US20220397322A1

US20220397322A1 - Cryogenic Cooling System

Info

Publication number: US20220397322A1
Application number: US17/347,741
Authority: US
Inventors: William S. Johnson
Original assignee: Applied Materials Inc
Current assignee: Applied Materials Inc
Priority date: 2021-06-15
Filing date: 2021-06-15
Publication date: 2022-12-15

Abstract

An improved cryogenic cooling system is disclosed. The cryogenic cooling system comprises a pressure sensing system disposed at or near the cryocooler to provide a more accurate representation of the pressure of the working gas within the cryocooler. By utilizing pressure measurements at the cryocooler, the thermal performance and net cooling capacity of the system may be improved. This may also improve the life of the cryocooler. Further, in some embodiments, pressure sensing systems are disposed at both the compressor and the cryocooler. In these embodiments, performance issues and potential failures may be monitored.

Description

FIELD

This disclosure describes systems and method for controlling and monitoring a cryogenic cooling system.

BACKGROUND

Cryogenic cooling systems are used to reduce the temperature of an environment to extremely low temperatures. Traditional closed loop gaseous cryogenic cooling systems are made up of two components; a compressor which is used to pressurize a working gas, and a cryocooler, which employs a refrigeration mechanism that uses the changing pressure of the working gas to extract heat from a system. In some embodiments, cryocoolers may be used in cryogenic vacuum pumps, which remove gasses from a vacuum chamber by condensing gasses in the vacuum chamber onto the cold surfaces attached to the cryocooler.
In certain embodiments, the cryocooler operates using a Gifford-McMahon cycle. In a Gifford-McMahon cycle, a working gas at two different pressures is utilized to perform heat exchange. The working gas in the supply line may be at a first pressure, while the working gas in the return line may be at a second pressure, lower than the first pressure. In some embodiments, the pressure difference between the first pressure and the second pressure is directly related to the cooling ability of the cryocooler. In other words, a cryogenic pump achieves the desired refrigeration by the expansion of the working gas within the cryocooler. The cryocooler may include one or more stages. In embodiments where two stages are utilized, the temperature in the first stage may be between 50K and 80K and the temperature in the second stage may be lower, such as between 10K and 20K. In embodiments where a single stage is utilized, the temperature may be as low as 40K.
Further, in certain embodiments, the compressor and the cryocooler may be physically located very close to one another. However, in other embodiments, the compressor and the cryocooler may be physically separated, such as by 10 meters or more. Additionally, in certain embodiments, the compressor may be used to provide pressurized gas to a plurality of cryocoolers.
Consequently, in certain embodiments, it is possible that the pressure of the working gas at the cryocooler is different than the pressure of the working gas at the compressor. This difference may affect the performance of the cryocooler.
Therefore, it would be advantageous if there were a system and method that improved cryocooler performance and net cooling capacity. Further, it would be beneficial if this system allowed the cryocooler and compressor to be physically separate with no degradation in performance.

