Patent Description:
An emitter provided with an electron source is used, for example, in an electron microscope and a semiconductor inspection device. An emitter disclosed in Patent Literature <NUM> has a first member having an electron emission characteristic and a second member covering the first member, and a groove having a predetermined size is provided between the first member and the second member. An electron gun disclosed in Patent Literature <NUM> includes an electron gun cathode and a holder holding the electron gun cathode, the electron gun cathode has a quadrangular flat surface at a tip thereof, and a tip portion thereof is exposed and protrudes from the holder (see <FIG> of Patent Literature <NUM>). Patent Literature <NUM> relates to an electron gun cathode for emitting electrons by being heated and a and a holder configured to cover the bottom and side surfaces of the electron gun cathode, wherein the electron gun cathode has a tip portion that is exposed to protrude from the holder, and, with application of electric field to the tip portion, emits electrons from the tip portion toward a forward direction. Patent Literature <NUM> relates to a conical and tapered cathode supporting member which has a cylindrical recess formed along the central axis direction from the tip, and a square pole electron gun cathode inserted into the recess from the tip side, and a coagulated carbon powder adhesive.

An electron source is extremely minute. Paragraph [<NUM>] of Patent Literature <NUM> describes that a size of the electron gun cathode is <NUM>×<NUM>×<NUM>. A skilled technique is required to manufacture an electron source (electron gun) configured of such a minute component.

The present disclosure provides a method for manufacturing an electron source that is useful for efficiently manufacturing a minute electron source. In addition, the present disclosure provides an electron source and an emitter provided with the electron source, which can sufficiently prevent a member emitting electrons from coming off a member holding it. Further, the present disclosure provides a device provided with the emitter.

A method for manufacturing an electron source according to the present invention is defined in present claim <NUM>.

According to the above manufacturing method, by selecting the first member and the second member that match each other in size from among the plurality of members in the step (C) and using these to perform the step (D), as described above, the portion of the side surface of the columnar portion abuts the inner surface of the hole of the second member, and the columnar portion can be fixed to the second member. For this reason, loss of members can be sufficiently reduced in manufacturing the electron source. That is, it is possible to sufficiently reduce manufacturing defects caused by mismatching in size between the columnar portion and the hole. Such defects include, for example, the columnar portion of the first member not entering the hole of the second member, the columnar portion not abutting the inner surface of the hole thereby coming off the hole, and the like.

The cross-sectional shapes of the columnar portions of the first members are not limited to the substantially quadrangular shape and may be substantially equilateral triangular shapes, as defined in present claim <NUM>. In this case, in the above step (C), a set of the first member and the second member that satisfy the following condition may be selected from the plurality of first members and the plurality of second members.

A diameter R<NUM> of a circumscribed circle of a substantial equilateral triangle is larger than a diameter R<NUM> of the hole and when the substantial equilateral triangle is disposed in a circle having the same diameter as the diameter R<NUM> of the hole, at least two corners of the substantial equilateral triangle come into contact with the circle.

An electron source according to the present invention is defined in present claim <NUM>.

According to the above electron source, it is possible to sufficiently inhibit the member (columnar portion) emitting electrons from coming off the member (tubular portion) holding it. A flat surface is preferably formed at a tip portion of the electron source by an electron emission surface of the columnar portion and an end face of the tubular portion. By forming such a flat surface, it is possible to sufficiently inhibit side emission of electrons.

An emitter is described which may be provided with the electron source. A device is described which may be provided with the emitter. Examples of the device provided with the emitter include, for example, an electron microscope, a semiconductor manufacturing device, and an inspection device.

According to the present disclosure, a method for manufacturing an electron source that is useful for efficiently manufacturing a minute electron source is provided. The resulting electron source and emitter provided with the electron source can sufficiently inhibit a member emitting electrons from coming off a member holding it. A device may be provided with the emitter.

In the following description, the same reference numerals will be used for the same elements or elements having the same functions, and repeated description thereof will be omitted. Also, the present invention is not limited to the following embodiments.

