Abstract:
A heat treating device ( 50 ) has a cooling sleeve that covers a treating vessel ( 56 ) and a heater ( 100 ). The cooling sleeve has a cylindrical base member ( 110 ) and a cooling pipe ( 112 ) spirally wound on the outer peripheral surface hereof. The cooling pipe ( 112 ) is brazed to the base member ( 110 ).

Description:
TECHNICAL FIELD 
   The present invention relates to a thermal processing system for processing objects, such as semiconductor wafers, by a thermal process and a cooling unit to be employed in the thermal processing system. 
   BACKGROUND ART 
   In general, a semiconductor wafer is subjected to various thermal processes including a film deposition process, an etching process, an oxidation process, a diffusion process and a modification process to fabricate semiconductor integrated circuits on the semiconductor wafer. When a batch vertical thermal processing system is used for carrying out those thermal processes, semiconductor wafers are transferred from cassettes containing a plurality of semiconductor wafers, for example about twenty-five semiconductor wafers, to a wafer boat. The wafer boat is capable of holding a plurality of semiconductor wafers in the range of about thirty to about one hundred and fifty wafers depending on the size of the wafers. The wafer boat is loaded into a processing vessel from below the processing vessel, and then the processing vessel is sealed hermetically. Then, the semiconductor wafers are processed by a predetermined thermal process, controlling process conditions including flow rates of process gases, process pressure and process temperature. 
   The conventional processing vessel is surrounded by a heater for heating the wafers, and a heat-insulating layer of a heat-insulating material, such as alumina or silica. The heat-insulating layer serves to keep the processing vessel hot and to ensure the security of space around the processing vessel. Recently, it has been found that there is a possibility that metallic impurities, such as B, Fe and Cu, contained in the hot heat-insulating layer gradually permeate the processing vessel formed of quartz, enter the processing vessel and contaminate the wafers to some extent. A thermal processing system not provided with any heat-insulating layer has been developed to avoid such possibility. In view of improving throughput, it is desired to decrease the heat capacity of the entire processing furnace to enable heating a processing vessel at a high heating rate. From such a viewpoint, a thermal processing system not provided with any heat-insulating layer is desired. 
   A conventional thermal processing system not provided with any heat-insulating layer like the foregoing heat-insulating layer will be described by way of example with reference to  FIG. 9 . The thermal processing system  2  has a vertical processing vessel  8  of quartz having a double-tube structure consisting of an inner tube  4  and an outer tube  6 . A quartz wafer boat  10  is held in a processing space S defined by the inner tube  4 . The wafer boat  10  holds a plurality semiconductor wafers W at vertical intervals. 
   A cap  12  is arranged to open and close the lower opening of the processing vessel  8 . A rotating shaft  16  is connected to the cap  12  through a magnetic fluid seal  14 . A rotating table  18  is mounted on top of the rotating shaft  16 , and a heat-insulating tube  20  is mounted on the rotating table  18 . The wafer boat  10  is mounted on the heat-insulating tube  20 . The cap  12  is connected to an arm  24  of a boar elevator  22  which is vertically movable. Thus, the cap  12  can be vertically moved together with the shaft  16  and the wafer boat  10 . The wafer boat  10  is inserted through the lower opening of the processing vessel  8  into the processing vessel  8 . 
   A stainless steel manifold  26  is joined to a lower end part of the processing vessel  8 . A plurality of gas nozzles, namely, two gas nozzles  28   a  and  28 B in the illustration, for supplying various process gases necessary for a thermal process (e.g., a film forming process) are extended through the manifold  26 . Gas supply systems  30 A and  30 B are connected to the gas nozzles  28 A and  28 B, respectively. The gas supply systems  30 A and  30 B are provided with flow controllers  32 A and  32 B, such as mass-flow controllers, for controlling gas flow rates, respectively. 
   Process gases supplied through the gas nozzles  28 A and  28 B into the processing vessel  8  flow upward in the processing space S in the inner tube  4  in which the wafers are held, reverse at the upper end of the processing space S, flow downward through an annular space between the inner tube  4  and the outer tube  6 , and are discharged from the processing vessel  8 . A discharge port  34  is formed in the side wall of the manifold  26 , and a not-shown vacuum pump for evacuating the processing vessel  8  is connected to the discharge port  34 . A plurality of bar-shaped heaters  36  each extending vertically are arranged around the processing vessel  8  so as to surround the processing vessel  8 . The heaters  36  heat the wafers W held in the processing vessel  8  at a predetermined temperature. 
