Patent Publication Number: US-2021180579-A1

Title: Cryopump and method of monitoring cryopump

Description:
RELATED APPLICATIONS 
     The contents of Japanese Patent Application No. 2018-164405, and of International Patent Application No. PCT/JP2019/030301, on the basis of each of which priority benefits are claimed in an accompanying application data sheet, are in their entirety incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     Certain embodiments of the present invention relate to a cryopump and a method of monitoring a cryopump. 
     Description of Related Art 
     A cryopump is a vacuum pump which captures gas molecules on a cryopanel cooled to a cryogenic temperature by condensation or adsorption to pump the gas molecules. The cryopump is generally used to realize a clean vacuum environment which is required for a semiconductor circuit manufacturing process or the like. Since the cryopump is a so-called gas storage type vacuum pump, it is necessary to regenerate the captured gas periodically to be discharged to an outside. 
     SUMMARY 
     According to an aspect of the present invention, there is provided a cryopump including an accommodation space for a condensed layer of gas. The cryopump includes a first-stage cryopanel that is cooled to a temperature higher than a condensation temperature of the gas and includes an inner surface of the first-stage cryopanel disposed so as to surround the accommodation space; a second-stage cryopanel that is cooled to a temperature equal to or lower than the condensation temperature of the gas, on which the condensed layer of the gas is deposited, and that is disposed so as to be surrounded by the inner surface of the first-stage cryopanel together with the accommodation space; a cryopump intake port that allows a passage of a first-stage heat load incident on the inner surface of the first-stage cryopanel from outside the cryopump and the gas entering the accommodation space from outside the cryopump; and a second-stage cryopanel monitoring unit that monitors an amount of condensed gas in the accommodation space based on a change in the first-stage heat load. 
     According to another aspect of the invention, there is provided a method of monitoring a cryopump. The cryopump includes a first-stage cryopanel having an inner surface of the first-stage cryopanel disposed so as to surround an accommodation space for a condensed layer of gas, and a second-stage cryopanel disposed so as to be surrounded by the inner surface of the first-stage cryopanel together with the accommodation space, the method includes cooling the first-stage cryopanel to a temperature higher than a condensation temperature of the gas and cooling the second-stage cryopanel to a temperature equal to or lower than the condensation temperature of the gas; depositing the condensed layer of the gas that enters the accommodation space from outside the cryopump through a cryopump intake port on the second-stage cryopanel; and monitoring an amount of condensed gas in the accommodation space based on a change in the first-stage heat load incident on the inner surface of the first-stage cryopanel from outside the cryopump through the cryopump intake port. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram schematically showing a cryopump according to an embodiment. 
         FIG. 2  is a control block diagram relating to the cryopump shown in  FIG. 1 . 
         FIGS. 3A and 3B  are diagrams for describing in principle a method of monitoring the cryopump according to an embodiment. 
         FIG. 4  is a graph showing a change in an operating frequency of a cryocooler during a vacuum pumping operation of the cryopump. 
         FIG. 5  is a flowchart showing a method of monitoring the cryopump according to an embodiment. 
         FIG. 6  is a flowchart showing a monitoring process shown in  FIG. 5  in more detail. 
         FIG. 7  is a diagram schematically showing a cryopump according to an embodiment. 
         FIG. 8  is a graph schematically showing an example of a condensed gas amount table according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A cryopump is normally provided with two types of cryopanels having different temperatures. A low temperature cryopanel is cooled to a cooling temperature of, for example, approximately 20K or less so as to condense a gas having a relatively high vapor pressure such as argon or nitrogen on the surface, and a high temperature cryopanel is cooled to a cooling temperature of, for example, approximately 80K or higher so that such gas does not condense. As the cryopump is used, a condensed layer of gas grows on a low-temperature cryopanel and can eventually come into contact with a high-temperature cryopanel. As a result, the gas is vaporized again at a contact part between the high-temperature cryopanel and the condensed layer and released to the surroundings. Thereafter, the cryopump cannot fully fulfill an original role. Therefore, the condensed layer present on the low-temperature cryopanel at the time of contact provides the maximum amount of gas (also referred to as a storage limit or maximum storage amount) that can be stored in the cryopump. 
     It is desirable to provide a technique for predicting during use of the cryopump that the amount of gas stored in the cryopump approaches the storage limit. 
     Any combination of the constituent elements described above, or replacement of constituent elements or expressions of the present invention with each other between methods, apparatuses, systems, or the like is also valid as an aspect of the present invention. 
     Hereinafter, modes for carrying out the present invention will be described in detail with reference to the drawings. In the description and the drawings, identical or equivalent constituent elements, members, and processing are denoted by the same reference numerals, and overlapping description is omitted appropriately. The scales or shapes of the respective parts shown in the drawings are set for convenience in order to facilitate description and are not interpreted to a limited extent unless otherwise specified. Embodiments are exemplification and do not limit the scope of the present invention. All features described in the embodiments or combinations thereof are not necessarily essential to the invention. 
       FIG. 1  is a diagram schematically showing a cryopump  10  according to an embodiment. The cryopump  10  is attached, for example, to a vacuum chamber  90  of a sputtering device, a vapor deposition device, or other vacuum process device, and is used to increase a degree of vacuum inside the vacuum chamber  90  to a level required for a desired vacuum process. The cryopump  10  includes a cryopump intake port (hereinafter, also referred to as an “intake port”)  12  for receiving a gas to be pumped from the vacuum chamber. The gas enters an internal space  14  of the cryopump  10  through the intake port  12 . 
     The cryopump  10  may be intended to be installed and used in a vacuum chamber in the shown direction, that is, with a posture of the intake port  12  facing upward. However, a posture of the cryopump  10  is not limited thereto, and the cryopump  10  may be installed in the vacuum chamber in another direction. 
     In the following, there is a case where the terms “axial direction” and “radial direction” are used in order to express the positional relationship between constituent elements of the cryopump  10  in an easily understandable manner. The axial direction represents a direction passing through the intake port  12  (a direction along of a cryopump center axis C passing through a center of the intake port  12  in  FIG. 1 ), and the radial direction represents a direction along the intake port  12  (a direction perpendicular to the center axis C). For convenience, with respect to the axial direction, there is a case where the side relatively close to the intake port  12  is referred to as an “upper side” and the side relatively distant from the intake port  12  is referred to as a “lower side”. That is, there is a case where the side relatively distance from the bottom of the cryopump  10  is referred to as an “upper side” and the side relatively close to the bottom of the cryopump  10  is referred to as a “lower side”. With respect to the radial direction, there is a case where the side close to the center (the center axis C in  FIG. 1 ) of the intake port  12  is referred to as an “inner side” and the side close to the peripheral edge of the intake port  12  is referred to as an “outer side”. Such expressions are not related to the disposition when the cryopump  10  is attached to the vacuum chamber. For example, the cryopump  10  may be attached to the vacuum chamber with the intake port  12  facing downward in the vertical direction. 
