Cryopump

Abstract

The cryopump includes a vessel having an open front, the open front including an inlet to the vessel, a radiation shield, and a two-stage refrigerator extending into the vessel, the first stage of the refrigerator being thermally coupled to the radiation shield. A first-stage array is disposed within the vessel and is also thermally coupled to the first-stage refrigerator. A cryopanel structure is coupled to the second stage of the refrigerator. The first-stage array includes a plurality of elements arranged at increasing distances from the inlet, with the elements closest to the inlet being between the cryopanel structure and the inlet, and the elements furthest from the inlet having a passageway through their centers. The elements closest to the inlet have smaller perimeters than the elements furthest from the inlet.

Description

[Technical Field]

[0001] The field of the invention relates to cryopumps, and in particular to two-stage cryopumps having a first stage at a temperature for trapping Type I gases such as water vapor and a second stage at a lower temperature for trapping Type II gases such as nitrogen and in some embodiments for cryoadsorption of Type III gases such as hydrogen. [Background technology]

[0002] A two-stage cryopump is formed from a low-temperature second-stage cryopanel array operating in the 4 to 25 K range, which can be coated with a trapping material such as charcoal. This cryopanel array acts as the primary pumping surface and is surrounded by a first-stage radiation shield, which operates in the 40 to 130 K temperature range and provides a radiation shield for the cryoarray, shielding it from Type I gases such as water vapor by trapping these gas molecules where they come into contact with the shield.

[0003] The radiation shield is located within the pump housing and is normally closed except for an inlet located between the cryopanel array and the pumping chamber, which is partially hidden by the front cryopanel of the first stage, which is thermally coupled to the radiation shield and serves as the pumping site for high-boiling-point type I gases such as water vapor.

[0004] During operation, as gas enters the pump vessel through the inlet, at least some of the Type I gases, such as water vapor, condense on the front array. Low-boiling-point gases pass through the front array and enter the radiation shield. Meanwhile, Type III gases, such as hydrogen, helium, and neon, which have significant vapor pressure at 4 K, are adsorbed by adsorbents, such as activated carbon, zeolite, or molecular sieves, that line the second-stage cryopanels.

[0005] In this way, gases flowing into the pump from the exhaust chamber are trapped, and a vacuum is created inside the pump chamber. One problem with cryopumps is that during operation, gas molecules reach a saturation state on the trapping surface, reducing their trapping capacity. Therefore, cryopumps must be periodically regenerated to release the trapped gas molecules.

[0006] There are competing factors to consider when designing a cryopump: while a high conductivity of gas into the pump improves pumping speed, it is advantageous to provide some shielding of the second-stage cryopanel from thermal radiation and from type I gases to reduce the heat load on the cryopanel. Type I gases that reach the cryopanel condense on the cryopanel, preventing type III gases from being cryosorbed. Furthermore, some type I gases, such as long-chain hydrocarbons, do not leave the array surface during regeneration, resulting in reduced pump performance over the remaining life of the pump. However, shielding the cryopanel from gas molecules results in reduced conductivity.

[0007] WO 2019 / 099728 discloses a two-stage cryopump in which some of these factors are addressed with an igloo-shaped front array that provides shielding for the cryopanels. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2019 / 099728 Summary of the Invention [Problem to be solved by the invention]

[0009] It would be desirable to provide a two-stage cryopump that has high conductivity to Type II and / or III gases, yet has effective shielding of the second stage surfaces from Type I gases. [Means for solving the problem]

[0010] A first aspect provides a cryopump comprising: a vessel including an open front region, the open front region including an inlet to the vessel; a radiation shield; a two-stage refrigerator extending into a sidewall of the vessel at a portion of the sidewall remote from the inlet, the portion of the sidewall at a point closer to the closed end of the vessel than the inlet, the first stage of the refrigerator being thermally coupled to the radiation shield; a first stage array disposed within the vessel and thermally coupled to the first stage of the refrigerator; and a cryopanel structure coupled to the second stage of the refrigerator, the first stage array comprising a plurality of elements arranged at increasing distances from the inlet, the elements closest to the inlet being located between the inlet and the cryopanel structure and having smaller perimeters than the elements farther from the inlet, each of the elements farther from the inlet having a passageway through its center.

