Patent Grant
7439654
Ultrasonic energy is used to promote mass transfer and chemical reactions in fluid systems for a wide variety of applications. One of these applications is ultrasonic cleaning, in which articles are immersed in a fluid bath while ultrasonic energy is introduced into the bath to enhance the cleaning process. Ultrasonic cleaning systems range from small countertop units used in dental offices and laboratories to large industrial units used in the food and chemical process industries. Ultrasonic cleaning systems also are used in the fabrication of electronic components to remove residues from parts and components following manufacturing steps such as lithography, etching, stripping, and chemical mechanical planarization. In another application, ultrasonic energy is used in sonochemical reactor systems to promote chemical reactions in fluid reaction media.
Many ultrasonic cleaning systems use a fluid bath at atmospheric pressure for immersing articles during cleaning. Other ultrasonic cleaning systems are operated at elevated pressures using pressurized liquids, condensing pressurized vapors, dense fluids, or supercritical fluids to effect cleaning of the articles in a pressurized vessel. Such pressurized ultrasonic cleaning systems are used, for example, in the electronics manufacturing industries to remove residues from parts and components during various fabrication steps. Pressurized ultrasonic processing systems may be used in the chemical industry to promote chemical reactions in sonochemical reaction systems.
Ultrasonic energy can be introduced into fluids by several methods. In one method, ultrasonic generators are submerged in the fluid and operated in situ to generate and transmit ultrasonic energy directly to the fluid. In another method, ultrasonic generators are attached to the outer surface of the vessel walls and the ultrasonic energy is transmitted through the vessel walls and into the fluid. In yet another method, ultrasonic energy is transmitted from external ultrasonic transducers via ultrasonic probes or horns passing through the vessel wall, wherein the ultrasonic energy is dissipated from the horns into the fluid.
The successful operation of high-pressure fluid processes with ultrasonic energy will require careful design of the ultrasonic probes that transmit the ultrasonic energy from an external transducer into the pressurized process fluid in a pressure vessel. There is a need in the art for new and improved designs for these ultrasonic probes and for appropriate seals to secure these probes in pressure vessel walls during pressurized operation.
These design requirements for ultrasonic probes and seals are met by the embodiments of the present invention. In one embodiment, a specifically designed ultrasonic probe comprises an elongate body having a first end and a second end, an ultrasonic transducer attached to the probe at or adjacent the first end, and an enlarged support section intermediate the ultrasonic transducer and the second end, wherein the enlarged support section has an equivalent diameter greater than an equivalent diameter of the body at any location between the enlarged support section and the ultrasonic transducer. This ultrasonic probe may be installed in a seal assembly which in turn may be installed in the wall of a pressure vessel.
The seal assembly comprises a seal body having a first end and a second end, an axis passing through the first end and the second end, and a coaxial cylindrical passage within the seal assembly between the first end and the second end. An elastomeric sealing ring is placed around the probe adjacent the enlarged support section and the ultrasonic probe is inserted in the passage in the seal assembly, wherein the elastomeric sealing ring is disposed between the enlarged support section of the probe and the second end of the seal assembly. When the seal assembly is installed in the wall of a pressurized vessel, the outward axial force on the probe caused by the pressure differential across the seal compresses the elastomeric sealing ring between the enlarged support section and the second end of the seal assembly. This forms a seal and also prevents the probe from being forced out of the seal body by the pressure differential.
An embodiment of the invention includes an ultrasonic probe comprising an elongate body having a first end and a second end, an ultrasonic transducer attached to the probe at or adjacent the first end, and an enlarged support section intermediate the ultrasonic transducer and the second end, wherein the enlarged support section has an equivalent diameter greater than an equivalent diameter of the body at any location between the enlarged support section and the ultrasonic transducer. The ultrasonic transducer may be a piezoelectric transducer or a magnetostrictive transducer. When the ultrasonic transducer is a magnetostrictive transducer, it may be formed by an electrical coil wrapped around a section of the probe between the first end and the enlarged support section. The probe may comprise a metal or metal alloy.
