Patent Description:
In a charged particle beam system such as an electron microscope or a focused ion beam system, an electron gun or an ion gun is used as a source of a charged particle beam. Emitters used in electron guns and ion guns have limited life and so they need to be exchanged periodically.

For example, patent document <NUM> discloses an electron beam generator having a filament (emitter) which can be easily replaced while maintaining the interior of the electron gun chamber at a high vacuum.

Patent document <NUM> discloses an electron microscope equipped with automatic beam alignment. The electron microscope can include a vacuum chamber having a receiving space to allow a measurement target specimen to be positioned inside the vacuum chamber. The electron microscope can also include an electron gun coupled to a top of the vacuum chamber with an insulating panel between the electron gun and the vacuum chamber and including a filament module configured to receive power from a power supply and emit an electron beam toward the measurement target specimen. The filament module can be connected to the power supply via a flexible wire inserted into a through hole of the insulating panel such that an assembly error is prevented from occurring when the filament module is coupled to the through hole and the electron beam emitted from the filament module is automatically aligned with a reference optical axis.

As described above, sources of charged particle beams such as electron guns and ion guns are required to have easily replaceable emitters.

One aspect of a charged particle beam source configured to release a charged particle beam aligned with an optical axis associated with the present invention comprises: a chamber having a top side in the direction of the optical axis and a side wall; a first unit including both a supportive insulator mechanically supporting a cable and a first set of terminals electrically connected to the cable the first unit further including a support member having a central axis coincident with the optical axis; and a second unit including both an emitter for emitting charged particles and a second set of terminals electrically connected to the emitter. The first unit is secured in a through-hole formed in the side wall of the chamber and the top side of the chamber has an opening through which the second unit (<NUM>) can be inserted in or removed from the chamber. The second unit can be attached and detached to and from the first unit. In the chamber, the emitter is placed on an optical axis when fitted to the support member, whereby the first and second sets of terminals are brought into contact with each other.

In this charged particle beam source, the second unit can be detachably attached to the first unit and so the emitter can be easily replaced. Furthermore, in this beam source, the emitter is placed on the optical axis, whereby the first and second sets of terminals are brought into contact with each other. This allows for easy replacement of the emitter.

One aspect of a charged particle beam system associated with the present invention includes the above-described charged particle beam source.

The preferred embodiments of the present invention are hereinafter described in detail with reference to the accompanying drawings. It is to be noted that the embodiments described below are not intended to unduly restrict the scope and spirit of the present invention delineated by the appended claims and that not all the configurations described below are the essential constituent components of the present invention.

An electron microscope associated with a first embodiment of the present invention is first described by referring to <FIG>, which shows the configuration of this electron microscope, <NUM>. The microscope <NUM> is an apparatus for capturing a scanned image of a sample S by scanning it with an electron probe. In the electron microscope <NUM>, scanned images include secondary electron images and elemental maps.

Referring still to <FIG>, the electron microscope <NUM> includes an electron gun <NUM> (one example of a charged particle beam source), condenser lenses <NUM>, scan coils <NUM>, an objective lens <NUM>, a sample stage <NUM>, a secondary electron detector <NUM>, an X-ray detector <NUM>, a high-voltage power supply <NUM>, and a high-voltage cable <NUM>. The electron gun <NUM> which emits an electron beam EB will be described in detail later.

The electron beam EB emitted from the electron gun <NUM> is focused into an electron probe by the action of the condenser lenses <NUM> and the objective lens <NUM>. The scan coils <NUM> deflect the electron beam EB in two dimensions. This makes it possible to scan the sample S with the electron probe.

The electron microscope <NUM> has an electron optical column <NUM> which forms and scans the electron probe. The electron optical column <NUM> is made up of the electron gun <NUM>, condenser lenses <NUM>, scan coils <NUM>, and objective lens <NUM>. An electron gun compartment <NUM> and an intermediate chamber <NUM> are formed in the electron optical column <NUM>. An electron emitter that is a source of electrons is housed in the electron gun compartment <NUM>. An electron optical system including the condenser lenses <NUM>, scan coils <NUM>, and objective lens <NUM> is housed in the intermediate chamber <NUM>.

The sample stage <NUM> is disposed in a sample chamber <NUM>, and the sample S is placed on the sample stage <NUM> which in turn can hold the sample S. The sample stage <NUM> has a drive mechanism for moving the sample S.

The secondary electron detector <NUM> detects secondary electrons released from the sample S in response to irradiation of the sample S with the electron beam EB. A secondary electron image can be obtained by scanning the sample S with the electron probe and detecting the secondary electrons emanating from the sample S by the secondary electron detector <NUM>. The electron microscope <NUM> may also be equipped with a backscattered electron detector for detecting backscattered electrons released from the sample S in response to irradiation of the sample S with the electron beam EB.

