Patent Description:
As a charged particle beam device, there are known a transmission electron microscope, a scanning electron microscope, an ion beam irradiation device, and the like. In the charged particle beam device, when a sample which is a target of observation, analysis, or machining must be cooled, a cooling apparatus is used.

For example, in the transmission electron microscope, a sample which is held by a sample holder is cooled by a cooling system. The cooling system is formed from a cooling apparatus which functions as a heat exchange device, a heat conductive member connected to the cooling apparatus, or the like. The heat conductive member is connected to a member which holds the sample or to a member which surrounds the sample.

In general, the cooling apparatus includes a storage container which stores a liquid coolant, and a housing which houses the storage container, and an internal space of the housing is set to vacuum (for example, refer to <CIT>). At an upper part of the storage container, a plurality of pipes are connected, and the housing holds the storage container via the plurality of pipes. The liquid coolant is, for example, liquid nitrogen, liquid helium, or the like.

In a cooling apparatus for a charged particle beam device, when a large amount of heat is transferred to the storage container which stores the liquid coolant, the liquid coolant in the storage container is vigorously vaporized and evaporated. That is, bubbling is caused. A vibration caused by the bubbling significantly affects an operation of the charged particle beam device. In order to suppress the bubbling, inflow of heat from the outside to the liquid coolant must be reduced to a maximum possible extent. From the viewpoint of reducing an amount of consumption of the liquid coolant also, reduction, to a maximum possible extent, of the heat inflow from the outside to the liquid coolant is desired.

An advantage of the present disclosure lies in reduction of heat inflow to the stored liquid coolant, in the cooling apparatus for the charged particle beam device.

<CIT> discloses an ultra-low temperature storage container that has a structure wherein a solid refrigerant tank that houses a solid refrigerant that is cooled by a freezer and a liquid refrigerant tank that holds a liquid refrigerant and is disposed to surround the solid refrigerant tank with a constant space are accommodated inside a vacuum container.

According to one aspect of the present disclosure, there is provided a cooling apparatus for a charged particle beam device, the cooling apparatus comprising: a primary storage container that has a primary storage space which stores a liquid coolant; a secondary storage container that surrounds the primary storage container; a secondary storage space being the gap between the primary storage container and the secondary storage container, wherein the secondary storage space is arranged to store a vaporized coolant generated by vaporization of the liquid coolant in the primary storage container , the vaporized coolant flowing through an upper opening of the primary container into the secondary storage space; a housing that houses the primary storage container and the secondary storage container; and a heat conductive member that is connected to the primary storage container and that transfers heat for cooling a sample which is irradiated with a charged particle beam, and an introduction pipe that is arranged to introduce the liquid coolant to the primary storage space, wherein a level of a lower end opening of the introduction pipe is lower than a level of the upper opening of the primary storage container so that the entrance of the liquid coolant into the secondary storage container can be prevented.

Embodiments of the present disclosure will now be described with reference to the drawings.

A cooling apparatus for a charged particle beam device according to an embodiment of the present disclosure comprises a primary storage container, a secondary storage container, a housing, and a heat conductive member. The primary storage container has a primary storage space which stores a liquid coolant. The secondary storage container has a form surrounding the primary storage container. The housing is a casing which houses the primary storage container and the secondary storage container. The heat conductive member is a member which is connected to the primary storage container, and which transfers heat for cooling a sample which is irradiated with a charged particle beam. A secondary storage space which stores a vaporized coolant generated by vaporization of the liquid coolant is provided between the primary storage container and the secondary storage container.

According to the structure described above, because the secondary storage space is provided between the primary storage container and the secondary storage container; that is, inside the secondary storage container, the vaporized coolant generated in the primary storage space moves from the primary storage space to the secondary storage space, and is accumulated in the secondary storage space. The secondary storage container is cooled at all times by the vaporized coolant. Because a temperature of the vaporized coolant generated in the primary storage space is close to a temperature of the liquid coolant, a state can be formed in which the primary storage container is wrapped with a low-temperature bracket. Radiant heat from the outside flows into the liquid coolant in the primary storage container via such a low-temperature bracket. Because of this configuration, heat inflow to the liquid coolant can be suppressed.

