JP2011153629A - Cryopump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to easily allow each of a plurality of different temperature regions inside a cryopump to fall within a desired temperature. <P>SOLUTION: The cryopump 100 comprises a first cooling stage 13, a cylinder member 12 extending from the first cooling stage 13, and a second cooling stage 14 provided at the terminal of the cylinder member 12 on the side opposite to the first cooling stage 13. Further, the cyropump 100 comprises a refrigerating machine 50 for generating a cold condition by the expanding operation of the working air inside the cylinder member 12 to cool down the second cooling stage 14 to lower temperature than that of the first cooling stage 13, and a radiation shield 40 which is thermally connected with the first cooling stage 13 and is penetrated by the cylinder member 12 so that the second cooling stage 14 is arranged inside the radiation shield 40. The cylinder member 12 has an outward-directed offset from the radiation shield 40 and extends from the inside of the radiation shield 40 to the outside thereof so that the first cooling stage 13 is arranged outside the radiation shield 40. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a cryopump.

  The cryopump is a vacuum pump that traps and exhausts gas molecules by condensation or adsorption onto a cryopanel cooled to a very low temperature. The cryopump is generally used to realize a clean vacuum environment required for a semiconductor circuit manufacturing process or the like.

  For example, Patent Document 1 describes a cryopump having a plurality of elongated panels that are radially attached to the back side of a heat shield panel in the gas intrusion direction and extend in the back direction from the heat shield panel.

JP-A-2-308985

  In the cryopump described above, the first heat stage of the refrigerator is attached to the bottomed cylindrical first cryopanel. Since the second heat stage of the refrigerator is disposed inside the first cryopanel, the length of the second cooling cylinder connecting the first heat stage and the second heat stage is limited by the size of the first cryopanel. . The length of the second cooling cylinder is one of the main factors that determine the temperature difference between the first heat stage and the second heat stage. For this reason, when the length of the second cooling cylinder is limited, for example, when it is desired to maintain the temperatures of the first and second heat stages within a relatively narrow temperature range, May be difficult to cool to range.

  In view of the above, an object of the present invention is to provide a cryopump that makes it easy to place each of a plurality of different temperature regions provided in the cryopump within a desired temperature range.

  A cryopump according to an aspect of the present invention includes a first cooling stage, a cylinder member extending from the first cooling stage, and a second cooling stage provided at a cylinder member end opposite to the first cooling stage. A refrigerator that generates cold by the expansion action of the working gas inside the cylinder member and cools the second cooling stage to a lower temperature than the first cooling stage, and is thermally connected to the first cooling stage, And a radiation shield that is penetrated by the cylinder member so that the two cooling stages are arranged inside. The cylinder member extends from the inside of the radiation shield to the outside so that the first cooling stage is disposed outside the radiation shield with an offset outward from the radiation shield.

  According to this aspect, the cylinder member of the refrigerator extends through the radiation shield to the outside of the radiation shield. For this reason, the length of the cylinder member can be determined without being limited by the size of the radiation shield. Therefore, the temperature difference between the first cooling stage and the second cooling stage can be adjusted flexibly.

  The offset may be adjusted such that when the first cooling stage is cooled to the target temperature, the second cooling stage is cooled below the required temperature.

  A heat transfer member that connects the first cooling stage and the radiation shield and surrounds the end of the cylinder member adjacent to the first cooling stage may be further provided.

  According to the present invention, each of a plurality of different temperature regions inside the cryopump can be easily accommodated in a desired temperature range.

It is a figure which shows typically one Example of a cryopump. It is a figure which shows typically the cryopump during exhaust operation. It is a figure showing typically a cryopump concerning one embodiment of the present invention. It is a figure which shows typically the cryopump during exhaust operation.

  FIG. 1 is a diagram schematically showing a cryopump 10. The cryopump 10 is attached to a vacuum chamber such as an ion implantation apparatus or a sputtering apparatus, and is used to increase the degree of vacuum inside the vacuum chamber to a level required for a desired process. The cryopump 10 includes a cryopump container 30, a radiation shield 40, and a refrigerator 50.

  The refrigerator 50 is a refrigerator such as a Gifford McMahon refrigerator (so-called GM refrigerator). The refrigerator 50 includes a first cylinder 11, a second cylinder 12, a first cooling stage 13, a second cooling stage 14, and a valve driving motor 16. The first cylinder 11 and the second cylinder 12 are connected in series. A first cooling stage 13 is installed on the side of the first cylinder 11 where the second cylinder 12 is joined, and a second cooling stage 14 is installed on the end of the second cylinder 12 far from the first cylinder 11. . The refrigerator 50 shown in FIG. 1 is a two-stage refrigerator, and achieves a lower temperature by combining two stages of cylinders in series. The refrigerator 50 is connected to the compressor 52 through the refrigerant pipe 18.