     Further, there is a case where a direction surrounding the axial direction is referred to as a “circumferential direction”. The circumferential direction is a second direction along the intake port  12  and is a tangential direction orthogonal to the radial direction. 
     The cryopump  10  includes a cryocooler  16 , a first-stage cryopanel  18 , a second-stage cryopanel  20 , and a cryopump housing  70 . The first-stage cryopanel  18  may be referred to as a high-temperature cryopanel part or a 100 K part. The second-stage cryopanel  20  may be referred to as a low-temperature cryopanel part or a 10 K part. 
     The cryocooler  16  is a cryocooler such as a Gifford McMahon type cryocooler (a so-called GM cryocooler), for example. The cryocooler  16  is a two-stage cryocooler. Therefore, the cryocooler  16  includes a first cooling stage  22  and a second cooling stage  24 . The cryocooler  16  is configured to cool the first cooling stage  22  to a first cooling temperature and cool the second cooling stage  24  to a second cooling temperature. The second cooling temperature is lower than the first cooling temperature. For example, the first cooling stage  22  is cooled to a temperature in a range of approximately 65 K to 120 K, preferably, in a range of 80 K to 100 K, and the second cooling stage  24  is cooled to a temperature in a range of approximately 10 K to 20 K. 
     Further, the cryocooler  16  includes a cryocooler structure part  21  that structurally supports the second cooling stage  24  on the first cooling stage  22  and structurally supports the first cooling stage  22  on a room temperature part  26  of the cryocooler  16 . Therefore, the cryocooler structure part  21  includes a first cylinder  23  and a second cylinder  25  that extend coaxially along the radial direction. The first cylinder  23  connects the room temperature part  26  of the cryocooler  16  to the first cooling stage  22 . The second cylinder  25  connects the first cooling stage  22  to the second cooling stage  24 . The room temperature part  26 , the first cylinder  23 , the first cooling stage  22 , the second cylinder  25 , and the second cooling stage  24  are linearly arranged in this order. 
     A first displacer and a second displacer (not shown) are reciprocally disposed in the interiors of the first cylinder  23  and the second cylinder  25 , respectively. A first regenerator and a second regenerator (not shown) are respectively incorporated into the first displacer and the second displacer. Further, the room temperature part  26  has a drive mechanism (although not shown in  FIG. 1 , for example, cryocooler motor  80 ) for reciprocating the first displacer and the second displacer. The drive mechanism includes a flow path switching mechanism that switches a flow path of a working gas (for example, helium) so as to periodically repeat the supply and discharge of the working gas to and from the interior of the cryocooler  16 . 
     The first cooling stage  22  is installed at a first-stage low temperature end of the cryocooler  16 . The first cooling stage  22  is a member that encloses the end part of the first cylinder  23  on the side opposite to the room temperature part  26  and surrounds a first expansion space of a working gas. The first expansion space is a variable volume formed inside the first cylinder  23  between the first cylinder  23  and the first displacer, and in which the volume changes with a reciprocating movement of the first displacer. The first cooling stage  22  is made of a metal material having a higher thermal conductivity than that of the first cylinder  23 . For example, the first cooling stage  22  is made of copper and the first cylinder  23  is made of stainless steel. 
     The second cooling stage  24  is installed at a second-stage low temperature end of the cryocooler  16 . The second cooling stage  24  is a member that encloses the end part of the second cylinder  25  on the side opposite to the room temperature part  26  and surrounds a second expansion space of the working gas. The second expansion space is a variable volume formed inside the second cylinder  25  between the second cylinder  25  and the second displacer, and in which the volume changes with a reciprocating movement of the second displacer. The second cooling stage  24  is made of a metal material having a higher thermal conductivity than that of the second cylinder  25 . The second cooling stage  24  is made of copper and the second cylinder  25  is made of stainless steel. 
     The cryocooler  16  is connected to a compressor (not shown) for the working gas. The cryocooler  16  cools the first cooling stage  22  and the second cooling stage  24  by expanding the working gas pressurized by the compressor in the interior thereof. The expanded working gas is recovered to the compressor and pressurized again. The cryocooler  16  generates cold by repeating a thermodynamic cycle including the supply and discharge of the working gas and the reciprocating movements of the first displacer and the second displacer in synchronization with the supply and discharge of the working gas. 
     The cryopump  10  shown in the drawing is a so-called horizontal cryopump. The horizontal cryopump is generally a cryopump in which the cryocooler  16  is disposed so as to intersect (usually, be orthogonal to) the center axis C of the cryopump  10 . The first cooling stage  22  and the second cooling stage  24  of the cryocooler  16  are arrayed in a direction perpendicular to the cryopump center axis C (horizontal in  FIG. 1  and in the direction of the center axis D of the cryocooler  16 ). 
     The first-stage cryopanel  18  includes a radiation shield  30  and an inlet cryopanel  32  and surrounds the second-stage cryopanel  20 . The first-stage cryopanel  18  is a cryopanel provided to protect the second-stage cryopanel  20  from radiant heat from outside the cryopump  10  or from the cryopump housing  70 . The first-stage cryopanel  18  is thermally coupled to the first cooling stage  22 . Accordingly, the first-stage cryopanel  18  is cooled to the first cooling temperature. The first-stage cryopanel  18  has a gap between the first-stage cryopanel  18  and the second-stage cryopanel  20 , and the first-stage cryopanel  18  is not in contact with the second-stage cryopanel  20 . The radiation shield  30  and the inlet cryopanel  32  may be formed of a metal material having a high thermal conductivity such as copper, and may be coated with a plating layer such as nickel or another coating layer. 
     The radiation shield  30  is provided to protect the second-stage cryopanel  20  from the radiant heat of the cryopump housing  70 . The radiation shield  30  is located between the cryopump housing  70  and the second-stage cryopanel  20  and surrounds the second-stage cryopanel  20 . The radiation shield  30  has a shield main opening  34  for receiving gas from the outside of the cryopump  10  into the internal space  14 . The shield main opening  34  is located at the intake port  12 . 
