WO2025191843A1 - Charged particle beam device - Google Patents

Abstract

To control deterioration of an observation image while maintaining time resolution of a detector, this charged particle beam device comprises: a charged particle source that exposes a sample to a charged particle beam; a detector that detects electrons emitted from the sample due to the exposure to the charged particle beam and that outputs an electrical signal; and a control unit that, on the basis of the electrical signal, generates an observation image and controls each component. The detector has: a scintillator that emits light when electrons are incident thereon; a light-receiving element that outputs an electrical signal corresponding to the amount of light emitted by the scintillator; and a long-wavelength light reduction unit that reduces the intensity of long-wavelength light having a relatively long emission wavelength, among the light emitted by the scintillator. The control unit controls the detector so as to reduce the intensity of the long-wavelength light if a parameter for the electrons incident on the scintillator exceeds a predetermined threshold, and so as not to reduce the intensity of the long-wavelength light if the parameter does not exceed the threshold.

Description

charged particle beam equipment

The present invention relates to a charged particle beam device equipped with a detector having a scintillator that emits light when electrons are incident on it.

Charged particle beam devices generate observation images of a sample by irradiating the sample with a beam of charged particles, such as an electron beam, and detecting secondary electrons, transmitted electrons, backscattered electrons, and X-rays emitted from the sample. The detector that detects the electrons has a scintillator that emits light when electrons are incident on it, and a photodetector that outputs an electrical signal corresponding to the amount of light emitted by the scintillator. The light emitted by the scintillator contains long-wavelength light, which has a relatively long emission wavelength, and short-wavelength light, which has a relatively short emission wavelength. Long-wavelength light has a longer decay time than short-wavelength light, which reduces the time resolution of the detector.

Patent Document 1 discloses a detection device equipped with an optical filter that reduces the intensity of light components with wavelengths greater than 650 nm in order to increase time resolution.

Special table 2015-505038 publication

However, Patent Document 1 does not give sufficient consideration to improving the electrical signal output from the detector. If the intensity of long-wavelength light, such as light components with wavelengths greater than 650 nm, is reduced using an optical filter, the electrical signal output from the detector will decrease while electrons are incident, resulting in a degradation of the image quality of the generated observation image.

The present invention therefore aims to provide a charged particle beam device that suppresses degradation of the observed image while maintaining the detector's time resolution.

In order to achieve the above object, the present invention provides a charged particle beam device comprising: a charged particle source that irradiates a sample with a charged particle beam; a detector that detects electrons emitted from the sample by the irradiation of the charged particle beam and outputs an electrical signal; and a control unit that generates an observation image based on the electrical signal and controls each unit; the detector has a scintillator that emits light when electrons are incident on it, a light-receiving element that outputs an electrical signal corresponding to the amount of light emitted by the scintillator, and a long-wavelength light reduction unit that reduces the intensity of long-wavelength light that has a relatively long wavelength among the light emitted by the scintillator; and the control unit controls the detector to reduce the intensity of the long-wavelength light if a parameter of the electrons incident on the scintillator exceeds a predetermined threshold, and not to reduce the intensity of the long-wavelength light if the parameter does not exceed the threshold.

The present invention provides a charged particle beam device that suppresses degradation of the observed image while maintaining the time resolution of the detector. Issues, configurations, and advantages other than those described above will become clear from the description of the following embodiments of the invention.

1 is a schematic diagram illustrating an example of the overall configuration of a charged particle beam device. FIG. 10 is a schematic diagram showing another example of the overall configuration of a charged particle beam device. FIG. 2 is a diagram illustrating the decay time of light emission from a scintillator. FIG. 1 is a diagram comparing the emission spectra of scintillators with the energy of incident electrons. FIG. 10 is a diagram comparing emission spectra with reduced long wavelength light depending on the energy of incident electrons. FIG. 2 is a schematic diagram showing an example of the configuration of a detector. FIG. 10 is a schematic diagram showing another example of the configuration of the detector. FIG. 10 is a schematic diagram showing another example of the configuration of the detector. FIG. 10 is a schematic diagram showing another example of the configuration of the detector.

