JPH0544642A - Cryopump equipped with low temperature trap - Google Patents

Abstract

PURPOSE:To increase the evacuation capacity by dividing each of a pump case and a shield into two parts in the longitudinal direction, installing a buffle on the front shield, installing the second refrigerator separately from a two-stage type helium refrigerator, and constituting a low temperature trap. CONSTITUTION:Each of a pump case 1 and a shield 6 is divided into two parts in the longitudinal direction, and a buffle 8 is installed on the front shield 6a, oppositely to an opened port part 2, and the low temperature part 10 of the second refrigerator 9 which is different from a two-stage type helium refrigerator 3 is installed, and a low temperature trap 11 is constituted. Accordingly, since the shield 6a of the low temperature trap 11 and the buffle 8 are cooled by the second refrigerator 9 different from the two-stage type helium refrigerator 3 for coolding a cryopanel 7, almost all the parts of the thermal load such as the radiation heat supplied from a vacuum device and the conduction heat of gas can be absorbed without applying load onto the two-stage type helium refrigerator 3. Accordingly, the evacuation capacity for the gas particle having high vapor pressure can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryopump with a cryogenic trap.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 1, a cryopump has a first stage d and a second stage e of a two-stage helium refrigerator c inside a pump case b having an opening a in the front. , A cylindrical shield f is attached to the first stage d, a cryopanel g is attached to the second stage e, and a baffle h facing the opening a is attached to the shield f. Generally prepared. i is an adsorbent provided on the inner surface of the cryopanel g.

An exhaust pipe connected to, for example, a vacuum chamber is connected to the opening a, and when the two-stage helium refrigerator c is operated, the first stage d is cooled to about 80K and the second stage e is about 15K. The baffle h is cooled to about 80K and the cryopanel g is cooled to about 15K by heat conduction from the stages d and e. Molecules with a low vapor pressure such as water vapor and oil vapor flying from the opening a into the pump case b are condensed in the baffle h, and, for example, nitrogen or argon gas molecules with a high vapor pressure are condensed in the cryopanel g and are not condensed. By adsorbing the adsorbent i with the hydrogen gas molecules having the property, the vacuum chamber connected to the opening a is evacuated to a high vacuum. The baffle h and the shield f absorb the radiant heat from the vacuum chamber and the heat load due to the heat conduction of gas, and bear the main heat load of the cryopump so that the heat load is not applied to the cryopanel g having a small heat capacity.

The exhaust capacity of the gas capable of condensing nitrogen, argon, etc. in the cryopanel g (the maximum amount that can be stored in the cryopump) is usually determined by the distance between the cryopanel g and the baffle h and the outer diameter of the cryopanel g. Decided. The reason is that when the thickness of the layer of nitrogen, argon, etc. condensed on the outer surface of the cryopanel g increases, the layers come into contact with the shield f and the baffle h, and the nitrogen etc. condensed at the contact point re-evaporates. This is because the exhaust will not proceed. Further, if the thickness of the condensed layer of nitrogen or the like is increased, a temperature gradient is formed in the layer, which increases the surface temperature and reduces the exhaust efficiency. When the cryopanel g reaches the exhaust capacity limit, the cryopump is returned to room temperature and the condensed nitrogen or the like is evaporated to perform regeneration.

[0005]

As described above, since the conventional cryopump is operated by one helium refrigerator, its refrigerating capacity is limited, and when the heat load from the outside becomes large, the pump action is caused. There was an inconvenience that I could not do it.
It is conceivable to provide a low temperature trap in front of the opening a of the cryopump in order to prevent heat load from being applied to the cryopump, but since the low temperature trap and the baffle are provided twice in the exhaust passage. However, there is a disadvantage that the conductance to the cryopanel g is reduced, the effective exhaust speed is reduced, and the exhaust time of the vacuum device is increased.

Further, if the distance between the cryopanel g and the baffle h is increased to increase the exhaust capacity, the length of the shield f is increased accordingly and the heat receiving area is increased accordingly, and the shield f is increased accordingly. There is a limit to increasing the distance because the amount of radiant heat entering the device increases. Further, since the refrigerating capacity is limited, in an apparatus that uses a large flow rate of argon such as a sputtering apparatus, the amount of argon used in the apparatus is limited by the refrigerating capacity of the refrigerator.

An object of the present invention is to provide a cryopump capable of increasing the exhaust capacity without reducing the exhaust speed.

[0008]

According to the present invention, a cylindrical shield attached to a first stage of a two-stage helium refrigerator and a two-stage stage of the two-stage helium refrigerator are provided inside a pump case. In a cryopump provided with a cryopanel attached and a baffle facing the opening of the pump case attached to the shield, the pump case and the shield are divided into two parts, a front shield and a front shield. The above object is achieved by attaching the baffle and attaching a low temperature section of the second refrigerator separate from the two-stage helium refrigerator to form a low temperature trap.

[0009]

When the vacuum pump is evacuated by the cryopump of the present invention, most of the heat load such as the radiant heat from the vacuum device and the conductive heat of gas is provided in front of the cryopump. Since it is absorbed in a low temperature trap that is cooled by a refrigerator separate from, the cryopanel no longer receives a heat load and its temperature drops,
Nitrogen and argon can be condensed more thickly, and the heat-receiving area of the shield does not increase even if the distance between the low temperature trap and the cryopanel is increased to increase the thickness of the condensed layer such as argon. The exhaust capacity can be increased without impairing the heat load absorption performance. Further, since the baffle is provided in the low temperature trap, the heat capacity of the one-stage stage for cooling the shield behind the cryopump becomes small, and the time required to cool from room temperature is correspondingly shortened.

