Ultraviolet light-generating target and method for manufacturing the same, and electron beam-excited ultraviolet light source

Abstract

An ultraviolet light-generating target comprising a substrate transmitting ultraviolet light; and a light-emitting layer provided on the substrate and emitting ultraviolet light in response to an electron beam, wherein the light-emitting layer is an amorphous layer formed of Al.sub.2O.sub.3 doped with Sc.

Claims

1. An ultraviolet light-generating target comprising: a substrate transmitting ultraviolet light; and a light-emitting layer provided on the substrate and emitting ultraviolet light in response to an electron beam, wherein the light-emitting layer is an amorphous layer formed of Al.sub.2O.sub.3 doped with Sc.

2. The ultraviolet light-generating target according to claim 1, wherein a thickness of the light-emitting layer is 2.0 m or less.

3. The ultraviolet light-generating target according to claim 1, wherein a doping concentration of the Sc in the light-emitting layer is 4.0 atomic % or less.

4. An electron beam-excited ultraviolet light source comprising: the ultraviolet light-generating target according to claim 1; and an electron source providing the electron beam to the ultraviolet light-generating target.

5. The electron beam-excited ultraviolet light source according to claim 4, wherein a thickness of the light-emitting layer is 2.0 M or less.

6. The electron beam-excited ultraviolet light source according to claim 4, wherein a doping concentration of the Sc in the light-emitting layer is 4.0 atomic % or less.

7. A method for manufacturing an ultraviolet light-generating target, comprising: vapor-depositing Al.sub.2O.sub.3 doped with Sc on a substrate transmitting ultraviolet light, to form an amorphous layer; and firing the amorphous layer.

8. The method for manufacturing an ultraviolet light-generating target according to claim 7, wherein a thickness of the amorphous layer is set at 2.0 m or less.

9. The method for manufacturing an ultraviolet light-generating target according to claim 7, wherein a doping concentration of the Sc in the amorphous layer is set at 4.0 atomic % or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram showing the internal configuration of an electron beam-excited ultraviolet light source;

(2) FIG. 2 is a side view showing the configuration of an ultraviolet light-generating target;

(3) FIG. 3 is a schematic diagram showing the configuration of a laser ablation apparatus;

(4) FIG. 4A is a graph showing the XRD patterns of the light-emitting layers of Examples 1 to 6;

(5) FIG. 4B is a graph showing the emission spectra of the light-emitting layers of Examples 1 to 6; and

(6) FIG. 5 is a graph showing the XRD patterns of the light-emitting layers of Examples 11 to 13.

(7) FIG. 6 is a graph showing the XRD patterns of the light-emitting layers of Examples 8, 12, 16, and 20;

(8) FIG. 7A is a graph showing the emission spectra of the light-emitting layers of Examples 7 to 10;

(9) FIG. 7B is a graph showing the emission intensities of the light-emitting layers of Examples 7 to 10;

(10) FIG. 8A is a graph showing the emission spectra of the light-emitting layers of Examples 11 to 14;

(11) FIG. 8B is a graph showing the emission intensities of the light-emitting layers of Examples 11 to 14;

(12) FIG. 9A is a graph showing the emission spectra of the light-emitting layers of Examples 15 to 18;

(13) FIG. 9B is a graph showing the emission intensities of the light-emitting layers of Examples 15 to 18;

(14) FIG. 10A is a graph showing the emission spectra of the light-emitting layers of Examples 19 to 22; and

(15) FIG. 10B is a graph showing the emission intensities of the light-emitting layers of Examples 19 to 22.

(16) FIGS. 11A, B, C, and D are respectively photographs in which the surfaces of the ultraviolet light-generating targets of Examples 8, 12, 16, and 20 on the aluminum layer sides are observed by an FE-SEM;

(17) FIG. 12 is a graph showing the emission spectra of the light-emitting layers of Examples 23 to 28;

(18) FIG. 13A is a graph showing the XRD patterns of the light-emitting layers of Examples 29 to 33;

(19) FIG. 13B is a graph showing the emission spectra of the light-emitting layers of Examples 29 to 33;

(20) FIG. 14A is a graph showing the XRD patterns of the light-emitting layers of Examples 34 to 38;

(21) FIG. 14B is a graph showing the emission spectra of the light-emitting layers of Examples 34 to 38; and

(22) FIGS. 15A, B, and C are respectively photographs in which the surfaces of the ultraviolet light-generating targets of Examples 27, 33, and 38 on the aluminum layer sides are observed by an FE-SEM.