  The compressor 52 compresses a refrigerant gas such as helium, that is, a working gas, and supplies the compressed gas to the refrigerator 50 through the refrigerant pipe 18. The refrigerator 50 cools the working gas by allowing it to pass through the regenerator, and further expands and cools it in the expansion chamber inside the first cylinder 11 and then in the expansion chamber inside the second cylinder 12. The regenerator is incorporated in the expansion chamber. Accordingly, the first cooling stage 13 installed in the first cylinder 11 is cooled to the first cooling temperature level, and the second cooling stage 14 installed in the second cylinder 12 is lower in temperature than the first cooling temperature level. To the second cooling temperature level. For example, the first cooling stage 13 is cooled to about 65K to 100K, and the second cooling stage 14 is cooled to about 10K to 20K.

  Along with the refrigerator 50, a control unit 20 and an AC power supply 22 are provided. The control unit 20 includes a frequency converter 24 and a frequency determination unit 26. The control unit 20 may also be configured to include a temperature sensor 28. The temperature sensor 28 is installed in the first cooling stage 13 of the refrigerator 50, detects the temperature of the first cooling stage 13, and transmits temperature information to the frequency determination unit 26. Note that the installation location of the temperature sensor 28 is not limited to the first cooling stage 13, and may be a location where the temperature is desired to be controlled, for example, any location of the second cooling stage 14, the first cylinder 11, or the second cylinder 12. A plurality of temperature sensors 28 may be installed at a plurality of locations. Thereby, it becomes possible to control the temperature of each location more finely.

  The working gas that has absorbed heat by sequentially expanding in the expansion chamber and has cooled each cooling stage passes through the regenerator again, and is returned to the compressor 52 through the refrigerant pipe 18. The flow of the working gas from the compressor 52 to the refrigerator 50 and from the refrigerator 50 to the compressor 52 is switched by a rotary valve (not shown) in the refrigerator 50. The valve drive motor 16 receives power supplied from the AC power supply 22 and rotates the rotary valve.

  The frequency converter 24 is provided between the valve driving motor 16 and the AC power supply 22, converts the frequency of the electric power supplied from the AC power supply 22, outputs it, and supplies it to the valve driving motor 16. The frequency determination unit 26 controls the frequency converter 24 based on the temperature information obtained from the temperature sensor 28. As shown in the figure, the frequency converter may be provided integrally with the control unit 20, or may be provided separately from the control unit 20.

  A cryopump 10 shown in FIG. 1 is a so-called horizontal cryopump. In general, the horizontal cryopump is a cryocooler in which the second cooling stage 14 of the refrigerator is inserted into the radiation shield 40 along a direction (usually an orthogonal direction) intersecting the axial direction of the cylindrical radiation shield 40. It is a pump. The present invention can be similarly applied to a so-called vertical cryopump. A vertical cryopump is a cryopump in which a refrigerator is inserted along the axial direction of the radiation shield.

  The cryopump container 30 has a portion (hereinafter referred to as a “body portion”) 32 formed in a cylindrical shape having an opening at one end and the other end closed. The opening is provided as an intake port 34 through which a gas to be exhausted from a vacuum chamber such as a sputtering apparatus enters. The air inlet 34 is defined by the inner surface of the upper end portion of the body portion 32 of the cryopump container 30. Further, an opening 37 for inserting the refrigerator 50 is formed in the body portion 32. One end of a cylindrical refrigerator housing portion 38 is attached to the opening 37 of the body portion 32, and the other end is attached to the housing of the refrigerator 50. The refrigerator accommodating portion 38 accommodates the first cylinder 11 of the refrigerator 50.

  A mounting flange 36 extends radially outward from the upper end of the body 32 of the cryopump container 30. The cryopump 10 is attached using a mounting flange 36 to a vacuum chamber such as a sputtering apparatus that is a volume to be exhausted.

  The cryopump container 30 is provided to separate the inside and the outside of the cryopump 10. As described above, the cryopump container 30 is configured to include the body portion 32 and the refrigerator housing portion 38, and the inside of the body portion 32 and the refrigerator housing portion 38 is kept airtight at a common pressure. Since the outer surface of the cryopump container 30 is exposed to the environment outside the cryopump 10 during operation of the cryopump 10, that is, while the refrigerator is operating, the outer surface of the cryopump container 30 is maintained at a temperature higher than that of the radiation shield 40. Typically, the temperature of the cryopump container 30 is maintained at the ambient temperature. Here, the environmental temperature refers to a temperature at a location where the cryopump 10 is installed or a temperature close to the temperature, for example, about room temperature.

