Cryopump

Abstract

A cryopump comprising: a vessel (10) including a heat shield (12) having a front opening (22) that forms an inlet to the vessel (10); a front array (20) thermally coupled to the heat shield (12) and mounted across the front opening (22); a cryopanel structure (30) mounted within the vessel (10); and a two-stage refrigerator extending into the vessel (10), a first stage of the refrigerator comprising: a two stage refrigerator thermally coupled to a heat shield (12) and a cooler second stage of the refrigerator thermally coupled to the cryopanel structure (30), wherein the vessel (10) comprises an elongated vessel in which a distance (40) between a surface of the cryopanel structure (30) closest to the front opening (22) and a surface of the front array (20) closest to the cryopanel structure (30) is between 0.6 and 1.2 times the diameter of the front opening (22).

Description

[Technical Field]

[0001] The field of the invention relates to cryopumps. [Background technology]

[0002] Cryopumps, particularly two-stage cryopumps, are configured to provide high vacuum by trapping Type I gases, such as water vapor, at the temperature of the first stage and Type II gases, such as nitrogen, at the temperature of the second stage. In some cases, they are configured to cryoadsorb Type III gases, such as hydrogen.

[0003] When such cryopumps are used to pump semiconductor process chambers, it is important that the cryopump be able to store large amounts of Type II gas and still restore chamber pressure between wafers. The longer the pump can function (storing gas and restoring pressure) without needing to be regenerated, the more valuable the pump is to the user. The internal volume, frost point temperature, and shielding of the cryopump, as well as how efficiently it forms frost, determine the gas capacity that can be stored.

[0004] Conventional cryopumps have used the same vessel size and internal volume for many years, from the 10K or 11K top plate to the 100K sputter plate. Traditionally, such cryopumps have a front opening with an 8-inch (20 cm) internal diameter corresponding to the opening of the process chamber being evacuated. Over that time, new processes have emerged, increasing pump performance requirements as cryopump regeneration intervals are expected to increase. Enhancements to existing array designs and shielding have been made to increase pump capacity and vacuum stability. Summary of the Invention [Problem to be solved by the invention]

[0005] It would be desirable to further increase the capacity of cryopumps to trap Type II gases, thereby extending the capacity of such pumps and the time between regenerations. [Means for solving the problem]

[0006] A first aspect provides a cryopump comprising: a vessel including a heat shield having a front opening, the front opening forming an inlet to the vessel; a front array thermally coupled to the heat shield and mounted across the front opening; a cryopanel structure mounted within the vessel; and a two-stage refrigerator extending into the vessel, a first stage of the refrigerator thermally coupled to the heat shield and a cold second stage of the refrigerator thermally coupled to the cryopanel structure; wherein the vessel comprises an elongated vessel, and a distance between a surface of the cryopanel structure closest to the front opening and a surface of the front array closest to the cryopanel structure is between 0.6 and 1.2 times the diameter of the front opening.

[0007] As mentioned above, cryopumps are often used to create and maintain a vacuum within semiconductor process chambers, such as physical vapor deposition processes. In such processes, it is important that the vacuum be maintained at a high vacuum level and that this high vacuum be quickly re-established when wafers are replaced. Because cryopumps are trap pumps, they must be periodically regenerated. Since pump regeneration means the process chamber is unavailable during that time, it would be advantageous to reduce the frequency of regeneration.

[0008] The frequency of regeneration is related to the pump's capacity and the number of gas molecules it can capture before the pump's operation deteriorates. Gas molecules are trapped as frost on the cryopanel, which grows toward the front opening. As the frost grows, a temperature gradient develops across the length of the frost, and if the frost becomes too warm, gas molecules begin to release, reducing the effectiveness of the pump. Furthermore, when cryopumps are used in the semiconductor processing industry, it is desirable to provide a compact pump so that they can be designed to fit into the limited spaces associated with semiconductor processing factories.

[0009] Conventionally, cryopumps are configured with an 8-inch (20.3 cm) front opening, comparable to the opening of a semiconductor process chamber. They are also configured so that the length from the base to the front opening is approximately 1.2 times the diameter, or 24.6 cm (9.7 inches), and the length from the top of the cryopanel structure to the bottom of the front array is less than half the diameter of the front opening, or approximately 3.8 inches (9.6 cm).

