Flow restrictor, cryopump and method of upgrading the cryopump

Abstract

This invention discloses a flow restrictor for limiting the flow rate of gas flowing into a cryogenic pump, and the cryogenic pump itself. The flow restrictor is configured to be installed in an inlet of the cryogenic pump and includes: an inlet assembly for providing a gas flow path into the cryogenic pump; a baffle plate installed to at least partially block the gas flow path through the inlet assembly; and an intermediate assembly connecting the baffle plate to the inlet assembly, the intermediate assembly including at least one aperture defining at least one gas flow path into the cryogenic pump. The baffle plate is configured to block the gas flow path through the inlet assembly such that, when installed on the cryogenic pump, there is no direct visual path through the inlet assembly to a cryogenic plate within the cryogenic pump.

Description

Technical Field

[0001] The field of this invention relates to cryogenic pumps and inlet flow restrictors for cryogenic pumps. Prior Technology

[0002] Flow restrictors or throttling plates are used to limit gas inflow into a cryogenic pump to limit pumping speed in processes such as PVD (Physical Vapor Deposition) and maintain a desired pressure in the processing chamber. These flow restrictors typically have multiple orifices of varying geometries through which Type II and Type III gases enter the pump, and whose size and number control flow rate or velocity. One potential problem with plates with orifices or openings is that, during viscous or continuous flow, the orifices are within the line of sight of the second-stage cryogenic plate in the pump, increasing radiative heat load and potentially causing preferential gas pumping at these points. Preferential gas pumping can cause a column of gas molecules condensing into "frost" to grow upwards from the second-stage cryogenic plate to the plate opening, especially during high gas flow rates. As the column moves further away from the cryogenic plate, it becomes warmer, receives an increased radiative load, and can begin to release gas, thus increasing the pressure in the chamber. The vapor pressure of the Type II gas rises due to the radiative load and / or the increase in the temperature of the warmer column, and the pressure in the pump / chamber subsequently increases. Type II gases are gases (such as nitrogen) that condense at the temperature of the second-stage cryogenic plate of a cryogenic pump, while Type III gases do not condense at such temperatures and are generally captured by an adsorbent on the cryogenic plate.

[0003] Figure 1 illustrates an example of a cryogenic pump according to prior art, having a throttling or flow-limiting plate 5. The flow-limiting plate 5 sits across the pump inlet and includes a plurality of orifices 7 through which gas flows into the pump. The size of the orifices is selected according to the desired pumping speed. The pump is a cryogenic pump and has a refrigeration unit 15, which has a first refrigeration heat exchange station 10 connected to the inner shell of the pump, the inner shell of the pump being insulated from the outer shell of the vacuum container 9. It also has a second-stage heat exchange station 11 connected to a second-stage cryogenic plate 12 and other adsorbent cryogenic plates 13. The upper cryogenic plate 12 will experience frost buildup 14 on its upper surface, with specific buildup forming a spiral at positions corresponding to the orifices 7. One potential problem with uneven frost buildup and radiant heat load is that pressure recovery inside the chamber takes longer and requires faster regeneration.

[0004] It is desirable to provide a cryogenic pump in which the time between regenerations is increased and the pressure recovery time inside the chamber is reduced. Summary of the Invention

[0005] A first embodiment provides a flow restrictor for limiting the flow rate of gas flowing into a cryogenic pump. The flow restrictor is configured to be installed in an inlet of the cryogenic pump. The flow restrictor includes: an inlet assembly for providing a gas flow path into the cryogenic pump; a baffle plate installed to at least partially block the gas flow path through the inlet assembly; and an intermediate assembly connecting the baffle plate to the inlet assembly. The intermediate assembly includes at least one aperture defining at least one gas flow path into the cryogenic pump. The baffle plate is configured to block the gas flow path through the inlet assembly such that, when installed on the cryogenic pump, there is no direct visual path through the inlet assembly to a cryogenic plate inside the cryogenic pump.

[0006] In some embodiments, the inlet assembly is located in a plane parallel to and offset from the baffle, such that when mounted on the cryogenic pump, the inlet assembly is located between the pressure chamber of the cryogenic pump and the baffle.

