EMITTER AND DEVICE PROVIDED WITH SAME

Abstract

An emitter according to the present disclosure includes: first and second heaters generating heat by energization; an electron source comprising a first material emitting an electron by being heated by the first and second heaters; and an intermediate member interposed between the electron source, and the first and second heaters, the intermediate member comprising a second material lower in thermal conductivity than the first material.

Claims

1. An emitter comprising: first and second heaters generating heat by energization; an electron source comprising a first material emitting an electron by being heated by the first and second heaters; and an intermediate member interposed between the electron source, and the first and second heaters, the intermediate member comprising a second material lower in thermal conductivity than the first material.

2. The emitter according to claim 1, wherein a length of a shortest path of the intermediate member passing from the heater to the electron source is 100 μm or more.

3. The emitter according to claim 1, wherein an electrical resistivity value of the intermediate member is 300 μΩ.Math.m or less, and an electrical resistivity value of the heater is 500 μΩ.Math.m or more.

4. The emitter according to claim 1, wherein the second material is at least one material selected from carbon, boron carbide, boron nitride, and rhenium.

5. The emitter according to claim 1, wherein the second material is glassy carbon.

6. The emitter according to claim 1, wherein the first material is a material selected from a group consisting of a rare earth boride, a refractory metal and an oxide, a carbide, and a nitride thereof, and a precious metal-rare earth alloy.

7. The emitter according to claim 1, wherein the intermediate member covers a surface of the electron source other than an electron emission surface.

8. A device comprising the emitter according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0013] FIG. 1A is a longitudinal sectional view schematically illustrating a first embodiment of an emitter according to the present disclosure, and FIG. 1B is a transverse sectional view of the emitter illustrated in FIG. 1A.

[0014] FIG. 2A is a longitudinal sectional view schematically illustrating a second embodiment of the emitter according to the present disclosure, and FIG. 2B is a transverse sectional view of the emitter illustrated in FIG. 2A.

[0015] FIG. 3A is a longitudinal sectional view schematically illustrating a third embodiment of the emitter according to the present disclosure, and FIG. 3B is a top view of the emitter illustrated in FIG. 3A.

[0016] FIG. 4 is a thermographic camera image showing the upper surface temperature of an emitter according to an example.

[0017] FIG. 5A is a longitudinal sectional view schematically illustrating an emitter according to a comparative example, and FIG. 5B is a longitudinal sectional view schematically illustrating a state where a material (lanthanum boride) configuring an electron source is deposited in the vicinity of the heater of the emitter illustrated in FIG. 5A.

DESCRIPTION OF EMBODIMENTS

[0018] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description, the same reference numerals will be used for the same or functionally identical elements with redundant description omitted. It should be noted that the present invention is not limited to the following embodiments.

First Embodiment

[0019] FIG. 1A is a longitudinal sectional view schematically illustrating an emitter according to a first embodiment, and FIG. 1B is a transverse sectional view of the emitter illustrated in FIG. 1A. An emitter 10 illustrated in these drawings includes an electron source 1, a pair of heaters 5a and 5b (first and second heaters) generating heat by energization, intermediate members 2a and 2b disposed between the electron source 1 and the heaters 5a and 5b, and a pair of conductive posts 7a and 7b disposed so as to sandwich these configurations. The electron source 1 is made of a material (first material) emitting electrons by being heated. The intermediate members 2a and 2b are made of a material (second material) lower in thermal conductivity than the material configuring the electron source 1. The heaters 5a and 5b are for heating the electron source 1. The pair of conductive posts 7a and 7b are for holding the electron source 1 and so on and energizing the heaters 5a and 5b. The emitter 10 is provided in, for example, an electron microscope, semiconductor manufacturing equipment, inspection equipment, or processing equipment. Each configuration of the emitter 10 will be described below.

[0020] (Electron Source)

[0021] The electron source 1 is made of the first material (electron emission material) having electron emission properties. A tip portion 1a of the electron source 1 is molded in a conical shape, and electrons are emitted from this tip portion 1a. In the present embodiment, the electron source 1 is exposed to each of side surfaces 10a and 10b of the emitter 10.

[0022] In the present embodiment, the part of the electron source 1 other than the tip portion 1a has a quadrangular prism shape (see FIGS. 1A and 1B). The length of the electron source 1 is, for example, 0.1 to 2 mm, and the length may be 0.2 to 1.5 mm or 0.2 to 1 mm. By the length being 0.1 mm or more, handling tends to be satisfactory. By the length being 2 mm or less, heating tends to be uniform. The quadrangular prism part of the electron source 1 has a substantially square sectional shape. The length of the side is, for example, 0.02 to 1 mm, and the length may be 0.05 to 0.5 mm or 0.05 to 0.15 mm.