SUMMARY

An improved cryogenic cooling system is disclosed. The cryogenic cooling system comprises a pressure sensing system disposed at or near the cryocooler to provide a more accurate representation of the pressure of the working gas within the cryocooler. By utilizing pressure measurements at the cryocooler, the thermal performance, net cooling capacity and/or efficiency of the cooling system may be improved. This may also improve the life of the cryocooler. Further, in some embodiments, pressure sensing systems are disposed at both the compressor and the cryocooler. In these embodiments, performance issues and potential failures may be monitored.
According to one embodiment, a cryogenic cooling system is disclosed. The cryogenic cooling system comprises a compressor; a cryocooler; a supply conduit and a return conduit connecting the compressor and the cryocooler; and a first pressure sensing system disposed at or proximate the cryocooler to measure at least one of: differential pressure between the supply conduit and the return conduit; pressure of the supply conduit; pressure of the return conduit. In certain embodiments, the cryogenic cooling system comprises a controller in communication with the first pressure sensing system. In some embodiments, the first pressure sensing system measures differential pressure between the supply conduit and the return conduit at or proximate the cryocooler. In certain embodiments, the compressor is regulated based on the differential pressure between the supply conduit and the return conduit measured at or proximate the cryocooler. In some embodiments, the controller detects impending failures in the cryocooler based on the differential pressure between the supply conduit and the return conduit at or proximate the cryocooler. In certain embodiments, the controller monitors the differential pressure over time to detect impending failures. In some embodiments, the controller monitors the differential pressure over time, creates a pressure vs. time curve and compares the pressure vs. time curve to a library of curves that represent different failure modes. In some embodiments, the cryogenic cooling system comprises a flow rate sensor to measure a flow rate of working gas in the supply conduit or the return conduit, and wherein the flow rate is used in conjunction with the differential pressure to detect an impending failure. In certain embodiments, the cryogenic cooling system comprises comprising a second cryocooler in communication with the supply conduit and the return conduit and having a first pressure sensing system disposed at or proximate the second cryocooler to measure at least one of: differential pressure between the supply conduit and the return conduit; pressure of the supply conduit; and pressure of the return conduit. In some embodiments, the compressor is regulated to achieve a minimum differential pressure between the supply conduit and the return conduit measured at or proximate the cryocooler and measured at or proximate the second cryocooler. In certain embodiments, the cryocooler comprises a valving system in communication with the supply conduit, the return conduit and a cylinder within the cryocooler, and wherein the first pressure sensing system comprises a pressure sensor in communication with the cylinder, such that the pressure sensor measures the pressure within the supply conduit or the return conduit, based on a state of the valving system.
According to another embodiment, a cryogenic cooling system is disclosed. The cryogenic cooling system comprises a compressor; a cryocooler; a supply conduit and a return conduit connecting the compressor and the cryocooler; a first pressure sensing system disposed at or proximate the cryocooler to measure at least one of: differential pressure between the supply conduit and the return conduit; pressure of the supply conduit; and pressure of the return conduit; and a second pressure sensing system disposed at or proximate the compressor to measure at least one of: differential pressure between the supply conduit and the return conduit; pressure of the supply conduit; and pressure of the return conduit. In certain embodiments, the cryogenic cooling system comprises a controller in communication with the first pressure sensing system and the second pressure sensing system. In certain embodiments, the first pressure sensing system and the second sensing system measure differential pressure between the supply conduit and the return conduit. In some embodiments, the controller estimates a pressure drop through the supply conduit or return conduit based on the differential pressure measured by the first pressure sensing system and the second pressure sensing system. In certain embodiments, the controller performs an action if the pressure drop through the supply conduit or return conduit is greater than a predetermined value. In certain embodiments, the pressure drop through the supply conduit or return conduit is determined based on measurements from the first pressure sensing system and the second pressure sensing system. In certain embodiments, the controller performs an action if the pressure drop through the supply conduit or return conduit is greater than a predetermined value. In certain embodiments, the controller monitors the pressure drop over time, creates a pressure vs. time curve and compares the pressure vs. time curve to a library of curves that represent different failure modes.
According to another embodiment, an ion implantation system is disclosed. The ion implantation system comprises an ion source to generate an ion beam; a processing chamber comprising a platen on which a workpiece may be disposed; beam line components to guide the ion beam from the ion source to the processing chamber; and a cryogenic cooling system in communication with the processing chamber, wherein the cryogenic cooling system comprises: a compressor; a cryocooler; a supply conduit and a return conduit connecting the compressor and the cryocooler; and a first pressure sensing system disposed at or proximate the cryocooler to measure at least one of: differential pressure between the supply conduit and the return conduit; pressure of the supply conduit; and pressure of the return conduit.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding of the present disclosure, reference is made to the accompanying drawings, which are incorporated herein by reference and in which:

FIG. 1 shows a cryogenic cooling system according to one embodiment;

FIG. 2 shows a P-V graph indicative of the operation of the cryocooler; and

FIG. 3 shows a cryogenic cooling system according to another embodiment;

FIG. 4 shows a cryogenic cooling system with multiple cryocoolers according to another embodiment; and

FIG. 5 shows an ion implantation system that utilizes the cryogenic cooling system described herein.