DETAILED DESCRIPTION

(23) Embodiments of the present invention will be described in detail below with reference to the drawings.

(24) FIG. 1 is a schematic diagram showing the internal configuration of an electron beam-excited ultraviolet light source according to one embodiment. As shown in FIG. 1, an electron beam-excited ultraviolet light source 1 comprises an evacuated glass container (electron tube) 2, an electron source 3 and an extraction electrode 4 disposed on the upper end side inside the container 2, and an ultraviolet light-generating target 11 disposed on the lower end side inside the container 2.

(25) A power supply portion 5 is electrically connected to the electron source 3 and the extraction electrode 4, and when an appropriate extraction voltage is applied between the electron source 3 and the extraction electrode 4 from the power supply portion 5, an electron beam EB accelerated by the high voltage is emitted from the electron source 3. The electron source 3 may be, for example, an electron source that emits a large area electron beam (for example, a cold cathode of carbon nanotubes or the like, or a hot cathode).

(26) The ultraviolet light-generating target 11 is set, for example, at ground potential, and a negative high voltage is applied to the electron source 3 from the power supply portion 5. The ultraviolet light-generating target 11 is irradiated with the electron beam EB thus emitted from the electron source 3. The ultraviolet light-generating target 11 is excited in response to this electron beam EB and generates ultraviolet light UV.

(27) FIG. 2 is a side view showing the configuration of the ultraviolet light-generating target 11. As shown in FIG. 2, the ultraviolet light-generating target 11 comprises a substrate 12, a light-emitting layer 13 provided on the substrate 12, and an ultraviolet light-reflecting layer (for example, an aluminum layer) 14 having electrical conductivity provided on the light-emitting layer 13. The substrate 12 is a plate-like member consisting of a material that transmits ultraviolet light, for example, sapphire (Al.sub.2O.sub.3), quartz (SiO.sub.2), or rock crystal (crystal of silicon oxide). The thickness of the substrate 12 may be, for example, 0.1 to 10 mm. The thickness of the ultraviolet light-reflecting layer 14 may be, for example, about 50 nm.

(28) The light-emitting layer 13 is excited in response to the electron beam EB shown in FIG. 1 and generates ultraviolet light UV. The light-emitting layer 13 is an amorphous layer formed of Al.sub.2O.sub.3 doped with Sc (Sc:Al.sub.2O.sub.3). The amorphous layer here encompasses, in addition to a layer having no orientation (crystallinity) at all, a layer having orientation (crystallinity) in part thereof and is defined as a layer which shows an intensity of the diffraction plane from Al.sub.2O.sub.3 of 200 cps (count per second) or less, and an intensities of the (042) and (0210) planes from (Sc,Al).sub.2O.sub.3 of 200 cps or less in In-plane X-ray diffraction (XRD) measurement using CuK rays at 45 kV and 200 mA.

(29) The light-emitting layer 13 preferably contains substantially no -phase Al.sub.2O.sub.3 (-Al.sub.2O.sub.3). Here, containing substantially no -phase Al.sub.2O.sub.3 means that in a diffraction pattern measured by an In-plane X-ray diffraction (XRD) method, the intensity of the peak from -phase Al.sub.2O.sub.3 is 200 cps or less.

(30) The doping concentration of Sc in Sc:Al.sub.2O.sub.3 forming the light-emitting layer 13 may be 0.1 atomic % or more, and is preferably 0.3 atomic % or more, more preferably 0.5 atomic % or more, further preferably 0.7 atomic % or more, and particularly preferably 0.8 atomic % or more in view of excellent ultraviolet light emission intensity. The doping concentration may be 5.0 atomic % or less, and is preferably 4.0 atomic % or less, more preferably 3.0 atomic % or less, further preferably 2.0 atomic % or less, and particularly preferably 1.5 atomic % or less in view of the excellent layer-forming properties and ultraviolet light emission intensity of the light-emitting layer 13.

