JP7723968B2 - stage - Google Patents

Description

The present invention relates to a stage, and in particular to a stage that can be cooled or heated from above the sample.

In recent years, advances have been made in high-resolution analysis using electron microscopes such as transmission electron microscopes (TEM) and scanning transmission electron microscopes (STEM). For example, there is a demand for high-resolution analysis, from nanometer-order to picometer-order resolution. Recently, "in-situ observation," in which a sample is cooled (or heated, electric or magnetic field applied, or rotated) while being observed inside the electron microscope, has been attracting attention. Sample cooling is particularly considered effective in reducing damage to the sample caused by the electron beam, and sample cooling from this perspective is also being attempted. For example, a known example of a device with a cooling means is a sample processing device using a scanning electron microscope. This device is equipped with a cooling stage in the sample chamber of the scanning electron microscope on which a sample with sublimated water is placed, and a manipulator that extends above the cooling stage and extracts required components of the sample under observation by the scanning electron microscope (Patent Document 1).

Japanese Unexamined Patent Publication No. 62-85840

Despite this need for cooling, conventional techniques, including the aforementioned Patent Document 1, only allow the sample to be attached to the top surface of the sample pedestal, and cooling is limited to the sample from below. In other words, with conventional cooling stages, it is common to affix the sample to the sample pedestal using double-sided tape or adhesive for observation. Existing methods are problem-free when it comes to observing temperature changes, and are rational in terms of the detector positioning. However, because samples always have thickness, with existing methods, the temperature changes from the bottom to the top of the sample, and the state of this change is observed.

When observing phenomena that occur due to temperature changes, such as phase transformations, it is highly likely that the phenomenon observed on the top surface is due to the transformation initiating from the thermally contacting bottom surface, with the process or results appearing on the surface. Therefore, in order to observe the 'initial stage' of material changes using temperature as a parameter, it is important to observe the surface where cooling or heating begins. However, with existing technology, temperature changes always occur from the bottom surface, making it difficult to capture this. This is a problem that can occur not only when cooling a sample, but also when heating a sample.

The present invention aims to solve the above problems by providing a stage that allows cooling or heating from above the sample.

To achieve the above objective, the inventor conducted extensive research into the stage mechanism, and as a result, came up with the present invention.

That is, the stage of the present invention is a stage having a sample pedestal on which a sample is mounted, a thermal insulating base installed under the sample pedestal, a heat conducting part installed on the top of the sample pedestal and made of a thermally conductive material, and a cooling part or a heating part, wherein the heat conducting part has a gap to prevent interference with an electron beam, and cools or heats the sample from above by coming into contact with the cooling part or the heating part .

Furthermore, in a preferred embodiment of the stage of the present invention, it is characterized by further comprising a thermoelectric element installed in proximity to the cooling section or the heating section.

Furthermore, in a preferred embodiment of the stage of the present invention, the heat conductive portion is extensible.

In a preferred embodiment of the stage of the present invention, the stage further comprises a sample pedestal holder that holds down the sample pedestal.

Furthermore, in a preferred embodiment of the stage of the present invention, a heat-conducting spacer having one or more holes is provided between the sample and the sample base holder.

Furthermore, in a preferred embodiment of the stage of the present invention, a leveling member is provided between the sample pedestal and the thermal insulating base.

Furthermore, in a preferred embodiment of the stage of the present invention, the thermoelectric element is a thermoelectric element that utilizes at least one of the Peltier effect and the Thomson effect.

Furthermore, in a preferred embodiment of the stage of the present invention, the heat dissipation side of the thermoelectric element is in contact with the cooling section, the heating section, or the heat conduction section.

Furthermore, in a preferred embodiment of the stage of the present invention, the cooling section is characterized by comprising at least one of a solid refrigerant, a liquid refrigerant, and a gas refrigerant.

The stage of the present invention has the advantageous effect of providing a stage that allows for cooling or heating from the top surface of the sample. Furthermore, the stage of the present invention has the advantageous effect of enabling accurate observation of the initial stages of material changes in the sample.

