JP3609474B2 - Cryopump - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a cryopump that is applied to, for example, a sputtering apparatus or an ion plating apparatus, and obtains a high vacuum by condensing gas molecules on a cryogenic panel and exhausting them.
[0002]
[Prior art]
Conventionally, as shown in FIG. 1, a cryopump has a first stage d and a second stage e of a small helium refrigerator c inside a pump case b having an intake port a opened to the outside. A shield g provided with a baffle f facing the air inlet a is fixed to the first stage d, and a bottomed cylindrical cryopanel h is fixed so as to cover the periphery of the second stage e This configuration is general. The cryopump is attached with the inlet port a communicating with, for example, a vacuum processing chamber of a sputtering apparatus, and the helium refrigerator c is operated to cool the shield g and the baffle f to about 70 K by the first stage d. In addition, the cryostage h is cooled to about 15K by the second stage e, and a gas having a low vapor pressure such as water in the gas in the vacuum processing chamber is condensed in the shield g and the baffle f and exhausted. A gas having a higher vapor pressure such as oxygen or argon is condensed on the outer surface of the cryopanel h and exhausted.
[0003]
[Problems to be solved by the invention]
In the conventional cryopump, in order to increase the exhaust speed, the shield g and the baffle f are opened to increase the conductance. Most of the gas enters the cryopanel h as shown by the arrows and condenses as shown by the oblique lines.
[0004]
However, in the conventional cryopump structure, a large amount of gas is condensed in the upper corner portion i of the outer surface of the cryopanel h and is not uniformly condensed over the entire cryopanel h. It was difficult.
[0005]
In order to increase the exhaust capacity, a structure that can increase the thickness of the condensing layer is necessary. For this purpose, the cryopanel h is shaped like a cone, or the distance X between the cryopanel h and the baffle f is X. It is necessary to take large. However, even if X is increased, if the condensed layer becomes thicker, a temperature gradient is generated in the condensed layer, and the surface temperature of the condensed layer becomes higher.
[0006]
The limit of the thickness of the condensed layer depends on the type and flow rate of the gas and the temperature and structure of the baffle f and cannot generally be determined to be a few millimeters. Since the rate is large and the condensation heat is relatively small, the maximum thickness can be about 40 to 50 mm. However, in the case of a gas having a low thermal conductivity of the condensate layer such as nitrogen or air and a high vapor pressure, even if X is increased, the exhaust limit is reached before the condensate layer contacts the baffle f.
[0007]
That is, if the geometric surface area of the portion of the cryopanel h where the gas condenses is A and the limit thickness of the condensed layer is t, the volume V (cm ³ ) of the condensed layer is approximately,
V = αAt ……………………… (1)
Given in. α is a proportionality coefficient. If the displacement of the cryopump is C (liter), the displacement is
C = 22.4ρV / M (2)
It becomes. ρ is the density of the condensed layer (g / cm ³ ), and M is the molecular weight (g / mol) of the gas.
The displacement when X> t is determined by the thickness t of the condensate layer, and the volume of the condensate layer is given by equation (1). The limit volume of the condensate layer when X <t is
V = αAX ……………………… (3)
It is.
In a normal cryopump, since X = about 20 to 30 mm, the limit volume of the condensed layer is calculated by the equation (3) in the case of pure argon.
Furthermore, when exhausting the gas to the outer surface of such a cryopanel h, the exhaust surface increases as the thickness of the condensing layer increases, so the exhaust speed increases and the exhaust speed changes. There are drawbacks. In a sputtering apparatus or the like, it is necessary to keep the process pressure constant. Therefore, a conductance valve for adjusting the conductance is provided between the cryopump and the vacuum processing chamber so that the change in the exhaust speed can be offset. It is necessary.
[0008]
The first object of the present invention is to provide a cryopump capable of obtaining a large exhaust capacity. Another object of the present invention is to provide a cryopump capable of exhausting at a stable exhaust speed.
[0009]
[Means for Solving the Problems]
In the present invention, a first stage and a second stage of a refrigerator are provided inside a pump case having an air inlet that is open to the outside, and the cylindrical shield attached to the first stage is A cryopump in which a baffle is fixed to an opening facing an intake port, and a bottomed cylindrical cryopanel facing the intake port is fixed to the second stage stage through the baffle. The bottom of the baffle is fixed to the second stage with the opening at one end of the cylindrical shape facing the air inlet, and the diameter of the rear part of the baffle is gradually reduced from the middle part in the gas molecule passage direction. Thus, the above-mentioned purpose is achieved. Further, the purpose of these is to form the diameter of the opening of the cryopanel larger than the diameter of the opening of the shield, and to pass the rear part of the baffle through the opening of the cryopanel into the inside of the cylinder of the cryopanel. This is preferably achieved by making the
[0010]
[Action]
Since the cryopanel is fixed to the second stage with the opening directed to the air inlet, gas molecules flowing into the cryopump from the air inlet are placed inside the cylinder of the cryopanel. It will condense. Therefore, a condensed layer is not formed on the outer peripheral surface of the cryopanel, and a conventional gap for forming a condensed layer is not required between the outer peripheral surface of the cryopanel and the inner peripheral surface of the shield. Accordingly, the diameter of the cryopanel can be increased, so that A in the above formula (1) is increased, and the inner length of the cryopanel can be evenly increased by increasing the axial length of the cryopanel. A can be increased so that it can be condensed to the exhaust gas, and the exhaust capacity can be increased. If the axial length is increased, the thickness of the condensate layer can be reduced even with the same exhaust capacity, so that the surface temperature of the condensate layer can be lowered and the exhaust performance is stabilized.