   A cylindrical cooling jacket  38  not including any heat-insulating material is arranged outside the heaters  36 . The cooling jacket  38  includes a cylindrical stainless steel inner shell  38 A and a cylindrical stainless steel outer shell  38 B, which define a space therebetween and are joined one another. A plurality of partition plates  40  are welded to the inner shell  38 A and the outer shell  38 B so as to form a meandering coolant passage  42  in the space between the shells  38 A and  38 B. When cooling water flows through the coolant passage  42 , the cooling jacket  38  functions as a heat-insulating layer to keep a space around the cooling jacket  38  at a safe temperature. 
   As the pressure of cooling water flowing through the cooling jacket  38  is comparatively high, usually about 5 kg/cm 2 , the inner shell  38 A and the outer shell  38 B must have a comparatively high strength to withstand such a high pressure. Therefore, the shells  38 A and  38 B have a big thickness t on the order of  6  mm. Hence, the cooling jacket  38  is heavy, and consequently, a large, complicated support structure is necessary for supporting the cooling jacket  38 . Since the partition plates  40  are welded at a space between the inner shell  38 A and the outer shell  38 B, the cooling jacket  38  is difficult to fabricate and needs a high manufacturing cost. If defective welding occurs, the cooling water will take a shortcut, and consequently, it is possible that irregular cooling occurs and wafers subjected to the thermal process are heated at widely different temperatures. If welding distortion occurs in or a weld bead is formed on the inner surface of the inner shell  38 A facing the processing vessel  8  at a part to which the partition plate  40  is welded, the reflectance changes locally at that part and, consequently, the wafers are heated at different temperatures, respectively. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in view of the foregoing problems to solve those problems effectively. Accordingly, it is an object of the present invention to provide a lightweight, highly efficient, highly reliable cooling unit and a thermal processing system employing the same. 
   To achieve the object, the present invention provides a cooling unit for a thermal processing system including a processing vessel for containing objects to be processed, and a heater for heating the objects contained in the processing vessel, the cooling unit including: a tubular base member adapted to contain the processing vessel and the heater therein; and a pipe member wound around the base member, brazed to a surface of the base member, and adapted to allow a coolant to flow therethrough. 
   The pipe member may be wound on an outer surface of the tubular base member. The pipe member may be spirally wound on an outer surface of the tubular base member. 
   The pipe member may include a plurality of pipe segments having separate coolant passages, respectively. In this case, preferably, the coolant is supplied to and discharged from the pipe segments individually. Preferably, the pipe segments are arranged on the tubular base member at different levels, respectively. 
   The cooling unit of the present invention may further include a coolant supply means for supplying a coolant into the cooling pipe member. 
   As occasion demands, the inner surface of the tubular base member may be subjected to a surface treatment to increase or decrease the heat reflectance thereof. Possible surface treatments to increase the heat reflectance include a mirror-finishing of the inner surface, and a film forming process for forming a film of a ceramic material or a metal on the inner surface. 
   The present invention also provides a cooling unit for a thermal processing system including a processing vessel for containing objects to be processed, and a heater for heating the objects held in the processing vessel, the cooling unit including: a cooling tube adapted to contain the processing vessel and the heater therein; wherein the cooling tube has a pipe member, which is coiled to form a tubular member and is adapted to allow a coolant to flow therethrough, surfaces of the pipe member define an outer surface and an inner surface of the cooling tube, and vertically adjacent portions of the pipe member are joined in close contact with each other so that no gap may be formed in the outer and the inner surfaces of the cooling tube. 
   The cooling unit of the present invention may further include a coolant supply means for supplying a coolant into the cooling pipe member. 
   The pipe member may be coiled spirally. 
   The pipe member may include a plurality of pipe segments having separate coolant passages, respectively. In this case, preferably, the coolant is supplied to and discharged from the pipe segments individually. Preferably, the pipe segments are arranged at different levels of the cooling tube, respectively. 
   As occasion demands, the inner surface of the cooling tube may be subjected to a surface treatment to increase or decrease the heat reflectance thereof. 
