Patent Publication Number: US-7593625-B2

Title: Fluid heating apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a fluid heating apparatus, and more specifically to a fluid heating apparatus that heats a flowing fluid by thermal radiation emitted from a heating lamp. 
     BACKGROUND ART 
     A semiconductor device fabricating process includes a fluid treatment that brings a process object, such as a semiconductor wafer, into contact with a processing fluid to treat the process object. In one example of the fluid treatment, the process object is immersed in a processing fluid, such as diluted hydrofluoric acid (DHF) or a rinse liquid, held in a cleaning tank in order to clean the process object. In another example of the fluid treatment, a mixed gaseous fluid of vaporized isopropyl alcohol (IPA) and nitrogen gas (N 2  gas) is supplied to a process object to dry the same. In general, the temperature of the processing fluid must be regulated at a designated target temperature in order to achieve the desired process result. To this end, a fluid heating apparatus for regulating the temperature of the processing fluid is employed. 
     JP09-210577A discloses such a fluid heating apparatus. The fluid heating apparatus includes a heating lamp, a transparent quartz tube surrounding the heating lamp, and a tubular container surrounding the transparent quartz tube to define a fluid-flowing space between the transparent quartz tube and the tubular container. The fluid supplied into the fluid-flowing space through a fluid inlet flows through the fluid-flowing space, where the fluid is heated by the thermal radiation emitted from the heating lamp, and flows out of the fluid-flowing space through a fluid outlet. In this fluid heating apparatus, the fluid is exposed to the thermal radiation emitted from the heating lamp and transmitted through the transparent quartz tube so that the fluid absorbs the energy of the thermal radiation to be heated. To put it briefly, the fluid is “directly” heated by the thermal radiation. 
     In general, a fluid heating apparatus of the foregoing direct-heating type has some problems. First, if the thermal-radiation absorption of the fluid is high, the fluid flowing through an area, remote from the heating lamp, in the fluid-flowing space is not sufficiently heated, while the fluid flowing through an area, near the heating lamp, in the fluid-flowing space is efficiently heated. Thus, sufficient heating efficiency can not be achieved. If the fluid is a flammable or volatile organic solvent such as IPA, the fluid must be heated with particular attention on the temperature control. 
     The fluid heating apparatus of JP09-210577A is further provided with plural metallic fins for heating a fluid of low thermal-radiation absorption. The metallic fins are circumferentially arrayed in the fluid-flowing space and extend in the fluid-flowing direction. If the thermal-radiation absorption of the fluid is low, the thermal radiation emitted from the heating lamp falls on the metallic fins to heat the same. The fluid is heated by the heat transfer from the metallic fins to the fluid. The fin structure is complicated, and thus costly. 
     As mentioned above, in a fluid heating apparatus of the foregoing direct-heating type, the transparent tube surrounding the heating lamp is typically made of quartz. If the fluid to be heated is DHF, the quartz material contacting with the fluid will be dissolved therein, and thus cannot be used. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the forgoing problems, and therefore the main object of the present invention is to provide a fluid heating apparatus which is capable of effectively and uniformly heating a fluid, and which can be fabricated at a reasonable cost. Preferably, the fluid heating apparatus can heat any sort of fluid. 
     In order to achieve the above objective, the present invention provides a fluid heating apparatus, which includes: a heating lamp; and a tubular structure having a fluid inlet allowing the fluid to be heated to flow into the tubular structure and a fluid outlet allowing the fluid having been heated to flow out of the tubular structure, wherein the tubular structure comprises at least one pipe arranged in a form of a tube surrounding the heating lamp, and at least a surface, facing the heating lamp, of the tubular structure is coated with a radiant-light-absorbing paint. 
     According to the present invention, the radiant-light-absorbing paint efficiently absorbs thermal radiation emitted from the heating lamp, the pipe is heated efficiently, and thus the fluid flowing through the pipe is heated efficiently through the heat transfer from the pipe to the fluid. The fluid is thus efficiently heated regardless of the sort of the fluid, or the thermal-radiation absorption of the fluid. 