DETAILED DESCRIPTION

The present disclosure describes an improved cryogenic cooling system. FIG. 1 shows this improved cryogenic cooling system according to a first embodiment. The cryogenic cooling system 10 comprises two main components; a compressor 20 and a cryocooler 50.
A supply conduit 30 and a return conduit 40 are in fluid communication with the compressor 20 and the cryocooler 50.
The compressor 20 is used to pressurize a working gas, such as helium or hydrogen, to a first pressure. In certain embodiments, the first pressure may be 400 psi or more. This working gas at the first pressure is directed through the supply conduit 30 toward the cryocooler 50. After exiting the cryocooler 50, the working gas in the return conduit 40 may be a pressure that is less than the first pressure, such as 200 psi. In certain embodiments, the compressor 20 attempts to maintain a differential pressure between the working gas in the supply conduit 30 and the working gas in the return conduit 40.
In certain embodiments, one or more couplings 35 may be used to attach the supply conduit 30 to the compressor 20 and the cryocooler 50. Additionally, though not shown, couplings 35 may be used to attach segments of conduit together to create a supply conduit 30 of the desired length. Similarly, one or more couplings 45 may be used to attach the return conduit 40 to the compressor 20 and the cryocooler 50. Additionally, though not shown, couplings 45 may be used to attach segments of conduit together to create a return conduit 40 of the desired length.
As shown in FIG. 1 , the cryocooler 50 comprises a movable displacer 55 disposed in a cylinder 60. The movable displacer 55 is driven by a motor 90. The motor 90 may be electric or pneumatic. In certain embodiments, the motor 90 may exist within the working gas volume and include a displacer drive seal 91. The connection between the motor 90 and the movable displacer 55 may exist within the volume of the return path. Thus, to prevent the working gas from flowing directly from the supply conduit 30 to the return conduit 40, displacer drive seals 91 are utilized. The cryocooler 50 also comprises a valving system 70 such that either the working gas from the supply conduit 30 is in fluid communication with the cylinder 60, or the working gas from the return conduit 40 is in fluid communication with the cylinder 60. The valving system 70 may comprise two separate valves 71, as shown in FIGS. 1 and 3 , or may comprise a single valve that selects between the supply conduit 30 and the return conduit 40.
Additionally, a regenerator material 65 may be disposed in the cryocooler 50 along the path through which the working gas travels. In certain embodiments, the regenerator material 65 may be disposed in the cylinder 60, or in the movable displacer 55.
In certain embodiments, a second and/or third stage may be employed, featuring additional volumes and displacers mechanically tied together to provide the system the ability to achieve lower temperatures.
Next, the operation of the cryocooler 50 will be described in reference to FIG. 1 and FIG. 2 , which illustrates the changes in the pressure and volume of the working gas during the cycle.
In operation, the valving system 70 is first configured to allow working gas from the supply conduit 30 to enter the cylinder 60. At this time, the movable displacer 55 may be at or near the first position where the displaced volume 62 in the cylinder 60 is at or near a minimum. This is shown as point 105 in FIG. 2 . As working gas from the supply conduit 30 enters the cylinder 60, it passes through the regenerator material 65, losing heat to the regenerator material 65. The working gas causes the pressure within the cylinder 60 and displaced volume 62 to increase, as shown in line 110, until it reaches a state where the pressure is at or near the pressure of the supply conduit 30 and the volume is at or near a minimum volume, as shown in point 120.
Also, at this time, the movable displacer 55 moves so as to expand the displaced volume 62. Thus, the volume in the displaced volume 62 increases while pressure stays roughly constant. This change in volume is shown in line 130 in FIG. 2 . The movable displacer 55 reaches the second position where the displaced volume 62 is at or near a maximum, designated at point 140 in FIG. 2 . At or near this time, the valving system 70 switches to allow the cylinder 60 to be in fluid communication with the return conduit 40. The change in pressure within the cylinder 60 causes a decrease in temperature, which results in cooling. This change in pressure is shown in line 150 of FIG. 2 and results in the state shown at point 160. As the working gas exits the cylinder 60, it passes through the regenerator material 65, which loses its heat to the working gas. While the valving system 70 remains in this position, the movable displacer 55 moves toward the first position, reducing the displaced volume 62. This change in volume is shown in line 170 and result in the state shown at point 105. The process then repeats.