<FIG> is a cross-sectional view schematically showing an electron source according to the present embodiment. <FIG> is a plan view showing a configuration of a tip of the electron source <NUM> shown in <FIG>. The electron source <NUM> is provided with a columnar portion <NUM> and an electron emission limiting member <NUM> disposed to surround the columnar portion <NUM>. The columnar portion <NUM> is made of a first material (an electron emission material) having an electron emission characteristic. An end face 1a of the columnar portion <NUM> is an electron emission surface, and a normal line thereof is in an electron emission direction. On the other hand, the electron emission limiting member <NUM> is made of a second material (an electron emission limiting material) having a larger work function than the first material. The electron emission limiting member <NUM> has a tubular portion 2a in which a hole <NUM> is formed and a base end portion 2b in which the hole <NUM> is not formed. The base end portion 2b forms a bottom 3a of the hole <NUM>. The hole <NUM> extends in a direction from an end face 2c toward the other end face 2d of the electron emission limiting member <NUM>. In the present embodiment, an opening area of the hole <NUM> is constant from the end face 2c toward the end face 2d.

As shown in <FIG>, the columnar portion <NUM> has a cross-sectional shape dissimilar to a cross-sectional shape of the hole <NUM> of the electron emission limiting member <NUM> and is fixed to the electron emission limiting member <NUM> in an abutting engagement with an inner surface of the hole <NUM>. In the present embodiment, in a cross-section orthogonal to a longitudinal direction of the columnar portion <NUM>, a shape of the columnar portion <NUM> is substantially square, and a shape of the hole <NUM> is substantially circular. In the present embodiment, a strength of the columnar portion <NUM> is higher than a strength of the tubular portion 2a, and a portion of a side surface of the columnar portion <NUM> is fixed to the tubular portion 2a in a biting engagement therewith. According to the electron source <NUM>, it is possible to sufficiently inhibit the columnar portion <NUM> from coming off from the electron emission limiting member <NUM>.

A flat surface is formed on a tip face of the electron source <NUM> by the end face 1a (electron emission surface) of the columnar portion <NUM> and the end face 2c of the electron emission limiting member <NUM>. Further, the entire side surface of the columnar portion <NUM> is covered with the tubular portion 2a. Since the columnar portion <NUM> does not protrude from the tubular portion 2a in this way, it is possible to sufficiently inhibit unnecessary emission of electrons, that is, side emission of electrons. For example, in order to obtain electrons with a larger current, a tip portion of the electron source <NUM> is heated to a high temperature of about <NUM> and a high electric field of several kV is applied to the electron source <NUM>. When such a high electric field is applied, surplus electrons may be generated from portions other than the tip portion of the electron source. Due to the space-charge effect, the surplus electrons may reduce brightness of an electron beam from the tip portion and may cause unnecessary heating of peripheral electrode components. In order to prevent this, by exposing only the electron emission portion (end face 1a of the columnar portion <NUM>) of the electron source <NUM> and covering other surfaces with the tubular portion 2a, only a high-brightness electron beam from the tip portion can be obtained. Also, the term "flat surface" used herein means that a difference in level between the end face 1a and the end face 2c is less than <NUM>. As long as this difference in level is less than <NUM>, the columnar portion <NUM> may protrude from the tubular portion 2a, or the end face 1a may be recessed from the end face 2c. This difference in level may be less than <NUM> or less than <NUM>.

By covering the entire side surfaces of the columnar portion <NUM> with the tubular portion 2a, the effect that occurrence of a phenomenon called a micro-discharge can be inhibited is also achieved. That is, in thermionic emission, electrons are emitted by heating an electron source to a high temperature. Along with this, when an electron emission material evaporates, it adheres to peripheral electrode components and forms fibrous crystals called whiskers. When charges are accumulated in the whiskers, micro-discharges are caused. The micro-discharges destabilize an electron beam and cause degradation of device performance. By covering the entire side surfaces of the columnar portion <NUM> with the tubular portion 2a, the sublimated electron emission material is trapped in the tubular portion 2a, which can reduce an amount of adhesion thereof to the peripheral electrode components and make the micro-discharges less likely to occur. Also, the tubular portion 2a covers the entire side surfaces of the columnar portion <NUM> without a gap partially in a circumferential direction thereof. Since the tubular portion 2a does not have any gap, side emission of electrons can be sufficiently inhibited.

The columnar portion <NUM> is made of an electron emission material (a first material). An electron emission material is a material that emits electrons when heated. An electron emission material has a lower work function than an electron emission limiting material and a higher strength than an electron emission limiting material. Examples of the electron emission material may include rare earth borides such as lanthanum boride (LaB<NUM>) and cerium boride (CeB<NUM>); high melting point metals such as tungsten, tantalum, hafnium and their oxides, carbides and nitrides; and noble metal-rare earth alloys such as iridium cerium. Work functions of these materials are as follows:.