Figure 1 shows a conceptual diagram of an example stage in one embodiment of the present invention, where Figure 1(a) is a side view of the stage in one embodiment of the present invention, Figure 1(b) is a cross-sectional view of the stage taken along line A-A in Figure 1(a), and Figure 1(c) is an enlarged view of part B in Figure 1(b). Figure 2 shows an embodiment of a thermoelectric element applicable to the present invention, where Figure 2(a) shows a cross-sectional view of a Peltier element, and Figure 2(b) shows a schematic diagram of the principle of the Peltier element. 3A and 3B are conceptual diagrams of an example of a stage according to an embodiment of the present invention, in which Fig. 3A is a perspective view of the stage according to an embodiment of the present invention, and Fig. 3B is a top view of the stage.

The stage of the present invention is characterized by comprising a sample pedestal for mounting a sample, a thermally insulating base installed below the sample pedestal, a thermally conductive part installed above the sample pedestal and made of a thermally conductive material, and a cooling or heating part. In this invention, the sample stage for mounting a sample is not particularly limited, including its shape and structure, as long as it is capable of mounting a sample to be observed in an electron microscope. In addition, in this invention, the cooling or heating part is not particularly limited, including its shape and structure, as long as it is capable of cooling or heating a sample to be observed in an electron microscope. Furthermore, in this invention, a thermally insulating base is installed below the sample pedestal to eliminate complex temperature factors and ensure accurate experimentation. First, let us explain the case of cooling, rather than heating, as follows. Typically, the sample is fixed (using double-sided tape or adhesive) on the bottom surface and cooled from below. Furthermore, since the electron beam is irradiated from above and electron microscopes are essentially observed in a vacuum, the top surface is almost completely thermally insulated (vacuum). Cooling from the bottom creates a temperature gradient across the top, but after a certain amount of time, the temperature cools evenly. This process is sufficient if you want to understand the changes in the sample material as a whole. Next, if you cool from the top, for example, by sandwiching the sample between the top and bottom, the top surface will also cool. However, cooling from the bottom will also occur. In this case, the effects of cooling from the top and bottom will be mixed. While this has the advantage of a small temperature gradient and firmly fixing the sample, it can be difficult to determine whether the change is due to cooling or cooling from the bottom when you want to understand changes on the top surface (observation surface). Now, consider the case where the bottom surface is not cooled but is not thermally insulated. In this case, heat flows in from the bottom. As a result, cooling the top surface is considered to be in the same state as heating the bottom surface at the same time. Heat flow from the bottom not only affects the temperature of the top surface, but also creates a temperature gradient across the entire sample, resulting in uneven temperature and making it difficult to accurately determine the temperature at which the change occurred. Furthermore, if the bottom surface is thermally insulated, this can be considered to be the exact opposite of cooling from the bottom surface. This makes it easier to interpret the phenomenon that has occurred. The need to thermally insulate the bottom surface has been explained above, but in this invention, the bottom surface can be thermally insulated by using a thermal insulating base installed below the sample pedestal. The above explanation was given using the case of cooling as an example, but the need to thermally insulate the bottom surface is similar when heating.

The present invention also includes a heat-conducting section that is installed on top of the sample pedestal and is made of a thermally conductive material. This allows the sample to be cooled or heated from above, and since the surface from which observation begins is the top surface of the sample, it is possible to observe from the surface from which cooling or heating begins, which was not possible with conventional methods, and ultimately makes it possible to accurately observe initial changes in the material.

In the present invention, thermally conductive materials that can be used in the heat conduction portion are not particularly limited, but examples include copper and copper alloys, aluminum and aluminum alloys, silver, gold, and tungsten.

Furthermore, in a preferred embodiment of the stage of the present invention, the heat-conducting part made of the thermally conductive material is in contact with the cooling part or the heating part. In the present invention, the heat-conducting part installed on the top of the sample pedestal comes into contact with the cooling part or the heating part, making it possible to cool or heat the sample from above.

In addition, while the present invention allows for both cooling and heating of samples, using a cooling unit offers the following advantages. By cooling the sample via a heat-conducting unit made of a thermally conductive material near the top surface of the sample, the cooled heat-conducting unit can function as a cold trap to prevent contamination.

When the term "cold trap" is used here, it can be understood as a device that cools and captures trace amounts of suspended matter (gases, such as hydrocarbons) in a vacuum. In other words, if there is gas in the vacuum, it is expected that it will be bombarded by the sample along with the electron beam and accumulate on the sample. When a cooling element is placed near the top surface, as in the present invention, a mechanism can be realized that surrounds the vicinity of the sample with a cooled metal element (cooling element) within a range that does not block the electron beam irradiation, creating a localized region with a high degree of vacuum. This allows for the creation of a mechanism that cools and condenses the gas that escapes in order to collect it, and ultimately prevents the gas present in the vacuum inside the electron microscope from coming into contact with the sample.