(31) The thickness of the light-emitting layer 13 may be 2.0 m or less, and is preferably 1.8 m or less, more preferably 1.6 m or less, further preferably 1.4 m or less, and particularly preferably 1.2 m or less in view of obtaining a preferred amorphous layer and excellent ultraviolet light emission intensity. The thickness of the light-emitting layer 13 may be 0.05 m or more, and is preferably 0.1 m or more, more preferably 0.5 m or more, further preferably 0.8 m or more, and particularly preferably 1.0 m or more in view of excellent ultraviolet light emission intensity.

(32) The light-emitting layer 13 having the configuration as described above emits ultraviolet light by being excited by an electron beam. The ultraviolet light emitted from the light-emitting layer 13 has an emission peak in a deep ultraviolet region of 230 to 250 nm in one embodiment. On the other hand, light in a vacuum ultraviolet region of about 200 nm is also emitted from the light-emitting layer 13. The present inventors presume that ultraviolet light is generated over such a wide wavelength range due to the fact that the light-emitting layer 13 is an amorphous layer.

(33) Next, a method for manufacturing the ultraviolet light-generating target 11 will be described. FIG. 3 is a schematic diagram showing the configuration of a laser ablation apparatus 21 used in this manufacturing method. As shown in FIG. 3, the laser ablation apparatus 21 comprises a vacuum container 22, a sample placement stage 23 disposed on the bottom surface of the vacuum container 22, a rotating holder 24 disposed in the upper portion of the vacuum container 22 (above the sample placement stage 23), a heater 25 disposed further above the rotating holder 24, a laser introduction port 26 that externally introduces a laser beam B, and a gas introduction port 27 that externally introduces a gas such as oxygen gas.

(34) A raw material 28 is placed on the sample placement stage 23. The rotating holder 24 supports the substrate 12 disposed above the raw material 28. Specifically, the rotating holder 24 holds the substrate 12 in such a way as to be rotatable around an axis A connecting the raw material 28 and the substrate 12, with one surface of the substrate 12 exposed opposite to the raw material 28.

(35) In this manufacturing method, first, Sc:Al.sub.2O.sub.3 is vapor-deposited on the substrate 12 to form an amorphous layer (first step). Specifically, first, as the raw material 28, a ceramic target of Al.sub.2O.sub.3 doped with a predetermined concentration of Sc is made. Next, the substrate 12 is provided and mounted on the rotating holder 24 of the laser ablation apparatus 21, and the raw material 28 made is placed on the sample placement stage 23. Then, the inside of the vacuum container 22 is evacuated, and the substrate 12 is heated to a predetermined temperature (for example, 800 C.) by the heater 25. Then, while oxygen gas is supplied to the inside of the vacuum container 22 from the gas introduction port 27, the laser beam (for example, a laser beam from a KrF excimer laser (wavelength 248 nm)) B is introduced from the laser introduction port 26 to irradiate the raw material 28 with the laser beam B. Thus, the raw material 28 evaporates in response to the laser beam B and scatters inside the vacuum container 22. Some of this scattering raw material 28 adheres to one exposed surface of the substrate 12, and an amorphous layer of Sc:Al.sub.2O.sub.3 is formed (ablation layer formation).

(36) The time during which Sc:Al.sub.2O.sub.3 is vapor-deposited in the first step is appropriately adjusted so that the amorphous layer reaches the desired thickness. The thickness of the amorphous layer may be set at 2.0 m or less, and is preferably set at 1.8 m or less, more preferably 1.6 m or less, further preferably 1.4 m or less, and particularly preferably 1.2 m or less in view of obtaining preferred amorphous layer and the excellent ultraviolet light emission intensity of the light-emitting layer 13. The thickness of the amorphous may be set at 0.05 m or more, and is preferably set at 0.1 m or more, more preferably 0.5 m or more, further preferably 0.8 m or more, and particularly preferably 1.0 m or more in view of the excellent ultraviolet light emission intensity of the light-emitting layer 13.

(37) Next, the amorphous layer of Sc:Al.sub.2O.sub.3 formed on one surface of the substrate 12 is fired (second step). Specifically, the substrate 12 on which the amorphous layer is formed is removed from the laser ablation apparatus 21 and placed into a firing apparatus. Then, by setting the temperature in the firing apparatus, for example, at a temperature higher than 1000 C., and maintaining the temperature for a predetermined time, the amorphous layer on the substrate 12 is fired (annealed). Thus, the light-emitting layer 13 is formed on one surface of the substrate 12.

