Light-emitting body, charged particle detector, electron microscope, and mass spectrometer

Abstract

This light-emitting body (10) converts incident charged particles into light, and the light-emitting body (10) is provided with a multiple quantum well structure (14C) that emits light upon incidence of charged particles. The thickness of a well layer (141) constituting the multiple quantum well structure (14C) is 0.2 nm or more and less than 1.5 nm. The concentration of an additive added to a barrier layer (142) and the well layer (141) constituting the multiple quantum well structure (14C) is greater than 4×1018cm-3 and less than or equal to 1×1020cm-3.　If the thickness of the well layer and the concentration of the additive of the barrier layer and the well layer can be optimized, the afterglow time can be reduced while maintaining the light emission intensity, and the high-speed responsiveness can be further enhanced.

Description

Light emitters, charged particle detectors, electron microscopes and mass spectrometers

[0001] One aspect of the present invention relates to a light emitter, a charged particle detector, an electron microscope, and a mass spectrometer.

[0002] Patent Document 1 describes a light emitter that converts incident electrons into light. The light emitter described in Patent Document 1 includes a substrate, a nitride semiconductor layer having a quantum well structure formed on one surface of the substrate, a cap layer stacked on the nitride semiconductor layer and made of a material having a larger band gap energy than the constituent material of the nitride semiconductor layer, and a metal back layer formed on the cap layer.

[0003] Patent No. 4365255

[0004] In the above-described light emitter, it is sometimes desirable to further improve the high-speed response in order to capture events that occur within a shorter time, for example. Therefore, an object of one aspect of the present invention is to provide a light emitter, a charged particle detector, an electron microscope, and a mass spectrometer that can further improve the high-speed response.

[0005] The present inventors have conducted extensive research and found that there is a correlation between the thickness of the well layer and the decay time in a light-emitting material. They have also found that there is a correlation between the concentration of an additive in a light-emitting material and the decay time, such that the greater the additive concentration, the shorter the decay time. On the other hand, they have found that when the additive concentration exceeds a certain level, for example, crystallinity deteriorates, resulting in a significant decrease in luminescence intensity and making practical use difficult. Therefore, the present inventors have conducted further extensive research and found that if the thickness of the well layer and the concentrations of the additives in the barrier layer and well layer can be optimized, the decay time can be shortened while maintaining the luminescence intensity, thereby enabling further improvement in high-speed response, thereby achieving one aspect of the present invention.

[0006] (1) That is, a light emitter according to one aspect of the present invention is a light emitter that converts incident charged particles into light, and has a multiple quantum well structure that emits light in response to the incidence of charged particles, the thickness of the well layer that constitutes the multiple quantum well structure is 0.2 nm or more and less than 1.5 nm, and the concentration of an additive added to the barrier layer and the well layer that constitute the multiple quantum well structure is 4×10 １８ cm －３ greater than 1×10 ２０ cm －３ The following is the result.

[0007] In this light-emitting device, the thickness of the well layer is 0.2 nm or more and less than 1.5 nm, and the concentration of the dopant in the barrier layer and the well layer is 4×10 １８ cm －３ greater than 1×10 ２０ cm －３ In this case, the thickness of the well layer and the concentrations of the additives in the barrier layer and well layer can be optimized based on the above findings, and it becomes possible to reduce the decay time while maintaining the luminescence intensity. Therefore, it is possible to further shorten the response time and further improve the high-speed response.

[0008] (2) In the light-emitting element described in (1) above, the well layer may have a thickness of 0.6 nm or more and less than 1.0 nm, which can further reduce the decay time.

[0009] (3) In the light-emitting device described in (1) or (2) above, the multiple quantum well structure may include a first barrier layer and a second barrier layer as barrier layers, the second barrier layer being located closer to the charged particle incident surface of the multiple quantum well structure than the first barrier layer, and the first barrier layer may be thicker than the second barrier layer. By changing the thickness of the barrier layer in this way depending on the distance from the charged particle incident surface, it is possible to improve the light conversion efficiency from low acceleration voltages to high acceleration voltages, and to increase the emission intensity.

[0010] (4) In the light-emitting element according to any one of (1) to (3), the well layer and the barrier layer may be nitride semiconductor layers, and the additive may contain silicon. In this case, the well layer and the barrier layer may be nitride semiconductor layers, and silicon may be used as the additive.

[0011] (5) A charged particle detector according to one aspect of the present invention includes the light emitter according to any one of (1) to (4) above, and a photodetector optically coupled to a surface of the multiple quantum well structure opposite to the charged particle incident surface, the photodetector having sensitivity to light emitted by the multiple quantum well structure. Since this charged particle detector also includes the light emitter described above, it is possible to further improve high-speed response.

[0012] (6) An electron microscope according to one aspect of the present invention comprises the light emitter according to any one of (1) to (4), a photodetector optically coupled to the surface of the multiple quantum well structure opposite the charged particle incidence surface and sensitive to light emitted by the multiple quantum well structure, and a chamber in which at least the light emitter is disposed, and an image of the sample is obtained by irradiating an electron beam onto the surface of a sample disposed in the chamber, guiding electrons from the sample to the light emitter, and correlating the irradiation position of the electron beam on the sample with the output of the photodetector. Since this electron microscope also comprises the light emitter described above, it is similarly possible to further improve high-speed response.