     The radiation shield  30  is provided with a shield front end  36  defining the shield main opening  34 , a shield bottom portion  38  which is located on the side opposite to the shield main opening  34 , and a shield side portion  40  connecting the shield front end  36  to the shield bottom portion  38 . The shield front end  36  forms a part of the shield side portion  40 . The shield side portion  40  extends in the axial direction from the shield front end  36  to the side opposite to the shield main opening  34 , and extends so as to surround the second cooling stage  24  in the circumferential direction. The radiation shield  30  has a tubular shape (for example, a cylinder) in which the shield bottom portion  38  is closed, and is formed in a cup shape. An annular gap  42  is formed between the shield side portion  40  and the second-stage cryopanel  20 . 
     The shield bottom portion  38  may be a member separate from the shield side portion  40 . For example, the shield bottom portion  38  may be a flat disk having substantially the same diameter as the shield side portion  40 , or may be attached to the shield side portion  40  on the side opposite to the shield main opening  34 . Further, at least a part of the shield bottom portion  38  may be open. For example, the radiation shield  30  may not be closed by the shield bottom portion  38 . That is, both ends of the shield side portion  40  may be open. 
     The shield side portion  40  has a shield side portion opening  44  into which the cryocooler structure part  21  is inserted. The second cooling stage  24  and the second cylinder  25  are inserted into the radiation shield  30  from outside the radiation shield  30  through the shield side portion opening  44 . The shield side portion opening  44  is an attachment hole formed in the shield side portion  40  and is, for example, circular. The first cooling stage  22  is disposed outside the radiation shield  30 . 
     The shield side portion  40  is provided with an attachment seat  46  for the cryocooler  16 . The attachment seat  46  is a flat portion for attaching the first cooling stage  22  on the radiation shield  30 , and is slightly depressed when viewed from outside the radiation shield  30 . The attachment seat  46  forms the outer periphery of the shield side portion opening  44 . The attachment seat  46  is closer to the shield bottom portion  38  than the shield front end  36  in the axial direction. The first cooling stage  22  is attached to the attachment seat  46 , whereby the radiation shield  30  is thermally coupled to the first cooling stage  22 . 
     The inlet cryopanel  32  is provided in the shield main opening  34  in order to protect the second-stage cryopanel  20  from radiant heat from an external heat source of the cryopump  10 . The heat source outside the cryopump  10  is, for example, a heat source inside the vacuum chamber  90  to which the cryopump  10  is attached. The inlet cryopanel  32  can limit not only radiant heat but also the entry of gas molecules. The inlet cryopanel  32  occupies a part of the opening area of the shield main opening  34  so as to limit the gas inflow through the shield main opening  34  to a desired amount. An annular open area  48  is formed between the inlet cryopanel  32  and the shield front end  36 . 
     The inlet cryopanel  32  is attached to the shield front end  36  by an appropriate attachment member and is thermally coupled to the radiation shield  30 . The inlet cryopanel  32  is thermally coupled to the first cooling stage  22  via the radiation shield  30 . The inlet cryopanel  32  has, for example, a plurality of annular or linear wing plates. Alternatively, the inlet cryopanel  32  may be a single plate-shaped member. 
     The second-stage cryopanel  20  is attached to the second cooling stage  24  so as to surround the second cooling stage  24 . Therefore, the second-stage cryopanel  20  is thermally coupled to the second cooling stage  24 , and the second-stage cryopanel  20  is cooled to the second cooling temperature. The second-stage cryopanel  20  is surrounded by the shield side portion  40  together with the second cooling stage  24 . 
     The second-stage cryopanel  20  includes a top cryopanel  60  facing the shield main opening  34 , a cryopanel member  62  disposed between the top cryopanel  60  and the shield bottom portion  38 , and a cryopanel attachment member  64 . The cryopanel members  62  are disposed on both sides of the second cooling stage  24  with the cryopump center axis C interposed therebetween. The cryopanel member  62  is disposed along a plane perpendicular to the cryopump center axis C. The top cryopanel  60  and the cryopanel member  62  are attached to the second cooling stage  24  via the cryopanel attachment member  64 . 
     Since the annular gap  42  is formed between the top cryopanel  60 , the cryopanel member  62 , and the shield side portion  40 , neither the top cryopanel  60  nor the cryopanel member  62  is in contact with the radiation shield  30 . The cryopanel member  62  is covered by the top cryopanel  60 . 
     The top cryopanel  60  is a part of the second-stage cryopanel  20  that is closest to the inlet cryopanel  32 . The top cryopanel  60  is disposed between the shield main opening  34  or the inlet cryopanel  32  and the cryocooler  16  in the axial direction. The top cryopanel  60  is located at the center of the internal space  14  of the cryopump  10  in the axial direction. Therefore, a large accommodation space  65  for a condensed layer is formed between the front surface of the top cryopanel  60  and the inlet cryopanel  32 . The accommodation space  65  for the condensed layer occupies the upper half of the internal space  14 . The axial height of the accommodation space  65  may be in the range of ⅓ to ⅔ of the axial length of the radiation shield  30 . 
     The top cryopanel  60  is a substantially flat cryopanel disposed vertically in the axial direction. That is, the top cryopanel  60  extends in the radial direction and the circumferential direction. The top cryopanel  60  is a disc-shaped panel having a size (for example, projected area) larger than that of the inlet cryopanel  32 . However, the relationship between the dimensions of the top cryopanel  60  and the inlet cryopanel  32  is not limited thereto, and the top cryopanel  60  may be smaller or both may have substantially the same dimensions. 
     The top cryopanel  60  is disposed so as to form a gap area  66  between the top cryopanel  60  and the cryocooler structure part  21 . The gap area  66  is a space formed in the axial direction between the rear surface of the top cryopanel  60  and the second cylinder  25 . The top cryopanel  60  and the cryopanel member  62  are formed of a metal material having a high thermal conductivity such as copper, and may be coated with a plating layer such as nickel. 
     The cryopanel member  62  is provided with an adsorbent  74  such as activated carbon. The adsorbent  74  is adhered to, for example, the rear surface of the cryopanel member  62 . It is intended that the front surface of the cryopanel member  62  functions as a condensing surface and the rear surface functions as an adsorption surface. The adsorbent  74  may be provided on the front surface of the cryopanel member  62 . Similarly, the top cryopanel  60  may have an adsorbent  74  on the front surface and/or rear surface. Alternatively, the top cryopanel  60  may not include the adsorbent  74 . 