[0010] The inventors have discovered that by elongating the vessel, specifically by increasing the distance between the cryopanel structure and the front array, the cryopump capacity, specifically the area in which frost is stored, can be increased while still effectively maintaining molecular trapping. Elongating the vessel by increasing this dimension provides additional space for the portion of the vessel that stores "frost" or trapped Type II gas. Furthermore, increasing the distance between the cryopanel structure and the front array allows the cryopanel structure to be further away from the front opening, which is a source of radiation, allowing the cryopanel structure to maintain a lower temperature, thus improving frost retention.

[0011] In some embodiments, the distance is between 0.7 and 0.9 times the diameter of the front opening.

[0012] In other embodiments, the distance is between 0.8 and 1.1 times the diameter of the front opening.

[0013] While the optimum length increase will depend on the circumstances, the pump configuration including the temperature of the second stage cryopanels and the effectiveness of the heat shield, and possibly the proposed use of the pump, in many situations it has been found that elongating the vessel so that the distance between the cryopanel structure and the front array is between 0.7 and 0.9 times the diameter of the front opening provides a particularly effective increase in storage capacity without unduly reducing gas capture stability.

[0014] In some embodiments, the diameter of the front opening is between 20 cm and 21 cm (7.8 inches and 8.2 inches) and the distance between the cryopanel structure and the front array is between 12 cm and 25 cm (4.7 inches and 10 inches).

[0015] In some embodiments, the second stage of the two-stage refrigerator is configured to maintain a temperature of the cryopanel below 9K.

[0016] As mentioned above, the storage capacity of a cryopump can be increased by increasing the volume available for storing frost. However, as frost grows toward the front opening, a temperature gradient develops across the length of the frost, and as this distance increases, it becomes increasingly difficult to maintain a low temperature in the portion of the frost closest to the front opening. Once the frost reaches a certain temperature, gas molecules begin to escape, reducing the efficiency of the pump. By providing a cryopanel structure with a low temperature, the length of the frost can be increased while the temperature of the surface away from the cryopanel remains low enough to firmly hold the gas molecules.

[0017] In some embodiments, the frontal array comprises a disc-shaped element and an annular element, the disc-shaped element and the annular element mounted axially displaced from one another, the annular element mounted closer to the front opening than the disc-shaped element, the diameter of the disc-shaped element being equal to or greater than the diameter of the opening in the annular element and less than the outer diameter of the annular element, and the outer diameter of the annular element being equal to or greater than the diameter of the front opening.

[0018] A further method for maintaining a low temperature within the vessel and protecting the increased volume of frost from radiation is to improve the effectiveness of the frontal array. By providing a frontal array with longitudinally displaced elements, the flow path into the vessel can be in an axial plane rather than a radial plane. This avoids or at least impedes line-of-sight flow into the vessel, protecting the vessel from external radiation and maintaining a lower temperature on top of the frost.

[0019] In some embodiments, the frontal array comprises an axially extending cylindrical element connecting the disc-shaped element and the annular element, the cylindrical element comprising a cylindrical surface, the cylindrical surface comprising a plurality of openings.

[0020] A further aspect provides a cryopump comprising: a vessel including a heat shield having a front opening forming an inlet to the vessel; a front array thermally coupled to the heat shield and mounted across the front opening; a cryopanel structure mounted within the vessel; and a two-stage refrigerator extending into the vessel, a first stage of the refrigerator thermally coupled to the heat shield and a cooler second stage of the refrigerator thermally coupled to the cryopanel structure, the second stage of the refrigerator configured to maintain a temperature of the cryopanel structure below 9 K.

[0021] A further aspect provides a cryopump comprising: a vessel including a heat shield having a front opening forming an inlet to the vessel; a frontal array thermally coupled to the heat shield and mounted across the front opening; a cryopanel structure mounted within the vessel; and a two-stage refrigerator extending into the vessel, a first stage of the refrigerator thermally coupled to the heat shield and a cooler second stage of the refrigerator thermally coupled to the cryopanel structure; the frontal array comprising a disk-shaped element and an annular element mounted axially displaced from one another, the annular element mounted closer to the front opening than the disk-shaped element, a diameter of the disk-shaped element equal to or greater than a diameter of the opening in the annular element and less than an outer diameter of the annular element, the outer diameter of the annular element equal to or greater than a diameter of the front opening.

[0022] In some embodiments, the frontal array comprises an axially extending cylindrical element connecting the disc-shaped element and the annular element, the cylindrical element comprising a cylindrical surface, the cylindrical surface comprising a plurality of openings.

[0023] Further particular and preferred aspects are set out in the dependent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate and in combinations other than those explicitly set out in the claims.

[0024] 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.

