Electron microscope

Abstract

The present invention improves the performance of an electron microscope. To this end, provided is an electron microscope comprising: a sample stand; a first cold finger that is disposed to the upstream side of the sample stand along an optical axis; a second cold finger that is disposed to the downstream side of the first cold finger along the optical axis so as to sandwich the sample stand; and a movable mechanism that moves the first cold finger and the second cold finger in the direction of insertion to or removal from the optical axis. The movable mechanism is configured such that a solid angle at which a sample placement part of the sample stand is covered by one or both of the first cold finger and the second cold finger can be changed.

Description

electron microscope

[0001] The present invention relates to an electron microscope, and more particularly to an electron microscope equipped with a cold finger.

[0002] In recent years, transmission electron microscopes (TEMs) and scanning electron microscopes (SEMs) have become well known as instruments for observing samples. When analyzing samples using these electron microscopes, contamination can adhere to the sample during observation. In this case, by using a cold finger cooled with liquid nitrogen or the like, the contamination can be adsorbed onto the cold finger rather than the sample.

[0003] Patent Document 1 (WO 2015 / 41267) describes a scanning electron microscope equipped with an anti-contamination trap in which the cooling part is cooled via a copper rod connected to a cooling tank.

[0004] International Publication No. 2015 / 41267

[0005] The adsorption efficiency of the cold finger improves as the distance between the cold finger and the sample decreases. However, if the cold finger is placed too close to the sample, problems arise, such as a limited tilt range for the holder holding the sample. Therefore, the shape and position of the cold finger may limit the analytical techniques that can be used. Furthermore, with the current trend toward core facilities, there is a demand for a single device to be able to perform a variety of analytical techniques.

[0006] The present invention has been conceived to solve such problems, and an object of the present invention is to improve the performance of electron microscopes.

[0007] A brief summary of a representative embodiment of the present invention will be given below.

[0008] An electron microscope according to one embodiment includes a sample stage, a first cold finger arranged upstream of the sample stage along an optical axis, a second cold finger arranged downstream of the first cold finger along the optical axis with the sample stage sandwiched between the first cold finger, and a movable mechanism that moves the first cold finger and the second cold finger in a direction of insertion and removal along the optical axis, wherein the movable mechanism is configured to change a solid angle that a sample placement portion of the sample stage is covered by one or both of the first cold finger and the second cold finger.

[0009] According to the present invention, the performance of an electron microscope can be improved.

[0010] FIG. 1 is a schematic diagram showing an electron microscope according to a first embodiment; FIG. 2 is a schematic diagram showing a cooling unit constituting the electron microscope according to the first embodiment; FIG. 3 is a schematic diagram showing a cold finger and a sample stage constituting the electron microscope according to a first example of the first embodiment; FIG. 4 is a schematic diagram showing a cold finger and a sample stage constituting the electron microscope according to a second example of the first embodiment; FIG. 5 is a schematic diagram showing a cold finger and a sample stage constituting the electron microscope according to a second example of the first embodiment; FIG. 6 is a schematic diagram showing a cold finger and a sample stage constituting the electron microscope according to a third example of the first embodiment; FIG. 7 is a schematic diagram showing a cold finger and a sample stage constituting the electron microscope according to a fifth example of the second embodiment; FIG. 8 is a plan view showing a cold finger and a sample stage constituting the electron microscope according to a sixth example of the third embodiment; FIG. 9 is a plan view showing a cold finger and a sample stage constituting the electron microscope according to a seventh example of the third embodiment; and FIG. 10 is a schematic diagram showing a cold finger and a sample stage constituting an electron microscope of a comparative example.

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In all drawings for explaining the embodiments, components having the same functions are designated by the same reference numerals, and repeated explanations thereof will be omitted. In addition, in the embodiments, explanations of the same or similar parts will not be repeated unless particularly necessary.

