Luminophores, electron beam detectors and scanning electron microscopes

Abstract

The light emitting body (10) is a light emitting body that converts input electrons into light, and includes a multiple quantum well structure (14C) that emits light by inputting electrons and an electron input surface (10a) disposed on the multiple quantum well structure (14C). One of the multiple barrier layers included in the multiple barrier layers constituting the multiple quantum well structure (14C) is thicker than the other barrier layers included in the multiple barrier layers and located on the electron input surface (10a) side relative to the one of the barrier layers. Thus, a light emitting body, an electron beam detector, and a scanning electron microscope that can improve light conversion efficiency from a small acceleration voltage to a large acceleration voltage are realized.

Description

Technical Field

[0001] The present invention relates to a luminophore, an electron beam detector and a scanning electron microscope. Background Art

[0002] Patent document 1 discloses a technology related to a light emitter used in an electron beam detector. The light emitter is a light emitter that converts input electrons into light, and includes a substrate and a nitride semiconductor layer composed of InGaN and GaN. The substrate is transparent to the wavelength of the light. The nitride semiconductor layer is formed on one side of the substrate and has a quantum well structure that emits light by the input of electrons.

[0003] Patent document 2 discloses a technology related to an electron beam excited light emitting epitaxial substrate and an electron beam excited light emitting device. The epitaxial substrate includes a substrate, a light emitting layer having a multiple quantum well structure disposed on the substrate, and a metal layer disposed on the light emitting layer. The band gap of the well layer of the light emitting layer increases stepwise from the metal layer side toward the substrate side along the thickness direction of the light emitting layer. The number of well layers having the same band gap decreases from the metal layer side toward the substrate side along the thickness direction of the light emitting layer. The well layer is composed of Al containing a dopant. x Ga 1-x N(0<x<1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2005-298603

[0007] Patent Document 2: Japanese Patent Application Publication No. 2016-015379 Summary of the invention

[0008] Technical problem to be solved by the invention

[0009] A light emitter that outputs light of a size corresponding to the current of the input electron beam is often used in an electron beam detector. In an electron beam detector, the current of the electron beam is measured by converting the intensity of the light output from the light emitter into an electrical signal. Such an electron beam detector can be used in devices such as scanning electron microscopes. In order to efficiently convert the input electron beam into light, the light emitter has a multiple quantum well structure.

[0010] In this luminous body, there is a situation where it is desired to improve the light conversion efficiency from a small acceleration voltage to a large acceleration voltage. When the acceleration voltage of the input electron beam is large, the electron beam reaches a deep position of the luminous body. Therefore, in order to improve the light conversion efficiency of the electron beam with a large acceleration voltage, it is preferred to thicken the multiple quantum well structure. In the case of thickening the multiple quantum well structure, there is a problem that the light conversion efficiency decreases for the electron beam with a small acceleration voltage that only reaches a shallow position of the luminous body.

[0011] An object of the present invention is to provide a light emitting body, an electron beam detector, and a scanning electron microscope capable of improving light conversion efficiency from a small accelerating voltage to a large accelerating voltage.

[0012] Technical means of solving problems

[0013] An embodiment of the present invention is a luminescent body. The luminescent body is a luminescent body that converts input electrons into light, including a multiple quantum well structure that emits light by inputting electrons and an electron input surface arranged on the multiple quantum well structure, wherein a first barrier layer included in a plurality of barrier layers constituting the multiple quantum well structure is thicker than a second barrier layer included in the plurality of barrier layers and located on the electron input surface side relative to the first barrier layer.

[0014] In the above-mentioned light emitting body, when electrons are inputted from the electron input surface side to the multiple quantum well structure, light is generated by light emission re-coupling (cathodoluminescence) of the well layer. This light is outputted to the outside of the light emitting body.

[0015] Here, because the second barrier layer at a relatively shallow position from the electron input surface is relatively thin, the well layer located on the opposite side of the electron input surface sandwiching the second barrier layer is arranged closer to the electron input surface. Therefore, the light conversion efficiency of the electron beam with respect to a small acceleration voltage can be improved. In addition, because the first barrier layer at a relatively deep position is relatively thick, the well layer located on the opposite side of the electron input surface sandwiching the first barrier layer is arranged away from the electron input surface. Therefore, the light conversion efficiency can also be maintained for the deep intrusion of the electron beam with a large acceleration voltage.

[0016] As will be described later, the electron beam expands in a hemispherical shape inside the light emitter, so the quantum wells densely arranged near the electron input surface can reliably capture electrons even at a large acceleration voltage. Thus, by changing the thickness of the barrier layer according to the distance from the electron input surface, the light conversion efficiency can be improved from a small acceleration voltage to a large acceleration voltage.

[0017] According to the inventors' understanding, there is a tendency for electrons to diffuse in a hemispherical shape inside the multiple quantum well structure, so the quantum well excitation density near the electron input surface becomes higher. Therefore, the excitation of the quantum well caused by the diffused electrons decreases in the depth direction. Therefore, it is preferred that the quantum well spacing near the electron input surface, that is, the barrier layer thickness, is thinner than the quantum well spacing farthest from the electron input surface, that is, the barrier layer thickness.

[0018] The embodiment of the present invention is an electron beam detector. The electron beam detector includes: a light emitting body of the above structure; a photodetector optically coupled to the surface on the opposite side of the electron input surface in the multiple quantum well structure and having sensitivity to the light emitted by the multiple quantum well structure; and a light transmitting component interposed between the light emitting body and the photodetector and integrating the light emitting body and the photodetector and having insulation properties.

[0019] According to the electron beam detector, the electron beam detection efficiency can be improved from a small acceleration voltage to a large acceleration voltage by using the light emitting body having the above structure. In addition, by interposing an insulating light-transmitting member between the light emitting body and the light detector, the light detector can be stably operated regardless of the voltage applied to the light emitting body.