The X-ray detector <NUM> detects characteristic X-rays produced in response to irradiation of the sample S with the electron beam EB. The X-ray detector <NUM> is an energy dispersive X-ray spectrometer, for example. Alternatively, the X-ray detector <NUM> may be a wavelength dispersive X-ray spectrometer. An elemental map can be generated by scanning the sample S with the electron probe and detecting characteristic X-rays emanating from the sample S by means of the X-ray detector <NUM>.

The high-voltage power supply <NUM> is electrically connected with the emitter of the electron gun <NUM> and with various electrodes via the high-voltage cable <NUM> and operates to supply a negative high voltage to the electron gun <NUM>.

<FIG> are schematic cross-sectional views of the electron gun <NUM> of the electron microscope <NUM> associated with the first embodiment. In <FIG>, there are shown X-, Y-, and Z-axes which are perpendicular to each other. As shown in these figures, the electron gun <NUM> includes the electron gun chamber <NUM>, a chamber cover <NUM> (<FIG>), a supportive insulator unit <NUM> (one example of a first unit), an emitter unit <NUM> (one example of a second unit), and an anode <NUM>. The electron gun <NUM> is a Schottky emission gun utilizing the Schottky effect in which if a strong electric field is applied to a substance, the potential barrier drops, resulting in emission of more thermoelectrons.

The electron gun compartment <NUM> in which the emitter unit <NUM> is housed is formed in the electron gun chamber <NUM> having a side wall <NUM>. A first pipe <NUM> is joined to, and extend through, the side wall <NUM>. An ultrahigh vacuum pump (not shown) (such as an ion pump) is connected to the first pipe <NUM> so that the inside of the electron gun chamber <NUM> can be maintained in an ultrahigh vacuum of below <NUM>-<NUM> Pa. A second pipe <NUM> is connected to the first pipe <NUM>, and a roughing vacuum pump (not shown) (such as an oil rotary pump) is connected to the second pipe <NUM>.

The electron gun chamber <NUM> has an opening on its top side, the opening being hermetically sealed by the chamber cover <NUM>. The chamber cover <NUM> has a flange provided with through-holes through which bolts <NUM> are passed to secure the flange to the electron gun chamber <NUM>.

The supportive insulator unit <NUM> includes a pipe <NUM>, an inner flange <NUM>, an outer flange <NUM>, a plate <NUM>, a support member <NUM>, a supportive insulator <NUM>, and electric terminals 28a, 28b, 28c. The insulator unit <NUM> is secured in a through-hole 11a formed in the side wall <NUM> of the electron gun chamber <NUM>. The pipe <NUM> is inserted in the through-hole 11a. The pipe <NUM> and the side wall <NUM> are welded together. The inner flange <NUM> is joined to the front end of the pipe <NUM>.

The supportive insulator <NUM> mechanically supports and electrically insulates the high-voltage cable <NUM> which is a high withstand voltage cable serving to connect together the high-voltage power supply <NUM> and the emitter unit <NUM>. The cable <NUM> has a plurality of core wires. The supportive insulator <NUM> is electrically insulative in nature and inserted in the pipe <NUM> of the insulator unit <NUM>. The outer flange <NUM> is welded, brazed, or otherwise bonded to the rear end of the supportive insulator <NUM>. The outer flange <NUM> is fastened to the inner flange <NUM> with bolts <NUM> via a metal O-ring <NUM>. As a result, hermetic sealing between the two flanges <NUM> and <NUM> can be accomplished.

The support member <NUM> providing mechanical support of the emitter unit <NUM> is mounted at the front end of the supportive insulator <NUM>. The plate <NUM> is brazed to the front end of the supportive insulator <NUM>. The support member <NUM> is secured to the insulator <NUM> via the plate <NUM>. Note that the insulative member that electrically insulates and mechanically supports the high-voltage cable <NUM> is not restricted to the supportive insulator <NUM>.

The support member <NUM> is a cylindrical member, for example, in which the emitter unit <NUM> is inserted and fitted. As a result, the emitter unit <NUM> is placed in position and an electron emitter <NUM> is placed on an optical axis OA which is parallel to the Z-axis in the illustrated example.

A plurality of electric terminals are secured to the front end of the supportive insulator <NUM>. These terminals are 28a, 28b, and 28c in the illustrated example and these terminals 28a-28c are electrically connected with the high-voltage cable <NUM>.

The terminal 28a of the insulator unit is an electrically conductive pipe, for example, and elongated in a direction orthogonal to the optical axis OA, i.e., elongated along the Y-axis. The terminals 28b and 28c of the insulator unit are electrically conductive pipes in the same way as the terminal 28a and are similar in shape to the terminal 28a.

<FIG> schematically shows the outer flange <NUM>. Each of the flanges <NUM> and <NUM> is provided with a hole for passage of a positioning pin <NUM>. Rotation of the insulator unit <NUM> can be prevented by inserting the positioning pin <NUM> into the holes of the flanges <NUM> and <NUM>.

