Patent Description:
A detector for detecting charged particles obtained by irradiating a sample with a charged particle beam such as an electron beam is provided in a charged particle beam apparatus that detects the charged particles. For example, when electrons emitted from a sample are detected by scanning the sample with an electron beam, the electrons are guided to a scintillator of the detector by applying a positive voltage of about <NUM> to <NUM> kV, which is called a post voltage, to an electron detector. Alternatively, a method in which a detector is provided on the trajectory of electrons, and electrons are caused to be incident on the scintillator without applying the post voltage is also conceivable. Light generated by the scintillator due to collision of electrons is guided to a light guide, converted into an electric signal by a photodetector such as a photoelectric tube, and becomes an image signal or a waveform signal.

<CIT> discloses a charged particle detector and a charged particle beam apparatus including a luminescence unit having a quantum well structure in which layers containing GaInN and GaN are stacked. In addition, <CIT> discloses a GaN-based compound semiconductor laminate having a quantum well structure including a well layer having a non-uniform thickness and a well layer having a uniform thickness.

<CIT> discloses a charged particle detector and a charged particle beam device with which it is possible to acquire a high luminous output while rapidly eliminating charged particles that are incident to a scintillator. <CIT> refer to a gallium nitride compound semiconductor laminate and manufacturing method thereof. <CIT> discloses a GaN based phosphors which emit light with sufficient brightness for practical purposes by the excitation with an electron beam.

In a scintillator having a quantum well structure, layers containing GaN, InGaN, and the like are alternately stacked, but, since lattice constants are different, distortion occurs in the structure, and there is a possibility that luminescence intensity decreases or afterglow intensity increases. If afterglow is generated, the afterglow hinders main detection of luminescence, and attenuation takes time. Thus, it becomes difficult to detect the luminescence at a high speed. The afterglow is generated due to various factors, and it is conceivable that yellow luminescence that is luminescence around a wavelength of <NUM> is a main factor.

<CIT> and <CIT> Aare characterized by an increase in response speed and an increase in luminescence intensity due to a change in quantum well structure and composition. However, none of <CIT> and <CIT> takes into consideration the decrease in afterglow intensity when the quantum well structures are stacked.

In view of the above circumstances, an object of the present invention is to provide a scintillator for a charged particle beam apparatus, which achieves both an increase in luminescence intensity and a decrease in afterglow intensity.

The invention is solved by the subject matter of the independent claims. The dependent claims describe optional embodiments of the invention. One aspect of a scintillator for a charged particle beam apparatus includes a substrate, a buffer layer provided on a surface of the substrate, a stacked body of a luminescent layer and a barrier layer, the stacked body being provided on a surface of the buffer layer, and a conductive layer provided on a surface of the stacked body. Then, the luminescent layer contains InGaN, the barrier layer contains GaN, and a ratio b/a of a thickness b of the barrier layer to a thickness a of the luminescent layer is from <NUM> to <NUM>.

In addition, one aspect of a charged particle beam apparatus is characterized by including an electron source that irradiates an analysis target object with an electron beam, and a secondary particle detector that detects secondary particles emitted when the analysis target object is irradiated with the electron beam, in which the secondary particle detector includes the above-described scintillator for a charged particle beam apparatus according to the present invention.

A more specific configuration of the present invention is described in the claims.

According to the present invention, it is possible to provide a scintillator for a charged particle beam apparatus that achieves both an increase in luminescence intensity and a decrease in afterglow intensity.

Objects, configurations, and advantageous effects other than those described above will be clarified by the descriptions of the following embodiments.

Hereinafter, a charged particle beam apparatus provided with a detector using a scintillator as a detection element will be described. An example of an electron microscope, particularly, a scanning electron microscope (SEM) as the charged particle beam apparatus will be described below.