   The present invention provides also a thermal processing system provided with the foregoing cooling unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal sectional view of an essential part of a thermal processing system including a cooling unit in a first embodiment according to the present invention; 
       FIG. 2  is a cross-sectional view of an essential part of the thermal processing system shown in  FIG. 1 ; 
       FIG. 3  is a perspective view of a heater bar shown in  FIG. 1 ; 
       FIG. 4  is a side elevational view of the cooling unit shown in  FIG. 1 ; 
       FIG. 5  is an enlarged sectional view of a part A in  FIG. 1 ; 
       FIG. 6  is a longitudinal sectional view of an essential part of a thermal processing system including a cooling unit in a second embodiment according to the present invention; 
       FIG. 7  is a side elevational view of the cooling unit shown in  FIG. 6 ; 
       FIG. 8  is an enlarged sectional view of a part B in  FIG. 6 ; and 
       FIG. 9  is a longitudinal sectional view of a conventional thermal processing system. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A cooling unit and a thermal processing system employing the cooling unit according to the present invention will be described with reference to the accompanying drawings. 
   First Embodiment 
   A first embodiment of the present invention will be described with reference to  FIGS. 1 to 5 . A thermal processing system  50  includes a processing vessel  56  of a double-tube structure. The processing vessel  56  has a tubular inner tube  52  of quartz and an outer tube  54  of quartz arranged coaxially outside the inner tube  52  with a predetermined gap. 
   A tubular manifold  58  of stainless steel is supported by the lower end of the processing vessel  56  via a sealing member  57 , such as an O-ring. The lower end of the inner tube  52  is supported by an annular support plate  58 A protruding radially inward from the inner surface of the manifold  58 . A quartz wafer boat  60  holding a plurality of semiconductor wafers W (i.e., objects to be processed) at vertical intervals is loaded into the processing vessel  56 . In a typical embodiment, the wafer boat  60  holds twenty-five 300 mm diameter wafers W at equal intervals. 
   The wafer boat  60  (i.e., object holding means) is placed on a rotating table  64  through a heat-insulating tube  62 . The rotating table  64  is supported on the top surface of a rotating shaft  68 , which penetrates a lid  66  for closing and opening the lower end opening of the manifold  58 . A magnetic fluid seal  70  is arranged at a portion of the lid  66  where the rotating shaft  68  penetrates. The magnetic fluid seal  70  seals the rotating shaft  68  hermetically, while permitting the free rotation of the rotating shaft  68 . A sealing member  72  such as an O-ring is interposed between the periphery of the lid  66  and the lower end of the manifold  58  to keep the processing vessel  56  hermetically sealed. 
   The rotating shaft  68  is mounted to the tip of an arm  76  extending from an elevating mechanism  74  generally called a boat elevator. The elevating mechanism  74  is capable of simultaneously vertically moving the wafer boat  60 , the lid  66  and so on. The side portion of the manifold  58  is provided with a discharge port  78  to discharge the atmosphere in the processing vessel  56  through the bottom portion of the space between the inner tube  52  and the outer tube  54 . An evacuating system including a vacuum pump, not shown, is connected to the discharge port  78 . A process gas supply means  80  is connected to the manifold  58  to supply process gases into the inner tube  52 . The process gas supply means  80  includes two process gas supply systems  82  and  84  respectively having gas nozzles  86  and  88  penetrating the side wall of the manifold  58 . Gas supply lines  94  and  96  respectively provided with flow controllers  90  and  92 , such as mass flow controllers, are connected to the gas nozzles  86  and  88 , respectively. Thus, the gas supply systems  82  and  84  can supply a plurality of kinds of gases necessary for a thermal process at controlled flow rates. The number of the gas supply systems is not limited to two, but the thermal processing system  50  may be provided with any number of process gas supply systems corresponding to the number of kinds of process gases necessary for the thermal process. 
   Heating means  98  is arranged outside the processing vessel  56  to heat the semiconductor wafers W. The heating means  98  includes a plurality of, for example, eight heater bars  100  (see  FIG. 2 ) arranged at equal intervals along a circumference around the processing vessel  56 . As shown in  FIG. 3 , each heater bar  100  is bent at the upper portion thereof to be in a U-shape. The vertical length of the heater bars  100  is longer than that of the wafer boat  60 . The heater bars  100  are extended vertically and close to the outer surface of the outer tube  54  of the processing vessel  56 . Lower ends of each heater bar  100  are bent in an L-shape having end parts  100 A. The end parts  100 A of the heater bars  100  are fastened to the manifold  58 . Thus, the heater bars  100  are supported upright on the manifold  58 . Each heater bar  100  may be a carbon wire heater formed by covering a carbon wire with a quartz layer. Each heater bar  100  is connected to a heater power source  106  by a feeder line  102  provided with a switch  104 . 