From the viewpoint of the electron emission characteristic, strength, and workability, the electron emission material forming the columnar portion <NUM> is preferably a rare earth boride. In a case in which the columnar portion <NUM> is made of a rare earth boride, the columnar portion <NUM> is preferably a single crystal machined such that the <<NUM>> orientation, which has a low work function and is likely to emit electrons, coincides with the electron emission direction. The columnar portion <NUM> can be formed into a desired shape by electrical discharge machining or the like. Since it is considered that an evaporation rate is slow on the side surfaces of the columnar portion <NUM>, they are preferably (<NUM>) crystal planes.

In the present embodiment, a shape of the columnar portion <NUM> is a quadrangular prism (see <FIG> and <FIG>). A length of the columnar portion <NUM> is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and still more preferably about <NUM>. When the length is <NUM> or more, handling tends to be good, and when the length is <NUM> or less, cracks and the like tend to be less likely to occur. A cross-sectional shape of the columnar portion <NUM> is substantially square. Lengths of its sides are preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and still more preferably about <NUM>.

The electron emission limiting member <NUM> is made of an electron emission limiting material. An electron emission limiting material has a higher work function than an electron emission material. By covering the side surfaces of the columnar portion <NUM> with the electron emission limiting member <NUM>, electron emission from the side surfaces of the columnar portion <NUM> is inhibited.

A difference (ΔW=W<NUM>-W<NUM>) between a work function W2 of the electron emission limiting member <NUM> and a work function W1 of the columnar portion <NUM> is preferably <NUM> eV or more, more preferably <NUM> eV or more, and still more preferably <NUM> eV or more.

Glassy carbon (for example, Glassy Carbon (trade name, manufactured by Reiho Manufacturing Co. )) is used for the electron emission limiting material.

In the present embodiment, as described above, the strength of the electron emission limiting material is lower than that of the electron emission material. The strengths of both materials can be evaluated, for example, by Vickers hardness. From the viewpoint of proper strength and workability, the material constituting the electron emission limiting member <NUM> preferably has a Vickers hardness of about <NUM> HV to <NUM> HV. Glassy carbon (having a Vickers hardness of about <NUM> HV) is suitable for the electron emission limiting material in that it has a moderate strength. A tip portion 2e (a portion of the tubular portion 2a) of the electron emission limiting member <NUM> is machined into a tapered shape, and the remaining portions (the remaining portion of the tubular portion 2a, and the base end portion 2b) are machined into a quadrangular prism shape. By machining the tip portion 2e of the electron emission limiting member <NUM> into a tapered shape, the effect that an electric field can be easily concentrated and electron emission efficiency can be improved is achieved. Also, a support member (not shown) may be provided around the electron emission limiting member <NUM>.

The electron emission material and the electron emission limiting material may be appropriately selected, for example, from the viewpoint of their work functions and strengths and used in combination. Suitable examples of the electron emission material include lanthanum boride (LaB<NUM>), cerium boride (CeB<NUM>), hafnium carbide, and iridium cerium. The electron emission limiting material is a glassy carbon (glass-like carbon).

Next, a method for manufacturing the electron source <NUM> will be described. The electron source <NUM> is manufactured through the following steps.

In the above step (C), a set of the first member <NUM> and the second member <NUM> that satisfy the following condition is selected from the plurality of first members <NUM> and the plurality of second members <NUM>. In the above step (D), by pressing the selected first member <NUM> into the hole <NUM> of the selected second member <NUM>, a portion of a side surface of the first member <NUM> abuts the inner surface of the hole <NUM> of the second member <NUM>, thereby fixing the first member <NUM> to the second member <NUM>. <Condition><MAT>.

Since the strength of the first member <NUM> is higher than the strength of the second member <NUM>, by pressing the first member <NUM> into the hole <NUM> of the second member <NUM>, a portion of the side surface of the first member <NUM> scrapes the inner surface of the hole <NUM> and bites into the second member <NUM>, whereby the first member <NUM> is fixed to the second member <NUM> (see <FIG>). In addition, the strength of the first member <NUM> and the second member <NUM> can be evaluated by Vickers strength, for example.

The first member <NUM> shown in <FIG> is made of an electron emission material. The first member <NUM> can be obtained by electrical discharge machining or the like from a block of the electron emission material. The first member <NUM> is a portion serving as the columnar portion <NUM> of the electron source <NUM>.

The second member <NUM> shown <FIG> is made of an electron emission limiting material. The second member <NUM> may be obtained by electrical discharge machining or the like from a block of the electron emission limiting material. The hole <NUM> of the second member <NUM> is a portion serving as the hole <NUM> of the electron source <NUM>. An opening area of the hole <NUM> is constant from the end face 12a toward the end face 12b.

