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

Abstract

To further enhance high-speed responsiveness.SOLUTION: A light emitting body 10 converts incident electrons into light. The light emitting body 10 includes a multi-quantum-well structure 14C that emits light upon incidence of electrons. A well layer 141 of the multi-quantum-well structure 14C is 0.2 nm or more and less than 1.5 nm thick. The concentration of additives added to a barrier layer 142 and the well layer 141 constituting the multi-quantum-well structure 14C is greater than 4×1018 cm-3 and equal to or less than 1×1020 cm-3.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4365255 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned light-emitting body, for example, in order to capture an event that occurs within a short time, it is sometimes desirable to further improve the high-speed response. Therefore, an object of one aspect of the present invention is to provide a light-emitting body, a charged particle detector, an electron microscope, and a mass spectrometer that can further improve the high-speed response. [Means for solving the problem]

[0005] The inventors of the present invention have conducted extensive research and found that there is a correlation between the thickness of the well layer and the afterglow time in the light emitter. They also found that there is a correlation between the concentration of the additive in the light emitter and the afterglow time, and that the higher the concentration of the additive, the shorter the afterglow time. On the other hand, they found that when the concentration of the additive exceeds a certain level, for example, the crystallinity deteriorates, so that the emission intensity is greatly reduced, making it difficult to use in practice. Therefore, the inventors of the present invention have conducted extensive research and found that if the thickness of the well layer and the concentration of the additive in the barrier layer and the well layer can be optimized, the afterglow time can be reduced while maintaining the emission intensity, and high-speed response can be further improved, thereby completing the present invention.

[0006] (1) That is, a light-emitting body according to one aspect of the present invention is a light-emitting body 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 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 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 additive 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 the well layer can be optimized based on the above findings, and it becomes possible to reduce the afterglow time while maintaining the emission 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 body 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 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 may be thicker than the second barrier layer. By changing the thickness of the barrier layer in accordance with the distance from the charged particle incident surface in this manner, it is possible to improve the light conversion efficiency from a low acceleration voltage to a high acceleration voltage, and to increase the emission intensity.

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

[0011] (5) A charged particle detector according to the present disclosure 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 incidence surface and having sensitivity to light emitted by the multiple quantum well structure. This charged particle detector also includes the light emitter described above, so that it is possible to further increase the high-speed response.

[0012] (6) An electron microscope according to the present disclosure 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 to the charged particle incidence surface and sensitive to the 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 a surface of a sample disposed in the chamber, guiding electrons from the sample to the light emitter, and associating the irradiation position of the electron beam on the sample with the output of the photodetector. This electron microscope also has the above-mentioned light emitter, and thus similarly enables high-speed response to be further improved.

[0013] (7) A mass spectrometer according to the present disclosure includes 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 to the charged particle incidence 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 section that spatially or temporally separates ions generated from a sample in the chamber according to their mass, and an electron conversion section to which the ions separated by the separation section are irradiated, and electrons emitted from the electron conversion section in response to the ions being incident on the electron conversion section are guided to the light emitter, and mass analysis of the sample is performed from the output of the photodetector. This mass spectrometer also includes the light emitter described above, and thus similarly enables high-speed response to be further improved. Effect of the Invention

