected obliquely above the sample, and the height of the sample is accurately measured by excluding an asymmetric waveform with a large detection error from the two-dimensional slit image. The two-dimensional slit light in Patent Document 1 is an example of the measurement light used for measuring the height of the sample.

[0004] Patent Document 2 also discloses that in order to prevent deterioration of the image quality of the observation image due to abnormal charging of the sample, light is irradiated onto the sample while a charged particle beam is irradiated. The light irradiated onto the sample in Patent Document 2 is an example of the state change light that changes the state of the sample.

[0005] JP-A-2007-132836, JP-A-2003-151483

[0006] However, in Patent Document 1 and Patent Document 2, insufficient consideration is given to downsizing the device. In order to introduce measurement light used for measuring the height of the sample and state change light that changes the state of the sample into an observation device such as a charged particle beam device, a passage hole through which light passes is required, and providing the passage hole individually increases the size of the device.

[0007] Therefore, an object of the present invention is to provide an optical device and a charged particle beam device capable of irradiating a sample with measurement light and state change light from a single passage hole.

[0008] To achieve the above objective, the present invention provides an optical device comprising: a measuring light source that emits measuring light used to measure the height of a sample; a through hole disposed between the measuring light source and the sample through which the measuring light passes; a state-changing light source that emits state-changing light used to change the state of the sample; and a control unit that controls each part, further comprising a beam combiner that guides the state-changing light to the through hole.

[0009] According to the present invention, it is possible to provide an optical device and a charged particle beam device capable of irradiating a sample with measurement light and state-changing light through a single through-hole. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments for carrying out the invention.

[0010] Figure 1 shows an example of the overall configuration of the optical device of Example 1. Figure 2 describes the height measurement system. Figure 3 shows an example of controlling the irradiation position and focus of the state-changing light. Figure 4 shows another example of controlling the irradiation position and focus of the state-changing light. Figure 5 shows another example of controlling the irradiation position and focus of the state-changing light. Figure 6 shows another example of controlling the irradiation position and focus of the state-changing light. Figure 7 shows a change in the incident angle of the state-changing light onto the sample. Figure 8 shows another example of controlling the irradiation position and focus of the state-changing light. Figure 9 shows an example of a configuration that suppresses aberrations of the measurement light. Figure 1 shows an example of the overall configuration of a charged particle beam equipped with the optical device of Example 1.

[0011] Hereinafter, embodiments of the optical apparatus and charged particle beam apparatus according to the present invention will be described with reference to the attached drawings. The charged particle beam apparatus is a device that detects secondary electrons and backscattered electrons generated from a sample by irradiating the sample with a charged particle beam such as an electron beam, and generates an observation image based on the detection signal, for example, a scanning electron microscope.

[0012] An example of the overall configuration of the optical apparatus of Example 1 will be explained using Figure 1. The optical apparatus 100 is a device that assists in the observation of the sample 101 by the sample observation unit 141 of a charged particle beam apparatus, etc., and measures the height of the sample 101 and changes the state of the sample 101. The sample observation unit 141 has an optical axis 140 shown by a dashed line in Figure 1, and the observation field is the intersection of the optical axis 140 and the surface of the sample 101 and its vicinity. The optical axis 140 is perpendicular to the horizontal plane having the X and Y axes and parallel to the Z axis.

[0013] The optical device 100 includes a measurement light source 111, a slit plate 112, a focusing lens 113, a detection lens 114, a light-receiving element 115, a state-changing light source 121, a beam shaper 122, a stage 123, a through hole 130, a beam combiner 131, and a control unit 150. The measurement light source 111, slit plate 112, focusing lens 113, detection lens 114, and light-receiving element 115 constitute a height measurement system for measuring the height of the sample 101.