[0011]
In addition, by making the diameter of the intake port smaller than the diameter of the cryopanel facing the intake port, the rear part of the baffle enters the inside of the cylinder of the cryopanel, so that the gas molecules are allowed to enter the cryopanel. Since it can be reliably guided to the inside of the cylinder and all of it can be condensed, the exhaust speed is determined only by the conductance of the baffle, and it is not affected by the amount of exhausted gas, that is, the amount of condensation, so stable exhaust Exhaust at speed.
[0012]
【Example】
An embodiment of the present invention will be described with reference to the drawings. In FIG. 2, reference numeral 1 denotes a cylindrical pump case having a circular intake port 2 opened to the outside. The first stage 5 at the end of the first stage cylinder 4 extending from a known small helium refrigerator 3 provided outside, and the second at the end of the second stage cylinder 6 continuous to the first stage cylinder 4. A stage stage 7 is provided. By the operation of the helium refrigerator 3, the first stage 5 is cooled to about 70K, and the second stage 7 is cooled to about 15K. A cylindrical shield 9 having a circular opening 8 facing the intake port 2 is attached to the first stage 5, and a baffle 10 is attached and fixed to the opening 8. In addition, a bottomed and cylindrical cryopanel 11 is attached and fixed to the second stage 7 so as to face the air inlet 2. The shield 9, the baffle 10, and the cryopanel 11 are made of a heat good conductor such as a copper material. As shown in the figure, the baffle 10 is formed by concentrically fixing a plurality of annular baffle members 10a having different diameters. It was set as the structure which guides a gas molecule toward.
[0013]
The above configuration is also provided in a conventional cryopump. However, in the present invention, the cylindrical cryopanel 11 has the bottom portion 13 in the second stage with the circular opening 12 facing the air inlet 2. 7, gas molecules flowing in from the air inlet 2 are condensed on the cylindrical inner surface 14 and exhausted, and a gas condensation layer is not formed on the outer surface 15 of the cylindrical shape by this configuration. The outer surface 15 of the panel 11 can be brought closer to the inner surface of the shield 9 to increase the diameter thereof, and the axial length of the cylindrical shape can also be increased. For this reason, the surface area of the cryopanel 11 is increased to increase the exhaust capacity, and a stable exhaust speed can be obtained by forming a condensed layer with a substantially uniform thickness on the entire inner surface 14.
[0014]
Also, codes D diameter of the intake port 2 represented by _B, the cryopanel 11 is formed smaller than the inner diameter D _C of the diameter or opening 12 facing the intake port 2, the from intake port 2 thus ensuring tightening the induction of the gas molecules to the interior of the cryopanel 11, the further the distance H _B from the bottom 13 in the axial direction of the than the length H _C cryopanel 11 cylindrical in the cryopanel 11 to the baffle 10 By shortening, the rear part of the baffle 10 is made to enter the inside of the cylinder of the cryopanel through the opening 12 of the cryopanel 11, and the gas molecules from the air inlet 2 are similarly reliably and reliably supplied to the cryopanel 11. I was guided to the inside.
[0015]
The opening 8 of the shield 9 is covered with a closing member 9a extending from the peripheral wall, and the periphery of the baffle 10 is airtightly attached to the inner edge of the closing member 9a, and the inside of the cryopanel 11 passes through the baffle. Only gas was allowed to enter.
[0016]
In the embodiment shown in FIG. 2, the cryopump of the present invention is configured such that the inlet 2 of the pump case 1 is connected to, for example, a vacuum processing chamber of a sputtering apparatus through an exhaust pipe, and the vacuum processing chamber is an oil rotary pump or the like. The helium refrigerator 3 is operated when the appropriate vacuum degree is obtained by the roughing pump of the first stage, and the first stage 5 is cooled to about 70K and the second stage 7 is cooled to about 15K. Among the gas molecules, gas molecules having a low vapor pressure of water or air are condensed on the shield 9 or the baffle 10, and gas molecules having a high vapor pressure such as argon are condensed on the cryopanel 11 to exhaust the vacuum processing chamber. However, since the cryopanel 11 is attached with the cylindrical opening 12 facing the intake port 2, gas molecules having a high vapor pressure mainly condense on the inner surface 14 of the cryopanel 11, Condensation layer 16 is formed as, the inner surface 14 so extends toward the intake port 2, the condensation layer 15 in a substantially uniform thickness throughout the inner surface 14 is formed. Since the outer peripheral surface of the cryopanel 11 is not necessary for gas condensation, the gap 17 between the inner surface of the shield 9 and the outer surface 15 of the cryopanel 11 is increased to increase the diameter of the cryopanel 11 so that gas molecules Since it can be formed in a narrow width that is difficult to enter, and the condensing area increases as the diameter increases, the exhaust capacity can be increased. Further, in the conventional cryopanel, even if the length in the axial direction of the cylindrical shape is increased to increase the condensation area, the clearance between the inner surface of the shield and the outer peripheral surface of the cryopanel is increased as the exhaust proceeds. As shown in the figure, the condensing phenomenon is narrowed due to the phenomenon of condensation at the corner i and the gas molecules are prevented from entering the back of the gap, so that the substantial condensation area is small. Since 12 is greatly open toward the air inlet 2, if the length of the cylinder in the axial direction of the cryopanel 11 is extended, the effective condensation area increases as it is, and the exhaust capacity increases. In addition, if the length is long, the thickness of the condensate layer becomes thin when exhausting the same displacement, so that the surface temperature of the condensate layer becomes low and a stable exhaust speed can be obtained.