The probe may have a circular cross section at any location between the first end and the second end, the cross section being defined as a section perpendicular to an axis defined by the first end and the second end. At least a portion of the probe between the enlarged support section and the second end may be cylindrical, wherein the diameter of the probe decreases discontinuously in this portion. Alternatively, the probe may have a circular cross section at all locations between the enlarged support section and the second end, wherein the diameter of the probe decreases continuously between the enlarged support section and the second end. The ratio of the distance between the first end and the enlarged support section to the distance from the enlarged support section to the second end may be between 1:10 and 10:1 Optionally, the probe may further comprise a detachable tip attached to the second end of the probe.
A related embodiment of the invention includes an ultrasonic probe comprising an elongate body having a first end and a second end, an ultrasonic transducer attached to the probe at or adjacent the first end, a cylindrical collar support section intermediate the ultrasonic transducer and the second end, wherein the probe is cylindrical between the first end and the collar support section, and wherein the collar support section has a diameter greater than diameter of the cylinder between the collar support section and the ultrasonic transducer.
An alternative embodiment relates to an ultrasonic probe comprising
The distance between the outer edge of the first longitudinal shoulder support section and the outer edge of the second longitudinal shoulder support section may be greater than the thickness of the planar body at any location between the longitudinal shoulder supports and the first end, the thickness of the planar body being defined as the perpendicular distance between the first and second sides.
In another embodiment of the invention, an ultrasonic probe assembly comprises
The cylindrical section of the ultrasonic probe typically extends beyond the first end of the seal body; the ultrasonic probe assembly may further comprise a compression fitting adapted to grip the ultrasonic probe and the first end of the seal body to maintain the ultrasonic probe in a coaxial position in the cylindrical passage of the seal assembly. The ultrasonic probe and the seal body may comprise a metal or metal alloy. The ultrasonic probe assembly may further comprise a transducer assembly attached to the first end thereof.
The elastomeric torroidal seal ring may comprise an elastomer selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, polyvinylidene fluoride, perfluoroalkoxy, polyethylene, unplasticized polyvinyl chloride, acrylonitrile butadiene styrene, acetal, cellulose acetate butyrate, nylon, polypropylene, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyamide, polyimide, thermosetting plastic, natural rubber, hard rubber, chloroprene, neoprene, styrene rubber, nitrile rubber, butyl rubber, silicone rubber, chlorosulfonated polyethylene, polychlorotrifluoroethylene, polyvinyl chloride elastomer, cis-polybutadiene, cis-polyisoprene, ethylene-propylene rubbers, carbon, and graphite.
The compression fitting may include a torroidal elastomeric ferrule comprising an elastomer typically selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, polyvinylidene fluoride, perfluoroalkoxy, polyethylene, unplasticized polyvinyl chloride, acrylonitrile butadiene styrene, acetal, cellulose acetate butyrate, nylon, polypropylene, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyamide, polyimide, thermosetting plastic, natural rubber, hard rubber, chloroprene, neoprene, styrene rubber, nitrile rubber, butyl rubber, silicone rubber, chlorosulfonated polyethylene, polychlorotrifluoroethylene, polyvinyl chloride elastomer, cis-polybutadiene, cis-polyisoprene, ethylene-propylene rubber, carbon, and graphite.
Another embodiment of the invention includes an ultrasonic processing system comprising
The cylindrical section of the ultrasonic probe typically extends beyond the first end of the seal body and the ultrasonic probe assembly may further comprise a compression fitting adapted to grip the ultrasonic probe and the first end of the seal body to maintain the ultrasonic probe in a coaxial position in the cylindrical passage of the seal assembly. The ultrasonic probe assembly may further comprise a transducer assembly attached to the first end thereof.
The pressure vessel may further comprise an inlet for introducing a fresh cleaning fluid into the pressure vessel and an outlet for withdrawing a contaminated cleaning fluid from the pressure vessel. The pressure vessel may further comprise an inlet port for introducing one or more contaminated articles into the pressure vessel and an outlet port for withdrawing one or more cleaned articles from the pressure vessel.
Another related embodiment of the invention includes a method of providing ultrasonic energy to a pressurized fluid comprising
The pressure of the pressurized fluid in the interior of the pressure vessel may be in the range of 10−3 to 680 atma. The ultrasonic energy typically is provided in a frequency range of 20 KHz to 2 MHz. The ultrasonic energy may be provided at a power density in the range of 0.1 to 10,000 W/in2.
