Abstract:
A system for megasonic processing of an article. In one aspect, the system for megasonic processing comprises a rotary support for supporting an article, a dispenser for applying a fluid to a surface of an article positioned on the rotary support; and a transducer assembly. The transducer assembly comprises (i) a transmitter positioned adjacent to the article on the rotary support so that when the fluid is applied to the surface of the article via the dispenser, a meniscus of the fluid is formed between a portion of the transmitter and the surface of the article and (ii) not more than one transducer coupled to the transmitter, the transducer adapted to oscillate at a frequency for propagating megasonic energy through the transmitter and into the meniscus of the fluid.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. application Ser. No. 11/375,907, filed Mar. 15, 2006, which is a continuation of U.S. application Ser. No. 10/726,774, filed Dec. 3, 2003, now U.S. Pat. No. 7,117,876, issued Oct. 10, 2006, which is a divisional of U.S. application Ser. No. 10/243,463, filed Sep. 12, 2002, now U.S. Pat. No.6,681,782, issued Jan. 27, 2004, which is a continuation of U.S. application Ser. No.09/953,504, filed Sep. 13, 2001, now U.S. Pat. No. 6,463,938, issued Oct. 15, 2002, which is a continuation of U.S. application Ser. No. 09/643,328, filed Aug. 22, 2000, now U.S. Pat. No. 6,295,999, issued Oct. 2, 2001, which is a continuation of U.S. application Ser. No. 09/057,182, filed Apr. 8, 1998, now U.S. Pat. No. 6,140,744, issued Oct. 31, 2000, which is a continuation-in-part of U.S. application Ser. No. 08/724,518, filed Sep. 30, 1996, now U.S. Pat. No. 6,039,059, issued Mar. 21, 2000. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to a system for megasonic processing of an article requiring high levels of cleanliness.  
       BACKGROUND OF THE INVENTION  
       [0003]     Semiconductor wafers are frequently cleaned in cleaning solution into which megasonic energy is propagated. Megasonic cleaning systems, which operate at a frequency over twenty times higher than ultrasonic, safely and effectively remove particles from materials without the negative side effects associated with ultrasonic cleaning.  
         [0004]     Megasonic energy cleaning apparatuses typically comprise a piezoelectric transducer coupled to a transmitter. Tile transducer is electrically excited such that it vibrates, and the transmitter transmits high frequency energy into liquid in a processing tank. The agitation of the cleaning fluid produced by tile megasonic energy loosens particles on the, semiconductor wafers. Contaminants are thus vibrated away from the surfaces of the wafer. In one arrangement, fluid enters the wet processing container from the bottom of the tank and overflows the container at the top. Contaminants may thus be removed from the tank through the overflow of the fluid and by quickly dumping the fluid.  
         [0005]     A gas impingement and suction cleaning process for electrostatographic reproducing apparatuses which utilizes ultrasonic energy and air under pressure is disclosed in U.S. Pat. No. 4,111,546, issued to Maret.  
         [0006]     A process for cleaning by cavitation in liquefied gas is disclosed in U.S. Pat. No. 5,316,591, issued to Chao et al. Undesired material is removed from a substrate by introducing a liquefied gas into a cleaning chamber and exposing the liquefied gas to cavitation-producing means. The shape of the horn to provide the cavitation is not disclosed in detail and does not concentrate the sonic agitation to a particular location within the cleaning vessel.  
         [0007]     In U.S. Pat. No. 4,537,511, issued to Frei, an elongated metal tube in a tank of cleaning fluid is energized in the longitudinal wave mode by a transducer that extends through a wall of the tank and is attached to the end of the tube. In order to compensate for relatively high internal losses, the radiating arrangement uses a relatively thin-walled tubular member.  
         [0008]     A need exists for an improved apparatus and method which can be used to clean semiconductor wafers.  
       SUMMARY OF THE INVENTION  
       [0009]     The above-referenced parent patent applications claim various forms of the invention. The present application is directed to additional embodiments of the invention.  
         [0010]     It is therefore an object of the present invention to provide a system for megasonic processing.  
         [0011]     It is therefore another object of the present invention to provide a system for megasonic processing of an article requiring extremely high levels of cleanliness.  
         [0012]     These and other objects are met by the present invention, which in one aspect is a system for megasonic processing of an article comprising: a rotary support for supporting an article; a dispenser for applying a fluid to a surface of an article positioned on the support; and a transducer assembly comprising (i) a transmitter positioned adjacent to the article on the rotary support so that when the fluid is applied to the surface of the article via the dispenser, a meniscus of the fluid is formed between a portion of the transmitter and the surface of the article and (ii) not more than one transducer coupled to the transmitter, the transducer adapted to oscillate at a frequency for propagating megasonic energy through the transmitter and into the meniscus of the fluid. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a side elevational view of one embodiment of the megasonic energy cleaning system of the present invention.  