     The cryopump  10  includes a gas flow adjusting member  50  configured to deflect the flow of gas flowing in from the shield main opening  34  from the cryocooler structure part  21 . The gas flow adjusting member  50  is configured to deflect the gas flow flowing into the accommodation space  65  through the inlet cryopanel  32  or the open area  48  from the second cylinder  25 . The gas flow adjusting member  50  may be a gas flow deflecting member or a gas flow reflecting member disposed above the cryocooler structure part  21  or the second cylinder  25  and adjacent thereto. The gas flow adjusting member  50  is locally provided at the same position as the shield side portion opening  44  in the circumferential direction. The gas flow adjusting member  50  has a rectangular shape when viewed from above. The gas flow adjusting member  50  is, for example, a single flat plate, and may be curved. 
     The gas flow adjusting member  50  extends from the shield side portion  40  and is inserted into the gap area  66 . However, the gas flow adjusting member  50  is not in contact with the top cryopanel  60 , the second cylinder  25 , and other parts of the second cooling temperature surrounding the gap area  66 . The gas flow adjusting member  50  is thermally coupled to the first cooling stage  22  via the radiation shield  30 . Therefore, the gas flow adjusting member  50  is cooled to the first cooling temperature. 
     The cryopump housing  70  is a casing of the cryopump  10 , which accommodates the first-stage cryopanel  18 , the second-stage cryopanel  20 , and the cryocooler  16 , and is a vacuum chamber configured to maintain the vacuum tightness of the internal space  14 . The cryopump housing  70  includes the first-stage cryopanel  18  and the cryocooler structure part  21  in a non-contact manner. The cryopump housing  70  is attached to the room temperature part  26  of the cryocooler  16 . 
     The intake port  12  is defined by a front end of the cryopump housing  70 . The cryopump housing  70  has an intake port flange  72  extending radially outward from a front end thereof. The intake port flange  72  is provided over the entire circumference of the cryopump housing  70 . The cryopump  10  is attached to the vacuum chamber  90  using the intake port flange  72 . 
     The cryopump housing  70  includes the cryopanel accommodation portion  76  that surrounds the radiation shield  30  in a non-contact manner with the radiation shield  30 , and the cryocooler accommodation portion  77  that surrounds the first cylinder  23  of the cryocooler  16 . The cryopanel accommodation portion  76  and the cryocooler accommodation portion  77  are integrally formed. 
     The cryopanel accommodation portion  76  has a cylindrical or dome-shaped shape in which the intake port flange  72  is formed at one end and the other end is closed as a housing bottom surface  70   a.  In addition to the intake port  12 , an opening through which the cryocooler  16  is inserted is formed on the side wall of the cryopanel accommodation portion  76  that connects the intake port flange  72  to the housing bottom surface  70   a.  The cryocooler accommodation portion  77  has a cylindrical shape extending from this opening to the room temperature part  26  of the cryocooler  16 . The cryocooler accommodation portion  77  connects the cryopanel accommodation portion  76  to the room temperature part  26  of the cryocooler  16 . 
     When the cryopump  10  is operated, first, the interior of the vacuum chamber  90  is roughed to approximately 1 Pa with another appropriate roughing pump before the operation. Thereafter, the cryopump  10  is operated. The first cooling stage  22  and the second cooling stage  24  are respectively cooled to the first cooling temperature and the second cooling temperature by the driving of the cryocooler  16 . Accordingly, the first-stage cryopanel  18  and the second-stage cryopanel  20  thermally coupled to these are also respectively cooled to the first cooling temperature and the second cooling temperature. 
     The inlet cryopanel  32  cools the gas flying from the vacuum chamber  90  toward the cryopump  10 . A gas having a sufficiently low vapor pressure (for example, 10 −8  Pa or less) at the first cooling temperature condenses on the surface of the inlet cryopanel  32 . This gas may be referred to as a first type gas (also referred to as a type-I gas). The first type gas is, for example, water vapor. In this manner, the inlet cryopanel  32  can pump the first type gas. A part of the gas whose vapor pressure is not sufficiently low at the first cooling temperature passes through the inlet cryopanel  32  or the open area  48  and enters the accommodation space  65 . Alternatively, the other part of the gas is reflected by the inlet cryopanel  32  and does not enter the accommodation space  65 . 
     The gas entered the accommodation space  65  is cooled by the second-stage cryopanel  20 . A gas having a sufficiently low vapor pressure (for example, 10 −8  Pa or less) at the second cooling temperature condenses on the surface of the second-stage cryopanel  20 . This gas may also be referred to as a second type gas (also referred to as a type-II gas). The second type gas is a gas that does not condense at the first cooling temperature. The second type gas is, for example, argon, nitrogen, and oxygen. In this manner, the second-stage cryopanel  20  can pump the second type gas. Since the second type gas directly faces the accommodation space  65 , a condensed layer of the second type gas can grow significantly on the front surface of the top cryopanel  60 . Since the cryopump  10  has a large accommodation space  65 , a large amount of second type gas can be stored. 
     A gas in which vapor pressure is not sufficiently low at the second cooling temperature is adsorbed on the adsorbent  74  of the second-stage cryopanel  20 . This gas may also be referred to as a third type gas (also referred to as a type-III gas). The third type gas is, for example, water vapor. In this manner, the second-stage cryopanel  20  can pump the third type gas. Therefore, the cryopump  10  can pump various gases by condensation or adsorption and can make the degree of vacuum of the vacuum chamber  90  reach a desired level. 
     As the pumping operation is continued, gas is accumulated in the cryopump  10 . The cryopump  10  is regenerated in order to discharge the accumulated gas to the outside. When the regeneration is completed, the pumping operation can be started again. 
     In this manner, the cryopump  10  is configured to have the accommodation space  65  for the condensed layer of a gas (for example, second type gas). The first-stage cryopanel  18  is disposed so as to surround the accommodation space  65 , and is cooled to a temperature higher than the condensation temperature of the second type gas. The second-stage cryopanel  20  is disposed so as to be surrounded by the inner surface of the first-stage cryopanel (for example, inner surface of the shield side portion  40 ) together with the accommodation space  65 , and is cooled to a temperature equal to or lower than the condensation temperature of the second type gas. The condensed layer of the second type gas is deposited on the second-stage cryopanel  20  (for example, top cryopanel  60 ). The intake port  12  allows the passage of the first-stage heat load (for example, radiant heat) incident on the inner surface of the first-stage cryopanel from outside the cryopump  10  (that is, vacuum chamber  90 ) and the gas entering the accommodation space  65  from outside the cryopump  10 . 