The pressurized fluid may comprise one or more components selected from the group consisting of carbon dioxide, nitrogen, methane, oxygen, ozone, argon, hydrogen, helium, ammonia, nitrous oxide, hydrogen fluoride, hydrogen chloride, sulfur trioxide, sulfur hexafluoride, nitrogen trifluoride, monofluoromethane, difluoromethane, tetrafluoromethane, trifluoromethane, trifluoroethane, tetrafluoroethane, pentafluoroethane, perfluoropropane, pentafluoropropane, hexafluoroethane, hexafluoropropylene, hexafluorobutadiene, octafluorocyclobutane, and tetrafluorochloroethane. The pressurized fluid may further comprise one or more processing agents selected from a group consisting of an acetylenic alcohol, an acetylenic diol, a dialkyl ester, hydrogen fluoride, hydrogen chloride, chlorine trifluoride, nitrogen trifluoride, hexafluoropropylene, hexafluorobutadiene, octafluorocyclobutane tetrafluorochloroethane, fluoroxytrifluoromethane (CF4O), bis(difluoroxy)methane (CF4O2), cyanuric fluoride (C3F3N3), oxalyl fluoride (C2F2O2), nitrosyl fluoride (FNO), carbonyl fluoride (CF2O), perfluoromethylamine (CF5N), an ester, an ether, an alcohol, a nitrile, a hydrated nitrile, a glycol, a monester glycol, a ketone, a fluorinated ketone, a tertiary amine, an alkanolamine, an amide, a carbonate, a carboxylic acid, an alkane diol, an alkane, a peroxide, a water, an urea, a haloalkane, a haloalkene, a beta-diketone, a carboxylic acid, an oxine, a tertiary amine, a tertiary diamine, a tertiary triamine, a nitrile, a beta-ketoimine, an ethylenediamine tetraacetic acid and derivatives thereof, a catechol, a choline-containing compound, a trifluoroacetic anhydride, an oxime, a dithiocarbamate, and combinations thereof.
The method may further comprise providing a sealable opening in the pressure vessel adapted to insert and withdraw one or more articles, inserting one or more contaminated articles into the pressure vessel prior to (b), cleaning the one or more contaminated articles during (c) and (d), depressurizing the pressure vessel by withdrawing a contaminated fluid therefrom, and withdrawing one or more cleaned articles therefrom. The fluid may comprise at least one component which undergoes a chemical reaction that is promoted by the ultrasonic energy introduced into the pressure vessel. The shoulder support section of the ultrasonic probe typically is located at a vibrational node between the first and second ends of the ultrasonic probe.
Another embodiment of the invention includes method for cleaning a contaminated wafer comprising:
The wafer may define a first plane and the ultrasonic probe may define a second plane, and the included angle between the first plane and the second plane may be between 10 degrees and 90 degrees.
Embodiments of the present invention are illustrated by the following drawings, which are not necessarily to scale.
The design of an ultrasonic probe for use in transmitting ultrasonic energy from an external transducer into a process fluid in a pressurized vessel must meet several important criteria. First, an appropriate seal assembly is required to seal the probe at the vessel wall to prevent leakage of the pressurized fluid from the vessel interior. Second, because the probe is vibrating at very high frequencies, it must be mounted in the seal assembly such that the high-frequency vibrations do not destroy the seal where the probe passes through the vessel wall. Third, the seal assembly design must ensure that the probe is held in place and is not subject to blowout because of a large pressure differential between the pressurized vessel interior and the surrounding atmosphere. In addition, the probe and seal assembly must be readily removable for seal maintenance and replacement of components when required. The various embodiments of the present invention address these design criteria as described below.
A first embodiment of an ultrasonic probe is shown in
Main probe body 1 is fitted at one end thereof (which is the first end of the probe) with ultrasonic transducer 3 in attached to the probe at junction or connection point 9. Ultrasonic transducer 3 may be joined or connected to the end of main probe body 1 at point 9 by any appropriate means to ensure proper ultrasonic contact. For example, the ultrasonic transducer may be bolted to the end of main probe body 1 by any type of bolt or bolt assembly (not shown) as is known in the art. The term ultrasonic contact is defined herein as any method of joining the transducer and probe body such that vibrational energy generated by the transducer is transmitted directly to the probe without significant energy loss or dissipation and without any significant change in the frequency and intensity of the ultrasonic vibrations. The term “without significant energy loss” as used here means that at least 75% of the sonic energy generated by the transducer is transferred to the end of main probe body 1 at point 9.