[0023] Examples of the electron emission material include rare earth borides such as lanthanum boride (LaB.sub.6) and cerium boride (CeB.sub.6); refractory metals such as tungsten, tantalum, and hafnium and oxides, carbides, and nitrides thereof; and precious metal-rare earth alloys such as iridium cerium.

[0024] From the viewpoint of electron emission properties, strength, and workability, the electron emission material configuring the electron source 1 is preferably a rare earth boride. In a case where the electron source 1 is made of a rare earth boride, the electron source 1 is preferably a single crystal processed such that the <100> orientation of easy electron emission matches the electron emission direction. The electron source 1 can be given a desired shape by, for example, electric discharge machining. The side surface of the electron source 1 is preferably a (100) crystal plane because the evaporation rate is considered to be slow.

[0025] The material configuring the electron source 1 is higher in thermal conductivity than the material configuring the intermediate members 2a and 2b. The thermal conductivity of the material configuring the electron source 1 is preferably 5 W/m.Math.K or more, more preferably 10 W/m.Math.K or more. By the thermal conductivity of this material being 5 W/m.Math.K or more, the entire electron source 1 tends to be sufficiently uniformly heated by heat from the heaters 5a and 5b. It should be noted that the upper limit value of the thermal conductivity of this material is, for example, 200 W/m.Math.K. The thermal conductivities of a plurality of materials are as follows. [0026] Lanthanum boride (LaB.sub.6): 60 W/m.Math.K [0027] Tungsten: 177 W/m.Math.K

[0028] A thermal conductivity value T.sub.E of the electron source 1 is preferably sufficiently larger than a thermal conductivity value T.sub.I of the intermediate members 2a and 2b. The ratio (T.sub.E/T.sub.I) of the thermal conductivity value T.sub.E of the electron source 1 to the thermal conductivity value T.sub.I of the intermediate members 2a and 2b is, for example, 7 to 13, and the ratio may be 8 to 12 or 10 to 11. By this ratio being within these ranges, the temperature of the heaters 5a and 5b at a time of energization can be moderately increased. The temperature of the heaters 5a and 5b at a time of energization can be made higher than the temperature of the electron source 1 by, for example, approximately 150 to 250° C. As a result, it is possible to suppress deposition of the material configuring the electron source 1 in the vicinity of the heaters 5a and 5b.

[0029] (Intermediate Member)

[0030] The intermediate members 2a and 2b are disposed so as to be in contact with and cover a pair of surfaces 1b and 1c of the electron source 1 (see FIG. 1B). The intermediate members 2a and 2b are exposed to each of the side surfaces 10a and 10b of the emitter 10. It is preferable that the length of the shortest path of the intermediate member passing from the heater to the electron source is 100 μm or more. In other words, in the present embodiment, the thickness of the intermediate member 2a (separation distance between the electron source 1 and the heater 5a) is preferably 100 μm or more, and the thickness may be 100 to 1000 μm or 300 to 800 μm.

[0031] The intermediate members 2a and 2b are made of a material (second material) lower in thermal conductivity than the material configuring the electron source 1. The thermal conductivity of the material configuring the intermediate members 2a and 2b is, for example, 100 W/mK or less, preferably 1 to 100 W/mK and more preferably 1 to 60 W/m.Math.K. The lower limit value of this value may be 2 W/m.Math.K or 3 W/m.Math.K. The upper limit value of this value may be 45 W/m.Math.K or 40 W/m.Math.K. By the thermal conductivity of this material being 1 W/m.Math.K or more, heat from the heaters 5a and 5b tends to be sufficiently transmitted to the electron source 1. On the other hand, by the thermal conductivity of this material being 100 W/m.Math.K or less, there is a tendency that a sufficient temperature difference can be caused between the heaters 5a and 5b and the electron source 1.

[0032] The material configuring the intermediate members 2a and 2b preferably contains a refractory metal or a carbide thereof and preferably contains at least one of metal tantalum, metal titanium, metal zirconium, metal tungsten, metal molybdenum, metal rhenium, tantalum carbide, titanium carbide, and zirconium carbide. In addition, this material may contain at least one of boron carbide and graphite (carbon material) and may contain at least one of niobium, hafnium, and vanadium. Glassy carbon (such as Glassy Carbon (product name, manufactured by Reiho Manufacturing Co., Ltd.)) may be used as this material. Boron nitride may be used as this material. The thermal conductivities of a plurality of materials are as follows. [0033] Metal rhenium: 48 W/m.Math.K [0034] Boron carbide: 35 W/m.Math.K [0035] Graphite: 80 to 250 W/m.Math.K [0036] Glassy carbon: 5.8 W/m.Math.K

[0037] The material configuring the intermediate members 2a and 2b is electrically conductive. From the viewpoint of suppressing excessive heat generation of the intermediate members 2a and 2b attributable to energization, it is preferable that the material configuring the intermediate members 2a and 2b is lower in electrical resistivity than the material configuring the heaters 5a and 5b. The electrical resistivity of the material configuring the intermediate members 2a and 2b is preferably 300 μΩ.Math.m or less, more preferably 100 μΩ.Math.m or less.