An embodiment of a charged particle beam device according to the present invention will now be described with reference to the accompanying drawings. A charged particle beam device is a device that irradiates a sample with a charged particle beam, detects secondary electrons, transmitted electrons, reflected electrons, X-rays, and the like emitted from the sample, and generates an observation image of the sample; for example, it is a scanning electron microscope that scans the sample with an electron beam.

An example of the overall configuration of a charged particle beam device will be described using Figure 1. The charged particle beam device 1a comprises an electron optical column 7, a sample chamber 8, and a control unit 10. The insides of the electron optical column 7 and the sample chamber 8 are maintained at a vacuum. The electron optical column 7 is equipped with an electron source 2 that emits an electron beam 3. The sample chamber 8 is equipped with a detector 6, in which a sample 4, which is the object to be observed, is placed. The detector 6 detects secondary electrons 5a emitted from the sample 4 when irradiated with the electron beam 3, and outputs an electrical signal.

The detector 6 has a scintillator 6a, a light guide 6b, and a photodetector 6c. The scintillator 6a is a material containing at least one element from the group consisting of Ga, Zn, In, Al, Cd, Mg, Ca, Sr, Y, Si, Gd, and Ce, and emits light when electrons are incident on it. The photodetector 6c is, for example, a photomultiplier tube or a semiconductor sensor, and outputs an electrical signal corresponding to the amount of light emitted by the scintillator 6a. The light guide 6b connects the scintillator 6a and the photodetector 6c, and transmits the light emitted by the scintillator 6a to the photodetector 6c, which is located outside the sample chamber 8. Note that if the photodetector 6c is located inside the sample chamber 8, the light guide 6b is not required. A positive voltage may be applied to the scintillator 6a to increase the number of relatively low-energy secondary electrons 5a incident on the scintillator 6a.

The control unit 10 is, for example, a computer with an arithmetic unit, and generates an observation image of the sample 4 based on the electrical signal output from the light-receiving element 6c, and controls each component.

Another example of the overall configuration of a charged particle beam device will be described using Figure 2. Like the charged particle beam device 1a, the charged particle beam device 1b is equipped with an electron optical column 7, a sample chamber 8, and a control unit 10, but the arrangement and shape of the detector 6 differs from that of the charged particle beam device 1a. The detector 6 of the charged particle beam device 1b is placed directly above the sample 4 and has a circular or U-shape with a space through which the electron beam 3 passes. The detector 6 placed directly above the sample 4 can efficiently detect backscattered electrons 5b, which are emitted in smaller quantities than secondary electrons 5a.

The decay time of the light emission from the scintillator 6a will be explained using Figure 3. The graph in Figure 3 shows an example of the change in the light emission intensity of the scintillator 6a over time, with the vertical axis representing light emission intensity and the horizontal axis representing time. The incident period is the period during which electrons are incident on the scintillator 6a, and the non-incident period is the period during which electrons are not incident on the scintillator 6a.

The intensity of the light emitted by the scintillator 6a due to the incidence of secondary electrons 5a and backscattered electrons 5b does not immediately reach zero when the non-incident period begins, but decays over time as shown in Figure 3. The decay time, which indicates the rate at which the light intensity decays during the non-incident period, varies depending on the emission wavelength, with long-wavelength light having a relatively long emission wavelength being longer than short-wavelength light having a relatively short emission wavelength. The decay time also differs depending on the type of scintillator 6a. Long-wavelength light is a light component with a wavelength longer than, for example, any of 450 nm to 600 nm.

The light emitted during the non-incident period is called afterglow, and becomes noise in the detector 6, reducing the time resolution. The reduction in time resolution can be suppressed by reducing the intensity of long-wavelength light, which has a long decay time.

The reduction in the intensity of long-wavelength light will be explained using Figures 4 and 5. The graph in Figure 4 is an example of the emission spectrum of the scintillator 6a, and the graph in Figure 5 is the same as Figure 4 with the intensity of long-wavelength light reduced, with the vertical axis representing emission intensity, the horizontal axis representing emission wavelength, and the depth axis representing time. Also, (a) in Figures 4 and 5 shows a case where the energy of the incident electrons is relatively high, and (b) shows a case where the energy of the incident electrons is relatively low, with time t0 being the incidence period and time t1 being the non-incidence period. The electrical signal output from the light-receiving element 6c has a value corresponding to the sum of the emission intensity of short-wavelength light and the emission intensity of long-wavelength light.