[0014] The height measurement system will be explained using Figure 2. The measurement light source 111 emits measurement light 110, which is the light irradiated onto the sample 101 and used to measure the height of the sample 101. The slit plate 112 has a slit that narrows the measurement light 110. The focusing lens 113 focuses the measurement light 110 narrowed by the slit plate 112 onto the sample 101. The measurement light 110 focused by the focusing lens 113 passes through the beam combiner 131 and the through hole 130 and irradiates the sample 101. The beam combiner 131 and the through hole 130 are positioned between the measurement light source 111 and the sample 101 and are transparent to the measurement light 110. The angle between the optical axis 140 and the measurement light 110 is the incident angle θ of the measurement light 110.

[0015] The measurement light 110 irradiated through the through hole 130 is reflected by the sample 101. The angle between the optical axis 140 and the reflected measurement light 110 is the reflection angle θ. The detection lens 114 focuses the measurement light 110 reflected by the sample 101 onto the photodetector 115. The photodetector 115 detects the measurement light 110 focused by the detection lens 114 and outputs the position of the measurement light 110. Since the position of the measurement light 110 moves when the height of the sample 101 changes, the amount of change in the height of the sample 101 ΔZ can be calculated from the amount of movement ΔS of the position of the measurement light 110 using, for example, the following formula.

[0016] ΔZ = ΔS / (2Md・sinθ) ... (Equation 1) Here, Md is the magnification of the detection lens 114.

[0017] Returning to the explanation of Figure 1, a state-changing system is constructed by a state-changing light source 121, a beam shaper 122, and a stage 123 to change the state of the sample 101. The state-changing light source 121 emits state-changing light 120, which is light irradiated onto the sample 101 and changes the state of the sample 101. The beam shaper 122 adjusts the illuminance distribution of the state-changing light 120, and for example, adjusts it so that the illuminance of the state-changing light 120 is uniform in the observation field of view of the sample observation unit 141. Various lenses such as spherical lenses, aspherical lenses, cylindrical lenses, axicon lenses, and metalenses, as well as diffractive optical elements, microlens arrays, spatial light modulators, and deformable mirrors can be used in the beam shaper 122. The stage 123 supports the state-changing light source 121 and the beam shaper 122 and moves in the direction of emission of the state-changing light 120 or in a direction perpendicular to the emission direction.

[0018] The beam combiner 131 allows the measurement light 110 to pass through and guides the state-changed light 120 to the through-hole 130 through which the measurement light 110 passes. In other words, the beam combiner 131 is a transparent plate on the side where the measurement light 110 is incident and a reflector on the side where the state-changed light 120 is incident. For example, a harmonic separator or a polarizing beam splitter can be used for the beam combiner 131. Because the beam combiner 131 guides the state-changed light 120 to the through-hole 130 through which the measurement light 110 passes, the measurement light 110 and the state-changed light 120 can be irradiated onto the sample 101 from a single through-hole 130. As a result, it is not necessary to provide separate through-holes 130, and the size of the optical device can be suppressed.

[0019] Furthermore, since the state-changing light 120 is irradiated onto the sample 101 at an incident angle θ, similar to the measurement light 110, if the beam shape of the state-changing light 120 is circular with a beam diameter D, an ellipse with a minor axis D and a major axis D / cosθ is formed on the surface of the sample 101.

[0020] The control unit 150 is, for example, a computer, and controls the operation of each part of the height measurement system and the state change system. Furthermore, the control unit 150 calculates the amount of movement ΔS of the measurement light 110 and the amount of change ΔZ of the height of the sample 101 based on the output from the light receiving element 115 of the height measurement system.

[0021] Incidentally, if the height of the sample 101 changes, the irradiation position of the state-changing light 120 may deviate from the optical axis 140 of the sample observation unit 141, or the focus of the state-changing light 120 may shift away from the sample 101. Therefore, the irradiation position of the state-changing light 120 and the focus of the state-changing light 120 are controlled based on the amount of change ΔZ of the height of the sample 101 measured using the measurement light 110.

[0022] An example of controlling the irradiation position and focus of the state-changing light 120 will be explained using Figure 3. The emission direction of the state-changing light 120 is the F-axis, and the L-axis is perpendicular to the FY plane. The irradiation position of the state-changing light 120, which has deviated from the optical axis 140 due to the height variation ΔZ of the sample 101, can be aligned with the optical axis 140 by moving the stage 123, which supports the state-changing light source 121 and the beam shaper 122, by ΔL in the direction of the L-axis. ΔL is calculated using the following formula.