[0011] The inventors have recognized that there are competing requirements for cryopumps in that Type II and / or Type III gases must be effectively trapped by good conductivity to reach the second-stage cryopanels. However, these cryopanels must be effectively shielded from both thermal radiation and Type I gases to maintain optimal temperatures long enough and protect the cryopanels from being overloaded with Type I gases, which would reduce their effectiveness. Conventionally, to prevent Type I gases from reaching the cryopanels, a frontal array is placed at the pump inlet. Such conventional frontal arrays include openings that allow gas molecules to enter the pump, often in a chevron configuration. Gas molecules arriving at the inlet either pass directly through the openings in the frontal array, are trapped at the surface, are deflected toward and trapped by a radiation shield in the pump sidewall, or are deflected back toward the pump chamber. One drawback of such an array is that for at least a portion of the inlet surface area, molecules moving perpendicular to the plane of the inlet have a direct line-of-sight path through the front array directly to the cryopanel, and Type I gases with the appropriate trajectory may travel directly to the cryopanel. Furthermore, deflection of gas molecules by the array at the inlet results in some Type II and III gas molecules being directed away from the pump inlet and not entering the pump, reaching the second stage array and reducing its conductivity and the pumping speed of the pump.

[0012] The inventors solve these problems by forming a first stage array with multiple elements located at different distances from the entrance, providing a barrier for at least some molecules traveling perpendicular to the plane of the entrance, and a through path for some molecules that have a component parallel to the plane of the entrance, such as molecules deflected by the side walls.

[0013] Additionally, the refrigerator is located away from the cryopump inlet, which reduces the chance that gas molecules will collide with the refrigerator elements and be deflected toward the inlet. This location also prevents the refrigerator elements from obscuring most of the top of the cryopanel structure, increasing the surface area encountered by Type II and III gases and improving the uniformity of capture of these gases by the cryopanel structure.

[0014] In this way, effective, targeted shielding is provided that allows for fast pumping while protecting the cryopanels from direct impact from Type I gas. In practice, the first-stage array, consisting of elements at different distances from the inlet, with suitable gas flow paths between them for molecules reflected from the vessel's radiation shield but preventing direct line-of-sight, is a good way to enable high hydrogen gas capture rates while shielding the second-stage cryopanels and cryosorbent materials. Furthermore, locating the refrigerator away from the inlet reduces unnecessary shielding of the cryopanel structure from hydrogen gas.

[0015] These ideas work together to enable both effective shielding and speed enhancement: in some embodiments, pumping speeds can be increased to hydrogen rates of 15,000 L / s or more while still shielding the cryoadsorption array from unwanted gases.

[0016] In some embodiments, the cryopanel structure has a diameter at its widest point that is less than 70%, preferably less than 55%, of the diameter of the vessel.

[0017] The cryopanel structure can be narrower or longer than conventional cryopanel structures, which increases the likelihood that gas molecules will reach the bottom of the cryopanel structure, thereby improving the uniformity of molecules captured by the cryopanel structure and increasing its effectiveness.

[0018] In some embodiments, the refrigerator extends into the vessel in a portion of the sidewall that is a distance from the inlet that is 60% or more of the length of the vessel.

[0019] To improve gas conductivity and reduce the resistance to gas flow that a refrigerator extending into the vessel may cause, it is positioned in the half of the vessel farthest from the inlet, preferably at least 60% into the vessel. At least 60% into the vessel means at least 60% along an axis perpendicular to the plane of the inlet and extending from the inlet to the bottom or closed end of the vessel. By positioning the refrigerator element deep within the vessel, the likelihood that Type II or III particles that strike the refrigerator element will be deflected out of the vessel or away from the cryopanel is reduced. Furthermore, the first stage array can be mounted above the refrigerator element, and the cryopanel can be mounted so that the majority of the structure is above the refrigerator and therefore not shielded by the refrigerator.

