WO2024100897A1

WO2024100897A1 - Charged particle beam device

Info

Publication number: WO2024100897A1
Application number: PCT/JP2022/042114
Authority: WO
Inventors: 大輔石川; 信裕岡井; 和之大野; 哲也新堀; 賢山木
Original assignee: 株式会社日立ハイテク
Priority date: 2022-11-11
Filing date: 2022-11-11
Publication date: 2024-05-16

Abstract

The purpose of the present disclosure is to provide a charged particle beam device that can measure an overall sample by making uniform a sample surface potential. In a charged particle beam device according to the present disclosure, a support member supporting a sample is formed using an insulating material, a surface, of a sample holder, that is in contact with the support member has a first concave portion that increases in depth from the outside of the support member toward the support member, and the support member is disposed in the first concave portion (see fig. 5A).

Description

Charged Particle Beam Device

This disclosure relates to a charged particle beam device that irradiates a sample with a charged particle beam.

In recent years, the market for AR/VR technology, such as wearable device displays, has expanded rapidly, increasing the demand for measuring the patterns of wafers (hereinafter referred to as "insulator wafers") that have insulator substrates such as quartz or sapphire. For this reason, scanning electron microscopes (hereinafter referred to as SEMs) used to inspect and measure semiconductor devices are required to stably measure insulator wafers with the same sensitivity and accuracy as conventional semiconductor wafer measurements, such as those for silicon.

　In an SEM, electrons are generated by applying a high voltage to an electron source, and are accelerated. The electrons are then focused by a focusing lens and irradiated onto the object to be measured. At this time, secondary electrons that are generated according to the shape of the object to be measured are observed by a detector to obtain an SEM image.

Electrons emitted from an electron source have various energies, and the energy spread (ΔE) varies depending on the type of electron source. The electrons contained in the electron beam have different energies, which causes the electron trajectory to focus at different points, resulting in a blurred image when formed (hereafter referred to as chromatic aberration). In general, the smaller the diameter of the electron beam, the smaller the effect of chromatic aberration. When chromatic aberration exists, the minimum diameter dc of the electron beam is given by dc = CcαΔE/E. Here, α is the focusing half angle for an electron beam with a certain acceleration voltage (E), and Cc is called the chromatic aberration coefficient of the objective lens, and is the proportional coefficient of ΔE/E. Cc is a function of the distance (working distance, WD) between the objective lens and the sample.

When the acceleration voltage of the electron beam irradiated to the measurement object is high, the ratio of the energy width of the electron source to the acceleration voltage (ΔE/E) becomes small, so the effects of chromatic aberration are reduced and the resolution is improved. In exchange, the irradiated electrons penetrate deeper and wider into the sample. This causes secondary electrons to be generated even in areas far from the electron beam irradiation point, so the obtained image contains information about the inside of the sample and the fine structure of the measurement object surface cannot be read. Conversely, when the acceleration voltage of the electron beam is low, the ratio of the energy width of the electron source to the acceleration voltage (ΔE/E) becomes large, so the effects of chromatic aberration are increased and the resolution is reduced. In exchange, the penetration depth of the irradiated electrons into the sample becomes shallower and narrower, allowing the sample surface to be clearly observed.

In order to measure wafer patterns using an SEM, it is necessary to irradiate the wafer with an electron beam of low acceleration voltage to obtain an image of the wafer's top surface. For this reason, we use the retarding method, in which an electron beam of high acceleration voltage, with a small ratio of electron energy width to acceleration voltage, is irradiated and decelerated just before the sample. A negative voltage of several kV (hereafter, retarding voltage) is applied to the stage (hereafter, sample holder) that holds the wafer on the back side of the wafer, forming a potential (hereafter, surface potential) on the wafer surface. By decelerating the electron beam irradiated with high acceleration voltage by the surface potential just before it hits the wafer, it is possible to obtain an image of the pattern on the wafer surface while suppressing chromatic aberration.

In the case of semiconductor wafers, the sample holder and the wafer surface to which the retarding voltage is applied have a uniform potential, so images with the same resolution can be obtained across the entire wafer. However, when measuring an insulating wafer with an insulating substrate such as quartz or sapphire, it is not possible to apply a voltage directly from the sample holder to the wafer. The wafer surface potential is affected by charging and dielectric polarization caused by electron beam irradiation. In addition, the greater the distance between the part of the sample holder surface to which the potential is set by applying the retarding voltage (hereinafter referred to as the retarding voltage application part) and the measurement object, the more the surface potential of the measurement object changes in the positive direction compared to the retarding voltage. Therefore, the acceleration voltage of the electron beam irradiated to the sample changes depending on the measurement position. As a result, the amount of information inside the sample changes for each measurement position, resulting in differences in the measurement images. Therefore, in the measurement of insulating wafers, a method is required to eliminate the change in wafer surface potential caused by charging and the change in distance between the sample holder and the measurement object, and to make the wafer surface potential uniform.