[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. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of a light emitter according to the first embodiment. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing the internal structure of the multiple quantum well structure of FIG. [Diagram 3] FIG. 3 is a graph showing the decay when the thickness of the well layer in the light emitting body of FIG. 1 is changed. [Figure 4] FIG. 4 is a graph showing the decay when the concentration of the additive in the luminescent material of FIG. 1 is changed. [Diagram 5] FIG. 5 is a graph showing the emission intensity when the thickness of the well layer in the light emitting body of FIG. 1 is changed. [Figure 6] FIG. 6 is a graph showing the luminescence intensity when the concentration of the additive in the luminescent material of FIG. 1 is changed. [Figure 7] FIG. 7 is a graph showing the relationship between Decay and luminous intensity in the luminous body of FIG. [Figure 8]FIG. 8 is a cross-sectional view showing the configuration of the electron beam detector according to the second embodiment. [Figure 9] FIG. 9 is a diagram illustrating roughly the configuration of a length-measuring SEM according to the third embodiment. [Figure 10] FIG. 10 is a diagram illustrating a schematic configuration of a mass spectrometer according to the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 the 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 constitutes 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 allows the nitride semiconductor layer 14 to be epitaxially grown. 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 main surface 12a. The first buffer layer 14A is grown at a relatively low temperature (for example, 400 °C or higher and 700 °C or lower) and has an amorphous structure mainly containing, for example, 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 more and 500 nm or less, and in one embodiment, it 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, crystals of GaN. In one example, the second buffer layer 14B is made of crystals of GaN. The second buffer layer 14B is epitaxially grown at a higher temperature (for example, 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 more and 10 μm or less, and in one example, it is 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 portion that emits light upon electron incidence and is a layer epitaxially grown on the second buffer layer 14B. FIG. 2 is a cross-sectional view showing an enlarged internal structure of the multiple quantum well structure 14C. As shown in FIG. 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 configured to contain a material that emits light upon receiving electrons. The well layer 141 is, for example, a nitride semiconductor layer mainly containing crystals of In x Ga 1-x N (0 <x <1). In one example, the well layer 141 is an In x Ga 1-xIt is composed of crystals of N (0 < x < 1). When electrons enter the multiple quantum well structure 14C, electron-hole pairs are formed, and light is emitted during the recombination process within the well layer 141 (cathodoluminescence). The compositions of the multiple well layers 141 that make up the multiple quantum well structure 14C are the same as each other, and the above composition x is equal to each other. In one embodiment, the composition x is 0.1. Also, the thicknesses of the multiple well layers 141 that make up the multiple quantum well structure 14C are equal to each other.

[0024] The bandgap energy of the barrier layer 142 is larger than the bandgap energy of the well layer 141. By sandwiching the well layer 141 between the barrier layers 142, electrons can be collected in the well layer 141 and efficiently converted into light. The barrier layer 142 is a nitride semiconductor layer mainly containing GaN crystals. In one example, the barrier layer 142 is composed of Si-doped GaN crystals. Note that the barrier layer 142 may further contain group III atoms other than Ga (for example, In). Even in that case, the compositions of the multiple barrier layers 142 that make up the multiple quantum well structure 14C are equal to each other.

[0025] The thicknesses of the multiple barrier layers 142 that make up the multiple quantum well structure 14C are different from each other. Specifically, each barrier layer 142 is thicker than the barrier layer 142 located on the electron incident surface 10a (see FIG. 1) side with respect to each barrier layer 142. In other words, the multiple barrier layers 142 become thicker as they are farther from the electron incident surface 10a, and the first-layer barrier layer 142 closest to the electron incident surface 10a is the thinnest among the multiple barrier layers 142. In a preferred example, the thickness of the first-layer barrier layer 142 closest to the electron incident surface 10a is 80% or less of the average thickness of the barrier layer 142, and more preferably 20% or less. The thickness of the second-layer barrier layer 142 (that is, the barrier layer 142 adjacent to the barrier layer 142 closest to the electron incident surface 10a) is 90% or less of the average thickness of the multiple barrier layers 142, and more preferably 80% or less.

[0026] In the multiple quantum well structure 14C of this embodiment, nine barrier layers 142 are provided. The first well layer 141 is provided between the first barrier layer 142 and the second barrier layer 142 counting from the electron incident surface 10a side. Thereafter, the n-th (n=2, . . . , 8) well layer 141 is provided between the n-th barrier layer 142 and the (n+1)-th barrier layer 142 counting from the electron incident surface 10a side. A barrier layer 143 (see FIG. 2) having the same composition as each barrier layer 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. It is also possible not to provide the barrier layer 143 as necessary.

[0027] In this embodiment, the barrier layer 142 becomes thicker as it is farther from the electron incident surface 10a in all of the multiple barrier layers 142, but for example, 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 on the electron incident surface 10a side with respect to the barrier layer 142, the effect of this embodiment described later is suitably achieved.

[0028] In this embodiment, the difference in thickness between adjacent barrier layers 142 becomes smaller as they are farther away 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. That is, 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 suitably achieved.

[0029] The conductive layer 18 is used as one electrode that guides electrons to the light emitter 10. The conductive layer 18 mainly contains, for example, a metal, and mainly contains aluminum (Al) in one embodiment. The thickness of the conductive layer 18 is, for example, 10 nm or more and 1000 nm or less, and is about 300 nm in one embodiment. When the conductive layer 18 mainly contains a metal, the conductive layer 18 also functions as a light reflecting film. That is, a part 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 part 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, and is then emitted to the outside of the light emitter 10 through the substrate 12.