[0020] The embodiment of the present invention is a scanning electron microscope. The scanning electron microscope includes: a light emitting body of the above structure; a photodetector optically coupled to the surface on the opposite side of the electron input surface in the multiple quantum well structure and having sensitivity to the light emitted by the multiple quantum well structure; and a vacuum chamber having at least the light emitting body disposed therein, scanning an electron beam on the surface of a sample arranged in the vacuum chamber, guiding secondary electrons and reflected electrons from the sample to the light emitting body, and photographing an image of the sample by making the scanning position of the sample correspond to the output of the photodetector.

[0021] According to the above-mentioned scanning electron microscope, by having the light emitting body of the above-mentioned structure, the electron beam detection efficiency can be improved from a small acceleration voltage to a large acceleration voltage. Therefore, even when the photographic object has a deep concave part and / or groove, etc., a large acceleration voltage can be used for the part and a small acceleration voltage can be used for the other part, and each can be photographed clearly.

[0022] Effects of the Invention

[0023] According to the embodiments of the present invention, it is possible to provide a light emitting body, an electron beam detector, and a scanning electron microscope capable of improving light conversion efficiency from a small acceleration voltage to a large acceleration voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a cross-sectional view showing the structure of the light emitting body 10 according to the first embodiment.

[0025] Figure 2 It is a cross-sectional view showing an enlarged internal structure of the multiple quantum well structure 14C.

[0026] Figure 3 (a) to (c) are diagrams showing the results of simulating the situation in which electrons enter and diffuse into the light-emitting body 10 using the Monte Carlo method.

[0027] Figure 4 It is a graph showing the relationship between the acceleration voltage of input electrons and the peak intensity of cathode luminescence. Curve G1 shows the relationship of the light emitting body 10 of this embodiment, and curve G2 shows the relationship when the thickness of multiple barrier layers 142 is made uniform as a comparative example.

[0028] Figure 5 Yes Figure 4 A graph showing an enlarged portion of the graph.

[0029] Figure 6 It is a cross-sectional view showing the structure of an electron beam detector 20 according to the second embodiment.

[0030] Figure 7 It is a diagram schematically showing the structure of a length measuring SEM 40 according to the third embodiment. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the light emitter, electron beam detector, and scanning electron microscope will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals are used for the same elements in the description of the accompanying drawings, and repeated descriptions are omitted. The present invention is not limited to these examples.

[0032] In the following description, a nitride semiconductor refers to a compound containing at least one of Ga, In, and Al as a Group III element and containing N as a main Group V element. Also, having light transmissivity means a property of transmitting 50% or more of target light.

[0033] (First embodiment)

[0034] Figure 1 1 is a cross-sectional view showing the structure of the light emitting body 10 according to the first embodiment, and shows a cross section along the thickness direction. The light emitting body 10 converts input electrons into light. Figure 1 As shown, the light emitting body 10 includes a substrate 12, a nitride semiconductor layer 14 provided on a main 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 input surface 10a.

[0035] The substrate 12 is a plate-shaped member having light transmittance relative to the wavelength of light output from the nitride semiconductor layer 14. The constituent material of the substrate 12 is not particularly limited as long as it is a material that can transmit the light output from the nitride semiconductor layer 14 and epitaxially grow 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.

[0036] The nitride semiconductor layer 14 includes a first buffer layer 14A provided on the primary surface 12 a 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.

[0037] 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 (e.g., 400° C. to 700° C.), and has, for example, an amorphous structure mainly containing gallium (Ga) and nitrogen (N). In one example, the first buffer layer 14A is composed of amorphous GaN. The thickness of the first buffer layer 14A is, for example, 5 nm to 500 nm, and in one embodiment, is 20 nm.

[0038] The second buffer layer 14B is also a layer for growing the multiple quantum well structure 14C with good crystallinity, for example, mainly containing GaN crystals. In one example, the second buffer layer 14B is composed of GaN crystals. The second buffer layer 14B is epitaxially grown at a higher temperature (for example, 700° C. to 1200° C.) than the first buffer layer 14A. The thickness of the second buffer layer 14B is, for example, 1 μm to 10 μm, and in one embodiment is 2.5 μm. The second buffer layer 14B may also be in contact with the first buffer layer 14A.

[0039] The multiple quantum well structure 14C is a portion that emits light by input of electrons, and is a layer epitaxially grown on the second buffer layer 14B. Figure 2 14C is a cross-sectional view showing an enlarged view of the internal structure of the multiple quantum well structure 14C. Figure 2 As shown, the multiple quantum well structure 14C has a structure in which well layers 141 and barrier layers 142 are alternately stacked.

[0040] The well layer 141 is composed of a material that accepts electrons and emits light, and in this embodiment, mainly contains In x Ga 1-x In one example, the well layer 141 is made of In doped with Si. x Ga 1-xN (0<x<1) crystal structure. The Si doping concentration is, for example, 2×10 18 cm -3 In this case, the well layer 141 emits light having a wavelength of about 415 nm when electrons are input. That is, when electrons enter the multiple quantum well structure 14C, electron-hole pairs are formed, and light is emitted during the process of re-coupling in the well layer 141 (cathodoluminescence).

[0041] The compositions of the multiple well layers 141 constituting the multiple quantum well structure 14C are the same, and the above-mentioned compositions x are equal to each other. In one embodiment, the composition x is 0.13. In addition, the thicknesses of the multiple well layers 141 constituting the multiple quantum well structure 14C are equal to each other. The thickness of each well layer 141 is, for example, not less than 0.2 nm and not more than 5 nm, and in one embodiment, it is 1.5 nm.