The amount of cooling may be related to the area enclosed in the graph shown in FIG. 2 . The amount of cooling is also related to the frequency of the movable displacer 55, which determines how often the cycle shown in FIG. 2 is executed. Given that the maximum volume of displaced volume 62 is fixed, the amount of cooling is most affected by the difference in pressure between the supply conduit 30 and the return conduit 40, and the frequency of the movable displacer 55.
Thus, in one embodiment, a first pressure sensing system 80 may be disposed at or near the cryocooler 50. In certain embodiments, the cryocooler 50 may include manifolding 51 within the cryocooler assembly, and the first pressure sensing system 80 may be disposed in the manifolding 51. In another embodiment, the first pressure sensing system 80 may be disposed at the couplings that are used to attach the cryocooler 50 to the supply conduit 30 and the return conduit 40. In another embodiment the sensors may be integrated into the valving system 70. In yet another embodiment, multiple cryocoolers 50 may be disposed near one another with shared manifolding and the first pressure sensing system 80 may be disposed at the shared manifolding. In each embodiment, the first pressure sensing system 80 is disposed as close as practical to the cryocooler 50. In certain embodiments, the first pressure sensing system 80 may be disposed at the coupling between the conduits and the cryocooler 50 or even closer to the cryocooler 50, and optionally within the cryocooler 50. Thus, as used in this disclosure, the phrase “at or proximate the cryocooler” is intended to denote any configuration where the first pressure sensing system 80 is disposed within the cryocooler 50, in the manifolding 51 of the cryocooler 50, or at the attachment points for the supply conduit 30 and the return conduit 40. In another embodiment, shown in FIG. 3 , the first pressure sensing system 80 may be in fluid communication with the warmer end of the cylinder 60.
In one embodiment, the first pressure sensing system 80 comprises a differential pressure sensor adapted to measure the difference in pressure between the supply conduit 30 and the return conduit 40 at or near the entrance to the cryocooler 50. In another embodiment, the first pressure sensing system 80 may comprise two pressure sensors, one to measure the pressure of each conduit. The pressure sensors may measure absolute pressure (i.e. the pressure relative to vacuum) or gauge pressure (i.e. the pressure relative to atmospheric pressure). Throughout this disclosure, the term “pressure” is meant to denote absolute pressure or gauge pressure, as distinguished from differential pressure.
In the embodiment shown in FIG. 3 , a single pressure sensor may be in fluid communication with the cylinder 60, such as the warmer end of the cylinder 60. This pressure sensor may be used to measure the pressure within the cylinder 60 while the supply valve or return valve is open to their respective conduit. In this way, a single pressure sensor may be used to monitor both the pressure within the supply conduit 30 and the return conduit 40, based on the state of the valving system 70.
The output or outputs from the first pressure sensing system 80 may serve as inputs to a controller 100. The controller 100 may include a processing unit, such as a microcontroller, a personal computer, a special purpose controller, or another suitable processing unit. The controller 100 may also include a non-transitory storage element, such as a semiconductor memory, a magnetic memory, or another suitable memory. This non-transitory storage element may contain instructions and other data that allows the controller 100 to perform the functions described herein.
For example, the controller 100 may be used to control the compressor 20, so as to maintain the desired pressure differential at the cryocooler 50. While the controller 100 is shown as being external to the compressor 20, in some embodiments, the controller 100 may be integrated into the compressor 20 or the cryocooler 50.
Thus, according to one embodiment, a first pressure sensing system 80 is used in conjunction with a controller 100 to regulate the compressor 20 so as to maintain a desired pressure difference between the supply conduit 30 and the return conduit 40 at or near the cryocooler 50. In addition, the controller 100 may also control the frequency of the movable displacer 55 so as to achieve the desired temperature on the cold end 61 of the cryocooler 50.
In certain embodiments, the compressor 20 may include a second pressure sensing system 21. In some embodiments, the second pressure sensing system 21 may be a differential pressure sensor, that measures the pressure difference between the supply conduit 30 and the return conduit 40 at or near the entrance and exit from the compressor 20. In certain embodiments, the differential pressure sensor may measure the pressure difference between the point of connection of the return conduit 40 and a location between the compressor pump and the adsorber within the compressor 20. In another embodiment, the second pressure sensing system 21 may comprise two pressure sensors, one to measure the pressure of each conduit at or near the entrance and exit from the compressor 20. In yet another embodiment, the second pressure sensing system 21 may comprise one pressure sensor to measure the pressure of the supply conduit 30 at or near the exit from the compressor 20. Thus, as used in this disclosure, the phrase “at or proximate the compressor” is intended to denote any configuration where the second pressure sensing system 21 is disposed within the compressor 20, or at the attachment points for the supply conduit 30 and the return conduit 40.