[0013] (7) A mass spectrometer according to one aspect of the present invention includes the light emitter according to any one of (1) to (4), a photodetector optically coupled to a surface of the multiple quantum well structure opposite to the charged particle incident surface and sensitive to light emitted by the multiple quantum well structure, a chamber in which at least the light emitter is disposed, a separation unit that spatially or temporally separates ions generated from a sample in the chamber according to their mass, and an electron conversion unit to which the ions separated by the separation unit are irradiated, where electrons emitted from the electron conversion unit in response to ions entering the electron conversion unit are guided to the light emitter, and mass analysis of the sample is performed based on the output of the photodetector. This mass spectrometer also includes the light emitter described above, which similarly enables faster response.

[0014] According to one aspect of the present invention, it is possible to provide a light emitter, a charged particle detector, an electron microscope, and a mass spectrometer that are capable of further improving high-speed response.

[0015] FIG. 1 is a cross-sectional view showing the configuration of a light emitter according to a first embodiment. FIG. 2 is an enlarged cross-sectional view showing the internal structure of the multiple quantum well structure of FIG. 1. FIG. 3 is a graph showing decay when the thickness of the well layer in the light emitter of FIG. 1 is changed. FIG. 4 is a graph showing decay when the concentration of an additive in the light emitter of FIG. 1 is changed. FIG. 5 is a graph showing emission intensity when the thickness of the well layer in the light emitter of FIG. 1 is changed. FIG. 6 is a graph showing emission intensity when the concentration of an additive in the light emitter of FIG. 1 is changed. FIG. 7 is a graph showing the relationship between decay and emission intensity in the light emitter of FIG. 1. FIG. 8 is a cross-sectional view showing the configuration of an electron beam detector according to a second embodiment. FIG. 9 is a diagram schematically showing the configuration of a length-measuring SEM according to a third embodiment. FIG. 10 is a diagram schematically showing the configuration of a mass spectrometer according to a fourth embodiment.

[0016] Hereinafter, the embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted.

[0017] [First Embodiment] Fig. 1 is a cross-sectional view showing the configuration of a light emitter 10 according to a first embodiment, showing a cross section along the thickness direction. The light emitter 10 converts incident charged particles, in this embodiment, electrons, into light. As shown in Fig. 1, the light emitter 10 includes a substrate 12, a nitride semiconductor layer 14 provided on a major surface 12a of the substrate 12, and a conductive layer 18 provided on the nitride semiconductor layer 14. The surface of the conductive layer 18 forms an electron incident surface (charged particle incident surface) 10a.

[0018] The substrate 12 is a plate-like member that is optically transparent to the wavelength of light emitted from the nitride semiconductor layer 14. The constituent material of the substrate 12 is not particularly limited as long as it transmits the light emitted from the nitride semiconductor layer 14 and is capable of epitaxially growing the nitride semiconductor layer 14. In one example, the substrate 12 is a sapphire substrate. In another example, the substrate 12 transmits light with a wavelength of 170 nm or more. The substrate 12 has a main surface 12a and a back surface 12b located on the opposite side to the main surface 12a.

[0019] The nitride semiconductor layer 14 includes a first buffer layer 14A provided on the primary surface 12a of the substrate 12, a second buffer layer 14B provided on the first buffer layer 14A, and a multiple quantum well structure 14C provided on the second buffer layer 14B.

[0020] The first buffer layer 14A is a layer for growing the multiple quantum well structure 14C with good crystallinity and is in contact with the primary surface 12a. The first buffer layer 14A is grown at a relatively low temperature (e.g., 400°C or higher and 700°C or lower) and has an amorphous structure containing, for example, mainly gallium (Ga) and nitrogen (N). In one example, the first buffer layer 14A is made of amorphous GaN. The thickness of the first buffer layer 14A is, for example, 5 nm or higher and 500 nm or lower, and in one example, is 20 nm.

[0021] The second buffer layer 14B is also a layer for growing the multiple quantum well structure 14C with good crystallinity and mainly contains, for example, GaN crystals. In one example, the second buffer layer 14B is made of GaN crystals. The second buffer layer 14B is epitaxially grown at a higher temperature (e.g., 700°C or higher and 1200°C or lower) than the first buffer layer 14A. The thickness of the second buffer layer 14B is, for example, 1 μm or higher and 10 μm or lower, and in one example, 2.5 μm. The second buffer layer 14B may be in contact with the first buffer layer 14A.

[0022] The multiple quantum well structure 14C is a layer that emits light in response to incident electrons and is epitaxially grown on the second buffer layer 14B. Figure 2 is an enlarged cross-sectional view showing the internal structure of the multiple quantum well structure 14C. As shown in Figure 2, the multiple quantum well structure 14C has a configuration in which well layers 141 and barrier layers 142 are alternately stacked.

