JPH04133253A - Electron beam device exhaust system using ion pump - Google Patents

Abstract

PURPOSE:To maintain high speed of gas exhausting by driving an aux. ion pump prior to starting, starting a main ion pump to perform exhaustion along with the aux. ion pump, and turning off the aux. pump to permit the main pump solely to perform exhaustion. CONSTITUTION:When a pressure gauge G1 gives a judgement such that the pressure in an electron gun chamber 2 has sunk below a certain value P1, a normal ion pump IP1 to exhaust the chamber 2 to an intermediate level of super-high vacuum is started along with another ion pump IP3 which is for exhaustion of the mirror barrel part. When a certain time has elapsed, valves V1, V2 are closed while another V3 is opened, and an ion pump IP2 proprietary for super-high vacuum is actuated. After a certain period of time has elapsed, the pump IP1 is turned off, and now the chamber 2 is solely exhausted by the pump IP2. When the pressure in a camera chamber 4 exhausted by a turbo molecular pump TMP is judged by a pressure gauge G2 as having sunk below a specified level P2, an air lock valve AV is opened, and the observing operation of electron microscope 1 is started.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to an evacuation system for electron beam equipment such as an electron microscope, and in particular, to an exhaust system that can perform extremely high vacuum evacuation by effectively utilizing the characteristics of an ion pump. This invention relates to an exhaust system consisting of two or more ion pumps with different characteristics.

[Conventional technology]

As shown in Figure 7, an ion pump (sputter ion pump) is equipped with an anode made of cylinders closely arranged in a honeycomb shape in a container, and a cathode made of two titanium plates narrowing from both sides. This pump is suitable for obtaining a high vacuum, as it applies a magnetic field perpendicularly to the cathode plate from the outside of the container that houses them. When electrons exist between the anode and cathode, they move in a spiral direction due to the influence of the magnetic field, heading toward the cylindrical anode, passing through it, and returning again, repeating a back-and-forth motion, making it impossible for them to reach the anode easily. . Therefore, there is a high probability that electrons will ionize residual gas molecules even in a high vacuum. Since the positive ions generated there have a larger mass than electrons, they head straight toward the cathode and sputter titanium by collision. A part of the positive ions sinks directly into the titanium plate and is captured, creating an exhaust effect. Also,
The sputtered titanium atoms mainly adhere to the anode surface, and the getter action of the clean titanium film formed there has a large exhaust effect. In contrast to the type shown in the figure (two-electrode type), there is a type (three-electrode type) in which the anode and container are placed at zero potential and a negative high voltage is applied to the cathode (three-electrode type).
From 4th edition, page 660. ).

In such an ion pump, for example, 10th
AVS National Vac, Symp, (1
963) pp. 185-190, when the product Bxd of the magnetic field strength B (k gausS) and the diameter d (inch) of the anode cylinder increases, the discharge intensity (1/P) sharply decreases. Extends to extremely high vacuum regions at very low pressures without causing any damage. Ion pump pumping speed S
(, e/s) is proportional to the discharge intensity (1/P), so B
A pump with a large Xd maintains a relatively high pumping speed at extremely high vacuum pressure. To increase the value of BXd,
It may be easier to increase the diameter d of the γ-node cylinder, but the number of γ-node cells that can be incorporated into the usable cathode area decreases in inverse proportion to d2. For the γ node located at the γ node, the lines of magnetic force are bent with respect to the cylinder axis, resulting in problems such as a decrease in the electron density of the Penning discharge. Therefore, in order to increase BXd and obtain a highly efficient Penning discharge cell with lines of magnetic force parallel to the discharge cell, B must be increased to 1. It is necessary to increase the size to about 5k gauss (in the case of 6 to 20 mm). On the other hand, B
Ordinary ion pump with relatively small Xd (B = 1
, around Ok gauss) is relatively low vacuum (10
``'~10-') region, Xd as shown above.
Compared to ultra-vacuum ion pumps with large pumping speeds, the pump has a pumping speed S that is comparable to or greater than that of ultra-vacuum ion pumps.

By the way, conventionally, for example, in an electron microscope, 10-"
One ion pump is installed in the electron gun chamber, which is equipped with a field emission electron gun that requires an extremely high vacuum on the order of Torr. It was evacuated to an ultra-high vacuum.

[Problem that the invention seeks to solve]

In order to cover such a wide pressure range, in conventional ion pumps, when designing parameters for Penning discharge, approximately the middle of the wide operating pressure range is used.
It is designed to obtain a large nominal pumping speed around X 10-' Torr, and the pumping speed in the 10-10 Torr region, which is the operating pressure of a field emission electron gun, is very small.