[0020] In some embodiments, the cryopanel structure has a length that is greater than 70% of the length of the vessel.

[0021] Providing a cryopanel structure with a length that spans most of the length of the pump vessel provides a large surface area for particles to impact and capture, thereby improving the effectiveness and life of the cryopanel structure during regeneration.

[0022] In some embodiments, the first stage array is attached to a mounting element, the mounting element being formed of a thermally conductive material coupled to the first stage refrigerator and each of the plurality of elements of the first stage array.

[0023] The first stage array is cooled to the temperature of the first stage of the refrigerator, a temperature suitable for trapping Type I gas. In some embodiments, this cooling is effectively provided by mounting the first stage array within the vessel on thermally conductive elements extending from the first stage of the refrigerator to each element of the first stage array, thereby maintaining the array at or near the temperature of the first stage refrigerator. In other embodiments, the first stage array can be mounted on a radiation shield that is itself thermally coupled to the first stage refrigerator. In such an arrangement, the first stage array may not be consistently maintained near the temperature of the first stage refrigerator as it would be if it were mounted on a thermally conductive mounting element.

[0024] All elements except for the element closest to the entrance penetrate through the center. Through the aisle The element may have a circular or ring-like configuration, and in some cases, may have a circular or ring-like configuration. The element closest to the inlet, located between the cryopanel structure and the inlet, may have a solid cross section rather than a circular configuration, and may provide shielding from the inlet of the cryopanel structure from both thermal radiation and at least some gas molecules moving directly from the inlet toward the cryopanel structure. Alternatively, the element may have several openings defining passages through it, and the openings may be at least partially covered by sloped flap-type surfaces for deflecting molecules toward the sidewalls.

[0025] In some embodiments, one end of the cryopanel structure extends into the first stage array, and at least one of the elements further extends from the inlet around the periphery of the one end of the cryopanel structure.

[0026] Having a first stage array formed of multiple elements located at different distances from the inlet means that it is not a flat structure, which allows the cryopanel structure to extend into the array, resulting in improved shielding for that portion of the cryopanel structure. This is the portion of the cryopanel array closest to the inlet, which traditionally receives the highest percentage of gas molecules. By providing improved shielding for this portion compared to portions of the cryopanel structure further from the inlet, gas molecules can be captured more uniformly along the length of the cryopanel structure.

[0027] In some embodiments, adjacent elements in the first stage array are configured such that, for at least some of the elements closest to the inlet, the outer periphery of one element is substantially equal to or smaller than the inner periphery of a subsequent element located further away from the pump inlet.

[0028] The elements can be arranged such that the outer periphery of one element is substantially the same as the inner periphery of a subsequent element further away from the inlet. Such an arrangement provides a substantially solid surface when viewed vertically through the inlet, the substantially solid surface having the dimensions of the outer periphery of the element furthest from the inlet. This provides an optically clear structure when viewed from the inlet, which is advantageous and provides effective shielding of the cryopanel. In practice, the elements provide a substantially solid surface when viewed vertically, and when positioned in the pump at a predetermined distance from the inlet, shield the cryopanel from further angles around the vertical when viewed from the inlet.

[0029] In this regard, the element of the first stage array closest to the inlet can be a predetermined distance within the pump so that molecules striking this surface are unlikely to have already passed the pump inlet and be deflected back into the exhaust chamber. In other embodiments, the element of the first stage array closest to the inlet can be located adjacent to the inlet.

[0030] In some embodiments, the outer perimeter of one element is slightly smaller than the inner perimeter of the subsequent element, providing clearance for molecules moving perpendicular to the plane of the inlet. In such cases, the difference between the inner and outer perimeters is generally small, no more than about 10%, allowing a small number of molecules moving perpendicular to the inlet of the array to pass through the array.