[0042] The band gap energy of the barrier layer 142 is greater than the band gap energy of the well layer 141. By sandwiching the well layer 141 between the barrier layers 142, electrons can be concentrated in the well layer 141 and efficiently converted into light. In this embodiment, the barrier layer 142 mainly contains GaN crystals. In one example, the barrier layer 142 is composed of GaN crystals doped with Si. The Si doping concentration is, for example, 2×10 18 cm -3 In addition, the barrier layer 142 may further contain a Group III atom other than Ga (eg, In). In this case, the compositions of the plurality of barrier layers 142 constituting the multiple quantum well structure 14C are also equal to each other.

[0043] The thicknesses of the plurality of barrier layers 142 constituting 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 input surface 10a (see Figure 1 In other words, the barrier layers 142 become thicker as they are farther from the electron input surface 10 a , and the first barrier layer 142 closest to the electron input surface 10 a is the thinnest among the barrier layers 142 .

[0044] In a preferred example, the thickness of the first barrier layer 142 closest to the electron input surface 10a is less than 80% of the average thickness of the barrier layer 142, and more preferably less than 20%. The thickness of the second barrier layer 142 (i.e., the barrier layer 142 adjacent to the barrier layer 142 closest to the electron input surface 10a) is less than 90% of the average thickness of the plurality of barrier layers 142, and more preferably less than 80%.

[0045] Table 1 shown below, as an example, shows the thickness of each barrier layer 142 when the thickness of the first and second barrier layers 142 is 9% and 65% of the average thickness of the barrier layer 142, respectively. Table 2 shown below, as another example, shows the thickness of each barrier layer 142 when the thickness of the first and second barrier layers 142 is 80% and 90% of the average thickness of the barrier layer 142, respectively. Table 3 shown below, as yet another example, shows the thickness of each barrier layer 142 when the thickness of the first and second barrier layers 142 is 20% and 80% of the average thickness of the barrier layer 142, respectively.

[0046] [Table 1]

[0047]

[0048] [Table 2]

[0049]

[0050] [Table 3]

[0051]

[0052] In these embodiments, 9 barrier layers 142 are provided. The first well layer 141 is provided between the first barrier layer 142 and the second barrier layer 142 from the electron input surface 10a side. Then, 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 from the electron input surface 10a side.

[0053] In addition, a barrier layer 143 having the same composition as each barrier layer 142 is provided between the last (ninth) well layer 141 and the second buffer layer 14B (see Figure 2 The thickness of the barrier layer 143 does not affect the characteristics of the light emitting body 10, and is, for example, 10 nm. In addition, the barrier layer 143 may not be provided as required.

[0054] In the embodiment of Table 1 above, the barrier layers 142 are thicker as they are farther from the electron input plane 10a among all the plurality of barrier layers 142, but even if, for example, a very small number of barrier layers 142 included in a large number of barrier layers 142 do not satisfy this condition, the effect of the present embodiment described below is not substantially affected. That is, when a barrier layer 142 (first barrier layer) included in the plurality of barrier layers 142 is thicker than another barrier layer 142 (second barrier layer) located on the electron input plane 10a side relative to the barrier layer 142, the effect of the present embodiment described below can be appropriately obtained.

[0055] In this case, the other barrier layer 142 may also be the first barrier layer 142 which is the closest to the electron input surface 10a and the thinnest. Alternatively, as described above, the thickness of the first barrier layer 142 which is the closest to the electron input surface 10a may be set to be less than 80% (more preferably less than 20%) of the average thickness of the barrier layer 142, and the thickness of the second barrier layer 142 may be set to be less than 90% (more preferably less than 80%) of the average thickness of the plurality of barrier layers 142.

[0056] Alternatively, when N (N is an integer greater than 1) barrier layers 142 are divided into a first group of N1 (1≤N1≤N-1) on the electron input surface 10a side and a second group of N2 (1≤N2≤N-1, and N1+N2=N) on the substrate 12 side, it can also be shown that the average thickness of the barrier layers 142 of the first group is smaller than the average thickness of the barrier layers 142 of the second group (in other words, the well layers 141 clamped by the first group are densely arranged, and the well layers 141 clamped by the second group are sparsely arranged).

[0057] In addition, the above Tables 1 to 3 also show the difference in thickness between adjacent barrier layers 142. In the example shown in Table 1, the difference in thickness between adjacent barrier layers 142 becomes smaller as the distance from the electron input surface 10a increases.

[0058] In the embodiment shown in Table 1, the difference in thickness between adjacent barrier layers 142 becomes smaller as they are farther from the electron input plane 10a among all the plurality of barrier layers 142, but even if, for example, a very small number of barrier layers 142 included in a large number of barrier layers 142 do not satisfy this condition, the following effects are hardly impaired. That is, when the difference in thickness between a pair of barrier layers 142 adjacent to each other included in the plurality of barrier layers 142 is smaller than the difference in thickness between another pair of barrier layers 142 adjacent to each other and located on the electron input plane 10a side relative to the pair of barrier layers 142, the following effects can be appropriately obtained.

[0059] Alternatively, the difference in thickness between the first barrier layer 142 and the second barrier layer 142 closest to the electron input surface 10a may be more than three times the average difference in thickness between the barrier layers 142 of the entire multiple quantum well structure 14C, and the difference in thickness between the second barrier layer 142 and the third barrier layer 142 may be more than 1.2 times the average difference in thickness between the barrier layers 142 of the entire multiple quantum well structure 14C.

[0060] The conductive layer 18 is used as an electrode for guiding electrons to the light emitting body 10. The conductive layer 18 mainly contains metal, and in one embodiment mainly contains Al. The thickness of the conductive layer 18 is, for example, not less than 10 nm and not more than 1000 nm, and in one embodiment is about 300 nm.