[0012] The X direction (X axis) and the Y direction (Y axis) are perpendicular to each other and are both directions along a horizontal plane. Here, the direction perpendicular to the X and Y directions is called the Z direction (Z axis) or up-down direction.

[0013] (Embodiment 1) An example of an electron microscope will be described below as an embodiment. An apparatus equipped with a retractable cold finger according to this embodiment is applicable to a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM). Here, a transmission electron microscope will be used as an example. Figure 1 is a schematic diagram showing the electron microscope according to this embodiment.

[0014] FIG. 1 shows a transmission electron microscope (TEM) 1 according to the present embodiment. The transmission electron microscope 1 has a lens barrel 102. Arranged in this order from top to bottom within the lens barrel 102 are an electron gun 103, a gun valve 104, a condenser lens 105, an objective lens 107, an intermediate lens 110, and a projection lens 111, which constitute an electron beam optical system. An intermediate chamber 112 is provided below the condenser lens 105, and a sample chamber 113 containing the objective lens 107 is provided below the intermediate chamber 112. A sample stage 3 is insertable into and removable from the sample chamber 113. A sample 10 is placed on the sample stage 3. The sample 10 is, for example, a carbon black or semiconductor wafer sample. The term "insertion and removal" as used herein refers to inserting the sample into or removing it from an irradiation area of ​​an electron beam emitted from the electron gun 103.

[0015] An observation chamber 115 is provided below the projection lens 111. Inside the observation chamber 115, from top to bottom, a fluorescent screen 117 and a detector (imaging unit, camera) 119 are provided. The detector (detector array) 119 is, for example, a camera equipped with a CCD (Charge Coupled Device) camera or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. An electron diffraction pattern is projected onto the detector 119. A fluorescent screen detector array (imaging unit, camera) 118 for imaging the fluorescent screen 117 inside the observation chamber 115 is provided on the side of the observation chamber 115.

[0016] A computer (control unit) 11 is installed outside the transmission electron microscope 1. The fluorescent screen 117 and the detector 119 are connected to the computer 11. A display unit (monitor) is connected to the computer 11. In other words, the display unit is a display device installed outside the transmission electron microscope 1. In addition, a cooling unit 2 equipped with a cold finger that can be inserted into and removed from the sample chamber 113 is attached to the electron tube 102.

[0017] The electron beam generated by the electron gun 103 is converged by a condenser lens 105 and irradiated onto the sample 10. The electron beam transmitted through the sample 10 on the sample stage 3 is imaged by an objective lens 107 and then magnified by an intermediate lens 110 and a projection lens 111. The magnified transmission image of the sample 10 is projected onto a fluorescent screen 117 or a detector 119. The transmission image projected onto the fluorescent screen 117 is captured by a fluorescent screen detector array 118 and stored in the computer 11. In this way, a transmission image (high-magnification image (magnified image) or an electron diffraction pattern (diffraction spots) projected onto the detector 119 by the electron beam transmitted through the sample 10 is obtained.

[0018] 2 is a schematic diagram showing a state in which the retractable cold fingers 23 and 24 are inserted into the lens barrel 102 in the optical axis direction in this embodiment. FIG. 2 is a cross-sectional view.

[0019] The cooling unit 2 includes a dewar 21 capable of containing liquid nitrogen and a movable mechanism (movable part) 22. The dewar 21 and the movable mechanism 22 are disposed outside the microscope column 102. The end of the movable mechanism 22 on the sample stage 3 side is provided with cold fingers 23 and 24, which are insertable and retractable in the optical axis direction, as components of the cooling unit 2. The movable mechanism 22 has the function of moving components in the radial direction of the cylindrical microscope column 102, which extends, for example, in the vertical direction (Z direction). The cooling unit 2 includes the movable mechanism 22, which allows the cold fingers 23 and 24 to be inserted and removed in the optical axis direction, thereby changing the solid angle of the sample 10 within the objective lens 107 and on the sample stage 3. That is, the movable mechanism 22 can move the cold fingers 23 and 24 in the direction of insertion and removal relative to the optical axis. By the above-described operation of the movable mechanism 22, the solid angle in which the sample placement portion 3a of the sample stage is covered by one or both of the cold fingers 23 and 24 can be changed.