First, a configuration of a charged particle beam apparatus on which a detector is mounted will be described. <FIG> is a schematic cross-sectional view illustrating a first example of the charged particle beam apparatus according to the present invention. As illustrated in <FIG>, a charged particle beam apparatus (electron microscope) 10a includes an analysis target object (sample) <NUM>, an electron source <NUM> that irradiates the sample <NUM> with an electron beam (primary electron beam) <NUM>, and a detector <NUM> that detects charged particles (secondary particles) <NUM> emitted from the sample <NUM> irradiated with the electron beam <NUM>. The electron source <NUM> is accommodated in an electron optical lens barrel <NUM>. The sample <NUM> is accommodated in a sample chamber <NUM>.

The detector <NUM> includes a scintillator <NUM>, a light guide <NUM>, and a photodetector <NUM>. Secondary particles <NUM> are drawn into the scintillator <NUM> of the detector <NUM> by applying a post voltage, and thus luminescence is caused in the scintillator <NUM>. Light emitted from the scintillator <NUM> is guided by the light guide <NUM> and converted into an electric signal by the photodetector <NUM>.

<FIG> is a schematic cross-sectional view illustrating a second example of the charged particle beam apparatus according to the present invention. In a charged particle beam apparatus (electron microscope) 10b illustrated in <FIG>, by disposing the scintillator <NUM> of the secondary particle detector <NUM> immediately above the sample <NUM>, the secondary particles <NUM> emitted from the sample <NUM> can be caused to be incident on the scintillator <NUM> without applying a post voltage. In addition, the scintillator <NUM> can detect the secondary particles <NUM> emitted in a wide angular range by expanding the surface on which the secondary particles <NUM> are incident. Therefore, even backscattered electrons having an amount smaller than that of the secondary electrons as the secondary particles <NUM> can be detected with high efficiency, and image observation and measurement with high accuracy can be performed.

In common with the charged particle beam apparatus 10a in <FIG> and the charged particle beam apparatus 10b in <FIG>, the scintillator <NUM> and the light guide <NUM> can have various shapes as long as the scintillator <NUM> and the light guide <NUM> do not block the trajectory of the primary electron beam <NUM>. For example, it is conceivable to have an annular shape centered on the primary electron beam <NUM>. The scintillator <NUM> may have a shape covering the entire surface of the light guide <NUM> or a shape covering a portion of the light guide <NUM>. In addition, the number of the photodetectors <NUM> may be one or plural, and may be placed at any position as long as luminescence of the scintillator <NUM> can be input. The photodetector <NUM> is disposed outside the sample chamber <NUM> in <FIG>, but may be disposed in the sample chamber <NUM>.

As the photodetector <NUM>, a photomultiplier tube, a photodetector using a semiconductor, or the like can be used. In addition, the light guide <NUM> is used for inputting light from the scintillator <NUM> to the photodetector <NUM> in <FIG>, but light may be input by another method or another disposition.

A signal obtained by the photodetector <NUM> is converted into an image and displayed in association with an electron beam irradiation position. An electron optical system for focusing the primary electron beam <NUM> on the sample <NUM> and irradiating the sample <NUM> with the primary electron beam <NUM>, that is, a deflector, a lens, an aperture, an objective lens, and the like are not illustrated. The electron optical system is installed in the electron optical lens barrel <NUM>. The sample <NUM> is in a movable state by being placed on a sample stage (not illustrated). The sample <NUM> and the sample stage are disposed in the sample chamber <NUM>. The sample chamber <NUM> is generally kept in a vacuum state. In addition, although not illustrated, the electron microscope is connected with a control unit that controls the whole operation and an operation of each component, a display unit that displays an image, an input unit that causes a user to input an operation instruction of the electron microscope, and the like.

The electron microscope is one example of the configuration. The charged particle beam apparatus in the present invention can be applied to other configurations as long as the charged particle beam apparatus is an electron microscope including the scintillator for a charged particle beam in the present invention, which will be described later. Further, the secondary particles <NUM> also include transmitted electrons, scanning transmitted electrons, and the like. In addition, although only one secondary particle detector <NUM> is illustrated in <FIG> for simplicity, a detector for detecting backscattered electrons, a detector for detecting secondary electrons, and the like may be separately provided, or a plurality of detectors may be provided for detecting the azimuth angle or the elevation angle with distinguishing between the azimuth angle or the elevation angle.