[0010]

EXAMPLE An example of the present invention will be described with reference to FIG.
In the figure, reference numeral 1 indicates a pump case of a cylindrical cryopump having an opening 2 at the front, and a two-stage type small helium refrigerator 3 is attached to the rear of the pump case 1, and the two-stage type The first stage 4 and the second stage 5 of the small helium refrigerator 3 are extended into the pump case 1. Inside the pump case 1, a copper cylindrical shield 6 is attached to the first stage 4, and a copper cryopanel having an adsorbent 7a such as activated carbon provided on the inner surface of the second stage 5. 7 is attached.

Although such a construction is similar to that of the conventional cryopump, in the case of the present invention, two pump cases 1 and two shields 6 are provided at the front and rear, that is, the pump case 1a and the shield at the front opening 2 side. 6a and a pump case 1b and a shield 6b on the rear two-stage small helium refrigerator 3 side, and a baffle 8 formed of a heat conductive material such as copper on the front shield 6a. And the low temperature section 10 of the second refrigerator 9 separate from the two-stage helium refrigerator 3 is attached to form the low temperature trap 11, which reduces the heat load of the cryopump and increases the exhaust capacity. The pumping speed can be kept constant without changing the conductance. As the second refrigerator 9, a one-stage helium refrigerator, a Freon refrigerator capable of cooling to about -120 to -130 ° C, or a liquid nitrogen storage refrigerator can be used. The opening 2 is connected to a vacuum device such as a sputtering device through an exhaust pipe 12 equipped with a partition valve.

When the inside of the vacuum apparatus is evacuated to a vacuum, the inside of the vacuum apparatus is evacuated to an appropriate degree of vacuum in advance and then the two-stage helium refrigerator 3 and the second refrigerator 9 of the cryopump are driven to shield the shield 6a. , 6b and the baffle 8 are cooled to about 80K and the cryopanel 7 is cooled to about 15K, the partition valve of the exhaust pipe 12 is opened, and the cryopump evacuates the vacuum chamber to a high vacuum. In this case, the gas from the vacuum device flowing into the pump case 1 from the exhaust pipe is first cooled by the shield 6a and the baffle 8 of the low temperature trap 11, and gas molecules having a low vapor pressure such as water vapor are shielded by the shield 6a and the baffle 8. Of the remaining gas molecules that have condensed and have not condensed, those with a low vapor pressure are condensed on the rear shield 6b, and gas molecules with a high vapor pressure such as nitrogen are condensed on the cryopanel 7. Further, non-condensable hydrogen gas molecules and neon gas molecules are adsorbed by the adsorbent 7a on the inner surface of the cryopanel 7.

Since the shield 6a and the baffle 8 of the low temperature trap 11 are cooled by the second refrigerator 9 which is separate from the two-stage helium refrigerator 3 which cools the cryopanel 7, radiant heat from the vacuum device and gas. Most of the heat load such as the conduction heat of the two-stage helium refrigerator 3 can be absorbed without burdening the two-stage helium refrigerator 3, so that the burden capacity of the two-stage helium refrigerator 3 is increased and gas is exhausted. The capacity is increased, and it is possible to improve the film quality by increasing the amount of argon gas used, for example, in a sputtering device, and the gas molecules such as nitrogen condensed in the cryopanel 7 are re-evaporated and cannot function as a pump. Can be eliminated. Even if the distance between the cryopanel 7 and the baffle 8 is increased, the two-stage helium refrigerator 3
The heat receiving area of the shield 6b for cooling does not change, and the radiant heat from the vacuum device can be prevented from increasing to increase the heat load of the two-stage helium refrigerator 3. High pressure gas molecules can be thickly condensed to increase the exhaust capacity.

[0014]

As described above, according to the present invention, the pump case and the shield of the cryopump are divided into two parts, the front and rear parts, and the baffle is attached to the divided front shield and the two-stage helium refrigerator. Second separate from
Since the low temperature part of the refrigerator is attached and configured as a low temperature trap, the distance between the cryopanel and the baffle can be made large without increasing the heat load of the two-stage helium refrigerator, and the heat load applied to the cryopump can be increased. Since the second refrigerator shares the burden, the burden on the two-stage helium refrigerator is reduced,
There is an effect that the exhaust capacity of gas molecules having a high vapor pressure can be increased, and an exhaust speed is not reduced.

[Brief description of drawings]

FIG. 1 is a cutaway side view of a conventional example.

FIG. 2 is a cutaway side view of an embodiment of the present invention.

[Explanation of symbols]

1, 1a, 1b Pump case 2 Opening part 3 Two-stage helium refrigerator 4 One-stage stage 5 Two-stage stage 6, 6a, 6b
Shield 7 Cryopanel 8 Baffle 9 Second refrigerator 10 Low temperature section 11 Low temperature trap

Claims (2)

[Claims] 1. A cylindrical shield attached to the first stage of a two-stage helium refrigerator inside a pump case,
In a cryopump in which a cryopanel attached to a two-stage stage of the two-stage helium refrigerator is provided, and a baffle facing the opening of the pump case is attached to the shield, the pump case and the shield are attached to front and rear sides. A low-temperature trap characterized by being divided into individual pieces, the baffle being attached to the divided front shield, and a low-temperature portion of a second refrigerator different from the two-stage helium refrigerator being attached to form a low-temperature trap. Cryo pump with. 2. The cryopump with a low temperature trap according to claim 1, wherein the second refrigerator is a one-stage helium refrigerator or a Freon refrigerator.