[0025] Embodiments of the present invention are further described below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a schematic diagram illustrating the difference between a conventional cryopump and a cryopump according to an embodiment. [Figure 2] 1 illustrates a schematic representation of a frontal array according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0027] Before describing the embodiments in detail, an overview will be given first.

[0028] Cryopumps, particularly those used in PVD (physical vapor deposition) processes, are required to store large amounts of Type II gas and restore chamber pressure between wafers. The longer a pump can operate (storing gas and restoring pressure) without the need for regeneration, the more valuable it is to users. Improvements have been made to conventional array designs and shielding to increase pump capacity and vacuum stability. These improvements have allowed for an increase in the physical volume available for frosting within the pump below the sputter plate. While these improvements have had some success in more efficiently utilizing the volume available for gas storage, they have not significantly increased the number of liters of gas that can be stored. To further increase the volume of pumps with conventional flange sizes, it has been proposed to elongate the pump, providing additional volume further from the front opening. In some embodiments, better heat shields and / or cooler second-stage cryopanels are provided to further increase gas storage capacity.

[0029] Essentially, the cryopump's internal volume, frost temperature, and shielding, as well as how efficiently the frost forms, determine the amount of gas that can be stored. Increasing the pump's effective gas volume by lengthening the vessel and cylindrical heat shield can increase capacity. Specifically, when lengthening is performed in conjunction with a refrigerator unit having an improved shielding sputter plate and / or a cooler second stage, storage capacity can be increased by up to 50%. Increasing the cryopump's volume is important for significantly increasing the storage capacity of Type II gases. Consequently, elongated cryopumps improve capacity and are particularly effective when configured with better shielding and / or a cooler second-stage cryopanel.

[0030] FIG. 1 shows a schematic comparison of a conventional cryopump on the left and a cryopump according to one embodiment on the right. The cryopump according to one embodiment has a longer and narrower vessel 10 compared to the conventional pump while utilizing the same vessel flange size. In some embodiments, the vessel length increases between 1 and 6 inches (2.5 and 15 cm). The narrower portion of the vessel is the portion surrounded by the radiation shield 12 and between the cryopanel structure 30 and the front array 20. This increased length increases the volume available for storing Type II gas as frost. It also increases the distance of the frost from the cryogenic cryopanel surface (~10 K to 100 K) to the sputter plate. In this way, the distance 40 between the top surface of the cryopanel structure 30 and the bottom surface of the front array increases, increasing the volume A available for frost storage.

[0031] In a conventional cryopump, shown schematically in the left-hand drawing and not to scale, the distance between the cryopanel structure and the front array is about half the diameter 42 of the front opening. In an embodiment, the vessel is elongated, increasing this distance to about 0.6 to 1.2 times the diameter, preferably between 0.7 and 0.9 times.

[0032] The cryopump includes a heat shield 12 that surrounds the frost storage area A. The heat shield extends between 0.6 and 1 inch (1.5 to 2.5 cm) above flange 15 to isolate the cryopump from the vacuum vessel.

[0033] The ability of the cryopump according to this embodiment to capture gas and subsequently recover pressure is increased by making the vessel 10 and heat shield 12 longer and increasing the internal length / volume of the heat shield 12. In this embodiment, the cryopump has a modified front array plate 20 across the front opening 22.

[0034] Additionally, the cryopump has a lower temperature second stage refrigerator that cools the cryopanel assembly 30. This lower temperature helps to lower the frost point temperature at the cryopanel assembly and correspondingly along the frost column, thereby compensating to some extent for the effect of increasing frost length on the top surface temperature of the frost.

[0035] As the frost grows and forms a longer column, it becomes more difficult to keep the top surface of the frost cool enough to suppress the release of gas molecules. Reducing the radiative heat load at the inlet by improving the shielding from the frontal array and / or reducing the temperature of the cryopanel structure and, consequently, the temperature at the bottom of the frost column, may each help to keep the temperature of the top surface of the frost column cool. If the temperature of the second stage of the refrigerator is reduced to below 10 K, preferably below 9 K, this helps to prevent or at least reduce the release of gas molecules.

[0036] A conventional front array plate 50 with holes in the form of louvers blocks most radiation but still allows some line-of-sight preferential pumping to occur. As the gas is pumped, it forms not a horizontally layered frost buildup, but rather crystalline vertical structures that look like threads. These crystalline "rods" begin to grow like millions of threads adhering to the cryopanel at the low temperature of ~10K, extending all the way to the 100K sputter plate or anything not below ~25K. Type II gas also pumps below the 10K cryopanel, forming on the lower panel and charcoal array, but in limited amounts.