Horn 7 operates as a booster to increase the amplitude of the ultrasonic waves generated by transducer 3 and transmitted by main probe body 1. The amplitude increases as the waves travel into progressively narrower sections of horn 7, and this focuses the ultrasonic energy for increased power density. For a stepped horn design illustrated by
The equivalent diameter of collar support section 5 is greater than the equivalent diameter of main probe body 1 for reasons described later. Horn 7 may be stepped as shown wherein the diameter of the horn decreases discontinuously between collar support section 5 and the second end of the probe. Alternatively, the diameter of the horn may decrease continuously between collar support section 5 and the second end of the probe. Other horn configurations may be used and typically the diameters of all sections of the horn are less than the diameter of main probe body 1.
Ultrasonic transducer 3, which is shown schematically, may be a piezoelectric crystal or crystal assembly activated by alternating current supplied via conductors 11 and 13. These crystals oscillate at ultrasonic frequencies in the range of 20 KHz to 2 MHz and are commercially available in many different configurations. Alternatively, ultrasonic transducer 3 may be a magnetostrictive transducer assembly comprising iron or nickel surrounded by an electromagnetic coil attached to conductors 11 and 13 wherein the alternating magnetic field induces ultrasonic vibrations in the transducer.
An alternative embodiment of the probe is shown in
The ultrasonic probes described above are designed to fit into a seal assembly for mounting the probe in the wall of a pressure vessel. An axial section of an exemplary seal assembly and probe is illustrated in
Threaded section 317 is designed to be sealably inserted into a threaded opening in the wall of a pressure vessel (not shown). Alternatively, instead of using threaded section 317, the seal body may be flanged at second end 311 and the flange designed to seal to a corresponding flanged opening in the wall of the pressure vessel. In another alternative, end 311 of seal body 303 may be welded directly to the opening in the pressure vessel. The outer diameters of seal ring 319 and collar support section 5 typically are smaller than the inner diameter of the threaded or flanged opening in the wall of the pressure vessel so that the probe can pass through the opening in the pressure vessel during installation.
Seal ring 319 is disposed between threaded section 317 and collar support section 5. This torroidal seal ring may have a thin front section which fits into the annulus between the outer surface of probe body 1 and the inner surface of the bore in seal body 303. The seal ring may have a thicker rear section which fits between second end 311 and an inner surface of collar support section 5. The dimensions of collar support section 5 should be designed appropriately for the anticipated differential operating pressure across the seal (i.e., the pressure difference between the interior of the pressure vessel and atmospheric pressure) formed by seal ring 319, collar support section 5, and the face of second end 311 of seal body 303. The radial height of collar support section 5, which is the distance that the collar support projects outward radially from, should be sufficient to avoid failure of the collar support section by compression. The axial thickness of collar support section 5 should be sufficient to avoid collar failure due to the axial shear caused by the pressure differential. The ratio of the distance between the end of probe body 1 and collar support section 5 to the distance from collar support section 5 to the end of horn 7 may be between 1:10 and 10:1
Ferrule 309 forms a packing gland in combination with follower ring 321 and threaded compression nut 323. Seal body 303, tapered throat 307, ferrule 309, follower ring 321, threaded compression nut 323, seal ring 319, second end 311, and collar support section 5 work in combination to locate main probe body 1 firmly and coaxially within the bore of seal body 303 such that the outer surface of main probe body 1 does not contact the inner surface of the bore in seal body 303. In addition, second end 311, seal ring 319, and collar support section 5 work in combination to seal main probe body 1 to seal body 303. These elements provide the sealing and centering functions for main probe body 1 by forcing collar support 5 axially against seal ring 319 and forcing seal ring 319 against second end 311, while simultaneously tightening compression nut 323 on threads 315 to push follower ring 321 against ferrule 309 and push ferrule 309 into tapered throat 307. The seal assembly then may be sealably threaded into a threaded opening in the wall of a pressure vessel. Alternatively, if seal body 303 is flanged at second end 311 instead of using threaded section 317, the flange is sealed to a corresponding flanged opening in the wall of the pressure vessel.