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

[0031] In the above example, trimethylgallium (Ga(CH3)3:TMGa) can be used as the Ga source, trimethylindium (In(CH3)3:TMIn) as the In source, ammonia (NH3) as the N source, hydrogen gas (H2) or nitrogen gas (N2) as the carrier gas, and monosilane (SiH4) as the Si source. Alternatively, other organometallic raw materials (e.g., triethylgallium (Ga(C2H5)3:TEGa), triethylindium (In(C2H5)3:TEIn), etc.) and other hydrides (e.g., disilane (Si2H4), etc.) may be used. In the above example, the MOVPE apparatus is used, but a hydride vapor phase epitaxy (HVPE) apparatus or a molecular beam epitaxy (MBE) apparatus may also be used. In addition, the growth temperatures are not limited to the temperatures described above.

[0032] In this embodiment, the well layer 141 has a thickness of 0.2 nm or more and less than 1.5 nm. Preferably, the well layer 141 has a thickness of 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 the "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] FIG. 3 is a graph showing the decay when the thickness of the well layer 141 in the light emitter 10 is changed. 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 represent actual measured values, and the lines represent values ​​calculated based on the actual measured values ​​(similar to the following graphs). In Example 1, the concentration of the additive is 4×10 18 cm -3 In Example 2, the additive concentration 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 in this example. The threshold value α is not particularly limited.

[0034] As shown in Fig. 3, it can be seen that the Decay changes in the form of a quadratic function with the change in the thickness of the well layer 141. 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 shows a similar tendency even if the concentration of the additive is changed. In the light-emitting body 10, if the thickness of the well layer 141 is thinner than 0.2 nm, it is not realistic from the viewpoint 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 the 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 4. If 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 when the thickness of the well layer 141 is 1.5 nm.

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

[0037] 5, it can be seen that the emission intensity increases as the thickness of the well layer 141 increases. It is estimated that the emission intensity will show a similar tendency even if 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 It can be seen that in this case, the emission intensity becomes smaller and is more likely to fall below the threshold value β.

[0038] FIG. 6 is a graph showing the emission intensity (arbitrary unit (au)) when the concentration of the additive in the light emitter 10 is changed. Example 8 is an example in which the thickness of the well layer 141 is 0.8 nm. Example 9 is an example in which the thickness of the well layer 141 is 0.2 nm. As shown in FIG. 6, the emission intensity decreases as the concentration of the additive increases. The amount of change in emission intensity decreases as the concentration of the additive increases. It is estimated that the emission 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 β, for example, when the thickness of the well layer 141 is 0.2 nm, the emission intensity is likely to decrease below the threshold value β.

[0039] As described above, in the light-emitting body 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 the 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. In this case, it is 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 on the electron incident surface 10a side with respect to the first barrier layer, and the first barrier layer is thicker than the second barrier layer. Since the second barrier layer located at a relatively shallow position from the electron incident surface 10a is relatively thin, the well layer 141 located on the opposite side of the electron incident surface 10a across the second barrier layer is disposed closer to the electron incident surface 10a. Therefore, it is possible to improve the light conversion efficiency for an electron beam with a small acceleration voltage. In addition, since the first barrier layer located at a relatively deep position is relatively thick, the well layer 141 located on the opposite side of the electron incident surface 10a across the first barrier layer is disposed farther from the electron incident surface 10a. Therefore, it is possible to maintain the light conversion efficiency even with respect to the deep penetration of an electron beam with a large acceleration voltage. Furthermore, since the electron beam spreads hemispherically inside the light emitter 10, the quantum wells densely arranged near the electron incident surface 10a reliably capture electrons even at high acceleration voltages. By changing the thickness of the barrier layer 142 according to the distance from the electron incident surface 10a in this way, the light conversion efficiency can be improved from low to high acceleration voltages, and the emission intensity can be increased.

[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 silicon as the additive for the well layer 141 and the barrier layer 142, which are nitride semiconductor layers.

[0043] In the light emitter 10, the second barrier layer is the 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 makes the position of 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 move away from the electron incident surface 10a. In this case, appropriate well layer arrangements can be realized according to various acceleration voltages, and the light conversion efficiency can be further improved. In the light emitter, the compositions of the well layers 141 are the same, which makes it easy to fabricate a multiple quantum well structure.