In an embodiment of the present disclosure, the secondary storage container is provided surrounding the primary storage container. When a bottom is provided in the secondary storage container, the vaporized coolant can be naturally stored inside the secondary storage container. Alternatively, a configuration may be employed in which the bottom is not provided in the secondary storage container, and the vaporized coolant is stored or circulated in the secondary storage container. Alternatively, a configuration may be employed in which the secondary storage space is provided at a lower side of the primary storage space or extends to the lower side of the primary storage space. In an embodiment of the present disclosure, an inside space of the housing is a vacuum space. As the charged particle beam device, a transmission electron microscope, a scanning electron microscope, an ion beam irradiation apparatus, and the like may be exemplified.

In an embodiment of the present disclosure, the primary storage container is thermally connected to the housing via the secondary storage container. According to this configuration, a heat conducting path from the housing to the primary storage container can be elongated, and a heat absorbing portion may be provided on the heat conducting path, so that the heat inflow to the primary storage container is reduced.

In an embodiment of the present disclosure, the housing holds an upper part of the secondary storage container, and a lower part of the secondary storage container is connected to a lower part of the primary storage container. In this configuration, the primary storage container is held by the housing via the secondary storage container. An upper part of the primary storage container is in an isolated state in which the upper part does not contact any structure at a periphery thereof.

According to the structure described above, the heat transferred from the housing to the upper part of the secondary storage container is transferred from the upper part of the secondary storage container to the lower part of the secondary storage container, and then from the lower part of the secondary storage container to the lower part of the primary storage container. Because the vaporized coolant exists in the secondary storage container and the secondary storage container itself is in a quite cooled state; that is, because the heat is absorbed by the vaporized coolant in the secondary storage container, the heat inflow to the liquid coolant in the primary storage container is reduced. In the secondary storage space, the vaporized coolant which becomes lighter by absorbing the heat naturally ascends, and is finally discharged to the outside. In place of the discharged vaporized coolant, cold vaporized coolant generated in the primary storage space flows into the secondary storage space. These actions take place simultaneously. With such a configuration, the secondary storage container is put in a cold state at all times.

In an embodiment of the present disclosure, the cooling apparatus further comprises a common bottom plate that functions as a bottom plate of the primary storage container and as a bottom plate of the secondary storage container. The common bottom plate is connected to the heat conductive member. The common bottom plate defines a bottom of the secondary storage space. According to this configuration, a number of components of the cooling apparatus can be reduced. In addition, a heat conducting efficiency can be improved.

In an embodiment of the present disclosure, the cooling apparatus further comprises an introduction pipe that introduces the liquid coolant to the primary storage space. A level of a lower end opening of the introduction pipe is lower than a level of an upper opening of the primary storage container. According to this configuration, entrance of the liquid coolant into the secondary storage container can be prevented.

In an embodiment of the present disclosure, the cooling apparatus further comprises a discharge pipe that discharges a vaporized coolant ascending from the secondary storage space. The discharge pipe is connected to the secondary storage container while being separated from the primary storage container. In an embodiment of the present disclosure, the cooling apparatus further comprises a radiation shield provided between the secondary storage container and the housing. According to this configuration, inflow of the radiant heat to the primary storage container can be further reduced.

<FIG> shows a transmission electron microscope <NUM> equipped with a cooling apparatus <NUM> according to a first embodiment of the present disclosure. Alternatively, the cooling apparatus <NUM> may be equipped in other charged particle beam devices.

The transmission electron microscope <NUM> has a lens barrel <NUM>. In a sample chamber <NUM> of the lens barrel, there is provided a sample holder <NUM> which holds a sample which is an observation target. The sample holder <NUM> is held by a holding mechanism <NUM>. More specifically, the sample holder <NUM> is held by an arm <NUM> of the holding mechanism <NUM>. Inside of the lens barrel <NUM> is vacuum. That is, the sample chamber <NUM> is a vacuum chamber.