         [0014]      FIG. 2  is a side cross-sectional view of the system shown in  FIG. 1 .  
         [0015]      FIG. 3  is an exploded perspective view of the probe assembly shown in  FIG. 1 .  
         [0016]      FIG. 4  is a side view of an alternative probe in accordance with the present invention.  
         [0017]      FIGS. 5   a - 5   c  are alternative probe tips which may be used in connection with the present invention.  
         [0018]      FIG. 6  is a schematic view of the probe of the present invention used with cleaning fluid being sprayed onto the upper surface of a wafer.  
         [0019]      FIG. 7  is a cross-sectional view on line  7 - 7  of  FIG. 6 .  
         [0020]      FIG. 8  is a schematic view of the probe cleaning both surfaces of a wafer.  
         [0021]      FIG. 9  is a schematic view of the probe of  FIG. 1  extending through discs to be cleaned.  
         [0022]      FIG. 9   a  is a fragmentary, cross sectional view of a cap for a probe tip.  
         [0023]      FIG. 9   b  is a fragmentary, cross sectional view of another probe tip cap.  
         [0024]      FIG. 10  is a schematic view of a probe vertically oriented with respect to a wafer.  
         [0025]      FIG. 11 a  side elevational, partially sectionalized view of another embodiment of the invention having an alternate means of coupling the probe to a support.  
         [0026]      FIG. 12  is a side elevational, partially sectionalized view of another embodiment of the invention having an alternate means of mounting the probe to the housing.  FIG. 13  is a side elevational, partially sectionalized view of another embodiment of the invention having an alternate arrangement for mounting the probe and an alternate probe construction.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]      FIGS. 1-3  illustrate a megasonic energy cleaning apparatus made in accordance with the present invention with an elongated probe  104  inserted through the wall  100  of a processing tank  101 . As seen, the probe is supported in cantilever fashion on one end exterior of the container. A suitable  0 -ring  102 , sandwiched between the probe  104  and the tank wall, provides a proper seal for the processing tank  101 . A heat transfer member  134 , contained within a housing  120 , is acoustically and mechanically coupled to the probe  104 . Also contained within the housing  120  is a piezoelectric transducer  140  acoustically coupled to the heat transfer member  134 . Electrical connectors  142 ,  154 , and  126  are connected between the transducer  140  and a source of acoustic energy (not shown).  
         [0028]     The housing supports an inlet conduit  124  and an outlet conduit  122  for coolant and has an opening  152  for electrical connectors. The housing is closed by an annular plate  118  with an opening  132  for the probe. The plate in turn is attached to the tank.  
         [0029]     Within the processing tank  101 , a support or susceptor  108  is positioned parallel to and in close proximity to the probe  104 . The susceptor  108  may take various forms, the arrangement illustrated including an outer rim  108   a  supported by a plurality of spokes  108   b  connected to a hub  108   c  supported on a shaft  110 , which extends through a bottom wall of the processing tank  101 . Outside the tank  101 , the shaft  110  is connected to a motor  112 .  
         [0030]     The elongated probe  104  is preferably made of a relatively inert, non-contaminating material, such as quartz, which efficiently transmits acoustic energy. While utilizing a quartz probe is satisfactory for most cleaning solutions, solutions containing hydrofluoric acid can etch quartz. Thus, a probe made of sapphire silicon carbide, boron nitride, vitreous carbon, glassy carbon coated graphite, or other suitable materials may be employed instead of quartz. Also, quartz may be coated by a material that can withstand HF such as silicon carbide or vitreous carbon.  
         [0031]     The probe  104  comprises a solid, elongated, constant cross-section spindle-like or rod-like cleaning portion  104   a,  and a base or rear portion  104   b.  The cross-section of the probe is preferably round and advantageously, the diameter of the cleaning portion  104   a  of the probe  104  is smaller in diameter than the rear portion  104   b  of the probe  104 . The tip of cleaning portion  104   a  terminates in a tip face/surface  104   c.  In a prototype arrangement the area of the rear face of the rear portion  104   b  is  25  times that of the tip face  104   c  of portion  104   a.  Of course, cross-sectional shapes other than circular may be employed.  
         [0032]     A cylindrically-shaped rod portion  104   a  having a small diameter is desirable to concentrate the megasonic energy along the length of the rod  104   a  . The diameter of the probe, however, should be sufficient to withstand mechanical vibration produced by the megasonic energy transmitted by the probe. Preferably, the radius of the rod portion  104   b  should be equal to or smaller than the wavelength of the frequency of the energy applied to it. This structure produces a desired standing surface wave action which directs energy radially into liquid contacting the rod. In a prototype, the radius of the cylindrical portion of the probe contained within the tank was approximately 0.2 of an inch and operated at a wave length of about 0.28 of an inch. This produced 3 to 4 wave lengths per inch along the rod length and has provided good results.  