Further, in an ion pump whose main operating pressure range is in the 10-10 Torr range, it is desirable to start it from an ultra-high vacuum at the lowest possible pressure in order to prevent problems such as oxidation of its active internal surface. however,
Conventionally, the ion pump was turned on after the ion pump was evacuated using an auxiliary pump such as a turbomolecular pump or an oil diffusion pump to a high vacuum pressure at which the ion pump could be started.

In addition, sometimes the ion pump itself was used to evacuate the electron gun chamber and the ion pump itself during baking. This is to prevent the emitted gas from the turbomolecular pump or oil diffusion pump line from entering the electron gun chamber, but this operation of the ion pump has traditionally caused the achievable pressure of the ion pump to be undesirably high. It was put away.

The present invention was made in view of this situation, and
The purpose is to provide an evacuation system that is capable of evacuation at a high evacuation speed even in the 10 to 10 To'r1 region, which is the operating pressure of a field emission electron gun, and has an extremely low achievable pressure.

[Failure to solve the problem]

To achieve the above object, an evacuation system using an ion pump in an electron beam apparatus according to the present invention includes at least A main ion pump with a relatively large product of the average magnetic flux density of the ion pump and the discharge cell cylinder diameter and an auxiliary ion pump with a relatively small product are installed in an ultra-high vacuum chamber, and when the exhaust system is started. In this case, the auxiliary ion pump is driven first, then the main ion pump is started and exhausted together with the auxiliary ion pump, and then the drive of the auxiliary ion pump is stopped or the auxiliary ion pump is shut off. The main ion pump is used to exhaust air using only the main ion pump.

[Effect]

In the present invention, a main ion pump and an auxiliary ion pump, which have a high pumping speed even in an ultra-high vacuum, are installed in an ultra-high vacuum chamber, and the auxiliary ion pump is driven in advance when the evacuation system is started. Then, the main ion pump is started to exhaust air together with the auxiliary ion pump, and then either the auxiliary ion pump is stopped, or the auxiliary ion pump is shut off, and the auxiliary ion pump is exhausted only by the main ion pump. The ion pump and the auxiliary ion pump share the exhaust pressure range, for example, 10-” To
High pumping speed can be ensured even in the extremely high vacuum region of the rr range. Furthermore, the pressure at startup of the main ion pump can be lowered by exhausting the auxiliary ion pump, and oxidation of the active internal surface can be minimized, resulting in an internal surface condition suitable for extremely high vacuum pumping. Because you can always maintain your ability,
Its exhaust performance will not deteriorate. Furthermore, auxiliary exhaust systems such as turbomolecular pumps and oil diffusion pumps that release a lot of gas such as water vapor are shut off when the auxiliary ion pump is started. It can be achieved.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration when an exhaust system according to an embodiment of the present invention is applied to a transmission electron microscope. The electron microscope 1 includes an electron gun chamber 2 that accommodates a field emission electron gun,
Lens barrel section 3 consisting of a focusing lens chamber, a sample chamber, and an imaging lens chamber
and a camera room 4 consisting of an image observation section and a camera section. An air valve AV is provided between the lens barrel section 3 and the camera chamber 4 to prevent atmospheric air from entering the lens barrel section 3 during film exchange. In the electron gun chamber 2, there is a normal ion pump IPI, and the average magnetic flux density is that of the ion pump IP1 in the Penning discharge chamber (anode cylinder) (approximately 1,
It is about 50% stronger than Q k gauss) and about 1.
An ion pump IP2 designed for ultra-high vacuum and designed for 5k Gauss is installed.

Then, a normal ion pump ['l is connected to a turbo molecular pump TMP (or oil diffusion pump) via valve V1.
is connected to this Turbomolecular PumpTM at startup.
P provides auxiliary exhaust. In addition, the lens barrel section 3 and the camera chamber 4
are connected to the turbomolecular pump TMP via valves V2 and V3, respectively. A rotary pump RP is connected to the exhaust side of the turbo molecular pump TMP. Further, an ion pump IP3 for exhausting the lens barrel portion is attached to the lens barrel portion 3. Furthermore, an ion pump IP2 dedicated to ultra-high vacuum, which is the final pump, an ion pump rP3 for exhausting the lens barrel, and a heater 5 for the beam in the electron gun chamber 2.
is provided. Moreover, pressure gauges 01 and G2 are attached to the electron gun chamber 2 and the camera chamber 4, respectively.