     Each of said at least one pipe may have an inner surface formed of a chemical-resistant synthetic resin. In this case, preferably, each of said at least one pipe may have a heat-conductive layer formed of a heat-conductive material, and the radiant-light-absorbing paint may be coated on the heat-conductive layer. 
     As the inner surface is formed of the chemical-resistant synthetic resin, a corrosive fluid can be heated without damaging the pipe. If the heat-conductive layer is provided, the heat generated in the radiant-light-absorbing paint due to the absorption of the thermal radiation is uniformly transferred to and distributed over the inner surface formed of the chemical-resistant synthetic resin through the heat-conductive layer, and thus the fluid can be heated uniformly, even if the inner surface is formed of the chemical-resistant synthetic resin having relatively low heat conductivity. 
     In one preferable embodiment, the tubular structure may comprise a plurality of straight pipes circumferentially arrayed around the heating lamp. In another preferable embodiment, the tubular structure may comprise a single pipe wound in a spiral configuration around the heating lamp. 
     The fluid heating apparatus may further include a tubular container accommodating the heating lamp and the tubular structure. The tubular container may have a light-reflective inner surface. 
     Due to the provision of the tubular container, dissipation of the thermal energy generated by the heating lamp can be suppressed, improving the heating efficiency. As the radiant light emitted from the heating lamp and leaked through gaps (if any) in the tubular structure is reflected by the light-reflective inner surface of the tubular container to fall on the outer surface of the tubular structure, the fluid can be heated more efficiently. 
     The fluid heating apparatus may further include an inert gas supply adapted to supply an inert gas into an interior of the tubular container. This configuration prevents penetration of external atmosphere into the tubular container, and achieves safer operation of the fluid heating apparatus. 
     The fluid heating apparatus may further include: a temperature sensor adapted to detect temperature of a fluid flowing through the tubular structure; a power supply adapted to regulate electric power to be supplied to the heating lamp, thereby to control calorific power generated by the heating lamp; a controller configured to generate a control signal based on the temperature detected by the temperature sensor and send the control signal to the power supply so that the temperature of the fluid coincides with a target value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing the whole structure of a cleaning system equipped with a fluid heating apparatus in a first embodiment of the present invention; 
         FIG. 2  is a longitudinal cross-sectional view of the fluid heating apparatus in the first embodiment of the present invention; 
         FIG. 3A  is a transverse cross-sectional view of the fluid heating apparatus taken along line IIIA-IIIA in  FIG. 2 ; 
         FIG. 3B  is an enlarged view of area IIIB in  FIG. 3A ; 
         FIG. 4A  is a longitudinal cross-sectional view of a fluid heating apparatus in a second embodiment of the present invention; 
         FIG. 4B  is a transverse cross-sectional view of the fluid heating apparatus taken along line IVB-IVB in  FIG. 4A ; 
         FIG. 5A  is an enlarged view of the lamp and the pipe shown in  FIG. 4A ; 
         FIG. 5B  is an enlarged view of area VB in  FIG. 5A ; 
         FIG. 6A  is a schematic diagram showing the structure of an IPA drying system equipped with a fluid heating apparatus in a third embodiment of the present invention; 
         FIG. 6B  is a cross sectional view of the heating apparatus taken along line VIB-VIB in  FIG. 6A ; 
         FIG. 7A  is an enlarged view of the lamp and the pipe shown in  FIG. 6A ; and 
         FIG. 7B  is an enlarged view of area VIIB in  FIG. 7A . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A fluid heating apparatus in a first embodiment of the present invention and a cleaning system equipped with the fluid heating apparatus will be described with reference to  FIGS. 1 ,  2 ,  3 A and  3 B. 