         [0033]     The probe cleaning portion  104   a  should be long enough so that the entire surface area of the wafer is exposed to the probe during wafer cleaning. In a preferred embodiment, because the wafer is rotated beneath the probe, the length of the cleaning portion  104   b  should be long enough to reach at least the center of the wafer. Therefore, as the wafer is rotated beneath the probe, the entire surface area of the wafer is close to the probe. Actually, the probe could probably function satisfactorily even if it does not reach the center of the wafer since megasonic vibration from the probe tip would provide some agitation towards the wafer center.  
         [0034]     The length of the probe is also determined by a predetermined number of wavelengths usually in increments of half wavelengths of the energy applied to the probe. In one embodiment, the length of the probe cleaning portion  104   a  equals nineteen wavelengths of the applied energy. Due to variations in transducers, it is necessary to tune the transducer to obtain the desired wavelength, so that it works at its most efficient point.  
         [0035]     The rear probe portion  104   b,  which is positioned exterior the tank, flares to a diameter larger than the diameter of the cleaning portion  104   a.  In a first embodiment of the present invention, shown in  FIGS. 1-3 , the diameter of the cross-section of the rear portion of the probe gradually increases to a cylindrical section  104   d.  The large surface area at the end of the rear portion  104   d  is advantageous for transmitting a large amount of megasonic energy which is then concentrated in the smaller diameter section  104   a.    
         [0036]     As illustrated in  FIG. 4 , in an alternative embodiment of the present invention, the diameter of the cross-section of the rear portion of the probe increases in stepped increments, rather than gradually. The stepped increments occur at wavelength multiples to efficiently transmit the megasonic energy. For example, in one embodiment, the thinnest portion  158  of the probe has a length of approximately nineteen wavelengths, the next larger diameter portion  160  is about three wavelengths in axial length and the largest diameter portion  162  is about four wavelengths in axial length. The goal is to simulate the results obtained with the tapered arrangement of  FIG. 1 .  
         [0037]      FIGS. 5   a - 5   c  depict further embodiments for the tip of the probe. The different probe tips may help cover a portion of the wafer surface that otherwise would not be covered by a flat probe end  157 . The probe may have a conical tip  164 , an inverted conical tip  166 , or a rounded tip  168 .  
         [0038]     The probe base  104   d  is acoustically coupled to a heat transfer member  134  and is physically supported by that member. The. probe end face is preferably bonded or glued to the support by a suitable adhesive material. In addition to the bonding material, a thin metal screen  141 , shown in  FIG. 3 , is sandwiched between the probe end and the member  134 . The screen with its small holes filled with adhesive provides a more permanent vibration connection than that obtained with the adhesive by itself. The screen utilized in a prototype arrangement was of the expanded metal type, only about 0.002 inch thick with flattened strands defining pockets between strands capturing the adhesive. The adhesive employed was purchased from E.V. Roberts in Los Angeles and formed by a resin identified as number 5000, and a hardener identified as number  61 . The screen material is sold by a U.S. company, Delkar. The probe can possibly be clamped or otherwise coupled to the. heat transfer member so long as the probe is adequately physically supported and megasonic energy is efficiently transmitted to the probe.  
         [0039]     As another alternative, the screen  141  may be made of a berylium copper, only about 0.001 inch thick, made by various companies using chemical milling-processes. One available screen holes for confining the resin that are larger than that of the Delkar.  
         [0040]     The heat transfer member  134  is made of aluminum, or some other good conductor of heat and megasonic energy. In the arrangement illustrated, the heat transfer member is cylindrical and has an annular groove  136 , which serves as a coolant duct large enough to provide an adequate amount of coolant to suitably cool the apparatus. Smaller annular grooves  138 ,  139  on both sides of the coolant groove  136  are fitted with suitable seals, such as O-rings  135 ,  137  to isolate the coolant and prevent it from interfering with the electrical connections to the transducer  140 .  
         [0041]     The transducer  140  is bonded, glued, or otherwise acoustically coupled to the rear flat surface of the heat transfer member  134 . A suitable bonding material is that identified as ECF  550 , available from Ablestick of Gardena, Calif. The transducer  140  is preferably disc shaped and has a diameter larger than the diameter of the rear end of the probe section  104   d  to maximize transfer of acoustic energy from the transducer to the probe. The heat transfer member is preferably gold-plated to prevent oxidizing of the aluminum and, hence, provide better bonding to the transducer and the probe. The member  134  should have an axial thickness that is approximately equal to an even number of wave lengths or half wave lengths of the energy to be applied to the probe.  
