Patent Publication Number: US-7217306-B2

Title: Trap apparatus

Description:
This is a divisional application of Ser. No. 10/387,567, filed Mar. 14, 2003, now U.S. Pat. No. 6,763,700 which is a divisional application of Ser. No. 09/986,672, filed Nov. 9, 2001, now U.S. Pat. No. 6,553,811. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a trap apparatus for use in an evacuating system for evacuating a vacuum chamber in a semiconductor fabrication apparatus or the like, and more particularly to a continuous processing trap apparatus having trap units disposed to switch between an exhaust path and a regeneration path. 
   2. Description of the Related Art 
   One conventional evacuating system will be described below with reference to  FIG. 14  of the accompanying drawings. In  FIG. 14 , a vacuum chamber  121  serves as a process chamber for use in a semiconductor fabrication process that is carried out by an etching apparatus, a chemical vapor deposition apparatus (CVD), or the like. The vacuum chamber  121  is connected to a vacuum pump  123  by a pipe  122 . The vacuum pump  123  serves to increase the pressure of a process exhaust gas from the vacuum chamber  121  to the atmospheric pressure. The vacuum pump  123  has heretofore been composed of an oil rotary pump, but mainly comprises a dry pump at present. 
   If the level of vacuum required by the vacuum chamber  121  is higher than the level of vacuum that can be achieved by the vacuum pump  121 , then an ultrahigh vacuum pump such as a turbo-molecular pump or the like is disposed upstream of the vacuum pump  123 . An exhaust gas processing apparatus  124  is disposed downstream of the vacuum pump  123 , and gas components that cannot be directly discharged into the atmosphere because of their toxicity and explosibility depending on the process are treated by a process such as adsorption, decomposition, absorption by the exhaust gas processing apparatus  124 , from which only harmless gases are discharged into the atmosphere. Necessary values are provided at appropriate positions of the pipe  122 . 
   The conventional evacuating system is disadvantageous in that if a substance having a high sublimation temperature is contained in the reaction by-products contained in the exhaust gas, then the gas is solidified while its pressure is being increased, and deposited in the vacuum pump, thus tending to cause a failure of the vacuum pump. 
   For example, if BCl 3  or Cl 2  which is a typical process gas for aluminum etching is used, then the remainder of the process gas of BCl 3  or Cl 2  and a reaction by-product of AlCl 3  are discharged from the process chamber by the vacuum pump. AlCl 3  is not deposited in the suction side of the vacuum pump because its partial pressure is low. However, while AlCl 3  is being discharged under pressure, its partial pressure rises, and it is deposited, solidified, and attached to the inner pump wall, resulting in a failure of the vacuum pump. The same problem occurs with reaction by-products of (NH 4 ) 2 SiF 6  and NH 4 Cl that are produced from a CVD apparatus for depositing films of SiN. 
   It has heretofore been attempted to heat the vacuum pump in its entirety to pass the reaction by-products in a gaseous state through the vacuum pump so that no solid substance is deposited in the vacuum pump. This attempt has been effective to prevent a solid substance from being deposited in the vacuum pump, but has been problematic in that a solid substance is deposited in the exhaust gas processing apparatus disposed downstream of the vacuum pump, thereby clogging a filled layer in the exhaust gas processing apparatus. 
   One solution is to install a trap apparatus upstream or downstream of the vacuum pump for trapping products for removal of components which will generate solid substances for thereby protecting various devices provided at the discharge path. The conventional trap apparatuses generally have such a poor trapping efficiency that about 60% of the components of the exhaust gas flows through the trap apparatus without being deposited in the trap unit. Those components flowing through the trap apparatus are deposited in downstream pipes and various devices. The reasons for the poor trapping efficiency are considered to be the fact that the exhaust gas flows in regions where the trapping efficiency is poor between an inner wall surface of the casing and the trap unit in the trap apparatus, and is unprocessed and discharged therefrom. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a continuous processing trap apparatus which is capable of increasing the trapping efficiency while maintaining conductance required by a vacuum chamber and also of stably regenerating a trap unit by removing trapped reaction by-products in inline arrangements. 
   According to the present invention, there is provided a trap apparatus including an exhaust passage for evacuating a hermetically sealed chamber by a vacuum pump, a hermetically sealed trapping and regenerating casing extending across the exhaust passage and a regenerating passage adjacent to the exhaust passage, a trap unit movably housed in the trapping and regenerating casing for selective movement between a trapping position connected to the exhaust passage and a regenerating position connected to the regenerating passage, valve bodies disposed one on each side of the trap unit and supporting seals on outer circumferential surfaces thereof which are held in contact with an inner circumferential surface of the trapping and regenerating casing for sealing the exhaust passage and the regenerating passage from each other, and a monitoring device for monitoring whether the seals are functioning normally. 