[0023] The well layer 141 is a light-emitting layer containing a material that receives electrons and emits light. x Ga 1-x The well layer 141 is a nitride semiconductor layer mainly containing crystals of InN (0<x<1). x Ga 1-x The multiple quantum well structure 14C is made of N (0<x<1) crystals. When electrons enter the multiple quantum well structure 14C, electron-hole pairs are formed, and light is emitted in the process of recombining in the well layers 141 (cathodoluminescence). The multiple well layers 141 constituting the multiple quantum well structure 14C have the same composition, and the composition x is equal to each other. In one embodiment, the composition x is 0.1. The multiple well layers 141 constituting the multiple quantum well structure 14C also have the same thickness.

[0024] The bandgap energy of the barrier layers 142 is larger than the bandgap energy of the well layers 141. By sandwiching the well layers 141 between the barrier layers 142, electrons can be collected in the well layers 141 and efficiently converted into light. The barrier layers 142 are nitride semiconductor layers mainly containing GaN crystals. In one example, the barrier layers 142 are made of GaN crystals doped with Si. The barrier layers 142 may further contain group III atoms other than Ga (e.g., In). Even in this case, the multiple barrier layers 142 constituting the multiple quantum well structure 14C have the same composition.

[0025] The thicknesses of the multiple barrier layers 142 constituting the multiple quantum well structure 14C are different from one another. Specifically, each barrier layer 142 is thicker than the barrier layer 142 located on the electron incident surface 10a (see FIG. 1 ) side of the barrier layer 142. In other words, the thickness of the multiple barrier layers 142 increases with increasing distance from the electron incident surface 10a, with the first barrier layer 142 closest to the electron incident surface 10a being the thinnest of the multiple barrier layers 142. In a preferred example, the thickness of the first barrier layer 142 closest to the electron incident surface 10a is 80% or less, more preferably 20% or less, of the average thickness of the barrier layers 142. The thickness of the second barrier layer 142 (i.e., the barrier layer 142 adjacent to the barrier layer 142 closest to the electron incident surface 10a) is 90% or less, more preferably 80% or less, of the average thickness of the multiple barrier layers 142.

[0026] The multiple quantum well structure 14C of this embodiment has nine barrier layers 142. The first well layer 141 is provided between the first and second barrier layers 142, counting from the electron incident surface 10a. The nth (n=2, ..., 8) well layer 141 is provided between the nth and (n+1)th barrier layers 142, counting from the electron incident surface 10a. A barrier layer 143 (see FIG. 2 ) having the same composition as each of the barrier layers 142 is provided between the last (ninth) well layer 141 and the second buffer layer 14B. The thickness of the barrier layer 143 does not affect the characteristics of the light emitter 10, but is, for example, 10 nm. If necessary, the barrier layer 143 may be omitted.

[0027] In this embodiment, the barrier layers 142 become thicker as they move away from the electron incident surface 10a in all of the multiple barrier layers 142, but as long as most of the multiple barrier layers 142 satisfy this condition, the effect of this embodiment is hardly impaired even if some of the barrier layers 142 do not satisfy this condition. In other words, when a certain barrier layer 142 (hereinafter also referred to as a "first barrier layer") included in the multiple barrier layers 142 is thicker than another barrier layer 142 (hereinafter also referred to as a "second barrier layer") located closer to the electron incident surface 10a than the first barrier layer 142, the effect of this embodiment, which will be described later, is suitably achieved.

[0028] In this embodiment, the difference in thickness between adjacent barrier layers 142 decreases with increasing distance from the electron incident surface 10a. Note that, for example, as long as most of the numerous barrier layers 142 satisfy this condition, the effect of this embodiment is hardly impaired even if some of the barrier layers 142 do not satisfy this condition. In other words, when the difference in thickness between a pair of adjacent barrier layers 142 included in the plurality of barrier layers 142 is smaller than the difference in thickness between another pair of adjacent barrier layers 142 located on the electron incident surface 10a side of the pair of barrier layers 142, the effect described below is preferably achieved.

[0029] The conductive layer 18 is used as one electrode that conducts electrons to the light emitter 10. The conductive layer 18 mainly contains, for example, a metal, and in one embodiment, mainly contains aluminum (Al). The thickness of the conductive layer 18 is, for example, 10 nm to 1000 nm, and in one embodiment, approximately 300 nm. When the conductive layer 18 mainly contains a metal, the conductive layer 18 also functions as a light reflecting film. That is, a portion of the light generated in the multiple quantum well structure 14C reaches the substrate 12 directly from the multiple quantum well structure 14C, passes through the substrate 12, and is emitted to the outside of the light emitter 10, while the remaining portion of the light generated in the multiple quantum well structure 14C reaches the conductive layer 18 from the multiple quantum well structure 14C, is reflected by the conductive layer 18, passes through the substrate 12, and is emitted to the outside of the light emitter 10.