[0031] Any gap between the elements when viewed vertically increases the conductivity, which is beneficial for pumping type III gases, but has some adverse effects on the heat load of the second stage, which increases due to contamination of the cryopanels by type I gases and reduced thermal shielding.

[0032] In some embodiments, the first stage array has a substantially igloo shape, with the elements being concentric, with the element closest to the entrance having the smallest perimeter and subsequent elements having perimeters of increasing size with distance from the entrance.

[0033] The first stage ray can have a substantially igloo shape with concentric elements of increasing size. In some cases, the elements can increase in size from the element closest to the entrance to the element furthest from the entrance, while in other embodiments, elements of the same size can be used at certain locations, with multiple elements closest to the entrance increasing in size.

[0034] In some embodiments, the elements are substantially flat, with the element closest to the inlet comprising a disk and subsequent elements comprising a ring.

[0035] The elements can have many forms, for example they can have an angular periphery and can conveniently be constructed as disks and rings, which provides symmetry in cross section and is particularly convenient when the radiation shield has a substantially cylindrical form.

[0036] In some embodiments, the disk has a solid cross section, while in other embodiments, the disk has several openings that provide several through passages through the disk, which openings can be at least partially obscured by angled surfaces arranged to deflect impinging molecules towards the radiation shield.

[0037] In some embodiments, the surfaces of the elements facing the inlet make an angle between 0 and 30 degrees with respect to the plane of the inlet, and are either parallel to the plane or angled so that the surface closest to the inlet faces the radiation shield. In some embodiments, if some of the elements are angled, the elements closest to the inlet make an angle of 0 degrees and additional elements can be angled.

[0038] In some cases, it is advantageous to slope the surface of the element so that particles striking the surface are deflected toward the radiation shield; in other embodiments, the surface of the element facing the inlet is substantially parallel to the plane of the inlet. Since sloped elements provide better shielding of the cryopanel structure but reduce conductivity, whether flat or slightly sloped elements are preferred depends on the requirements of the pump. In either case, because the first stage array is within the pump, even vertically deflecting flat elements may still retain molecules that arrive vertically within the pump, since such deflected molecules may collide with other molecules before reaching the inlet.

[0039] In some embodiments, the elements of the first stage array furthest from the inlet are mounted closest to the first stage of the refrigerator, and the elements of the first stage array closest to the inlet are between 5 and 15% inside the vessel.

[0040] In some embodiments, the first stage array extends from a point between 5 and 15% into the vessel to a point between 25 and 40% into the vessel.

[0041] As mentioned above, the first stage array is not a flat array, but rather extends longitudinally within the pump, potentially along 10 to 35% of the vessel length. The longitudinal extent of the array provides effective shielding of the cryopanel structure along a significant portion of its length, leading to a more uniform distribution of captured molecules on the surface of the cryopanel structure.

[0042] In some embodiments, the cryopanel structure comprises a plurality of panels having a substantially cylindrical outer skin extending from a central axis and having at least one tapered end, one of the at least one tapered end extending into the first stage inlet array.

[0043] While the cryopanel structure can have many configurations, a convenient configuration is one having multiple panels extending from a central axis, with the structure's outer skin having a substantially cylindrical shape that matches but is smaller than the shape of the cylindrical radiation shield. The structure can have at least one tapered end that extends to the first stage array, and in some embodiments, both ends can be tapered.

[0044] Such an integrated structure may have multiple cryopanels with adsorbents, such as charcoal, on both sides for trapping Type III gases, such as hydrogen. This structure allows the number of panels to be varied depending on the rate and volume of Type II or III gases required for a particular application, providing a flexible design that can be optimized for a particular application. In some implant applications, the number of panels depends on the rate and volume of hydrogen.

[0045] In some embodiments, the portion of the cryopanel structure that extends into the first stage array constitutes at least 20%, preferably at least 30% of the cryopanel structure.

[0046] In some embodiments, the radiation shield is substantially cylindrical with a flat portion that extends into the cylinder for coupling to the refrigerator, the flat portion extending into the cylinder by less than 8%, preferably less than 6%, of the diameter of the cylinder.