         [0042]     The transducer  140  and the heat transfer member  134  are both contained within the housing  120  that is preferably cylindrical in shape. The heat transfer member is captured within an annular recess  133  in an inner wall of the-housing  120 .  
         [0043]     The housing is preferably made of aluminum to facilitate heat transfer to th coolant. The housing has openings  144  and  146  for the outlet  122  and the inlet conduit  124  for the liquid coolant. On its closed end, the housing  134  has an opening  152  for the electrical connections  126  and  154 . Openings  148 ,  150  allow a gaseous purge to enter and exit the housing  120 .  
         [0044]     An open end of the housing  120  is attached to the annular plate  118  having the central opening  132  through which extends the probe rear section  104   d.  The annular plate has an outer diameter extending) beyond the housing  120  and has a plurality of holes organized in two rings through an inner ring of holes  131 , a plurality of connectors  128 , such as screws, extend to attach the plate  118  to the housing  120 . The annular plate  118  is mounted to the tank wall  100  by a plurality of threaded fasteners  117  that extend through the outer ring of plate holes  130  and thread into the tank wall  100 . The fasteners also extend through sleeves or spacers  116  that space the plate  118  from the tank wall. The spacers position the transducer and flared rear portion  104   b  of the probe outside the tank so that only the cleaning portion of the probe and the probe tip extend into the tank. Also, the spacers isolate the plate  118  and the housing from the tank somewhat, so that vibration from the heat transfer member, the housing and the plate to the wall is minimized.  
         [0045]     The processing tank  101  is made of material that does not contaminate the wafer. The tank should have an inlet (not shown) for introducing fluid into the tank and an outlet (not shown) to carry away particles removed from the article.  
         [0046]     As the size of semiconductor wafers increases, rather than cleaning a cassette of wafers at once, it is more practical and less expensive to use a cleaning apparatus and method that cleans a single wafer at a time. Advantageously the size of the probe of the present invention may vary in length depending on the size of the wafer to be cleaned.  
         [0047]     A semiconductor wafer  106  or other article to be cleaned is placed on the support  108  within the tank  101 . The wafer is positioned sufficiently close to the probe so that the agitation of the fluid between the probe and the wafer loosens particles on the surface of the wafer. Preferably, the distance between the probe and surface of the wafer is no greater than about 0.1 of an inch.  
         [0048]     The motor  112  rotates the support  108  beneath the probe  104  so that the entire upper surface of the article is sufficiently close to the vibrating probe  104  to remove particles from the surface of the article. To obtain the necessary relative movement between the probe and the wafer  106 , an arrangement could be provided wherein the wafer is moved transversely beneath the probe. Also, an arrangement could be provided wherein the support  108  remains in place while a probe moves above the surface of the wafer  106 .  
         [0049]     When the piezoelectric transducer  140  is electrically excited, it vibrates at a high frequency. Preferably the transducer is energized at megasonic frequencies with the desired wattage consistent with the probe size length and work to be performed. The vibration is transmitted through the heat transfer member. 134  and to the elongated probe  104 . The probe  104  then transmits the high frequency energy into cleaning fluid between the probe and the wafer. One of the significant advantages of the arrangement is that the large rear portion of the probe can accommodate a large transducer, and the smaller forward probe portion concentrates the megasonic vibration into a small area so as to maximize particle loosening capability. Sufficient fluid substance between the probe and the wafer will effectively transmit the energy across the small gap between the probe and the wafer to produce the desired cleaning. As the surface area of the wafer  106  comes within close proximity to the probe  104 , the agitation of the fluid between the probe  104  and the wafer  106  loosens particles on the semiconductor wafer  106 . Contaminants are thus vibrated away from the surfaces of the wafer  106 . The loosened particles may be carried away by a continued flow of fluid.  
         [0050]     Applying significant wattage to the transducer  140  generates considerable heat, which could present damage to tie transducer  140 . Therefore, coolant is pumped through the housing  120  to cool the member  134  and, hence, the transducer.  
         [0051]     A first coolant, preferably a liquid such as water, is introduced into one side of the housing  120 , circulates around the heat transfer member  134  and exits the opposite end of the housing  120 . Because the heat transfer member  134  is made of a good thermal conductor, significant quantities of heat may be easily conducted away by tile liquid coolant. The rate of cooling can, of course, be readily monitored by changing the flow rate and/or temperature of the coolant.  
         [0052]     A second, optional coolant circulates over the transducer by entering and exiting the housing  120  through openings  148 ,  150  on the closed end of the housing. Due to the presence of the transducer  140  and the electrical wiring  142 ,  154 , an inert gas such as nitrogen is used as a coolant or as a purging gas in this portion of the housing.  