  The radiation shield 40 is disposed inside the cryopump container 30. The radiation shield 40 is formed in a cylindrical shape having an opening at one end and closed at the other end, that is, a cup shape. The radiation shield 40 may be configured in an integral cylindrical shape as shown in FIG. 1 or may be configured so as to form a cylindrical shape as a whole by a plurality of parts. The plurality of parts may be arranged with a gap therebetween.

  Both the body 32 and the radiation shield 40 of the cryopump container 30 are formed in a substantially cylindrical shape and are arranged coaxially. The inner diameter of the body portion 32 of the cryopump container 30 is slightly larger than the outer diameter of the radiation shield 40, and the radiation shield 40 is slightly spaced from the inner surface of the body portion 32 of the cryopump container 30 with the cryopump container 30. Are arranged in a non-contact state. That is, the outer surface of the radiation shield 40 faces the inner surface of the cryopump container 30. Note that the shapes of the body portion 32 and the radiation shield 40 of the cryopump container 30 are not limited to a cylindrical shape, and may be a cylindrical shape having any cross section such as a rectangular cylindrical shape or an elliptical cylindrical shape. Typically, the shape of the radiation shield 40 is similar to the shape of the inner surface of the body portion 32 of the cryopump container 30.

  The radiation shield 40 is provided as a radiation shield that mainly protects the second cooling stage 14 and the low-temperature cryopanel 60 thermally connected thereto from heat radiation from the cryopump container 30. The second cooling stage 14 is disposed substantially on the central axis of the radiation shield 40 in the internal space of the radiation shield 40. The radiation shield 40 is fixed in a state where it is thermally connected to the first cooling stage 13, and is cooled to a temperature comparable to that of the first cooling stage 13.

  The low-temperature cryopanel 60 includes a plurality of panels 64, for example. For example, each of the panels 64 has a shape of a side surface of a truncated cone, that is, an umbrella-like shape. Each panel 64 is attached to a panel attachment member 66 attached to the second cooling stage 14. Each panel 64 is usually provided with an adsorbent (not shown) such as activated carbon. For example, the adsorbent is bonded to the back surface of the panel 64.

  The panel mounting member 66 has a cylindrical shape with one end closed and the other end opened. The closed end is attached to the upper end of the second cooling stage 14 and the cylindrical side surface is the second cooling stage 14. Is extended toward the bottom of the radiation shield 40. A plurality of panels 64 are attached to the cylindrical side surface of the panel attachment member 66 at intervals. An opening for passing the second cylinder 12 of the refrigerator 50 is formed on the cylindrical side surface of the panel mounting member 66.

  A baffle 62 is provided at the intake port of the radiation shield 40 in order to protect the second cooling stage 14 and the low-temperature cryopanel 60 thermally connected thereto from heat radiation from a vacuum chamber or the like. The baffle 62 is formed in a louver structure or a chevron structure, for example. The baffle 62 may be formed concentrically around the central axis of the radiation shield 40, or may be formed in another shape such as a lattice shape. The baffle 62 is attached to the end of the radiation shield 40 on the opening side, and is cooled to a temperature similar to that of the radiation shield 40.

  A refrigerator mounting hole 42 is formed on the side surface of the radiation shield 40. The refrigerator mounting hole 42 is formed in the center of the side surface of the radiation shield 40 with respect to the central axis direction of the radiation shield 40. The refrigerator mounting hole 42 of the radiation shield 40 is provided coaxially with the opening 37 of the cryopump container 30. The second cylinder 12 and the second cooling stage 14 of the refrigerator 50 are inserted from the refrigerator attachment hole 42 along a direction perpendicular to the central axis direction of the radiation shield 40. The radiation shield 40 is fixed in a state where it is thermally connected to the first cooling stage 13 in the refrigerator mounting hole 42.

  The cryopump 10 is provided with a refrigerator cover 70 that surrounds the second cylinder 12 of the refrigerator 50. The refrigerator cover 70 is formed in a cylindrical shape having a slightly larger diameter than the second cylinder 12, one end is attached to the second cooling stage 14, and the other end extends toward the refrigerator attachment hole 42 of the radiation shield 40. ing. A gap is provided between the refrigerator cover 70 and the radiation shield 40, and the refrigerator cover 70 and the radiation shield 40 are not in contact with each other. The refrigerator cover 70 is thermally connected to the second cooling stage 14 and is cooled to the same temperature as the second cooling stage 14.