[0007] The inventors recognized the problems associated with a conventional flow restrictor mounted on the inlet of a cryogenic pump and solved these problems by providing a two-stage flow restrictor having an inlet assembly axially displaced from a baffle. The baffle blocks the inlet assembly to prevent gas from entering the pump through the inlet, forcing the gas to circulate around the baffle and through an intermediate assembly into the flow path. Therefore, gas entering the cryogenic pump is diverted around the baffle assembly through at least one orifice in the intermediate assembly and enters the flow path through the inlet assembly. In this way, the baffle element separates the direct line of sight of the inlet from the cryogenic plates and avoids the preferred pumping path provided by the orifices directly facing the cryogenic plates.

[0008] In some embodiments, the inlet assembly has an annular shape that defines an orifice, which defines the airflow path. The annular shape of the inlet assembly forming a single orifice provides more uniform flow across the cross-sectional area of ​​the inlet and helps to suppress preferential frost buildup at specific sites on the cryogenic plates.

[0009] In some embodiments, the intermediate component includes a plurality of pores.

[0010] The intermediate component may have a single orifice connecting the baffle and the inlet component, or it may have multiple orifices. The size and / or number of these orifices can be selected to limit the flow rate to a desired level depending on the requirements of the cryogenic pump. When multiple orifices are present, selecting both the size and number of orifices allows for precise control of the flow rate.

[0011] In some embodiments, one surface of the intermediate component including the at least one aperture forms an angle between 120° and 60° with the baffle.

[0012] It is advantageous that the intermediate component is angled relative to the baffle and the inlet component so that the orifices do not face directly toward the cryogenic plates. In this way, it is advantageous that it forms an angle between 60° and 120° with the plane of the baffle and, in some embodiments, is substantially perpendicular to the baffle.

[0013] In some embodiments, the intermediate component includes a cylinder.

[0014] In some embodiments, the outer periphery of one of the entry components extends beyond the outer periphery of one of the shields.

[0015] The advantageous geometry of the baffle and one of the inlet components allows the baffle to extend beyond the outer periphery of the inlet component, rather than extending all the way to the outer periphery of the orifice. In this way, the orifice is directly blocked by the baffle, but a path is provided for gas to enter the pump around the edge of the baffle and then through one of the intermediate components.

[0016] Although the geometry of the shield and the entrance assembly can take many forms such as rectangular, square or elliptical, in some embodiments the shield and the inner assembly have a substantially circular outer perimeter.

[0017] A circular cross-section in a cryogenic pump generally promotes more uniform flow.

[0018] In some embodiments, the at least one pore of the intermediate component is configured to limit the flow rate into the cryogenic pump to a predetermined flow rate.

[0019] The size and / or number of the pores in the intermediate component can be selected according to the desired flow rate of the procedure performed in the chamber evacuated by the cryogenic pump.

[0020] A second embodiment provides a cryogenic pump comprising: a pump inlet; a refrigeration unit; a cryogenic plate configured to be cooled by the refrigeration unit; and including a flow restrictor according to a first embodiment, the flow restrictor being installed in one inlet of the cryogenic pump such that the flow restrictor restricts the flow of gas into the inlet.

[0021] A third embodiment provides a method for upgrading a cryogenic pump, comprising: removing a throttle plate installed across an inlet of the cryogenic pump to limit the flow rate into the cryogenic pump; and replacing the throttle plate with a flow limiter according to a first embodiment.

[0022] Further specific and preferred embodiments are described in the appended independent and supplementary technical solutions. The features of the supplementary technical solutions may be appropriately combined with the features of the independent technical solutions, in addition to the combinations explicitly described in the technical solutions.