[0047] The radiation shield is cylindrical, so in order to bond the shield to the refrigerator flange when the flange is flat, the radiation shield has a flat portion that corresponds to the shape of the flange that extends into the vessel. This results in a protruding surface that extends from the radiation shield above the refrigerator element. This provides a surface against which the gas will impinge and be deflected back toward the inlet. The inventors recognized the potential problems with this arrangement and provided a design that keeps the flat portion as small as practicable for good bonding, while also reducing the size of the extension of this portion into the cylinder, and therefore the protruding surface, thereby improving conductivity.

[0048] The refrigerator extends into the portion of the cryopanel assembly furthest from the inlet.

[0049] By mounting the cryopanel assembly to the refrigerator such that the refrigerator extends into the cryopanel assembly away from the inlet, the likelihood of the refrigerator assembly being affected by gas molecules is reduced. Additionally, because the majority of the cryopanel assembly is above the refrigerator, a significant length of the structure is not shielded by the refrigerator at all, thereby improving conductivity. The refrigerator extends into the half of the cryopanel assembly farthest from the inlet.

[0050] In some embodiments, the cryopanels are coated with carbon to adsorb some type III gases, such as hydrogen.

[0051] Further particular and preferred aspects are set out in the dependent and dependent claims. Features from the dependent claims may be combined with features of the independent claims as appropriate or in combinations other than those explicitly set out in the claims.

[0052] Where features of a device are described as operable to provide a certain functionality, this should be understood to include features of a device that provide that functionality or that are adapted or configured to provide that functionality. Embodiments of the present invention are further described below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0053] [Figure 1] 1 illustrates a first stage array according to one embodiment. [Figure 2] 1 illustrates a second stage cryopanel structure attached to a refrigerator element and spanning the first stage array, according to one embodiment. [Figure 3] 1 illustrates a cryopump according to one embodiment. [Figure 4] 1 shows a cross section through a cryopump according to one embodiment. [Figure 5] 1 shows a further cross section through a cryopump according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0054] Before describing the embodiments in detail, an overview will be given first. As new implant processes are developed and a more consistent vacuum environment is required to maintain the vacuum conditions of the process, the demands on the cryopumps are becoming more stringent.

[0055] The inventors have recognized that the cryopump array geometry is important for improving the vacuum conditions provided by the cryopump. Taking the "implant" process as an example, cryopumps are often used to generate the necessary high vacuum, hydrogen is the primary gas component, and contamination from photoresist is a major issue. Embodiments provide one or more of three major design improvements to impart contamination resistance and increase hydrogen pumping speed.

[0056] 1) Cryopanel Optimization: The geometry of the second stage array has been redesigned to be more elongated and narrower than previous models, improving hydrogen pumping performance. The second stage array is protected from gas contamination and radiation by the "igloo" first stage array. The cryopanel structure and igloo array are geometrically designed to complement each other, enhancing thermal and type I gas shielding while improving type III gas conductivity.

[0057] 2) The geometric design of the first stage or "igloo" inlet baffle provides high hydrogen performance and excellent resistance to gas contamination of the second stage array.

[0058] 3) Refrigerator Location: The refrigerator is strategically lower within the vessel than conventional designs, allowing for better gas conductivity and creating a longer array pumping path with fewer first strike contaminant strikes. In addition to being lower within the vessel, the refrigerator has a smaller penetration cross-section, improving conductivity.

[0059] The above design changes are intended to achieve higher pumping speeds, especially for type III gases, less contamination of the second stage array, lower radiation loads on the second stage, and lower temperatures in the first stage or igloo array, all of which contribute to a more stable vacuum pump.

[0060] The location of the refrigerator near the bottom of the vacuum vessel is one aspect to improve the overall performance of the pump. 1) Good conductivity: There is less shielding of type II or type III gases such as hydrogen entering the pump, allowing more gas to reach the cryopanel.