[0023] ΔL = ΔZ・sinθ …(Equation 2) Furthermore, the focus of the state-changing light 120, which is shifted from the sample 101 due to the height variation ΔZ of the sample 101, can be adjusted to the sample 101 by moving the stage 123, which supports the state-changing light source 121 and the beam shaper 122, by ΔF in the direction of the F axis. Note that ΔF is calculated using the following equation.

[0024] ΔF = ΔZ・cosθ …(Equation 3) The movement of the stage 123 in the L-axis direction or the F-axis direction, based on the measured value of the height variation ΔZ of the sample 101, is controlled by the control unit 150. Furthermore, according to (Equation 3), the larger the incident angle θ, the smaller the amount of movement ΔF of the stage 123 in the F-axis direction can be. For example, when θ = 45°, ΔF = 0.7・ΔZ, whereas when θ = 80°, it can be reduced to ΔF = 0.17・ΔZ.

[0025] Using Figure 4, another example of controlling the irradiation position and focus of the state-changing light 120 will be explained. If the state-changing light source 121 is a laser light source, the weight of the state-changing light source 121 will increase, and the stage 123 that moves while supporting the state-changing light source 121 will also become larger. Therefore, in Figure 4, the state-changing light source 121 remains fixed, and only the relatively lightweight beam shaper 122 is moved by the stage 123 in the direction of the L axis or the F axis. Thus, the configuration illustrated in Figure 4 makes it possible to miniaturize the optical device 100.

[0026] Using Figure 5, another example of controlling the irradiation position and focus of the state-changing light 120 will be explained. When the beam shaper 122 is a diffractive optical element, high-precision axial alignment between the state-changing light source 121 and the beam shaper 122 is required, making it difficult to move only the beam shaper 122 in the direction of the L axis.

[0027] Therefore, in Figure 5, a tilt mirror 500 is added that reflects the state-changing light 120 emitted from the beam shaper 122 toward the beam combiner 131. The tilt angle α of the tilt mirror 500 is changeable and is controlled by the control unit 150. That is, the control unit 150 controls the irradiation position of the state-changing light 120 by changing the tilt angle α based on the measured value of the height variation ΔZ of the sample 101.

[0028] The tilt mirror 500 can be a galvanometer mirror or a piezoelectric mirror, etc. The focus of the state-changing light 120 is controlled by the control unit 150 moving the beam shaper 122 in the direction of the F axis based on the fluctuation amount ΔZ.

[0029] By the way, if the irradiation field of the phase-changing light 120 on the surface of the sample 101 is too large compared to the observation field of the sample observation unit 141, it becomes necessary to use a high-power light source for the phase-changing light source 121, which leads to increased costs. To reduce the irradiation field of the phase-changing light 120, the Working Distance (WD), which is the distance from the beam shaper 122 to the focal point of the phase-changing light 120, should be shortened. However, in the configurations of Figures 1, 4, and 5, the distance from the beam shaper 122 to the sample 101 is the WD, and because the WD is long, it is difficult to reduce the irradiation field of the phase-changing light 120. Therefore, the WD is shortened by placing a focusing lens 113 between the beam shaper 122 and the through hole 130.

[0030] Using Figure 6A, an example of a configuration for controlling the irradiation position and focus of the state-changing light 120 while shortening the WD will be explained. In Figure 6A, the focusing lens 113, which is positioned between the slit plate 112 and the beam combiner 131 in Figure 5, is positioned between the beam combiner 131 and the through hole 130. When the focal length of the focusing lens 113 is f, the distance from the focusing point of the state-changing light 120 to the front main surface of the focusing lens 113 is a, and the distance from the rear main surface of the focusing lens 113 to the sample 101 is b, the focusing lens 113 is positioned at a location that satisfies 1 / f = 1 / a + 1 / b. Since the focusing point of the state-changing light 120 is on the WD surface 600, which is WD away from the beam shaper 122, the distance from the WD surface 600 to the front main surface of the focusing lens 113 is a.

