JPS5923417B2 - Exhaust system for electron microscopes, etc. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust system for an electron microscope, etc., which can minimize backflow accidents of oil from a main vacuum pump.

In high-vacuum electron optical equipment such as electron microscopes, backflow of oil (steam) from the main pump may occur, and if the inside of the lens barrel gets dirty with oil, this will seriously impede the operation of the microscope and require cleaning the lens barrel and restarting the equipment. It takes a lot of time and money to restore normal conditions.

Therefore, countermeasures have been taken to prevent oil backflow, but the conventional method is to attach a vacuum gauge to the high vacuum section (for example, the barrel section) or the back pressure side of the main pump, and the gauge When an abnormal pressure that would increase backflow was detected, the high vacuum valve in the exhaust system was closed to prevent oil from flowing into the lens barrel.

However, in such a system, there is a certain time delay for one vacuum gauge to detect abnormal pressure.

(Thermal conduction gauges, such as the commonly used Villany gauge, have a slow response.

)2 Delays occur in the operation of electrical circuits such as relays that make up the safety system.

3. There is a time delay in mechanical operation until the high vacuum valve starts operating and airtightness is established.

Due to such reasons, even if the valve is closed by the vacuum gauge signal, oil from the main pump has already entered the mirror etc.
This often contaminates the inside of the lens barrel.

The present invention solves the above-mentioned drawbacks by closing at least the main valve immediately before a change in operation that may increase the back pressure of the main vacuum pump, such as when there is a leak in the air lock chamber or during roughing, thereby preventing a dangerous situation. After a short period of time has passed, the main valve is opened, and the back pressure of the main pump is detected, and if the value is abnormal, the main valve is closed regardless of other operations. The method is distinctive.

The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 1 is an exhaust system diagram showing an embodiment of the present invention, and 1 indicates a microscope column.

The column has an electron gun chamber, a focusing lens section, and a sample chamber section.

It consists of an imaging lens section, and an air chamber 2 for sample exchange is connected to the sample chamber section.

Also, a camera room 3 is connected under the collar A1.
An air lock valve is provided between the column and the air lock chamber 2 and camera chamber ■1. v2 is provided respectively.

4 is a main pump such as an oil diffusion pump, 5 is an auxiliary pump such as an oil rotary pump, and both are connected by an exhaust pipe 6.

The column, camera room 3 and main pump 4 are connected to the exhaust pipe 7.
Auxiliary pump 5 and column 1° air lock chamber 2. The camera room 3 and the like are connected through an exhaust pipe 8.

A cutoff valve v3 is provided in the middle of the exhaust pipe 6, and main valves v4 and 5 are provided in the middle of the exhaust pipe 7 that connects the main pump 4, the column 1, and the camera room 3, and furthermore, the auxiliary pump 5 and the column 1° A roughing valve V6 is installed in the middle of the exhaust pipe 8 connecting the air lock chamber 2 and camera chamber 3. V7 and ■8 are provided.

■9, ■1o, and ■11 are column leak valves, respectively. The air lock chamber leak valve and camera chamber leak valve are shown.

As such a valve, for example, a solenoid valve that is easy to control is used, and a driving current is supplied from the control device 9 to the driving section of the answering valve.

On the other hand, a vacuum gauge 10 such as a Villany gauge is provided on the back pressure side of the main pump 4, that is, on the exhaust pipe 6, and constantly monitors the back pressure of the main pump.

The output signal of this gauge is sent to the control circuit 11, and it is determined whether or not there is an abnormality.

If the signal is an abnormal value, that is, the back pressure of the main pump 4 is close to the critical back pressure, the main valve V
4. (2) A current is supplied to the drive unit 5 to close the valve.

When the above-mentioned abnormal condition is canceled, the current supply to the two-way valve ＼ is stopped, and the current supply to the two-way valve ＼ is stopped. ■5 is opened.

The control of answers in such a system will be explained below.