[0020] FIG. 3 shows a schematic diagram of the tip shape of the cold finger of this embodiment. FIG. 3 is a side view showing the cold finger and the sample stage with a portion cut away. As shown in FIG. 3, the cold fingers 23 and 24 at least partially overlap each other in the Z direction (up-down direction). The Z direction is the direction along the optical axis. The optical axis direction in this application refers to the direction toward the optical axis, not the direction along the optical axis. The optical axis is the central axis of the electron beam irradiated from the electron gun 103 toward the sample 10 and the detector 119 in FIG. 1 . The phrase "insertable in the optical axis direction" here means that the object can be inserted or removed to a position overlapping with the optical axis by moving the object, for example, perpendicularly or obliquely to the optical axis.

[0021] The cold fingers 23 and 24 can be reciprocated in the X direction (radial direction of the lens barrel 102) by the movable mechanism 22. The cold fingers 23 and 24 can also be moved up and down in the Z direction (extension direction of the lens barrel 102) by the movable mechanism 22.

[0022] The cold fingers 23 and 24, the sample 10, and the sample stage 3 are aligned in the X direction in a plan view. The sample 10 is placed on the sample stage 3 near the end of the sample stage 3 extending in the X direction, covering the upper opening (sample placement portion 3a) of a hole that penetrates the sample stage 3 in the vertical direction. The end of the sample stage 3 here refers to the portion that includes the sample placement portion (sample holder) 3a and continues continuously in the X direction while maintaining a substantially constant thickness in the Z direction. It does not refer to the spherical portion at the tip of the sample stage 3 and its thickest portion on the opposite side, as shown in FIG. 3 . The sample stage 3 is rotatable around an axis that corresponds to the extension direction (X direction) of the sample stage 3, as indicated by the white arrow in FIG. 3 . Here, the sample stage 3 can rotate ±60 degrees, for example. Hereinafter, tilting the sample 10 and the sample stage 3 by this axial rotation will be referred to as tilting.

[0023] Cold fingers 23 and 24 are provided at the tip of the cooling unit 2. Each of the cold fingers 23 and 24 is made of, for example, a plate-shaped metal plate extending in the X direction and having a thin thickness in the Z direction. The cold finger 23 is disposed above the cold finger 24 in the Z direction. In other words, the cold finger 23 is disposed upstream of the sample stage along the optical axis, and the cold finger 24 is disposed downstream of the sample stage along the optical axis.

[0024] Each of the cold fingers 23 and 24 is fixed to a part of the movable mechanism 22 (see FIG. 2 ), and their relative positions do not change. The cold finger 23 has an opening 31 a penetrating the cold finger 23 in the Z direction. The cold finger 24 has openings 31 b and 32 penetrating the cold finger 24 in the Z direction. The openings 31 a and 32 are aligned in the X direction, and the opening 32 is located closer to the sample stage 3 than the opening 31 b.

[0025] The cold finger 23 is shorter in the X direction than the cold finger 24, and the cold finger 24 extends to a position closer to the sample stage 3 than the cold finger 23. The openings 31a and 31b overlap in a plan view. The opening 32 is provided at a position that does not overlap with the cold finger 23 and the opening 31a in a plan view. In other words, the opening 32 is spaced apart from the cold finger 23 and the opening 31a in a plan view. That is, the cold finger 23 terminates closer to the movable mechanism 22 in the X direction than the opening 32. In this way, the cold finger 23 or 24 has multiple openings (openings 31a, 31b, and 32) arranged in the insertion / removal direction (X direction) for passing the optical axis.