Next, the scintillator <NUM> for a charged particle beam apparatus (also simply referred to as a "scintillator" below) in the present invention will be described. In the present specification, the scintillator refers to an element that causes a charged particle beam to be incident and thus causes light to be emitted. <FIG> is a schematic cross-sectional view illustrating an example of the scintillator for a charged particle beam apparatus according to the present invention.

As illustrated in <FIG>, the scintillator <NUM> has a configuration in which a substrate <NUM>, a buffer layer <NUM>, a stacked body <NUM> of a luminescent layer <NUM> and a barrier layer <NUM>, and a conductive layer <NUM> are stacked in this order. The buffer layer <NUM>, the stacked body <NUM>, and the conductive layer <NUM> constitute a scintillator luminescence unit <NUM>. The conductive layer <NUM> is formed on the side on which the charged particles as a detection target are incident in the charged particle beam apparatus.

As the material of the scintillator <NUM>, for example, sapphire as the substrate <NUM>, GaN as the buffer layer <NUM>, InGaN as the luminescent layer <NUM>, GaN as the barrier layer <NUM>, and Al as the conductive layer <NUM> can be used. The buffer layer <NUM>, the luminescent layer <NUM>, and the barrier layer <NUM> can be formed by chemical vapor deposition (CVD). The stacked body <NUM> made of the above-described materials has a quantum well structure, and can obtain high luminescence intensity.

The substrate <NUM> has, for example, a disk shape of <NUM> to <NUM> inch ϕ. An object obtained by causing the buffer layer <NUM> and the stacked body <NUM> to grow, forming the conductive layer <NUM>, and then cutting the resultant of the forming into a predetermined size can be used as the scintillator. The interface between the substrate <NUM> and the buffer layer <NUM> may have a flat structure or an uneven structure. For example, when a structure in which a protruding structure having a structure pitch of <NUM> to <NUM> and a structure height of <NUM> to <NUM> is continuously formed is used, the probability that light emission in the stacked body <NUM> can be extracted to the substrate <NUM> side increases, and the luminescence output can be improved.

The thickness of the buffer layer <NUM> is preferably equal to or more than <NUM>. The secondary particles <NUM> incident from the conductive layer <NUM> side do not reach the substrate <NUM> by setting the thickness of the buffer layer <NUM> to be equal to or more than <NUM>. Thus, luminescence due to the incidence of the charged particle beam on the substrate <NUM> can be suppressed.

By stacking the luminescent layer <NUM> and the barrier layer <NUM>, carriers (electrons e-, holes h+) generated by the secondary particles <NUM> in the barrier layer <NUM> move inside the barrier layer <NUM>. When the carriers reaches the luminescent layer <NUM> and recombination occurs, light is emitted. However, since the luminescent layer <NUM> and the barrier layer <NUM> have different compositions and different lattice constants, there is a possibility that distortion occurs in the structure due to a difference in lattice constant, and a decrease in luminescence intensity or an increase in yellow luminescence intensity being the main factor of afterglow occurs.

In general, since the barrier layer <NUM> is made thicker than the luminescent layer <NUM>, the lattice constant of the stacked body <NUM> mainly depends on the barrier layer <NUM>. However, when the luminescent layer <NUM> is stacked, the lattice constants of both the layers are deviated and distortion occurs, and this causes a decrease in crystallinity and an increase in afterglow.

As described above, since the stacked body <NUM> of the luminescent layer <NUM> and the barrier layer <NUM> has the quantum well structure, high luminescence intensity can be obtained. However, since the luminescent layer <NUM> and the barrier layer <NUM> having different lattice constants are stacked, distortion occurs, and thus crystallinity decreases, and afterglow increases. As a result of intensive studies, the present inventors have found that, by determining the thickness b of the barrier layer <NUM> in accordance with the thickness a of the luminescent layer <NUM>, it is possible to suppress the occurrence of distortion, suppress a decrease in crystallinity, and reduce afterglow. The present invention is based on this finding.