Referring back to <FIG>, the emitter unit <NUM> includes a flange <NUM>, a second set of terminals 32a, 32b, 32c, an insulative member <NUM>, feedthroughs 34a, 34b, 34c, the electron emitter <NUM>, a holder <NUM>, electrodes 37a, 37b, and an extraction electrode <NUM>. The flange <NUM> is cylindrical and inserted inside the support member <NUM>. The flange <NUM> is brought into fitting engagement with the support member <NUM>, whereby the emitter <NUM> is placed in position. The flange <NUM> and the support member <NUM> are secured with bolts <NUM>.

The terminals 32a, 32b, and 32c are fixed on the insulative member <NUM>. The terminal 32a has electrical conductivity and is made of a resilient body. For example, the terminal 32a is a leaf spring. Each of the other two terminals 32b and 32c has electrical conductivity and is a leaf spring in the same way as the first-mentioned terminal 32a.

The terminal 32a is connected with the feedthrough 34a and has a front end in which a spiral groove is formed. The terminal 32a is secured to the insulative member <NUM> with nuts <NUM>. Similarly, the terminal 32b is connected with the feedthrough 34b and fastened to the insulative member <NUM> with nuts <NUM>, and the terminal 32c is connected with the feedthrough 34c and affixed to the insulative member <NUM> with nuts <NUM>.

The feedthroughs 34a, 34b, and 34c are inserted in, and mechanically supported and electrically insulated by, the supportive insulative member <NUM>. The feedthrough 34a is connected with one terminal of the emitter <NUM>. The feedthrough 34b is connected with the other terminal of the emitter <NUM>. Consequently, the emitter <NUM> and the high-voltage power supply <NUM> can be electrically interconnected.

A suppressor (not shown) is disposed between the emitter <NUM> and the extraction electrode <NUM> and applied with a negative potential relative to the emitter <NUM>. The feedthrough 34c is electrically connected with the suppressor and also with the flange <NUM> via a metallization layer deposited on the insulative member <NUM>. The flange <NUM> is in contact with the suppressor and thus the suppressor can be electrically connected with the high-voltage power supply <NUM>. In the electron gun <NUM>, the suppressor and the high-voltage cable <NUM> can be electrically interconnected via the metallization layer and so members which would otherwise cause electric discharge can be reduced in number. This can reduce the possibility that the emitter <NUM> will be damaged.

The emitter <NUM> is a source of electrons and consists of a tungsten chip whose surface is coated with zirconium oxide, for example. The emitter <NUM> is mechanically supported by the feedthroughs 34a and 34b. The emitter <NUM> and the feedthrough 34a are secured by a bolt 7a. The emitter <NUM> and the feedthrough 34b are secured by a bolt 7b.

The holder <NUM> is cylindrical in shape and surrounds the emitter <NUM>. The emitter <NUM> is fitted inside the holder <NUM>. Consequently, the emitter <NUM> can be placed in position. The flange <NUM> is brazed to the insulative member <NUM>. The holder <NUM> and the flange <NUM> are secured with nuts <NUM>.

The extraction electrode <NUM> is positioned under the emitter <NUM> and provided with a hole for passage of electrons released from the emitter <NUM>. The extraction electrode <NUM> is mechanically supported by the electrodes 37a and 37b. The electrode 37a is in threaded engagement with the flange <NUM>. The electrode 37b is secured to the electrode 37a with a screw. The extraction electrode <NUM> is coupled to the front end of the electrode 37b and can be mechanically adjusted in position by a position adjusting screw (not shown).

An extraction voltage is applied to the extraction electrode <NUM> to extract electrons from the emitter <NUM>. The support member <NUM> is electrically connected with the high-voltage cable <NUM> and in contact with the flange <NUM>. Therefore, the extraction voltage is applied to the extraction electrode <NUM> via the high-voltage cable <NUM>, support member <NUM>, flange <NUM>, and electrodes 37a, 37b.

The anode <NUM> is located under the extraction electrode <NUM>. An apertured plate <NUM> is mounted to the front end of the anode <NUM>, is in threaded engagement with a holder <NUM>, and provides an orifice or aperture between the interior of the electron gun chamber <NUM> and the intermediate chamber <NUM> that resides immediately below the gun chamber <NUM>. The orifice passes an electron beam and maintains the pressure difference between the two chambers. The holder <NUM> is secured to the anode <NUM>.

In the electron gun <NUM>, electrical current is supplied from the high-voltage power supply <NUM> to the emitter <NUM> via the high-voltage cable <NUM> to heat the emitter <NUM>. Also, a negative high voltage is applied from the high-voltage power supply <NUM> to the emitter <NUM> via the high-voltage cable <NUM>. Furthermore, a potential that is negative relative to the emitter <NUM> is applied to the suppressor from the high-voltage power supply <NUM> via the high-voltage cable <NUM>. In addition, the extraction voltage is applied to the extraction electrode <NUM> from the high-voltage power supply <NUM> via the high-voltage cable <NUM>.