When the probe assembly is sealed into the pressure vessel and the vessel is pressurized with a high pressure fluid, the pressure differential between the vessel interior and the surrounding atmosphere forces collar support 5 axially against seal ring 319 and forces seal ring 319 against second end 311, thereby forming a pressure-activated seal. Thus increasing the pressure in the vessel will increase the force of collar support 5 axially against seal ring 319 and the force of seal ring 319 against second end 311.
The probe may be ultrasonically vibrated by means of an ultrasonic transducer attached to threaded stud 301 as described later. Ferrule 309 and seal ring 319 preferably are elastomeric materials which serve to isolate the vibrating probe body 1 from the fixed seal body 303. In addition, as described above, seal ring 319 seals probe body 1 to seal body 303 at end 311. Ferrule 309 and seal ring 319 may comprise any elastomeric material and may be selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, polyvinylidene fluoride, perfluoroalkoxy, polyethylene, unplasticized polyvinyl chloride, acrylonitrile butadiene styrene, acetal, cellulose acetate butyrate, nylon, polypropylene, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyamide, polyimide, thermosetting plastic, natural rubber, hard rubber, chloroprene, neoprene, styrene rubber, nitrile rubber, butyl rubber, silicone rubber, chlorosulfonated polyethylene, polychlorotrifluoroethylene, polyvinyl chloride elastomer, cis-polybutadiene, cis-polyisoprene, ethylene-propylene rubber, carbon, and graphite.
The various elements of the probe and seal assembly of
The end of horn 7 may have a detachable tip of any shape. In one embodiment, the detachable tip may have the same diameter as the end of horn 7. In other embodiments, the detachable tip may have other geometries that are designed to direct or radiate ultrasonic energy in a particular manner for a given application.
Main probe body 1 and horn 7 vibrate or oscillate as ultrasonic waves pass from an ultrasonic generator attached to threaded stud 301 to the tip of horn 7. The amplitude of the axially-directed oscillations varies along the length of the main probe body and horn and is a function of the probe and horn geometry. The amplitude reaches maxima at the vibrational antinodes and reaches minima at the vibrational nodes. The seal assembly of
The probe and seal assembly of
The probe and seal assembly of
The pressure vessel of
Larger and more complex pressure vessel systems may be required for commercial ultrasonic cleaning applications. An example of an advanced ultrasonic cleaning system using the ultrasonic probe and seal assembly systems, described above is illustrated in
Multiple probe and seal assemblies are mounted in vessel lid 503. In this illustration, four assemblies are installed in a radial configuration to expose the rotating wafer to uniform ultrasonic energy waves 514. The four assemblies include ultrasonic transducers 515, 517, 519, and 521 and probes 523, 525, 527, and 529, wherein each probe includes main probe body 1, collar support section 5, and horn 7 as illustrated in
Pressurized fluid for the cleaning process is introduced through inlet line 539 at the center of vessel lid 503, flows radially through the interior of the vessel, under circular baffle 541, and exits via multiple outlet lines 543 located around the outer edge of the vessel. The pressurized fluid alternatively may be introduced via a shower head, multiple inlet tubes, or other inlet devices known in the art. The flow of cleaning fluid continuously sweeps contaminants, reactants, and undesirable contaminants from the surface of the wafer and out through the multiple outlets. The internal volume of vessel 501 should be minimized to minimize processing time and materials requirements.
In order to expose the surface of wafer 509 to a uniform level of ultrasonic energy, the power settings of the transducers may be maintained at different levels at the different radial locations such that transducer 515 has the highest setting and transducer 521 has the lowest setting. The tangential velocity of the wafer is lower near the center and higher near the periphery, and the power settings for transducers 515, 517, 519, and 521 may be selected to provide a relatively uniform time-integrated exposure to ultrasonic energy across the entire wafer surface.
A schematic sectional side view of the system of
An alternative probe geometry may be used in which the probe is planar rather than cylindrical as described in
Planar probe 701 may be installed in pressure vessel wall 719 by means of two parallel seal assemblies 721 and 723, which are sealed or welded to pressure vessel wall 719 at parallel joints 725 and 727 formed between the seal assembly and the vessel wall. Seal assemblies 721 and 723 are mirror images of each other, and the following description of the elements of seal assembly 721 therefore applies to the corresponding elements of seal assembly 723. Seal assembly 721 comprises seal body 729, seal cap 731, seal bolt 732, seal bolt washer 733, seal nut 735, follower 737, elastomeric packing gland 739, and elastomeric shoulder seal 741.