In a preferred embodiment of the stage of the present invention, the cooling section is characterized by comprising at least one of a solid refrigerant, a liquid refrigerant, and a gas refrigerant. The refrigerant used in the cooling section can be selected appropriately depending on the application and is not particularly limited. From the perspective of versatility, a preferred medium is a liquid. While a liquid (such as water) can be used to adjust the temperature using a general-purpose device (a cooling chiller), being a fluid can be a source of vibration. Liquid nitrogen or liquid helium can also be used as the liquid.

Furthermore, in the present invention, the cooling unit may be a solid refrigerant, as this can reduce the impact of vibrations caused by water flow or pulsating flow to nearly zero compared to water cooling. That is, in the present invention, the heat dissipation surface of a Peltier element or the like can be cooled with a solid refrigerant such as dry ice. This makes it possible to reduce the impact of vibrations caused by water flow or pulsating flow to nearly zero compared to water cooling. Furthermore, in the case of a solid, it is difficult to adjust the temperature of the cooling unit, but this can be controlled using a thermoelectric element, as described below.

On the other hand, flowing cooling gas at a minute flow rate is also less affected by vibration, and can therefore be used in the present invention. Examples of cooling gases include gasified liquid nitrogen. This allows for effective cooling of the sample. In the present invention, the cooling gas is not limited to liquid nitrogen. It is believed that simply passing weak gas through a heat dissipation surface is practically unaffected by vibration. Therefore, as described above, even when a solid refrigerant is actually used as the cooling unit, it is sufficient to pass cold air through a gap rather than pressing it against the heat dissipation surface. Similarly, when liquid nitrogen gas is used, passing the cooling gas through the heat dissipation surface allows for observation without being affected by vibration. The difficulty of adjusting the temperature of the cooling unit can be addressed by using a thermoelectric element, as described below.

In a preferred embodiment of the stage of the present invention, the heat conductive portion is extendable. That is, an extendable heat conductive portion is provided extending laterally from the cooling or heating portion. A sample can be placed on a separately prepared thermally insulating portion, and the heat conductive portion can be extended above the sample to cool or heat it. That is, a sample pedestal portion with a thermally insulated structure can be prepared outside the stage, and then the heat conductive portion can be extended above the sample pedestal. The sample can then be sandwiched between the heat conductive portion and the sample pedestal. This structure can also be a preferred embodiment of the present invention. In the figures described below, the structure is stacked on the stage to save space, but it is also possible to extend the heat conductive path to a location away from the stage. The extendable heat conductive portion can have any shape, such as an arm or clamp. In the present invention, the extendable heat conductive portion can be made of a thermally conductive material as described above. The heat conductive portion is not particularly limited in shape or structure, as long as it is capable of contacting the cooling or heating portion and transmitting the cold or heat source from the cooling or heating portion to the sample.

In a preferred embodiment of the stage of the present invention, the stage further comprises a thermoelectric element installed adjacent to the cooling unit or the heating unit. As described above, in an embodiment in which an extensible heat conduction unit is provided, the thermoelectric element can be installed on the heat conduction unit. In the present invention, the placement position of the thermoelectric element is not particularly limited as long as it is installed adjacent to the cooling unit or the heating unit. The thermoelectric element makes it possible to efficiently set the required temperature for the sample, i.e., to control the temperature. In an embodiment using a thermoelectric element, the cooling/heating response is good, minimizing the effects of thermal drift. Furthermore, the good cooling/heating response allows for precise temperature control. In an embodiment using a thermoelectric element, cooling and heating can be achieved with a single element simply by reversing the direction of current flow. At the same time, the fast cooling and heating response makes it easy to set the desired temperature. Furthermore, precise temperature control is possible by adjusting the input power output, allowing for precise temperature control and minimizing the effects of thermal drift.

In a preferred embodiment of the stage of the present invention, the heat conduction part has a gap that prevents interference with the electron beam. In this invention, the heat conduction part is installed above the sample. Therefore, if the heat conduction part is located at a position where the electron beam is irradiated, that part will interfere with the electron beam. The heat conduction part can be configured to be curved to prevent interference with the electron beam, but interference can also be prevented by providing a gap. For example, a circular hole can be provided in the heat conduction path on the top surface of the sample to prevent interference with the electron beam. The gap does not necessarily have to be circular; it can be square and can be configured so that plates press down on the sample from both sides or multiple directions. However, a circular gap is preferable from the perspective of considering isotropic heat conduction to the sample.