[0026] The distance Z1 between the cold fingers 23, 24 in the Z direction is relatively small and is slightly larger than the thickness of the untilted sample stage 3 in the Z direction. The end of the sample stage 3 has a width in the depth direction (Y direction) of FIG. 3 that is larger than the thickness of the sample stage 3. The distance Z1 between the cold fingers 23, 24 in the Z direction is smaller than the maximum length (height) in the Z direction of the end of the sample stage 3 when tilted at 60 degrees.

[0027] The cold fingers 23, 24 are cooled by liquid nitrogen contained in the dewar 21 (see FIG. 2 ), and their temperature is, for example, approximately −196° C. When observing a sample 10 using the transmission electron microscope 1, if contaminants (foreign matter) adhere to the sample 10, the observation will be hindered. The contaminants referred to here are, for example, dirt made of hydrocarbon gas molecules. In contrast, by arranging the low-temperature cold fingers 23, 24 near the sample 10, the contaminants are preferentially adsorbed onto the cold fingers 23, 24, thereby obtaining good observation results.

[0028] Next, examples of the operation of the cold finger during observation will be described with reference to Examples 1 to 3.

[0029] Example 1 As Example 1, an example will be described in which electron beam irradiation observation is performed at a position where the sample 10 (sample mounting portion 3 a) is spaced from the cold fingers 23 and 24 in a plan view, as shown in FIG. 3 . In this case, the sample 10 (sample mounting portion 3 a) and the sample stage 3 are not covered by either the cold fingers 23 or 24, so the solid angle of the sample 10 is large, and the sample stage 3 can be tilted without restriction. By using image data obtained while tilting the sample, for example, a three-dimensional structure of the sample 10 can be obtained. A portion of the electron beam irradiated from the electron gun 103 passes through the sample 10 and reaches the fluorescent screen 117 and the detector 119. The openings 31 a, 31 b, and 32 are spaced from the optical axis of the electron beam.

[0030] Furthermore, since the sample 10 (sample mounting portion 3 a) is exposed, EDX (Energy Dispersive X-ray) analysis is also possible. In other words, an EDX analyzer irradiates a sample with an electron beam perpendicularly from above, detects characteristic X-rays reflected over a wide area on the sample surface, and analyzes the X-rays by energy to perform compositional analysis of the sample. In FIG. 3 , there is nothing blocking the vicinity of the top surface of the sample 10, so the solid angle covering the sample 10 is large, making EDX analysis possible. The solid angle refers to the solid angle when the EDX detector is viewed from the point of incidence of the electron beam on the sample, and a larger value indicates higher detection efficiency.

[0031] Example 2 Example 2 will describe an example in which observation by electron beam irradiation is performed in a state in which the cold fingers 23, 24 are inserted further in the optical axis direction than in FIG. 3, as shown in FIG. 4. Here, the sample 10 and sample mounting portion 3a overlap with the opening 32 in a plan view. That is, the sample 10 and sample mounting portion 3a overlap with the cold finger 24 in a plan view and are exposed from the cold finger 23. A portion of the electron beam irradiated from the electron gun 103 passes through the sample 10 and opening 32 in this order, and reaches the fluorescent screen 117 and the detector 119. The openings 31a, 31b are spaced apart from the optical axis of the electron beam.

[0032] In this way, at positions where the sample 10 is not covered by the cold finger 23, the sample 10 is close to the cold finger 24, and therefore the efficiency of adsorption of contaminants is relatively high. Here, since the sample stage 3 is close to the cold finger 24, there are restrictions on the tilt of the sample stage 3 compared to Figure 3, but the solid angle of the sample 10 is large, so EDX analysis is possible. However, as shown in Figure 5, if part of the cooling unit 2 including the cold fingers 23, 24 is moved downward from the state shown in Figure 4, the sample stage 3 can be tilted in the same way as in Figure 3.