If both pressure sensor systems comprise differential pressure sensors, the controller 100 may receive two inputs; the differential pressure at or near the compressor 20 from the second pressure sensing system 21, and the differential pressure at or near the cryocooler 50 from the first pressure sensing system 80. The controller 100 may then estimate the pressure drop through the supply conduit 30 and the return conduit 40. For example, if the pressure differential at the compressor 20 is 200 psi, and the pressure differential at the cryocooler 50 is 180 psi, the controller 100 may assume that the pressure drop through each conduit is equal and therefore each conduit represents a pressure drop of 10 psi.
In certain embodiments, both pressure sensor systems comprise at least two pressure sensors; a first to measure the pressure of the supply conduit 30 and a second to measure the return conduit 40. In these embodiments, the controller 100 may receive at least four inputs and may directly calculate the pressure drop through each conduit.
In certain embodiments, the second pressure sensing system 21 allows a pressure sensing of either the supply conduit 30 or the return conduit 40. In these embodiments, the first pressure sensing system 80 may comprise at least one pressure sensor to measure the pressure of the same conduit at or near the cryocooler 50. This configuration allows the controller 100 to receive pressure readings from both ends of one of the conduits and calculate the pressure drop through the conduit. The controller 100 may then estimate that the pressure drop through the other conduit is roughly equal to the calculated pressure drop.
Thus, in each of these embodiments, the controller 100 may be able to determine or estimate the pressure drop through the supply conduit 30 and the return conduit 40. In doing so, the controller 100 may be better able to control and monitor the cryogenic cooling system 10.
For example, as stated above, in one embodiment, the compressor 20 is controlled based on the pressure differential measured at or near the cryocooler 50. This improves the net cooling capacity of the cryocooler 50. For example, as stated above, the cooling is a function of the pressure differential, the displaced volume and the frequency of the movable displacer 55.
Net cooling (Q) may be represented as:
Q=f*ΔP*V,
where f is the frequency of the movable displacer 55, V is the displaced volume 62, and ΔP is the difference in pressure between the supply conduit 30 and the return conduit 40, as seen by the cryocooler 50.
Thus, if the pressure differential is controlled based on measurements made at the cryocooler 50, as opposed to measurements made at the compressor 20, the pressure differential may be higher. Consequently, to achieve the same cooling, the frequency of the movable displacer 55 may be reduced. Also, the system may vary the pressure at the cryocooler 50 so as to cause the reciprocating frequency of the compressor 20 to be optimized for higher or lower heat loads.
In certain embodiments, the first pressure sensing system 80 is used in conjunction with the second pressure sensing system 21 to regulate the compressor 20. For example, the controller 100 may use the values from the first pressure sensing system 80 to control the compressor 20, but may also use the second pressure sensing system as a backup or a failover system.
Additionally, the first pressure sensing system 80 may be used to monitor and diagnose performance issues in the cryocooler 50. For example, a differential pressure drop outside an expected range of values may be indicative of an impending failure. For example, in certain embodiments, an application specific threshold may be adopted. In one embodiment, this application specific threshold may be a drop in the differential pressure of greater than 10%. Specifically, an unexpected differential pressure may be indicative of a leak within the cylinder 60, such as a faulty displacer drive seal 91 or faulty valve 71 within valving system 70. Alternatively, an unexpected differential pressure may be indicative that the working gas is flowing directly from the supply conduit 30 to the return conduit 40, a condition referred to as blow-by. Additionally, an unexpected differential pressure may be indicative of clogging of the movable displacer 55. Thus, in certain embodiments, the controller 100 may take an action upon detecting a differential pressure that is outside an expected range of values.
Furthermore, providing pressure sensing at the cryocooler 50, in addition to pressure sensing at the compressor 20 has other applications. As described above, by utilizing a first pressure sensing system 80 and a second pressure sensing system 21, it is possible for the controller 100 to determine or estimate the pressure drop through each conduit.