         [0053]     An alternative arrangement for coupling the probe end  104   b  to the member  134  is illustrated in  FIG. 11 . Instead of having the probe bonded to the member  134 , a so-called vacuum grease is applied to the screen  141 , and the probe is pressed against the member  134  by a coil spring  143 . Vacuum grease is a viscous grease which can withstand pressures on opposite sides of a joint without leaking or being readily displaced. In a prototype arrangement, the combination of the grease and the metal spring provided a reliable acoustic coupling. As may be seen in  FIG. 11 , the housing  120  instead of being mounted directly to the plate  118 , is mounted to the plate  118  by standoffs, which comprise the sleeves  116  and the fasteners  117 . The sleeves  116  and the fasteners  117  are shorter than that shown in  FIG. 2 , such that the plate  118  surrounds the tapered portion of the probe. This leaves a gap between the housing  120  and the plate  118 . The coil spring  143  is positioned in this gap and compressed between the plate  118  and the tapered portion of the probe. Thus, the spring presses the probe toward the member  134 . This arrangement acoustically couples the probe to the heat transfer member  134 . A Teflon sleeve  149  is preferably positioned over the first coil of the spring  143  adjacent the probe so that the metal spring does not damage the quartz probe.  
         [0054]     An arrangement is illustrated in  FIG. 6 , wherein the probe assembly of  FIG. 1  is shown in conjunction with a tank  200  which is open on its upper end and has a drain line  202  in its lower end. The probe  104  is shown extending through a slot  203  into the tank above a wafer  106  mounted on a suitable support  208  including an annular rim  208   a,  a plurality of spokes  208   b,  joined to a hub  208   c  positioned on the upper end of a shaft  210  rotated by a motor  212 .  
         [0055]     In use, deionized water or other cleaning solution is sprayed onto the upper surface of the wafer from a nozzle  214  while the probe  104  is being acoustically energized. The liquid creates a meniscus  115  between the lower portion of the probe and the adjacent upper surface of the rotating wafer. This is schematically illustrated in  FIG. 7 . The liquid provides a medium through which the megasonic energy is transmitted to the surface of the wafer to loosen particles. These loosened particles are flushed away by the continuously flowing spray and the rotating wafer. When the liquid flow is interrupted, a certain amount of drying action is obtained through centrifical force of the liquid off of the water.  
         [0056]     The probe assembly may be conveniently mounted on a suitable support, schematically illustrated at  216 . The support is capable of pivoting the assembly upwardly, as indicated by the arrow in  FIG. 6 , to facilitate the installation and removal of wafers. Alternatively, the slot  203  may instead be formed as a hole, closed at the top, and the probe may be moved radially in and out.  
         [0057]      FIG. 8  illustrates an alternative or addition to the arrangement of  FIG. 6  wherein both the lower and upper sides of a wafer are cleaned. A spray nozzle  254  extends through a side wall of a tank  200  and is angled upwardly slightly so that cleaning fluid may be sprayed between the spokes  208   b  and onto the lower surface of a wafer  106  and is directed radially inwardly so that as the wafer rotates, the entire lower surface is sprayed with the fluid. The wafer is subjected to megasonic energy by the probe  104  in the same manner as described above in connection with  FIG. 6 . This agitation vibrates the wafer as well as the fluid on the lower surface of the wafer which is radially aligned with the probe as the wafer rotates. This. agitation loosens particles on the lower surface of the wafer, and the particles are flushed away with the fluid which falls or drips from the lower surface of the wafer.  
         [0058]     Various fluids may be employed as the spray applied to the wafer in  FIGS. 6 and 8 . In addition to liquid or high pressure gas, so-called dry ice snow may be applied. Va-Tran Systems, Inc. of Chula Vista, Calif. markets a product under the trademark SNO GUN for producing and applying such material. A major advantage of that approach is that there is no disposal problem after cleaning. Contamination is carried away from the clean surface in a stream of inert, harmless vapor. Disposal costs of cleaning media are eliminated. Advertising literature regarding the SNO GUN product states that cleaning with dry ice snow removes particles more thoroughly than blowing with dry nitrogen. It is said that the device removes even sub-micron particles as tiny as 0.2 microns, which are difficult or impossible to remove with a nitrogen jet. Such technology is further described in U.S. Pat. No. 5,364,474, which is incorporated herein by reference.  
         [0059]     Referring to  FIG. 9 , the probe assembly of  FIG. 1  is shown mounted to a wall of a tank  300 . The probe  104  extends generally horizontally through central openings in a plurality of vertically orientated substrates such as “compact discs”  302 . The discs may be mounted in a cassette immersed in the tank with the holes in the discs aligned with the probe. The cassette carrying the discs can then be moved laterally so that the probe extends through the holes in the discs, without actually contacting the discs. The tank is filled with liquid, such as deionized water to completely cover the discs. The probe is then vibrated by megasonic energy in the manner described above in connection with  FIG. 1 . The agitation produced by the probe is transmitted into the cleaning liquid between the discs to loosen particles on the surfaces of the discs. The energy propagates radially outward from the probe such that both sides of each disc are exposed to such energy. Cleaning liquid may be introduced into the container in continuous flow and allowed to overflow the upper end of the container to carry away loosened particles.  