Patent Document 1 describes a method of placing a sample on support pins arranged on a stage and applying a voltage to a flat electrode arranged between the stage and the sample, thereby making the potential uniform within a certain range (hereinafter referred to as the inspection area) on the sample surface where the electron beam is irradiated.

JP 2020-085838 A

In Patent Document 1, a flat electrode is placed on the stage of the SEM, and a voltage is applied to it to equalize the potential within the inspection area. However, in this document, the range of the inspection area is within the range of the flat electrode, and the flat electrode is placed inside the platform that supports the sample (hereinafter referred to as the support pin), so the range in which the potential can be equalized and measured is limited relative to the size of the sample.

This disclosure has been made in consideration of the above problems, and aims to provide a charged particle beam device that can measure the entire surface of a sample by making the sample surface potential uniform.

In the charged particle beam device disclosed herein, the support member that supports the sample is formed using an insulating material, and the surface of the sample holder that contacts the support member has a first recess that increases in depth from the outside of the support member toward the support member, and the support member is disposed within the first recess.

The charged particle beam device according to the present disclosure can measure the entire surface of the sample by making the sample surface potential uniform. Other configurations, advantages, and effects of the present disclosure will become clear from the description of the embodiments below.

1 is a configuration diagram of a charged particle beam device 1 according to a first embodiment. As an example, a front view of the sample holder 112 in which the sample 111 is supported by four support stages 201 is shown. FIG. 2B is a side view of FIG. 2A. FIG. 2 is a diagram showing a schematic diagram of a potential distribution in the vicinity of a sample 111. 1 is a cross-sectional view of the sample 111, the sample holder 112, and the support table 201, taken along a line passing through the center 200 of the support table. Illustrated is a difference in the surface potential of the sample 111 for each primary electron beam irradiation point 125 with respect to the surface potential at position R3 as a reference. 1 shows a side cross-sectional view of a support base in which the material of the support base 201 is changed to an insulating material (hereinafter, referred to as an insulating support base 201a). Illustrated is a difference in the surface potential of the sample 111 for each primary electron beam irradiation point 125 with respect to the surface potential at position R3 as a reference. 1 shows a side cross-sectional view of an inclined recess 202 formed around an insulating support base 201a. 5B is a side cross-sectional view in which the inclined recess 202 in FIG. 5A is changed to a stepped recess 204. FIG. Illustrated is a difference in the surface potential of the sample 111 for each primary electron beam irradiation point 125 with respect to the surface potential at position R3 as a reference. The results of comparing the maximum change in the surface potential of the sample 111 for each material of the support table 201 and each inclination angle 203 are shown. In this example, the inside of the insulating support base 201a is cylindrical, and an inclined recess 211 is disposed inside the support base. This shows a configuration example in which a stepped recess 212 is disposed on the inside of a cylindrical support base 205 . 4B is a side cross-sectional view showing an example of a configuration in which the charged particle beam device 1 further includes an electrode 301 for preventing charging and dielectric polarization of the sample 111 in addition to the configuration shown in FIG. 4A. FIG. 8A shows equipotential lines 124 in the case where the aperture through which the primary electron beam 121 passes is set to a size such that misalignment of the electrode 301 does not cause a problem. This is a cross-sectional view showing a configuration of sample 111 and sample holder 112, insulating support base 201a, and electrode 301 with an enlarged hole diameter for the passage hole shown in Figure 8B, to which an inclined recess 202 with an inclination angle 203 has been added. Illustrated is a difference in the surface potential of the sample 111 for each primary electron beam irradiation point 125 with respect to the surface potential at position R3 as a reference.

<First embodiment>
1 is a configuration diagram of a charged particle beam device 1 according to a first embodiment of the present disclosure. The charged particle beam device 1 is configured as an electron microscope. The charged particle beam device 1 includes an electron source 101, a condenser lens 102, a condenser lens 103, an aperture 104, a reflector 105, an ExB deflector 106, a detector 107, a deflector 108, a deflector 109, an objective lens 110, a sample holder 112, a stage 113, a retarding power supply 114, a display 115, and a storage device 116.

The stage 113 can move horizontally to measure the entire surface of the sample 111. A voltage is applied to the stage 113 from a retarding power supply 114. A sample holder 112 is placed on the stage 113, and the sample 111 is held by the sample holder 112. By manipulating the stage 113, it is possible to move the sample holder 112 and the sample 111 held by it horizontally. The control device is a device for controlling the operation of each part, and is, for example, a computer. The storage device 116 stores a control table 117 that defines the control conditions such as the voltage and current of each part. The control device can also read the control table 117 from the storage device 116 and control each part based on the control conditions defined in the control table 117.