[0031] According to the configuration illustrated in Figure 6A, the WD can be shortened, so the irradiation field of the state-changing light 120 on the surface of the sample 101 can be reduced, and the state-changing light source 121 does not need to be a high-power light source.

[0032] Furthermore, even if the size and shape of the beam emitted from the beam shaper 122 do not match the desired specifications, the beam size and shape can be adjusted by adjusting the magnification of the focusing lens 113 or by using an anisotropic magnification lens in the focusing lens 113. In addition, by placing a beam profiler that measures the illuminance distribution on the WD surface 600, it becomes easier to align the axes of the state-changing light source 121 and the beam shaper 122.

[0033] Furthermore, the irradiation position of the state-changing light 120 is controlled by changing the tilt angle α of the tilt mirror 500, and the focus of the state-changing light 120 is controlled by moving the beam shaper 122 in the F-axis direction.

[0034] However, when the tilt angle α of the tilt mirror 500 is changed, the angle of incidence of the state-changed light 120 onto the sample 101 also changes. In Figure 6B, the state-changed light 120 before changing the tilt angle α is shown as a solid line, and the state-changed light 120 after changing the tilt angle α is shown as a dotted line. That is, as the tilt angle α is changed, the angle of incidence and the angle of reflection of the state-changed light 120 in the beam combiner 131 change, and therefore the angle of incidence onto the sample 101 also changes. A change in the angle of incidence of the state-changed light 120 onto the sample 101 changes the effect that the state-changed light 120 has on the sample 101, so it is desirable that the angle of incidence of the state-changed light 120 onto the sample 101 remain constant.

[0035] Therefore, as illustrated in Figure 7A, the tilt mirror 500 is positioned at the front focal point 700 of the focusing lens 113. The light emitted from the front focal point 700 of the focusing lens 113 becomes a parallel beam after passing through the focusing lens 113. Therefore, by positioning the tilt mirror 500 at the front focal point 700 of the focusing lens 113, even when the tilt angle α of the tilt mirror 500 is changed to control the irradiation position of the state-changing light 120, the incident angle of the state-changing light 120 on the sample 101 can be kept constant, as shown in Figure 7B.

[0036] Furthermore, in order to control the irradiation position of the state-changing light 120 in accordance with the fluctuation in the height of the sample 101, the amount of angle change Δα when changing the tilt angle α of the tilt mirror 500 can be calculated by the following formula.

[0037] Δα = 0.5arctan{ΔZ・sinθ / (M・N)} ... (Equation 4) Here, ΔZ is the amount of change in the height of the sample 101, θ is the angle of incidence of the state-changing light 120 onto the sample 101, M is the magnification of the focusing lens 113, and N is the distance from the focal point of the state-changing light 120 to the tilt mirror 500.

[0038] Alternatively, the angle change Δα of the tilt mirror 500 may be calculated using the following formula.

[0039] Δα = 0.5arctan(ΔZ・sinθ / F) …(Equation 5) Here, F is the focal length of the condensing lens 113 and the distance from the condensing lens 113 to the sample 101.

[0040] An example of a configuration for suppressing aberrations in the measurement light 110 will be explained using Figure 8. If the beam combiner 131 is placed in a region where the light spreads or a region where the light focuses, the aberrations in the beam combiner 131 will increase. Therefore, it is desirable to place the beam combiner 131 in a region where the light is a parallel beam.

[0041] In Figure 8, a collimating lens 801 is positioned between the measurement light source 111 and the beam combiner 131. A slit plate 112 is positioned at the front focal point 802 of the collimating lens 801. The collimating lens 801 makes the measurement light 110 a parallel beam, so the beam combiner 131 is positioned in the region where the measurement light 110 is a parallel beam. As a result, aberrations of the measurement light 110 are suppressed in the beam combiner 131, improving the accuracy of height measurement of the sample 101. The measurement light 110, which has become a parallel beam, is then focused onto the sample 101 by a focusing lens 113.

