JPH03208245A - Low temperature scanning type microscope - Google Patents

Abstract

PURPOSE:To cool specimen stages in a short time, and thereby enable urgent observation and element analysis as well by using an integrated circulation type cooler for cooling No.1 specimen stage, and also using a separated circulation type cooler for cooling No.2 specimen stage. CONSTITUTION:A specimen 9 which is cooled and frozen in a reserved exhaust chamber 12 in advance is rested on No.1 stationary specimen stage 6 which has been kept at low temperature in a specimen chamber (vacuum) 1, and is cut off by a knife unit 15 attached to the specimen stage 6. The specimen 9 which has been cut off, is transshipped to No.2 movable specimen stage 7 which has been kept at low temperature in the same specimen chamber 1, the specimen 9 is then set up at a specified position by the movable stage 7. The observation of a surface condition and element analysis are then performed in a state that the specimen 9 set up is in a cooled and frozen condition. In this case, No.1 stationary specimen stage 6 is cooled by an integrated circulation type cooler 16 mounted while being hermetically penetrated through the wall of the specimen chamber 1, and No.2 movable specimen chamber 7 is cooled by a separated circulation type cooler 20 mounted while being hermetically penetrated through the wall of the specimen chamber 1.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a low-temperature scanning electron D? Concerning the cooling device for the 1L mirror. [Prior art] When observing and conducting elemental analysis of water-containing samples or biological samples using a scanning electron microscope, these samples are cooled and frozen, cut into pieces with a knife, and the cut surfaces are made conductive if necessary. Coating with metal film for this purpose.

A cryo-scanning electron microscope is a device in which a sample cooling stage, a knife unit, and a coating unit are integrated into a scanning electron microscope. Figure 2 (al is a diagram showing an example of the structure of the sample holding part of a conventional low-temperature scanning electron microscope, and Figure 2 (bl is a sectional view taken along line A-A in Figure 2 fal). Vacuum sample chamber 1 After closing the gate valve 13, the preliminary exhaust chamber 12 is brought to atmospheric pressure, and the sample insertion lid 11 is removed.
After attaching the sample holder 8 to which the sample 9 previously cooled with liquid nitrogen outside the holder I is fixed to the sample feeding rod 11a attached to the holder 1, the preliminary evacuation chamber 12 is evacuated. After reaching a predetermined degree of vacuum, the gate valve 13 is opened, and the sample holder 8 to which the sample 9 is fixed is placed on the first sample stage 6 in the sample chamber 1. This sample stage 6 is cooled and maintained at a low temperature by a tank 5a containing liquid nitrogen 4, and the sample 9
is also kept at a low temperature. 15 is a knife unit, which is normally cooled by being in contact with the sample stage 6 as shown in the figure.
It moves to the upper part using a mechanism not shown and cuts sample 9.
Reference numeral 14 denotes a coating unit, which coats the cut surface of the sample 9 with a metal film to impart i-electrification, if necessary. The sample holder 8 with the sample 9 fixed thereon is further placed on the second sample stage 7 in the sample chamber 1 using the sample feed rod 11a. This sample stage 7 similarly includes liquid nitrogen 4
The temperature is maintained at a low temperature by the tank 5b containing the water.
Here, the first sample stage 6 is fixed, and the tank 5a
However, the second sample stage 7 is movable with an attached drive mechanism (not shown), and is indirectly cooled through a flexible heat transfer body 10 made of stranded copper wire. has been done. The sample 9 is set at a predetermined position by this movable sample stage, and surface shape observation and elemental analysis are performed in a cooled and frozen state.