  The operation of the cryopump 10 having the above configuration will be described below.

  The temperature sensor 28 measures the temperature of the first cooling stage 13 and transmits the measurement result to the frequency determination unit 26. The frequency determination unit 26 determines the frequency based on the temperature information obtained from the temperature sensor 28. For example, the frequency determining unit 26 determines to increase the output frequency of the frequency converter 24 when the temperature of the first cooling stage 13 acquired from the temperature sensor 28 is higher than the set target temperature, and the first cooling is performed. When the temperature of the stage 13 is lower than the target temperature, it is determined to lower the output frequency of the frequency converter 24. Then, the frequency determination unit 26 transmits the determination result to the frequency converter 24.

  The frequency converter 24 receives a signal from the frequency determining unit 26, converts the frequency of the AC power supply 22, and supplies power to the valve driving motor 16. For example, when the output frequency is increased, the rotation speed of the valve driving motor 16 is increased, and the rotation of the rotary valve is increased. As a result, the intake / exhaust of the working gas in the refrigerator 50 is switched more quickly, the amount of working gas intake / exhaust per unit time increases, and the amount of heat absorbed by the working gas per unit time also increases. Accordingly, the first cooling stage 13 is cooled to the set target temperature. Accordingly, as the first cooling stage 13 is cooled, the temperature of the second cooling stage 14 is further lowered.

  Conversely, when the temperature of the first cooling stage 13 is lower than the desired temperature, the frequency determination unit 26 determines to lower the output frequency of the frequency converter 24. And the frequency converter 24 receives the signal from the frequency determination part 26, converts the electric power supplied from AC power supply 22 into a low frequency, and outputs it. Thereby, the rotation cycle of the valve drive motor 16 is lengthened, and the intake / exhaust cycle of the refrigerator 50 is delayed. Then, the intake / exhaust amount of the working gas per unit time is reduced, and the endothermic amount of the working gas per unit time is also reduced. Thereby, the temperature of the 1st cooling stage 13 rises, and the temperature of the 2nd cooling stage 14 also rises in connection with this.

  In this way, the control unit 20 controls the frequency of the refrigeration cycle of the refrigerator 50, and the first cooling stage 13 has a heat load due to radiation from the cryopump container 30 and heat absorption due to expansion of the working gas at the target temperature. Are adjusted to balance.

  FIG. 2 is a diagram schematically showing the cryopump 10 during the exhaust operation. As shown in FIG. 2, an ice layer made of condensed gas is deposited on the low-temperature cryopanel 60 of the cryopump 10. When the volume to be exhausted of the cryopump 10 is, for example, a vacuum chamber of a sputtering apparatus, the main component of this ice layer is, for example, argon. This ice layer grows and increases in thickness with the exhaust operation time.

  In the cryopump 10, not only the low-temperature cryopanel 60 but also the refrigerator cover 70 is cooled by the second cooling stage 14, so that the gas is condensed in the refrigerator cover 70 and an ice layer is deposited. Since the refrigerator cover 70 can also be used as a part of the cryopanel, the gas occlusion amount of the cryopump 10 can be increased. Moreover, since the formation of an ice layer on the second cylinder 12 is suppressed by covering the second cylinder 12 with the refrigerator cover 70, it is possible to make the degree of vacuum unstable.

  This unstable degree of vacuum is caused by the temperature gradient on the surface of the second cylinder 12. A temperature gradient is generated on the surface of the second cylinder 12 from the second cooling temperature of the second cooling stage 14 to the first cooling temperature of the first cooling stage 13. The temperature range from the second cooling temperature to the first cooling temperature includes the boiling point of the gas (for example, argon) condensed in the low-temperature cryopanel 60. Therefore, a position corresponding to the temperature of the gas boiling point exists on the surface of the second cylinder 12. As the ice layer deposits on the low-temperature cryopanel 60, the thermal load on the low-temperature cryopanel 60 also increases, so the temperature of the low-temperature cryopanel 60 can also vary. Then, the gas boiling point temperature position on the surface of the second cylinder 12 also moves (left and right in the figure).