(38) The firing atmosphere in the second step may be, for example, a vacuum or the air. The firing temperature in the second step may be, for example, 1800 C. or less, and is preferably 1700 C. or less, more preferably 1600 C. or less, further preferably 1500 C. or less, and particularly preferably 1400 C. or less in view of the excellent layer-forming properties and ultraviolet light emission intensity of the light-emitting layer 13. The firing temperature in the second step may be, for example, 1200 C. or more. The firing time in the second step may be, for example, 1 to 5 hours.

(39) Next, the ultraviolet light-reflecting layer 14 is formed on the light-emitting layer 13, for example, by vapor deposition (third step). The method for vapor-depositing the ultraviolet light-reflecting layer 14 may be a known method. The ultraviolet light-generating target 11 as shown in FIG. 2 is obtained by the above first to third steps.

EXAMPLES

(40) The present invention will be more specifically described below based on Examples, but the present invention is not limited to the following Examples.

Examples 1 to 6

(41) In Examples 1 to 6, as a raw material 28, a ceramic target of Al.sub.2O.sub.3 doped with 2.0 atomic % of Sc was made. This ceramic target was placed on the sample placement stage 23 of a laser ablation apparatus 21, and a substrate (sapphire substrate) 12 having a diameter of 2 in. was mounted on a rotating holder 24. The distance between the ceramic target and the sapphire substrate was 150 mm. Then, the inside of a vacuum container 22 was evacuated, and the sapphire substrate was heated to 500 C. Then, while oxygen gas was supplied to the inside of the vacuum container 22, the ceramic target was irradiated with a laser beam B to form an amorphous layer of Sc:Al.sub.2O.sub.3 on the sapphire substrate. At this time, a KrF excimer laser (150 mJ, 40 Hz) was used as the laser light source of the laser beam B. The laser beam B irradiation time in Examples 1 to 6 was set as shown in Table 1.

(42) Then, the sapphire substrate on which the amorphous layer was formed was placed into a firing apparatus and heated in a vacuum (10.sup.2 Pa) at 1500 C. for 2 hours to obtain a light-emitting layer on the sapphire substrate. For the light-emitting layer of each of ultraviolet light-generating targets obtained in Examples 1 to 6, In-plane X-ray diffraction (XRD) measurement was performed. The results are shown in FIG. 4A. It is seen that for all of Examples 1 to 6, the light-emitting layer is an amorphous layer.

(43) A 50 nm aluminum layer was formed on the light-emitting layer to make an ultraviolet light-generating target. Each of the ultraviolet light-generating targets obtained in Examples 1 to 6 was irradiated with an electron beam with acceleration voltage: 10 kV, amount of current: 200 A, and diameter: 2 mm, and the emission spectrum and the emission intensity at this time were measured. The emission spectrum measurement results are shown in FIG. 4B. The emission intensity measurement results are shown in Table 1.

(44) TABLE-US-00001 TABLE 1 Laser Thickness beam of light- Emission XRD Emission irradiation emitting intensity pattern spectrum time (min) layer (nm) (mW) (FIG. 4A) (FIG. 4B) Example 1 5 98 7.8 G11 G21 Example 2 15 237 10.0 G12 G22 Example 3 30 460 13.2 G13 G23 Example 4 45 742 14.5 G14 G24 Example 5 60 863 14.8 G15 G25 Example 6 90 1663 16.0 G16 G26

Examples 7 to 22

(45) The making and evaluation of a light-emitting layer and an ultraviolet light-generating target were performed as in Example 6 except that the doping concentration of Sc in the ceramic target that was the raw material 28 and the firing temperature were changed as shown in Table 2. The measurement results of In-plane X-ray diffraction (XRD) measurement in Examples 8, 11 to 14, 16, and 20 are shown in FIGS. 5 and 6, the emission spectrum measurement results in Examples 7 to 22 are shown in FIGS. 7A, 8A, 9A, and 10A, and the emission intensity measurement results in Examples 7 to 22 are shown in FIGS. 7B, 8B, 9B, and 10B. For Examples 8, 12, 16, and 20, the surfaces of the ultraviolet light-generating targets on the aluminum layer sides were observed by an FE-SEM. Their photographs are shown in FIG. 11A (Example 8), FIG. 11B (Example 12), FIG. 11C (Example 16), and FIG. 11D (Example 20) respectively.