[0042] Furthermore, when the wavelength of the measurement light 110 and the wavelength of the phase-changing light 120 are different, it is preferable to use an achromatic lens for the focusing lens 113. By using an achromatic lens for the focusing lens 113, the measurement light 110 and the phase-changing light 120, which have different wavelengths, can be focused onto the sample 101. As a result, even when the wavelength of the measurement light 110 and the wavelength of the phase-changing light 120 are different, the accuracy of height measurement of the sample 101 is improved, and the phase-changing light 120 can be appropriately irradiated onto the sample 101.

[0043] A telecentric lens may also be used for the condensing lens 113. Since a telecentric lens has a flat focal plane, when the tilt angle α of the tilt mirror 500 is changed, the state-changed light 120 emitted from the condensing lens 113 shifts in parallel. Also, since a telecentric lens focuses light to a position proportional to the angle of incidence to the lens, the amount of angle change Δα of the tilt mirror 500 can be calculated by the following equation.

[0044] Δη = 0.5ΔΖ・sinθ / F … (Equation 6) In (Equation 4) and (Equation 5), the relationship between the amount of change ΔΖ in the height of the sample 101 and the amount of angular change Δη of the tilt mirror 500 is non-linear, whereas in (Equation 6) it is linear. Therefore, by using a telecentric lens for the condenser lens 113, the angle control of the tilt mirror 500 becomes easier.

[0045] Using FIG. 9, an example of the overall configuration of a charged particle beam apparatus including the optical device of Example 1 will be described. The charged particle beam apparatus 900 includes an electron gun 901, an objective lens 903, a detector 905, and a sample stage 906 inside a vacuum chamber 907.

[0046] The electron gun 901 emits an electron beam 902 that irradiates the sample 101. The objective lens 903 focuses the electron beam 902 on the sample 101. The detector 905 detects the signal electrons 904 emitted from the sample 101 due to the irradiation of the electron beam 902 and transmits a detection signal to the control unit 150. In the control unit 150, an observation image of the sample 101 is generated based on the transmitted detection signal. The sample stage 906 holds the sample 101 and moves in the XYZ directions. When the sample stage 906 moves in the XY directions, the observed region of the sample 101 changes, and when it moves in the Z direction, the height of the sample 101 changes.

[0047] Also, on the top plate 908, which is a part of the vacuum chamber 907, there is provided an integrated unit including a measurement light source 111, a slit plate 112, a condenser lens 113, a state change light source 121, a beam shaper 122, a stage 123, a through hole 130, and a beam combiner 131, and an integrated unit including a detection lens 114 and a light receiving element 115. That is, a part of the height measurement system and the state change system are integrated. Note that the optical device provided on the top plate 908 is not limited to the configuration of FIG. 1 and may be those exemplified in FIGS. 4, 5, 6A, 7A, and 8.

[0048] According to the configuration of FIG. 9, since the measurement light 110 emitted from the measurement light source 111 and the state change light 120 emitted from the state change light source 121 pass through the common passage hole 130, an increase in the size of the charged particle beam apparatus 900 including the optical device can be suppressed. Further, since a part of the height measurement system and the state change system are integrated, even when a displacement occurs in a part of the height measurement system such as the measurement light source 111 due to deformation of the vacuum chamber 907 or the like, a similar displacement occurs in the state change system. As a result, the displacements occurring in both cancel each other out, and the adverse effects due to deformation of the vacuum chamber 907 or the like are suppressed.

[0049] As described above, the embodiments of the present invention have been described. The present invention is not limited to the above embodiments, and the components can be modified and embodied without departing from the gist of the invention. Also, a plurality of components disclosed in the above embodiments may be appropriately combined. Further, some components may be deleted from all the components shown in the above embodiments.

[0050] Optical device 100, sample 101, measurement light 110, measurement light source 111, slit plate 112, condenser lens 113, detection lens 114, light receiving element 115, state change light 120, state change light source 121, beam shaper 122, stage 123, passage hole 130, beam combiner 131, optical axis 140, sample observation unit 141, control unit 150, tilt mirror 500, WD plane 600, front focal point 700, collimating lens 801, front focal point 802, charged particle beam apparatus 900, electron gun 901, electron beam 902, objective lens 903, signal electron 904, detector 905, sample stage 906, vacuum chamber 907, top plate 908.