         [0060]     Because some megasonic energy will be transmitted through the end of the probe with the probe tip immersed in the liquid, a small cap  306  is positioned on the tip of the probe with the cap containing an air space  308  between two glass walls  306   a  and  306   b,  as shown in  FIG. 9   a.  Since megasonic energy does not travel through ambient air to any significant degree, the cap prevents the loss of energy through the end of the probe. An alternative cap  310  shown in  FIG. 9   b  employs a short section of glass tubing  212  attached to the end of the probe. As seen, the outer diameter of the tube is equal to the outer diameter of the probe, and the outer end of the tube spaced from the probe is closed by a disc  314 .  
         [0061]      FIG. 10  illustrates another embodiment of the probe of the invention. A probe assembly  400  is shown which is similar to the assembly of  FIG. 1  except that the probe  404  is much shorter than the probe  104  in  FIG. 1 . In addition, the assembly  400  is oriented with the probe extending generally vertically, generally perpendicular to the surface of the horizontal wafer  106 . Cleaning fluid is applied to the upper surface of the wafer, and the lower tip of the probe is in contact with this fluid. Consequently, megasonic energy is transmitted through this medium onto the surface of the wafer causing loosening of particles. Since the sides of the probe are not exposed to this medium, there is no appreciable megasonic energy transmitted from the vertical sides of the probe. Instead, such megasonic energy is concentrated into the tip. The tip can be moved radially with respect to the wafer as the wafer rotates so as to apply megasonic energy to the entire surface of the wafer. Alternatively, the probe may traverse the entire upper surface. Any suitable support  410  containing a mechanism to provide the desired movement may be employed.  
         [0062]     As mentioned above, the preferred form of the probe assembly includes a probe made of inert material such as quartz and a heat transfer member coupled to the rear of the probe made of a good heat conducting material such as aluminum. Since it is the cylindrical portion of the probe which is in contact with the cleaning fluid and is positioned adjacent the wafer, an alternative arrangement could be devised wherein a forward portion, such as section  104   a  in  FIG. 1  could be made of the inert material and the rear portion  104   b  could be made of aluminum and hence could be made as one piece with the heat transfer member  134 . This of course means that the joint between the two components would be at the rear of the cylindrical portion  104   a  . While such a bonding area would not be as strong as the arrangement illustrated in  FIG. 1 , it may be useful in certain situations.  
         [0063]     In the other direction, there may be some applications in which it is not necessary to employ quartz or other such inert material for the probe. Instead, the entire probe could be made of aluminum or other such material. In that situation, the heat transfer member could then be made as a one-piece unit with the probe. Also, with a metal probe it may be practical to spray the cleaning fluid through the probe itself. For example in the arrangement of  FIG. 10 , fluid inlet could be located in the side of the large diameter end of the probe and an outlet can be located in the end face of the small diameter probe end. The fluid would also serve as a coolant to cool the transducer, particularly if dry ice snow were employed.  
         [0064]     The embodiment of  FIG. 12  has a number of similarities to the other embodiments, but has some important distinctions. That arrangement includes a cup-shaped housing  520  similar to the housing  120  in  FIG. 2 , but inverted with respect to the housing  120 . The housing  520  includes a closed end wall  520   a  having a surface  520   b  facing the interior of the housing  520  and having an exterior surface  520   c  facing away from the housing. Coupled to the interior end wall surface  520   b  is a disc-shaped transducer  540  analogous to the transducer  140  referred to above in connection with  FIGS. 2 and 3 . The transducer  540  is preferably bonded to the wall surface  520   b  in the same manner mentioned above in connection with  FIGS. 2 and 3 . The probe  504  comprises a solid elongated, constant cross-section spindle-like or rod-like cleaning portion  504   a.  The large end  504   b  of a probe  504  is acoustically coupled to the housing end wall exterior surface  520   c.  The acoustic coupling is accomplished by the use of a coil spring  543  surrounding the probe  504  and reacting against the spring retainer plate  518  to press the large end  504   b  of the probe towards the housing end wall  520   a.  As discussed in connection with  FIG. 3 , a screen  141 , together with an appropriate viscous material, is sandwiched between the large end of the probe and the end wall  520   a.  The coil spring adjacent the large end of the probe has a sleeve or sleeve portions  544  made of a material which will not damage the probe. The O-ring  521  is held in place and compressed against the end wall  520   a  and the probe by a retainer ring  519  having a surface  519   a  which presses against the O-ring  521 . The O-ring  521  thus prevents the escape of the viscous material from between the probe and the housing end wall, and centers the probe. The retainer ring is attached to the housing by a plurality of bolts  525  which extend through the retainer ring and thread into the housing. The spring  543  is captured and compressed by a reaction plate  518  which surrounds the probe and is attached to the housing by a plurality of fasteners  528  which thread into the retainer ring  519  and are spaced from it by sleeves  516  surrounding the fasteners  528 . For convenience of illustration, the fasteners  525  and  528  are all shown in the same plane in  FIG. 12 . In actual practice, the fasteners  528  would preferably be on the same bolt hole diameter as the fasteners  525 , and they of course would be spaced with respect to the fasteners  525 . Also, the fasteners would not necessarily be spaced  180 E apart as illustrated, but would be spaced in whatever mainer is practical.  