[0030] An example of a method for fabricating the light-emitting body 10 will be described. First, the substrate 12 is introduced into the growth chamber of a metal-organic vapor phase epitaxy (MOVPE) apparatus and heat-treated in a hydrogen atmosphere at 1100°C for 10 minutes to clean the main surface 12a. Then, the temperature of the substrate 12 is lowered to 500°C, and a first buffer layer 14A is deposited. After that, the temperature of the substrate 12 is raised to 1100°C, and a second buffer layer 14B is epitaxially grown. Thereafter, the temperature of the substrate 12 is lowered to 800°C, and In is deposited. x Ga 1-x The N / GaN multiple quantum well structure 14C is then formed. The substrate 12 is then transferred into a deposition apparatus, and a conductive layer 18 is formed on the multiple quantum well structure 14C, thereby completing the fabrication of the light emitter 10.

[0031] In the above example, trimethylgallium (Ga(CH)3:TMGa) can be used as the Ga source, trimethylindium (In(CH)3:TMIn) can be used as the In source, ammonia (NH) can be used as the N source, hydrogen gas (H) or nitrogen gas (N) can be used as the carrier gas, and monosilane (SiH) can be used as the Si source. Alternatively, other metalorganic sources (e.g., triethylgallium (Ga(CH)3:TEGa), triethylindium (In(CH)3:TEIn), etc.) and other hydrides (e.g., disilane (SiH) can be used). In addition, although the above example uses an MOVPE system, a hydride vapor phase epitaxy (HVPE) system or a molecular beam epitaxy (MBE) system can also be used. In addition, the growth temperatures are not limited to those described above.

[0032] In this embodiment, the thickness of the well layer 141 is 0.2 nm or more and less than 1.5 nm. Preferably, the thickness of the well layer 141 is 0.6 nm or more and less than 1.0 nm. The additive added to the barrier layer 142 and the well layer 141 (hereinafter simply referred to as "additive") contains silicon. The concentration of the additive is 4×10 １８ cm －３ greater than 1×10 ２０ cm －３ The additive is also called a dopant, and the concentration of the additive is also called a Si doping concentration.

[0033] 3 is a graph showing the decay when the thickness of the well layer 141 in the light emitter 10 is changed. The decay is the afterglow time and is defined as the time it takes for the intensity to fall from 90% to 10% of the peak intensity. In the graph, the circles in the data indicate actual measured values, and the lines in the data indicate values ​​calculated based on the actual measured values ​​(the same applies to the following graphs). In Example 1, the concentration of the additive was 4×10 １８ cm －３ In Example 2, the concentration of the additive is 1.5×10 １９ cm －３In this example, the threshold value α is set based on the decay time of a typical light emitter, and is set to 3.5 ns. The threshold value α is not particularly limited.

[0034] As shown in Figure 3, it can be seen that the decay changes in a quadratic function manner as the thickness of the well layer 141 changes. In the example shown, the quadratic function of the decay has a bottom when the thickness of the well layer 141 is between 0.2 nm and 1.5 nm (around 0.8 nm in this case). It is estimated that the relationship between the decay and the thickness of the well layer 141 will show a similar tendency even if the concentration of the additive is changed. In the light emitter 10, a well layer 141 thickness thinner than 0.2 nm is not realistic from the standpoint of manufacturing or practical use.

[0035] FIG. 4 is a graph showing the decay when the concentration of the additive in the light emitter 10 is changed. Example 3 is an example in which the thickness of the well layer 141 is 0.8 nm. Example 4 is an example in which the thickness of the well layer 141 is 1.5 nm. As shown in FIG. 4, it can be seen that the decay decreases as the concentration of the additive increases. It can be seen that the amount of change in decay decreases as the concentration of the additive increases. It is estimated that the relationship between the decay and the concentration of the additive will show a similar tendency even if the thickness of the well layer 141 is changed. When the concentration of the additive is 4×10 １８ cm －３ , when the thickness of the well layer 141 is 1.5 nm, the decay becomes large and the possibility of exceeding the threshold value α increases.

[0036] 5 is a graph showing the luminescence intensity (arbitrary units (a.u.)) when the thickness of the well layer 141 in the light emitter 10 is changed. １８ cm －３ In Example 6, the concentration of the additive is 1.5×10 １９ cm －３ In Example 7, the concentration of the additive is 1×10 ２０ cm －３ The threshold value β is a value set based on the luminous intensity of a general light emitter, and is set to 5000 in this example. The threshold value β is not particularly limited.

[0037] As shown in FIG. 5, the thicker the well layer 141, the higher the emission intensity. It is estimated that the emission intensity exhibits a similar tendency even when the concentration of the additive is changed. When the thickness of the well layer 141 is smaller than 0.2 nm, for example, when the concentration of the additive is 1×10 ２０ cm －３ In this case, it can be seen that the emission intensity becomes smaller and is more likely to fall below the threshold value β.