In a preferred embodiment of the stage of the present invention, the heat dissipation side of the thermoelectric element is in contact with the cooling unit, heating unit, or heat conduction unit. In other words, in this invention, the thermoelectric element may be positioned adjacent to the cooling unit, heating unit, or heat conduction unit. For example, the cooling unit, heating unit, or heat conduction unit, such as a solid refrigerant, may be pressed against the heat dissipation side (heat dissipation surface), or a gap may be provided to allow cold air to be applied. When applying cold air, either natural convection or forced convection using a fan or the like may be used. However, if forced convection generates vibrations, natural convection is preferable, depending on the level of forced convection. Even in the case of natural convection, the solid refrigerant has a sufficiently low temperature, creating a large temperature gradient between the heat dissipation surface and the cold air from the cooling unit, such as a solid refrigerant. This creates sufficient heat transfer and is believed to adequately cool the heat dissipation surface. Note that forced convection is more effective than natural convection, and water cooling is more effective than air cooling for heat dissipation.

In a preferred embodiment of the present invention, the thermoelectric element is a thermoelectric element that utilizes at least one of the Peltier effect and the Thomson effect. The Peltier effect (also called the Peltier effect) is the effect of converting electrical energy into thermal energy, and is a phenomenon in which a temperature difference occurs between the two ends of two dissimilar metals (or semiconductors) when the two ends are connected and an electric current is passed through them. This is particularly called a Peltier element and is used to cool precision instruments, wine cellars, and the like. The Thomson effect is the effect of generating heat other than Joule heat (heat is absorbed when the current is reversed) that occurs when an electric current is passed through a uniform metal (or dissimilar metals) with a temperature gradient. Both are capable of generating and absorbing heat.

In addition, a heat dissipation member may be installed between the thermoelectric element and the cooling unit, heating unit, or heat conduction unit to efficiently dissipate heat from the thermoelectric element.

In a preferred embodiment of the stage of the present invention, the thermoelectric element is a Peltier element, which provides good cooling and heating response and minimizes the effects of thermal drift. Peltier elements are also called Peltier elements (thermo-modules), which is a general term for elements that utilize the Peltier effect. The currently mainstream structure that is considered to have the best performance is called the "π-type," which has a structure like that shown in Figure 2. By passing a current through a PN junction using a P-type semiconductor and an N-type semiconductor, heat can be dissipated between the P-N and absorbed between the N-P.

The principle is as follows. Figure 2 shows one embodiment of a thermoelectric element applicable to the present invention. Figure 2(a) shows a cross-sectional view of a Peltier element, and Figure 2(b) shows a schematic diagram of the Peltier element's principle. In Figure 2(a), 21 indicates the hot-side metal (mainly Cu), 22 indicates the ceramic substrate (mainly alumina), 23 indicates the heat dissipation surface, 24 indicates the N-type semiconductor, 25 indicates the P-type semiconductor, 26 indicates the electric wire, 27 indicates the power source, 28 indicates the heat absorption, 29 indicates the conduction band of the N-type semiconductor, 30 indicates the heat dissipation, 31 indicates the positive side, 32 indicates the heat absorption side, 33 indicates the valence band, 34 indicates the heat dissipation side, 35 indicates the negative side, 36 indicates the cold-side metal (mainly Cu), 37 indicates the cold-side metal (mainly Cu), 38 indicates electrons, 39 indicates holes, and 40 indicates the conduction band of the P-type semiconductor.