For example, if the controller detects a large pressure drop through one or both of the conduits, this may be indicative of an issue with the conduits. In certain embodiments, a pressure drop of more than a predetermined threshold may be indicative of an issue. In some embodiments, that predetermined threshold may be more than 10 PSI and may be adjusted for installation specific geometry such as line length, line diameter, line material, and number of couplings. For example, a kink or obstruction in a conduit would result in a large pressure drop through the conduit. Additionally, an incorrectly installed coupling may cause such a large pressure drop due to the self sealing refrigerant fittings not opening completely. Additionally, a conduit of excessive length may result in a large pressure drop.
In certain embodiments, a flow rate sensor 37 may be incorporated into the cryogenic cooling system 10. For example, a flow rate sensor 37 may be disposed to measure the flow rate of the working gas in the supply conduit 30 or the return conduit 40. In other embodiments, the flow rate sensor 37 may be disposed in the cryocooler 50 or compressor 20.
Thus, in certain embodiments, the controller 100 may utilize the first pressure sensing system 80 and the second pressure sensing system 21 in conjunction with other operating parameters such as the flow rate of the working gas, as measured by the flow rate sensor 37, to determine a specific mode of failure. For example, a high flow with a small differential pressure may be indicative of a condition where the working gas is bypassing the displacer drive seals 91 or any combination of the valves 71 within the valving system 70.
Additionally, the first pressure sensing system 80 and the second pressure sensing system 21 may be utilized with the controller 100 to generate pressure vs time curves for either the differential pressure or the pressure at the cryocooler 50, the supply conduit 30 or return conduit 40. The controller 100 may compare these pressure vs time curves to a library of identified failure mode curves for the purpose of diagnostics. In one example, the controller 100 may detect a subtle change in differential pressure or pressure at the supply or return that occurs over time. This may be indicative of a failing or clogged valve 71 in the valving system 70. Alternatively, this may be indicative of a failing displacer drive seal 91.
Alternatively, a simpler approach of monitoring for a change in pressure over a particular time period may be employed.
Thus, in some embodiments, the controller 100 measures or estimates the pressure drop through the supply conduit 30 and/or the return conduit 40, and performs an action if the pressure drop exceeds a predetermined value.
The actions described above may take many forms. In one embodiment, the action may comprise an alert to an operator. This alert may be visual, such as a warning light, a message on a display unit, a message over a communication path to a host control system, a signal relay or similar element to signal a failure to the host control system or another electronic, fiber optic, or pneumatic means of communicating with a host control system. Alternatively, the alert may be audio, such as a warning tone. In another embodiment, the action may be to disable the compressor 20 and/or the cryocooler 50 until the issue has been addressed.
FIG. 4 shows another embodiment. In this embodiment, the compressor 20 is used to supply working gas to multiple cryocoolers 50. A first pressure sensing system 80 is disposed at or near each cryocooler 50. The outputs from each of these first pressure sensing systems 80 is in communication with the controller 100. By having visibility to different first pressure sensing systems 80, the controller 100 is better able to monitor the activities of each cryocooler 50. For example, the controller 100 may regulate the compressor 20 such that the differential pressure at each cryocooler 50 is at least a predetermined minimum value. In this way, each cryocooler 50 is ensured to have a pressure differential that is equal to or greater than some predetermined minimum.
In addition, by having access to the pressure at the various cryocoolers 50, the controller 100 may be able to detect anomalies or other issues. For example, if the pressure (either differential, gauge or absolute) at one of the cryocoolers 50 is significantly different from the pressure at the other cryocoolers 50, this may signify one of the issues described above. Thus, the controller 100 may initiate an action if the pressure at one or more of the cryocoolers 50 is different from the pressure at other cryocoolers by more than a predetermined value.
The cryocooling system described herein may be used as a cryogenic pump in an ion implantation system. FIG. 5 shows a representative illustration of an ion implantation system that utilizes the cryogenic cooling system described here.
The ion implantation system includes an ion source 500. In certain embodiments, the ion source 500 may be an RF ion source. In another embodiment, the ion source 500 may be an indirectly heated cathode (IHC). Other embodiments are also possible. For example, the plasma may be generated in a different manner, such as by a Bernas ion source, a capacitively coupled plasma (CCP) source, microwave or ECR (electron-cyclotron-resonance) ion source. The manner in which the ions is generated is not limited by this disclosure.