When the sample is a biological sample or the like, the sample is set in a cooled state. An apparatus for cooling the sample is the cooling apparatus <NUM>. A shield <NUM> is a member which surrounds the sample holder <NUM>. Radiant heat is blocked by the shield <NUM>. A heat conductive member <NUM> formed from a hard material having a superior heat conductance (for example, copper) is provided between the sample holder <NUM> and the cooling apparatus <NUM>. The heat conductive member <NUM> has, for example, a rod-shape form.

A heat conductive member <NUM> which is flexible is provided between a tip end of the heat conductive member <NUM> and the sample holder <NUM>. In addition, a heat conductive member <NUM> which is flexible is provided between the tip end of the heat conductive member <NUM> and the shield <NUM>. Each of the heat conductive members <NUM> and <NUM> is formed from a soft material having a superior heat conductance (for example, a silver foil). On the shield <NUM>, there are formed an incidence opening and an emission opening for allowing electron beams to pass through. When viewed from above, a central axis of the heat conductive member <NUM> and a central axis of the arm <NUM> cross each other.

The cooling apparatus <NUM> will now be described. A housing <NUM> has a circular tubular shape. An inside space <NUM> of the housing <NUM> is vacuum. In the housing <NUM>, a primary storage container <NUM> having a circular tubular shape is placed, and a secondary storage container <NUM> having a circular tubular shape is placed wrapping or surrounding the primary storage container <NUM>. The primary storage container <NUM> functions as a liquid coolant container. An inside space of the primary storage container <NUM> is a primary storage space <NUM>, and the liquid coolant is stored therein. The liquid coolant is, for example liquid nitrogen. A liquid surface sensor <NUM> is placed along a center axis of the primary storage space <NUM>. The liquid surface sensor <NUM> has a heat insulating structure, and there is only a very little heat conduction via the liquid surface sensor <NUM>.

The secondary storage container <NUM> is a container which stores a vaporized coolant. The secondary storage container <NUM> functions as a vaporized coolant container. An inside space of the secondary storage container <NUM> is a secondary storage space <NUM>. In other words, a gap between the primary storage container <NUM> and the secondary storage container <NUM> is the secondary storage space <NUM>. The liquid coolant is evaporated and vaporized in the primary storage space <NUM>, and the vaporized coolant is generated. The vaporized coolant flows from an upper part of the primary storage space <NUM> into the secondary storage space <NUM> provided at a periphery of the primary storage space <NUM>. The vaporized coolant having a temperature increased (that is, having a weight reduced) due to radiant heat or the like in the secondary storage space <NUM> ascends in the secondary storage space <NUM>, and flows out to the outside. In place of the vaporized coolant which has flowed out, cold vaporized coolant from the primary storage space <NUM> flows into the secondary storage space <NUM>. These actions take place simultaneously.

A detection signal from the liquid surface sensor <NUM> is sent via a signal line <NUM> to a controller <NUM>. The controller <NUM> controls supply of the liquid coolant based on the detection signal. More specifically, the controller <NUM> controls an operation of a coolant supplying portion <NUM> having a tank <NUM>. The tank <NUM> is a supply source of the liquid coolant. The liquid coolant from the liquid coolant supplying portion <NUM> is sent via a pipe <NUM> to the cooling apparatus <NUM>.

Next, a structure and an operation of the cooling apparatus <NUM> will be described in detail with reference to <FIG>. As described above, the cooling apparatus <NUM> comprises the housing <NUM>, the primary storage container <NUM>, and the secondary storage container <NUM>. The inside space of the primary storage container <NUM> is the primary storage space <NUM>, and the inside space of the secondary storage container <NUM> is the secondary storage space <NUM>. The primary storage space <NUM> is a circular column-shape space which stores the liquid coolant, and the secondary storage space <NUM> is an annular space which stores the vaporized coolant. The primary storage container <NUM> and the primary storage space <NUM> are surrounded by the secondary storage space <NUM> except for a bottom portion.

More specifically, the housing <NUM> is formed from, for example, a metal such as stainless steel, and includes a body 30A having a circular tubular shape, a ceiling wall 30B having a circular disk shape, and a bottom wall 30C having a circular disk shape. The body 30A is connected to an outer end of a hollow connection member <NUM>. An inside space of the connection member <NUM> and the inside space <NUM> of the housing <NUM> are connected to each other. An inner end of the connection member <NUM> is connected to an outer wall of the lens barrel <NUM>.