Seal body 729, seal cap 731, seal bolt 732, seal bolt washer 733, seal nut 735, follower 737, packing gland 739, shoulder support 709, and shoulder seal 741 work in combination to locate main probe body 713 firmly between seal assemblies 721 and 723. The outer surface of main probe body 713 does not contact the inner surfaces of seal cap 731, follower 737, and seal body 729. Likewise, the opposite parallel surface (not visible) of main probe body 713 does not contact the corresponding seal cap, follower, and seal body of seal assembly 723. A gap is formed between the outer side of main probe body 713 and the inner surfaces of seal cap 731, follower 737, and seal body 729. Likewise, a similar gap is formed on the opposite side of main probe body 713. Shoulder seal 741 has a thin upper section which fits into the gap between the lower portion of seal body 729 and planar surface portion 717 of main probe body 713. The shoulder seal has a thicker lower section which fits between shoulder support 709 and the bottom of seal body 729.
The functions of these elements for sealing and locating planar probe 701 are provided by forcing shoulder support 709 against shoulder seal 741, thereby forcing shoulder seal 741 against the bottom of seal body 729 and into the gap between seal body 729 and planar surface portion 717 of main probe body 713. Seal bolt 732 and seal nut 735 are tightened to compress packing gland 739 between follower 737 and the lower part of seal body 729, thereby forcing packing gland 739 against and planar surface portion 717 of main probe body 713. The same procedure is used for the corresponding elements in seal assembly 723 on the opposite side of planar probe 701. Shoulder support 709 and shoulder seal 741 ensure that planar probe 701 cannot slip out of seal assembly 721 when high pressures occur on the interior of pressure vessel wall 719.
The probe may be ultrasonically vibrated by means of one or more ultrasonic transducers (not shown) attached to first end 703. Main probe body 713 and horn 711 vibrate or oscillate as ultrasonic waves pass from the ultrasonic generator to second end 705 of planar probe 701. The amplitude of the axially-directed oscillations varies along the length of the main probe body and horn, and the amplitude is a function of the probe and horn geometry. The amplitude reaches maxima at the vibrational antinodes and reaches minima at the vibrational nodes. The seal assemblies 721 and 723 of
The second end 705 of horn 711 may have a detachable tip of any shape. In one embodiment, the detachable tip may have the same shape as the end of horn 711. In other embodiments, the detachable tip may have other geometries that are designed to direct or radiate ultrasonic energy in a particular manner for a given application.
The elastomeric materials of packing gland 739 and shoulder seal 741 serve to isolate the vibrating planar probe 701 from seal body 703 and follower 737. In addition, as described above, packing gland 739 and shoulder seal 741 seal planar probe 701 to seal body 729, thereby sealing the interior of the vessel from the external atmosphere. Packing gland 739 and shoulder seal 741 may comprise any elastomeric material and may be selected from the group consisting of tetrafluoroethylene, chlorotrifluoroethylene, polyvinylidene fluoride, perfluoroalkoxy, polyethylene, unplasticized polyvinyl chloride, acrylonitrile butadiene styrene, acetal, cellulose acetate butyrate, nylon, polypropylene, polycarbonate, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyamide, polyimide, thermosetting plastic, natural rubber, hard rubber, chloroprene, neoprene, styrene rubber, nitrile rubber, butyl rubber, silicone rubber, chlorosulfonated polyethylene, polychlorotrifluoroethylene, polyvinyl chloride elastomer, cis-polybutadiene, cis-polyisoprene, ethylene-propylene rubber, carbon, and graphite.
The various elements of the probe and seal assembly of
The probe and seal assembly of
The dimensions of planar probe 701 should be designed appropriately for the anticipated differential operating pressure across the seal (i.e., the pressure difference between the interior of pressure vessel 719 and atmospheric pressure) formed by shoulder seal 741, seal body 729, and shoulder support 709. The thickness of shoulder support 709, which is the distance that the shoulder support projects outward perpendicularly from planar probe 701, should be sufficient to avoid failure of the collar support section by compression. The axial thickness of shoulder support 709 should be sufficient to avoid collar failure due to shear parallel to the plane of planar probe 701 caused by the pressure differential.