  As a result, when the second cylinder 12 is exposed without the refrigerator cover 70, a part of the ice layer deposited on the second cylinder 12 is rapidly vaporized due to the temperature change of the surface of the second cylinder 12 and is vacuumed. The degree gets worse. For example, if the temperature of the second cooling stage 14 rises and the gas boiling point position moves in a direction approaching the second cooling stage 14, the gas condensed to the original gas boiling point position cannot maintain the condensed state. It will be rapidly vaporized.

  A similar phenomenon can occur when the refrigerator cover 70 is provided. That is when the ice layer deposited on the refrigerator cover 70 contacts the radiation shield 40. The end of the refrigerator cover 70 is close to the radiation shield 40 so as to minimize the exposure of the surface of the second cylinder 12. For this reason, when an ice layer grows at the end of the refrigerator cover 70 close to the radiation shield 40, it can come into contact with the radiation shield 40. The ice layer in contact with the radiation shield 40 is heated by the radiation shield 40 and is rapidly vaporized. In this case, it is difficult for the cryopump 10 to further increase the degree of vacuum. Therefore, the gas occlusion amount when the ice layer on the refrigerator cover 70 contacts the radiation shield 40 determines the maximum occlusion amount of the cryopump 10.

  However, if there is no contact of the ice layer with the radiation shield 40, it is possible in principle to realize a larger occlusion amount. In principle, the cryopump 10 can be evacuated until the gas vapor pressure on the surface of the ice layer deposited on the low temperature cryopanel 60 exceeds the vacuum level to be achieved. If the gas vapor pressure at the ice layer surface exceeds the vacuum level to be achieved, vaporization from the ice layer will dominate rather than gas condensation from the atmosphere to the ice layer. I can't. There is a temperature distribution in which the temperature gradually rises from the cryopanel surface toward the ice layer surface, and the gas vapor pressure on the ice layer surface is determined by the temperature of the ice layer surface. Therefore, the ice layer grows and becomes thick, the ice layer surface temperature increases, and the gas occlusion amount of the cryopump 10 when the gas vapor pressure on the ice layer surface exceeds the vacuum level to be achieved is the given low-temperature cryogenic. The maximum occlusion amount under the panel 60 is obtained. If the ice layer contacts the radiation shield 40 before reaching this maximum storage amount, only a maximum storage amount smaller than this potential maximum storage amount can be obtained.

  FIG. 3 is a diagram schematically illustrating the cryopump 100 according to the embodiment of the present invention. The cryopump 100 shown in FIG. 3 is different from the cryopump 10 shown in FIG. 1 in that the radiation shield 40 is connected to the first cooling stage 13 via the first sleeve 80 for heat transfer. Another difference is that the second sleeve 82 as the refrigerator cover 70 extends through the radiation shield 40. In the following description, for the sake of brevity, the description common to the cryopump 100 shown in FIG. 3 and the cryopump 10 shown in FIG. 1 is omitted as appropriate.

  The cryopump 100 includes an interference suppression structure that avoids interference between the ice layer deposited on the refrigerator cover 70 and the radiation shield 40. This interference suppression structure has, for example, a double sleeve structure extending along the axial direction of the refrigerator 50. In the cryopump 100, a frost storage space 84 is formed between the first sleeve 80 and the second sleeve 82 constituting the double sleeve to store the terminal end of the condensed gaseous ice layer. It is one feature. The size of the frost storage space 84 is adjusted so that the ice layer does not contact the portion cooled to the first cooling temperature before reaching the maximum occlusion amount of the cryopump 100. The ice layer deposited on the refrigerator cover 70 is accommodated in the frost accommodating space 84 while avoiding interference with the radiation shield 40. That is, the frost storage space 84 is dimensioned so that a gap is maintained up to the maximum occlusion amount between the ice layer deposited at the portion cooled to the second cooling temperature and the portion cooled to the first cooling temperature. It has been adjusted.

  A refrigerator insertion hole 43 is provided on the side surface of the radiation shield 40. The refrigerator insertion hole 43 is provided at a position corresponding to the opening 37 of the trunk portion 32 of the cryopump container 30. The refrigerator insertion hole 43 is formed coaxially with the opening 37 and smaller in diameter than the refrigerator insertion hole 43.