Electrons emitted from the electron source 101 are focused by

condenser lenses

102 and 103, and are irradiated onto the sample 111 as a primary electron beam 121 (charged particle beam). The aperture 104 is a member that determines the aperture angle of the primary electron beam 121 at the objective lens 110, and has a hole through which the primary electron beam 121 passes. Deflectors 108 and 109 deflect the primary electron beam 121 to scan it over the sample 111.

The objective lens 110 is a lens that focuses the deflected primary electron beam 121, and thins the primary electron beam 121 by a magnetic field generated by a current flowing through an internal coil.

Signal particles 122 are emitted from the sample 111 irradiated with the primary electron beam 121. In general, signal particles emitted with an energy of 50 eV or less are called secondary electrons, and signal particles emitted with an energy of more than 50 eV and close to that of the primary electron beam 121 are called backscattered electrons. The signal particles 122 collide with the reflector 105 above the sample 111. When the signal particles 122 collide with the reflector 105, tertiary electrons 123 are emitted from the reflector 105. The tertiary electrons 123 are deflected by the electric field in the ExB deflector 106 and detected by the detector 107. The electric field and magnetic field in the ExB deflector 106 also act on the primary electron beam 121, but the effects of the two cancel each other out on the primary electron beam 121, so the primary electron beam 121 travels straight toward the sample.

The tertiary electrons 123 detected by the detector 107 are A/D converted from analog data to digital data in the order of measurement. The control device uses the digital data to create a measurement image of the sample 111. The measurement image is output on the display 115.

The accuracy of the measurement image can be adjusted by the amount of landing energy of the primary electron beam 121 incident on the sample 111. Therefore, a negative voltage of several kV (hereinafter, retarding voltage) is applied to the sample 111 by the retarding power supply 114 connected to the stage 113, thereby forming an electric field between the sample 111 and the objective lens 110 that decelerates the primary electron beam 121.

The voltage application path from the stage 113 to the sample 111 will be explained. The sample holder 112 is placed on the stage 113 to which the retarding power supply 114 is connected. To prevent damage or the generation of foreign matter caused by direct contact between the sample 111 and the sample holder 112, the sample holder 112 has multiple support tables 201 (support members) on which the sample 111 is placed. The support tables 201 are made of a conductive material in order to apply a retarding voltage to the sample 111. The retarding voltage that forms the surface potential is applied to the sample 111 via the stage 113, the sample holder 112, and the support tables 201. This allows the acceleration voltage of the primary electron beam 121 to be adjusted as desired. The surface potential also serves to accelerate the signal particles 122 generated on the sample upward.

However, the sample 111 to be measured is not limited to conductive samples; it may be insulating, such as Si, quartz, or sapphire, covered with a thin insulating film. In such cases, a uniform surface potential cannot be formed on the sample 111 due to the influence of the support table 201. This makes it impossible to control the amount of energy of the primary electron beam 121 irradiated onto the sample 111 using the retarding voltage, and an image with the desired resolution cannot be obtained. In the following description, the sample 111 is assumed to be an insulating wafer.

The relationship between the sample 111, sample holder 112, and support table 201 will be explained using Figures 2A, 2B, and 2C.

FIG. 2A shows a front view of the sample holder 112 when the sample 111 is supported by four support tables 201 as an example. The holding of the sample 111 is omitted. The support tables 201 are placed on the surface of the sample holder 112 and at arbitrary positions (support points) within the surface of the sample 111, and support the sample 111 at four points.

FIG. 2B is a side view of FIG. 2A. The support table 201 is disposed between the sample 111 and the sample holder 112 to prevent damage or the generation of foreign matter caused by direct contact between the sample 111 and the sample holder 112, and is configured as a protrusion that supports the sample 111. The support table 201 also serves as a passage for conducting the retarding voltage applied to the sample holder 112 to the sample 111, and forming an electric field in the sample to decelerate the primary electron beam 121.

Figure 2C is a schematic diagram showing the potential distribution near the sample 111. Here, the potential distribution when the primary electron beam 121 is irradiated from the objective lens 110 arranged above the sample 111 with respect to the center of the sample 111 is shown. Equipotential lines 124 show the potential when the primary electron beam 121 is irradiated to the sample 111. A retarding voltage is applied to the sample holder 112 and the support table 201. The sample 111, which is an insulating wafer placed in an electric field, is polarized with a bias toward positive and negative. The front surface of the sample 111 is negatively polarized, and the back surface is positively polarized. The voltage applied to the sample 111, which is an insulator, changes depending on the distance between the retarding voltage application part (the part of the surface of the sample holder 112 or the surface of the support table 201 where the potential is set by the retarding voltage) and the sample 111. As a result, the surface potential of the sample 111 differs between, for example, the upper part of the support table 201 and other parts. This is because the top surface of the sample holder 112 and the top surface of the support table 201 are at the same potential.