The secondary storage container <NUM> is formed from, for example, a metal such as stainless steel or copper, and includes a body 34A and a ceiling wall 34B. In the present embodiment, the body 34A and the ceiling wall 34B are formed from stainless steel. A common bottom plate <NUM> has a circular disk shape, and functions as a bottom wall of the secondary storage container <NUM>. The common bottom plate <NUM> is formed from a material having a superior heat conductance (for example, copper).

The primary storage container <NUM> is formed from a material having a superior heat conductance (for example, copper), and includes a body 32A and an opening 32B. The common bottom plate <NUM> functions as a bottom wall of the primary storage container <NUM>. The body 32A has a tubular shape, and the opening 32B is circular. The primary storage container <NUM> is enclosed in the secondary storage container <NUM>. As described above, the bottom walls of the primary and secondary storage containers <NUM> and <NUM> are integrated.

An upper structure <NUM> connects the housing <NUM> and the secondary storage container <NUM>. In other words, the housing <NUM> holds the secondary storage container <NUM> (and the primary storage container <NUM>) via the upper structure <NUM>. The secondary storage container <NUM> holds the primary storage container <NUM> or the like. In summary, the housing <NUM> holds the secondary storage container <NUM>, the common bottom plate <NUM>, the primary storage container <NUM>, and the heat conductive member <NUM> via the upper structure <NUM>.

The upper structure <NUM> has tubular members <NUM>, <NUM>, and <NUM>. These tubular members <NUM>, <NUM>, and <NUM> penetrate through and are fixed on the ceiling wall 30B of the housing <NUM>. Lower ends of the tubular members <NUM>, <NUM>, and <NUM> are connected to the ceiling wall 34B of the secondary storage container <NUM>.

The pipe <NUM> passes inside the tubular member <NUM>, and a nozzle <NUM> is formed at a lower end portion of the pipe <NUM>. A cap <NUM> is provided on the tubular member <NUM>, and holds the pipe <NUM>. A lower end opening (ejection port) of the nozzle <NUM> passes through the opening 32B of the primary storage container <NUM>, and extends to the inside of the primary storage space <NUM>. This configuration prevents entry of the liquid coolant into the secondary storage space <NUM> during ejection (refer to reference numeral <NUM>) of the liquid coolant by the nozzle <NUM>.

The liquid surface sensor <NUM> is a rod-shaped member, and passes inside the tubular member <NUM>. A cap <NUM> is provided on the tubular member <NUM>, and holds the liquid surface sensor <NUM>. The tubular member <NUM> functions as a port for discharging the vaporized coolant. A cap <NUM> is provided on the tubular member <NUM>, and a pipe <NUM> is connected to the cap <NUM>. Each of the tubular members <NUM>, <NUM>, and <NUM> is formed from, for example, a metal such as stainless steel. Alternatively, each of the caps <NUM>, <NUM>, and <NUM> may be formed from a material having a superior heat insulating characteristic.

As already described, intermediate portions of the three tubular member <NUM>, <NUM>, and <NUM> are fixed on the ceiling wall 30B of the housing <NUM>, and the lower ends of the three tubular members <NUM>, <NUM>, and <NUM> are fixed on the ceiling wall 34B of the secondary storage container <NUM>. With this configuration, the housing <NUM> holds the secondary storage container <NUM> and the primary storage container <NUM>. Here, the housing <NUM> itself does not contact the secondary storage container <NUM>. A vacuum layer exists between the housing <NUM> and the secondary storage container <NUM>. Main portions (portions other than a bottom portion) of the primary storage container <NUM> are separated from peripheral structures, and are in a non-contact state with these structures.

The common bottom plate <NUM> is fixed to an end 24A of the heat conductive member <NUM>. In reality, the heat conductive member <NUM> is held by the housing <NUM> via the secondary storage container <NUM> by this fixation. In this manner, the housing <NUM> supports all of the structures which are inside the housing <NUM> via the upper structure <NUM>.