[0017]
Gas molecules flowing from the intake port 2 of the pump case 1 are guided to the inside of the cryopanel 11 through the baffle 10, and the diameter of the opening 12 of the cryopanel 11 is larger than the diameter of the opening 8 of the baffle 10. Since the gas molecules are large, the gas molecules are surely guided into the cylinder of the cryopanel 11, and since there are no obstacles in the cylinder, the gas molecules condense on the entire inner surface 14 with a substantially uniform thickness. Further, by allowing the rear part of the baffle 10 to enter the cylinder of the cryopanel 11 through the opening 12, gas molecules do not flow in a direction detouring the upper edge of the opening 12, and it is ensured. Can be guided into the cylinder of the cryopanel 11.
[0018]
In the above embodiment, the refrigerator 3 is mounted on the axis of the pump case 1, but in order to reduce the overall height of the cryopump, an extension cylinder 1a is provided on the side of the pump case 1 as shown in FIG. The first stage and the second stage 5, 7 of the refrigerator 3 may be inserted through the second stage 7, and the cryopanel 11 may be provided on the second stage 7 through the heat transfer angle member 18. Further, the baffle 10 only needs to satisfy the conditions of H _C ≧ H _B and D _C ≧ D _B , and the baffle having a larger diameter at the intermediate portion in the gas molecule passage direction as shown in FIG. It is also possible to adopt a structure in which gas molecules are reflected using the member 10 b and guided into the cylinder of the cryopanel 11. Since the pumping speed and the thickness distribution of the condensed layer are determined by the shape of the baffle, it is necessary to pay attention to the design.
[0019]
【The invention's effect】
As described above, according to the present invention, the cylindrical cryopanel fixed to the second stage provided inside the pump case of the cryopump is in a state where the cylindrical opening is directed to the intake port. Since the bottom portion is fixed to the second stage, gas molecules flowing from the intake port of the pump case condense inside the cylinder of the cryopanel, and no condensation layer is formed on the outer peripheral surface of the cryopanel. The diameter of the cryopanel can be increased by bringing the outer peripheral surface of the cryopanel closer to the inner surface of the shield, or the condensation area can be increased by increasing the axial length of the cryopanel. Therefore, if the exhaust capacity can be increased and the axial length is increased, the thickness of the condensate layer can be reduced even with the same exhaust capacity. The diameter of the opening of the cryopanel is made larger than the diameter of the opening of the shield, and the rear part of the baffle enters the inside of the cryopanel, thereby reliably There are effects such as being able to guide molecules into the cylinder of the cryopump.
[Brief description of the drawings]
1 is a cut-away side view of a conventional example. FIG. 2 is a cut-away side view of an embodiment of the present invention. FIG. 3 is a cut-away side view of another embodiment of the present invention. Cutaway side view of the machine 【Explanation of symbols】
DESCRIPTION OF SYMBOLS 1 Pump case 2 Air inlet 3 Refrigerator 5 1st stage 7 2nd stage 8 Opening part 9 Shield 9a Closure member 10 Baffle 11 Cryopanel 12 Opening part 13 Bottom part 14 Inner surface 15 Outer surface

Claims (4)

A first stage and a second stage of a refrigerator are provided inside a pump case having an intake port that is open to the outside, and is opposed to the intake port of a cylindrical shield attached to the first stage stage. A cryopump in which a baffle is fixed to the opened opening, and a bottomed cylindrical cryopanel facing the intake port is fixed to the second stage through the baffle.
Fixing the bottom of the cryopanel to the second stage with the opening at one end of the cylinder facing the air inlet ;
A cryopump characterized in that the diameter of the rear portion of the baffle is gradually reduced from at least an intermediate portion in the gas molecule passage direction . The cryopump according to claim 1, wherein the diameter of the opening of the cryopanel is formed larger than the diameter of the opening of the shield. 2. The cryopump according to claim 1, wherein a rear portion of the baffle is caused to enter a cylindrical interior of the cryopanel through an opening of the cryopanel. 4. The cryopump according to claim 1, wherein the periphery of the baffle and the inner edge of the opening of the shield are hermetically attached so that only the gas that has passed through the baffle enters the inside of the shield. .

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