The details of the support stage 201 and the change in the sample surface potential for each position are explained using Figures 3A and 3B.

Figure 3A is a cross-sectional view of the sample 111, sample holder 112, and support table 201, passing through the support table center 200. It is assumed that the support table 201 in Figure 3A is made of a conductive material. The objective lens 110 is installed above the sample 111, and the primary electron beam 121 is irradiated to the irradiation point 125 on the sample 111. The equipotential lines 124 generated by the voltage applied to the sample 111 and support table 201 at this time are shown. The irradiation position R0 of the primary electron beam 121 when irradiated to the support table center 200 is set as the origin, and the irradiation positions when the sample holder 112 is moved horizontally at regular intervals are R1, R2, and R3, respectively. R1 to R3 in Figure 3A respectively indicate the positional relationship of the primary electron beam irradiation point 125. R1 is the position on the support table 201. R2 is the end face position of the support table 201. R3 is a position away from the support table 201, and there is no support table 201 directly below the sample 111, only the sample holder 112.

When the support base 201 is conductive, the retarding voltage is applied up to the top surface of the support base 201, so that the surface potential of the sample 111 at the point in contact with the support base 201 (for example, position R0 in Figure 3A) is more strongly affected by the retarding voltage and changes in the negative direction compared to position R3 (flat portion).

Figure 3B shows the difference in surface potential of the sample 111 for each primary electron beam irradiation point 125, with the surface potential at position R3 as the reference. The vertical axis shows the surface potential difference when the surface potential of the sample 111 on the flat part (position R3) of the sample holder 112 is set to 0 V, and the horizontal axis shows the electron beam irradiation position R when the sample holder 112 is moved horizontally with the support table center 200 as the base point. Here, the sample surface potential difference is shown with the flat part as the reference when the sample holder 112 is moved horizontally at a constant interval, such as from R0 to R3 shown in Figure 3A. In R0 to R2, where the distance between the surface of the sample 111 and the retarding voltage application part is close, the value of the surface potential of the sample 111 becomes close to the value of the retarding voltage, so it changes in the negative direction. Conversely, in R3, the distance between the sample 111 and the retarding voltage application part is farther, so the value of the surface potential of the sample 111 changes in the positive direction.

An example of the shape of the support table 201 and the sample surface potential in embodiment 1 will be described using Figures 4A and 4B.

FIG. 4A shows a side cross-sectional view of a support table in which the material of the support table 201 has been changed to an insulator (hereinafter, insulating support table 201a). As in FIG. 3A, the primary electron beam 121 is irradiated to the irradiation point 125 on the sample 111. At this time, the equipotential lines 124 formed by the voltage applied to the sample 111 and the insulating support table 201a are shown. R0 to R3 are the same as in FIG. 3A. Since the retarding voltage cannot be applied directly to the insulating support table 201a and the retarding voltage is no longer conducted to the upper part of the support table, the equipotential lines 124 change in the direction approaching the sample holder 112 compared to FIG. 3A. Accordingly, the surface potential of the sample 111 at the part in contact with the insulating support table 201a changes in the positive direction compared to FIG. 3A. However, due to the dielectric polarization of the insulating support table 201a, the equipotential lines are distorted near the insulating support table 201a.

Figure 4B shows the difference in surface potential of the sample 111 for each primary electron beam irradiation point 125, with the surface potential at position R3 as the reference. The vertical axis shows the surface potential difference when the surface potential of the sample 111 on the flat part of the sample holder 112 is set to 0 V, and the horizontal axis shows the electron beam irradiation position R when the sample holder 112 is moved horizontally with the support stage center 200 as the base point. Here, the sample surface potential is shown with the flat part as the reference when the sample holder 112 is moved horizontally at regular intervals, such as from R0 to R3 shown in Figure 4A. The solid line shows the surface potential when the conductive support stage 201 shown in Figure 3B is used, and the dashed dotted line shows the surface potential when the insulating support stage 201a is used.

By changing the material of the support base to an insulator, it is possible to prevent the retarding voltage from being applied to the top surface of the support base. In addition, there is no difference in the distance between the surface to which the potential is set by applying the retarding voltage and the surface of the sample 111 between the location where the insulating support base 201a is located and other locations. This is because the potential of the insulating support base 201a is not affected by the retarding voltage. As a result, the equipotential lines 124 on the insulating support base 201a change in a direction approaching the sample holder 112 compared to Figure 3A. However, due to the dielectric polarization of the insulating support base 201a in addition to the sample 111, the sample surface potential changes in the negative direction at R0 to R2. As a result, the amount of change in the sample 111 surface potential cannot be reduced to a negligible value.