Claims

1. An optical device comprising: a measuring light source that emits measuring light used to measure the height of a sample; a through hole disposed between the measuring light source and the sample through which the measuring light passes; a state-changing light source that emits state-changing light used to change the state of the sample; and a control unit that controls each part, further comprising a beam combiner that guides the state-changing light to the through hole.

2. An optical apparatus according to claim 1, wherein the control unit controls the irradiation position of the state-changing light based on the amount of change in the height of the sample measured using the measurement light.

3. An optical apparatus according to claim 2, further comprising a beam shaper disposed between the state-changing light source and the beam combiner for adjusting the illuminance distribution of the state-changing light, wherein the control unit moves the state-changing light source and the beam shaper in a direction perpendicular to the emission direction of the state-changing light.

4. An optical apparatus according to claim 3, wherein the control unit sets the amount of movement ΔL of the state-changing light source and the beam shaper to ΔL = ΔZ・sinθ when the amount of variation is ΔZ and the angle of incidence of the state-changing light to the sample is θ.

5. An optical apparatus according to claim 2, further comprising a beam shaper disposed between the state-changing light source and the beam combiner for adjusting the illuminance distribution of the state-changing light, wherein the control unit controls the irradiation position by moving the beam shaper in a direction perpendicular to the emission direction of the state-changing light.

6. An optical device according to claim 2, further comprising: a beam shaper disposed between the state-changing light source and the beam combiner for adjusting the illuminance distribution of the state-changing light; a tilt mirror disposed between the beam shaper and the beam combiner for reflecting the state-changing light toward the beam combiner, wherein the control unit controls the irradiation position by changing the angle of the tilt mirror.

7. An optical apparatus according to claim 1, wherein the control unit controls the focus of the state-changing light based on the amount of change in the height of the sample measured using the measurement light.

8. An optical device according to claim 7, further comprising a beam shaper disposed between the state-changing light source and the beam combiner for adjusting the illuminance distribution of the state-changing light, wherein the control unit controls the focus by moving the beam shaper in the direction of emission of the state-changing light.

9. An optical apparatus according to claim 7, further comprising a focusing lens disposed between the beam combiner and the through hole, wherein the focusing lens is positioned such that 1 / f = 1 / a + 1 / b when the focal length of the focusing lens is f, the distance from the convergence point of the state-changing light to the front main surface of the focusing lens is a, and the distance from the rear main surface of the focusing lens to the sample is b.

10. An optical device according to claim 9, further comprising: a beam shaper disposed between the state-changing light source and the beam combiner for adjusting the illuminance distribution of the state-changing light; a tilt mirror disposed between the beam shaper and the beam combiner for reflecting the state-changing light toward the beam combiner; the control unit controls the irradiation position of the state-changing light by changing the angle of the tilt mirror; and the tilt mirror is positioned at the front focal point of the focusing lens.

11. An optical apparatus according to claim 10, wherein the control unit sets the angle change amount Δα of the tilt mirror to Δα = 0.5arctan{ΔZ・sinθ / (M・N)} when the amount of variation is ΔZ, the angle of incidence of the state-changing light onto the sample is θ, the magnification of the focusing lens is M, and the distance from the focusing point to the tilt mirror is N.

12. An optical apparatus according to claim 1, further comprising a collimating lens disposed between the measuring light source and the beam combiner, and a focusing lens disposed between the beam combiner and the through hole.

13. An optical device according to claim 12, characterized in that when the wavelength of the measurement light and the wavelength of the state change light are different, the focusing lens is an achromatic lens.

14. An optical device according to claim 12, characterized in that the focusing lens is a telecentric lens.

15. A charged particle beam apparatus comprising the optical apparatus described in claim 1, characterized in that an observation image of the sample is generated by irradiating the sample with a charged particle beam.

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