[0023] When a device feature is described as operable to provide a function, it should be understood that this includes a device feature that provides the function or is adapted or configured to provide the function. Simple Explanation of the Diagram

[0024] Embodiments of the present invention will now be further described with reference to the accompanying drawings, wherein:

[0025] Figure 1 shows a cryogenic pump and flow restrictor based on one of the prior art techniques;

[0026] Figure 2 shows a current limiter according to one embodiment;

[0027] Figure 3 shows a top view of one of the current limiters with the baffle removed;

[0028] Figure 4 shows a top view of a flow restrictor and a cryogenic pump including the flow restrictor according to one embodiment; and

[0029] Figure 5 shows a view of the interior of a self-pump toward the inlet of a flow restrictor according to one embodiment. Implementation

[0030] Before discussing the embodiments in more detail, an overview is provided first.

[0031] The embodiment provides a second-stage frost or cryogenic plate utilizing an indirect orifice / opening scheme, such as a throttling plate, sputtering plate, or flow restrictor, configured to suppress the negative pumping effects of Type II gas or radiation. The objective is to allow overall Type II gas storage on the second-stage cryogenic plate to increase the amount of Type II gas that can be stored. In this regard, more can be stored if the gas is pumped uniformly, and the gas partial pressure within the pump will increase if one area accumulates condensed gas faster than other areas.

[0032] In one embodiment, the flow restrictor serves as an orifice (having one or more openings) and allows Type II and Type III gases to enter the pump at a rate or velocity controlled by the size and number of orifices. It is configured such that the orifice is at an angle to the pump inlet and does not provide a direct line of sight to the cryogenic plate.

[0033] The cryogenic pump is configured such that the flow restrictor operates at a temperature between 45K and 110K, i.e., it is connected to the first stage of the two-stage refrigeration unit. In an embodiment, the flow restrictor is mounted on the inner wall of the pressurization chamber cooled by the first-stage heat exchange station. The second-stage cryogenic plate operates between 8K and 16K and may have charcoal or similar adsorbent material for pumping type III gases. The second-stage cryogenic plate may or may not be configured to shield type II gases from the adsorbent material used for type III gases. In this regard, plate 13 in the embodiment of FIG4 may include a charcoal-covered cryogenic plate shielded by the upper cryogenic plate 12.

[0034] The flow restrictor is designed to match the speed of Type II and Type III gas regulating pumps with the (PVD) programmed gas flow rate and achieve a predicted pressure within the vacuum chamber. The amount of the opening or orifice should be carefully designed to ensure the pump provides a predictable and consistent pumping rate. When a flow restrictor is used in a pump inlet, a higher vacuum is achieved below the flow restrictor opening, and a lower vacuum is achieved on the chamber side.

[0035] Flow restrictor or throttling plate pumps are primarily used in viscous or continuous flow patterns, such as in physical vapor deposition (PVD) processes. As the viscous flow reaches the flow restrictor, any opening / orifice in the second-stage cryogenic plate, which is either directly "facing" the pump, can cause preferential gas pumping. Cryogenic vacuum pumps always have a radiative heat load, but proper shielding can mitigate its impact on the second stage. Most cryogenic pumps have a high freezing capacity in their first stage; therefore, intercepting the heat load at the flow restrictor is advantageous. Most cryogenic pumps have a lower freezing capacity in their second stage, and high heat loads and non-uniform gas loads should be avoided. When preferential gas pumping is allowed through the inlet opening / orifice, the line-of-sight path grows a "spiral," which hinders pump efficiency over time. Therefore, suppressing viscous gas flow to allow it to enter through the flow restrictor in a direct path to the second stage is beneficial for improving pumping efficiency.

[0036] In this respect, cryogenic pumps are "capture" pumps; therefore, any gas pumped at a cryogenic pressure (below its vapor pressure) onto its surface will remain trapped until the cryogenic plate is "regenerated" or warmed to release it to the safety valve / roughing valve. All cryogenic pumps have a limited amount of gas that can be pumped before the pump pressure drops to the point where the desired process cannot proceed. When a particular process has a very high flow rate of one of the Type II gases, the pump stores this gas as frost on the second-stage plate, and when the frost reaches the flow restrictor or the condensed gas (frost) becomes too warm, the pump will not operate as intended. The time between regenerations is primarily controlled by the pump's maximum storage capacity for Type II gases and the gas flow rate. Capture is crucial for pump users because increased capture reduces the frequency of regeneration. Providing more uniform capture increases the amount of gas captured before the effect of condensed gas suppresses the pump's efficiency to the point where regeneration is required.