[0045] Fig. 7 is a graph showing the relationship between Decay and luminous intensity in the light emitter 10. The figure 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 in the light emitter 10, the larger the Decay, the higher the luminous intensity.

[0046] In this embodiment, the incident electrons are converted into light, but the present invention is not limited thereto. The present 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 a property of transmitting 50% or more of the target light, for example.

[0047] [Second embodiment] Fig. 8 is a cross-sectional view showing the configuration of an electron beam detector 20 according to the 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 the 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 the light generated in the light emitter 10 onto the light incident surface 30a.

[0049] Between the optical member 22 and the photodetector 30, a light-transmitting adhesive layer AD2 is interposed, and the relative positions between the optical member 22 and the photodetector 30 are fixed by the adhesive layer AD2. The adhesive layer AD2 mainly contains, for example, a light-transmitting resin. In addition, between the rear surface 12b of the substrate 12 of the light emitter 10 and the optical member 22, an adhesive layer AD1 is interposed. The adhesive layer AD1 includes a SiN layer ADa provided on the rear surface 12b, and a SiO2 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 SiO2 layer ADb are in contact with each other. The SiO2 layer ADb and the optical member 22 are fused to each other. Since both the SiO2 layer ADb and the optical member 22 are silicide oxides, they can be fused by heating.

[0050] The SiO2 layer ADb is formed on the SiN layer ADa by sputtering or the like, so that the bonding strength between the SiN layer ADa and the SiO2 layer ADb is extremely strong. Similarly, the SiN layer ADa is also formed on the rear surface 12b of the substrate 12 by sputtering or the like, so that 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 the reflection of light generated in the multiple quantum well structure 14C on the rear 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 this order, 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 to the electron incident surface 10a via the substrate 12, the adhesive layer AD1, the optical member 22, and the adhesive layer AD2. That is, the photodetector 30 is optically coupled to the surface of the multiple quantum well structure 14C opposite to the electron incident surface 10a (see FIG. 1). The photodetector 30 has sensitivity to the 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 a light entrance window 31b, and an electrode section 33 including an electron multiplier section and an anode are disposed inside the vacuum vessel 31. The electron multiplier section includes, for example, a microchannel plate or a mesh-type dynode.

[0053] The light incidence surface 30a is the outer surface of the light incidence window 31b, and light incident on the light incidence surface 30a passes through the light incidence window 31b and enters the photocathode 32. The photocathode 32 performs photoelectric conversion in response to the incidence of light, and emits the generated photoelectrons into the internal space of the vacuum vessel 31. The 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 taken out of the photodetector 30 via one of the multiple pins penetrating the stem plate 31c. The potential of the metallic side tube 31a is 0V, 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, and thus can achieve a 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 thereto, 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 showing a schematic configuration of a length-measuring SEM 40 according to the third embodiment. The length-measuring SEM 40 includes an SEM 41 that acquires an image 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 sample wafer 45 is mounted, an electron source 47 which irradiates the sample wafer 45 with an electron beam EB1, and a plurality of electron beam detectors 20 (three are illustrated in the figure) which detect electrons (secondary electrons and reflected electrons) generated from the sample wafer 45. The configuration of the electron beam detectors 20 is the same as that of the second embodiment. The SEM 41 includes an electron lens (not shown) which focuses the electron beam EB1 on the sample wafer 45, a deflector (not shown) which scans the electron beam EB1 over the sample wafer 45, and an image generator 48 which 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 a vacuum (reduced pressure) atmosphere. A movable stage 46, an electron source 47, 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 of the electron beam detectors 20 are electrically connected to each other via wiring. The image generator 48, the controller 42, the memory 43, and the calculator 44 are electrically connected to each other 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 guided to the electron beam detector 20 as the electron beam EB2. The electron beam detector 20 converts the electron beam EB2 into an electric signal, and outputs the electric signal according to the amount of current of the electron beam EB2. By synchronizing and matching 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 a function of controlling the transport of the sample wafer 45, a function of controlling the movable stage 46, a function of controlling the irradiation position of the electron beam EB1, and a function of controlling the scanning of the electron beam EB1. The storage unit 43 has an area for storing acquired image data and an area for storing imaging conditions (e.g., acceleration voltage, etc.). The calculation unit 44 has a function of calculating the dimensions of the components (e.g., groove width) based on the shading (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., CPU, GPU, etc.).