[0033] Example 3 In Example 3, as shown in FIG. 6 , an example will be described in which the cold fingers 23 and 24 are inserted further in the optical axis direction than in FIG. 4 , and the sample 10 is covered from both the top and bottom by the cold fingers 23 and 24, and observation is performed by electron beam irradiation. Here, the sample 10 and sample mounting portion 3a overlap with the openings 31a and 31b in a plan view. In other words, the sample 10 and sample mounting portion 3a are sandwiched between the openings 31a and 31b in the Z direction. A portion of the electron beam irradiated from the electron gun 103 passes through the opening 31a, the sample 10, and 31b in this order, and reaches the fluorescent screen 117 and the detector 119. The opening 32 is spaced apart from the optical axis of the electron beam.

[0034] In this case, by arranging the cold fingers 23 and 24 near the sample 10, it is possible to realize the position that provides the best adsorption efficiency of contaminants among the examples shown in Figures 3 to 6. That is, in terms of the adsorption efficiency of contaminants, Example 3 is superior to Example 2, which is superior to Example 1. Furthermore, the tiltable angle of the sample stage 3 is larger in Example 1 than in Example 2, and larger in Example 2 than in Example 3. Furthermore, EDX analysis can be performed in Examples 1 and 2.

[0035] As described in the first to third embodiments, in plan view, the movable mechanism 22 can open (expose) the sample placement portion 3a from the cold fingers 23, 24 on either the upstream or downstream side of the optical axis.

[0036] 11 , a comparative transmission electron microscope may have a cold finger configuration in which a rod-shaped cold finger 25 is placed in proximity to the sample stage 3, and the low-temperature cold finger 25 adsorbs contaminants. However, with a rod-shaped cold finger 25, it is difficult to bring the cold finger 25 close to the sample 10 so as to surround the sample 10, and it is also difficult to adjust the solid angle of the sample 10 according to the observation mode. As a result, it is difficult to improve the efficiency of adsorption of contaminants with the comparative transmission electron microscope.

[0037] 3 to 6, the present embodiment provides openings 31a, 31b, and 32, and cold fingers 23 and 24 of different lengths are arranged so as to be insertable and removable in the optical axis direction. Here, by overlapping or separating the sample 10 with the openings 31a and 31b or the opening 32, it is possible to increase the rate of contamination adsorption, easily adjust the tiltable angle of the sample stage 3, and easily adjust whether or not EDX analysis can be performed.

[0038] In this embodiment, by making the lengths of the cold fingers 23, 24 different, various observation conditions can be created depending on the relative positions of the insertable and removable cold fingers 23, 24, the sample stage 3, and the sample 10.

[0039] Here, the three patterns shown in Figures 3, 4, and 6 have been described as examples. However, when focusing on the efficiency of contaminant adsorption, the adsorption efficiency can be adjusted as desired by adjusting the distance between the insertable and removable cold fingers 23, 24 and the optical axis, so the positions of the cold fingers 23, 24 are not limited to those described in the above examples.

[0040] Second Embodiment A second embodiment will be described below in which the lengths of two cold fingers are the same and the distance between the cold fingers can be changed depending on their positions.

[0041] As shown in FIG. 7 , in this embodiment, the two cold fingers 41 and 42 have the same length in the X direction. That is, the terminal positions of the cold fingers 41 and 42 overlap in a plan view. The cold finger 41 has an opening 31 a and an opening 32 a located closer to the sample stage 3 than the opening 31 a, and the cold finger 41 has an opening 31 b and an opening 32 b located closer to the sample stage 3 than the opening 31 b. The openings 31 a and 31 b overlap each other in a plan view, and the openings 32 a and 32 b overlap each other in a plan view. As in the first embodiment, the cold fingers 41 and 42 can be inserted and removed in the optical axis direction by the movable mechanism 22.