<FIG> is a cross-sectional view schematically showing a state in which the first member <NUM> is pressed into the hole <NUM> of the second member <NUM>. <FIG> is a plan view showing a relationship in size between the first member <NUM> and the hole <NUM> of the second member <NUM>. Parts of the side surfaces of the first member <NUM> (four corners 11c) bite into the second member <NUM>. Although <FIG> illustrates a state in which the first member <NUM> reaches deep into the hole <NUM>, the first member <NUM> does not have to reach deep into the hole <NUM>.

In the step (C), the second member <NUM> having the first member <NUM> and the hole <NUM> that satisfy the following condition are selected. <Condition> <MAT>.

In the inequality (<NUM>), L<NUM> indicates a length of a diagonal of a cross-section (substantially square) of the first member <NUM>, and R<NUM> indicates a diameter of the hole <NUM>.

A value of L<NUM>/R<NUM> more preferably satisfies the inequality (1a), further preferably satisfies the inequality (1b), and particularly preferably satisfies the inequality (1c). <MAT> <MAT> <MAT>.

A structure 15A shown in <FIG> was obtained by cutting out the portion surrounded by the quadrangular-shaped broken line in <FIG>. In the structure 15A, the first member <NUM> protrudes from the end face 12a. by grounding a protruding portion 11a of the first member <NUM> with, for example, abrasive paper, the end face 1a (electron emission surface) is formed, and an outer side of the second member <NUM> is machined into a quadrangular prism shape. Thus, a quadrangular prism body 15B shown in <FIG> is obtained. The electron source <NUM> shown in <FIG> is obtained by tapering one end portion of the quadrangular prism body 15B. Also, an order of machining is not limited thereto, and for example, from the state shown in <FIG>, first, the protruding portion 11a may be cut to form a flat surface, and then the portion surrounded by the quadrangular-shaped broken line in <FIG> may be cut out. In addition, the shape of the second member <NUM> after machining is not limited to a quadrangular prism shape, and for example, in a substantially cylindrical electron source, only the portion sandwiched between heaters may be flattened (see <FIG>).

According to the above manufacturing method, by selecting the first member <NUM> and the second member <NUM> that match each other in size from the plurality of members in the step (C) and performing the step (D) using these, loss of these members can be sufficiently reduced. That is, it is possible to sufficiently reduce manufacturing defects caused by mismatching in size between the first member <NUM> and the hole <NUM>. Such defects include, for example, the first member <NUM> not entering the hole <NUM>, the first member <NUM> not abutting the inner surface of the hole <NUM> thereby coming off the hole <NUM>, and the like.

According to the above manufacturing method, by going through the step of cutting the protruding portion 11a of the first member <NUM>, the flat surface is formed at the tip portion of the electron source <NUM> by the end face 1a (electron emission surface) of the columnar portion <NUM> and the end face 2c of the tubular portion 2a. Since the columnar portion <NUM> does not protrude from the tubular portion 2a, as described above, unnecessary emission of electrons, that is, side emission of electrons can be sufficiently inhibited, and micro-discharges caused by generation of whiskers can also be inhibited.

<FIG> is a cross-sectional view schematically showing an example of an emitter. An emitter <NUM> shown in <FIG> is provided with the electron source <NUM>, a carbon heater <NUM> disposed around the electron source <NUM>, electrode pins 17a and 17b, an insulator <NUM>, and a suppressor <NUM>. The carbon heater <NUM> is for heating the electron source <NUM>. The electrode pins 17a and 17b are for energizing the carbon heater <NUM>. The suppressor <NUM> is for inhibiting a surplus current. Also, the electron source <NUM> may be configured to be heated by means other than the carbon heater <NUM>.

Examples of devices provided with the emitter <NUM> include an electron microscope, a semiconductor manufacturing device, an inspection device, and a machining device.

Although the embodiment of the present disclosure has been described in detail above, the present invention is not limited to the above embodiment. For example, in the above embodiment, the columnar portion <NUM> having a substantially square cross-sectional shape has been illustrated (see <FIG> and <FIG>), but the cross-sectional shape of the columnar portion <NUM> may be substantially quadrangular other than substantially square, and for example, it may be substantially rectangular, substantially rhombic, or substantially parallelogram.

In a case in which the cross-sectional shape of the first member <NUM> is substantially quadrangular other than substantially square, the above L<NUM>/R<NUM> shows the following values.