[0038] FIG. 6 is a graph showing the luminous intensity (arbitrary units (a.u.)) when the concentration of the additive in the light emitter 10 is changed. Example 8 is an example where the thickness of the well layer 141 is 0.8 nm. Example 9 is an example where the thickness of the well layer 141 is 0.2 nm. As shown in FIG. 6, the luminous intensity decreases as the concentration of the additive increases. The amount of change in the luminous intensity decreases as the concentration of the additive increases. It is estimated that the luminous intensity will show a similar tendency even if the thickness of the well layer 141 is changed. When the concentration of the additive is 1×10 ２０ cm －３ , for example, when the thickness of the well layer 141 is 0.2 nm, the emission intensity is likely to decrease and fall below the threshold value β.

[0039] As described above, in the light emitter 10, the thickness of the well layer 141 is 0.2 nm or more and less than 1.5 nm, and the concentration of the additive in the barrier layer 142 and the well layer 141 is 4×10 １８ cm －３ greater than 1×10 ２０ cm －３ In this case, the thickness of the well layer 141 and the concentrations of the additives in the barrier layer 142 and the well layer 141 can be optimized, and the decay can be reduced while maintaining the emission intensity. Therefore, the response time can be further shortened, and high-speed response can be further improved.

[0040] In the light emitter 10, the thickness of the well layer 141 is 0.6 nm or more and less than 1.0 nm, which makes it possible to further reduce the decay.

[0041] In the light emitter 10, the multiple quantum well structure 14C includes a first barrier layer and a second barrier layer as the barrier layer 142. The second barrier layer is located closer to the electron incident surface 10a than the first barrier layer, and the first barrier layer is thicker than the second barrier layer. Because the second barrier layer, which is located relatively shallower from the electron incident surface 10a, is relatively thin, the well layer 141, which is located on the opposite side of the second barrier layer from the electron incident surface 10a, is located closer to the electron incident surface 10a. This improves the light conversion efficiency for electron beams with low acceleration voltages. Furthermore, because the first barrier layer, which is located relatively deep, is relatively thick, the well layer 141, which is located on the opposite side of the first barrier layer from the electron incident surface 10a, is located farther from the electron incident surface 10a. This makes it possible to maintain the light conversion efficiency even when electron beams with high acceleration voltages penetrate deep into the well layer. Furthermore, since the electron beam spreads hemispherically inside the light emitter 10, the densely arranged quantum wells near the electron incident surface 10a reliably capture electrons even at high acceleration voltages. By varying the thickness of the barrier layer 142 in this way depending on the distance from the electron incident surface 10a, it is possible to improve the light conversion efficiency from low to high acceleration voltages, and increase the emission intensity.

[0042] In the light emitter 10, the well layer 141 and the barrier layer 142 are nitride semiconductor layers, and the additive contains silicon. In this case, it is possible to use the well layer 141 and the barrier layer 142 as nitride semiconductor layers and to use silicon as the additive.

[0043] In the light emitter 10, the second barrier layer is closest to the electron incident surface 10a among the multiple barrier layers 142. In this case, the second barrier layer is the thinnest among the multiple barrier layers 142. This brings the well layer closest to the electron incident surface 10a closer to the electron incident surface 10a, thereby further improving the light conversion efficiency for an electron beam with a small acceleration voltage.

[0044] In the light emitter 10, the barrier layers 142 become thicker as they are further away from the electron incident surface 10a. In this case, an appropriate well layer arrangement can be achieved depending on various levels of acceleration voltage, further improving the light conversion efficiency. In the light emitter, the well layers 141 have the same composition, which makes it easy to fabricate a multiple quantum well structure.

[0045] 7 is a graph showing the relationship between decay and luminescence intensity in the light emitter 10. The graph shows data obtained when the thickness of the well layer 141 and the concentration of the additive are changed. As shown in FIG. 7, it can be confirmed that the light emitter 10 exhibits a relationship in which the luminescence intensity increases as the decay increases.

[0046] In this embodiment, incident electrons are converted into light, but this is not limiting. This embodiment may be any light-emitting body that converts incident charged particles into light. In the above embodiment, the nitride semiconductor refers to a compound that contains at least one of Ga, In, and Al as a group III element and N as a main group V element. Having optical transparency refers to, for example, the property of transmitting 50% or more of the target light.

[0047] [Second Embodiment] Fig. 8 is a cross-sectional view showing the configuration of an electron beam detector 20 according to a second embodiment, showing a cross section along the thickness direction. As shown in Fig. 8, the electron beam detector 20 includes the light emitter 10 of the first embodiment, an insulating optical member 22, and a photodetector 30. The optical member 22 is an example of a light-transmitting member (light guide member). The optical member 22 has insulating properties and is interposed between the light emitter 10 and the photodetector 30 to integrate the light emitter 10 and the photodetector 30.

[0048] The rear surface 12b of the substrate 12 of the light emitter 10 and the light incident surface 30a of the photodetector 30 are optically coupled via an optical member 22. Specifically, one end surface of the optical member 22 is bonded to the light incident surface 30a, and the other end surface of the optical member 22 is bonded to the light emitter 10. The optical member 22 may be a light guide such as a fiber optic plate (FOP), or may be a lens that focuses light generated in the light emitter 10 onto the light incident surface 30a.