[Problem to be solved by the invention]

In the aforementioned cryo-scanning electron microscope that uses a cooling method using a tank filled with liquid nitrogen, its cooling performance is such that it takes about 60 minutes at the first sample stage and about 60 minutes at the first sample stage to reach the predetermined cooling temperature of -130°C. Sample stage 2 required approximately 90 minutes, and there was a problem in that it took too much time to prepare when urgent sample observation and elemental analysis were required. Additionally, since liquid nitrogen vaporizes over time, it had to be replenished several times during observation, which resulted in poor experimental efficiency. Additionally, for emergency observation and elemental analysis, it was necessary to constantly supply a considerable amount of liquid nitrogen for cooling. The object of the present invention is to solve the above-mentioned problems and to
The object of the present invention is to provide a low-temperature scanning electron microscope that does not require the constant preparation of a considerable amount of liquid nitrogen for cooling the stage, and can be cooled in a short period of time for emergency observation and elemental analysis. [Means for solving the problem] In order to solve the above-mentioned problem I, a pre-chilled and frozen sample is placed on a fixed first sample stage kept at a low temperature in the vacuum chamber of the present invention, and a sample attached to this sample stage is placed. The cut sample is placed on a movable second sample stage kept at a low temperature in the same vacuum chamber, and the sample is set at a predetermined temperature by this movable sample stage and cooled. In cryogenic scanning electron microscopy, which performs surface topography observation and elemental analysis in a frozen state,
The second sample stage is cooled by an integrated circulating cooler installed hermetically through the wall of the vacuum chamber, and the movable second sample stage is cooled by a separate circulating cooler installed hermetically through the wall of the vacuum chamber. Cooled by a type cooler. [Function] In the cryogenic scanning electron microscope of the present invention, instead of the conventional cooling method using a tank containing liquid nitrogen for cooling the first and second sample stages, an integrated circulation system is used for cooling the first sample stage. A separate circulation type cooler was used to cool the second sample stage. Both circulation type coolers utilize the effect of the refrigerant compressed and dissipated by the condenser, which expands to a lower temperature.As this low-temperature refrigerant circulates to the tip of the cold head, its cooling performance is extremely high. expensive. Its thermal resistance is small and each sample stage is cooled quickly. In particular, the second sample stage is movable, and while conventionally it was indirectly cooled through a flexible heat transfer body using copper strands, it is now directly cooled by refrigerant circulation. big. In addition, an integrated circulation type cooler is one in which the main body and cold head are integrated, and a separate type circulation type cooler is one in which the main body and cold head are separated, and the two are connected by a flexible tube. It is. Cooling performance is the same for both types, but the separate type requires more manpower to operate the combustor. [Example] Fig. 1 (Al is a cross-sectional view of the sample holding part of a low temperature scanning electron microscope according to an embodiment of the present invention, Fig. 1(b) is Fig. 1fa)
This is a sectional view taken along line A-A. Close the gate valve l3 and pre-exhaust chamber 1
2 to atmospheric pressure, remove the sample insertion lid 11, and attach the sample holder 8 to which the sample 9 previously cooled with liquid nitrogen outside the apparatus is fixed to the sample feeding rod 11a attached to the insertion lid 11. The preliminary evacuation chamber 12 is evacuated. After reaching a predetermined degree of vacuum, the gate valve 13 is opened, and the sample holder 8 to which the sample 9 is fixed is placed on the first sample stage 6 in the sample chamber 1. The sample stage 6 is cooled and kept at a low temperature by an integrated circulating cooler 16, and the sample 9 is also kept at a low temperature.

Here, 16a is a cold head of this cooler 16, which cools the first sample stage 6 via the stand 19. Reference numeral 15 denotes a knife unit, which is normally kept in contact with the sample stage 6 as shown in the figure to cool it, and is moved to the upper part by a mechanism not shown to cut the sample 9. A coating unit 14 coats the cut surface of the sample 9 with a metal film for imparting conductivity, if necessary. The sample holder 8 to which the sample 9 is fixed is further transferred to the movable second sample stage 7 in the sample chamber 1 using the sample feed rod 11a.

This movable sample stage 7 is cooled and kept at a low temperature by a separate circulating cooler 20. Here, 20a is a cold head of this cooler 20, which cools the second sample stage 7 via a mounting base l9.