In Figure 2(a), the negative pole is connected to metal 36 on the N-type semiconductor 24 side. Therefore, voltage pushes electrons from the conduction band of metal 36 up into the conduction band 29 of N-type semiconductor 24. At this time, because there is an energy gap between the conduction band of metal 36 and the conduction band 29 of N-type semiconductor 24, the electrons absorb thermal energy from metal 36, thereby cooling it. The electrons then flow and fall from the conduction band 29 of N-type semiconductor 24 into the conduction band of metal 21. The energy gap between the two bands causes the electrons to release thermal energy. In this way, metal 21 on the hot side is heated. Furthermore, the flowing electrons fall from the conduction band of metal 21 into holes 39 flowing through the P-type semiconductor 25, releasing thermal energy and heating metal 21 on the hot side. In the P-type semiconductor 25, voltage generates holes 39, which flow from the cold side 37 to the hot side 21. The electrons generated at that time are pushed up into the conduction band of the cold-side metal by the voltage, absorbing thermal energy according to the energy gap and cooling the cold-side metal 37. In this way, heat is carried from the cold side to the hot side of the Peltier module as a result of the current flow. In addition to the thermal energy carried by the current, there is also thermal energy carried by thermal conduction, but because the thermal energy carried by thermal conduction flows in the opposite direction, the less of it there is, the better the performance of the Peltier module. In other words, removing the thermal energy from the hot side as quickly as possible using a heat sink or similar will allow the Peltier module to perform well. Simply put, electrons carry (remove) heat.

There are no particular restrictions on the semiconductor material, and any can be used, but Bi-Te semiconductors are considered to have the best performance and are the mainstream.

Generally, Peltier device performance can be measured by the temperature difference ΔT that can be achieved relative to the temperature Th when the temperature on the heat-dissipating side is constant. For example, for Th = 75, 50, or 25°C, ΔT = 93, 85, or 75. If the heat-dissipating surface were simply cooled to, say, liquid nitrogen temperature (-196°C), the heat-absorbing surface would likely exceed minus 200°C. However, due to the characteristics of the material, in reality, ΔT is estimated to be 10°C at temperatures near liquid nitrogen. The lower the temperature, the less heat there is to excite electrons, reducing the Peltier cooling capacity. Additionally, the lower the temperature, the greater the electrical resistance of the semiconductor, causing it to self-heat due to current, resulting in a reduction in overall cooling capacity.

In addition, in a preferred embodiment of the present invention, the heat radiation side of the thermoelectric element is in contact with the cooling unit, heating unit, or heat conduction unit, from the viewpoint that, when cooling, it is possible to set a lower temperature by cooling the heat radiation side of the thermoelectric element, and, when heating, it is possible to heat with less load by warming the heat radiation side of the thermoelectric element. The following examples mainly describe the case of cooling, but in the present invention, heating is also possible using a thermoelectric element. Since the bottom surface of the thermoelectric element cools during heating, it is necessary to heat the heating unit (process at a higher temperature than the bottom surface). In this case, it can function as a heating unit rather than a cooling unit.

While the phenomenon is simply reversed when it comes to heating compared to cooling, the practicality of Peltier elements and other thermoelectric devices (whether multi-stage or not) also influences their practicality. Basically, when aiming for the lowest possible temperatures, multi-stage thermoelectric devices, such as Peltier elements, can be used. In this case, a pyramid-like structure can be used, with the heat-absorbing surface (top layer) being smaller and the heat-dissipating surface becoming larger. This structure is used because, since the larger the surface area, the greater the heat absorption capacity, the heat absorbed by the smaller upper layer can be dissipated by the larger lower layer. When using a device for heating by reversing the polarity of the current, it is not as simple as this. Heat from the larger lower layer tends to flow into the smaller upper layer all at once. If the upper layer cannot absorb the heat, heat accumulates in the middle layer, which tends to be higher than the upper layer. For this reason, it is thought that most Peltier elements, even when used for heating, will reach around +100°C (a temperature at which the solder at the joint does not deteriorate). Peltier elements create heat absorption and heat dissipation surfaces through the movement of electrons, and by controlling the amount of current passed through the Peltier element, it is, in principle, possible to precisely control the temperature from near room temperature to the negative range. These effects enable stable, high-resolution observations.

In a preferred embodiment of the stage of the present invention, the stage further comprises a sample pedestal holder for holding the sample pedestal, from the viewpoint of firmly fixing the sample to suppress vibration and thermal drift and ensuring sufficient thermal contact. When the sample must be fixed from the underside, the height must be adjusted each time depending on the sample thickness. However, the sample pedestal holder makes it possible to fix various samples. For example, a ring screw type sample pedestal holder can be used to accommodate various sample thicknesses. The sample pedestal holder does not necessarily have to be a screw, and can also be a leaf spring, coil spring, clamp mechanism, etc. A screw type sample pedestal holder is preferable because it allows for adjustable clamping pressure and ensures sufficient thermal contact. The material of the sample pedestal holder, such as the ring screw, can be one with high thermal conductivity, such as gold, silver, copper, aluminum, copper, or alloys of these. Furthermore, the material of the sample pedestal holder is preferably a material different from that of the heat conduction path to avoid galling due to the same metal.