[0049] An optically transparent adhesive layer AD2 is interposed between the optical member 22 and the photodetector 30, and the relative positions of the optical member 22 and the photodetector 30 are fixed by the adhesive layer AD2. The adhesive layer AD2 mainly contains, for example, an optically transparent resin. An adhesive layer AD1 is interposed between the rear surface 12b of the substrate 12 of the light emitter 10 and the optical member 22. The adhesive layer AD1 includes a SiN layer ADa provided on the rear surface 12b and a SiO layer ADb provided on the SiN layer ADa. In one example, the rear surface 12b and the SiN layer ADa are in contact with each other, and the SiN layer ADa and the SiO layer ADb are in contact with each other. The SiO layer ADb and the optical member 22 are fused to each other. Because the SiO layer ADb and the optical member 22 are both made of silicon dioxide, they can be fused to each other by heating.

[0050] The SiO layer ADb is formed on the SiN layer ADa by sputtering or the like, so the bonding strength between the SiN layer ADa and the SiO layer ADb is extremely strong. Similarly, the SiN layer ADa is also formed on the back surface 12b of the substrate 12 by sputtering or the like, so the bonding strength between the SiN layer ADa and the substrate 12 is also extremely strong. Therefore, the substrate 12 and the optical member 22 are firmly bonded via the adhesive layer AD1. The SiN layer ADa also functions as an anti-reflection film, suppressing or reducing reflection of light generated in the multiple quantum well structure 14C at the back surface 12b.

[0051] In the electron beam detector 20 having such a structure, light generated in the multiple quantum well structure 14C in response to the incidence of electrons passes through the adhesive layer AD1, the optical member 22, and the adhesive layer AD2 in sequence and reaches the light incident surface 30a of the photodetector 30.

[0052] As described above, the light incident surface 30a of the photodetector 30 is optically coupled to the surface of the multiple quantum well structure 14C opposite the electron incident surface 10a via the substrate 12, adhesive layer AD1, optical member 22, and adhesive layer AD2. In other words, the photodetector 30 is optically coupled to the surface of the multiple quantum well structure 14C opposite the electron incident surface 10a (see FIG. 1). The photodetector 30 is sensitive to light emitted by the multiple quantum well structure 14C. The photodetector 30 is, for example, a photomultiplier tube. In this case, the photodetector 30 includes a vacuum vessel 31. The vacuum vessel 31 includes a metal side tube 31a, a light incident window 31b that closes the top opening of the side tube 31a, and a stem plate 31c that closes the bottom opening of the side tube 31a. A photocathode 32 formed on the inner surface of the light entrance window 31b and an electrode section 33 including an electron multiplier section and an anode are arranged inside the vacuum vessel 31. The electron multiplier section includes, for example, a microchannel plate or a mesh-type dynode.

[0053] The light incident surface 30a is the outer surface of the light incident window 31b, and light incident on the light incident surface 30a passes through the light incident window 31b and enters the photocathode 32. The photocathode 32 performs photoelectric conversion in response to the incident light and emits the generated photoelectrons into the internal space of the vacuum container 31. These photoelectrons are multiplied by the electron multiplier of the electrode unit 33. The multiplied electrons are collected by the anode of the electrode unit 33. The electrons collected by the anode of the electrode unit 33 are extracted to the outside of the photodetector 30 via one of multiple pins that penetrate the stem plate 31c. The potential of the metal side tube 31a is 0 V, and the photocathode 32 is electrically connected to the side tube 31a.

[0054] As described above, the electron beam detector 20 also has the light emitter 10, which makes it possible to further improve the high-speed response. Note that, although the present embodiment is directed to the electron beam detector 20 into which electrons are incident, the present invention is not limited to this and any charged particle detector into which charged particles are incident may be used.

[0055] [Third Embodiment] The electron beam detector 20 (see FIG. 8) of the second embodiment can be used in an electron microscope, for example, a scanning electron microscope (SEM). FIG. 9 is a diagram schematically showing the configuration of a length-measuring SEM 40 according to the third embodiment. The length-measuring SEM 40 includes an SEM 41 that acquires images of an object to be inspected, a control unit 42 that performs overall control, a storage unit 43 that stores the acquired images, etc. on a magnetic disk, a semiconductor memory, etc., and a calculation unit 44 that performs calculations according to a program.

[0056] The SEM 41 includes a movable stage 46 on which a specimen wafer 45 is mounted, an electron source 47 that irradiates the specimen wafer 45 with an electron beam EB1, and a plurality of electron beam detectors 20 (three are illustrated in the figure) that detect electrons (secondary electrons and backscattered electrons) generated from the specimen wafer 45. The configuration of the electron beam detectors 20 is the same as that of the second embodiment. The SEM 41 also includes an electron lens (not shown) that focuses the electron beam EB1 on the specimen wafer 45, a deflector (not shown) that scans the electron beam EB1 over the specimen wafer 45, and an image generation unit 48 that digitally converts signals from the electron beam detectors 20 to generate a digital image.