[0037] The flow restrictor or throttling plate of the embodiment has a top or baffle that can be circular but can be of any shape. The baffle may be smaller than the inlet plate and there exists a spacer or intermediate component between the two plates that allows Type II gas to enter the cryogenic pump. The flow path through the spacer may be substantially 90° to the pump inlet. The spacer or intermediate component separates the baffle from the inlet plate and provides a path for gas deflected by the baffle to flow into the pump between the two plates and across the outer edge of the inlet plate through an opening in the inlet plate. The opening may be circular, but it can be of any shape. The top or baffle may be suspended over the spacer to further shield radiation and unwanted gases from entering the cryogenic pump.

[0038] One configuration of the flow limiter in this way allows for reduced radiative heat load and provides overall defrosting pumping without the drawbacks of visual or priority gas pumping. This uneven gas load and reduced radiation on the second-stage cryogenic plate keep the second-stage cryogenic plate colder and increase gas trapping capacity.

[0039] This flow restrictor is designed to allow gas to be routed through openings / orifices of any shape within the intermediate spacer. This configuration allows for random gas pumping and provides a substantially uniform, monolithic frost buildup across the entire surface area of ​​the second-stage cryogenic plate. This monolithic gas pumping helps to prevent frost on the second-stage cryogenic plate from contacting the warmer first-stage radiation shield or flow restrictor.

[0040] The baffle is important for maximizing or at least increasing Type II gas frost pumping and radiation reduction to allow for longer regeneration intervals.

[0041] Figure 2 illustrates a flow restrictor 40 according to one embodiment. In this embodiment, the flow restrictor 40 has a circular cross-section and includes a baffle 1 mounted on an intermediate assembly 3 via a lower surface 1A. The intermediate assembly 3 is in the form of a cylinder having a perforation 3A around a longitudinal surface. The intermediate assembly 3 is mounted on an inlet assembly 2, which includes a protrusion 4 for mounting the flow restrictor 40 onto the inner wall of a cryogenic pump.

[0042] A flow restrictor 40 is installed at the inlet of the cryogenic pump and limits the flow rate entering the pump. A baffle 1 obstructs the view of the cryogenic plate inside the pump from the inlet, while an orifice 3A provides a path for gas to flow into the pump through one of the orifices in the middle of the inlet assembly 2. This provides substantially uniform flow across the cross-section of the airflow path provided by the orifice in assembly 2. The size and number of orifices 3A can be selected to restrict the flow of gas into the pump to a rate required to maintain the pressure within the pump at a desired rate.

[0043] Figure 3 shows a top view of the pump from which the baffle 1 has been removed. This shows the inlet assembly 2 with an orifice 2A providing a path for airflow into the pump. The upper surface of the intermediate spacer assembly 3 is also shown.

[0044] Figure 4 shows a cryogenic pump according to one embodiment with a flow restrictor mounted thereon. The flow restrictor is also shown as a side view and viewed from above, with the baffle 1 in place.

[0045] The cryogenic pump has a refrigeration unit 15, whose cooling is used to cool a first-stage refrigeration heat exchange station 10 on which a flow restrictor 40 is mounted, and a second-stage refrigeration heat exchange station 11 for cooling an upper cryogenic plate 12 and other cryogenic plates 13. These lower cryogenic plates may be coated with an adsorbent material for adsorbing type III gases. The upper plate 12 shields the lower plate 13 from type II gases, which condense on the upper plate 12.

[0046] This figure illustrates the accumulation of Type II condensed gas in the form of frost 14 formed by gas molecules trapped on cryogenic plate 12. It shows how, when the flow restrictor is in the appropriate position, a uniform accumulation of frost exists, allowing significantly more gas to be captured before the frost reaches the flow restrictor. This more uniform gas flow and the corresponding increase in time between uniform capture and the allowable regeneration of frost accumulation are achieved, in some embodiments, by up to 50%.