[0061] When the conductive layer 18 mainly includes 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 directly reaches the substrate 12 from the multiple quantum well structure 14C, passes through the substrate 12 and is output to the outside of the light emitting body 10, but 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 then passes through the substrate 12 and is output to the outside of the light emitting body 10.

[0062] Here, an embodiment of a method for manufacturing the light emitting body 10 is described. First, the substrate 12 is introduced into the growth chamber of a metal-organic vapor phase epitaxy (MOVPE) device, and a heat treatment is performed at 1100°C / 10 minutes in a hydrogen atmosphere to purify the main surface 12a. Then, the temperature of the substrate 12 is lowered to 500°C, and the first buffer layer 14A is deposited. After that, the temperature of the substrate 12 is raised to 1100°C to epitaxially grow the second buffer layer 14B.

[0063] Then, the temperature of the substrate 12 is lowered to 800°C to form In x Ga 1-x N / GaN multiple quantum well structure 14C The composition x is in the range of 0.1 to 0.2, and is 0.15 in this embodiment, but the composition ratio is not limited to the above range as long as the band gap of the well layer 141 is smaller than the band gap of the barrier layer 142 .

[0064] Then, the substrate 12 is moved into a vapor deposition device, and a conductive layer 18 is formed on the multiple quantum well structure 14C, thereby completing the manufacture of the light emitting body 10 .

[0065] In the above example, trimethylgallium (Ga(CH3)3:TMGa) can be used as a Ga source, trimethylindium (In(CH3)3:TMIn) can be used as an In source, ammonia (NH3) can be used as a N source, hydrogen (H2) or nitrogen (N2) can be used as a carrier gas, and monosilane (SiH4) can be used as a Si source. Alternatively, other organic metal raw materials (such as triethylgallium (Ga(C2H5)3:TEGa), triethylindium (In(C2H5)3:TEIn) and other hydrides (such as disilane (Si2H4)) can also be used.

[0066] In the above example, a 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, each growth temperature is not limited to the above temperature.

[0067] The effects obtained by the light emitting body 10 of the present embodiment having the above structure are described. In the light emitting body 10, when electrons are input to the multiple quantum well structure 14C from the electron input surface 10a side, light is generated by light emission recoupling (cathodoluminescence) of the well layer 141. The light is transmitted through the substrate 12 and output to the outside of the light emitting body 10.

[0068] Here, Figure 3 (a) to (c) are diagrams showing the results of simulation using the Monte Carlo method of electrons entering and diffusing in the light emitting body 10, and the density of electrons is shown by light and dark colors. The darker the color, the higher the electron density. Figure 3 (a) to (c) respectively represent the cases where the acceleration voltage of the electron beam is 10 kV, 30 kV, and 40 kV. As can be seen from these figures, when the acceleration voltage of the electron beam is small, the electrons diffuse only in the shallow area of ​​the light-emitting body 10 and do not penetrate deep. In contrast, when the acceleration voltage of the electron beam is large, the electrons penetrate deep areas in the light-emitting body 10. In addition, the diffusion direction of the electrons in the light-emitting body 10 is irregular and expands in a roughly hemispherical shape.

[0069] As described above, in a light emitting body that converts electrons into light, there is a case where it is desired to improve the light conversion efficiency from a small acceleration voltage to a large acceleration voltage. Figure 3 As shown in (c), when the acceleration voltage of the input electron beam is large, the electron beam reaches a deep position of the light-emitting body. Therefore, in order to improve the light conversion efficiency of the electron beam with a large acceleration voltage, it is desirable to thicken the multiple quantum well structure. In order to thicken the multiple quantum well structure, the barrier layer can be thickened. However, in this case, for the electron beam with a small acceleration voltage that only reaches a shallow position of the light-emitting body, the problem of reduced light conversion efficiency occurs.

[0070] In this embodiment, the barrier layer 142 at a position relatively shallow from the electron input surface 10a is thinner than the barrier layer 142 at a relatively deep position. Therefore, the well layer 141 located on the opposite side of the electron input surface 10a sandwiching the barrier layer 142 at a relatively shallow position is arranged closer to the electron input surface 10a than when the barrier layer 142 has a uniform thickness. Therefore, the resistance to the electron input surface 10a can be improved. Figure 3 The light conversion efficiency of an electron beam at a small accelerating voltage as shown in (a).

[0071] Furthermore, the barrier layer 142 at a relatively deep position is thicker than the barrier layer 142 at a relatively shallow position. Therefore, the well layer 141 located on the opposite side of the electron input surface 10a with the barrier layer 142 at a relatively deep position sandwiched therebetween is arranged away from the electron input surface 10a. Figure 3 Even when the electron beam has a large acceleration voltage as shown in (c), deep penetration can maintain the light conversion efficiency.

[0072] In addition, if Figure 3 As shown in (c), the electron beam expands in a hemispherical shape inside the light emitting body 10, so the quantum wells densely arranged near the electron input surface 10a can reliably capture electrons even at a large acceleration voltage. Thus, by changing the thickness of the barrier layer 142 according to the distance from the electron input surface 10a, the light conversion efficiency can be improved from a small acceleration voltage to a large acceleration voltage.

[0073] According to the knowledge of the present inventors, electrons tend to diffuse in a hemispherical shape inside the multiple quantum well structure 14C, and the quantum well excitation density near the electron input surface 10a becomes high. Therefore, the excitation of the quantum well caused by the diffused electrons decreases in the depth direction. Therefore, it is preferred that the quantum well spacing near the electron input surface 10a, that is, the thickness of the barrier layer 142, is thinner than the quantum well spacing farthest from the electron input surface 10a, that is, the thickness of the barrier layer 142.