[0061] 2) A unified cryopanel / mount design for the second stage is possible. Cryopanel symmetry improves pumping uniformity for Type II / III gases across the cryopanel surface. This uniformity is crucial for Type II / III gas pumping speed and capacity, leaving all panels available for more uniform delivery of these gases without overwhelming any panel with gas. If localized saturation occurs due to non-uniform cryopanel design, this renders those panels unavailable for more molecules to enter. This results in an unbalanced pumping condition, as the remaining cryopanels are overloaded, causing the cryopump to pressure up faster than expected and rapidly reducing the pumping speed of Type III gases.

[0062] 3) The refrigerator cylinder is located low within the pump and, in conjunction with the enhanced Igloo inlet array, shields the cryopanels from unwanted radiation and many first-strike photoresist contaminations. The inlet array design is attached to a thermally conductive element extending from the first stage of the refrigerator, allowing it to be maintained at a lower temperature than a typical inlet array configuration coupled to a radiation shield.

[0063] FIG. 1 shows an igloo-shaped first-stage array 10 according to one embodiment. The array is formed of multiple elements 12, 14 arranged at increasing distances from the inlet to the pump. The element closest to the pump is the disk 12, and additional elements 14 of increasing size are arranged at increasing distances from the inlet to the pump. This igloo-shaped inlet baffle or array is attached to the first stage of the refrigeration elements via a thermally conductive member 36 (see FIG. 2). This thermally conductive member allows the igloo to be maintained at a temperature close to that of the first-stage refrigeration elements, reducing hot spots on the igloo surface and allowing the surface to remain at a reduced temperature, thereby providing improved capture of Type I gases. Additionally, the radiation shield can be cooled compared to a radiation shield coupled to a conventional first-stage array that extends across the inlet, thus also providing improved capture of Type I gases. In this embodiment, the disk 12 is a solid disk; in other embodiments, the disk 12 can have openings in the disk to allow some molecules to pass through. In some cases, these openings may be shielded to some extent by flaps that extend partially across the openings and are angled to deflect molecules towards the radiation shield.

[0064] 2 shows the first stage array 10 spanning the sidewall of the pump vessel and coupled to refrigerator elements 30 supporting the second stage cryopanel assembly 20. The second stage cryopanel assembly 20 extends into the first stage array 10 such that the elements of the first stage array 10 surround the portion of the second stage cryopanel assembly 20 closest to the inlet. This improves shielding of this portion of the cryopanel assembly, reduces the probability of gas molecules contacting high portions, and improves the uniformity of molecule capture along the length of the cryopanel assembly, thereby increasing the life and effectiveness of the cryopanel assembly.

[0065] Refrigerator elements 30 extend into the enclosure and constitute the first stage refrigerator elements at the temperature of the first stage, which are coupled to the first stage array 10 via thermally conductive mounts 36, allowing the first stage array to be maintained at or near the temperature of the first stage refrigerator elements in a uniform and effective manner. Thermally conductive mounts 36 extend around the periphery of the first stage array, contacting each element at two points and providing effective cooling for the array.

[0066] The second stage cryopanel assembly is attached to the second stage refrigerator element and is therefore cooled to the temperature of the second stage. The refrigerator element 30 extends into the lower portion of the pump vessel away from the inlet and supports the lower half of the cryopanel assembly such that the upper half of the cryopanel assembly is not shielded from the gas molecules entering the pump. This in turn leads to better distribution of the gas molecules over the cryopanel assembly.

[0067] The cryopanel structure 20 is longer and thinner than conventional cryopanel structures, which improves conductivity and uniformity of Type II and III gas capture and allows better access to the bottom of the cryopanels. Additionally, the lower location of the refrigerator relative to the pump inlet improves conductivity and increases pumping speed.