   The thermal processing system  50  is provided with a cooling unit  108  according to the present invention. The cooling unit  108  includes a tubular member (i.e., base member)  110  surrounding the processing vessel  56  and the heater bars  100 , a cooling pipe  112  (i.e. pipe member) wound round and brazed to the side wall of the tubular member  110 , and a coolant supply means  114  for supplying a coolant into the cooling pipe  112 . In this specification, the assembly of the tubular member  110  and the cooling pipe  112  will be referred to as “cooling tube”. 
   The tubular member  110  has a cylindrical portion serving as a side wall of the tubular member  110 , and a ceiling portion closing the upper end opening of the cylindrical portion. The tubular member  110  is formed of a metal, such as aluminum, stainless steel or such. The thickness t 1  of the tubular member  110  may be very small, for example, about 1.5 mm. 
   The cooling pipe  112  is formed of a metal, such as stainless steel, aluminum, titanium, copper or such. Preferably, the cooling pipe  112  has a rectangular or square cross section. When the cooling pipe  112  has such a cross section, the cooling pipe  112  can be easily bonded to the tubular member  110  and can have a large contact area, vertically adjacent portions of the cooling pipe  112  can be easily bonded, and gaps are rarely formed between the vertically adjacent portions of the cooling pipe  112 . However, the cooling pipe  112  may have a cross section of any shape, such as an elliptic shape, other than the rectangular or square shape. Preferably, the cooling pipe  112  is wound helically on the side wall, preferably on the outer surface of the side wall so as to cover the side wall substantially entirely. Although it is preferable to wind the cooling pipe  112  such that the vertically adjacent portions of the cooling pipe  112  are in close contact with each other without forming any gaps therebetween as shown in  FIGS. 4 and 5 , slight gaps are permitted in this embodiment. As shown in  FIG. 5 , a surface of the cooling pipe  112  facing the outer surface of the side wall of the tubular member  110  is bonded entirely to the tubular member  110  with a brazing filler metal  116 . Since the tubular member  110  and the cooling pipe  112  are metallurgically bonded together, a very high heat transfer efficiency can be achieved between the tubular member  110  and the cooling pipe  112 . 
   In the event that vertically adjacent portions contact each other as shown in  FIG. 5 , it is preferable, in view of enhancing strength, to bond together the vertically adjacent portions of the cooling pipe  112  by welding or brazing. Although not shown in  FIG. 5 , the vertically adjacent portions of the cooling pipe  112  shall be brazed together if the brazing process is carried out with the arrangement shown in  FIG. 5 . 
   When the thermal processing system  50  uses a high process temperature in the range of, for example, about 600 to about 1200° C. for a thermal process, the inner surface of the side wall of the tubular member  110  is subjected to a surface treatment to enhance the heat reflectance of the inner surface. Possible surface treatments include film forming processes, such as plating processes and sputtering processes. By using such a film forming process, a film  118  of a ceramic material, such as titanium nitride, or a metal, such as copper, chromium, nickel or gold, is formed on the inner surface of the side wall of the tubular member  110  (see  FIG. 5 ). Due to the provision of the film  118  having a high heat reflectance, heat rays which are radiated by the heater bars  100  and the processing vessel  56  and fall on the tubular member  110  are reflected toward the heater bars  100  and the processing vessel  56 , whereby heating efficiency can be enhanced. 
   The surface treatments for increasing the heat reflectance include mirror-finishing of the inner surface of the tubular member  110 . The mirror-finished surface has a surface roughness Ry less than several micrometers measured on the basis of “Surface Roughness—Definition and Indication” specified in JIS (Japanese Industrial Standards) B0601, 1994. Preferably, the surface roughness Ry of the mirror-finished surface is 5 μm or below, more preferably, 1 μm or below. An optional known polishing method, such as a mechanical polishing method, a chemical polishing method or an electrochemical polishing method, may be used for the mirror-finishing. 