[0074] In addition, as in the present embodiment, the barrier layer 142 closest to the electron input surface 10a among the plurality of barrier layers 142 may be the thinnest among the plurality of barrier layers 142. In this case, the well layer 141 closest to the electron input surface 10a is located closer to the electron input surface 10a. Therefore, the light conversion efficiency for electron beams with a small acceleration voltage can be further improved.

[0075] In addition, as in the present embodiment, the thickness of the first barrier layer 142 closest to the electron input surface 10a among the plurality of barrier layers 142 may be less than 80% of the average thickness of the plurality of barrier layers 142. In this case, the position of the well layer 141 closest to the electron input surface 10a is close to the electron input surface 10a. Therefore, the light conversion efficiency of the electron beam with a small acceleration voltage can be further improved. More preferably, the thickness of the first barrier layer 142 is less than 20% of the average thickness of the plurality of barrier layers 142.

[0076] In addition, as in the present embodiment, the thickness of the second barrier layer 142 adjacent to the barrier layer 142 closest to the electron input surface 10a among the plurality of barrier layers 142 may be 90% or less of the average thickness of the plurality of barrier layers 142. More preferably, the thickness of the second barrier layer 142 is 80% or less of the average thickness of the plurality of barrier layers 142.

[0077] In addition, as in the present embodiment, there may be a plurality of barrier layers 142, and the thickness may be gradually increased as the barrier layers 142 are further away from the electron input surface 10a. In this case, the arrangement of the well layers 141 may be appropriately adjusted according to the acceleration voltage, thereby further improving the light conversion efficiency.

[0078] In addition, as in the present embodiment, it is preferred that the difference in thickness between the barrier layers 142 adjacent to each other is made smaller the further away from the electron input surface 10a. As described above, inside the multiple quantum well structure 14C, electrons have a tendency to diffuse in a hemispherical shape. Therefore, the amount of diffused electrons decreases exponentially in the depth direction. Therefore, by making the difference in thickness between the barrier layers 142 adjacent to each other smaller the further away from the electron input surface 10a, a more appropriate configuration of the well layer 141 corresponding to the amount of diffused electrons at each depth can be achieved, which can greatly improve the light conversion efficiency.

[0079] In addition, as in the present embodiment, the compositions of the plurality of well layers 141 may be the same as each other. In this case, the multiple quantum well structure 14C can be easily manufactured.

[0080] Here, the results of verifying the above-mentioned effects are described. Figure 4 The curve G1 is a graph showing the relationship between the acceleration voltage of the input electrons and the peak intensity of the cathode luminescence (CL) (specifically, the peak count value of the luminescence spectrum at each acceleration voltage) of the light emitting body 10 (the thickness of the barrier layer 142 is shown in Table 1) of the present embodiment. In addition, Figure 4 The curve G2 is a curve showing the relationship when the thickness of the plurality of barrier layers 142 is made uniform as a comparative example. Figure 5 Yes Figure 4 A graph showing a part of the graph in enlarged form. In the graph G2, the thickness of the barrier layer 142 is assumed to be 225 nm. In addition, the number of layers of the barrier layer 142 in the graphs G1 and G2 is 9.

[0081] In this embodiment (curve G1), as Figure 5 As shown in FIG. 1 , the peak intensity of CL in the region with a small acceleration voltage is larger than that of the comparative example (curve G2). In particular, when the acceleration voltage is 6 kV, the peak intensity of CL is about 5 times that of the comparative example (curve G2), and is about 2 times that of the comparative example (curve G2) when the acceleration voltage is 8 kV. Such a significant difference is believed to be caused by making the first barrier layer 142 extremely thin (21 nm) in this embodiment.

[0082] In addition, refer to Figure 4In the region where the acceleration voltage exceeds 40 kV, the CL peak intensity of the comparative example (curve G2) gradually decreases as the acceleration voltage increases. This is believed to be caused by the gradual increase in the number of electrons penetrating the multiple quantum well structure as the acceleration voltage increases.

[0083] In contrast, the decrease in CL peak intensity of the present embodiment (curve G1) with the increase in acceleration voltage is suppressed compared to the comparative example (curve G2). This suggests that the light conversion efficiency is significantly improved compared to the comparative example (curve G2) by reliably capturing spherically expanded electrons using the densely arranged quantum wells near the surface at high acceleration voltage.

[0084] (Second embodiment)

[0085] Figure 6 1 is a cross-sectional view showing the structure of the electron beam detector 20 involved in the second embodiment, showing a cross section along the thickness direction. The electron beam detector 20 includes the light-emitting body 10 of the first embodiment, an insulating optical component (light-guiding component) 22, and a photodetector 30. The optical component 22 is an example of a light-transmitting component of this embodiment, has insulating properties, is interposed between the light-emitting body 10 and the photodetector 30, and integrates the light-emitting body 10 and the photodetector 30.

[0086] The back surface 12b of the substrate 12 of the light emitting body 10 and the light incident surface 30a of the light detector 30 are optically coupled via the optical component 22. Specifically, one end surface of the optical component 22 is bonded to the light incident surface 30a, and the other end surface of the optical component 22 is bonded to the light emitting body 10. The optical component 22 may be a light guide such as a fiber optical plate (FOP), or a lens that focuses the light generated by the light emitting body 10 on the light incident surface 30a.

[0087] A light-transmitting adhesive layer AD2 is interposed between the optical component 22 and the photodetector 30, and the relative position between the optical component 22 and the photodetector 30 is fixed by the adhesive layer AD2. The adhesive layer AD2 mainly contains, for example, a light-transmitting resin. In addition, an adhesive layer AD1 is interposed between the back surface 12b of the substrate 12 of the light-emitting body 10 and the optical component 22.