[0042] The distance between the cold fingers 41, 42 is greater at the tip end, i.e., at the locations where the openings 32a, 32b are formed, than at the locations where the openings 31a, 31b are formed. That is, the lower surface of the cold finger 41 (the surface facing the cold finger 42) has a step between the openings 31a and 32a, and the thickness from the vicinity of the opening 32a to the terminal end on the sample stage 3 side is smaller than the thickness near the opening 31a. Also, the upper surface of the cold finger 42 (the surface facing the cold finger 41) has a step between the openings 31b and 32b, and the thickness from the vicinity of the opening 32b to the terminal end on the sample stage 3 side is smaller than the thickness near the opening 31a.

[0043] That is, between the cold fingers 41, 42, the distance Z2 near the openings 32a, 32b is larger than the distance Z3 near the openings 31a, 31b. In other words, each of the cold fingers 41, 42 has a first region on the tip side (toward the sample stage 3) in the X direction and a second region located on the opposite side of the first region from the sample stage 3. The shortest distance Z3 between the cold fingers 41, 42 in the Z direction in the second region is smaller than the shortest distance Z2 between the cold fingers 41, 42 in the Z direction in the first region. The openings 31a, 31b are formed in the first region, and the openings 32a, 32b are formed in the second region. That is, the cold fingers 41, 42 are thicker in the regions having the openings 31a, 31b and thinner in the regions having the openings 32a, 32b.

[0044] The gap Z2 is relatively large, larger than the gap Z1 shown in FIG. 3 . The gap Z3 is smaller than the gap Z2, while the gap Z1 is the same size, being slightly larger than the thickness of the untilted sample stage 3 in the Z direction. The end of the sample stage 3 has a width greater than the thickness of the sample stage 3 in the depth direction (Y direction) of FIG. 7 . The gap Z3 is smaller than the maximum length (height) in the Z direction when the end of the sample stage 3 is tilted at 60 degrees. Thus, multiple regions of the cold fingers 23, 24 with different spacings between them are aligned in the insertion / removal direction (X direction). Therefore, the movable mechanism 22 can change the distance by which the cold fingers 23, 24 sandwich the sample support portion 3 a.

[0045] Examples of the operation of the cold finger during observation will be described below with reference to Examples 4 and 5.

[0046] Example 4 Example 4 will be described as an example in which observation is performed by irradiating the sample 10 (sample mounting portion 3a) with an electron beam at a position where the sample 10 overlaps with the openings 32a and 32b in a plan view, as shown in Fig. 7. A portion of the electron beam irradiated from the electron gun 103 passes through the opening 32a, the sample 10, and 32b in this order, and reaches the fluorescent screen 117 and the detector 119. The openings 31a and 31b are spaced apart from the optical axis of the electron beam.

[0047] In this case, the sample stage 3 can be tilted without any restrictions at the position where the cold fingers 41 and 42 overlap with the sample 10. Furthermore, by arranging the cold fingers 41 and 42 near the sample 10, the efficiency of adsorption of contaminants is improved compared to the first and second embodiments.

[0048] Example 5 As Example 5, an example will be described in which observation by electron beam irradiation is performed at a position where the sample 10 (sample mounting portion 3a) overlaps with the openings 31a and 31b in a plan view, as shown in Figure 8. In this case, the cold fingers 41 and 42 are inserted further toward the optical axis (toward the sample stage 3) compared to Figure 7. A portion of the electron beam irradiated from the electron gun 103 passes through the opening 31a, the sample 10, and 31b in this order, and reaches the fluorescent screen 117 and the detector 119. The openings 32a and 32b are spaced apart from the optical axis of the electron beam.

[0049] In this case, in the area having the openings 31a and 31b, the spacing Z3 at which the sample stage 3 is sandwiched is small, so the tilt angle of the sample stage 3 is limited, but by being closer to the cold fingers 41 and 42, the efficiency of adsorption of contamination is maximized.

[0050] In Examples 1 to 3, the contaminant adsorption efficiency, the tiltable angle of the sample stage 3, and the limitations on EDX analysis were controlled by moving the cold fingers 23 and 24 away from the optical axis. In Examples 4 and 5, contrary to Example 3, the contaminant adsorption efficiency, the tiltable angle of the sample stage 3, and the limitations on EDX analysis were controlled by inserting the cold fingers 41 and 42 toward the optical axis. In Example 4, the solid angle of the sample 10 is larger than in Example 5, and therefore the detection efficiency in EDX analysis is high.