Specifically, regarding the relation between the thickness a of the luminescent layer <NUM> and the thickness b of the barrier layer <NUM>, b/a is preferably set to be from <NUM> to <NUM>. If b/a is less than <NUM>, the deviation of the lattice constant, which has occurred in the luminescent layer <NUM> cannot be suppressed in the barrier layer <NUM>, and thus there is a possibility that distortion occurs and afterglow increases. In addition, if b/a is more than <NUM>, there is a possibility that an arrival probability of carriers moving in the barrier layer <NUM> to the luminescent layer <NUM> decreases, and the luminescence intensity decreases. In addition, it is desirable that b/a be from <NUM> to <NUM>, in order to highly exhibit the effects of further improving the luminescence intensity and decreasing the afterglow intensity.

The barrier layer <NUM> is preferably doped with Si. For example, Si is preferably doped so that the order of the concentration of Si in the barrier layer <NUM> is from <NUM><NUM> to <NUM><NUM> cm-<NUM>. If Si is doped, the mobility of carriers in the barrier layer <NUM> is improved, and the arrival probability to the luminescent layer <NUM> increases. Therefore, even when the barrier layer <NUM> is thickened, the recombination probability of carriers can be maintained, and the afterglow intensity can be reduced without reducing the luminescence intensity.

If the order of the concentration of Si to be doped is less than <NUM><NUM> cm-<NUM>, the mobility of carriers becomes insufficient when the barrier layer <NUM> is thickened, and thus there is a possibility that the luminescence intensity decreases. In addition, if the order of the concentration of Si is more than <NUM><NUM> cm-<NUM>, the change amount of the lattice constant of the barrier layer <NUM> due to Si doping increases, and thus there is a possibility that distortion occurs in the stacked body <NUM>. Furthermore, in order to highly exhibit the effects of improving the luminescence intensity and decreasing the afterglow intensity, it is desirable that the concentration of Si in the barrier layer <NUM> have the order of <NUM><NUM> to <NUM><NUM> cm-<NUM>.

Also in the luminescent layer <NUM>, Si may be doped in order to improve the mobility of carriers, but the order of the concentration of Si in the luminescent layer <NUM> is preferably equal to or less than <NUM><NUM> cm-<NUM>. If the order of the concentration of Si is more than the order of <NUM><NUM> cm-<NUM>, the difference in lattice constant between the luminescent layer <NUM> and the barrier layer <NUM> increases, and thus there is a possibility that distortion occurs in the stacked body <NUM>, and the luminescence intensity decreases or the afterglow intensity increases.

The concentrations of Si in the luminescent layer <NUM> and the barrier layer <NUM> can be measured by secondary ion mass spectrometry (SIMS) or the like.

The thickness b of the barrier layer <NUM> is preferably set to be from <NUM> to <NUM>. If the thickness b is less than <NUM>, there is a possibility that distortion occurs in the stacked body <NUM>, and thus a decrease in luminescence intensity and an increase in afterglow intensity are caused. In addition, if the thickness b is thicker than <NUM>, there is a possibility that an arrival probability of carriers moving in the barrier layer <NUM> to the luminescent layer <NUM> decreases, and the luminescence intensity decreases.

It is preferable that a plurality of luminescent layers <NUM> and a plurality of barrier layers <NUM> are alternately stacked. If the barrier layer <NUM> is thick, the number of generated carriers increases. However, if the barrier layer is too thick, there is a possibility that the arrival probability of carriers to the luminescent layer <NUM> decreases, and the luminescence intensity decreases. At this time, by alternately stacking a plurality of the luminescent layers <NUM> and a plurality of the barrier layers <NUM>, the total thickness of the barrier layers <NUM> included in the stacked body <NUM> can be increased while maintaining the thickness of each barrier layer <NUM>. Thus, it is possible to achieve both an increase in the number of carriers and an improvement in the arrival probability of carriers to the luminescent layer <NUM>.

The thickness of the stacked body <NUM> is preferably from <NUM> to <NUM>. If the thickness of the stacked body <NUM> is less than <NUM>, the number of carriers generated in the barrier layer <NUM> is small. Thus, the luminescence intensity decreases. In addition, if the stacked body <NUM> is thicker than <NUM>, there is a possibility that, even though light is emitted, the light is absorbed in the stacked body <NUM> before reaching the buffer layer <NUM> side, and the light extraction amount from the scintillator decreases.