When the energy of the incident electrons is relatively high, as in Figure 4(a), the emission intensity of the long-wavelength light is greater than that of the short-wavelength light, and the afterglow of the long-wavelength light may exceed the detection limit of the light-receiving element 6c. Therefore, by reducing the intensity of the long-wavelength light, as in Figure 5(a), the afterglow of the long-wavelength light can be made below the detection limit, preventing a decrease in time resolution.

On the other hand, when the energy of the incident electrons is relatively low, as in Figure 4(b), the emission intensity of the long-wavelength light is lower than that of the short-wavelength light, and the afterglow of the long-wavelength light may fall below the detection limit of the light-receiving element 6c. When the emission intensity of the long-wavelength light is lower than that of the short-wavelength light, reducing the intensity of the long-wavelength light, as in Figure 5(b), reduces the emission intensity at time t0, which is the incidence period, and the quality of the observed image deteriorates.

In other words, by controlling whether or not to reduce the emission intensity of long-wavelength light depending on the energy of the electrons incident on the scintillator 6a, it is possible to suppress degradation of the observed image while maintaining the time resolution of the detector 6. The higher the acceleration voltage of the electron beam 3, the higher the energy of the incident electrons. Furthermore, the energy of the incident electrons is higher when they are backscattered electrons 5b than when they are secondary electrons 5a. Note that the higher the voltage applied to the scintillator 6a, the higher the energy of the incident electrons, so the energy of secondary electrons 5a incident when a voltage is applied to the scintillator 6a may be higher than the energy of backscattered electrons 5b when no applied voltage is present.

Furthermore, the control of whether or not to reduce the emission intensity of long-wavelength light is not limited to being based on the energy of the incident electrons. For example, even if the emission intensity of long-wavelength light is lower than that of short-wavelength light, if the number of incident electron particles is relatively large, the afterglow of the long-wavelength light may exceed the detection limit of the light-receiving element 6c. In other words, whether or not to reduce the emission intensity of long-wavelength light may be controlled according to the number of electron particles incident on the scintillator 6a. The number of incident electron particles increases as the irradiation density of the electron beam 3 increases.

Using Figure 6, an example of a detector 6 that controls the reduction in the intensity of long-wavelength light will be described. The detector 6 illustrated in Figure 6(a) has a scintillator 6a, a variable transmittance filter 60, a light guide 6b, and a light receiving element 6c. The scintillator 6a, light guide 6b, and light receiving element 6c are the same as those in the detector 6 in Figure 1, so their description will be omitted.

The variable transmittance filter 60 is an optical filter, such as a liquid crystal element, that is disposed between the scintillator 6a and the light guide 6b and that varies the transmittance of long-wavelength light. The transmittance of the variable transmittance filter 60 is controlled by the control unit 10. More specifically, if the parameters of the electrons incident on the scintillator 6a exceed a predetermined threshold, the transmittance of the long-wavelength light is lowered so as to reduce the intensity of the long-wavelength light. If the parameters of the incident electrons do not exceed the threshold, the transmittance of the long-wavelength light is increased so as not to reduce the intensity of the long-wavelength light.

The parameters of the incident electrons include, for example, energy and particle number. If the parameter of the incident electrons is energy, the transmittance of long-wavelength light is reduced when the incident electrons are backscattered electrons 5b or when the acceleration voltage of the electron beam 3 is equal to or greater than a predetermined value. Even when the incident electrons are secondary electrons 5a, the transmittance of long-wavelength light is reduced when the voltage applied to the scintillator 6a is equal to or greater than a predetermined value. Here, the predetermined value is any value between 0.1 kV and 100 kV. The threshold value for the energy of the incident electrons is the energy value at which the intensity of long-wavelength light is greater than the intensity of short-wavelength light, and is determined in advance depending on the type of scintillator 6a.

If the parameter of the incident electrons is the number of particles, the transmittance of long-wavelength light is reduced when the irradiation density of the electron beam 3 is equal to or greater than a predetermined value. The irradiation density of the electron beam 3 is calculated based on the current value of the electron beam 3 and the magnification of the observed image. The threshold value for the number of particles of the incident electrons is the number of particles at which the intensity of long-wavelength light exceeds a predetermined value, for example, the number of particles at which the afterglow of long-wavelength light exceeds the detection limit of the light-receiving element 6c, and is determined in advance depending on the type of scintillator 6a.