[0060] As described above, the length measuring SEM 40 also has the light emitting body 10, and thus can achieve a 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 showing a schematic configuration of a mass spectrometer 60 according to a fourth embodiment. As shown in FIG. 10, the mass spectrometer 60 includes an electron beam detector 20 (see FIG. 8) having a similar configuration to that of the second embodiment, a vacuum chamber (chamber) 61 in which at least a light emitter 10 (shown) of the electron beam detector 20 is disposed in an internal space having a vacuum (reduced pressure) atmosphere, a separation unit AZ that spatially or temporally separates ions generated from a sample in the vacuum chamber 61 according to their mass, and dynodes DY1 and DY2 that are electron conversion units to which the ions separated in the separation unit AZ are irradiated.

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

[0063] For example, if separation unit AZ is a flight tube, ions take different times to pass through the flight tube depending on their mass, and as a result, they arrive at different times at dynodes DY1 and DY2. If separation unit AZ uses a magnetic field to change the flight trajectory of each ion depending on its mass, then varying the magnetic flux density of separation unit AZ will cause ions of different masses to pass through aperture AP. Therefore, the mass of each ion can be determined by monitoring the change over time in the electrical signal output from 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] [Variations] One aspect of the present invention is not limited to the above embodiment, and various other modifications are possible.

[0066] In the above embodiment, the compositions of the well layer 141 and the barrier layer 142 constituting 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 have optical transparency to the emission wavelength of the multiple quantum well structure 14C.

[0067] In the above embodiment, the well layer 141 and the barrier layer 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. In the above embodiment, the well layer 141 and the barrier layer 142 of the multiple quantum well structure 14C are doped with In. 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, 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. In addition, the optical member 22 is not limited to a linear shape, and may be a curved shape, and the size can also be changed as appropriate.

[0069] In the above embodiment, the multiple quantum well structure 14C is 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 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 4×10 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 approximately 1×10 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", "manufacture" and "design" in the above can be performed in accordance with known standards and regulations 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. [Explanation of symbols]

[0071] 10...light emitter, 10a...electron incident surface (charged particle incident surface), 12...substrate, 12a...main surface, 12b...rear 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 section, 40...length measuring SEM, 41...scanning electron microscope (SEM), 42...control section, 43...storage section, 44...calculation section, 45...sample wafer, 46...movable stage, 47...electron source, 48...image generating section, 50, 61...vacuum chamber (chamber), 141...well layer, 142, 143...barrier layer, AZ...separation section, DY1, DY2...dynode (electron conversion section).

Claims

1. A light emitter that converts incident charged particles into light, a multi-quantum well structure that emits the light upon 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; The concentration of the dopant added to the barrier layers and the well layers constituting the multiquantum 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 emitter 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 multiple quantum well structure includes a first barrier layer and a second barrier layer as the barrier layer, the second barrier layer is located on a charged particle incidence surface side of the multiple quantum well structure with respect to the first barrier layer, The phosphor of claim 1 , wherein the first barrier layer is thicker than the second barrier layer.

4. the well layer and the barrier layer are nitride semiconductor layers, The phosphor according to claim 1 or 2, wherein the additive comprises silicon.

5. The light emitter according to claim 1 or 2, a photodetector optically coupled to a surface of the multiple quantum well structure opposite to the charged particle incidence surface, the photodetector being sensitive to the light emitted by the multiple quantum well structure.

6. The light emitter according to claim 1 or 2, a photodetector optically coupled to a surface of the multiple quantum well structure opposite to the charged particle incidence surface and sensitive to the light emitted by the multiple quantum well structure; a chamber in which at least the light emitter is disposed; An electron microscope that irradiates an electron beam onto a surface of a sample placed in the chamber, guides electrons from the sample to the light emitter, and obtains an image of the sample by correlating the irradiation position of the electron beam on the sample with the output of the photodetector.

7. The light emitter according to claim 1 or 2, a photodetector optically coupled to a surface of the multiple quantum well structure opposite to the charged particle incidence surface and sensitive to the light emitted by the multiple quantum well structure; a chamber within which at least the light emitter is disposed; a separation unit that spatially or temporally separates ions generated from the sample in the chamber according to their mass; an electron conversion unit to which the ions separated by the separation unit are irradiated; A mass spectrometer that guides electrons emitted from the electron conversion unit in response to incidence of ions on the electron conversion unit to the light emitter, and performs mass analysis of the sample from the output of the photodetector.

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