The details of the sample holder 112 with a recess on the outer periphery and the sample surface potential will be explained using Figures 5A, 5B, 5C, and 6.

Figure 5A shows a side cross-sectional view of an inclined recess 202 formed around an insulating support base 201a. Around the insulating support base 201a, an inclined recess 202 (first recess) is arranged, which deepens at a certain inclination angle 203 toward the support base center 200. As in Figure 4A, the primary electron beam 121 is irradiated to the irradiation point 125 on the sample 111. At this time, equipotential lines 124 formed by the voltage applied to the sample 111 and the insulating support base 201a are shown. The surface potential of the sample 111 is affected by the dielectrically polarized insulating support base 201a and changes in the negative direction as it approaches the support base center 200. Therefore, a recess is formed near the insulating support base 201a, which deepens toward the support base center 200. The insulating support base 201a is placed within this recess. By placing the insulating support 201a in the recess, the distance between the sample 111 and the retarding voltage application unit in the vicinity of the insulating support 201a is increased. This shifts the surface potential of the sample 111 in the positive direction, and cancels the negative potential change caused by the dielectric polarization of the insulating support 201a. Therefore, the amount of change in the surface potential of the sample 111 for each position can be further reduced.

FIG. 5B shows a side cross-sectional view in which the inclined groove 202 in FIG. 5A has been changed to a stepped groove 204. Changing the shape of the groove to a stepped shape has the same effect of reducing the amount of change in the surface potential of the sample 111 as the inclined groove. As mentioned above, the surface potential of the sample 111 changes depending on the distance between the sample 111 and the retarding voltage application section, so it is possible to adjust the surface potential of the sample 111 by changing the depth of the step and the width to the next step.

Figure 5C shows the difference in surface potential of the sample 111 for each primary electron beam irradiation point 125, with the surface potential at position R3 as the reference. The vertical axis shows the surface potential difference when the surface potential of the sample 111 on the flat part of the sample holder 112 is set to 0V, and the horizontal axis shows the electron beam irradiation position R when the sample holder 112 is moved horizontally with the support center 200 as the base point. Here, the sample surface potential is plotted with the flat part as the reference when the sample holder 112 is moved horizontally at regular intervals, such as R0 to R3 shown in Figure 4A. The dashed line shows the surface potential of the sample 111 when the insulating support 201a shown in Figure 4B is used. The two-dot dashed line shows the surface potential of the sample 111 when the recess is arranged as in Figure 5A. The effect of reducing the amount of change in surface potential due to the stepped digging 204 is equivalent to that of the sloping digging 202 shown in FIG. 5B, which has an inclination angle formed by the oblique side connecting the lower end of the insulating support base 201a and the surface of the sample holder 112, and the corners A and B of the stepped digging 204.

Figure 6 shows the results of comparing the maximum change in the surface potential of the sample 111 for each material and inclination angle 203 of the support base 201. The vertical axis shows the maximum change in the surface potential of the sample 111 based on the flat part, and the horizontal axis shows the material of the support base and the inclination angle 203 to be compared. In the absence of an indentation, the maximum change in the surface potential of the sample is less than one-third that of the conductive support base by making the support base material insulating. When the inclination angle 203 of the indentation placed on the outer periphery of the insulating support base 201a is set to 45° or less, the change in the surface potential in the positive direction due to the indentation is greater than the change in the surface potential in the negative direction due to the dielectric polarization of the sample 111 and the insulating support base 201a. By setting the inclination angle 203 of the indentation placed on the outer periphery of the insulating support base 201a to 60°±15°, the change in the surface potential of the sample is smaller than when only the insulating support base 201a is placed. According to the data example in FIG. 6, it can be seen that by making the support base insulating, the amount of change in surface potential can be suppressed to a fraction of that of a conductive support base. Furthermore, by forming a recess in the sample holder 112, it can be seen that the amount of change in surface potential can be further suppressed to a fraction of that of a conductive support base.

Since the amount of change in the surface potential of the sample 111 crosses zero and changes from positive to negative, by changing the inclination angle 203 of the inclined recess 202, the amount of change in the surface potential can be set to zero and the surface potential of the sample 111 can be made uniform. As a result, the potential change occurring on the surface of the sample 111 can be reduced to a negligible level, making it possible to obtain an image with the desired resolution.

In Figures 5A to 6, an example has been described in which the potential difference between the surface potential of the portion of sample 111 that is supported by insulating support base 201a (e.g., R0) and the surface potential of the portion that is not supported (e.g., R3) is nearly zero. It is desirable for this potential difference to be zero. However, it should be noted that the effect of this embodiment can be achieved to the extent that this potential difference can be suppressed in the presence of an indentation more than in the absence of an indentation.

