JPH0580591B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a vacuum evacuation device used in an electron microscope or the like.

[Background of the invention]

In electron microscopes, in order to prevent two things: contamination caused by organic molecules floating near the sample adhering to the sample, and discharge phenomena within the electron gun.
The electron gun chamber and sample chamber are kept at high vacuum. Therefore,
These electron gun chambers and sample chambers are equipped with evacuation devices that evacuate these chambers to create a high vacuum, or conversely take in gas to bring it to atmospheric pressure.

By the way, in this case, even if the electron gun chamber and sample chamber are made to have a high vacuum pressure, there will be evaporation of oils and fats adsorbed on the chamber walls, gas release from the vacuum sealing rubber gasket or vacuum grease, and even if the electron beam passes through the electron beam path. The above-mentioned contamination or discharge phenomenon occurs due to the released gas from the photographic emulsion flowing back into the sample chamber from the camera chamber.

Conventionally, in order to remove various gas components and organic molecules such as dust that cause contamination or discharge phenomena, the organic gas in the electron gun chamber is replaced with chamber nitrogen gas to prevent discharge. In the sample chamber, a cooling trap is used to collect floating gas molecules and dust. Furthermore, in order to prevent the gas emitted from the photographic emulsion from flowing back into the sample chamber, the sample chamber and the electron gun chamber are vacuum-shielded, as shown in Japanese Utility Model Publication No. 1532/1983. .

However, in none of these methods is any consideration given to the possibility that dust remaining in the sample chamber may adhere to the sample and damage the sample during exhaust and leakage. For this reason, when the sample is a semiconductor wafer, there is a problem in that dust adheres to the semiconductor wafer during exhaust or leakage, making the semiconductor wafer unusable.

In this case, it is possible to suppress dust flying up by gradually changing the exhaust pressure and leak pressure, but it takes a long time for exhaust and leak, and
This is undesirable because it causes the sample observation process to take a long time.

[Purpose of the invention]

An object of the present invention is to provide a vacuum evacuation device that can prevent dust remaining in the sample chamber from adhering to the sample during evacuation and leakage, and can quickly complete the evacuation and leakage operations.

[Summary of the invention]

According to the present invention, the exhaust passage and the leak passage are configured so that the exhaust pressure and the leak pressure can be switched in a plurality of stages.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, a vacuum container 1 is preliminarily evacuated by a pre-evacuation pump system 7 via a main evacuation pipe 2, a pre-evacuation pulp 4 and a pre-evacuation pipe 6. Then, the vacuum gauge 16 detects that the air has been evacuated to a predetermined vacuum region (viscous flow region) from atmospheric pressure, and then the main exhaust valve 3 is opened.
The main exhaust pump system 5 evacuates to a high vacuum. on the other hand,
When leaking the vacuum container 1 to atmospheric pressure, the gas from the leak gas source 15 is pumped through the pressure regulating valves 12 and 1.
3, 14, leak gas valves 10, 11, filter 9, and vacuum valve 8 into the vacuum container 1 to bring it to atmospheric pressure.

In the above configuration, let us consider the phenomenon of dust generation that occurs during the exhaust and leak processes. Generally speaking, dust 19 remaining in the vacuum chamber 1 flies up as shown in FIG. Most of the time, it sticks. Therefore, the exhaust pressure and leak pressure may be adjusted to eliminate this phenomenon of dust flying up.

Therefore, in the case of evacuation, in the case of evacuation, as shown in the evacuation pressure characteristics in FIG.
From this point on, the method used is to switch to the main exhaust system, which has a higher exhaust speed, for exhaust. The solid line in FIG. 3 is an exhaust characteristic curve according to the present invention, and the broken line is an exhaust curve when exhausting from atmospheric pressure to a high vacuum region while maintaining slow exhaust. In the characteristic diagram, both the horizontal and vertical axes are expressed on a logarithmic scale. As is clear from this, there is a large difference in exhaust time.

On the other hand, in the case of a leak, operations are performed in accordance with the leak pressure characteristics shown in FIG. That is, first, the pressure regulating valve 12 is adjusted to the lowest pressure, and then the regulating valves 13,
Adjust the pressure to a high level of 14, and then press each valve 8, 1.
0, 11 and filter 9 are kept closed. Next, open the vacuum valve 8 and introduce the lowest pressure gas in the leak system into the vacuum container 1, allowing it to leak to point B in Figure 4, then open the valve 10 and introduce the next highest pressure gas. to leak to the pressure at point C, and finally close valve 1 on the highest pressure line.
1 to allow the vacuum container 1 to leak to atmospheric pressure.

By using the above method, it is possible to leak data in an extremely short time compared to the method of performing a slow leak from the beginning. In this case, a leak system with three levels of pressure difference is used, but this needs to be selected individually depending on the size of the vacuum vessel 1, etc.
For example, in the case of this embodiment, if the third stage slow leak is performed from point B, it will take a long time as indicated by the dotted line in FIG.

Each point of vacuum pressure A, B, and C in the exhaust/leak operation described below is detected by guiding the output signal of the vacuum gauge 16 to the control circuit 17, and based on this detected value, the valves 10, 11, etc. are opened/closed. controlled. In this case, for a certain vacuum evacuation system,
The time required to reach points A, B, and C can also be controlled as a parameter.

FIG. 2 shows another embodiment of the present invention, in which the control circuit 17 is activated in response to the output signal of the vacuum gauge 16.
controls the conductance of the variable conductance valves 3', 4', and 8', and performs exhaust and leak with slow exhaust and slow leak curves that are substantially similar to the characteristic curves shown in FIGS. 3 and 4.

According to this embodiment, there are advantages that the leak system is simplified and that the exhaust/leak curve can be linearly and freely controlled, so that it can be applied to various types of vacuum containers.

〔Effect of the invention〕

As is clear from the above description, the present invention has the excellent effect of preventing residual dust in the sample chamber from adhering to the sample during evacuation and leakage without prolonging the evacuation time and leakage time. .

[Brief explanation of the drawing]

Figure 1 is a system diagram showing one embodiment of the present invention, Figure 2 is a system diagram showing an embodiment of the present invention.
The figure is a system diagram showing another embodiment of the present invention, and FIGS. 3 and 4 are diagrams showing examples of exhaust pressure characteristics and leak pressure characteristics in the embodiment. 1... Vacuum chamber, 3, 4, 8... Vacuum valve, 5... Main exhaust system, 7... Preliminary exhaust system, 9... Filter, 1
0,11...Leak gas valve, 12,13,1
4...Pressure regulating valve, 15...Leak gas source, 17...
Control circuit, 16... True instrument, 18... Wafer sample, 1
9...Dust.

Claims (1)

[Claims] 1. In a vacuum evacuation device having a vacuum pump that evacuates a vacuum chamber and a gas source that causes the vacuum chamber to leak to atmospheric pressure via a leak system path, a leak system in which the leak pressure can be switched to multiple levels in the leak system path. A vacuum evacuation device characterized by being configured with a duct.