The detector 6 illustrated in Figure 6(b) differs from that in (a) in that the variable transmittance filter 60 is positioned between the light guide 6b and the light receiving element 6c. The rest of the configuration is the same as in (a).

The detector 6 illustrated in Figure 6(c) has a scintillator 6a, a variable transmittance filter 60, and a light-receiving element 6c, with the variable transmittance filter 60 positioned between the scintillator 6a and the light-receiving element 6c. The functions of the scintillator 6a, variable transmittance filter 60, and light-receiving element 6c are the same as in (a) and (b).

Instead of the variable transmittance filter 60, the detector 6 may be provided with a fixed transmittance filter, an optical filter that absorbs at least a portion of the long-wavelength light and has a constant transmittance. The control unit 10 controls the position of the fixed transmittance filter via a sliding or rotating mechanism in accordance with the parameters of the incident electrons. That is, if the parameter exceeds a threshold value, the fixed transmittance filter is placed between the scintillator 6a and the light-receiving element 6c to reduce the intensity of the long-wavelength light, and if the threshold value is not exceeded, the fixed transmittance filter is removed from between the scintillator 6a and the light-receiving element 6c.

Alternatively, instead of the variable transmittance filter 60, a prism that refracts long-wavelength light may be provided in the detector 6. The control unit 10 controls the direction of the prism via a rotary mechanism according to the parameters of the incident electrons. In other words, the orientation of the prism is controlled so that if the parameter exceeds a threshold value, long-wavelength light is prevented from entering the light-receiving element 6c, and if the parameter does not exceed the threshold value, long-wavelength light is allowed to enter the light-receiving element 6c.

Using Figure 7, another example of a detector 6 that controls the reduction in the intensity of long-wavelength light will be described. The detector 6 illustrated in Figure 7 has a scintillator 6a, an optical fiber 70, and a photodetector 6c. The scintillator 6a and photodetector 6c are similar to those in the detector 6 in Figure 1, so their description will be omitted. The optical fiber 70 is a transmission path that transmits the light emitted by the scintillator 6a to the photodetector 6c. It is made of a material that transmits long-wavelength light at a slower rate than short-wavelength light, and has a length that results in a difference of about microseconds in the transmission time between short-wavelength light and long-wavelength light. The control unit 10 utilizes the difference in transmission time to perform switching control so that the photodetector 6c receives short-wavelength light and does not receive long-wavelength light. In other words, when the parameter exceeds the threshold, the photodetector 6c is turned on during periods when short-wavelength light is transmitted, and turned off during periods when long-wavelength light is transmitted.

Instead of switching the light receiving element 6c, a shutter that is opened and closed by the control unit 10 may be provided upstream of the light receiving element 6c. In other words, when the parameter exceeds the threshold value, the shutter is opened during the period when short wavelength light is transmitted, and closed during the period when long wavelength light is transmitted.

Using Figure 8, another example of a detector 6 that controls the reduction in the intensity of long-wavelength light will be described. The detector 6 illustrated in Figure 8 has a scintillator 6a, a spectroscope 80, and a photodetector 6c. The scintillator 6a is similar to the detector 6 in Figure 1, so its description will be omitted. The spectroscope 80 separates the light emitted by the scintillator 6a into short-wavelength light and long-wavelength light. The photodetector 6c is an element that outputs an electrical signal corresponding to the amount of light emitted by the scintillator 6a, and has a first photodetector 6c1 that receives long-wavelength light and a second photodetector 6c2 that receives only short-wavelength light. The control unit 10 controls the first photodetector 6c1 according to the parameter of the incident electrons. That is, if the parameter exceeds a threshold, the first photodetector 6c1 is turned off and only the electrical signal from the second photodetector 6c2 is received; if the parameter does not exceed the threshold, the first photodetector 6c1 is turned on and electrical signals are received from both the second photodetector 6c2 and the first photodetector 6c1.

By controlling the detector 6 as described using Figures 6 to 8, it is possible to reduce the intensity of long-wavelength light according to the parameters of the electrons incident on the scintillator 6a. That is, when the parameters of the incident electrons are high, it is possible to achieve the effect shown in Figure 5(a), and when the parameters are low, it is possible to achieve the effect shown in Figure 4(b). As a result, it is possible to suppress degradation of the observed image while maintaining the time resolution of the detector 6.

