JPH05172054A - Cryopump - Google Patents

Abstract

PURPOSE:To provide a clean cryopump by reducing the amount of gas released by treatments for preventing reflections on the respective inner surfaces of a shield and a baffle. CONSTITUTION:In a cryopump wherein a cylindrical metallic shield 7 having an open end is provided around a first-stage cold head 4 located within a pump case 1 with a metallic baffle 8 provided to the opening of the shield, the shield and the baffle are plated at their inner surfaces with black chromium. Thereby gas released from the shield and the baffle during regeneration of the cryompump is reduced so much that the inconvenience of a vacuum vessel being contaminated by gas released during the regeneration can be eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryopump that adsorbs gas molecules and exhausts them.

[0002]

2. Description of the Related Art Conventionally, a cryopump is usually used for obtaining an ultra-high vacuum, and an internal or external pump case having a gas inlet opening communicating with a vacuum chamber through an exhaust pipe or an exhaust port is used. It is equipped with a first-stage cold head that is driven by the refrigerator of FIG. And the first
A tubular metal shield having an opening corresponding to the inflow opening is attached to the multi-stage cold head, and a metal baffle is attached to the opening of the shield. A cryopanel is attached to the second-stage cold head. Gas having a high condensation temperature, such as water vapor, of the gas molecules flowing in from the inflow opening of the pump case is condensed and discharged to a baffle cooled to about 80K through a shield, and gas having a low condensation temperature such as nitrogen. The molecules are condensed on a cryopanel cooled to about 15K and exhausted. The shield is usually made of a copper material, and the outer peripheral surface thereof is plated with Ni so as to reflect the radiant heat from the outside, and the radiant heat entering the inside from the opening of the shield is reflected to the cryopanel. In order to prevent the arrival, it is also practiced to apply an epoxy black paint on the inner surface of the shield and the inner surface of the baffle.

[0003]

A cryopump has poor exhaust performance when the amount of gas molecules condensed in a baffle or a cryopanel increases. Therefore, the cryopump should be returned to room temperature or heated (baked out) at an appropriate time. It is necessary to perform regeneration to remove condensed gas molecules. At the time of regeneration, where the temperature inside the pump rises, organic gas is released from the paint applied to the inner surface of the shield and baffle, and the gas reaches the inside of the vacuum tank through the exhaust pipe from the inside of the pump and reaches there. There was the inconvenience of pollution.

It is an object of the present invention to provide a clean cryopump by reducing the amount of released gas based on the antireflection treatment of the shield and the inner surface of the baffle.

[0005]

According to the present invention, a first stage cold head inside a pump case of a cryopump,
Provided with a cylindrical metal shield with one end opened, in which a metal baffle was provided in the opening of the shield, by applying black chrome plating to the inner surface of the shield and the inner surface of the baffle, The above-mentioned purpose is achieved. When the shield and the baffle are degassed in a vacuum after being attached to the black chrome plating, the released gas is further reduced.

[0006]

[Function] The radiant heat entering the inside of the shield of the cryopump is suppressed because the inner surfaces of the shield and the baffle are black, and the radiant heat rarely reaches the cryopanel. Similarly, the temperature of the cryopanel can be maintained at an extremely low temperature. Also, during regeneration, the inner surfaces of the shield and baffle are treated with black chrome plating, so the release of organic gases is significantly less than before, and the shield is degassed in vacuum after black chrome plating. A cryopump equipped with a baffle can particularly reduce the amount of released gas and can solve the above-mentioned problem of contamination of the vacuum chamber.

[0007]

EXAMPLE An example of the present invention will be described with reference to FIG.
Reference numeral 1 in FIG. 1 denotes a pump case of a cryopump having a gas inflow opening 2 communicating with a vacuum chamber through an exhaust pipe or an exhaust port, and inside the pump case 1, an external refrigerator 3 is provided. A first stage cold head 4 that is driven and cooled to about 80K and a second stage cold head 5 that is cooled to about 15K are provided. Inside the pump case 1, a cylindrical copper or other metal shield 7 having an opening 6 corresponding to the inflow opening 2 is attached to the first-stage cold head 4, and the opening 6 is made of copper or the like. The metal baffle 8 is attached. Reference numeral 9 is a tubular cryopanel made of metal such as copper attached to the second-stage cold head 5, and in many cases activated carbon is attached to the inner surface thereof.

The above construction is not particularly different from that of a normal cryopump, and the outer peripheral surfaces of the shield 7 and the baffle 6 may be Ni-plated so as to reflect radiant heat from the outside. In the case of the present invention, black chrome plating 12 is applied to the inner surfaces of the shield 7 and the baffle 6, that is, the sides 10 and 11 facing the cryopanel 9, as shown in FIGS. 2 and 3. did. The black chrome plating 12 is, for example, chromic acid 250 g / l and ammonium sulfamate 10 to 10.
A plating solution in which 20 g / l and 5 to 25 g / l of boric acid are mixed, a current density of 20 to 100 A / dm ² , 15 to 35 ° C.
In done by energizing 5-50 minutes, preferably after the plating treatment, 1 × 10 ^{- 2} Pa or less degassing treatment while heating to 150 to 200 ° C. in a vacuum at a pressure of 6
Do more than an hour.

In the cryopump incorporating the shield 7 and the baffle 6 thus produced, when the pump is in operation, the gas having a high condensation temperature such as water vapor of the gas molecules flowing from the inflow opening 2 of the pump case 1 has a high shield temperature. Through which it is condensed and discharged to the baffle 6 cooled to about 80K, and gas molecules having a low condensation temperature such as nitrogen are condensed and discharged to the cryopanel 9 cooled to about 15K,
Radiant heat from the outside is reflected by the Ni plating on the outer peripheral surfaces of the shield 7 and the baffle 6. Further, the radiant heat entering from the opening 6 of the shield 7 to the inside thereof is prevented from reaching the cryopanel 9 due to the black chrome plating 12 on the inner surfaces of the shield 7 and the baffle 6. When the cryopump is regenerated, the gas is hardly released from the black chrome plating 12 of the shield 7 and the baffle 6, and the vacuum chamber is not contaminated with the released gas as in the conventional case.

[0010]

As described above, in the present invention, since black chrome plating is applied to the inner surface of the shield and the inner surface of the baffle of the cryopump, the gas emitted from the shield and the baffle during regeneration of the cryopump is extremely small, This has the effect of eliminating the inconvenience of contaminating the vacuum chamber with the released gas during regeneration.

[Brief description of drawings]

FIG. 1 is a cutaway side view of an embodiment of the present invention.

[Fig. 2] Partial enlarged view of the shield

[Fig. 3] Partially enlarged view of the baffle

[Explanation of symbols]

1 Pump case 4 1st stage cold head 6 Opening 7 Shield 8 Baffle 12 Black chrome plating

Claims (2)

[Claims] 1. A cryopump in which a first-stage cold head inside a pump case is provided with a cylindrical metallic shield having an opening at one end, and a metallic baffle is provided at the opening of the shield. The cryopump is characterized in that the inner surface of the shield and the inner surface of the baffle are plated with black chrome. 2. The cryopump according to claim 1, wherein the shield and the baffle are attached with the black chromium plating and then degassed in a vacuum.