In the electron gun <NUM>, if electrical current is supplied to the emitter <NUM> and the emitter <NUM> becomes heated, a strong electric field produced across the surface of the emitter <NUM> by the extraction electrode <NUM> extracts electrons from the emitter <NUM>. At this time, the unwanted thermoelectrons released from the emitter <NUM> are blocked by the suppressor and are not emitted from the electron gun <NUM>. The electrons extracted from the emitter <NUM> are accelerated by the anode <NUM> at ground potential and focused by the condenser lenses <NUM>.

<FIG> is a typical cross-sectional view illustrating a step of replacing the emitter <NUM>. First, the interior of the electron gun chamber <NUM> is placed at atmospheric pressure. Then, the bolts <NUM> of <FIG> are taken away and the chamber cover <NUM> is removed from the gun chamber <NUM>. The bolts <NUM> fastening together the emitter unit <NUM> and support member <NUM> as shown in <FIG> are removed.

Then, as shown in <FIG>, the emitter unit <NUM> is raised and taken out through the top opening of the electron gun chamber <NUM>. The bolt 7a fastening together the feedthrough 34a and the emitter <NUM> as shown in <FIG> and the bolt 7b fastening together the feedthrough 34b and the emitter <NUM> are loosened, and the emitter <NUM> are then taken out. A new emitter <NUM> is mounted.

In particular, the new emitter <NUM> is fastened to the feedthroughs 34a and 34b with the bolts 7a and 7b. At this time, the emitter <NUM> is fitted to the holder <NUM> and placed in position. In the emitter unit <NUM> on which the new emitter <NUM> has been mounted, the emitter <NUM> and the extraction electrode <NUM> are adjusted in position. The emitter unit <NUM> is put into a furnace and baked, thus degassing the emitter unit <NUM>, i.e., gas occluded in the emitter unit <NUM> can be forcibly removed.

After the baking, the emitter unit <NUM> is inserted into the support member <NUM> of the insulator unit <NUM> along the Z-axis from the top opening of the electron gun chamber <NUM>. As a result, the emitter unit <NUM> is fitted to the support member <NUM> and the emitter <NUM> is placed in position.

The support member <NUM> has a central axis coincident with the optical axis OA. In the electron gun <NUM>, the surface of the inner flange <NUM> which comes into contact with the outer flange <NUM> is precisely placed in position such that when the surface of the inner flange <NUM> touches the outer flange <NUM>, the central axis of the support member <NUM> becomes coincident with the optical axis OA. Therefore, securing the outer flange <NUM> to the inner flange <NUM> results in coincidence of the center axis of the support member <NUM> with the optical axis OA. Consequently, fitting the emitter unit <NUM> to the support member <NUM> places the emitter <NUM> on the optical axis OA.

The surface 25a of the support member <NUM> that comes into contact with the flange <NUM> determines the position of the emitter unit <NUM> as taken in the Z direction. Accordingly, fitting the emitter unit <NUM> to the support member <NUM> determines the position of the emitter <NUM> as taken in the Z direction. In this way, in the electron gun <NUM>, fitting the emitter unit <NUM> to the support member <NUM> can place the emitter <NUM> in position.

Inserting the emitter unit <NUM> into the support member <NUM> brings the terminal 32a of the emitter unit <NUM> into contact with the terminal 28a of the insulator unit. The terminal 32c is a resilient leaf spring. The emitter unit terminal 32c comes into contact with the terminal 28c of the insulator unit <NUM> and undergoes flexure. This assures that the emitter unit terminal 32c is connected with the insulator unit terminal 28c.

Similarly, inserting the emitter unit <NUM> into the support member <NUM> brings the emitter unit terminal 32a into contact with the insulator unit terminal 28a. The terminal 32a is a resilient leaf spring. The terminal 32a comes into contact with the terminal 28a and undergoes flexure. Hence, the emitter unit terminal 32a can be connected with the insulator unit terminal 28a with certainty.

Similarly, inserting the emitter unit <NUM> into the support member <NUM> brings the terminal 32b into contact with the terminal 28b. The terminal 32b is a resilient leaf spring. The terminal 32b comes into contact with the terminal 28b and undergoes flexure. This ensures that the terminal 32b is connected with the terminal 28b. Because the terminals of the emitter unit <NUM> come into contact with the terminals of the insulator unit <NUM>, the emitter unit <NUM> and the high-voltage power supply <NUM> are electrically interconnected. After inserting the emitter unit <NUM> into the support member <NUM>, the flange <NUM> and the support member <NUM> are secured together with bolts <NUM>.