The number of the luminescent layers <NUM> and the number of the barrier layers <NUM> are preferably set to be from <NUM> to <NUM>, respectively. If the number of layers is less than <NUM>, there is a possibility that the stacked body <NUM> cannot be thickened, and the luminescence intensity is lowered. In addition, if the number of layers is more than <NUM>, there is a possibility that distortion occurs by stacking a large number of layers having different lattice constants, and thus a decrease in luminescence intensity and an increase in afterglow intensity are caused. Furthermore, since the stacked body <NUM> becomes thick, there is a possibility that light is absorbed in the stacked body <NUM> and the light extraction amount decreases.

The thickness of the conductive layer <NUM> is preferably set to be from <NUM> to <NUM>. If the conductive layer <NUM> is thinner than <NUM>, there is a possibility of charging when the secondary particles <NUM> are incident. In addition, if the conductive layer <NUM> is thicker than <NUM>, there is a possibility that energy is lost when the secondary particles <NUM> pass through the conductive layer <NUM>, and the incident amount of the charged particle beam on the stacked body <NUM> decreases. As the material of the conductive layer <NUM>, other materials, alloys, and the like can be used in addition to Al as long as the material is a conductive material.

The layer thicknesses of the buffer layer <NUM>, the luminescent layer <NUM>, the barrier layer <NUM>, and the conductive layer <NUM>, the number of the buffer layers <NUM>, the number of the luminescent layers <NUM>, the number of the barrier layers <NUM>, and the number of the conductive layers <NUM> can be measured by using a transmission electron microscope (TEM), an X-ray, or the like.

In the case of an LED (light emitting diode), carriers are recombined at a pn junction portion between a p-type semiconductor and an n-type semiconductor by current injection, and thus light is emitted. On the other hand, in the scintillator illustrated in <FIG>, excitation of carriers by charged particles incident in the n-type structure and light emission due to the recombination are caused. Therefore, light can be emitted without the pn junction.

In the scintillator described above, light can be propagated not only in an up-down direction in the scintillator (direction from the conductive layer <NUM> toward the substrate <NUM>) but also in a left-right direction. Therefore, regarding the scintillator <NUM> having a large incident surface of the secondary particles <NUM> from the sample <NUM> as illustrated in <FIG>, even when the light guide <NUM> guides light to the photodetector <NUM> having a surface provided at an angle of <NUM> degrees with the incident surface, the detection efficiency of light in the photodetector <NUM> can be improved by light propagating inside the scintillator <NUM>.

<FIG> is a graph showing the relation between the ratio b/a of the thickness b of the barrier layer <NUM> to the thickness a of the luminescent layer <NUM>, the luminescence intensity, and the afterglow intensity. In <FIG>, a scintillator having peak luminescence intensity in the vicinity of <NUM> is used, and a value obtained by integrating the intensity at <NUM> to <NUM> is shown as the luminescence intensity. The afterglow intensity was shown by the ratio of the intensity of yellow luminescence at <NUM> to the peak luminescence intensity at the vicinity of <NUM>.

As illustrated in <FIG>, it was understood that the afterglow intensity was sufficiently reduced (<NUM>% or less) in a section in which b/a is <NUM> to <NUM>. In addition, it is understood that the luminescence intensity can be maintained at the same level at this time. That is, it is understood that, by setting b/a to <NUM> to <NUM>, the decrease in the luminescence intensity can be suppressed and the afterglow intensity can be decreased.

<FIG> is a graph showing the relation between the Si concentration of the barrier layer <NUM>, the luminescence intensity, and the afterglow intensity. The results of evaluating the luminescence intensity and the afterglow intensity by the same method as in <FIG> are shown. From this graph, it is understood that, if the order of the Si concentration is set to be <NUM><NUM> to <NUM><NUM> cm-<NUM>, the afterglow intensity decreases to be equal to or less than <NUM>% of the luminescence intensity. That is, it is understood that the afterglow intensity can be decreased by setting the Si concentration to the order of <NUM><NUM> to <NUM><NUM> cm-<NUM>.