  The refrigerator 50 is disposed through the refrigerator insertion hole 43 and the opening 37. The refrigerator is arranged such that the second cooling stage 14 is surrounded and disposed inside the radiation shield 40, and the first cooling stage 13 is disposed inside the refrigerator housing portion 38 of the cryopump container 30 outside the radiation shield 40. 50 is inserted into the refrigerator insertion hole 43. For this reason, the first cooling stage 13 is positioned outside the radiation shield 40 with an outward offset from the radiation shield 40. The diameters of the opening 37 of the cryopump container 30 and the refrigerator accommodating portion 38 are larger than the diameter of the first cooling stage 13. For this reason, the first cooling stage 13 can be arranged at an arbitrary position inside the refrigerator housing portion 38 with respect to the longitudinal direction of the refrigerator 50, and the offset between the first cooling stage 13 and the radiation shield 40. The size of can be freely selected. The second cylinder 12 and the refrigerator cover 70 pass through the refrigerator insertion hole 43 and the opening 37, and the second cylinder 12 and the refrigerator cover 70 intersect with the side surface of the radiation shield 40.

  The radiation shield 40 is fixed to and thermally connected to the first cooling stage 13 by the first sleeve 80. The first sleeve 80 is formed in a cylindrical shape, and flanges are provided at both ends for attachment to the radiation shield 40 and the first cooling stage 13 with bolts or the like. The first sleeve 80 extends from the first cooling stage 13 to the radiation shield 40 toward the second cooling stage 14. The diameter of the first sleeve 80 is the same as that of the refrigerator insertion hole 43 of the radiation shield 40, and the length is equal to the offset between the radiation shield 40 and the first cooling stage 13. The first sleeve 80 is a heat transfer member that thermally connects the first cooling stage 13 to the radiation shield 40. The thickness of the first sleeve 80 is larger than the thickness of the radiation shield 40 in consideration of, for example, heat transfer characteristics. May be. Further, since the first sleeve 80 is formed in a cylindrical shape so as to surround the second sleeve 82 cooled to a lower temperature, the first sleeve 80 is a radiation shield that shields heat radiation from the outside to the second sleeve 82. It also functions as a part.

  Since the first cooling stage 13 is separated from the radiation shield 40 outside the radiation shield 40, the length of the second cylinder 12 is relatively long. The length of the second cylinder 12 is longer by the offset amount between the first cooling stage 13 and the radiation shield 40 than when the first cooling stage 13 is directly attached to the radiation shield 40. By increasing the length of the second cylinder 12, the temperature difference between the first cooling stage 13 and the second cooling stage 14 can be increased. Therefore, the cooling temperature of the second cooling stage 14 when the cooling temperature of the first cooling stage 13 is set to a predetermined target temperature can be further lowered. As a result, the low temperature cryopanel 60 is cooled to a lower temperature, and the gas occlusion amount of the cryopump 100 can be increased.

  In a multistage refrigerator, there is a predetermined relationship between the temperatures of the cooling stages. For example, in a two-stage refrigerator, when one temperature of the first cooling stage 13 and the second cooling stage 14 is determined under a certain condition, the other temperature is uniquely determined. For example, when the first cooling stage 13 is maintained at a desired target temperature, the temperature of the second cooling stage 14 is uniquely determined under certain conditions. Here, a minimum load state is assumed as a certain condition. The minimum load state is a state where the load on each cooling stage becomes the lowest during the operation of the cryopump 10 and the cooling temperature of the second cooling stage 14 can be maintained at the lowest temperature. Here, consider a case where it is desired to cool the second cooling stage 14 below a certain required temperature while maintaining the first cooling stage 13 at a desired target temperature.

  When the required temperature is lower than the temperature of the second cooling stage 14 that is uniquely determined when the first cooling stage 13 is maintained at the target temperature in the minimum load state, the second temperature is maintained while maintaining the first cooling stage 13 at the target temperature. The cooling stage 14 cannot be cooled below its required temperature. In this case, if the intake / exhaust cycle in the refrigerator 50 is accelerated, the temperature of the second cooling stage 14 can be lowered, but the temperature of the first cooling stage 13 is also lower than the target temperature. In order to cope with this, in the present invention, when the temperature of the first cooling stage 13 is cooled to the target temperature, the radiation shield 40 and the first cooling stage 13 are cooled so that the second cooling stage is cooled below the required temperature. The offset amount between them, that is, the length of the second cylinder 12 is adjusted. Thereby, the 2nd cooling stage 14 can be cooled below to required temperature, maintaining the temperature of the 1st cooling stage 13 at desired target temperature.

  In order to bring both the first cooling stage 13 and the second cooling stage 14 into a desired temperature range, for example, a refrigerator having sufficient freezing capacity is used, and the first cooling stage 13 and the second cooling stage 14 are heated with heaters, respectively. By doing so, it is possible to adjust the temperature. However, this is overheated and then heated by a heater, which is inferior in energy saving. On the other hand, according to the present embodiment, the first cooling stage 13 and the second cooling stage 14 can both be set to a desired temperature range without using a heater by adjusting the cylinder length. A cryopump excellent in performance is provided.