     Further, a gate valve  92  is installed between the cryopump  10  and the vacuum chamber  90 . The gate valve  92  is disposed adjacent to the intake port  12 . The intake port flange  72  is attached to one side of the gate valve  92 , and the opening portion of the vacuum chamber  90  is attached to a side opposite to the gate valve  92 . When the gate valve  92  is open, the first-stage heat load and the second type gas can enter the accommodation space  65  from the vacuum chamber  90  through the intake port  12 . When the gate valve  92  is closed, the intake port  12  is closed. Therefore, the first-stage heat load and the second type gas do not enter the accommodation space  65 . The gate valve  92  may be provided by a supplier other than the manufacturer of the cryopump  10 , or may be provided by the manufacturer of the cryopump  10  together with the cryopump  10 . 
     Further, a gate valve controller  94  that controls the gate valve  92  may be provided. The gate valve controller  94  is configured to control the opening and closing of the gate valve  92 . The gate valve controller  94  may form a part of the control device of the vacuum process device having the vacuum chamber  90 . The gate valve controller  94  may be communicably connected to a cryopump controller (hereinafter, also referred to as a CP controller)  100  that controls the cryopump  10 . The gate valve controller  94  may be configured to output a signal indicating the open/closed state of the gate valve  92  (for example, gate valve closing signal G indicating that the gate valve  92  is closed) to the CP controller  100 . The gate valve controller  94  may form a part of the cryopump controller (hereinafter, also referred to as a CP controller)  100  that controls the cryopump  10 , or may be provided as a single unit. 
       FIG. 2  is a control block diagram relating to the cryopump  10  shown in  FIG. 1 . 
     Such a control configuration of the cryopump  10  is realized by elements and circuits such as a CPU and memory of the computer as a hardware configuration, is realized by a computer program or the like as a software configuration, and in  FIG. 2 , it is shown as a functional block realized by cooperation as appropriate. It is understood by those skilled in the art that these functional blocks can be realized in various forms by combining hardware and software. 
     The cryopump  10  includes the CP controller  100 . The CP controller  100  includes a CPU that executes various arithmetic processes, a ROM that stores various control programs, a RAM that is used as a work area for data storage and program execution, an input/output interface, and a memory. Further, the CP controller  100  is configured to be able to communicate with a higher-level controller (not shown) for controlling the vacuum process device to which the cryopump  10  is attached. 
     The cryocooler  16  includes a cryocooler motor  80  as a drive source for driving the thermodynamic cycle of the cryocooler  16  and a cryocooler inverter  82  that controls the power of the specified voltage and frequency supplied from an external power source such as a commercial power source and supplies the power to the cryocooler motor  80 . The cryocooler inverter  82  converts the input power from the external power source and outputs the input power to the cryocooler motor  80  according to the operating frequency of the cryocooler  16  controlled by the CP controller  100 . In this manner, the cryocooler motor  80  is driven by the operating frequency determined by the CP controller  100  and output from the cryocooler inverter  82 . The cryocooler motor  80  and the cryocooler inverter  82  may be attached to the room temperature part  26  shown in  FIG. 1 . 
     The operating frequency (also referred to as operating speed) of the cryocooler  16  represents the operating frequency or rotation speed of the cryocooler motor  80 , the operating frequency of the cryocooler inverter  82 , the frequency of the thermodynamic cycle of the cryocooler  16  (for example, refrigeration cycle such as GM cycle), or any of these frequencies. The frequency of the thermodynamic cycle is the number of times per unit time of the thermodynamic cycle performed in the cryocooler  16 . 
     Further, the cryocooler  16  includes a cryopanel temperature sensor  84 . The cryopanel temperature sensor  84  is attached to the first cooling stage  22  and measures the temperature of the first-stage cryopanel  18 . The cryopanel temperature sensor  84  may be attached to the first-stage cryopanel  18 . The cryopanel temperature sensor  84  is communicably connected to the CP controller  100  so as to periodically measure the temperature of the first-stage cryopanel  18  and output a signal indicating a measured temperature value to the CP controller  100 . 
     The CP controller  100  includes a first-stage temperature control unit  102  that controls the operating frequency of the cryocooler  16  to cool the first-stage cryopanel  18  to the first-stage target temperature. The first-stage temperature control unit  102  is configured to determine the operating frequency of the cryocooler  16  (for example, by PID control) as a function of the deviation between the first-stage target temperature and a measured temperature of the first-stage cryopanel  18 . 
     When the heat load on the first-stage cryopanel  18  increases, the temperature of the first-stage cryopanel  18  can increase. In a case where a measured temperature of the cryopanel temperature sensor  84  is higher than the first-stage target temperature, the first-stage temperature control unit  102  increases the operating frequency of the cryocooler  16 . As a result, the frequency of the thermodynamic cycle in the cryocooler  16  is also increased (that is, the cooling capacity of the cryocooler  16  is increased), and the first-stage cryopanel  18  is cooled toward the first-stage target temperature. On the contrary, in a case where the measured temperature of the cryopanel temperature sensor  84  is lower than the target temperature, the operating frequency of the cryocooler  16  is reduced and the cooling capacity is lowered, and the first-stage cryopanel  18  is heated toward the first-stage target temperature. In this manner, the temperature of the first-stage cryopanel  18  can be kept in the temperature range near the first-stage target temperature. Since the operating frequency of the cryocooler  16  can be appropriately controlled according to the first-stage heat load, such control helps to reduce the power consumption of the cryopump  10 . 
     Further, the CP controller  100  includes a second-stage cryopanel monitoring unit  104  that monitors the amount of condensed gas in the accommodation space  65  based on the change in the first-stage heat load. The second-stage cryopanel monitoring unit  104  may be configured to receive a signal (for example, gate valve closing signal G) indicating an open/closed state of the gate valve  92  from the gate valve controller  94 . Details of the second-stage cryopanel monitoring unit  104  will be described later. 
       FIGS. 3A and 3B  are diagrams for describing in principle a method of monitoring the cryopump  10  according to an embodiment.  FIG. 3A  shows an initial situation in which there is no condensed layer of the second type gas, and  FIG. 3B  shows a situation in which the condensed layer  68  of the second type gas grows on the top cryopanel  60  during the vacuum pumping operation of the cryopump  10 . The condensed layer  68  is ice or frost of a gas such as a second type gas. The radiant heats  86   a  and  86   b  and the gas molecules  88  of the second type gas enter the accommodation space  65  from outside the cryopump  10  through the open area  48  of the intake port  12 . The radiant heats  86   a  and  86   b  and the gas molecules  88  of the second type gas enter from the vacuum chamber  90  into the cryopump  10  along a linear path. The approach angle can be determined depending on the design of the vacuum chamber  90 , including the location of the heat source and gas inlet in the vacuum chamber  90 . For convenience, the exemplary incident paths of the radiant heats  86   a  and  86   b  are shown by solid arrows, and the exemplary incident paths of the gas molecules  88  of the second type gas are shown by dashed arrows. 