[0047] Figure 5 shows a view from below the flow restrictor, illustrating the cryogenic boss or support 4 used to mount the flow restrictor onto the inner shell of the cryogenic pump. Figure 5 also shows the baffle plate viewed through the orifice 2A in the inlet assembly 2. It can be seen that the baffle plate 1 completely blocks the orifice 2A to block the direct line of sight between the inside and outside of the pump.

[0048] The flow restrictor 40 of the embodiment is adapted to be installed in the inlet of a cryogenic pump, and in some embodiments, it is installed on the inner wall of the pump housing. In an embodiment, a cryogenic pump can be upgraded as follows: any existing throttling plate is removed and a flow restrictor 40 of one embodiment is placed in the inlet, such that the airflow entering the pump is redirected around the baffle plate through the intermediate assembly to the orifice in the inlet assembly, thereby providing a uniform airflow across the cross-section of the pump inlet.

[0049] Although illustrative embodiments of the invention have been disclosed in detail with reference to the accompanying drawings, it should be understood that the invention is not limited to the precise embodiments and that those skilled in the art can make various changes and modifications to it without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0050] 1: Blind 1A: Lower surface 2: Entry Component 2A: Orifice 3: Intermediate components 3A: Porosity 4: Protrusions / Cold / Warm Seats or Supports 5: Current limiting plate 7: Orifice 9: Vacuum container 10: First-stage chiller heat exchange station 11: Second-stage chiller heat exchange station 12: Second-stage cold temperature plate / upper low temperature plate 13: Adsorbent cold / warm plate / lower plate 14: Frost 14A: Frost Spiral 15: Refrigeration Unit 40: Current limiter

Claims

1. A flow restrictor (5) for limiting the flow rate of gas flowing into a cryogenic pump, the flow restrictor being configured to be installed in an inlet of the cryogenic pump, the flow restrictor comprising: An inlet assembly (2) includes an orifice (2A) for providing an airflow path into the cryogenic pump; a baffle (1) installed to block the airflow path through the inlet assembly; and an intermediate assembly (3) connecting the baffle to the inlet assembly, the intermediate assembly including a plurality of orifices (3A) defining an airflow path into the cryogenic pump; The inlet assembly is configured to lie in a plane parallel to the baffle and axially offset from the intermediate assembly, such that when installed in the inlet of the cryogenic pump, the inlet assembly is located between a pressurization chamber of the cryogenic pump and the baffle; the baffle is configured to block the airflow path through the orifice (2A) of the inlet assembly, such that when installed on the cryogenic pump, there is no direct visual path through the orifice (2A) of the inlet assembly to a cryogenic plate inside the cryogenic pump; wherein one outer periphery of the inlet assembly extends beyond one outer periphery of the baffle and one outer periphery of the baffle extends beyond one periphery of the orifice of the inlet assembly.

2. The flow restrictor of claim 1, wherein the inlet assembly has an annular shape that defines an orifice that defines the airflow path.

3. A current limiter as claimed in claim 1 or 2, wherein one surface of the intermediate component of the at least one aperture forms an angle between 120° and 60° with the baffle.

4. The flow limiter of claim 3, wherein the surface of the intermediate component of the at least one aperture is substantially perpendicular to the baffle.

5. A current limiter as requested in item 1 or 2, wherein the intermediate component comprises a cylinder.

6. A current limiter as claimed in claim 1 or 2, wherein the baffle and the inner component have a substantially circular outer periphery.

7. A flow limiter as claimed in claim 1 or 2, wherein the orifices of the intermediate component are configured to restrict the flow into the cryogenic pump to a predetermined flow rate.

8. A cryogenic pump, comprising: Pump inlet; One freezing unit; A low-temperature plate, configured to be cooled by the refrigeration unit; And a flow restrictor as described in any of the aforementioned claims 1 to 7, wherein the flow restrictor is installed in one of the inlets of the cryogenic pump such that the flow restrictor limits the airflow entering one of the inlets.

9. A method for upgrading a cryogenic pump, comprising: Remove a throttle plate that is installed across one of the inlets of the cryogenic pump to restrict the flow into the cryogenic pump; and replace the throttle plate with a flow restrictor as described in any of the aforementioned claims 1 to 7.

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