In such an evacuation system, the ion pump IP2, which is dedicated to ultra-high vacuum, can only be activated in areas that have become ultra-high vacuum (pressure below the 10-'Torr range) due to exhaust by the normal ion pump IPI. ing. By simultaneously exhausting the above IPI and IF5, 10-BTo
After being evacuated to the rr range, the IPI for startup is normally switched off, and IF5 is used to evacuate to an extremely high vacuum of 10-” Torr or more.Here, the reason for switching off the IPI is that the IPI is Since the vacuum is being evacuated under high pressure, a large amount of gas is attached to the cathode surface in the form of titanium compounds. This is due to the fact that this attached gas is re-released and IPl becomes a gas release source, whereas when the switch is turned off, the attached gas remains in a stable form and almost no gas is re-released. .

FIG. 2 shows a flowchart for such an operation. First, in STI, turbo molecular pump TMP and rotary pump RP are started, and in ST2, after closing valves v3 and AV, valves V1 and V2 are opened, and turbo molecular pump TMP is used to open electron gun chamber 2 and lens barrel Start exhausting. In Sr3, it is determined whether the pressure in the electron gun chamber 2 measured by the pressure gauge 61 has become smaller than a predetermined value P1.If it is determined that the pressure in the electron gun chamber 2 has become smaller than this value P1, in Sr1 The normal ion pump IP1 for evacuating to an intermediate ultra-high vacuum and the ion pump IP3 for evacuating the lens barrel are started.

After measuring the passage of a predetermined time using Sr5 (the pressure in the electron gun chamber 2 has decreased to below 10-8 TorrL as described above), the valves v1 and V2 are opened at Sr1.
After closing the valve V3 (close the valve V3), turn on the ion pump IP2 dedicated to ultra-high vacuum at Sr7 and start it up. After that, in Sr1, after measuring the passage of a predetermined time (electron gun chamber 2J), the pressure is changed to IPI and I as described above.
By F5, it has decreased to 10'□9Tt:rr range. ), in S79, the ion pump IPit
Cut. Thereby, the electron gun chamber 2 is evacuated by the ion pump IP2. At 5TIO, the pressure in the camera chamber 4 exhausted by the turbo molecular pump TMP is measured by the pressure gauge 02, and it is determined whether the pressure has become smaller than a predetermined value P2. When it is determined that the value has become smaller than this value P2, the aerostat valve AV is opened at 5TII, and the observation operation of the electron microscope 1 can be started.

Now, if the electron gun chamber 2, ion pump IP2, etc. are exposed to the atmosphere, water vapor will adhere to their inner surfaces and a large amount of gas will be released during the initial stage of exhaust, so it is necessary to perform a baking process (vacuum baking process). .

During vacuum baking of the electron gun chamber 2 and ion pumps IP2 and IF5, the beta heater 5 is electrically connected to the auxiliary pump TM.
P beta-processes the electron gun chamber 2 and ion pumps IP2 and IF5. After the initial large gas release is finished and steady gas release occurs, the TPI is operated, the auxiliary bomb line is shut off, and the IPI is exhausted to perform the subsequent baking process. . . , FIG. 3 shows a flowchart of such an operation, but since the procedure is clear from the diagram, a detailed explanation will be omitted.

Fig. 4 shows a modification of Fig. 1. Differences from the embodiment 17) The ion pump IPI for startup is attached to the electron gun chamber 2 via the cutoff valve 4. It is. In this case, simultaneous exhaust by lPi and IF5 is required to exhaust to the L 0-9 Torr range;
By closing the cutoff valve v4 instead of turning off the switch, the vacuum is evacuated to an extremely high vacuum of 10'□l0 Torr or more using only IF5. In other words, when evacuating to ultra-high vacuum using the ultra-high vacuum dedicated ion pump IP2, 1Pl is completely separated from the electron gun chamber 2, so the ion pump IPI, which is attached to a large amount of gas, is This means that the emission source is completely eliminated, and it is possible to reach extremely high vacuums at lower pressures. Note that after closing the cutoff valve V4, the ion pump IPI may be turned off, but this is not always necessary. FIG. 5 shows a flowchart of the exhaust operation in this case, and FIG. 6 shows a flowchart of the exhaust operation during the baking process. These correspond to FIGS. 2 and 3E, respectively. The only difference from the cases shown in FIGS. 2 and 3 is that the opening/closing operation of the valve V4 is added, and there is no operation of turning off the IPI switch, and the other points are the same. The steps are more detailed than shown in the diagram, so a detailed explanation will be omitted.