     As shown in  FIG. 3A , a part of the radiant heat  86   a  is incident on the inner surface of the first-stage cryopanel, for example, the inner surface of the radiation shield  30 , and is the first-stage heat load. In the drawing, the radiant heat  86   a  is incident on the inner peripheral surface of the shield side portion  40 , and depending on the incident angle of the radiant heat  86   a,  the radiant heat  86   a  can also be incident on the inner peripheral surface of the shield front end  36  or the upper surface of the shield bottom portion  38 . A part of the other radiant heat  86   b  is incident on the upper surface of the second-stage cryopanel  20 , for example, the top cryopanel  60 , and is a second-stage heat load. As described above, the first-stage heat load is removed by the first cooling stage  22  of the cryocooler  16 , and the second-stage heat load is removed by the second cooling stage  24  of the cryocooler  16 . 
     Since the second type gas is cooled and condensed by the second-stage cryopanel  20 , the gas molecules  88  of the second type gas are deposited on the top cryopanel  60  as the condensed layer  68  of the second type gas, as shown in  FIG. 3B . The condensed layer  68  can also be deposited on the cryopanel member  62 , and is not shown here. Since the inlet cryopanel  32  is disposed at the center of the intake port  12  and the open area  48  is formed around the inlet cryopanel  32 , the growth rate of the condensed layer  68  and the resulting thickness (axial height) of the condensed layer  68  increases at the outer edge and is decreased at the center. Therefore, as shown in the drawing, the condensed layer  68  has a shape that rises below the open area  48  and has a recess below the inlet cryopanel  32 . 
     As the condensed layer  68  grows further, the condensed layer  68  eventually comes into contact with any part of the first-stage cryopanel  18  (for example, shield front end  36 , shield side portion  40 , and/or inlet cryopanel  32 ). Since the cooling temperature of the first-stage cryopanel  18  is higher than the condensation temperature of the second type gas and the first-stage cryopanel  18  cannot condense the second type gas, the condensed layer  68  is again vaporized at the contact part with the first-stage cryopanel  18 . The second type gas stored in the cryopump  10  as the condensed layer  68  is discharged again, and thereafter the cryopump  10  cannot provide the pumping function of the second type gas. That is, the cryopump  10  reaches a storage limit at the time of contact between the first-stage cryopanel  18  and the condensed layer  68 . 
     When the cryopump housing  70  is provided with a viewport or other peephole, the worker can predict whether or not the storage limit is reached soon by visually observing the condensed layer  68  from outside the cryopump  10  through the peephole. However, in general, existing cryopumps  10  do not have such a peephole. The condensed layer  68  cannot be visually observed during the vacuum pumping operation of the cryopump  10 . As another method, an attempt is made to know the time when the storage limit is reached from the cumulative amount of the second type gas introduced into the vacuum chamber  90 . However, the storage limit depends on a specific shape of the condensed layer  68  because the storage limit depends on the physical contact between the first-stage cryopanel  18  and the condensed layer  68 . Therefore, it is difficult to accurately predict the time when the storage limit is reached only from the cumulative introduction amount of the second type gas into the vacuum chamber  90 . 
     Therefore, in this document, a new technique is proposed for predicting in real time that the amount of the second type gas stored in the cryopump  10  is approaching the storage limit during the vacuum pumping operation of the cryopump  10 . In the embodiment, the amount of condensed gas in the accommodation space  65  is monitored based on the change in the first-stage heat load. 
     This concept is based on the fact that a ratio of the first-stage heat load to the second-stage heat load incident on the cryopump  10  through the intake port  12  changes according to the volume and/or shape of the condensed layer  68 . When the volume and/or shape of the condensed layer  68  changes, the first-stage heat load and the second-stage heat load change, respectively, and the cooling balance of the first-stage cryopanel  18  and the second-stage cryopanel  20  by the cryocooler  16  changes. Therefore, by measuring the change in the first-stage heat load, it is possible to acquire information indicating the change in the volume and/or shape of the condensed layer  68 . 
     As described above with reference to  FIG. 3A , in the absence of the condensed layer  68 , a part of the radiant heat  86   a  is the first-stage heat load and a part of the other radiant heat  86   b  is the second-stage heat load. When the condensed layer  68  grows, both the radiant heats  86   a  and  86   b  can enter the condensed layer  68  as shown in  FIG. 3B . The condensed layer  68  serves as a so-called wall that shields the radiant heat  86   a  toward the inner surface of the first-stage cryopanel. Since the condensed layer  68  is deposited on the top cryopanel  60 , the radiant heats  86   a  and  86   b  incident on the condensed layer  68  serve as the second-stage heat load. As described above, as the height of the condensed layer  68  in the axial direction increases as the condensed layer  68  grows, the first-stage heat load tends to decrease and the second-stage heat load tends to increase. It can be said that the amount of the second type gas stored in the condensed layer  68  correlates with the first-stage heat load (or the second-stage heat load). 
     Therefore, in a case where the first-stage heat load is decreased, it may be determined that the amount of condensed gas in the accommodation space  65  is increased. Further, in a case where the first-stage heat load increases (since the amount of condensed gas gradually increases during the vacuum pumping operation of the cryopump  10 , although such a situation is unlikely to occur), it can be determined that the amount of condensed gas in the accommodation space  65  is decreased. In this manner, the amount of condensed gas in the accommodation space  65  can be monitored based on the change in the first-stage heat load. 
     The change in the first-stage heat load can be measured as a change in at least one operating parameter of the cryocooler  16 . In the cryopump  10  in which the operating frequency of the cryocooler  16  is controlled so as to cool the first-stage cryopanel  18  to the first-stage target temperature, the change in the first-stage heat load can be measured as a change in the operating frequency of the cryocooler  16 . 
       FIG. 4  shows a change in an operating frequency of the cryocooler  16  during a vacuum pumping operation of the cryopump  10 . In  FIG. 4 , a vertical axis represents the operating frequency [Hz] of the cryocooler  16  and a horizontal axis represents the amount [std L] of the second type gas (argon gas) supplied to the vacuum chamber  90 , which corresponds to the amount of the second type gas (also referred to as the storage amount) condensed in the condensed layer  68  shown in  FIG. 3B . 