One chamber wall, referred to as the extraction plate, includes an extraction aperture. The extraction aperture may be an opening through which the ions generated in the ion source chamber are extracted and directed toward a workpiece 510. The extraction aperture may be any suitable shape. In certain embodiments, the extraction aperture may be oval or rectangular shaped, having one dimension, referred to as the width (x-dimension), which may be much larger than the second dimension, referred to as the height (y-dimension). In certain embodiments, a ribbon ion beam is extracted from the ion source 500. In other embodiments, a spot ion beam is extracted from the ion source 500.
Disposed outside and proximate the extraction aperture of the ion source 500 are extraction optics 503. In certain embodiments, the extraction optics 503 comprises one or more electrodes. Each electrode may be a single electrically conductive component with an aperture disposed therein. Alternatively, each electrode may be comprised of two electrically conductive components that are spaced apart so as to create the aperture between the two components. The electrodes may be a metal, such as tungsten, molybdenum or titanium. One or more of the electrodes may be electrically connected to ground. In certain embodiments, one or more of the electrodes may be biased using an extraction power supply. The extraction power supply may be used to bias one or more of the electrodes relative to the ion source 500 so as to attract ions through the extraction aperture.
Located downstream from the extraction optics 503 is a mass analyzer 520. The mass analyzer 520 uses magnetic fields to guide the path of the extracted ions. The magnetic fields affect the flight path of ions according to their mass and charge. A mass resolving device 521 that has a resolving aperture 522 is disposed at the output, or distal end, of the mass analyzer 520.
By proper selection of the magnetic fields, only those ions that have a selected mass and charge will be directed through the resolving aperture 522. Other ions will strike the mass resolving device 521 or a wall of the mass analyzer 520 and will not travel any further in the system.
A collimator 585 is disposed downstream from the mass resolving device 521. The collimator 585 accepts the ions that pass through the resolving aperture 522 and creates a ribbon ion beam formed of a plurality of parallel or nearly parallel beamlets.
The extraction optics 503, the mass analyzer 520, the mass resolving device 521, and the collimator 585 may be considered beam line components that guide the ion beam from the ion source 500 to the processing chamber 590. Of course, the ion implantation system may include other beamline components, such as a scanner to create a ribbon beam from a spot ion beam, and additional electrodes to accelerate or decelerate the beam and other elements.
The final ion beam 555 impacts the workpiece 510 disposed on the platen 560 within a processing chamber 590. The processing chamber 590 may be maintained at near vacuum conditions, which may be less than 100 mTorr. In certain embodiments, the processing chamber 590 is maintained at less than 10 mTorr. In certain embodiments, the processing chamber 590 is maintained at less than 1E-4 Torr. The pressure within the processing chamber 590 may be such that the mean free path of molecules within the processing chamber 590 is at least greater than the dimension of the processing chamber 590. This may be achieved through the use of one or more cryogenic cooling systems 10 that are in communication with the processing chamber 590 and act as cryogenic pumps.
Thus, the cryogenic cooling systems described herein may be applied to ion implantation systems to create near vacuum conditions within a processing chamber.
The system described herein has many advantages. First, as described above, by regulating the compressor 20 to deliver the desired differential pressure at the cryocooler 50, it may be possible to reduce the frequency of the movable displacer 55. This may increase the life of the cryocooler 50, by reducing wear of internal seals, valves 71, motor 90, and/or rotary to linear translation mechanisms, such as scotch yokes.
Second, by having visibility to the differential pressure at the cryocooler 50, it may be possible for the controller 100 to identify issues, such as blow-by, failed valves 71, ruptured or worn seals, clogged compressor adsorber(s) and clogged displacers. In response, the controller 100 may initiate an action which allows the operator to address the issue in a timely manner.
Third, by having visibility to the pressure at both ends of the supply conduit 30 and/or return conduit 40, it is possible for the controller 100 to determine the pressure drop through the conduits. An unexpectedly high pressure drop may be indicative of an issue, such as an improperly installed coupling, a kink or obstruction in the conduit, or clogged compressor adsorber. In response, the controller may initiate an action which allows the operator to address the issue in a timely manner.
The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.