[0051] Here, by making the thickness of the tip portions of the cold fingers 41 and 42 different from that of the other portions, the cold fingers 41 and 42 can create various observation states depending on the positions of the sample stage 3 and the sample 10.

[0052] Although two patterns, Examples 4 and 5, have been described here, when focusing on the efficiency of adsorption of contaminants, the adsorption efficiency can be adjusted as desired by adjusting the positions of the sample 10 and the insertable and removable cold fingers 41 and 42. Therefore, the positions of the cold fingers 41 and 42 are not limited to those described in the above examples.

[0053] (Embodiment 3) Figures 9 and 10 show a cold finger and a sample stage according to this embodiment. Figures 9 and 10 are plan views.

[0054] The insertable / removable cold finger and sample stage can be inserted / removed at any angle relative to the objective lens in the lens barrel. Figures 9 and 10 show an example in which the cold finger and sample stage are inserted / removed perpendicular to the extension direction (up / down direction) of the lens barrel. Cooling unit 2 has cold finger 51 that can be inserted / removed into lens barrel 102 and cold finger 52 that can be inserted / removed into lens barrel 102.

[0055] Each of the cold fingers 51, 52 has an opening 53 and an opening 54 that has a different size (diameter) than the opening 53. The openings 53, 54 are circular in plan view. The diameter of the opening 53 is larger than the diameter of the opening 54. The openings 53, 54 penetrate each of the cold fingers 51, 52 in the Z direction. Each of the cold fingers 51, 52 also has a notch (cutout portion) 55. The cold finger 51 is disposed upstream of the sample stage 3 along the optical axis, and the cold finger 52 is disposed downstream of the cold finger 51 along the optical axis, with the sample stage 3 sandwiched between them.

[0056] Here, the direction in which the cold fingers 51 and 52 are inserted and removed is the Y direction, and the direction in which the sample stage 3 is inserted and removed is the X direction. That is, these directions are perpendicular to each other in a plan view. The cold fingers 51 and 52 have the same shape in a plan view and extend in the Y direction. Although the outlines of the cold fingers 51 and 52 overlap each other in a plan view, the relative positions of the cold fingers 51 and 52 are shifted in FIGS. 9 and 10 for ease of understanding.

[0057] The centers of the circular openings 53 and 54 of the cold finger 51 are aligned in the Y direction. The same applies to the cold finger 52. In a plan view, the openings 53 of the cold fingers 51 and 52 overlap each other, and the openings 54 of the cold fingers 51 and 52 overlap each other.

[0058] In a plan view, a notch 55 is provided on one side surface of the cold finger 51 in the short direction (X direction). In a plan view, the notch 55 is provided on the side surface of the cold finger 51 where the sample stage 3 is inserted into the microscope barrel 102. The cold finger 52 also has a notch 55 at the same position as the cold finger 51. In the cooling unit 2, the notch 55, the opening 54, and the opening 53 are arranged in this order from the movable mechanism 22 side (the side where the cold fingers 51 and 52 are supported) toward the tips of the cold fingers 51 and 52 in the Y direction.

[0059] 9 and 10 do not show the openings 53 and 54 of the cold finger 52 that are shielded by the cold finger 51. Also, FIG. 9 does not show the sample 10 that is shielded by the cold finger 51.

[0060] 9, the sample stage 3 is covered with cold fingers 51 and 52. This maximizes the efficiency of contaminant adsorption. A portion of the electron beam emitted from the electron gun 103 passes through, for example, the opening 53 in the cold finger 51, the sample 10, and the opening 53 in the cold finger 52, in that order, before reaching the fluorescent screen 117 and the detector 119. The opening 54 and the notch 55 are spaced apart from the optical axis of the electron beam.