Note that if high-energy electrons and low-energy electrons arrive at different positions and the respective arrival positions are known, there is no need to control the detector 6. For example, if the arrival positions of high-energy backscattered electrons 5b1 and low-energy backscattered electrons 5b2 are known, the intensity of the long-wavelength light may be reduced at the arrival position of the high-energy backscattered electrons 5b1, and the intensity of the long-wavelength light may not be reduced at the arrival position of the low-energy backscattered electrons 5b2.

Using Figure 9, an example of a detector 6 will be described that reduces the intensity of long-wavelength light at the arrival position of high-energy reflected electrons 5b1, but does not reduce the intensity of long-wavelength light at the arrival position of low-energy reflected electrons 5b2. The detector 6 located at the arrival position of low-energy reflected electrons 5b2 has a scintillator 6a, a light guide 6b, and a photodetector 6c. The detector 6 located at the arrival position of high-energy reflected electrons 5b1 has a scintillator 6a, a long-wavelength light absorbing portion 90, a light guide 6b, and a photodetector 6c. The scintillator 6a, light guide 6b, and photodetector 6c are the same as those in the detector 6 in Figure 1, so their description will be omitted. The long-wavelength light absorbing portion 90 absorbs long-wavelength light, and is located somewhere between the scintillator 6a and the photodetector 6c.

In the scintillator 6a on which high-energy reflected electrons 5b1 are incident, the emission intensity of long-wavelength light is higher than that of short-wavelength light, and the afterglow of long-wavelength light reduces the time resolution. Therefore, by reducing the intensity of long-wavelength light using the long-wavelength light absorbing section 90, the reduction in time resolution can be suppressed. On the other hand, in the scintillator 6a on which low-energy reflected electrons 5b2 are incident, the emission intensity of long-wavelength light is lower than that of short-wavelength light, and the afterglow of long-wavelength light is not enough to reduce the time resolution. Therefore, by not providing the long-wavelength light absorbing section 90 and not reducing the intensity of long-wavelength light, the emission intensity during the incident period can be prevented from being reduced.

The above describes an embodiment of the present invention. The present invention is not limited to the above embodiment, and the components can be modified and embodied without departing from the spirit of the invention.

1a, 1b: charged particle beam device, 2: electron source, 3: electron beam, 4: sample, 5a: secondary electrons, 5b: backscattered electrons, 5b1: high-energy backscattered electrons, 5b2: low-energy backscattered electrons, 6: detector, 6a: scintillator, 6b: light guide, 6c: photodetector, 6c1: first photodetector, 6c2: second photodetector, 7: electron optical column, 8: sample chamber, 10: control unit, 60: variable transmittance filter, 70: optical fiber, 80: spectrometer, 90: long-wavelength light absorbing unit.

Claims (15)