[0088] The adhesive layer AD1 includes a SiN layer ADa provided on the back surface 12b and a SiO2 layer ADb provided on the SiN layer ADa. In one example, the back 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 component 22 are fused to each other. The SiO2 layer ADb and the optical component 22 are both silicon oxides, so they can be fused by heating.

[0089] The SiO2 layer ADb is formed on the SiN layer ADa using a sputtering method or the like, so the coupling force between the SiN layer ADa and the SiO2 layer ADb is extremely high. Similarly, the SiN layer ADa is also formed on the back side 12b of the substrate 12 by a sputtering method or the like, so the coupling force between the SiN layer ADa and the substrate 12 is also extremely high. Therefore, the substrate 12 and the optical component 22 are firmly bonded via the adhesive layer AD1. In addition, the SiN layer ADa also acts as an anti-reflection film, suppressing or reducing the reflection of light generated in the multiple quantum well structure 14C on the back side 12b.

[0090] In the electron beam detector 20 having such a structure, light generated in the multiple quantum well structure 14C in response to input of electrons sequentially passes through the adhesive layer AD1 , the optical component 22 , and the adhesive layer AD2 to reach the light incident surface 30 a of the photodetector 30 .

[0091] As described above, the light incident surface 30a of the photodetector 30 is optically coupled to the surface of the multi-quantum well structure 14C opposite to the electron input surface 10a via the substrate 12, the adhesive layer AD1, the optical component 22, and the adhesive layer AD2. The photodetector 30 has sensitivity to light emitted from the multi-quantum well structure 14C.

[0092] The photodetector 30 is, for example, a photomultiplier tube. In this case, the photodetector 30 includes a vacuum container 31. The vacuum container 31 is configured to include a metal side tube 31a, a light incident window (panel) 31b that closes the opening at the top of the side tube 31a, and a stem plate 31c that closes the opening at the bottom of the side tube 31a. Inside the vacuum container 31, a photocathode 32 formed on the inner surface of the light incident window 31b and an electrode portion 33 including an electron multiplier portion and an anode are arranged. The electron multiplier portion includes, for example, a microchannel plate or a mesh type dynode.

[0093] The light incident surface 30a is the outer surface of the light incident window 31b, and the 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 according to the incident light and releases the generated photoelectrons into the internal space of the vacuum container 31.

[0094] The photoelectrons are multiplied by the electron multiplying section of the electrode section 33. The multiplied electrons are collected by the anode of the electrode section 33. The electrons collected by the anode of the electrode section 33 are taken out to the outside of the photodetector 30 via any one of the plurality of pins 31p penetrating the rod plate 31c. In addition, a predetermined potential is given to the electron multiplying section of the electrode section 33 via other pins 31p. The potential of the metal side tube 31a is 0V, and the photocathode 32 is electrically connected to the side tube 31a.

[0095] The electron beam detector 20 of the present embodiment described above includes the light emitting body 10 of the first embodiment. Therefore, the electron beam detection efficiency can be improved from a small acceleration voltage to a large acceleration voltage. In addition, the insulating optical component 22 is interposed between the light emitting body 10 and the photodetector 30, and the photodetector 30 can be stably operated regardless of the voltage applied to the light emitting body 10.

[0096] (Third embodiment)

[0097] The electron beam detector 20 according to the second embodiment can be used in a scanning electron microscope (Scanning Electron Microscope: SEM), a mass spectrometer, and the like. Figure 7 1 is a diagram schematically showing the structure of a length measuring SEM 40 according to the third embodiment. The length measuring SEM 40 includes a SEM 41 for acquiring an image of an object to be inspected, a control unit 42 for overall control, a storage unit 43 for storing acquired images, etc. in a magnetic disk or semiconductor memory, and a calculation unit 44 for performing calculations according to a program.

[0098] The SEM 41 includes a movable stage 46 for carrying a sample wafer 45, an electron source 47 for irradiating the sample wafer 45 with an electron beam EB1, and a plurality of (three are shown in the figure) electron beam detectors 20 for detecting secondary electrons and reflected electrons generated from the sample wafer 45. The structure of the electron beam detector 20 is the same as that of the second embodiment. Furthermore, the SEM 41 includes an electron lens (not shown) for converging the electron beam EB1 on the sample wafer 45, a deflector (not shown) for scanning the electron beam EB1 on the sample wafer 45, and an image generation unit 48 for digitally converting the signals from each electron beam detector 20 to generate a digital image.

[0099] The movable stage 46, the electron source 47, and at least the light emitter 10, the electron lens, and the deflector of the electron beam detector 20 are housed in a vacuum chamber 50. The image generation unit 48 and each electron beam detector 20 are electrically connected to each other via wiring. The image generation unit 48, the control unit 42, the storage unit 43, and the calculation unit 44 are electrically connected to each other via a data bus 49.

[0100] When the electron beam EB1 is irradiated to the sample wafer 45 and scanned on the surface of the sample wafer 45, secondary electrons and reflected electrons are released from the surface of the sample wafer 45 and guided as the electron beam EB2 to the electron beam detector 20. The electron beam detector 20 converts the electron beam EB2 into an electrical signal and transmits the electron beam EB2 to the pin 31p (refer to Figure 6 By synchronizing the scanning position of the electron beam EB1 with the output of the electron beam detector 20, an image of the sample wafer 45 can be captured.

[0101] The control unit 42 has functions of controlling the transport 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 storage unit 43 has an area for storing acquired image data and an area for storing imaging conditions (such as acceleration voltage, etc.). The calculation unit 44 has a function of calculating the size of the structure (such as the width of the groove) based on the depth (contrast) in the image data.

[0102] The control unit 42 and the computing unit 44 may be configured as hardware designed to realize each function, or may be configured to be installed as software and executed using a general-purpose computing device (such as a CPU or a GPU).