Then, as shown in <FIG>, the chamber cover <NUM> is fastened to the electron gun chamber <NUM> with bolts <NUM>, and the top opening of the electron gun chamber <NUM> is closed off by the chamber cover <NUM>. The interior of the electron optical column <NUM> is evacuated to a vacuum. Then, the whole electron optical column <NUM> of the electron microscope <NUM> is baked. Because of the steps described thus far, the emitter <NUM> can be replaced.

In the electron gun <NUM>, the insulator unit <NUM> is secured in the through-hole 11a formed in the side wall <NUM> of the electron gun chamber <NUM>. The emitter unit <NUM> can be detachably attached to the insulator unit <NUM>. Also, in the electron gun chamber <NUM>, the emitter <NUM> is placed on the optical axis OA to bring the insulator unit terminal 28a and the emitter unit terminal 32a into contact with each other. The insulator unit terminal 28b and the emitter unit terminal 32b are brought into contact with each other. In addition, the insulator unit terminal 28c and the emitter unit terminal 32c are brought into contact with each other.

In this way, in the electron gun <NUM>, the emitter unit <NUM> can be attached to and detached from the insulator unit <NUM> and so the emitter <NUM> can be replaced easily. Also, in the electron gun <NUM>, placing the emitter <NUM> on the optical axis OA brings the terminals of the emitter unit <NUM> into contact with their respective terminals of the insulator unit <NUM>. Consequently, the emitter <NUM> can be replaced easily.

Furthermore, in the electron gun <NUM>, the emitter unit <NUM> can be removed independently of the insulator unit <NUM> and, therefore, during replacement of the emitter <NUM>, a less number of members need to be worked on than conventional. This can improve the workability. Furthermore, since the emitter unit <NUM> can be baked by itself, the baking time can be shortened.

If the emitter <NUM>, extraction electrode <NUM>, and supportive insulator <NUM> constitute a single, unitary assembly, for example, when the emitter <NUM> is taken out of the electron optical column <NUM>, the large assembly must be worked on and hence the workability is low. Also, it is difficult to bake this unitary assembly by itself, thus prolonging the baking time.

In the electron gun <NUM>, the insulator unit <NUM> is mounted to the side wall <NUM> of the electron gun chamber <NUM> and so the high-voltage cable <NUM> can be introduced from a side of the electron optical column <NUM>. Therefore, the height of the electron gun <NUM> can be suppressed as compared, for example, with the case where the high-voltage cable <NUM> is introduced from above the gun.

In the electron gun <NUM>, the insulator unit <NUM> has the support member <NUM> that mechanically supports the emitter unit <NUM>. Supporting the emitter unit <NUM> with the support member <NUM> places the emitter <NUM> on the optical axis OA. Also, the terminals of the emitter unit <NUM> are brought into contact with their respective terminals of the insulator unit <NUM>. In this way, in the electron gun <NUM>, since the emitter unit <NUM> is mechanically supported by the support member <NUM>, the emitter <NUM> is placed in position. This makes it unnecessary to mechanically adjust the position of the emitter <NUM> with a screw or the like. Accordingly, the emitter <NUM> can be replaced in a short time. Furthermore, the non-necessity of mechanical adjustment of the position of the emitter <NUM> makes it unnecessary to use a mechanical part having a large surface area such as bellows. In consequence, the interior of the electron gun chamber <NUM> can be maintained at a high vacuum.

In the electron gun <NUM>, the support member <NUM> is cylindrical. Inserting the emitter unit <NUM> into the support member <NUM> places the emitter <NUM> on the optical axis OA. Therefore, in the electron gun <NUM>, the emitter <NUM> can be replaced in a short time and the interior of the electron gun chamber <NUM> can be maintained at a high vacuum.

In the electron gun <NUM>, each terminal of the emitter unit <NUM> is a resilient body which consists of a leaf spring, for example. Therefore, in the electron gun <NUM>, it is assured that the terminals of the emitter unit <NUM> are brought into contact with their respective terminals of the insulator unit <NUM>.

In the first embodiment described above, each terminal of the emitter unit <NUM> is a resilient leaf spring. Alternatively, each terminal of the insulator unit <NUM> may be a resilient leaf spring.

An electron microscope associated with a second embodiment is next described. In this electron microscope, <NUM>, the type of the mounted electron gun can be varied. In the following description, only differences with the electron microscope <NUM> of the first embodiment are set forth; a description of similarities is omitted.

<FIG> is a typical cross-sectional view of an electron gun assembly <NUM> of the electron microscope <NUM> associated with the second embodiment. Those members of the electron gun assembly <NUM> which are similar in function to their respective counterparts of the above-described electron gun <NUM> are indicated by the same reference numerals as in the foregoing figures and a detailed description thereof is omitted.

