JPS6245419Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an exhaust system using a cryopump in an electron microscope or the like.

In order to reduce contamination of samples in transmission electron microscopes, scanning electron microscopes, etc., it is necessary to keep the inside of the microscope body clean (oil-free). For this purpose, it is conceivable to use a cryopump instead of the conventionally commonly used oil diffusion pump.

However, since such cryopumps perform adiabatic expansion using a piston,
The movement of the piston generates low-frequency vibrations with relatively large amplitudes, and there is a risk that these vibrations will be transmitted to the electron microscope mirror body, resulting in a decrease in resolution, so sufficient countermeasures against vibrations are required. For this purpose, it is conceivable to firmly fix the cryopump to the floor.
This method has the advantage of allowing the cryopump to be installed directly below the mirror, but it requires foundation work and is very difficult to handle, as foundation work must be done every time the mirror is installed. It becomes troublesome,
Moreover, it has the disadvantage of increasing costs. In order to prevent this drawback, it is possible to install the cryopump at a considerable distance from the mirror body, but this inevitably requires the use of a long exhaust pipe, which increases the exhaust resistance and reduces the exhaust time. It has the disadvantage of being long.

In order to solve this problem, the present invention supports a cryopump by suspending it from an exhaust pipe connected to a mirror body via a bellows.
In this case, when the inside of the mirror body is evacuated (vacuumed), the cryopump is pulled upward by the back pressure and the bellows is compressed, which is essentially the same result as fixing the cryopump directly to the exhaust pipe. Vibrations may be transmitted to the mirror body.

Therefore, the purpose of the present invention is to prevent the bellows from being compressed by such pump back pressure, thereby preventing the low frequency vibrations generated by the cryopump from being transmitted to the mirror body.

In order to achieve the above object, the present invention includes a mirror body 1,
An exhaust pipe 9 connected to the mirror body, and a floor 8 via a vibration isolator 6 to hold the mirror body and the exhaust pipe.
A pedestal 5 placed on top and a fin 1 at its tip.
4 and a valve control mechanism section 16 that holds the cylinder 13, the fin 14 has a diameter larger than the diameter of the cylinder 13, and is equipped with a cryopump, which is also used by the exhaust pipe 9. or a separately provided member, which connects the upper end of the bellows to the members 9, 10 at a position below the fins when the cryopump is attached to the members 9, 10 surrounding the fins. At the same time, by connecting the lower end of the bellows 11 to the valve control mechanism section 16 and arranging the bellows so as to surround the cylinder, the valve control mechanism section 16 can be placed in a non-contact manner with respect to the floor. A weight 18 or a spring 22 suspended from the members 9 and 10 to make the diameter of the bellows 11 smaller than the diameter of the members 9 and 10 and to cancel the compressive force applied to the bellows 13 by creating a vacuum inside the mirror body. is attached to the valve control mechanism structure 16.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention, and 1 is a mirror body of a scanning electron microscope. Inside the mirror body are an electron gun chamber 2, a focusing lens section 3, and a sample chamber 4.
are arranged in sequence, and the mirror body 1 is attached to a pedestal 5. The frame 5 is equipped with a vibration isolator 6.
The books are placed on the floor 8 by book supports 7a to 7d (7c and 7d are not shown). A main exhaust pipe 9 is connected to the bottom of the sample chamber 4, and a cryopump main body 12 is connected to the main exhaust pipe via a casing 10 and a bellows 11 made of stainless steel. In this case, the lower end of the cryopump body 12 is floating above the floor 8. In other words, the cryopump main body is connected to the main exhaust pipe 9 via the bellows 11.
It is supported by hanging from.

The cryopump main body 12 has a cylinder 1 that houses a piston and serves as an expansion chamber for helium gas.
3 and the first installed above this cylinder,
It is comprised of second fins 14 and 15 and a valve control mechanism section 16 including a motor for controlling the input and output of helium gas into the cylinder 13. The general operating principle is that helium gas compressed from a compressor (not shown) is introduced into the cylinder 13 via the valve controller 16 and adiabatically expanded, thereby lowering the temperature of the helium gas to an extremely low temperature (10°K). temperature), and the first and second fins 1 are heated by the ultra-low temperature helium gas.
4 and 15 are cooled to condense gas molecules onto the fins, thereby maintaining the inside of the mirror body 1 at a high vacuum. Also, low pressure helium gas is supplied to the valve control mechanism section 1.
6 and is discharged outside the cylinder 13 and collected by the compressor. Note that a buttful 17 is attached to the first fin 14.

Since the diameter of the fin 14 is larger than the diameter of the cylinder 13, the cryopump 1 is connected to the main exhaust pipe 9.
The configuration for installing 2 is as follows. That is, a cryopump casing 10 is connected to the exhaust pipe 9. The upper end of the bellows 11 is connected to the casing 10, and the lower end of the bellows 11 is connected to a valve control mechanism section 1, which will be described later.
Connect to 6. At this time, the connection position of the bellows 11 with the casing is positioned below the fins 14, so that the bellows 11 surrounds the cylinder 13. The valve control mechanism section 16 is suspended from the casing 10 so as not to contact the floor 8.
In order to minimize the compressive force applied to the bellows 11, the diameter of the bellows 11 is made smaller than the diameter of the casing 10.