   When the thermal processing system  50  uses a low process temperature in the range of, for example, about 50 to about 600° C. for a thermal process, the inner surface of the side wall of the tubular member  110  is subjected to a surface treatment for reducing the heat reflectance of the inner surface, such as a blackening process, to increase temperature dropping rate in a low-temperature range. Such a surface treatment may be a coating of a black paint, or a surface-roughening process, such as a thermal spraying process or a blasting process. 
   Referring again to  FIG. 4 , the cooling pipe  112  is divided into a plurality of (four, in  FIG. 4 ) segments  112 A,  112 B,  112 C and  112 D. The segments  112 A to  112 D cover four parts at different heights of the processing vessel  56 , respectively. An inlet port  120  for introducing a coolant and an outlet port  122  for discharging the coolant are respectively formed at the opposite ends of each segment  112 A to  112 D of the cooling pipe  112 . A single continuous coolant passage may be formed in the cooling pipe  112  without dividing the cooling pipe  112  into plural segments. 
   Referring to  FIG. 1 , the coolant supply system  114  includes a coolant circulating line  124  provided with a coolant circulation pump  126  and a cooling heat exchanger  128  for cooling the heated coolant. The supply section of the coolant circulating line  124  is branched into a plurality of branch lines, which are respectively connected to the inlet ports  120  of the segments  112 A to  112 D of the cooling pipe  112 . The return section of the coolant circulating line  124  is branched into a plurality of branch lines, which are respectively connected to the outlet ports  122  of the segments  112 A to  112 D of the cooling pipe  112 . The coolant supply system  114  may be configured so that a coolant once passed through the cooling pipe  112  is discharged from the coolant supply system  114  without circulating the same. The coolant may be water, but is not limitative. 
   A thermal process to be carried out by the thermal processing system structured as mentioned above will be explained. The wafer boat  60  holding semiconductor wafers W is inserted into the processing vessel  56  from below the processing vessel  56 , and then the lid  66  closes the lower end opening of the manifold  58  to seal the processing vessel  56 . Subsequently, the interior of the processing vessel  56  is evacuated and is maintained at a predetermined process pressure, electric power is supplied to the heater bars  100  to raise the wafer temperature. After the temperature of the wafers W has been stabilized at the process temperature, predetermined process gases are supplied into the processing vessel  56  at controlled flow rates through the nozzles  86  and  88  of the process gas supply systems  82  and  84  of the process gas supply unit  80 . 
   At the same time, the coolant supply means  114  is operated to supply the coolant through the coolant supply line  124  into the segments  112 A to  112 D of the cooling pipe  112 . Thus, the thermal treatment of the wafers W can be carried out while the cooling unit  108  and ambient space around the cooling unit  108  are maintained at safe low temperatures. 
   After the thermal process for the wafers W has been completed, the supply of the electric power to the heater bars  100  and the supply of the process gas to the processing vessel  56  are stopped, whereas the supply of the coolant into the cooling pipe  112  is continued to cool the processing vessel  56  and the semiconductor wafers W held in the processing vessel  56  to a predetermined handling temperature. After the wafers W have been cooled to the handling temperature, the processed wafers W are unloaded from the processing vessel  56 . 
   As mentioned above, the cooling unit  108  of the present invention has the cooling pipe  112  wound around and bonded by brazing to the tubular member  110 . Therefore, the cooling pipe  112  is able to withstand the pressure of the coolant satisfactorily even if the cooling pipe  112  has a small wall thickness. Since the cooling unit  108  does not need any member corresponding to the heavy inner shell  38 A and the heavy outer shell  38 B (see  FIG. 9 ) of the conventional cooling unit, the cooling tube can be light-weight. The cooling unit  108  does not require welding work required by the conventional cooling unit for welding the partition plates  40  to the shells  38   a  and  38 B (see  FIG. 9 ). Thus the cooling unit  108  can be manufactured at a low manufacturing cost, and has improved cooling ability and reliability. 
   Since the cooling pipe  112  is metallurgically bonded to the tubular member  110  through the brazing filler metal  116 , a very high thermal conductivity between the tubular member  110  and the cooling pipe  112  can be achieved, resulting in an enhanced cooling efficiency. 
   When the cooling unit  108  of the present invention is employed, the processing vessel  56  does not need to be surrounded by a heat-insulating layer having a large heat capacity. Consequently, the heating rate at which the wafers W and the processing vessel  56  are heated can be greatly increased and hence throughput can be improved. 