In the above measurement, the scintillator having a peak luminescent wavelength in the vicinity of <NUM> was used, but it was understood that, when the peak luminescent wavelength was increased up to the vicinity of <NUM> by changing the In concentration or the like of the luminescent layer <NUM>, the same result was obtained.

In the above description, an example in which the scintillator is applied to a detector such as a scanning electron microscope has been mainly described, but the scintillator for a charged particle beam apparatus in the present invention may be adopted as a detector of a mass spectrometer.

The mass spectrometer performs mass separation of ions by an electromagnetic action, and measures a mass/charge ratio of ions to be measured. <FIG> is a schematic cross-sectional view illustrating a third example of the charged particle beam apparatus according to the present invention. <FIG> illustrates a configuration of a mass spectrometer as a charged particle beam apparatus 10c. A mass spectrometer 10c illustrated in <FIG> includes an ionization unit <NUM> that ionizes a sample as an analysis target, a mass separation unit <NUM> that mass-selects ions extracted by the ionization unit <NUM>, a conversion dynode (conversion electrode) <NUM> that converts ions mass-selected by the mass separation unit <NUM> into charged particles by colliding the ions with an electrode, and a secondary particle detector <NUM> that detects the charged particles generated by the conversion dynode <NUM>.

As a method of ionization of the ionization unit <NUM>, there are ESI (Electrospray Ionization), APCI (Atmospheric Pressure Chemical Ionization), MALDI (Matrix-Assisted Laser Desorption Ionization), APPI (Atmospheric Pressure Photo-Ionization), and the like. In addition, as the mass separation unit <NUM>, there are a QMS (Quadrupole Mass Spectrometer) type, an Iontrap type, a time-of-flight type, an FT-ICR (Fourier Transform Ion Cyclotron Resonance) type, an Orbitrap type, and a combination type thereof.

The secondary particle detector <NUM> has the same configuration as the secondary particle detector <NUM> illustrated in <FIG>, and includes the scintillator <NUM> for a charged particle beam apparatus in the present invention. By applying the scintillator <NUM> for a charged particle beam apparatus in the present invention, it is possible to provide the mass spectrometer 10c capable of performing high-speed and high-sensitivity analysis.

As described above, according to the present invention, it has been shown that it is possible to provide a scintillator for a charged particle beam apparatus that achieves both an increase in luminescence intensity and a decrease in afterglow intensity.

Note that, the present invention is not limited to the above example, and various modifications may be provided. For example, the above examples are described in detail in order to explain the present invention in an easy-to-understand manner, and the above embodiments are not necessarily limited to a case including all the described configurations. Further, some components in one embodiment can be replaced with the components in another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Regarding some components in the embodiments, other components can be added, deleted, and replaced.

In the above-described embodiment of the present invention, the SEM and the mass spectrometer have been described as examples of the charged particle beam apparatus in the present invention, but the charged particle beam apparatus in the present invention is not limited thereto. Application to other devices using an ion beam is also possible.

Claim 1:
A scintillator for a charged particle beam apparatus (10a, 10b), the scintillator (<NUM>) comprising:
a substrate (<NUM>);
a buffer layer (<NUM>) provided on a surface of the substrate (<NUM>);
a stacked body (<NUM>) of a luminescent layer (<NUM>) and a barrier layer (<NUM>), the stacked body (<NUM>) being provided on a surface of the buffer layer (<NUM>); and
a conductive layer (<NUM>) provided on a surface of the stacked body (<NUM>),
wherein the luminescent layer (<NUM>) contains InGaN, and
the barrier layer (<NUM>) contains GaN,
characterized in that
a ratio b/a of a thickness b of the barrier layer (<NUM>) to a thickness a of the luminescent layer (<NUM>) is from <NUM> to <NUM>,
wherein
the barrier layer (<NUM>) contains Si, and
an order of concentration of Si is from <NUM><NUM> cm-<NUM> to <NUM><NUM> cm-<NUM>.