[0057] The critical dimension SEM 40 includes a vacuum chamber (chamber) 50 whose internal space is kept under a vacuum (reduced pressure) atmosphere. A movable stage 46, an electron source 47, and at least the light emitter 10 of the electron beam detectors 20, an electron lens, and a deflector are disposed inside the vacuum chamber 50. The image generator 48 and each electron beam detector 20 are electrically connected to one another via wiring. The image generator 48, controller 42, memory 43, and calculator 44 are electrically connected to one another via a data bus 49.

[0058] When the electron beam EB1 is scanned over the surface of the specimen wafer 45 while irradiating the specimen wafer 45 with the electron beam EB1, electrons are emitted from the surface of the specimen wafer 45 and are guided as an electron beam EB2 to the electron beam detector 20. The electron beam detector 20 converts the electron beam EB2 into an electric signal, which is output in accordance with the amount of current of the electron beam EB2. By synchronizing and correlating the scanning position of the electron beam EB1 with the output of the electron beam detector 20, an image of the specimen wafer 45 can be acquired.

[0059] The control unit 42 has the functions of controlling the transportation of the sample wafer 45, controlling the movable stage 46, controlling the irradiation position of the electron beam EB1, and controlling the scanning of the electron beam EB1. The memory unit 43 has an area for storing acquired image data and an area for storing imaging conditions (e.g., acceleration voltage). The calculation unit 44 has the function of calculating the dimensions of the structure (e.g., groove width) based on the contrast in the image data. The control unit 42 and the calculation unit 44 may be configured as hardware designed to realize each function, or may be implemented as software and configured to be executed using a general-purpose calculation device (e.g., a CPU or GPU).

[0060] As described above, the length-measuring SEM 40 also includes the light emitter 10, and thus can further improve the high-speed response.

[0061] [Fourth Embodiment] The electron beam detector 20 (see FIG. 8) of the second embodiment can be used in a mass spectrometer. Fig. 10 is a diagram schematically illustrating the configuration of a mass spectrometer 60 according to the fourth embodiment. As shown in Fig. 10, the mass spectrometer 60 includes an electron beam detector 20 (see FIG. 8) having a configuration similar to that of the second embodiment, a vacuum chamber (chamber) 61 in which at least the light emitter 10 (shown) of the electron beam detector 20 is disposed in an internal space maintained at a vacuum (reduced pressure), a separation unit AZ that spatially or temporally separates ions generated from a sample in the vacuum chamber 61 according to their masses, and dynodes DY1 and DY2 that are electron conversion units onto which the ions separated by the separation unit AZ are irradiated.

[0062] In mass spectrometer 60, electrons emitted from dynodes DY1 and DY2 in response to ions incident on them are guided to light emitter 10, and mass analysis of the sample is performed from the output of electron beam detector 20. Specifically, in mass spectrometer 60, when an appropriate potential is applied to aperture AP and a negative potential is applied to dynode DY1, which is located on the opposite side of aperture AP from separator AZ, positive ions located within separator AZ pass through aperture AP and collide with dynode DY1, and electrons are emitted from the surface of dynode DY1 upon collision, and these are guided as electron beam e3 to electron beam detector 20. A positive potential is applied to dynode DY2, and when negative ions are extracted from separator AZ, these negative ions collide with dynode DY2, and electrons are emitted from the surface of dynode DY2 upon collision, and these electrons are guided as electron beam e3 to electron beam detector 20. In response to the incidence of the electron beam e3, the electron beam detector 20 outputs an electrical signal.

[0063] For example, if the separator AZ is a flight tube, the ions will take different amounts of time to pass through the flight tube depending on their mass, resulting in different times to reach the dynodes DY1 and DY2. Furthermore, if the separator AZ uses a magnetic field to change the flight trajectory of each ion depending on its mass, varying the magnetic flux density of the separator AZ will cause the ions passing through the aperture AP to differ in mass. Therefore, the mass of each ion can be determined by monitoring the change over time in the electrical signal output from the electron beam detector 20.

[0064] As described above, the mass spectrometer 60 also includes the light emitter 10, and thus can achieve a high-speed response.

[0065] [Modifications] One aspect of the present invention is not limited to the above-described embodiment, and various other modifications are possible.

[0066] In the above embodiment, the compositions of the well layers 141 and the barrier layers 142 that constitute the multiple quantum well structure 14C are not limited to the above example. Although the above example shows an example in which the first buffer layer 14A and the second buffer layer 14B are GaN layers, other compositions may be applied as long as they are nitride semiconductors that contain at least one of In, Al, and Ga as a group III element, contain N as a main group V element, and are optically transparent to the emission wavelength of the multiple quantum well structure 14C.

[0067] In the above embodiment, the well layers 141 and the barrier layers 142 of the multiple quantum well structure 14C are doped with Si, but the present invention is not limited to this and other impurities (e.g., Mg) may be doped therein. x Al y Ga 1-x-y N (0≦x≦1, 0≦y≦1, 0≦x+y≦1). Therefore, in addition to the above-mentioned combination of InGaN / GaN, other combinations such as InGaN / AlGaN, InGaN / InGaN, and GaN / AlGaN are possible. Alternatively, the well layer 141 and the barrier layer 142 may be made of semiconductors other than nitride semiconductors.