An example of an advanced ultrasonic cleaning system using the ultrasonic probe and seal assembly systems described above is illustrated in
A probe and seal assemblies similar to those of
Pressurized fluid for the cleaning process may be introduced through inlet line 821 at the center of vessel lid 803, flows radially through the interior of the vessel, under circular baffle 823, and exits via multiple outlet lines 825 located around the outer edge of the vessel. The pressurized fluid alternatively may be introduced via a shower head, multiple inlet tubes, or other inlet devices known in the art. The flow of cleaning fluid continuously sweeps contaminants, reactants, and undesirable contaminants from the surface of the wafer and out through the multiple outlets. The internal volume of vessel 801 should be minimized to minimize processing time and materials requirements. The pressure and temperature in the vessel may be monitored by pressure and temperature probes 826 and 828, respectively.
An alternative wafer cleaning system which uses the probe and seal assembly of
Wafer carrier system 903 comprises wafer carrier 922 mounted on carrier rod 925 and wafer carrier 922 has a recessed surface 924 for holding a wafer. Carrier rod 925 is adapted to move wafer carrier forward or backward linearly along the axis of reactor 901 by rack and pinion linear actuator 927 and stepping motor 929 mounted on wafer carrier seal plate 930.
Ultrasonic probe assembly 931, which uses components similar to those of the planar ultrasonic probe assemblies in
In one method of operation, reactor 901, wafer carrier system 903, ultrasonic probe assembly 931, front gate valve or door assembly 917, rear gate valve or door assembly 921, and wafer lifting system 923 are joined and sealed together to provide a pressurizable reactor system. The six components 901, 903, 905, 917, 921 and 931 of this system are operated in a programmed sequence of twenty one steps. In step 1, the system is in its initial status: ultrasonic transducer 931 is off, pressurized cleaning fluid flow inlet 920 is closed, the pressure of the reactor chamber 901 is set at an initial low pressure, and wafer carrier 922 is retracted into isolated cleaning chamber 901. The wafer lifting pins 923 are down, the loadlock/wafer loader gate valve 921 is open, and there is no wafer in the loadlock 901.
At this point in the sequence a wafer loader robot (not shown) or operator (not shown) delivers a contaminated wafer (not shown) into the loadlock chamber 905 for cleaning. The wafer is placed onto the lowered lifting pins by the robot or operator, and the pins are then raised. In the next six steps of the operating sequence, the wafer loading is completed. The steps proceed as follows: (2) the loadlock/wafer loader gate valve 921 closes; (3) the pressure in the loadlock chamber 905 is equalized with that of the cleaning chamber 901 by opening a valve in a bypass line (not shown) around cleaning chamber/loadlock gate valve 917; (4) the pressurized flow inlet is opened, allowing pressurized cleaning fluid to enter the cleaning chamber 901, and the loadlock chamber pressurizes as cleaning fluid flows continuously through the cleaning chamber and passes to the chamber's outlet line; (5) cleaning chamber/loadlock gate valve 917 then opens; (6) carrier block 922 is then extended to a position under the wafer by actuating stepping motor 929; and (7) the wafer is lowered onto carrier block 922 using wafer lifting mechanism 923.
In step 8, stepping motor 929 is again actuated, but in the reverse direction, and carrier block 922 begins to move back into cleaning chamber 901 and carry the wafer into the cleaning chamber. In step 9, ultrasonic transducer 933 is activated and ultrasonic energy begins to pass into the cleaning fluid, exposing the wafer to the cleaning process. The stepping motor then reverses direction in step 10, exposing the wafer to the second pass under the ultrasonically-activated probe.
In the next five steps the wafer is returned to loadlock chamber 905. The steps proceed as follows: (11) the ultrasonic transducer is de-activated; (12) the pins lift the wafer off the carrier block 922; (13) carrier block 922 retracts into the cleaning chamber; and (14) cleaning chamber/loadlock chamber gate valve 917 is closed as (15) the pressurized cleaning fluid inlet is closed.