[0068] FIG. 3 is a view through the pump inlet 40. As can be seen, the interior surface of the pump vessel includes an inner element 42, which is a radiation shield. When viewed through the inlet, the first stage array effectively shields the second stage array when viewed perpendicularly through the inlet, protecting it from radiative loading and process-induced contaminants. The axial spacing between elements allows access to the cryopanel by molecules with a velocity component parallel to the inlet, as deflected by the radiation shield 42. Molecules deflected by the radiation shield will primarily be Type II or Type III gases, as the radiation shield traps Type I gases. The lower portion of the cryopanel structure is not surrounded by the front array, allowing easier access to this portion by molecules traveling deeper within the pump.

[0069] 4 is a side view of the pump housing with a portion cut away to reveal the interior. As can be seen, the refrigerator 30 extends to the bottom of the pump housing away from the inlet, with the first stage of the refrigerator element 34 thermally coupled to a thermally conductive mount 36 that carries the radiation shield 42 and the first stage array 10.

[0070] Thermally conductive mounts 36 extend around the igloo structure, contacting each element at two 180-degree opposed locations, providing good thermal coupling between these elements and the first stage of the refrigerator elements. In this way, there is a good thermal path directly from the first stage refrigerator elements to each element in the first stage array, enabling the array to be maintained at a cool and uniform temperature.

[0071] The second stage refrigerator 32 is coupled to second stage cryopanels (not shown) to maintain them at a lower second stage temperature. The refrigerator elements 30 are positioned toward the bottom of the pump vessel, thus reducing gas blockage due to the refrigerator elements extending into the pump.

[0072] FIG. 5 is a cross-sectional view of the pump showing the first stage array 10, the refrigerator element 30, and how they are coupled. In particular, the refrigerator element is shown held within the pump housing and coupled to the radiation shield. The radiation shield is now flattened to provide a sealed interface with the flat flange of the refrigerator element, and above the interface, the radiation shield has a protrusion 44 that reflects this flattening and provides a surface against which molecules can impinge and be deflected toward the inlet. In this embodiment, the protrusion is reduced in size compared to conventional cryopumps, designed to extend into the cylinder by less than 8% of the cylinder diameter, and in most embodiments, less than 6%. This reduces obstruction to gas molecules entering the pump, improving pumping speed.

[0073] Figure 5 shows the temperature difference between different parts of the first stage. The first stage refrigerator elements are the coldest part at approximately 65 K, the first stage array is maintained at a temperature of 71-72.5 K, and the radiation shield is cooler toward the refrigerator side, but reaches temperatures above 75 K on the opposite side. In a conventional cryopump where the first stage array is adjacent to the inlet, this inlet array reflects the temperature of the warmer part of the radiation shield, which is above 75 K. Thus, embodiments provide a cooler first stage array with a more uniform temperature than conventional cryopumps, improving trapping of type I gases.

[0074] To summarize conventional cryopump designs, the second stage array is shielded by a planar radiation baffle, or front array, attached to the inlet. This baffle is attached adjacent to the inlet and on top of the radiation shield. Like a large umbrella, gas molecules are blocked and repelled from the pump before they approach the second stage array. Additionally, the refrigerator cylinder and first stage mount are traditionally located high on the pump, blocking many Type II and III molecules, such as hydrogen, from reaching the second stage array.

[0075] In contrast, embodiments provide a second stage array shielded by multiple inlet radiation baffles positioned at different distances from the inlet within the pump. This array configuration blocks fewer molecules at the pump inlet, allowing more molecules to arrive at a position where they will impinge on the surface of the second stage array. This design also improves shielding of the second stage array from Type I gases, reducing contamination and radiation exposure of the second stage. The second stage array is enhanced in a trinity of combinations with the shape of the first stage array and the placement of the bottom refrigerator.