The electron gun assembly <NUM> includes a Schottky emitter unit <NUM> constituting a Schottky emission gun shown in <FIG> and a CFEG emitter unit 30D constituting a cold field emission gun (CFEG) shown in <FIG>. In the electron gun assembly <NUM>, either the Schottky emitter unit <NUM> or the CFEG emitter unit 30D can be mounted to the insulator unit <NUM>.

A cold field emission gun (CFEG) applies a strong electric field to the emitter 35a at room temperature and emits electrons by the tunnel effect. In the CFEG emitter unit 30D, the emitter 35a is a tungsten chip, for example.

The Schottky emitter unit <NUM> shown in <FIG> has three terminals 32a, 32b, and 32c. On the other hand, the CFEG emitter unit 30D has no suppressor and so has two terminals electrically connected to the emitter 35a. For example, the CFEG emitter unit 30D may have the third terminal 32c which is a dummy terminal. No restriction is imposed on the number of terminals of the CFEG emitter unit 30D.

As shown in <FIG>, the electron gun assembly <NUM> includes a vacuum pump <NUM> that is a non-evaporable getter pump, for example, which utilizes the gettering action, i.e., the pump performs pumping by adsorbing gaseous molecules onto the surface of a solid material.

The vacuum pump <NUM> can be mounted to the chamber cover <NUM> and includes a base plate <NUM> coated with a non-evaporable getter which adsorbs and removes gaseous molecules. Examples of such a non-evaporable material include titanium, zirconium, and alloys thereof. The vacuum pump <NUM> can be detachably mounted to the chamber cover <NUM>.

In the electron gun assembly <NUM>, if the emitter unit 30D has been mounted to the insulator unit <NUM>, a high voltage is applied from the high-voltage power supply <NUM> to the emitter 35a via the high-voltage cable <NUM>. Also, an extraction voltage is applied from the high-voltage power supply <NUM> to the extraction electrode <NUM> also via the high-voltage cable <NUM>.

In the electron gun assembly <NUM>, if the extraction voltage is applied to the extraction electrode <NUM>, electrons are released from the electron emitter 35a by the tunnel effect and then accelerated by the anode <NUM> at ground potential. The electrons are then focused by the condenser lenses <NUM>.

The operation of the electron gun assembly <NUM> when the emitter unit <NUM> has been mounted is similar to the operation in the first embodiment and a description thereof is omitted.

In the following, there will be presented a case where the Schottky emitter unit <NUM> is replaced by the CFEG emitter unit 30D. First, the interior of the electron gun chamber <NUM> is put at atmospheric pressure. Then, the bolts <NUM> shown in <FIG> are removed, and the chamber cover <NUM> is taken out from the electron gun chamber <NUM>. Subsequently, the bolts <NUM> (<FIG>) fastening together the Schottky emitter unit <NUM> and the support member <NUM> are removed.

Then, as shown in <FIG>, the emitter unit <NUM> is raised and taken out through the top opening of the electron gun chamber <NUM>. The CFEG emitter unit 30D is then baked and inserted into the support member <NUM> of the insulator unit <NUM> along the Z-axis from the top opening of the electron gun chamber <NUM>. Consequently, the CFEG emitter unit 30D is fitted to the support member <NUM> and the emitter 35a is placed in position.

Inserting the CFEG emitter unit 30D into the support member <NUM> brings the terminals of the CFEG emitter unit 30D into contact with their respective terminals of the insulator unit <NUM>, so that these emitter unit terminals undergo flexure. As a result, the CFEG emitter unit 30D and the high-voltage power supply <NUM> are electrically interconnected. After inserting the CFEG emitter unit 30D into the support member <NUM>, the flange <NUM> and the support member <NUM> are secured together with the bolts <NUM>.

The base plate <NUM> is then mounted to the chamber cover <NUM>. The chamber cover <NUM>, along with the base plate <NUM>, is secured to the electron gun chamber <NUM> with the bolts <NUM>. The top opening of the electron gun chamber <NUM> is closed off by the chamber cover <NUM>. The interior of the electron optical column <NUM> is evacuated to a vacuum.

The whole electron optical column <NUM> of the electron microscope <NUM> is then baked. As a result, the non-evaporable getter can be activated. Because of the processing steps described so far, the Schottky emitter unit <NUM> can be replaced by the CFEG emitter unit 30D.

The electron gun assembly <NUM> includes the vacuum pump <NUM> mounted to the chamber cover <NUM> that seals off the electron gun chamber <NUM>. In the electron gun assembly <NUM>, the insulator unit <NUM> is secured in the through-hole 11a formed in the sidewall <NUM> of the electron gun chamber <NUM> and so the vacuum pump <NUM> can be mounted to the chamber cover <NUM>. The interior of the electron gun chamber <NUM> can be maintained at a high vacuum by the vacuum pump <NUM>.