[0038] By the electrical resistivity of this material being 300 μΩ.Math.m or less, excessive heat generation of the intermediate members 2a and 2b attributable to energization tends to be suppressible. It should be noted that the lower limit value of the electrical resistivity of this material is, for example, 0.1 μΩ.Math.m, and the value may be 0.3 μΩ.Math.m or 1.0 μΩ.Math.m. The electrical resistivities of a plurality of materials are as follows. [0039] Metal rhenium: 0.2 μΩ.Math.m [0040] Graphite: 5 to 15 μΩ.Math.m [0041] Glassy carbon: 42 μΩ.Math.m

[0042] (Heater)

[0043] The heaters 5a and 5b are made of a high-electrical resistivity material and generate heat by energization. The electrical resistivity of the material configuring the heaters 5a and 5b is preferably 500 to 1000 μΩ.Math.m, more preferably 600 to 900 μΩ.Math.m. By the electrical resistivity of this material being 500 μΩ.Math.m or more, the electron source 1 tends to be sufficiently heatable by energization. On the other hand, by the electrical resistivity of this material being 1000 μΩ.Math.m or less, sufficient energization tends to be possible. Examples of the material configuring the heaters 5a and 5b include pyrolytic graphite and hot-pressed carbon. It should be noted that the electrical resistivity (typical value) of pyrolytic graphite is 800 μΩ.Math.m.

[0044] An electrical resistivity value R.sub.H of the heaters 5a and 5b is preferably sufficiently larger than an electrical resistivity value R.sub.I of the intermediate members 2a and 2b. The ratio (R.sub.H/R.sub.I) of the electrical resistivity value R.sub.H of the heaters 5a and 5b to the electrical resistivity value R.sub.I of the intermediate members 2a and 2b is, for example, 12 to 20, and the ratio may be 13 to 19 or 14 to 18. By this ratio being 12 or more, the temperature of the heaters 5a and 5b at a time of energization can be sufficiently increased, and deposition of the material configuring the electron source 1 in the vicinity of the heaters 5a and 5b tends to be suppressible. On the other hand, by this ratio being 20 or less, there is a tendency that the loss of electric power for heating the heaters 5a and 5b can be reduced.

Second Embodiment

[0045] FIG. 2A is a longitudinal sectional view schematically illustrating an emitter according to a second embodiment, and FIG. 2B is a transverse sectional view of the emitter illustrated in FIG. 2A. An emitter 20 illustrated in these drawings differs from the emitter 10 according to the first embodiment in that the four side surfaces of the columnar portion of the electron source 1 are covered with an intermediate member 2. In other words, the intermediate member 2 is interposed between the electron source 1 and the heaters 5a and 5b in the present embodiment whereas the intermediate member 2a is interposed between the electron source 1 and the heater 5a and the intermediate member 2b is interposed between the electron source 1 and the heater 5b in the first embodiment. By the four side surfaces of the columnar portion of the electron source 1 being covered with the intermediate member 2, it is possible to, for example, suppress the diffusion of evaporated matter from the electron source and uniformly heat the electron source. It should be noted that the material of the intermediate member 2 may be the same as the material of the intermediate members 2a and 2b according to the first embodiment.

Third Embodiment

[0046] FIG. 3A is a longitudinal sectional view schematically illustrating an emitter according to a third embodiment, and FIG. 3B is a transverse sectional view of the emitter illustrated in FIG. 3A. In an emitter 30 illustrated in these drawings, an intermediate member 3 comprises a columnar portion 3a and a conical part 3b. An opening portion 4 is provided in the tip portion of the conical part 3b, and the electron source 1 is inserted in the opening portion 4. The surface of the tip of the electron source 1 is an electron emission surface 1f. It should be noted that the material of the intermediate member 3 may be the same as the material of the intermediate members 2a and 2b according to the first embodiment.

[0047] In the present embodiment, the electron source 1 has a quadrangular prism shape (see FIGS. 3A and 3B). The length of the electron source 1 is, for example, 0.1 to 1 mm, and the length may be 0.2 to 0.6 mm or 0.3 mm. By the length being 0.1 mm or more, handling tends to be satisfactory. By the length being 1 mm or less, cracking or the like tends to be less likely to occur. The electron source 1 has a substantially square sectional shape. The length of the side is, for example, 20 to 300 μm, and the length may be 50 to 150 μm or 100 μm.

[0048] In the present embodiment, the columnar portion 3a of the intermediate member 3 has a quadrangular prism shape (see FIGS. 3A and 3B). The columnar portion 3a has a substantially square sectional shape. The length of the side is, for example, 0.5 to 2 mm, and the length may be 0.6 to 1 mm or 0.7 to 0.9 mm.