     Referring to  FIG. 1 , the cleaning system includes: a cleaning tank  10  having an inner tank  11  that holds a cleaning liquid L, such as diluted hydrofluoric acid (DHF) or a rinse liquid (e.g., deionized water), and an outer tank  12  surrounding the upper opening of the inner tank  11  to receive the cleaning liquid overflowing from the inner tank  11 ; cleaning liquid supply nozzles  14  arranged at a lower area of the interior of the inner tank  11 ; a circulation passage  15  having a first end connected to the cleaning liquid supply nozzles  14  and a second end connected to a drain port  12   a  arranged at a bottom of the outer tank  12 . A circulation pump  16 , a filter  17  and a fluid heating apparatus  20  are arranged in the circulation passage  15  in that order from the drain-port  12   a  side. A wafer boat  13  is arranged in the inner tank  11  to hold a plurality of (e.g., 50 pcs.) semiconductor wafers W (hereinafter simply referred to as “wafer”). A drain pipe (not shown) provided thereon with a drain valve (not shown) is connected to a bottom of the inner tank  11 . A cleaning liquid source (not shown) is arranged to supply a cleaning liquid L to the outer tank  12 . 
     Referring to  FIGS. 2 ,  3 A and  3 B, the fluid heating apparatus  20  includes a tubular container  22 , which may be formed of a stainless steel. A heat-insulating material is arranged on inner surfaces of the tubular container  22 . A heating lamp, typically a halogen lamp  23 , is arranged in the tubular container  22  and extends along the longitudinal axis of the tubular container  22 . A tubular structure  26  is arranged in the tubular container  22  to surround the halogen lamp  23  with an annular gap being formed between the halogen lamp  23  and the tubular structure  26 . The tubular structure  26  has a fluid inlet  24  and a fluid outlet  25 . The end openings of the tubular container  22  are respectively covered with end caps  22   a  and  22   b  each provided thereon with a heat-insulating material. 
     In the first embodiment, the tubular structure  26  comprises a plurality of straight pipes  26   a  circumferentially arrayed around the halogen lamp  23  to be in a form of a tube. Each of the straight pipes  26   a  extends parallel to the halogen lamp  23 . In view of heating efficiency, circumferentially adjacent pipes  26   a  are preferably in close contact with each other, but may be in close proximity while remaining a slight gap therebetween as long as leakage of radiant light (thermal radiation) emitted from the halogen lamp  23  to the exterior of the tubular structure  26  can be prevented or suppressed to a negligible level. At least a portion, facing the halogen lamp  23 , of each pipe  26   a  is coated with a radiant-light-absorbing paint, typically a black paint  27 . In the illustrated embodiment, the whole surface of each pipe  26   a  is coated with the black paint  27 . 
     As shown in  FIGS. 3A and 3B , each pipe  26   a  has a two-layer structure and thus includes an inner layer  28   a  and an outer layer  28   b . The inner layer  28   a  is formed of a chemical-resistant material, specifically a synthetic resin such as polytetrafluoroethylene, which is not dissolved in hydrofluoric acid. Thus, the pipe  26   a  has an inner surface of a chemical-resistant synthetic resin. The outer layer  28   b  is formed of a heat-conductive material such as a metallic material (e.g., aluminum or a stainless steel). The black paint  27  is coated on the heat-conductive outer layer  28   b.    
     Due to the foregoing structure, the black paint  27  efficiently absorbs radiant light (thermal radiation) emitted from the halogen lamp  23 , so that the black paint  27  is heated efficiently. The heat is transferred from the black paint  27  to the inner layer  28   a  through the heat-conductive outer layer  28   b  uniformly. Thus, the fluid flowing through each pipe  26   a  can be heated uniformly and efficiently. 
     The both ends of each pipe  26   a  are respectively connected to ring-shaped manifolds  29   a  and  29   b . In this embodiment, the tubular structure  26  is composed of the pipes  26   a  and the manifolds  29   a  and  29   b . The manifold  29   a  has a fluid inlet  24  serving as the fluid inlet of the tubular structure  26 ; and the manifold  29   b  has a fluid outlet  25  serving as the fluid outlet of the tubular structure  26 . A part of the circulation passage  15  upstream of the tubular structure  26  connected to the filter  17  passes through one end of the tubular container  22  and is connected to the fluid inlet  24  of the manifold  29   a ; while a part of the circulation passage  15  downstream of the tubular structure  26  connected to the cleaning liquid nozzle  14  passes through the other end of the tubular container  22  and is connected to the fluid outlet  25  of the manifold  29   b.    