[0103] The length measurement SEM 40 according to the present embodiment includes the light emitting body 10 according to the first embodiment. Thus, the electron beam detection efficiency can be improved from a small acceleration voltage to a large acceleration voltage. Therefore, even when the sample wafer 45 has a deep recess and / or groove, a large acceleration voltage can be used for the portion and a small acceleration voltage can be used for the other portion, and each portion can be clearly photographed.

[0104] For example, when measuring the shape (wiring width, etc.) of each layer in a multilayer semiconductor device such as a semiconductor memory device, a small acceleration voltage (e.g., 3 to 5 keV) is sufficient to allow secondary electrons and reflected electrons to reach the light emitting body 10 from the outermost layer of the semiconductor device, but a large acceleration voltage (e.g., 30 keV or more) is required to allow secondary electrons and reflected electrons to reach the light emitting body 10 from the deepest layer. According to the length measurement SEM 40 of this embodiment, the electron beam detection efficiency can be improved from a small acceleration voltage to a large acceleration voltage, so that the shape and size of each layer of the multilayer semiconductor device can be clearly measured.

[0105] The light emitter, electron beam detector and scanning electron microscope are not limited to the above-mentioned embodiments and configuration examples, and various modifications are possible. For example, the composition, dopant concentration and thickness of the well layer 141 and barrier layer 142 constituting the multiple quantum well structure 14C are not limited to the above-mentioned examples.

[0106] In addition, the above example shows an example in which the first buffer layer 14A and the second buffer layer 14B are GaN layers, but other compositions can also be used as long as the nitride semiconductor contains at least one of In, Al and Ga as group III elements and contains N as the main group V element and is light-transmissive with respect to the emission wavelength of the multiple quantum well structure 14C.

[0107] In the above example, 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 thereto and other impurities (such as Mg) may be doped or no doping may be required.

[0108] In addition, the well layer 141 and the barrier layer 142 of the multiple quantum well structure 14C can be made of 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 InGaN / GaN combination, for example, InGaN / AlGaN, InGaN / InGaN, GaN / AlGaN and other combinations can also be used. Alternatively, the well layer 141 and the barrier layer 142 can also be composed of other semiconductors besides nitride semiconductors.

[0109] In the above example, the number of well layers 141 and barrier layers 142 is 9, respectively, but the number of well layers 141 and barrier layers 142 may be any number greater than 2. The thickness of the barrier layer 142 shown in Table 1 is only an example, and the barrier layer 142 may have various other thicknesses.

[0110] also, Figure 6 The photodetector 30 is not limited to a photomultiplier tube, and may be, for example, an avalanche diode. In addition, the optical component 22 is not limited to a straight line shape, and may be a curved line shape, and the size may be appropriately changed.

[0111] The light-emitting body of the above-mentioned embodiment is set to the following structure: it is a light-emitting body that converts input electrons into light, including a multiple quantum well structure that emits light through the input of electrons and an electron input surface arranged on the multiple quantum well structure, and the first barrier layer included in the multiple barrier layers constituting the multiple quantum well structure is thicker than the second barrier layer included in the multiple barrier layers and located on the electron input surface side relative to the first barrier layer.

[0112] In the above-mentioned luminous body, the following structure can also be set: the second barrier layer is the barrier layer closest to the electron input surface among the multiple barrier layers. In addition, in this case, the following structure can also be set: the second barrier layer is the thinnest among the multiple barrier layers. As a result, the position of the well layer closest to the electron input surface is closer to the electron input surface. Therefore, the light conversion efficiency of the electron beam with a small acceleration voltage can be further improved.

[0113] In the above-mentioned light-emitting body, it is also possible to set the structure as follows: the second barrier layer is the barrier layer closest to the electron input surface among the multiple barrier layers, and the thickness of the second barrier layer is less than 80% of the average thickness of the multiple barrier layers. In this case, the position of the well layer closest to the electron input surface is close to the electron input surface. Therefore, the light conversion efficiency of the electron beam with a small acceleration voltage can be further improved. In addition, in the above-mentioned structure, it is also possible to set the structure as follows: the thickness of the second barrier layer is less than 20% of the average thickness of the multiple barrier layers.

[0114] In addition, in the above-mentioned light-emitting body, the following structure may be adopted: the first barrier layer is a barrier layer adjacent to the barrier layer closest to the electron input surface among the plurality of barrier layers, and the thickness of the first barrier layer is less than 90% of the average thickness of the plurality of barrier layers. In addition, in the above-mentioned structure, the following structure may be adopted: the thickness of the first barrier layer is less than 80% of the average thickness of the plurality of barrier layers.

[0115] In the above-mentioned light emitting body, a structure may be provided in which the plurality of barrier layers become thicker as they are farther from the electron input surface. In this case, appropriate well layer configuration can be achieved according to various acceleration voltages, and light conversion efficiency can be further improved.

[0116] In the above-mentioned light emitting body, a structure may be adopted in which the difference in thickness between adjacent barrier layers becomes smaller as the distance from the electron input surface increases.

[0117] In the above-mentioned light emitting body, the composition of the plurality of well layers constituting the multiple quantum well structure may be the same as each other. In this case, the multiple quantum well structure can be easily produced.

[0118] The electron beam detector of the above embodiment is configured as follows: it includes: a light-emitting body of the above structure; a light detector optically coupled to the surface on the opposite side of the electron input surface in the multiple quantum well structure and having sensitivity to the light emitted by the multiple quantum well structure; and a light-transmitting component interposed between the light-emitting body and the light detector and integrating the light-emitting body and the light detector and having insulating properties.