In a case in which an electron source in which the columnar portion <NUM> has a substantially equilateral triangular cross-sectional shape is manufactured, the first member <NUM> and the hole <NUM> (second member <NUM>) which satisfy the following condition are selected in the step (C).

A diameter R<NUM> of a circumscribed circle of the substantial equilateral triangle is larger than a diameter R<NUM> of the hole and when the substantial equilateral triangle is disposed in a circle having the same diameter as the diameter R<NUM> of the hole <NUM>, at least two corners of the substantial equilateral triangle come into contact with the circle. In <FIG>, a solid-line circle R is a circle having the diameter R<NUM>, and a dashed-dotted line circle RT is a circumscribed circle of a substantial equilateral triangle T.

In the above embodiment, the case in which the opening area of the hole <NUM> is constant in the extending direction has been illustrated, but the hole of the electron emission limiting member <NUM> may have a reduced diameter portion in which the opening area decreases from the end face 2c toward the end face 2d. An electron source 10A shown in <FIG> has the same configuration as the electron source <NUM> except for the shape of the hole. A hole <NUM> in the electron source 10A is configured of a hole 4a on the end face 2c side, a hole 4b on the end face 2d side, and a tapered portion 4c (reduced diameter portion) therebetween. An inner diameter of the hole 4b is smaller than an inner diameter of the hole 4a. In this case, as shown in <FIG>, as long as the columnar portion <NUM> scrapes an inner surface of the hole 4b and bites into the electron emission limiting member <NUM>, thereby being sufficiently fixed, the columnar portion <NUM> may not bite into the electron emission limiting member <NUM> in the hole 4a, as shown in <FIG>. Also, although the tapered portion 4c in which the inner diameter continuously decreases has been illustrated as the reduced diameter portion here, the inner diameter of the reduced diameter portion may be reduced in stages. The hole of the second member <NUM> may similarly have a reduced diameter portion.

According to the present disclosure, the method for manufacturing an electron source that is useful for efficiently manufacturing a minute electron source is provided. the resulting electron source and the emitter provided with the same, which can sufficiently inhibit the member emitting electrons from coming off the member holding it are provided. Further, a device may be provided with the emitter.

Claim 1:
A method for manufacturing an electron source (<NUM>) comprising steps of:
(A) preparing a plurality of first members (<NUM>) each provided with a columnar portion (<NUM>) made of a first material having an electron emission characteristic and with an end face (1a);
(B) preparing a plurality of second members (<NUM>,<NUM>) each made of a second material having a higher work function and a lower strength than the first material, wherein the second material is glassy carbon, and each of which comprising a tubular portion (2a) in which a hole (<NUM>,<NUM>) extending in a direction from one end face (2c) toward the other end face (2d) is formed;
(C) selecting one first member (<NUM>) from the plurality of first members (<NUM>) and selecting one second member (<NUM>,<NUM>) from the plurality of second members (<NUM>,<NUM>); and
(D) pressing the columnar portion (<NUM>) of the selected first member (<NUM>) into the hole (<NUM>,<NUM>) of the selected second member (<NUM>,<NUM>),
wherein, in a cross-section orthogonal to a longitudinal direction of the columnar portion (<NUM>), each of the columnar portions (<NUM>) of the plurality of first members (<NUM>) has a substantially quadrangular cross-sectional shape, and
each of the holes (<NUM>,<NUM>) of the plurality of second members (<NUM>,<NUM>) has a substantially circular cross-sectional shape,
in the step (C), a set of the first member (<NUM>) and the second member (<NUM>,<NUM>) satisfying the following condition is selected from the plurality of first members (<NUM>) and the plurality of second members (<NUM>,<NUM>),
<Condition> <MAT>
in the inequality (<NUM>), L<NUM> indicates a length of the longer one of two diagonals of the substantially quadrangular shape, and R<NUM> indicates a diameter of the hole (<NUM>,<NUM>), and
in the step (D), by pressing the columnar portion (<NUM>) into the hole (<NUM>,<NUM>) of the second member (<NUM>,<NUM>), a portion of a side surface of the columnar portion (<NUM>) abuts an inner surface of the tubular portion (2a) of the second member (<NUM>,<NUM>), thereby fixing the columnar portion (<NUM>) to the second member (<NUM>,<NUM>); and
wherein the end face (1a) of the columnar portion (<NUM>) and the one
end face (2c) of the second member (<NUM>,<NUM>) form a flat surface, and wherein the entire side-surface of the columnar portion (<NUM>) is covered by the tubular portion (2a).