[0037] The storage volume can be increased by increasing the length of the gas storage volume, lowering the temperature of the second stage cryopanels, and reducing radiative / preferential pumping of the gas. Furthermore, doing this by elongating the vessel is cheaper and easier to manufacture than building a larger vessel with a larger flange size.

[0038] The extensions can be from 1 inch up to 6 inches in length (2.5 cm to 15 cm).

[0039] The improved frontal array shielding and / or lower second stage temperatures are particularly useful in this embodiment, but are also applicable for use in other cryopumps.

[0040] FIG. 2 shows a frontal array of a conventional cryopump and a frontal array of one embodiment in more detail. The diagram on the left shows a conventional frontal array 50, and the diagram on the right shows a frontal array sputter plate 22 according to one embodiment, viewed from above (left) and below (right). As shown, there is an upper disk-shaped plate 20a and a lower annular plate 20b. The disk-shaped plate has a diameter larger than the diameter of the opening in the annular plate 20b. Between the upper disk-shaped plate 20a and the inner diameter of the lower annular plate 20b is a cylindrical element 20c with openings 21. These openings are in an axially extending wall; in this way, there is no direct line of sight between the interior and exterior of the vessel, allowing for effective shielding of frost within the vessel from radiation.

[0041] Although exemplary embodiments of the present invention are disclosed in detail herein with reference to the accompanying drawings, it should be understood that the invention is not limited to the precise embodiments, and that various changes and modifications may result 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]

[0042] 10 Cryopump container 12 Heat shield 15 flange 20 Front Array 20a Upper circular plate 20b Annular plate 20c Cylindrical element 21 Aperture 22 Front opening 30 Cryopanel structure 40 Length between cryopanel structure and front array 42 Diameter of front opening 50 Conventional front array

Claims

1. A cryopump comprising: a vessel including a heat shield having a front opening, the front opening forming an entrance to the vessel; a front array thermally coupled to the heat shield and mounted across the front opening; a cryopanel structure mounted in the vessel; a two-stage refrigerator extending into the vessel, a first stage of the refrigerator thermally coupled to the heat shield and a cooler second stage of the refrigerator thermally coupled to the cryopanel structure; Equipped with the vessel comprises an elongated vessel, wherein a distance between a surface of the cryopanel structure closest to the front opening and a surface of the front array closest to the cryopanel structure is between 0.6 and 1.2 times the diameter of the front opening; a cryopump, wherein the front array comprises a disk-shaped element and an annular element, the disk-shaped element and the annular element mounted axially displaced from each other, the annular element mounted closer to the front opening than the disk-shaped element, the diameter of the disk-shaped element being equal to or greater than the diameter of the opening of the annular element and less than the outer diameter of the annular element, and the outer diameter of the annular element being equal to or greater than the diameter of the front opening.

2. 2. The cryopump of claim 1, wherein the distance is between 0.7 and 0.9 times the diameter of the front opening.

3. 2. The cryopump of claim 1, wherein the diameter of the front opening is between 20 cm and 21 cm (7.8 inches and 8.2 inches) and the distance between the cryopanel structure and the front array is between 12 cm and 25 cm (4.7 inches and 10 inches).

4. 2. The cryopump of claim 1, wherein the second stage of the two-stage refrigerator is configured to maintain a temperature of the cryopanel structure below 9K.

5. 2. The cryopump of claim 1, wherein the frontal array comprises an axially extending cylindrical element, the cylindrical element connecting the disk-shaped element and the annular element, the cylindrical element comprising a cylindrical surface, the cylindrical surface comprising a plurality of openings.

6. A cryopump, a vessel including a heat shield having a front opening, the front opening forming an entrance to the vessel; a front array thermally coupled to the heat shield and mounted across the front opening; a cryopanel structure mounted in the vessel; a two-stage refrigerator extending into the vessel, a first stage of the refrigerator thermally coupled to the heat shield and a cooler second stage of the refrigerator thermally coupled to the cryopanel structure; Equipped with a cryopump, wherein the front array comprises a disk-shaped element and an annular element, the disk-shaped element and the annular element mounted axially displaced from each other, the annular element mounted closer to the front opening than the disk-shaped element, the diameter of the disk-shaped element being equal to or greater than the diameter of the opening of the annular element and less than the outer diameter of the annular element, and the outer diameter of the annular element being equal to or greater than the diameter of the front opening.

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