The electron gun assembly <NUM> includes the Schottky emitter unit <NUM> and the CFEG emitter unit 30D capable of being replaced by the Schottky emitter unit <NUM>. The two emitter units <NUM> and 30D are different in mechanism of electron emission. Therefore, with the electron gun assembly <NUM>, the sample S can be observed or analyzed using the plural electron guns which are different in mechanism of electron emission.

For example, the electron gun assembly <NUM> can be operated as a Schottky electron gun by mounting the Schottky emitter unit <NUM> to the insulator unit <NUM>, and the electron gun assembly <NUM> can be operated as a cold field emission gun (CFEG) by mounting the CFEG emitter unit 30D to the insulator unit <NUM>.

In the above embodiment, the Schottky emitter unit <NUM> constituting a Schottky electron gun and the CFEG emitter unit 30D constituting a CFEG electron gun can be replaced with each other. Types of replaceable electron gun emitter unit are not restricted to these two. For example, the electron gun assembly <NUM> may further include an emitter unit constituting a thermionic emission electron gun. That is, the electron gun assembly <NUM> may be operated as a thermionic emission electron gun. In this way, the electron gun assembly <NUM> can include plural types of emitter unit capable of operating as electron guns which are different in mechanism of electron emission.

The emitters of the two emitter units <NUM> and 30D may be made of different materials. For example, the emitter unit <NUM> may constitute a thermionic emission electron gun and its emitter <NUM> may be made of lanthanum hexaboride. The emitter unit 30D may constitute a thermionic emission electron gun and its emitter 35a may be made of tungsten.

The number of terminals of an emitter unit may be varied according to the type of the emitter unit. At this time, the number of terminals of the insulator unit <NUM> may be varied according to the number of terminals of the emitter unit. For example, the insulator unit <NUM> may have plural terminals each of which can be switched to operative or inoperative state according to the number of terminals of the used emitter unit.

An electron microscope, <NUM>, associated with a third embodiment is next described. This electron microscope <NUM> is different in electron gun configuration from the electron microscope <NUM> shown in the above-cited <FIG>. In the following description, only differences with the above-stated electron microscope <NUM> associated with the first embodiment are described. A description of similarities is omitted.

The electron microscope <NUM> associated with the third embodiment has an electron gun <NUM> as shown in a typical cross-sectional view of <FIG>. Those members of the electron gun <NUM> which are similar in function to their respective counterparts of the above stated electron gun <NUM> are indicated by the same reference numerals as in the foregoing figures and a detailed description thereof is omitted.

As shown in <FIG>, in the electron gun <NUM>, the insulator unit <NUM> has the support member <NUM> providing mechanical support of the emitter unit <NUM>, whereby the emitter <NUM> is placed on the optical axis OA. The terminals of the emitter unit <NUM> are brought into contact with their respective terminals of the insulator unit <NUM>.

On the other hand, in the electron gun <NUM>, as shown in <FIG>, the emitter unit <NUM> is mounted to the chamber cover <NUM>, which in turn is mounted in the electron gun chamber <NUM>. As a result, the emitter <NUM> is placed on the optical axis OA. The terminals of the emitter unit <NUM> are brought into contact with their respective terminals of the insulator unit <NUM>.

The emitter unit <NUM> is mounted to the chamber cover <NUM> as described above. As shown in <FIG>, the insulative member <NUM> is interposed between the chamber cover <NUM> and the emitter unit <NUM> and can provide electrical insulation between the flange <NUM> of the emitter unit <NUM> and the chamber cover <NUM>.

The emitter unit <NUM> is mechanically supported by the chamber cover <NUM>. In the electron gun <NUM>, the support member <NUM> of the insulator unit <NUM> does not mechanically support the emitter unit <NUM>. In the electron gun <NUM>, the support member <NUM> comes into contact with the flange <NUM> of the emitter unit <NUM> to thereby electrically interconnect the high-voltage power supply <NUM> and the extraction electrode <NUM>. Although not illustrated, the emitter unit <NUM> and the support member <NUM> may not be in direct contact with each other, and a pin mounted to the support member <NUM> may come into contact with the flange <NUM> to thereby electrically interconnect the high-voltage power supply <NUM> and the extraction electrode <NUM>. The emitter <NUM> is placed in position by mounting the chamber cover <NUM> in the electron gun chamber <NUM>.

First, the interior of the electron gun chamber <NUM> is placed at atmospheric pressure. Then, the bolts <NUM> are removed, and the chamber cover <NUM> having the emitter unit <NUM> secured thereto is taken out of the electron gun chamber <NUM>.

Then, the insulative member <NUM> is taken out from the chamber cover <NUM>. The insulative member <NUM> is then removed from the emitter unit <NUM>. Then, the emitter <NUM> is taken out from the emitter unit <NUM> and a new emitter <NUM> is mounted.

In the emitter unit <NUM> having the new emitter <NUM> mounted thereon, the emitter <NUM> and the extraction electrode <NUM> are adjusted in position. Then, the emitter unit <NUM> is put into a furnace and baked.