  The second sleeve 82 as the refrigerator cover 70 extends through the radiation shield 40 from the second cooling stage 14 toward the first cooling stage 13. A clearance having a width D is provided between the second sleeve 82 and the radiation shield 40. The second sleeve 82 is formed in a cylindrical shape and surrounds almost the entire second cylinder 12. The second sleeve 82 extends from the refrigerator insertion hole 43 of the radiation shield 40 to the outside of the radiation shield 40 by a length h. The second sleeve 82 extends to the front of the first cooling stage 13, has a gap with the first cooling stage 13, and is not in contact with the first cooling stage 13. For example, it is desirable to determine the length of the second sleeve 82 so that the end of the second sleeve 82 is not visible when viewed from the outside of the cryopump.

  The radius of the second sleeve 82 is shorter than the radius of the first sleeve 80 by the length D. Therefore, an annular frost accommodating space 84 having a length h and a diameter D is formed inside the first sleeve 80 at the end of the second sleeve 82 on the first cooling stage 13 side. The length h is preferably set to be equal to or longer than the length D. For example, the length h may be four or more times the length D. Thus, by making the length h relatively long, the ice layer can be made difficult to contact the first cooling stage 13.

  The frost storage space 84 is sized so that the ice layer deposited on the second sleeve 82 does not come into contact with the portion cooled to the first cooling temperature before the gas storage amount of the cryopump 100 reaches the maximum storage amount. Is set. That is, the size is set so that the ice layer deposited on the second sleeve 82 does not contact the radiation shield 40, the first sleeve 80, and the first cooling stage 13. The frost storage space 84 is a recess formed on the inner surface of the radiation shield 40. Therefore, it is difficult for gas molecules to reach the frost storage space 84 from the inlet 34 of the cryopump 100. In this way, by forming the frost storage space 84 so as to be recessed when viewed from the air inlet 34, gas molecules entering the frost storage space 84 are suppressed, and the ice layer deposition rate in the frost storage space 84 is moderate. It becomes. Therefore, the time until the ice layer comes into contact with the first cooling temperature region can be increased, and the exhaust operation of the cryopump 100 can be continued for a long time.

  The maximum occlusion amount is, for example, the maximum gas occlusion amount that achieves a desired degree of vacuum inside the cryopump container 30. The maximum occlusion amount is, for example, the gas occlusion amount when the gas vapor pressure on the surface of the ice layer deposited on the low-temperature cryopanel 60 becomes equal to the desired degree of vacuum. Here, the desired degree of vacuum may be a recovery pressure set as a pressure that should be reached within a predetermined time after the gas inflow to the cryopump 100 is stopped.

  FIG. 4 is a diagram schematically showing the cryopump 100 during the exhaust operation. As shown in FIG. 4, an ice layer made of condensed gas is deposited on the low-temperature cryopanel 60 of the cryopump 100. When the volume to be exhausted of the cryopump 10 is, for example, a vacuum chamber of a sputtering apparatus, the main component of this ice layer is, for example, argon. This ice layer grows and increases in thickness with the exhaust operation time. Thus, the exhaust operation can be continued until the vapor pressure on the ice layer surface exceeds the recovery pressure due to the temperature gradient generated in the thickness direction of the ice layer.

  According to this embodiment, since an ice layer can be accommodated also in the frost accommodation space 84 as shown in figure, the gas occlusion amount of the cryopump 100 can be enlarged. The frost storage space 84 is set so that the ice layer does not contact the radiation shield 40 or the first cooling stage 13 until the maximum storage amount of the cryopump 100 is reached. The maximum occlusion amount that can be enjoyed in a practical manner can be realized. Furthermore, since the second cylinder 12 can be lengthened by taking an offset between the radiation shield 40 and the first cooling stage 13, the low-temperature cryopanel 60 can be cooled to a lower temperature. This also contributes to an increase in the storage amount of the cryopump 100.

  In the above, this invention was demonstrated based on the Example. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiment, and various design changes are possible, various modifications are possible, and such modifications are within the scope of the present invention. By the way.

  For example, the radiation shield 40 and the first sleeve 80 are formed as separate members, but are not limited thereto. The radiation shield 40 and the heat transfer member may be integrally formed. In this case, the radiation shield 40 may include a heat transfer section that extends along the refrigerator 50 from the side surface of the radiation shield 40 toward the outside of the radiation shield 40 and is attached to the first cooling stage 13.