         [0065]     Positioned within the cup-shaped housing  520  is an annular heat transfer member  534  which has an external diameter sized to fit snugly within the housing  520 . An annular groove  536  in the exterior of the heat transfer member  534 , creates a liquid cooling channel in combination with the inner surface of the housing  520 . A pair of O-rings  537  that fit within annular grooves in the heat transfer member seal the coolant channel  536  so that the remainder of the interior of the housing is sealed from the liquid. This prevents interference with the electrical energy being supplied to the transducer. Further, transducer vibration energy is not dissipated into the interior of the housing, but instead is transmitted into the housing end wall  520   a  and into the probe  504 . The heat transfer member  534  is axially captured within the housing by means of an annular shoulder  520   d  and by a housing end plate  560 . A plurality of fasteners  528  connect the plate  560  to the housing. A liquid coolant inlet  562   a  is mounted in an opening in the end plate  560  and threads into a passage  519  in the heat transfer member that extends axially and then radially into the annular channel  536 . A similar outlet fitting  562   b  mounts in the end plate  560  diametrically opposed from the  562   a  fitting, and threads into another passage  519  that extends axially and radially into the channel  536 .  
         [0066]     A plurality of axially extending bores  563  are also formed in the heat transfer member  534 , aligned with gas inlets  561   a, b  formed in the plate  560 . The inlets  561   a, b  and bores  563  are shown in the same plane with the passages  519  for convenience. In actual practice, the bores  563  would preferably not be in the same plane as the passages  519 , and instead would be circumferentially offset, and could also be formed in the same circle around the center of the heat transfer member  534 . The inlets  561   a, b  through the end plate  560  for the fittings  562   a  and  562   b  would likewise be moved to be aligned with the passages  563 .  
         [0067]     The electrical connection for the transducer  540  is illustrated by the wire  554 , although the more complete connection would be as shown in  FIG. 3 . That wire extends through a fitting  528  which in turn is connected to an electrical cord  526 .  
         [0068]     In operation, there are a number of advantages to the embodiment illustrated in  FIG. 12 . By coupling the transducer and the probe to the housing end wall, more energy may be transmitted to the probe than. with the corresponding amount of power applied to the transducer in the arrangement of  FIG. 2 , inasmuch as the housing end wall has less mass than the mass of the heat transfer member  140  shown in.  FIG. 3 . While some energy is lost into the other portions of the housing, there is a net increase in efficiency. The relatively thin end wall has fewer internal energy reflections than a thicker wall simply because of the reduced mass. However, in addition the housing end wall does not have the discontinuities caused by the grooves in the heat transfer member of  FIG. 2 , or by the O-ring in the grooves.  
         [0069]     By making the housing  520  of aluminum or other material which is a relatively good thermal energy conductor, the heat generated by the transducer can be readily dissipated with the arrangement of  FIG. 12 . The heat transfer member  534  can be made of the desired axial length without concern for its mass because it is not to be vibrated as in the arrangement of  FIG. 2 . The cooling liquid enters through the fitting  562   a,  flows axially and then radially into the channel  536 , where it splits into two branch flows in opposite directions, that meet on the other side of the heat transfer member. and flow out the fitting.  562   b.    
         [0070]     Similarly, cooling gas such as nitrogen can be connected to one or more of the bores  563  in the heat transfer member and into the central area of the housing. The gas is exhausted through one of the bores  563  leading to a second outlet  561   b.  Two passages  563  are illustrated in  FIG. 12 . Three are preferable, but more or less may be utilized if desired. To perform an additional function, bolts may be threaded into the bores  563  to assist in withdrawing the heat transfer member from the housing.  