In a preferred embodiment of the stage of the present invention, a thermally conductive spacer with one or more holes is provided between the sample and the sample pedestal holder to uniformly cool and heat the observation area, since a temperature gradient occurs from the heat-conducting portion toward the center of the sample. For example, when a ring screw is used as the sample pedestal holder, a temperature gradient occurs from the vicinity of the ring screw toward the center of the sample. Therefore, in order to uniformly cool and heat the observation area, it may be preferable to lay a mesh-like thermal conduction path over the sample. For example, a thermally conductive spacer with multiple holes can be placed between the sample pedestal holder, such as a ring screw, and the sample. While this reduces the observable field of view, it can reduce the temperature gradient between the outer edge and the center of the holes. Furthermore, electrolytically polished samples, for example, have a gentle depression from the outer edge to the center, which may make thermal contact with the sample pedestal holder, such as a ring screw, difficult. In such cases, a relatively soft metal foil, such as indium foil (which may have holes), can be inserted between the sample and the thermally conductive spacer.

In a preferred embodiment of the stage of the present invention, a leveling member is provided between the sample pedestal and the thermally insulating base to improve thermal contact. Ideally, the top and bottom surfaces of an SEM sample are parallel after polishing, but in reality, they are slightly misaligned. Furthermore, there is no guarantee that the sample pedestal portion on the stage and the sample pedestal holder, such as a ring screw, will be parallel as well. Because the sample must be fixed to the sample pedestal, if the respective components and the sample are not parallel, gaps may form, resulting in insufficient thermal contact and poor heat transfer. Therefore, by placing a leveling member directly below the sample pedestal, a mechanism can be created in which the top surface of the sample becomes parallel to the sample pedestal holder, depending on the force with which the sample pedestal holder, such as a ring screw, presses the sample. The leveling member used in the present invention is not particularly limited, but may be, for example, a ball or spring, centrally located or multiple balls or springs, arranged in a balanced arrangement. A leveling member such as a ball can also provide thermal insulation between the sample pedestal and the bridge (thermally insulating base).

The following describes the stages of one embodiment of the present invention with reference to the drawings, but the present invention is not intended to be limited to these.

Figure 1 shows a conceptual diagram of an example stage in one embodiment of the present invention. Figure 1(a) shows a side view of the stage in one embodiment of the present invention, Figure 1(b) shows a cross-sectional view of the stage along the A-A cross section of Figure 1(a), and Figure 1(c) shows an enlarged view of part B of Figure 1(b). In Figure 1, 1 is a thermally insulating base, 2 is a heat-conducting part, 3 is a cooling or heating connection part, 4 is a thermoelectric element (if a thermoelectric element is required), 5 is a cooling or heating part (or a connection part with a cooling or heating part), 6 is a heat dissipation member, 7 is a sample, 8 is a sample base, 9 is a heat-conducting spacer, 10 is a bridge, 11 is a leveling member, and 12 and 50 are sample holders (ring screws in this case).

The role of each component and the connections between them in one embodiment of the stage of the present invention are described below with reference to the figures. First, there is the stage body. While Figure 1 shows an embodiment with a thermoelectric element 4, the thermoelectric element 4 is optional. If the thermoelectric element 4 is not present, the portion containing the thermoelectric element 4 can be replaced with a cooling unit, a heating unit, or a heat conduction unit. Since this embodiment uses a thermoelectric element 4, a heat dissipation member (heat dissipation treatment member) 6 may be provided as needed, as shown in the figure. In this embodiment, the heat source (cooling or heating) from the cooling or heating unit (or connection to the cooling or heating unit) 5 passes through the heat dissipation member 6, the cooling or heating connection 3, the thermoelectric element 4, and the heat conduction unit 2 to reach the top of the sample. The heat source (cooling or heating) can be transferred to the sample 7 via the heat conduction unit 2, the ring screw 12 (in the embodiment using a sample pedestal holder), or the heat conduction spacer 9 (in the embodiment using a heat conduction spacer). In this embodiment, a ball is used as the leveling member. If the upper and lower members are not parallel to the sample surface, there is a risk that proper thermal contact will not be achieved. Therefore, in this example, a ball is placed directly below the sample pedestal, so that the upper surface of the sample becomes parallel to the ring screw in response to the force with which the ring screw presses the sample. At the same time, the ball can also have the effect of thermally insulating the sample pedestal and bridge. In this example, a ball is used, but it is also possible to place one or multiple balls in a balanced arrangement around the spring.