[0119] The scanning electron microscope of the above-mentioned embodiment is configured as follows: it includes: a light-emitting body of the above-mentioned structure; a light detector which is optically coupled to the surface on the opposite side of the electron input surface in the multiple quantum well structure and has sensitivity to the light emitted by the multiple quantum well structure; and a vacuum chamber in which at least the light-emitting body is arranged, an electron beam is scanned on the surface of a sample arranged in the vacuum chamber, secondary electrons and reflected electrons from the sample are guided to the light-emitting body, and an image of the sample is photographed by making the scanning position of the sample correspond to the output of the light detector.

[0120] Industrial Applicability

[0121] The present invention can be used as a light emitting body, an electron beam detector, and a scanning electron microscope capable of improving light conversion efficiency from a small acceleration voltage to a large acceleration voltage.

[0122] Explanation of symbols

[0123] 10…light emitting body, 10a…electron input 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 component, 30…photodetector, 30a…light incident surface, 31…vacuum container, 31a…side tube, 31b…light incident window, 31c…rod plate, 31p…pin, 32…photocathode , 33…electrode part, 40…length measuring SEM, 41…scanning electron microscope (SEM), 42…control part, 43…storage part, 44…calculation part, 45…sample wafer, 46…movable mounting table, 47…electron source, 48…image generating part, 49…data bus, 50…vacuum chamber, 141…well layer, 142, 143…barrier layer, AD1, AD2…adhesive layer, ADa…SiN layer, ADb…SiO2 layer, EB1, EB2…electron beam.

Claims

1. A luminous body, characterized in that: It is a light-emitting body that converts the electrons input from the electron input surface into light. include: A multiple quantum well structure that emits the light by input of the electrons; and The electron input surface is disposed on the multiple quantum well structure and exposed, A first barrier layer included in the plurality of barrier layers constituting the multiple quantum well structure is thicker than a second barrier layer included in the plurality of barrier layers and located on the electron input surface side where the electrons are input relative to the first barrier layer.

2. The luminous body according to claim 1, characterized in that: The second barrier layer is a barrier layer closest to the electron input surface among the plurality of barrier layers.

3. The luminous body according to claim 2, characterized in that: The second barrier layer is the thinnest among the plurality of barrier layers.

4. The luminous body according to claim 2, characterized in that: The thickness of the second barrier layer is less than 80% of an average thickness of the plurality of barrier layers.

5. The luminous body according to claim 3, characterized in that: The thickness of the second barrier layer is less than 80% of an average thickness of the plurality of barrier layers.

6. The luminous body according to claim 4, characterized in that: The thickness of the second barrier layer is less than 20% of an average thickness of the plurality of barrier layers.

7. The luminous body according to claim 5, characterized in that: The thickness of the second barrier layer is less than 20% of an average thickness of the plurality of barrier layers.

8. The luminous body according to any one of claims 2 to 7, characterized in that: The first barrier layer is a barrier layer adjacent to a barrier layer closest to the electron input surface among the plurality of barrier layers, and a thickness of the first barrier layer is less than 90% of an average thickness of the plurality of barrier layers.

9. The luminous body according to claim 8, characterized in that: The thickness of the first barrier layer is less than 80% of an average thickness of the plurality of barrier layers.

10. The luminous body according to any one of claims 1 to 7, characterized in that: The plurality of barrier layers become thicker as they are farther away from the electron input surface.

11. The luminous body according to claim 8, characterized in that: The plurality of barrier layers become thicker as they are farther away from the electron input surface.

12. The luminous body according to claim 9, characterized in that: The plurality of barrier layers become thicker as they are farther away from the electron input surface.

13. The luminous body according to any one of claims 1 to 7, characterized in that: The difference in thickness between the adjacent barrier layers becomes smaller as the distance from the electron input surface increases.

14. The luminous body according to claim 8, characterized in that: The difference in thickness between the adjacent barrier layers becomes smaller as the distance from the electron input surface increases.

15. The luminous body according to claim 9, characterized in that: The difference in thickness between the adjacent barrier layers becomes smaller as the distance from the electron input surface increases.

16. The luminous body according to claim 10, characterized in that: The difference in thickness between the adjacent barrier layers becomes smaller as the distance from the electron input surface increases.

17. The luminous body according to claim 11, characterized in that: The difference in thickness between the adjacent barrier layers becomes smaller as the distance from the electron input surface increases.

18. The luminous body according to claim 12, characterized in that: The difference in thickness between the adjacent barrier layers becomes smaller as the distance from the electron input surface increases.

19. The luminous body according to any one of claims 1 to 7, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

20. The luminous body according to claim 8, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

21. The luminous body according to claim 9, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

22. The luminous body according to claim 10, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

23. The luminous body according to claim 11, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

24. The luminous body according to claim 12, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

25. The luminous body according to claim 13, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

26. The luminous body according to claim 14, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

27. The luminous body according to claim 15, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

28. The luminous body according to claim 16, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

29. The luminous body according to claim 17, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

30. The luminous body according to claim 18, characterized in that: The compositions of the plurality of well layers constituting the multiple quantum well structure are identical to each other.

31. An electron beam detector, characterized in that: include: The luminous body according to any one of claims 1 to 30; a light detector optically coupled to a surface of the multiple quantum well structure opposite to the electron input surface and having sensitivity to the light emitted from the multiple quantum well structure; and A light-transmitting member is interposed between the light-emitting body and the light-detector to integrate the light-emitting body and the light-detector and has an insulating property.

32. A scanning electron microscope, characterized in that: include: The luminous body according to any one of claims 1 to 30; a light detector optically coupled to a surface of the multiple quantum well structure opposite to the electron input surface and having sensitivity to the light emitted from the multiple quantum well structure; and A vacuum chamber having at least the light emitting body arranged therein, An electron beam is scanned on the surface of a sample arranged in the vacuum chamber, secondary electrons and reflected electrons from the sample are guided to the light emitter, and an image of the sample is photographed by matching the scanning position of the sample with the output of the photodetector.

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