     As shown in  FIG. 4 , the operating frequency of the cryocooler  16  tends to decrease as the storage amount increases. As the storage amount increases and the condensed layer  68  grows, the first-stage heat load is decreased as described above. When the first-stage heat load is reduced, the temperature of the first-stage cryopanel  18  detected by the cryopanel temperature sensor  84  can be lowered. However, since the temperature of the first-stage cryopanel  18  is controlled to the first-stage target temperature, the operating frequency of the cryocooler  16  is actually reduced, the cooling capacity of the cryocooler  16  is lowered, and the first-stage cryopanel  18  is held at the first-stage target temperature. Although illustrated are the test results by the present inventor for the cryopump  10  having a specific design, it is confirmed that various cryopumps  10  also have the same tendency. 
     The vertical axis of  FIG. 4  shows a first threshold value S 1  and a second threshold value S 2 , and the horizontal axis shows a design storage limit value VL. The first threshold value S 1  corresponds to the operating frequency of the cryocooler  16  that can be taken when the storage amount of the second type gas by the cryopump  10  reaches the design storage limit value VL. The second threshold value S 2  corresponds to the operating frequency of the cryocooler  16  that can be taken when the storage amount of the second type gas by the cryopump  10  reaches an allowable storage amount VA. Here, the allowable storage amount VA is a value obtained by subtracting a predetermined margin from the design storage limit value VL. The margin may be as large as, for example, within 20%, or within 10%, or within 5% of the design storage limit value VL, or may be larger than, for example, 1% of the design storage limit value VL. The first threshold value S 1  and the second threshold value S 2  can be appropriately determined experimentally or empirically. 
     Therefore, in a case where the operating frequency of the cryocooler  16  is reduced to the first threshold value S 1  or the second threshold value S 2  during the vacuum pumping operation of the cryopump  10 , it can be considered that the storage amount of the second type gas is approaching the storage limit. The operating frequency of the cryocooler  16  can be used as an index showing the storage amount of second type gas, that is, the amount of condensed gas in the accommodation space  65  in real time. As described above, by monitoring the operating frequency of the cryocooler  16 , it is possible to predict in real time that the storage amount of the second type gas is approaching the storage limit during the vacuum pumping operation of the cryopump  10 . 
       FIG. 5  is a flowchart showing a method of monitoring the cryopump  10  according to an embodiment. This method includes a cooling process (S 10 ), a deposition process (S 12 ), and a monitoring process (S 14 ). 
     The cooling process (S 10 ) includes cooling the first-stage cryopanel  18  to a temperature higher than the condensation temperature of the second type gas, and cooling the second-stage cryopanel  20  to a temperature equal to or lower than the condensation temperature of the second type gas. For example, the cooling process (S 10 ) includes controlling the operating frequency of the cryocooler  16  to cool the first-stage cryopanel  18  to the first-stage target temperature by the first-stage temperature control unit  102  of the CP controller  100 . 
     As shown in  FIG. 3B , the deposition process (S 12 ) includes depositing the condensed layer  68  of the second type gas that enters the accommodation space  65  from outside the cryopump  10  through the intake port  12  on the second-stage cryopanel  20 . 
     The monitoring process (S 14 ) includes monitoring the amount of condensed gas in the accommodation space  65 , based on the change in the first-stage heat load incident on the inner surface of the first-stage cryopanel  18  from outside the cryopump  10  through the intake port  12 . As described above, the amount of condensed gas in the accommodation space  65  mainly corresponds to the amount of the second type gas captured in the condensed layer  68  condensed on the top cryopanel  60 . 
     For example, the monitoring process (S 14 ) includes determining that the amount of condensed gas is increased in a case where the first-stage heat load is reduced by the second-stage cryopanel monitoring unit  104  of the CP controller  100  (for example, in a case where the operating frequency of the cryocooler  16  is reduced). Further, the second-stage cryopanel monitoring unit  104  may determine that the amount of condensed gas is decreased in a case where the first-stage heat load increases (for example, in a case where the operating frequency of the cryocooler  16  increases). 
       FIG. 6  is a flowchart showing the monitoring process (S 14 ) shown in  FIG. 5  in more detail. First, the second-stage cryopanel monitoring unit  104  acquires the operating frequency of the cryocooler  16  from the first-stage temperature control unit  102  (S 16 ). 
     The operating frequency of the cryocooler  16  may change as the amount of heat input from the vacuum chamber  90  to the cryopump  10  through the intake port  12  changes. The amount of heat input from the vacuum chamber  90  may depend, for example, on the vacuum process performed in the vacuum chamber  90 . Such a change in thermal conditions in the vacuum chamber  90  may lead to an error in estimating the amount of condensed gas based on the operating frequency of the cryocooler  16 . Therefore, it is preferable that the second-stage cryopanel monitoring unit  104  acquires the operating frequency of the cryocooler  16  at the timing when the radiant heat incident on the intake port  12  from outside the cryopump  10  is a default value. In this manner, the influence of changes in thermal conditions in the vacuum chamber  90  can be reduced or prevented. 
     The timing may be set, for example, during the closure of the gate valve  92 . Therefore, the second-stage cryopanel monitoring unit  104  may acquire the operating frequency of the cryocooler  16  in response to the gate valve closing signal G. By closing the gate valve  92 , the intake port  12  is closed, and the internal space  14  of the cryopump  10  is isolated from the vacuum chamber  90 . Therefore, the heat input from the vacuum chamber  90  to the cryopump  10  through the intake port  12  is restricted or substantially blocked. By thermally separating the vacuum chamber  90  from the cryopump  10  in this manner, the second-stage cryopanel monitoring unit  104  can acquire the operating frequency of the cryocooler  16  in which the influence of the change in the thermal conditions in the vacuum chamber  90  is reduced or prevented. 
     The second-stage cryopanel monitoring unit  104  may acquire the operating frequency of the cryocooler  16  or other operating parameters from the first-stage temperature control unit  102  when the operation state of the cryocooler  16  is stabilized. For example, the second-stage cryopanel monitoring unit  104  may acquire the operating frequency of the cryocooler  16  when a predetermined time is elapsed from the reception of the gate valve closing signal G or other above timing. Alternatively, the second-stage cryopanel monitoring unit  104  may acquire the operating frequency of the cryocooler  16  when the rate of change of the operating frequency of the cryocooler  16  falls within a predetermined threshold value after the above timing. In this manner, it is possible to avoid acquiring the operating frequency of the cryocooler  16  in a transient state such as immediately after the gate valve  92  is closed. 
     Subsequently, the second-stage cryopanel monitoring unit  104  compares the acquired operating frequency of the cryocooler  16  with the threshold value S (S 18 ). The threshold value S may be either the first threshold value S 1  or the second threshold value S 2  shown in  FIG. 4 . 