It is desirable that the surface of the sample holder 112 that contacts the support base 201 is larger than the planar size of the sample 111. This makes it possible to provide a uniform surface potential over the entire surface of the sample 111. The same applies to the following embodiments.

<Embodiment 2>
A configuration example of the charged particle beam device 1 according to the second embodiment of the present disclosure will be described with reference to Figures 7A and 7B. The matters described in the first embodiment but not described in the second embodiment can also be applied to the second embodiment unless there are special circumstances.

Figure 7A shows an example in which the inside of the insulating support base 201a is cylindrical (hereinafter, cylindrical support base 205), and an inclined recess 211 is arranged inside the support base. Figure 7A is a cross-sectional view of the sample 111, sample holder 112, and cylindrical support base 205 passing through the support base center 200. The objective lens 110 is placed directly above the sample 111. It is assumed that the sample 111 is irradiated with a primary electron beam 121. The bottom surface of the cylindrical support base 205 has a hole for passing a conductive fixing screw 207, and a conductive fixing part (hereinafter, inclined fixing part 206) with an inclination angle 203 at the end of the upper surface is fixed by a screw 207 inserted from the bottom of the sample holder 112.

The retarding voltage applied to the sample holder 112 is applied to the inclined fixing part 206 via the conductive fixing screw 207. The inclined part of the inclined fixing part 206 forms an inclined recess 211 inside the inner wall of the cylindrical support base 205, thereby lowering the position of the surface of the sample holder 112. As described below, the inclined recess 211 can cancel at least a part of the change in the surface potential of the sample 111.

Figure 7B shows an example of a configuration in which a stepped recess 212 is arranged inside the cylindrical support base 205. As in Figure 7A, the bottom surface of the cylindrical support base 205 has a hole for passing a conductive fixing screw 207, and a conductive fixing part (hereinafter, stepped fixing part 208) with a stepped cut at the end of the top surface is fixed by the conductive fixing screw 207 inserted from the bottom of the sample holder 112. The retarding voltage applied to the sample holder 112 is applied to the stepped fixing part 208 via the conductive fixing screw 207. The stepped part of the stepped fixing part 208 forms a stepped recess 212 on the inside of the cylindrical support base 205, thereby lowering the surface position of the sample holder 112.

As shown in Figures 4A and 4B, at the contact portion between the sample 111 and the insulating support 201a, the insulating support 201a is dielectrically polarized in addition to the sample 111, so the sample surface potential changes in a negative direction compared to other portions. Therefore, by making the shape of the support cylindrical, the contact area between the sample 111 and the insulating support 201a is reduced, and the potential change caused by the dielectric polarization is reduced. Furthermore, for the negative surface potential change occurring at the contact portion between the sample 111 and the cylindrical support 205, a slanted groove 211 or a stepped groove 212 is formed on the inside of the cylindrical support 205 to increase the distance between the retarding voltage application portion and the sample 111, and the surface potential of the sample 111 is changed in a positive direction. The sample surface potential change occurring at the contact portion between the cylindrical support 205 and the sample 111 is canceled by the groove arranged on the inside of the cylindrical support 205, thereby reducing the surface potential change of the sample 111 occurring near the support portion.

The recess on the inside of the cylindrical support base 205 can be effective to the extent that it is formed to cancel at least a portion of the change in the sample surface potential that occurs at the contact area between the cylindrical support base 205 and the sample 111. By combining this with the recess on the outer periphery of the support base described in embodiment 1, the change in the surface potential can be further suppressed.

<Third embodiment>
In the configuration shown in Fig. 5A in which an inclined recess 202 having an inclination angle 203 is disposed near an insulating support base 201a, the surface potential of the sample 111 is uniformly shifted in the positive direction compared to the retarding voltage due to the dielectric polarization of the sample 111 and the insulating support base 201a, charging due to irradiation with the primary electron beam 121, and a change in distance from the retarding voltage application unit. Therefore, in the third embodiment of the present disclosure, a configuration for suppressing the uniform shift in the surface potential of the sample 111 will be described with reference to Figs. 8A, 8B, 9, and 10. The matters described in the first and second embodiments but not described in the third embodiment can also be applied to the third embodiment unless there are special circumstances.

FIG. 8A is a side cross-sectional view showing an example configuration in which the charged particle beam device 1 further includes an electrode 301 for preventing charging and dielectric polarization of the sample 111 in addition to the configuration shown in FIG. 4A. The electrode 301 is placed above the sample 111, and a negative voltage of the same polarity and value as the sample holder 112 is applied to it. The objective lens 110 is placed above the electrode 301, and the primary electron beam 121 is irradiated to an irradiation point 125 on the sample 111. The equipotential lines 124 formed by the voltages applied to the sample 111 and the insulating support stand 201a at this time are shown. R0 to R3 are the same as in FIG. 4A.