Figure 3 shows a conceptual diagram of an example stage in one embodiment of the present invention. Figure 3(a) shows a perspective view of the stage in one embodiment of the present invention, and Figure 3(b) shows a top view of the stage. In Figure 3, 51 indicates a thermally conductive spacer, 52 indicates a gap provided in the thermally conductive portion, and 53 indicates a fixture for fixing the thermally insulating base.

As such, the stage of the present invention can be suitably used in scanning electron microscopes, providing a mechanism that allows for cooling and heating from above the sample. In other words, the present invention makes it possible to effectively control the sample fixation method and heat conduction direction when cooling and heating a sample inside a scanning electron microscope (SEM). This may make it possible to observe the initial stages of phenomena (such as phase transformations) that occur due to temperature changes. Furthermore, in the case of cooling, the presence of a cooling element near the observation surface acts as a cold trap, which has been found to contribute to reducing contamination.

In the above embodiment, the heat conduction path (heat conduction section) from the cooling/heating source is routed in an arm-like manner to the top surface of the sample, and a thermally insulated mechanism is devised for the sample pedestal, allowing for cooling and heating from the top surface. However, the heat conduction path does not necessarily have to be routed as shown in the figure, and may extend laterally from the cooling surface. On the other hand, the bottom surface of the sample must be thermally insulated, and in this example, the cooling surface is fixed to the frame as a bridge (thermal insulating base), but this is not particularly limited. Furthermore, the bridge (thermal insulating base) can preferably be made of a material with low thermal conductivity, such as resin or titanium.

By heating or cooling the sample from above, it is possible to observe the sample in situ, making it applicable in a wide range of technical fields.

1. Thermal insulating base
2 heat conduction part 3 cooling or heating connection part 4 thermoelectric element (if thermoelectric element is required)
5. Cooling or heating unit (or connection to the cooling or heating unit)
6 Heat dissipation member 7 Sample 8 Sample base 9 Heat conductive spacer 10 Bridge 11 Level adjustment member 12, 50 Sample holder (in this case, ring screw)
21 Hot side metal (mainly Cu)
22 Ceramic substrate (mainly alumina)
23 Heat dissipation surface 24 N-type semiconductor 25 P-type semiconductor 26 Electric wire 27 Power source 28 Heat absorption 29 Conduction band of N-type semiconductor 30 Heat dissipation 31 Positive side 32 Heat absorption side 33 Valence band 34 Heat dissipation side 35 Negative side 36 Cold side metal (mainly Cu)
37 Cold side metals (mainly Cu)
38 Electrons 39 Holes 40 Conduction band of P-type semiconductor 51 Thermally conductive spacer 52 Air gap provided in thermally conductive portion 53 Fixture for fixing thermal insulating base

Claims (9)

A stage having a sample pedestal for mounting a sample, a thermal insulating base installed under the sample pedestal, a heat conducting part installed on the top of the sample pedestal and made of a thermally conductive material, and a cooling part or a heating part, wherein the heat conducting part has a gap to prevent interference with an electron beam, and cools or heats the sample from above by coming into contact with the cooling part or the heating part . 2. The stage according to claim 1 , further comprising a thermoelectric element disposed adjacent to the cooling unit or the heating unit. 3. The stage according to claim 1 , wherein the heat conducting portion is extensible. 4. The stage according to claim 1 , further comprising a sample pedestal holder for holding the sample pedestal. 5. The stage according to claim 4 , further comprising a thermally conductive spacer having one or more holes between the sample and the sample pedestal holder. 6. The stage according to claim 1 , further comprising a leveling member between the sample pedestal and the thermal insulating base. 3. The stage according to claim 2 , wherein the thermoelectric element is a thermoelectric element utilizing at least one of the Peltier effect and the Thomson effect. 3. The stage according to claim 2 , wherein the heat radiation side of the thermoelectric element is in contact with the cooling part, the heating part, or the heat conduction part. 2. The stage according to claim 1 , wherein the cooling portion is made of at least one of a solid refrigerant, a liquid refrigerant, and a gas refrigerant.