[0076] Although exemplary embodiments of the present invention are disclosed in detail herein with reference to the accompanying drawings, it should be understood that the present invention is not limited to the precise embodiments, and that various changes and modifications may be made by those skilled in the art without departing from the scope of the present invention as defined by the appended claims and their equivalents. [Explanation of symbols]

[0077] 10 First Stage Array 12 disk elements 14 Ring-shaped elements 20 Cryopanel structure 30 Refrigerator element 32 Second stage refrigerator element 34 First stage refrigerator element 36 First stage array mount 40 Entrance 42 Radiation Shield 44 Radiation shield protrusion

Claims

1. A cryopump comprising: a container including an open front area, the open front area including an entrance to the container; A radiation shield; a two-stage refrigerator extending into the sidewall of the vessel at a portion of the sidewall remote from the inlet, the portion of the sidewall at a point closer to the closed end of the vessel than the inlet, a first stage of the two-stage refrigerator thermally coupled to the radiation shield; a first stage array disposed within the vessel and thermally coupled to the first stage of the two-stage refrigerator through mounting elements extending within the radiation shield from the two-stage refrigerator toward the inlet; a cryopanel structure coupled to a second stage of the two-stage refrigerator; Equipped with the first stage array comprises a plurality of elements arranged at increasing distances from the inlet, one element of the plurality of elements closest to the inlet is located between the inlet and the cryopanel structure and has a smaller outer periphery than all other elements of the plurality of elements, each of the plurality of elements other than the element closest to the inlet has a passageway passing through a center of the element, and the mount element positions all of the plurality of elements at a position closer to the inlet than the two-stage refrigerator.

2. 2. The cryopump of claim 1, wherein the cryopanel structure has a diameter at its widest point that is less than 70% of the diameter of the vessel.

3. 3. The cryopump of claim 1, wherein the two-stage refrigerator extends into the vessel at a portion of the side wall that is at least 60% of the length of the vessel from the inlet.

4. 4. The cryopump according to claim 1, wherein the cryopanel structure has a length that is greater than 70% of the length of the vessel.

5. 5. The cryopump of claim 1, wherein the mounting element is formed from a thermally conductive material coupled to the first stage of the two-stage refrigerator and each of the plurality of elements of the first stage array.

6. 6. A cryopump as described in any one of claims 1 to 5, wherein one end of the cryopanel structure extends into the first stage array, and at least one of the elements further surrounds the outer periphery of the one end of the cryopanel structure from the inlet.

7. 7. A cryopump as described in any one of claims 1 to 6, wherein adjacent elements of the first stage array are configured such that, for at least some of the elements close to the inlet, the outer periphery of one element is substantially equal to or smaller than the inner periphery of a subsequent element located further away from the inlet.

8. 8. The cryopump of claim 1, wherein the first stage array has a substantially igloo shape, the elements being concentric, the element closest to the inlet having the smallest outer perimeter and subsequent elements having perimeters that increase in size with distance from the inlet.

9. 9. A cryopump according to claim 1, wherein the elements are substantially flat, the element closest to the inlet having a disk shape and the subsequent elements being rings.

10. 10. A cryopump as described in any one of claims 1 to 9, wherein the surface of the element facing the inlet is at an angle between 0 and 30 degrees with respect to the plane of the inlet and is either parallel to the plane or inclined so that the surface closest to the inlet faces the radiation shield.

11. 11. The cryopump of claim 1, wherein the elements of the first stage array farthest from the inlet are mounted nearest the first stage of the two-stage refrigerator, and a surface of the first stage array nearest the inlet is between 5 and 15% within the vessel.

12. 12. The cryopump of claim 11, wherein the first stage array extends from a point between 5 and 15% into the vessel to a point between 25 and 40% into the vessel.

13. 13. A cryopump as described in claim 6, or any of claims 6 to 12 when dependent on claim 6, wherein the cryopanel structure comprises a plurality of panels having a substantially cylindrical outer skin extending from a central axis and having at least one tapered end, one of the at least one tapered end extending into the first stage array.

14. 14. The cryopump of claim 13, wherein the portion of the cryopanel structure that extends into the first stage array comprises at least 20% of the cryopanel structure.

15. 15. The cryopump of claim 1, wherein the radiation shield is substantially cylindrical and includes a flat portion that extends into a cylinder for coupling to the two-stage refrigerator, the flat portion extending into the cylinder by less than 8% of a diameter of the cylinder.

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