A hole for the primary electron beam 121 is placed at the center of the electrode 301, and a negative voltage equal to the retarding voltage is applied to the electrode 301. Therefore, no electric field is generated between the sample holder 112 and the electrode 301, and dielectric polarization of the sample 111 can be prevented. In addition, by decelerating the primary electron beam 121 with the voltage (retarding voltage) applied to the electrode 301, it is possible to control the acceleration voltage of the primary electron beam 121 by the retarding voltage, and it becomes possible to obtain an image with the desired resolution.

However, this method has the problem that the primary electron beam 121 is decelerated on the surface of the electrode 301 rather than on the surface of the sample 111, so the distance the decelerated electrons travel before irradiating the sample 111 is long. As mentioned above, when the acceleration voltage of the electron beam is low, the ratio (ΔE/E) between the energy width of the electron source and the acceleration voltage becomes large, so the effect of chromatic aberration also becomes large. By the time the low-acceleration-voltage electron beam decelerated by the electrode 301 is irradiated to the sample 111, chromatic aberration increases, resulting in a decrease in resolution.

In addition, to make the surface potential of the sample 111 the same as the retarding voltage, the diameter of the central hole of the electrode 301 must be made very small. However, there is also the issue that, when the amount of positional deviation of the electrode 301 is the same, the smaller the central hole diameter, the greater the decrease in resolution.

FIG. 8B shows equipotential lines 124 when the passage hole of the primary electron beam 121 shown in FIG. 8A is sized so that misalignment of the electrode 301 does not cause a problem. The other configurations are the same as those in FIG. 8A. When the diameter of the passage hole arranged in the electrode 301 is increased (for example, the hole diameter is made larger than the surface size of the insulating support base 201a), the effect of misalignment of the electrode 301 is reduced. On the other hand, in the vicinity of the passage hole, potential changes occur in the surface potential of the sample 111 due to charging, dielectric polarization, and the distance between the retarding voltage application unit and the sample 111. As a result, the surface potential of the sample 111 becomes non-uniform, and it becomes impossible to control the acceleration voltage of the primary electron beam 121 by the retarding voltage. Therefore, in addition to the configuration of FIG. 8B, the configuration of embodiment 1 can be used in combination.

Figure 9 is a cross-sectional view of the sample 111, sample holder 112, insulating support 201a, and electrode 301 with a large hole diameter passing through the support center 200 shown in Figure 8B, with an inclined recess 202 with an inclination angle 203 added. At this time, the equipotential lines 124 formed by the voltage applied to the sample 111 and insulating support 201a are shown. Also, the position R0 of the primary electron beam 121 when irradiated to the support center is set as the origin, and the sample holder 112 is moved horizontally at regular intervals to R1, R2, and R3, respectively. R1 to R3 in Figure 9 show the positional relationship of the primary electron beam irradiation point 125. Here, R1 is the position on the insulating support 201a, R2 is the end face position of the insulating support 201a, and R3 is a position away from the insulating support 201a, and there is no insulating support 201a directly below the sample 111, only the sample holder 112.

Figure 10 shows the difference in surface potential of the sample 111 for each primary electron beam irradiation point 125, with the surface potential at position R3 as the reference. The vertical axis shows the surface potential of the sample 111, and the horizontal axis shows the electron beam irradiation position R when the sample holder 112 is moved horizontally with the support table center 200 as the base point. Here, the retarding voltage applied to the sample 111 when the sample holder 112 is moved horizontally at a constant interval, such as from R0 to R3 shown in Figures 8A, 8B, and 9, is Vr, and the surface potential in Figures 8A, 8B, and 9 are plotted. The solid line shows the surface potential of the sample 111 generated in Figure 8A, the dashed line shows the surface potential of the sample 111 generated in Figure 8B, and the dashed double-dot line shows the surface potential of the sample 111 generated in Figure 9.

As described in FIG. 8A, by arranging the electrode 301 to which the retarding voltage is applied above the sample 111, no electric field is generated between the sample holder 112 and the electrode 301, and dielectric polarization of the sample 111 can be prevented. In the vicinity of the primary electron beam 121 passage hole arranged in the electrode 301, the insulating support 201a shown in FIG. 5A of the first embodiment and the inclined grooves 202 arranged around it cancel out potential changes, so that the amount of change in the surface potential of the sample 111 for each irradiation position can be reduced as shown in FIG. 5C. In addition, since the retarding voltage is applied to the electrode 301, the retarding voltage application portion approaches the surface of the sample 111. As a result, the surface potential of the sample 111 changes in the negative direction, and the deviation between the surface potential of the sample 111 and the retarding voltage is suppressed.