     Arranged near the fluid outlet  25  of the tubular structure  26  is a temperature sensor  30 , which measures temperature of a cleaning liquid L flowing out of the fluid outlet  25 . A power regulator  40  is electrically connected to the halogen lamp  23  to control calorific power generated by the halogen lamp  23 . The temperature sensor  30  and the power regulator  40  are electrically connected to a central processing unit (CPU)  50 . Temperature measured by the temperature sensor  30  is sent to the CPU  50 , and the CPU  50  send a control signal to the power regulator  50 , so that the temperature of the cleaning liquid L is controlled to coincide with a target temperature such as 80° C. 
     A light-reflective member  60  may be arranged on the inner surface of the tubular container  22 , as shown by chain-dotted lines in  FIG. 2 . Thus, radiant light emitted from the halogen light  23  and passed through gaps (if any) between adjacent pipes  26   a  is reflected by the light-reflective member  60  to fall on the outer surface of the tubular structure  26 , so that the tubular structure  26  is more efficiently heated. 
     In operation, the circulation pump  15  is driven, so that a cleaning liquid L overflowing from the inner tank  11  flows through the circulation passage  15  to be supplied into the tubular structure  26  through the fluid inlet  24 . Radiant light emitted by the halogen lamp  23  is absorbed by the black paint  27  coated on each straight pipe  26   a  of the tubular structure  26 , and the absorbed heat is transmitted to the whole inner surface of each straight pipe  26   a  uniformly. Thus, the cleaning liquid L flowing through each straight pipe  26   a  is heated up to a designated temperature such as 80° C. The temperature of the cleaning liquid L is controlled by means of the temperature sensor  30 , the power regulator  40  and the CPU  50  in the foregoing manner. The heated cleaning liquid L flows out of the tubular structure  26  through the fluid outlet  25 , and is supplied to the cleaning liquid supply nozzles  14  to be jetted therefrom toward the wafers W held in the inner tank  11 . 
     Second Embodiment 
     The fluid heating apparatus in a second embodiment of the present invention will be described with reference to  FIGS. 4A ,  4 B,  5 A and  5 B. 
     In the second embodiment of the fluid heating apparatus  20 A, the tubular structure  26 A comprises a single pipe  70 , which is wound in a spiral configuration around the heating lamp  23  to be in a form of a tube. The tubular structure  26 A surrounds the halogen lamp  23  with an annular gap being formed between the halogen lamp  23  and the tubular structure  26 A. The spiral axis of the pipe  70  coincides with the longitudinal axis of the halogen lamp  23 . In view of the heating efficiency, adjacent portions of the pipe  70  with respect to the spiral-axis direction are preferably in close contact with each other, but may be in close proximity while remaining a slight gap therebetween as long as leakage of radiant light emitted from the halogen lamp  23  to the exterior of the tubular structure  26 A can be prevented or suppressed to a negligible level. The pipe  70  has one end portion thereof serving as a fluid inlet  24  of the tubular structure  26 A and extending straightly through the end cap  22   a , and the other end portion thereof serving as a fluid outlet  25  of the tubular structure  26 A and extending straightly through the end cap  22   b.    
     The cross-sectional structure of the spiral pipe  70  is essentially the same as that of the straight pipe  26   a  in the first embodiment, and thus the description thereof is omitted. Also in the second embodiment, the cleaning liquid L flown into the tubular structure  26 A through the fluid inlet  24  is heated by the radiant light emitted from the halogen lamp in a manner essentially the same as that in the first embodiment, and flows out of the tubular structure  26 A through the fluid outlet  25 . In  FIGS. 4A ,  4 B,  5 A and  5 B, the elements designated by the same reference numerals in  FIGS. 1 ,  2 ,  3 A and  3 B are the same as those in  FIGS. 1 ,  2 ,  3 A and  3 B, and thus the description thereof is omitted. 