Reference numeral 18 denotes an annular weight fixed to the cryopump main body 12, and this weight is used to cancel the upward suction force of the cryopump main body 12 due to back pressure when the inside of the mirror body 1 is evacuated. .

19 and 20, when the inside of the mirror body 1 leaks and the back pressure to the cryopump body 12 is released,
These hook-shaped wires are used to prevent the bellows 11 from being stretched by the weight 18. One wire 19 is fixed to the casing 10, and the other wire 20 is fixed to the weight 18 (cryo pump main body 12). The two wires are separated from each other as shown in the figure when the back pressure applied to the cryopump body 12 and the load of the weight 18 (actually including the load of the cryopump body) are balanced, and the wires are separated from each other as shown in the figure. The two are configured to engage when the applied back pressure is removed. Note that 21 is an auxiliary exhaust pipe for connecting the electron gun chamber 2 and the sample chamber 4.

By attaching the weight 18 to the cryopump main body 12 in this way, the back pressure applied to the cryopump main body due to the exhaust inside the mirror body 1 can be canceled out with a simple configuration, so that the bellows 11 is compressed. The bellows 11 can attenuate the low-frequency vibrations generated by the cryopump 12, thereby preventing a decrease in resolution.

In the above embodiment, a case was described in which a weight was used to cancel the back pressure applied to the cryopump body, but instead of the weight, as shown in FIG.
and valve control mechanism section 16 (cryo pump main body 1
2) may be provided between.

Furthermore, although the case has been described in which the main exhaust pipe 9 is installed at the bottom of the sample chamber 4, the main exhaust pipe is fixed to the pedestal 5 while being placed behind the mirror body 1, and the main exhaust pipe and the inside of the mirror body are fixed. The configuration may be such that each chamber is connected with a sub-exhaust pipe.

Furthermore, although the case where the present invention is applied to a scanning electron microscope has been described, it can be similarly applied to a transmission electron microscope, an electron exposure apparatus, and the like.

Further, in the embodiment described above, by making the exhaust pipe 9 also serve as a casing, the casing 10
You may also omit it.

As described in detail above, in the present invention, the members 9 and 10 that surround the fins are used as members that are combined with the exhaust pipe 9 or are provided separately.
When installing the cryopump, the upper ends of the bellows are connected to the members 9 and 10 at a position below the fins, and the lower end of the bellows 11 is connected to the valve control mechanism section 16 to connect the bellows. By arranging the valve control mechanism section 16 to surround the cylinder, the valve control mechanism section 16 is suspended from the members 9 and 10 so as not to come into contact with the floor, and the bellows 13 is evacuated by creating a vacuum inside the mirror body. A weight 18 or a spring 22 is used to cancel the compressive force applied to the valve control mechanism section 16.
Since the bellows is attached to the cryopump, it is possible to prevent the bellows from being compressed, thereby allowing the bellows to almost completely attenuate the low frequency vibrations generated by the cryopump.

In addition, since the bellows 11 is arranged in a position surrounding the cylinder 13 and its diameter is made smaller than the diameter of the members 9 and 10, the force applied to the bellows is proportional to the cross-sectional area (square of the diameter) of the bellows due to evacuation. The compressive force can be reduced, which allows the use of smaller weights or smaller springs with smaller spring constants.

[Brief explanation of the drawing]

FIG. 1 is a schematic structural diagram showing one embodiment of the present invention, and FIG. 2 is a schematic structural diagram of main parts showing another embodiment of the present invention. 1: mirror body, 2: electron gun chamber, 3: focusing lens section,
4: Sample chamber, 5: Frame, 6: Vibration isolator, 7a, 7
b: Pillar, 8: Floor, 9: Main exhaust pipe, 11: Bellows, 12: Cryopump body, 18: Weight, 2
2: Coil spring.

Claims (1)

[Scope of utility model registration request] a mirror body 1; an exhaust pipe 9 connected to the mirror body;
Vibration isolator 6 to hold these mirror bodies and exhaust pipes
It has a pedestal 5 placed on a floor 8 via a pedestal 5, a cylinder 13 having a fin 14 at its tip, and a valve control mechanism part 16 that holds the cylinder 13. The diameter of the fin 14 is equal to the diameter of the cylinder 13. When attaching the cryopump to the members 9 and 10 that surround the fins and are provided with a cryopump having a diameter larger than that of the exhaust pipe 9 or are provided separately, By connecting the upper ends of the bellows to the members 9 and 10 at a position below the fins and connecting the lower end of the bellows 11 to the valve control mechanism section 16, the bellows are arranged so as to surround the cylinder. , the valve control mechanism section 16 is suspended from the members 9, 10 so as not to contact the floor, and the diameter of the bellows 11 is adjusted to
An electron microscope or the like characterized in that a weight 18 or a spring 22 is attached to the valve controller section 16 to cancel the compressive force applied to the bellows 13 by making the diameter of the bellows smaller than the diameter of the bellows 13 by creating a vacuum inside the mirror body. Exhaust system.