<Modifications of the present disclosure>
The present disclosure is not limited to the above-described embodiments, and includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present disclosure, and it is not necessary to include all of the configurations described. In addition, a part of an embodiment can be replaced with a configuration of another embodiment. In addition, a configuration of another embodiment can be added to a configuration of an embodiment. In addition, a part of the configuration of each embodiment can be added to, deleted from, or replaced with a part of the configuration of another embodiment.

In the above embodiment, an electron microscope is given as an example of a charged particle beam device 1, but the configuration according to the present disclosure can also be applied to other devices that irradiate charged particle beams.

In the above embodiments, examples of the sample 111 made of an insulating material include, for example, a semiconductor wafer or a photomask that uses an insulating material as a substrate, but are not limited to these, and the present disclosure can be applied to other insulating samples.

1: Charged particle beam device, 101: Electron source, 102: Condenser lens 1, 103: Condenser lens 2, 104: Aperture, 105: Reflector, 106: ExB deflector, 107: Detector, 108: Deflector 1, 109: Deflector 2, 110: Objective lens, 111: Sample 111: Sample holder, 113: Stage, 114: Retarding power supply, 115: Display, 116: Storage device, 121: Primary electron beam beam, 122: secondary electron beam, 123: tertiary electron beam, 124: equipotential line, 125: primary electron beam irradiation point, 200: support base center, 201: support base, 201a: insulating support base, 202: inclined recess, 203: inclination angle, 204: stepped recess, 205: cylindrical support base, 206: inclined fixed portion, 207: fixing screw, 208: stepped fixed portion, 211: inclined recess, 212: stepped recess, 301: electrode

Claims

A charged particle beam device for irradiating a sample with a charged particle beam, comprising:
A support member on which the sample is placed;
A sample holder supporting the support member;
Equipped with
The support member is formed using an insulating material,
a surface of the sample holder that contacts the support member has a first recess that increases in depth from an outer side of the support member toward the support member;
The charged particle beam device, wherein the support member is disposed in the first recess.
The charged particle beam device according to claim 1 , wherein the first recess is configured by a slope or a step that becomes deeper from an outer side of the support member toward the support member.
3. The charged particle beam device according to claim 2, wherein the inclination has an angle of 60°±15° with respect to the surface of the sample holder.
2. The charged particle beam apparatus according to claim 1, wherein the surface of the sample holder that comes into contact with the support member has an area larger than that of the sample.
The charged particle beam device further includes a power supply that applies a voltage to the sample holder to generate an electric field that decelerates the charged particle beam;
the support member is arranged to support the sample by a plurality of support points;
The first recess is
2. The charged particle beam device according to claim 1, wherein, when the power supply is applying the voltage, a potential difference between a potential of a portion of the sample that is supported by the support point and a potential of a portion of the sample that is not supported by the support point is smaller than a potential difference in a case where the first recess does not exist.
2. The charged particle beam device according to claim 1, wherein the support member has a cylindrical shape and is configured to support the sample by a top portion of the cylinder.
7. The charged particle beam device according to claim 6, wherein the surface of the sample holder that comes into contact with the support member has a second recess whose depth increases from the inside of the cylindrical shape toward the inner wall of the cylindrical shape.
The charged particle beam device further includes a power supply that applies a voltage to the sample holder to generate an electric field that decelerates the charged particle beam;
8. The charged particle beam device according to claim 7, wherein the second recess is configured to cancel at least a portion of a fluctuation in the surface potential of the sample caused by dielectric polarization of the support member at a contact portion where the support member and the sample are in contact with each other by increasing the distance between the portion of the sample holder to which the voltage is applied and the sample compared to other portions of the sample holder.
The charged particle beam device further includes an electrode disposed between a beam source that emits the charged particle beam and the sample;
The charged particle beam device further includes a power supply that applies a voltage to the sample holder to generate an electric field that decelerates the charged particle beam;
2. The charged particle beam device according to claim 1, wherein the power supply applies to the electrode a voltage having the same polarity as a voltage applied to the sample holder by the power supply, thereby suppressing dielectric polarization of the sample.
10. The charged particle beam device according to claim 9, wherein the power supply applies to the electrode a voltage value that is the same as a voltage value that is applied to the sample holder.
the electrode has a hole through which the charged particle beam passes;
The charged particle beam device according to claim 9 , wherein an opening size of the hole is larger than a planar size of the support member.
2. The charged particle beam device according to claim 1, wherein the sample is a semiconductor substrate using an insulating material as a substrate.