   Since the cooling pipe  112  is divided into the plurality of segments  112 A to  112 D and the coolant is supplied into the segments  112 A to  112 D individually, vertical distribution of cooling efficiency on the processing vessel  56  is suppressed. Consequently, uneven temperature distribution in a batch of the wafers W can be suppressed, and the wafers W can thus be uniformly processed. 
   The cooling pipe  112  may be bonded to the inner surface of the side wall of the tubular member  110  instead of bonding the cooling pipe  112  to the outer surface of the side wall of the tubular member  110 . 
   The cooling pipe  112  may be disposed horizontally or vertically spirally instead of spirally winding the cooling pipe  112  around the tubular member  110 . 
   Second Embodiment 
   A second embodiment of the present invention will be described with reference to  FIGS. 6 to 8 , in which component parts like or corresponding to those shown in  FIGS. 1 to 5  are denoted by the same reference characters and the description thereof will be omitted to avoid duplication. 
   The cooling tube of the cooling unit in the first embodiment is built by winding the cooling pipe  112  around the tubular member  110  and bonding the cooling pipe  112  to the tubular member  110 . In the cooling unit in the second embodiment, a cooling tube (cooling jacket)  134  is formed from only cooling pipes  112  and does not include any member corresponding to the tubular member  110 . In the second embodiment, the structure of the cooling unit except for the cooling tube portion, and the structure of the thermal processing system are the same as those in the first embodiment. 
   In the second embodiment, the cooling tube  134  is fabricated in the following manner. A cooling pipe  112  having a rectangular or square cross section is wound spirally around a vertical axis. Vertically adjacent portions of the cooling pipe  112  are bonded together by brazing using a brazing filler metal  132 . The method of bonding together the vertically adjacent parts of the cooling pipe  112  is not limited to brazing; the vertically adjacent parts of the cooling pipe  112  may be bonded together by an optional bonding method, such as a welding method, provided that the joints of the vertically adjacent portions are sufficiently strong. 
   As shown in  FIG. 7 , the cooling pipe  112 , similarly to the cooling pipe  112  of the first embodiment, is divided into a plurality of, for example, four segments  112 A,  112 B,  112 C and  112 D. A coolant supply means  124  supplies a coolant to and discharged from the segments  112 A to  112 D of the cooling pipe individually. 
   As shown in  FIG. 8 , the inner surface of the cooling tube  134 ,similarly to the first embodiment, is subjected to a surface treatment by providing a coating  136  to increase or to decrease the heat reflectance of the inner surface of the cooling tube  134 . 
   The cooling tube shown in  FIG. 6  has an opened upper end, which may be closed by a lid. 
   The advantageous effects of the second embodiment are substantially the same as those of the first embodiment. Since the second embodiment does not have any member corresponding to the tubular member  110  of the first embodiment, the cooling tube of the second embodiment is lighter than that of the first embodiment. Since the cooling tube has a smaller heat capacity, the heating rate and cooling rate can be increased, which enables the further improvement of throughput. The fabricating process is simplified and the manufacturing cost can be reduced. Since the cooling tube of the first embodiment has the tubular member  110 , the inner circumference of the cooling tube can be easily smoothed. Consequently, in the first embodiment, the inner circumference of the cooling tube reflects heat rays uniformly, the temperatures of the plurality of wafers W are distributed in a narrow range and each wafer W can be further uniformly heated. 
   Although the tubular structure is formed by spirally winding the cooling pipe in the first and the second embodiments, the construction of the tubular structure is not limited thereto. For example, the tubular structure may be built by: dividing the cooling pipe into a plurality of pipe segments, bending each of the pipe segments in a ring, vertically stacking the rings of the pipe segments, and bonding together the vertically adjacent rings of the pipe segments. The coolant is supplied into and discharged from the pipe segments individually. 
   Although the coolant is supposed to be water in the first and the second embodiment, the coolant is not limited to water and any suitable coolant, such as GALDEN® or FLUORINERT®, other than water may be used. 
   Although the processing vessel  56  in each of the first and the second embodiments has a double-tube structure consisting of the inner tube  52  and the outer tube  54 , the processing vessel is not limited thereto and may have a single-tube structure. The objects to be processed are not limited to semiconductor wafers and may be glass substrates or LCD substrates.