     Although the foregoing description has been made for embodiments in which the fluid heating apparatus is applied to a semiconductor wafer cleaning system, the fluid heating apparatus may be applied to a cleaning system for cleaning a process object other than a semiconductor wafer, such as a glass substrate for an LCD (liquid crystal display). The fluid to be heated by the fluid heating apparatus is not limited to DHF, or a fluid in liquid state. The fluid may be a gaseous fluid or a misty fluid. 
     Third Embodiment 
       FIGS. 6A ,  6 B,  7 A and  7 B show an IPA drying system for drying semiconductor wafers by using a mixed gas of IPA vapor and N 2  gas, which is equipped with a fluid heating apparatus  20 B in the third embodiment of the present invention. The IPA drying system includes: a process container  80  adapted to accommodate semiconductor wafers W (i.e., process objects) therein; a fluid supply nozzle  81  for jetting a mixed gas of IPA vapor and N 2  gas toward the semiconductor wafers W accommodated in the process container  80 ; a fluid heating apparatus  20 B in a third embodiment according to the present invention; and a two-fluid nozzle  82  for atomizing IPA liquid by using N 2  gas. 
     The fluid heating apparatus  20 B in the third embodiment differs from the fluid heating apparatus  20 A in the second embodiment only in the following respects. 
     First, the cross-sectional structure of the spiral pipe  70 A of the fluid heating apparatus  20 B is different from that of the spiral pipe  70  of the fluid heating apparatus  20 A. The spiral pipe  70 A has a single-layer structure, and comprises a stainless pipe which itself has a good thermal conductivity. As IPA is not corrosive, the provision of an inner layer made of a chemical resistant synthetic resin is not necessary (but may be provided). The black paint  27  is coated on the stainless pipe (see  FIG. 7B ). One end of the spiral pipe  70 A serving as a fluid inlet  24  of the tubular structure is connected to an outlet port  83  of the two-fluid nozzle  82 . 
     Second, the tubular container  21  of the fluid heating apparatus  20 B is further provided at the end cap thereof with a purge gas supply port  86 . N 2  gas (i.e., inert gas) is supplied into the tubular container  21  through the purge gas supply port  86 , whereby the interior of the tubular container  21  can be purged, preventing a flammable or volatile fluid (such as IPA vapor) from penetrating into the interior of the tubular container  21 , achieving a safer operation of the fluid heating apparatus  20 B. 
     In operation, a mixed fluid of atomized IPA and N 2  gas flows into the spiral pipe  70 A of the fluid heating apparatus  20 B, where the atomized IPA is vaporized, and thus a mixed gaseous fluid of IPA vapor and N 2  gas flows out of the fluid heating apparatus  20 B. The mixed gaseous fluid of IPA vapor and N 2  gas is supplied to the fluid supply nozzle  81  and is jetted thereform toward the semiconductor wafers W to dry the same. Also in this embodiment, the fluid heating apparatus  20 B is capable of heating a fluid efficiently. 
     In  FIGS. 6A ,  6 B,  7 A and  7 B, the elements designated by the same reference numerals in  FIGS. 4A ,  4 B,  5 A and  5 B are the same as those in  FIGS. 4A ,  4 B,  5 A and  5 B, and thus the description thereof is omitted. 
     The third embodiment may be modified by substituting the tubing structure comprising plural straight pipes  20   a  of the first embodiment with the spiral pipe  70 A of the tubing structure  20 B. 
     Two or more fluid heating apparatuses  20 B may be connected in series. In this case, the upstream-side fluid heating apparatus  20 B may heat the fluid to vaporize the same, and the downstream-side fluid heating apparatus  20 B may heat the vaporized fluid to a designated process temperature. 
     In the foregoing embodiments, the halogen lamp  23  may be replaced with another sort of thermal-radiating lamp, such as an infrared lamp.