In the next four steps, the loadlock chamber is further de-pressurized and, if necessary, is evacuated. The steps proceed as follows: (16) the cleaning chamber and loadlock chamber pressure falls as the pressurized cleaning fluid exits the cleaning chamber, and this venting process produces a set low pressure in the cleaning chamber and loadlock chamber; then, (17) the valve in the bypass line (not shown) around cleaning chamber/loadlock gate valve 917 is closed. In some cases, the loadlock may be evacuated further in order to equilibrate the loadlock pressure with that of an attached robotic wafer loading system (not shown). If further loadlock evacuation is necessary, then (18) the vent valve in a vacuum line (not shown) extending from the loadlock chamber is opened to complete evacuation of the loadlock chamber. Following this evacuation of the loadlock chamber, (19) this vent line valve is closed, and the loadlock chamber is left in an evacuated condition.
In the final two steps of the operating sequence, the cleaned wafer is unloaded. In step 20 the wafer is lowered by lowering the lifting pins of wafer lifter 923. Finally, in step 21 loadlock/wafer loader gate valve 921 is opened and the wafer is removed by the loader robot or operator. At this point the system has returned to its initial (step 1) status.
The estimated time required to complete the steps is as follows: steps 1 to 7 (loading), approximately 10 seconds; steps 8, 9 and 10 (cleaning), approximately 48 seconds; steps 11 to 21 (unloading), approximately 20 seconds; total time required to complete the sequence, approximately 78 seconds. Steps 8, 9 and 10 may be accomplished in less time in an optimized cleaning process.
The ultrasonic cleaning systems described above may use a wide variety of pressurized cleaning fluids and optional processing agents mixed with the cleaning fluids. A cleaning fluid may be in the form of a pressurized condensing vapor, a pressurized saturated or subcooled liquid, a dense fluid, or a supercritical fluid. The pressurized cleaning fluid may comprise one or more components selected from the group consisting of carbon dioxide, nitrogen, methane, oxygen, ozone, argon, hydrogen, helium, ammonia, nitrous oxide, hydrogen fluoride, hydrogen chloride, sulfur trioxide, sulfur hexafluoride, nitrogen trifluoride, monofluoromethane, difluoromethane, tetrafluoromethane, trifluoromethane, trifluoroethane, tetrafluoroethane, pentafluoroethane, perfluoropropane, pentafluoropropane, hexafluoroethane, hexafluoropropylene, hexafluorobutadiene, octafluorocyclobutane, and tetrafluorochloroethane. The pressurized fluid may further comprise one or more processing agents selected from a group consisting of an acetylenic alcohol, an acetylenic diol, a dialkyl ester, hydrogen fluoride, hydrogen chloride, chlorine trifluoride, nitrogen trifluoride, hexafluoropropylene, hexafluorobutadiene, octafluorocyclobutane tetrafluorochloroethane, fluoroxytrifluoromethane (CF4O), bis(difluoroxy)methane (CF4O2), cyanuric fluoride (C3F3N3), oxalyl fluoride (C2F2O2), nitrosyl fluoride (FNO), carbonyl fluoride (CF2O), perfluoromethylamine (CF5N), an ester, an ether, an alcohol, a nitrile, a hydrated nitrile, a glycol, a monester glycol, a ketone, a fluorinated ketone, a tertiary amine, an alkanolamine, an amide, a carbonate, a carboxylic acid, an alkane diol, an alkane, a peroxide, a water, an urea, a haloalkane, a haloalkene, a beta-diketone, a carboxylic acid, an oxine, a tertiary amine, a tertiary diamine, a tertiary triamine, a nitrile, a beta-ketoimine, an ethylenediamine tetraacetic acid and derivatives thereof, a catechol, a choline-containing compound, a trifluoroacetic anhydride, an oxime, a dithiocarbamate, and combinations thereof.
Typical operating parameters for the systems described above may include fluid pressures in the range of 10−3 to 680 atma, temperatures in the range of ambient to 95° C., ultrasonic energy frequencies in the range of 20 KHz to 2 MHz, and ultrasonic power densities in the range of 0.1 to 10,000 W/in2. Articles being cleaned may be exposed to ultrasonic energy for 30 to 120 seconds. Frequency sweeping may be used in which the frequency is varied during the cleaning period according to a predetermined frequency profile.
The following Examples illustrate embodiments of the present invention but do not limit the invention to any of the specific details described therein.
A probe as described with reference to
A planar probe as described with reference to
A 3.8 cm×3.8 cm silicon wafer test fragment containing silicon debris particles was cleaned in a small scale reactor similar to that of
The procedure of Example 1 was repeated but without the use of ultrasonic energy. It was observed that the silicon debris particles were not removed from the wafer test fragment.
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