In <FIG>, h1 shows a level of the ceiling of the secondary storage space <NUM>, h2 shows a level of the opening of the primary storage container <NUM>, and h3 shows a level of the ejection opening of the nozzle <NUM>. These parameters are in a relationship of h1 > h2 > h3. When the liquid coolant is vaporized in the primary storage container <NUM> and the vaporized coolant is thereby generated, as shown by reference numeral <NUM>, the vaporized coolant flows over an upper edge of the body 32A of the primary storage container <NUM>, and into the secondary storage space <NUM> in the secondary storage container <NUM>. In the secondary storage space <NUM>, vaporized coolant which is heated by the radiant heat or conducted heat and which thus becomes lighter ascends. In place of the heated and lightened vaporized coolant, cold and heavy vaporized coolant from the primary storage space <NUM> flows into the secondary storage space <NUM>. As shown by reference numeral <NUM>, the ascended vaporized coolant flows through an upper side in the secondary storage container <NUM>, and into the tubular member <NUM>, and is discharged via the pipe <NUM> to the outside. Alternatively, a backflow prevention valve which prevents entry of the atmospheric air may be provided on the pipe <NUM>. According to this configuration, generation of frost or ice due to inflow of the atmospheric air can be prevented.

Thus, in the secondary storage space <NUM>, the cold vaporized coolant is accumulated at all times. The secondary storage container <NUM> itself is put in a low-temperature state. With respect to radiant heat 82A and 82B, the secondary storage container <NUM> (and the secondary storage space <NUM>) functions as a blocking member or an absorbing member of the radiant heat, and prevents the radiant heat 82A and 82B from directly reaching the primary storage container <NUM>. In addition to the body 34A, the ceiling wall 34B also realizes the radiant heat blocking function.

As shown by arrows A, B, C, D, and E, the heat of the outside flows into the ceiling wall 34B of the secondary storage container <NUM> via the upper structure <NUM>. The heat is transferred from the ceiling wall 34B to the body 34A, and then from the body 34A via the common bottom plate <NUM> to the body 32A of the primary storage container <NUM>. In this manner, because a heat conducting path with a fold-back is formed and a heat absorbing portion is present in the midway thereof, an amount of heat inflow due to heat conduction to the primary storage container becomes very small. Alternatively, a plurality of fold-backs may be provided on the heat conducting path.

As described, the secondary storage container <NUM> and the secondary storage space <NUM> function as a low-temperature bracket, from the viewpoint of radiation. The secondary storage container <NUM> and the secondary storage space <NUM> function as a heat absorbing element from the viewpoint of heat conduction. In the present embodiment, the liquid surface sensor <NUM> is provided, and the controller controls the amount of supply of the liquid coolant based on the detection signal from this sensor. Thus, overflow of the liquid coolant from the primary storage container <NUM> can be prevented. Because direct heat inflow with respect to the upper part of the primary storage container <NUM> is avoided, even when a relatively large amount of liquid coolant is introduced into the primary storage container <NUM>, bubbling does not tend to be caused. As a result, the cooling capability of the cooling apparatus <NUM> can be significantly improved.

<FIG> shows a cross section shown in <FIG> by reference numeral <NUM>. Specifically, a multiplexed structure of concentric circles, including the body 30A of the housing, the body 34A of the secondary storage container, and the body 32A of the primary storage container, is shown. The inside of the body 32A is the primary storage space <NUM>, the inside of the body 34A is the secondary storage space <NUM>, and the inside space <NUM> of the body 30A is a vacuum space.

<FIG> shows a cooling apparatus <NUM> according to a comparative example. A storage container <NUM> is provided in a housing <NUM>. The housing <NUM> holds the storage container <NUM> via an upper structure <NUM>. A bottom wall <NUM> of the storage container <NUM> is connected to a heat conductive member <NUM>. An inside space of the storage container <NUM> is a storage space <NUM> which stores a liquid coolant. A vaporized coolant generated by vaporization in the storage space is pushed out from the storage space to the outside, as shown by reference numeral <NUM>.