     In a case where the operating frequency of the cryocooler  16  is below the threshold value S (Y in S 18 ), the second-stage cryopanel monitoring unit  104  may determine that the amount of condensed gas exceeds the reference value (S 20 ). In a case where the threshold value S is the first threshold value S 1 , the reference value corresponds to the design storage limit value VL. In a case where the threshold value S is the second threshold value S 2 , the reference value corresponds to the allowable storage amount VA. The second-stage cryopanel monitoring unit  104  may be configured to output that the amount of condensed gas exceeds the reference value. For example, the second-stage cryopanel monitoring unit  104  may be configured to indicate to the worker in the form of an image, sound, or other appropriate form that the amount of condensed gas exceeds the reference value. 
     In a case where the operating frequency of the cryocooler  16  exceeds the threshold value S (N in S 18 ), the second-stage cryopanel monitoring unit  104  determines that the amount of condensed gas is below the reference value (S 22 ). Similarly, the second-stage cryopanel monitoring unit  104  may be configured to output that the amount of condensed gas is below the reference value. 
     In this manner, the monitoring process (S 14 ) is ended. The monitoring process (S 14 ) may be repeated each time the gate valve  92  is allowed to be closed, periodically, or at any other appropriate frequency. 
       FIG. 7  is a diagram schematically showing a cryopump  10  according to an embodiment. As shown, the cryocooler  16  may include a variable output heater  96  for heating the first cooling stage  22 , such as an electric heater. The heater  96  may be attached to the first cooling stage  22 . Alternatively, the heater  96  may be attached to any part of the first-stage cryopanel  18 . 
     In this case, the first-stage temperature control unit  102  may controls the output of the heater  96  (for example, the voltage and/or current supplied to the heater  96 ) to cool the first-stage cryopanel  18  to the first-stage target temperature. The first-stage temperature control unit  102  may be configured to determine the output of the heater  96  (for example, by PID control) as a function of the deviation between the first-stage target temperature and the measured temperature of the first-stage cryopanel  18 . 
     When the heat load on the first-stage cryopanel  18  increases, the temperature of the first-stage cryopanel  18  can increase. In a case where the measured temperature of the cryopanel temperature sensor  84  is higher than the first-stage target temperature, the first-stage temperature control unit  102  reduces the output of the heater  96 . As a result, the first-stage cryopanel  18  is cooled toward the first-stage target temperature. On the contrary, in a case where the measured temperature of the cryopanel temperature sensor  84  is lower than the target temperature, the first-stage temperature control unit  102  increases the output of the heater  96 . As a result, the first-stage cryopanel  18  is heated toward the first-stage target temperature. In this manner, the temperature of the first-stage cryopanel  18  can be kept in the temperature range near the first-stage target temperature. 
     The second-stage cryopanel monitoring unit  104  monitors the amount of condensed gas in the accommodation space  65  based on the change in the first-stage heat load, and more specifically, it may be determined that the amount of condensed gas in the accommodation space  65  is increased when the first-stage heat load is decreased. Therefore, the second-stage cryopanel monitoring unit  104  may be configured to acquire the output of the heater  96  from the first-stage temperature control unit  102  and compare the output of the heater  96  with the threshold value. The second-stage cryopanel monitoring unit  104  may determine that the amount of condensed gas exceeds the reference value in a case where the output of the heater  96  exceeds the threshold value. The second-stage cryopanel monitoring unit  104  may determine that the amount of condensed gas falls below the reference value in a case where the output of the heater  96  does not reach the threshold value. 
     The second-stage cryopanel monitoring unit  104  may acquire the output of the heater  96  from the first-stage temperature control unit  102  at the timing when the radiant heat incident on the intake port  12  from outside the cryopump  10  is a default value. The timing may be set while the gate valve  92  is closed. 
     As described above, in the cryopump  10  according to the embodiment, the amount of condensed gas in the accommodation space  65  is monitored based on the change in the first-stage heat load. Since the change in the first-stage heat load reflects the change in the shape of the condensed layer  68 , compared with the existing attempt to predict the arrival of the storage limit only from the cumulative amount of the second type gas introduced into the vacuum chamber  90 , the amount of condensed gas in the cryopump  10  can be estimated more accurately. It can be predicted during use of the cryopump that the amount of gas stored in the cryopump  10  is approaching the storage limit. 
     More specifically, the change in the first-stage heat load is measured as the change in the operating parameter of the cryocooler  16  such as the operating frequency of the cryocooler  16  or the heater output, and the amount of condensed gas in the accommodation space  65  is monitored based on the measured change in the operating parameter. In this manner, it is possible to predict in real time that the storage amount of the second type gas is approaching the storage limit during the vacuum pumping operation of the cryopump  10 . 
     The cryopump  10  can be continued to be used until the storage amount approaches the storage limit as compared with the related art, and a regeneration interval (period from the previous regeneration to the next regeneration) of the cryopump  10  can be lengthened. It is easier to adapt a regeneration schedule of the cryopump  10  to the production plan in the vacuum process device so as to improve a throughput of the vacuum process device to which the cryopump  10  is attached. 
     The present invention has been described above based on the examples. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, various design changes can be made, various modification examples can be made, and such modification examples are also within the scope of the present invention. 
     In one embodiment, as shown in  FIG. 8 , the second-stage cryopanel monitoring unit  104  may include a condensed gas amount table  106  in which a plurality of values of the amount of condensed gas are associated with the value of the operating parameter of the cryocooler  16  (for example, operating frequency or output of the heater  96 ). The condensed gas amount table  106  may have a look-up table, a function, or any other form. The second-stage cryopanel monitoring unit  104  may acquire the operating parameter of the cryocooler  16  from the first-stage temperature control unit  102 . The second-stage cryopanel monitoring unit  104  may calculate an estimated value of the amount of condensed gas from the operating parameter of the cryocooler  16  and the condensed gas amount table  106 . The second-stage cryopanel monitoring unit  104  may be configured to output the calculated estimated value of the amount of condensed gas in an image, sound, or other appropriate form. In this manner, the cryopump  10  can estimate the amount of condensed gas in real time. 
     In the above description, the horizontal cryopump has been exemplified. However, the present invention is also applicable to other vertical cryopumps. The vertical cryopump refers to a cryopump in which the cryocooler  16  is disposed along the center axis C of the cryopump  10 . Further, the internal configuration of the cryopump, such as the arrangement, the shape, the number, or the like of a cryopanel, is not limited to the specific embodiment described above. Various known configurations can be appropriately adopted. 
     INDUSTRIAL APPLICABILITY 
     An embodiment of the present invention can be used in the field of the cryopump and the method of monitoring the cryopump. 
     It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.