         [0071]     The assembly illustrated in  FIG. 12  may be used in connection with a wall mounted arrangement such as that shown in.  FIG. 1 , or may be used with a system such as that as illustrated in  FIG. 8 , wherein the probe assembly is moved into or out of position with respect to a wafer to facilitate insertion and removal of wafers. As mentioned above, such a probe may be moved out of the way by mounting it on a bracket that will pivot it in the direction of the arrow  218  shown in  FIG. 8 , or it may be on a track arrangement (not shown) which will move it radially inwardly and outwardly with respect to the wafer and its supporting member. The assembly of  FIG. 12  may be mounted to these other structures in any suitable fashion, such as by making connections to the end plate  560 .  
         [0072]     The arrangement of  FIG. 13  includes a generally tubular or cylindrical housing  620 . Positioned within the housing is a heat transfer member  634  having an outer annular wall  634   a  which fits snugly within a surrounding annular wall of the housing  620 . The heat transfer member  634  has an annular channel  636  formed in its outer surface that faces the surrounding housing wall to form a coolant passage. A coolant inlet  644  in the housing wall leads into the passage and an outlet  646  on the opposite side of the housing leads out of the passage.  
         [0073]     As seen in  FIG. 13 , the heat transfer member  634  has somewhat of an H-shaped cross section created by a central disc-shaped wall  634   b  integrally tonned with the surrounding annular wall  634   a.  As seen, the central wall  634   b  is relatively thin and it is radially aligned with the surrounding coolant passage  636 . The heat transfer member is axially captured within the housing by an internal shoulder on one end of the housing and by an end plate  660  on the other end.  
         [0074]     A piezoelectric transducer  640  is acoustically coupled to one side of the central wall  634   b,  such as in the same manner discussed above in connection with the other embodiments. A probe  604  is acoustically coupled to the other side of the central wall  634   b.  Again, this may be done in various ways, such as the screen and grease technique discussed above. An O-ring  621  surrounds the base of the probe and is compressed against the probe and the central wall  634   b  by a cylindrical portion of an end member  619  having a flange attached to the end of the housing  620 . The O-ring confines the coupling grease and helps center the probe  604 . The probe is pressed against the central wall  634   b  by a spring  643  compressed between an annular spring retainer plate  618  and the probe  604 .  
         [0075]     The housing and heat transfer member illustrated in  FIG. 13  may be used with the probes illustrated in the above-mentioned embodiments, but it is illustrated in  FIG. 13  with an alternate probe construction. Instead of having the probe made of one piece, it is formed in separate portions including a base  605  adjacent the central wall  634   b  of the heat transfer member, and an elongated cleaning rod  606 . The base  605  has a cylindrical exterior with a reduced diameter portion  605   a  on the end spaced from the central wall  634   b.  One end of the spring  643  surrounds the base portion  605   a  and engages the shoulder on the base  605  adjacent the portion  605   a.  The rod  606  of the probe fits within a central socket formed in the base  605 . It is bonded to the base by a suitable adhesive which will not interfere with the transmission of the megasonic energy provided by the transducer  640  and propagated through the central wall  634   b  and the base  605  of the probe.  
         [0076]     The base  605  call have a frusto-conical configuration just as the rear portion of the probe in  FIG. 12 , and the spring  643  could then engage the sloping side wall of such shape rather than having the step configuration shown in  FIG. 13 . Also, in theory, the rod  606  could have a tapered end and the spring could engage it as suggested by  FIG. 12 .  
         [0077]     A primary purpose of having a probe made of two different portions is that one portion can be made of a different material from the other. For example, the base  605  can be utilized in any cleaning operation since it does not contact the cleaning solution; however, the rod  606  must be compatible with the cleaning solution. Thus, if the cleaning solution is compatible with quartz, a one-piece arrangement such as that illustrated in  FIG. 1  or  FIG. 12  could be conveniently utilized. If, however, the cleaning solution is not compatible with quartz, such as a solution containing hydrofluoric acid, a material for the rod is needed that is compatible, such as vitreous carbon, while the base can be quartz. It is currently difficult to obtain vitreous carbon in a shape such as that illustrated in  FIG. 12 . However, a straight cylindrical rod is more readily available. Hence, it is practical to utilize it in the arrangement illustrated in  FIG. 13 . Of course any other desirable combination of suitable materials for the rod and the base may be employed.  
         [0078]     As mentioned above, the arrangement of  FIG. 13  is particularly desirable from the standpoint that the transmission of megasonic energy is efficient through the thin wall portion of the heat exchange member, but yet the heat exchange process is very efficient. This is because the transducer, which is the heat generator, is in direct contact with the heat transfer member, which is in direct contact with the coolant passage  636 . It should be recognized that other heat transfer arrangements may be employed. For example, if the heat transfer member has sufficient surface area, it might be possible to have it air-cooled rather than liquid-cooled. It should also be recognized that various other modifications of that type may be made to the embodiments illustrated without departing from the scope of the invention, and all such changes are intended to fall within the scope of the invention, as defined by the appended claims.