By the way, the ion pump IPI in the embodiment of FIG.
, IF5 configuration and (), instead of using two pumps that are constructed completely independently, one ion pump is provided with two Penning discharge sputtering chambers (pump element chambers), and the magnetic field of one discharge sputtering chamber is The strength is the same as the conventional 7 culm degree (
B = i, around 1 kga USS), and the magnetic field strength of other discharge sputtering chambers is stronger due to exhaustion in ultra-high vacuum.
(B=I.

It is also possible to connect each of them to an independent drive power source and to control each of them using an independent ion pump, as shown in FIG. 2 or 3.

In addition, as a manufacturing modification of the ion pump IP2 dedicated to ultra-high vacuum installed in the electron gun chamber 2, there is a strong magnetic field strength (
B=1. 5k gauss) In order to easily realize a discharge cell, the permanent magnet itself is manufactured using the conventional material and thickness, and the gap length between the magnetic poles is narrowed to about 2/3 of that of the conventional one, and accordingly the discharge cell cylinder (anode) The height of
By reducing the distance between the anode and cathode (T1), and without changing the magnet material or increasing the thickness of the magnetic material yoke, it is possible to realize an ion pump dedicated to ultra-high vacuum with strong magnetic field strength. .

Although the case where the electron gun chamber of a transmission electron microscope is evacuated has been described above, it is clear that the present invention is not limited to this and can be applied to an exhaust device of other electron beam devices. It is also clear that the present invention is not limited to the above embodiments and that various modifications are possible.

〔Effect of the invention〕

According to the evacuation system using an ion pump provided in the electron beam apparatus of the present invention, a main ion pump and an auxiliary ion pump, which have a high evacuation speed even in an ultra-high vacuum, are installed in an ultra-high vacuum chamber, and when the evacuation system is started, In this case, the auxiliary ion pump is driven first, then the main ion pump is started and exhausted together with the auxiliary ion pump, and then the drive of the auxiliary ion pump is stopped or the auxiliary ion pump is shut off. The main ion pump and the auxiliary ion pump share the exhaust pressure range, for example, 10" To
High pumping speed can be ensured even in the extremely high vacuum region of the rr range. In addition, the pressure at startup of the main ion pump can be lowered by exhausting the auxiliary ion pump, and oxidation of the active internal surface can be minimized, resulting in an internal surface condition suitable for extremely high vacuum pumping. You can always maintain
Its exhaust performance will not deteriorate. Furthermore, auxiliary exhaust systems such as turbomolecular pumps and oil diffusion pumps that release a lot of gas such as water vapor are shut off when the auxiliary ion pump is started. It can be achieved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration when an exhaust system according to an embodiment of the present invention is applied to a transmission electron microscope, FIG. 2 is a flowchart of the operation at startup of the exhaust system in FIG. 1, and FIG.
The figures are a flowchart of the operation of the exhaust system in Figure 1 during beta processing, Figure 4 is a diagram showing the configuration of another embodiment, and Figure 5 is a diagram showing the configuration of another embodiment.
Figure 6 is a flowchart similar to Figure 2 for the exhaust system in Figure 4, Figure 6 is a flowchart similar to Figure 3 for the exhaust system in Figure 4, and Figure 7 is for explaining the configuration and operation of the ion pump. This is a diagram. l...Transmission electron microscope, 2...Electron gun chamber, 3...
・Lens barrel part, 4...Camera chamber, 5...Heater, AV・
...Aerodynamic valve, IPI...Normal ion pump, IF5...Ion pump for ultra-high vacuum, Vl, V
2, v3, V4...valve, TMP...turbo molecular pump, RP...rotary pump, G1, G2...
・Pressure gauge box 1fi Applicant: JEOL Co., Ltd. Agent Patent attorney: Hiroshi Nirasawa (7 others) P Figure 4 P

Claims (1)

[Claims] (1) In an exhaust system for evacuating an ultra-high vacuum chamber of an electron beam device to an extremely high vacuum using an ion pump, the main ion whose product of at least the average magnetic flux density of the ion pump and the discharge cell cylinder diameter is relatively large is A pump and an auxiliary ion pump whose product is relatively small are installed in an ultra-high vacuum chamber, and when the exhaust system is started, the auxiliary ion pump is driven first, and then the main ion pump is driven. An electron beam device characterized in that the electron beam device is started and evacuated together with the auxiliary ion pump, and then the drive of the auxiliary ion pump is stopped or the auxiliary ion pump is shut off so that exhaust is performed only by the main ion pump. Exhaust system using an ion pump.