This cooler 20 is a separate type, with a main body and a cold head 20a.
are separated and connected by a flexible tube 20b. Therefore, the cold head 20a is movable, and instead of being cooled indirectly through a flexible heat transfer body using stranded copper wire, the cold head 20a cools directly. The sample 9 is set at a predetermined position by this movable sample stage, and surface shape observation and elemental analysis are performed in a cooled and frozen state.

Both an integral circulating cooler attached to a fixed first sample stage and a separate circulating cooler attached to a movable second sample stage are capable of using helium gas as the working fluid, e.g. It is suitable for obtaining extremely low temperatures in Stirling cycle coolers. The principle is a Combrenosa compression cylinder. The expansion cylinder 1 drive motor etc. of the cold throat are all housed in one space, and the rotation of the drive motor repeats the compression process and the expansion process.
During the compression process, heat is radiated by the cooling fins provided on the compression cylinder, and during the expansion process, heat is absorbed from the cold head in the expansion cylinder.The expanded and low-temperature refrigerant is circulated to the tip of the cold head. Its cooling performance is extremely high.

The body type is one in which the main body and cold head are integrated, while the separate type has the main body and cold head separated, and the two are connected by a flexible tube. Cooling performance is the same for both types, but the input to the combustor is greater for the separate type. In the present invention, when using these circulation type coolers with a cooling temperature of 80KC-193℃ and a cooling capacity of 1 joule/second (lwatt), the first
It took about 10 minutes for the sample stage to reach the predetermined cooling temperature of -130°C. This required approximately 60 minutes in the conventional method. For the second sample stage as well, it took about 10
The conventional method required approximately 90 minutes. In addition, with a circulation cooler of the specifications mentioned above,
The input power is 35W for the integrated type and 45W for the separate type, and by using both in appropriate locations, a large cooling effect can be obtained with a small input.

〔Effect of the invention〕

According to the present invention, in a cryo-scanning electron microscope, the fixed first sample stage is an integrated circulating cooler that requires little human power, and the movable second sample stage is a separate cooling type with a movable cold head. By cooling each stage in a separate device, it takes about 10 minutes to reach the predetermined cooling temperature of −130° C. for both the first and second sample stages with a small input of 80 W (integrated type 35 W and separated type 45 W). this is,
Conventionally, the first sample stage required 60 minutes and the second sample stage 90 minutes, but this now enables emergency observation and elemental analysis.

Additionally, by using a circulating cooler, the conventional need to constantly prepare a considerable amount of liquid nitrogen to cool the sample stage is no longer necessary.

[Brief explanation of drawings]

FIG. 1(a) is a cross-sectional view of the sample holding part of a cryo-scanning electron microscope according to an embodiment of the present invention, and FIG.
Figure 2 (ta+) is a cross-sectional view of the sample holding part of a conventional cryo-scanning electron microscope, and Figure 2 (mountain) is a cross-sectional view taken along line A-A in Figure 2 (fat). 1: Sample chamber (vacuum)
6: First sample stage (fixed), 7: Second sample stage (movable), 9: Sample, 15: Knife unit, 16: Integrated circulation cooling / 6 1st sample stage (movable) Fig. 1

Claims (1)

[Claims] 1) Place a sample that has been cooled and frozen in advance on a fixed first sample stage that is kept at a low temperature in a vacuum chamber, cut it into pieces with a knife unit attached to this sample stage, and then keep the cut sample at a low temperature in the same vacuum chamber. In a low-temperature scanning electron microscope, the sample is transferred to a second movable sample stage held, the sample is set at a predetermined position by this movable sample stage, and the surface shape is observed and elemental analysis is performed in a cooled and frozen state. The fixed first sample stage is cooled by an integrated circulating cooler mounted hermetically through the wall of the vacuum chamber, and the movable second sample stage is mounted hermetically through the wall of the vacuum chamber. A low-temperature scanning electron microscope characterized by being cooled by a separate circulating cooler.