a charged particle source that irradiates a sample with a charged particle beam;
a detector that detects electrons emitted from the sample by irradiation with the charged particle beam and outputs an electrical signal;
a charged particle beam device including a control unit that generates an observation image based on the electrical signal and controls each unit,
the detector includes a scintillator that emits light in response to incidence of electrons, a light receiving element that outputs an electrical signal corresponding to the amount of light emitted by the scintillator, and a long wavelength light reducing unit that reduces the intensity of long wavelength light, which has a relatively long emission wavelength, among the light emitted by the scintillator;
The control unit controls the detector to reduce the intensity of the long-wavelength light if a parameter of electrons incident on the scintillator exceeds a predetermined threshold, and not to reduce the intensity of the long-wavelength light if the parameter does not exceed the threshold. The charged particle beam device according to claim 1,
the parameter is the energy of electrons incident on the scintillator;
The charged particle beam device is characterized in that the control unit controls the detector depending on whether the electrons incident on the scintillator are secondary electrons or backscattered electrons. The charged particle beam device according to claim 1,
the parameter is the energy of electrons incident on the scintillator;
The charged particle beam device is characterized in that the control unit controls the detector in accordance with an acceleration voltage of the charged particle beam. The charged particle beam device according to claim 1,
the parameter is the energy of electrons incident on the scintillator;
A pull-in voltage, which is a voltage for pulling in electrons emitted from the sample, is applied to the scintillator;
The charged particle beam device is characterized in that the control unit controls the detector in accordance with the value of the pull-in voltage. The charged particle beam device according to claim 1,
the parameter is the number of electron particles incident on the scintillator,
The charged particle beam device is characterized in that the control unit controls the detector in accordance with the irradiation density of the charged particle beam. The charged particle beam device according to claim 1,
the scintillator contains at least one element selected from Ga, Zn, In, Al, Cd, Mg, Ca, Sr, Y, Si, Gd, and Ce;
the parameter is the energy of electrons incident on the scintillator;
A charged particle beam device characterized in that the threshold is an energy value at which the intensity of long-wavelength light is greater than the intensity of short-wavelength light, which has a relatively short emission wavelength, and is determined depending on the type of scintillator. The charged particle beam device according to claim 1,
the scintillator contains at least one element selected from Ga, Zn, In, Al, Cd, Mg, Ca, Sr, Y, Si, Gd, and Ce;
The parameter is the number of electron particles incident on the scintillator,
The charged particle beam device is characterized in that the threshold value is a value of the number of particles at which the intensity of the long wavelength light becomes equal to or greater than a predetermined value, and is determined depending on the type of the scintillator. The charged particle beam device according to claim 1,
the long wavelength light reduction unit has a variable transmittance filter that changes the transmittance of the long wavelength light,
The charged particle beam device is characterized in that the control unit controls the transmittance of the variable transmittance filter in accordance with the parameter. The charged particle beam device according to claim 1,
the long wavelength light reducing unit has a fixed transmittance filter that absorbs at least a portion of the long wavelength light,
The charged particle beam device is characterized in that the control unit controls the position of the fixed transmittance filter in accordance with the parameter. The charged particle beam device according to claim 1,
the long-wavelength light reducing unit has a prism that refracts the long-wavelength light,
The charged particle beam device is characterized in that the control unit controls the orientation of the prism in accordance with the parameter. The charged particle beam device according to claim 1,
the long-wavelength light reducing unit includes an optical fiber that connects the scintillator and the light receiving element and has a slower transmission speed of the long-wavelength light than of the short-wavelength light having a relatively short emission wavelength;
The charged particle beam device is characterized in that the control unit turns on the light receiving element during a period in which the short wavelength light is transmitted, and turns off the light receiving element during a period in which the long wavelength light is transmitted. The charged particle beam device according to claim 1,
the long wavelength light reducing unit includes an optical fiber connected to the scintillator, the optical fiber having a slower transmission speed for the long wavelength light than for the short wavelength light having a relatively short emission wavelength, and a shutter that is provided between the optical fiber and the light receiving element and that opens and closes;
The charged particle beam device is characterized in that the control unit opens the shutter during a period in which the short wavelength light is transmitted, and closes the shutter during a period in which the long wavelength light is transmitted. The charged particle beam device according to claim 1,
the long wavelength light reduction unit has a spectroscope that separates light into short wavelength light having a relatively short emission wavelength and the long wavelength light,
the light receiving element has a first light receiving section that receives the long wavelength light and outputs an electrical signal, and a second light receiving section that receives only the short wavelength light and outputs an electrical signal;
The charged particle beam device is characterized in that the control unit controls the first light receiving unit in accordance with the parameter. The charged particle beam device according to claim 1,
A charged particle beam device, wherein the long wavelength light has a wavelength longer than any one of 450 nm to 600 nm. a charged particle source that irradiates a sample with a charged particle beam;
a detector that detects electrons emitted from the sample by irradiation with the charged particle beam and outputs an electrical signal;
a charged particle beam device including a control unit that generates an observation image based on the electrical signal and controls each unit,
the detector comprises a first detection unit having a scintillator that emits light in response to incidence of electrons and a light-receiving element that outputs an electrical signal corresponding to the amount of light emitted by the scintillator, and a second detection unit having the scintillator, the light-receiving element, and a long-wavelength light absorbing unit that absorbs long-wavelength light having a relatively long emission wavelength among the light emitted by the scintillator,
the first detection unit is provided at a position where low-energy reflected electrons reach,
The charged particle beam device is characterized in that the second detection unit is provided at a position where high-energy reflected electrons reach.