After the baking, the emitter unit <NUM> is mounted on the insulative member <NUM>, and the insulative member <NUM> having the emitter unit <NUM> mounted thereon is mounted to the chamber cover <NUM>. The chamber cover <NUM> is secured to the electron gun chamber <NUM> with the bolts <NUM>.

At this time, the chamber cover <NUM> and the electron gun chamber <NUM> are fitted together. This places the emitter unit <NUM> in position. As a result, the emitter <NUM> is placed on the optical axis OA. The terminals of the emitter unit <NUM> come into contact with their respective terminals of the insulator unit <NUM>. The emitter <NUM> can be placed in position by mounting the chamber cover <NUM> having the emitter unit <NUM> mounted thereon to the electron gun chamber <NUM> in this way.

Then, the interior of the electron optical column <NUM> is evacuated to a vacuum, and the whole electron optical column <NUM> is baked. Because of the processing steps described so far, the emitter <NUM> can be replaced.

In the electron gun <NUM>, the emitter unit <NUM> is mounted to the chamber cover <NUM> which in turn is mounted to the electron gun chamber <NUM>, whereby the emitter <NUM> is placed on the optical axis OA and the terminals of the emitter unit <NUM> are brought into contact with the respective terminals of the insulator unit <NUM>. Consequently, in the electron gun <NUM>, the emitter <NUM> can be replaced easily.

An electron microscope, <NUM>, associated with a fourth embodiment is next described. <FIG> is a schematic cross-sectional view of an electron gun <NUM> for use in this electron microscope <NUM>. In the following description, those members of the electron gun <NUM> which are functionally similar to their counterparts of the foregoing electron gun <NUM> are denoted by the same reference numerals as in the foregoing figures and a detailed description thereof is omitted.

As shown in <FIG>, the electron gun <NUM> has an alignment coil <NUM> which deflects the electron beam released from the emitter <NUM>. As a result, the electron beam released from the electron gun <NUM> can be aligned with the optical axis OA, i.e., the beam can be axially aligned.

For example, when the emitter unit <NUM> is supported on the support member <NUM> of the insulator unit <NUM> and placed in position, if the emitter <NUM> deviates from the optical axis OA, the electron beam released from the electron gun <NUM> can be aligned to the optical axis OA using the alignment coil <NUM>.

In this example, the alignment coil <NUM> is mounted in the electron gun using the emitter unit <NUM> that is a Schottky emission gun. The alignment coil <NUM> may also be mounted in an electron gun other than Schottky emission guns.

It is to be understood that the present invention is not restricted to the above embodiments but rather can be practiced in various modified forms without departing from the scope of protection defined by the appended claims. For example, in the above-stated first through fourth embodiments, the charged particle beam system associated with the present invention is a scanning electron microscope. The charged particle beam system associated with the present invention is not restricted to scanning electron microscopes. The charged particle beam system associated with the present invention may also be a scanning transmission electron microscope (STEM), a scanning electron microscope (SEM), an electron probe microanalyzer (EMPA), an electron beam lithography system, or the like. Furthermore, in the description of the foregoing first through fourth embodiments, the charged particle beam source associated with the present invention is an electron gun equipped with an electron emitter that emits electrons. The charged particle beam source associated with the present invention may also be a charged particle beam source equipped with a charged particle emitter that releases charged particles other than electrons. For example, the charged particle beam source associated with the present invention may be an ion gun equipped with an emitter that releases ions. Additionally, the charged particle beam system associated with the present invention may be a focused ion beam (FIB) system.

Claim 1:
A charged particle beam source (<NUM>) configured to release a charged particle beam aligned with an optical axis (OA) comprising:
a chamber (<NUM>) having a top side in the direction of the optical axis (OA) and a side wall (<NUM>);
a first unit (<NUM>) including both a supportive insulator (<NUM>) mechanically supporting a cable (<NUM>) and a first set of terminals (28a-c) electrically connected to the cable (<NUM>); the first unit (<NUM>) further including a support member (<NUM>) having a central axis coincident with the optical axis (OA); and
a second unit (<NUM>) including both an emitter (<NUM>) for emitting charged particles and a second set of terminals (32a-c) electrically connected to the emitter (<NUM>), the second unit (<NUM>) being capable of detachably mounted to the first unit (<NUM>);
wherein the first unit (<NUM>) is secured in a through-hole (11a) formed in the side wall (<NUM>) of the chamber (<NUM>) and the top side of the chamber (<NUM>) has an opening through which the second unit (<NUM>) can be inserted in or removed from the chamber (<NUM>); and
wherein the emitter (<NUM>) is placed on an optical axis (OA) within the chamber (<NUM>) when fitted to the support member (<NUM>), whereby the first and second sets of terminals are brought into contact with each other.