[0068] In the above embodiment, the number of layers of the well layers 141 and the barrier layers 142 is nine, but the number of layers of the well layers 141 and the barrier layers 142 may be any number equal to or greater than two. In the above embodiment, the photodetector 30 is not limited to a photomultiplier tube and may be, for example, an avalanche photodiode. Furthermore, the optical member 22 is not limited to a linear shape and may be a curved shape, and its size can also be changed as appropriate.

[0069] In the above embodiment, the multiple quantum well structure 14C has a structure in which the first barrier layer on the substrate 12 side is thicker than the second barrier layer on the electron incident surface 10a side (a so-called inclined structure), but is not particularly limited to this, and the thicknesses of the multiple barrier layers 142 may be the same as or different from each other.

[0070] The above numerical values ​​may include errors in measurement, manufacturing, design, etc. １８ cm－３ " is exactly 4 x 10 １８ cm －３ Not only that, but also about 4 x 10 １８ cm －３ Including the above "1 x 10 ２０ cm －３ " is exactly 1 x 10 ２０ cm －３ Not only that, but also about 1 x 10 ２０ cm －３ The above "0.6 nm" includes not only exactly 0.6 nm but also approximately 0.6 nm. The above "1.0 nm" includes not only exactly 1.0 nm but also approximately 1.0 nm. The "measurement," "manufacturing," and "design" in the above can be carried out in accordance with known standards and specifications, such as JIS. The above "equal" and "same" include not only completely equal and completely the same, but also approximately equal and approximately the same.

[0071] 10...light emitter, 10a...electron incident surface (charged particle incident surface), 12...substrate, 12a...main surface, 12b...back surface, 14...nitride semiconductor layer, 14A...first buffer layer, 14B...second buffer layer, 14C...multiple quantum well structure, 18...conductive layer, 20...electron beam detector, 22...optical member, 30...photodetector, 30a...light incident surface, 31...vacuum vessel, 32...photocathode, 33...electrode portion, 40...length-measuring SEM, 41...scanning electron microscope (SEM), 42...controller, 43...storage portion, 44...arithmetic portion, 45...sample wafer, 46...movable stage, 47...electron source, 48...image generating portion, 50, 61...vacuum chamber (chamber), 141...well layer, 142, 143...barrier layer, AZ...separator, DY1, DY2...dynode (electron conversion portion).

Claims

1. A light emitter that converts incident charged particles into light, comprising a multiple quantum well structure that emits the light in response to the incidence of the charged particles, the thickness of a well layer constituting the multiple quantum well structure is 0.2 nm or more and less than 1.5 nm, and the concentration of an additive added to the barrier layer and the well layer constituting the multiple quantum well structure is 4×10 １８ cm －３ Greater than 1×10 ２０ cm －３ The following is a light-emitting body.

2. The light-emitting body according to claim 1, wherein the well layer has a thickness of 0.6 nm or more and less than 1.0 nm.

3. The light-emitting body according to claim 1 or 2, wherein the multiple quantum well structure is configured to include a first barrier layer and a second barrier layer as the barrier layers, the second barrier layer is located on the charged particle incident surface side of the multiple quantum well structure with respect to the first barrier layer, and the first barrier layer is thicker than the second barrier layer.

4. The light-emitting body according to claim 1 or 2, wherein the well layer and the barrier layer are nitride semiconductor layers, and the additive contains silicon.

5. A charged particle detector comprising: a light emitter according to claim 1 or 2; and a photodetector optically coupled to a surface of said multiple quantum well structure opposite to the charged particle incidence surface, said photodetector having sensitivity to the light emitted by said multiple quantum well structure.

6. An electron microscope comprising: a light emitter as claimed in claim 1 or 2; a photodetector optically coupled to the surface of said multiple quantum well structure opposite to the charged particle incidence surface and sensitive to the light emitted by said multiple quantum well structure; and a chamber in which at least said light emitter is disposed, said electron microscope irradiating an electron beam onto a surface of a sample disposed in said chamber, guiding electrons from said sample to said light emitter, and acquiring an image of said sample by correlating the irradiation position of the electron beam on said sample with the output of said photodetector.

7. A mass spectrometer comprising: a light emitter as claimed in claim 1 or 2; a photodetector optically coupled to a surface of said multiple quantum well structure opposite to the charged particle incidence surface and sensitive to the light emitted by said multiple quantum well structure; a chamber in which at least said light emitter is disposed; a separation section which spatially or temporally separates ions generated from a sample in said chamber according to their mass; and an electron conversion section which is irradiated with ions separated by said separation section, wherein electrons emitted from said electron conversion section in response to ions being incident on said electron conversion section are guided to said light emitter, and mass analysis of said sample is performed from the output of said photodetector.

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