[0061] Although the case where the opening 53 and the sample 10 overlap has been described as an example here, the opening 54 may also overlap the sample 10. By selecting either the openings 53 or 54, each having a different hole diameter, as the opening to overlap the sample 10, it is also possible to improve the contrast for cutting scattered electrons. In other words, when multiple openings are lined up in the insertion / removal direction, the contrast of the formed image can be changed by using the movable mechanism 22 to change the opening through which the optical axis passes to one of the multiple openings.

[0062] 10 , by inserting the cold fingers 51 and 52 further toward the optical axis compared to FIG. 9 , the sample stage 3 and the sample 10 can be placed in the notch 55. That is, in a plan view, the sample stage 3 and the sample 10 are located in the notch 55 and are separated from the cold fingers 51 and 52. In other words, the sample stage 3 and the sample 10 do not overlap with the cold fingers 51 and 52.

[0063] In this position, the adsorption efficiency of the cold fingers 51 and 52 is maintained high, and there is no restriction on sample tilt, allowing for analysis by EDX. That is, the sample 10 is surrounded by the cold fingers 51 and 52 on three sides in the Y direction and one side in the X direction in plan view, resulting in high adsorption efficiency of contaminants. Furthermore, because the sample 10 and sample stage 3 are exposed from the cold fingers 51 and 52 in plan view, the sample stage 3 can be tilted, and the large solid angle allows for analysis by EDX.

[0064] Moreover, by selecting either the opening 53 or 54 having a different hole diameter as the opening that overlaps the sample 10, it is possible to improve the contrast for cutting scattered electrons.

[0065] The invention made by the inventors has been specifically described above based on the embodiments thereof. However, the present invention is not limited to the above embodiments and can be modified in various ways without departing from the spirit of the invention. For example, the above-described embodiments have been described in detail to clearly explain the technical content, and the invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0066] The present invention can be widely used in electron microscopes.

[0067] REFERENCE SIGNS LIST 1 transmission electron microscope 2 cooling section 3 sample stage 3a sample mounting section 10 sample 11 computer 21 dewar 22 moving mechanism 23, 24, 25, 41, 42, 51, 52 cold finger 31a, 31b, 32, 32b, 32b, 53, 54 opening 101 transmission electron microscope 102 lens barrel 103 electron gun 104 gun valve 105 condenser lens 107 objective lens 110 intermediate lens 111 projection lens 112 intermediate chamber 113 sample chamber 115 observation chamber 117 fluorescent screen 118 fluorescent screen detector array 119 detector

Claims

1. An electron microscope comprising: a sample stage; a first cold finger arranged upstream of the optical axis relative to the sample stage; a second cold finger arranged downstream of the optical axis relative to the first cold finger, sandwiching the sample stage between them; and a movable mechanism that moves the first cold finger and the second cold finger in the direction of insertion and removal from the optical axis, wherein the movable mechanism is configured to be able to change the solid angle covered by one or both of the first cold finger and the second cold finger of the sample mounting portion of the sample stage.

2. An electron microscope according to claim 1, wherein the first cold finger or the second cold finger has a plurality of openings arranged in the insertion / removal direction for passing the optical axis.

3. An electron microscope as described in claim 1, wherein the first cold finger and the second cold finger have different lengths in the insertion / removal direction, and the movable mechanism is configured to be able to expose the sample placement portion from either the cold finger on the upstream or downstream side of the optical axis in a plan view.

4. An electron microscope as described in claim 1, wherein a plurality of regions in which the first cold finger and the second cold finger are spaced apart from one another in a different manner are arranged in the insertion / removal direction, and the movable mechanism is configured to be able to change the distance at which the first cold finger and the second cold finger sandwich the sample placement portion.

5. An electron microscope as claimed in claim 2, wherein the movable mechanism is configured to be able to change the contrast of the formed image by changing the aperture through which the optical axis passes to one of the plurality of apertures.

Images