[0049] By the surface of the electron source 1 other than the electron emission surface being covered with the intermediate member 3, electron emission from the surface other than the electron emission surface is suppressed. Although the tip of the electron source 1 may or may not protrude from the tip of the conical part 3b of the intermediate member 3, it is preferable that the tip of the electron source 1 does not protrude from the tip of the conical part 3b of the intermediate member 3. By the tip of the electron source 1 not protruding from the intermediate member 3, unnecessary electron emission, that is, lateral electron emission can be sufficiently suppressed. For example, in order to obtain electrons of a larger current, the tip portion of the electron source 1 is heated to a high temperature of approximately 1550° C. and a high electric field of several kV is applied to the electron source 1. When such a high electric field is applied, surplus electrons can be generated from the non-tip part of the electron source as well. Due to the space charge effect, this surplus electron may reduce the brightness of an electron beam from the tip part or cause unnecessary heating of a surrounding electrode component. In order to prevent this, only the surface of the tip of the electron source 1 is exposed, the other surface is covered with the intermediate member 3, and only a high-brightness electron beam can be obtained from the tip part. It should be noted that the tip of the electron source 1 may be recessed with respect to the tip of the conical part 3b of the intermediate member 3.

[0050] By covering the entire side surface of the electron source 1 with the intermediate member 3, there is also the effect of being capable of suppressing the occurrence of a phenomenon called microdischarge. In other words, in thermionic emission, electrons are emitted by heating an electron source to a high temperature. The resultant electron emission material evaporation results in adhesion to a surrounding electrode component and fibrous crystals called whiskers. Microdischarge results from charge accumulation in this whisker to result in electron beam destabilization and device performance decline. By covering the entire side surface of the electron source 1 with the intermediate member 3, the sublimated electron emission material is trapped in the intermediate member 3, the amount of adhesion to a surrounding electrode component can be reduced, and microdischarge can be made unlikely to occur. It should be noted that the intermediate member 3 covers the entire side surface of the electron source 1 without having a cut at a circumferential part. Since the intermediate member 3 is cut-less, lateral electron emission can be sufficiently suppressed.

[0051] The present invention is not limited to the embodiments of the present disclosure described in detail above. For example, although the electron source exemplified in the above embodiments has a columnar portion with a substantially square sectional shape, the sectional shape of the columnar portion may be substantially polygonal instead of being substantially square. For example, the shape may be substantially rectangular, substantially rhombic, substantially parallelogrammic, substantially triangular (for example, substantially equilateral-triangular), or substantially regular-hexagonal. The sectional shape of the opening portion 4 in the third embodiment may not match the sectional shape of the electron source. For example, the shape may be substantially circular, substantially rhombic, substantially parallelogrammic, substantially triangular (for example, substantially equilateral-triangular), or substantially regular-hexagonal.

EXAMPLES

[0052] Hereinafter, the present disclosure will be described based on an example and a comparative example. It should be noted that the present invention is not limited to the following examples.

EXAMPLE

[0053] Using the materials shown in Table 1, an emitter having the same configuration as the emitter illustrated in FIG. 1 was produced. The length of the electron source was approximately 0.3 mm, and the length of one side of the columnar portion was approximately 100 μm. The thickness of the intermediate member (separation distance between the electron source and the heater) was set to 300 μm.

TABLE-US-00001 TABLE 1 Intermediate Electron source member Heater Material Lanthanum Glassy Pyrolytic boride (LaB.sub.6) carbon graphite Thermal conductivity 60 5.8 5 to 10 [W/m .Math. K] Electrical resistivity 0.08 42 791 [μΩ .Math. m]

[0054] The temperature of the heater was 1768° C. when the emitter was energized under constant current control such that the temperature of the electron source was 1550° C. FIG. 4 is a thermographic camera image showing the upper surface temperature of the emitter according to the example. According to the present inventors' examinations, it is preferable from the viewpoint of lanthanum boride deposition prevention that the temperature of the heater is 1700 to 1800° C. when the electron source is heated to 1550° C.

COMPARATIVE EXAMPLE

[0055] An emitter identical in configuration to the example except that no intermediate member was disposed between the electron source and the heater was produced (see FIG. 5A). The temperature of the heater was 1634° C. when the emitter was energized under constant current control such that the temperature of the electron source was 1550° C.

INDUSTRIAL APPLICABILITY

[0056] Provided according to the present disclosure are an emitter capable of maintaining high reliability even during long-term operation and a device provided with the same.

REFERENCE SIGNS LIST

[0057] 1: electron source, 1f: electron emission surface, 2, 2a, 2b, 3: intermediate member, 5a, 5b: heater, 10, 20, 30: emitter.