  The first sleeve 80 as the heat transfer member has a cylindrical shape, but may have any shape as long as the radiation shield 40 and the first cooling stage 13 are thermally connected. For example, the heat transfer member may have a conical side surface shape in which the diameter of the first sleeve 80 decreases as the distance from the refrigerator insertion hole 43 of the radiation shield 40 increases outward. In this way, since the frost storage space 84 can be made relatively wide in the vicinity of the refrigerator insertion hole 43, it is possible to make it difficult for the ice layer to contact the radiation shield 40 or the first sleeve 80. Further, the heat transfer member may protrude into the radiation shield 40.

  The refrigerator cover 70 and the second sleeve 82 may not necessarily cover the entire second cylinder 12. The refrigerator cover 70 and the second sleeve 82 cover at least a portion of the surface of the second cylinder 12 where the temperature fluctuates in a temperature range including the boiling point of the gas to be exhausted (for example, the central portion of the second sleeve 82). The shapes of the refrigerator cover 70 and the second sleeve 82 may be determined. In this way, the surface of the second cylinder 12 that is not covered with the refrigerator cover 70 is always at a considerably low temperature or at a considerably high temperature than the boiling point of the gas to be exhausted. Therefore, it is possible to prevent the ice layer deposited on the surface of the second cylinder 12 from causing pressure instability.

  The refrigerator cover 70 and the second sleeve 82 may be shaped so as to shield the surface of the second cylinder 12 exposed when viewed from the air inlet of the cryopump 100. In this way, the refrigerator cover 70 can prevent gas molecules entering from the inlet of the cryopump 100 from reaching the surface of the second cylinder 12 directly. Therefore, the accumulation of an ice layer on the surface of the second cylinder 12 can be reduced.

  The lengths of the refrigerator cover 70 and the second sleeve 82 are preferably determined so that the temperature at the end portion is lower than the boiling point of the gas to be exhausted. A certain temperature gradient occurs on the surface of the refrigerator cover 70, and the temperature can increase as the distance from the second cooling stage 14 increases. Therefore, if the length is determined so that the temperature at the end is sufficiently low in this way, the entire refrigerator cover 70 can be maintained at a temperature lower than the boiling point of the gas to be exhausted to condense the gas. it can. Alternatively, the refrigerator 50 may be adjusted so that the temperatures at the end portions of the refrigerator cover 70 and the second sleeve 82 are lower than the boiling point of the gas to be exhausted.

  The refrigerator cover 70 and the second sleeve 82 may not be cooled to the same temperature as the second cooling stage 14 of the refrigerator 50. For example, the refrigerator cover 70 may be thermally connected to the second cylinder 12 of the refrigerator 50. In this case, the part of the second cylinder 12 to which the refrigerator cover 70 is connected is preferably selected from parts having a temperature at which the gas to be exhausted maintains a solid state.

  DESCRIPTION OF SYMBOLS 10 Cryopump, 11 1st cylinder, 12 2nd cylinder, 13 1st cooling stage, 14 2nd cooling stage, 20 Control part, 30 Cryo pump container, 40 Radiation shield, 43 Refrigerator insertion hole, 50 Refrigerator, 60 Low temperature cryopanel, 70 refrigerator cover, 80 first sleeve, 82 second sleeve.

Claims (4)

A first cooling stage, a cylinder member extending from the first cooling stage, and a second cooling stage provided at the end of the cylinder member opposite to the first cooling stage, and expansion of the working gas inside the cylinder member A refrigerator that generates cold by the action and cools the second cooling stage to a temperature lower than that of the first cooling stage;
An opening for receiving the refrigerator is formed in a side surface, the first cooling stage is arranged outside, and the second cooling stage is arranged inside, and the radiation is thermally connected to the first cooling stage. A shield,
A refrigerator cover covering at least a part of the cylinder member,
The cryopump is characterized in that the cylinder member includes a portion whose temperature fluctuates in a temperature range including a boiling point of a gas to be exhausted, and the refrigerator cover covers at least the portion.   The cryopump according to claim 1, wherein the refrigerator cover is thermally connected to a portion of the cylinder member having a temperature at which a gas to be exhausted maintains a solid state.   The cryopump according to claim 1, wherein the refrigerator cover has a shape that shields a surface of the cylinder member that is exposed when viewed from an inlet of the cryopump. The cylinder member extends from the inside of the radiation shield to the outside so that the first cooling stage is disposed outside the radiation shield with an offset outward from the radiation shield.
The cryopump according to claim 1, wherein the refrigerator cover extends through a radiation shield.

Images