(1) In the case of leaking the air lock chamber 2 (2) In the case of rough evacuation of the air lock chamber 2, the valve operations are automatically controlled by the control device 9. The main valve ■4
and/or the closing operation of the valve 5 is performed immediately before the change in operation that increases the back pressure of the main pump 4, i.e., in relation to the opening operation of the leakage valves ■1o, ■1, and the opening operation of the roughing valves V7tV8. Moreover, the valve ■1oV10. V7. ■Since the main valves V4, V will not be opened several to ten seconds after the opening operation in step 8, it is important to appropriately select the time during which the main valves V, V5 are closed. Since the main pump and the vacuum chamber (color 1, camera room 3) are shut off while there is a possibility that the back pressure of pump 4 may increase, even if an oil backflow accident occurs, the vacuum chamber/＼ will not be able to enter. is prevented.

On the other hand, as mentioned above, the back pressure of the main pump 4 is constantly monitored by the gauge 10, and when the back pressure exceeds a certain value, the main valves V4 and V are closed (controlled). When the back pressure of the main pump increases during leakage or rough evacuation, the main valves V4 and V5 are forcibly closed based on this.

That is, the control device 9 performs v4.v4 according to the above sequence.
If abnormal pressure occurs while V5 is closed, gauge 10
Main valve by thread ■4. A close signal is sent to V5, and this state is maintained until there is no abnormal pressure.

As stated above, even if the airtightness of V7 and ■8 is insufficient at the time of a leak, or even if the airtightness of V3 is insufficient during rough evacuation, the main valves ■4 and ■5 will be Since it is always closed, oil from the main pump will not flow back into the column 1 or camera chamber 3.

FIG. 2 shows another embodiment of the present invention, in which two main pumps (4a and 4b) are used and are connected in cascade for differential pumping.

In this example, the main pump 4a reaches a relatively low vacuum, and the main pump 4b reaches a relatively high vacuum. 4a is connected to the camera room and the back pressure side of 4b, and 4b is connected to column 1. has been done.

As is clear from the description of the embodiment in FIG. 1, the main valve v4 is only closed for about ten seconds at most, so valves ① and 2 are provided on the back pressure side of the pump 4b in addition to this valve. It was designed to close.

In this case, the control by the control device 9 and the control by the control circuit 11 may be performed by ■1□.

When the main pump 4a and the column 1 are shut off by the valve v1□ in this way, the main pump 4a and the column 1 are kept evacuated by the other main pump 4b. Can perform oil backflow prevention operation.

The embodiment shown in FIG. 3 has two main pumps 4a.

4b is connected in parallel and applied to a system that configures differential pumping. ■4. The operation of V1□ is similar to that in FIG.

Although the above description has been made using an electron microscope as an example, the present invention can be directly applied to high-precision electron optical devices such as a scanning electron microscope, an X-ray analyzer, and even an electron beam exposure device.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 3 are exhaust system diagrams showing embodiments of the present invention. 1: Column, 2: Airlock room, 3: Camera room, 4:
Main pump, 5: Auxiliary pump, 6, 7 and 8: Exhaust pipe, 9
: Control device, 10: Vacuum gauge, 11: Control circuit, Vl
, V2: F-0 check valve, ■3: Shutoff valve, ■4. ■
5: Main valve, ■6. V7゜■8: Roughing valve, V9, Vl
o, V,: Leak valve.

Claims (1)

[Claims] 1. A high vacuum chamber, an air lock chamber connected to the high vacuum chamber via an isolation valve, a main vacuum pump such as an oil diffusion pump or a turbomolecular pump, an auxiliary pump that exhausts its back pressure side, and the high vacuum A main valve installed between the pumps, a valve between the air lock chamber and the main vacuum pump, a leak valve that introduces gas into the air lock chamber, and a rough vacuum valve installed between the air lock chamber and the auxiliary pump. a detector for detecting the degree of vacuum on the back pressure side of the main vacuum pump;
Immediately before the valve is driven due to leakage or rough evacuation of the air lock chamber, the main valve is automatically closed, and in the closed state, the output signal from the detector is monitored to control the main vacuum pump. If the back pressure side pressure is lower than the reference value, the main valve for draining liquid is kept open for a certain period of time, and if the pressure is higher than the reference value, the operation of opening the main valve is stopped. An exhaust system for an electron microscope, etc., characterized by comprising a control means.