Claims

What is claimed is:

1. A cryogenic cooling system, comprising:

a compressor;

a cryocooler;

a supply conduit and a return conduit connecting the compressor and the cryocooler; and

a first pressure sensing system disposed at or proximate the cryocooler to measure at least one of:

differential pressure between the supply conduit and the return conduit;

pressure of the supply conduit; and

pressure of the return conduit.

2. The cryogenic cooling system of claim 1, further comprising a controller in communication with the first pressure sensing system.

3. The cryogenic cooling system of claim 2, wherein the first pressure sensing system measures differential pressure between the supply conduit and the return conduit at or proximate the cryocooler.

4. The cryogenic cooling system of claim 3, wherein the compressor is regulated based on the differential pressure between the supply conduit and the return conduit measured at or proximate the cryocooler.

5. The cryogenic cooling system of claim 3, wherein the controller detects impending failures in the cryocooler based on the differential pressure between the supply conduit and the return conduit at or proximate the cryocooler.

6. The cryogenic cooling system of claim 5, wherein the controller monitors the differential pressure over time to detect impending failures.

7. The cryogenic cooling system of claim 5, wherein the controller monitors the differential pressure over time, creates a pressure vs. time curve and compares the pressure vs. time curve to a library of curves that represent different failure modes.

8. The cryogenic cooling system of claim 5, further comprising a flow rate sensor to measure a flow rate of working gas in the supply conduit or the return conduit, and wherein the flow rate is used in conjunction with the differential pressure to detect an impending failure.

9. The cryogenic cooling system of claim 2, further comprising a second cryocooler in communication with the supply conduit and the return conduit and having a first pressure sensing system disposed at or proximate the second cryocooler to measure at least one of:

differential pressure between the supply conduit and the return conduit;

pressure of the supply conduit; and

pressure of the return conduit.

10. The cryogenic cooling system of claim 9, wherein the compressor is regulated to achieve a minimum differential pressure between the supply conduit and the return conduit measured at or proximate the cryocooler and measured at or proximate the second cryocooler.

11. The cryogenic cooling system of claim 1, wherein the cryocooler comprises a valving system in communication with the supply conduit, the return conduit and a cylinder within the cryocooler, and wherein the first pressure sensing system comprises a pressure sensor in communication with the cylinder, such that the pressure sensor measures the pressure within the supply conduit or the return conduit, based on a state of the valving system.

12. A cryogenic cooling system, comprising:

a compressor;

a cryocooler;

a supply conduit and a return conduit connecting the compressor and the cryocooler;

differential pressure between the supply conduit and the return conduit;

pressure of the supply conduit; and

pressure of the return conduit; and

a second pressure sensing system disposed at or proximate the compressor to measure at least one of:

differential pressure between the supply conduit and the return conduit;

pressure of the supply conduit; and

pressure of the return conduit.

13. The cryogenic cooling system of claim 12, further comprising a controller in communication with the first pressure sensing system and the second pressure sensing system.

14. The cryogenic cooling system of claim 13, wherein the first pressure sensing system and the second sensing system measure differential pressure between the supply conduit and the return conduit.

15. The cryogenic cooling system of claim 14, wherein the controller estimates a pressure drop through the supply conduit or return conduit based on the differential pressure measured by the first pressure sensing system and the second pressure sensing system.

16. The cryogenic cooling system of claim 15, wherein the controller performs an action if the pressure drop through the supply conduit or return conduit is greater than a predetermined value.

17. The cryogenic cooling system of claim 13, wherein a pressure drop through the supply conduit or return conduit is determined based on measurements from the first pressure sensing system and the second pressure sensing system.

18. The cryogenic cooling system of claim 17, wherein the controller performs an action if the pressure drop through the supply conduit or return conduit is greater than a predetermined value.

19. The cryogenic cooling system of claim 17, wherein the controller monitors the pressure drop over time, creates a pressure vs. time curve and compares the pressure vs. time curve to a library of curves that represent different failure modes.

20. An ion implantation system comprising:

an ion source to generate an ion beam;

a processing chamber comprising a platen on which a workpiece may be disposed;

beam line components to guide the ion beam from the ion source to the processing chamber; and

a cryogenic cooling system in communication with the processing chamber, wherein the cryogenic cooling system comprises:

a compressor;

a cryocooler;

differential pressure between the supply conduit and the return conduit;

pressure of the supply conduit; and

pressure of the return conduit.