(46) TABLE-US-00002 TABLE 2 Emission Emission Doping spectrum intensity concentra- Firing XRD (FIGS. 7A, (FIGS. 7B, tion temper- pattern 8A, 9A, 8B, 9B, of Sc ature (FIGS. 5 and and (atomic %) ( C.) and 6) 10A) 10B) Example 7 0.5 1500 G51 G61 Example 8 0.5 1600 G41 G52 G62 Example 9 0.5 1700 G53 G63 Example 10 0.5 1800 G54 G64 Example 11 1.0 1500 G31 G71 G81 Example 12 1.0 1600 G32, G42 G72 G82 Example 13 1.0 1700 G33 G73 G83 Example 14 1.0 1800 G34 G74 G84 Example 15 2.0 1500 G91 G101 Example 16 2.0 1600 G43 G92 G102 Example 17 2.0 1700 G93 G103 Example 18 2.0 1800 G94 G104 Example 19 4.0 1500 G111 G121 Example 20 4.0 1600 G44 G112 G122 Example 21 4.0 1700 G113 G123 Example 22 4.0 1800 G114 G124

(47) For Example 16 (G43) and Example 20 (G44), the orientation of Al.sub.2O.sub.3 (.circle-solid. in FIG. 6) and the orientation of (Sc,Al).sub.2O.sub.3 (.square-solid. in FIG. 6) were observed. The peak intensity from the orientation of (Sc,Al).sub.2O.sub.3 in Example 16 (G43) was 53 cps. The peak intensity from the orientation of Al.sub.2O.sub.3 in Example 20 (G44) was 92 cps, and the peak intensity from the orientation of (Sc,Al).sub.2O.sub.3 was 103 cps at around 33.6 ((042) plane) and 37 cps at around 56.4 ((0210) plane).

(48) From FIGS. 7A, 8A, 9A, and 10A, it is seen that for all of Examples 7 to 22, it is seen that ultraviolet light can be generated over a wide wavelength range. From FIGS. 7B, 8B, 9B, and 10B, it is seen that among these Examples, the emission intensity is maximum when the doping concentration of Sc is 1.0 atomic %.

Examples 23 to 38

(49) The making and evaluation of a light-emitting layer and an ultraviolet light-generating target were performed as in Example 1 except that the laser beam B irradiation time and the firing temperature were changed as shown in Table 3, and the firing atmosphere was changed to the air. The measurement results of In-plane X-ray diffraction (XRD) measurement in Examples 29 to 38 are shown in FIGS. 13A and 14A, and the emission spectrum measurement results in Examples 23 to 38 are shown in FIGS. 12, 13B, and 14B respectively. For Examples 27, 33, and 38, the surfaces of the ultraviolet light-generating targets on the aluminum layer sides were observed by an FE-SEM. Their photographs are shown in FIG. 15A (Example 27), FIG. 15B (Example 33), and FIG. 15C (Example 38) respectively.

(50) TABLE-US-00003 TABLE 3 Emission Laser Thickness XRD spectrum beam of light- Emission pattern (FIGS. 12, irradiation emitting intensity FIGS. 13A 13B, and time (min) layer (nm) (mW) and 14A) 14B) Example 23 5 80 9.0 G131 Example 24 15 210 10.0 G132 Example 25 30 440 12.5 G133 Example 26 45 660 14.6 G134 Example 27 60 1100 14.8 G135 Example 28 90 1400 G136 Example 29 5 90 6.6 G141 G151 Example 30 15 220 10.9 G142 G152 Example 31 30 430 13.0 G143 G153 Example 32 45 650 13.7 G144 G154 Example 33 60 1100 15.6 G145 G155 Example 34 5 80 11.2 G161 G171 Example 35 15 210 G162 G172 Example 36 30 420 12.2 G163 G173 Example 37 45 680 12.9 G164 G174 Example 38 60 1200 14.3 G165 G175

(51) From FIGS. 12, 13B, and 14B, it is seen that for all of Examples 23 to 38, ultraviolet light can be generated over a wide wavelength range.

DESCRIPTION OF SYMBOLS

(52) 1 . . . electron beam-excited ultraviolet light source, 3 . . . electron source, 11 . . . ultraviolet light-generating target, 12 . . . substrate, 13 . . . light-emitting layer.