According to the structure of the comparative example, radiant heat from the housing <NUM> can easily reach the storage container <NUM>. In addition, as shown by arrows F, G, and H, the heat is directly transferred to the storage container <NUM> via the upper structure <NUM>. With this configuration, bubbling tends to be easily caused in the storage container <NUM>. In particular, the bubbling tends to be easily caused when a relatively large amount of liquid coolant is introduced into the storage container <NUM>. In addition, in this case, an amount of consumption of the liquid coolant becomes large.

On the contrary, according to the cooling apparatus of the first embodiment shown in <FIG>, with the secondary storage container and the secondary storage space, the heat transferred to the liquid coolant in the primary storage container can be significantly reduced in comparison to the comparative example, and the bubbling can be effectively suppressed. At the same time, the amount of consumption of the coolant is reduced.

<FIG> shows a cooling apparatus <NUM> according to a second embodiment of the present disclosure. Elements which are already described are assigned the same reference numerals and their descriptions will not be repeated. This is similarly applicable to <FIG> to be described next.

In <FIG>, a secondary storage container <NUM> is provided in a manner to wrap the primary storage container <NUM>, in the housing <NUM>. A bottom wall <NUM> of the secondary storage container <NUM> is fixed at an intermediate position of the primary storage container <NUM>. That is, the secondary storage container <NUM> does not extend to a bottom plate <NUM>, and the secondary storage container <NUM> and the bottom plate <NUM> do not contact each other. Reference numeral <NUM> shows a gap between the secondary storage container <NUM> and the bottom plate <NUM>.

According to this configuration, although entry of the radiant heat to the primary storage container <NUM> via the gap <NUM> is of a concern, the direct heat transfer to a heat conductive member <NUM> via the secondary storage container <NUM> can be avoided.

<FIG> shows a cooling apparatus <NUM> according to a third embodiment of the present disclosure. In the housing <NUM>, the primary storage container <NUM> is provided, and the secondary storage container <NUM> is provided wrapping the primary storage container <NUM>. A circular tubular radiation shield <NUM> is provided between the secondary storage container <NUM> and the housing <NUM>. The radiation shield <NUM> wraps an entirety of the secondary storage container <NUM> in a non-contacting manner. The radiation shield <NUM> is formed from, for example, copper. As shown by reference numeral 132A, the radiation shield <NUM> is fixed to and held by the upper structure <NUM>. An opening 132B is formed at a lower part of the radiation shield <NUM>, and the heat conductive member <NUM> passes through the opening 132B in a non-contacting manner.

According to the third embodiment, the radiant heat reaching the secondary storage container <NUM> can be reduced, and, consequently, along with the radiant heat blocking action of the secondary storage container <NUM>, the radiant heat reaching the primary storage container <NUM> can be significantly reduced. While the lower part of the radiation shield <NUM> may be connected to the heat conductive member <NUM>, by employing a non-contacting configuration, the heat transferred to the heat conductive member <NUM> can be reduced.

Claim 1:
A cooling apparatus for a charged particle beam device, the cooling apparatus comprising:
a primary storage container (<NUM>) that has a primary storage space (<NUM>) which stores a liquid coolant;
a secondary storage container (<NUM>, <NUM>) that surrounds the primary storage container (<NUM>);
a secondary storage space (<NUM>) being the gap between the primary storage container (<NUM>) and the secondary storage container (<NUM>, <NUM>), wherein the secondary storage space (<NUM>) is arranged to store a vaporized coolant generated by vaporization of the liquid coolant in the primary storage container (<NUM>), the vaporized coolant flowing through an upper opening (32B) of the primary container (<NUM>) into the secondary storage space (<NUM>);
a housing (<NUM>) that houses the primary storage container (<NUM>) and the secondary storage container (<NUM>, <NUM>); and
a heat conductive member (<NUM>) that is connected to the primary storage container (<NUM>) and arranged to transfer heat to cool a sample which is irradiated with a charged particle beam, and
an introduction pipe (<NUM>) that is arranged to introduce the liquid coolant to the primary storage space (<NUM>), wherein a level of a lower end opening of the introduction pipe (<NUM>) is lower than a level of the upper opening (32B) of the primary storage container (<NUM>) so that the entrance of the liquid coolant into the secondary storage container (<NUM>, <NUM>) can be prevented.