   The continuous processing trap apparatus thus constructed is capable of increasing the trapping efficiency while maintaining conductance required by a vacuum chamber and also of performing a regenerating process in inline arrangements. The continuous processing trap apparatus has seals capable of hermetically sealing trapping and regenerating chambers from each other in the trapping and regenerating casing, and also a monitoring mechanism for monitoring whether the seals are functioning normally. The continuous processing trap apparatus can thus simultaneously and stably trap, and remove reaction by-products in exhaust gases, i.e. regenerate the trap unit. Consequently, the burden on the operator who performs maintenance of the trap apparatus is greatly lightened. 
   It is preferable to provide double seals disposed on each of the outer circumferential surfaces of the valve bodies, and a seal monitoring mechanism for monitoring pressure variations or flow rate variations in hermetically sealed spaces between the double seals. It is also preferably to provide a pressure sensor for detecting such pressure variations or flow rate variations. Flow rate variations may be detected by a mass flow meter. 
   The seal monitoring mechanism may preferably comprise a device for creating a vacuum or pressurization in the hermetically sealed spaces and monitoring a sealing capability of the seals based on a variation in the vacuum or pressurization. 
   The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a view of a trap apparatus according to an embodiment of the present invention; 
       FIG. 2A  is an axial cross-sectional view of the trap apparatus shown in  FIG. 1 ; 
       FIG. 2B  is a cross-sectional view taken along line A—A of  FIG. 2A ; 
       FIG. 3A  is a cross-sectional view showing a seal member spreading device of the trap apparatus shown in  FIGS. 2A and 2B  in such a state that a value body is moved; 
       FIG. 3B  is a cross-sectional view showing the seal member spreading device of the trap apparatus shown in  FIGS. 2A and 2B  in such a state that the value body is stopped (sealed); 
       FIG. 4  is a cross-sectional view of a mechanism for moving valve bodies of the trap apparatus shown in  FIGS. 2A and 2B ; 
       FIG. 5  is a cross-sectional view of another mechanism for moving valve bodies of the trap apparatus shown in  FIGS. 2A and 2B ; 
       FIG. 6  is a cross-sectional view of a trap apparatus having valve bodies with double seals; 
       FIG. 7  is a cross-sectional view of a trap apparatus with a seal monitoring mechanism; 
       FIG. 8  is a cross-sectional view of a trap apparatus with a seal monitoring mechanism according to a modification of the seal monitoring mechanism shown in  FIG. 7 ; 
       FIGS. 9A and 9B  are views of a trap unit according to the present invention; 
       FIGS. 10A and 10B  are views of a trap unit according to a modification of the trap unit shown in  FIGS. 9A and 9B ; 
       FIG. 11  is a view of a trap unit according to a modification of the rap unit shown in  FIGS. 9A and 9B ; 
       FIGS. 12A and 12B  are views of a cooling jacket for a structural body which supports fins; 
       FIG. 13  is a view of another cooling jacket; and 
       FIG. 14  is a block diagram of a conventional evacuating system. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described below with reference to the drawings. 
     FIGS. 1 and 2  show a continuous processing trap apparatus  10  according to an embodiment of the present invention. The continuous processing trap apparatus  10  is disposed across an exhaust passage  16  through which a hermetically sealed chamber  12  is evacuated by a vacuum pump  14 , and regeneration passages  18  adjacent to the exhaust passage  16 . The vacuum pump  14  is shown as a single vacuum pump, but a plurality of vacuum pumps connected in successive stages may be provided. An exhaust gas processing apparatus  20  is provided downstream of the vacuum pump  14  for removing harmful substances from exhaust gases. The exhaust gases are discharged from the vacuum (hermetically sealed) chamber  12  via the exhaust passage  16  by the vacuum pump  14 . The continuous processing trap apparatus  10  is connected to the exhaust passage  16  between the hermetically sealed chamber  12  and the vacuum pump  14 , for trapping reaction by-products in the exhaust gases. 
   The continuous processing trap apparatus  10  includes a trapping and regenerating casing  32  which has an exhaust position and two regenerating positions one on each side of the exhaust position. The exhaust passage  16  is connected to the continuous processing trap apparatus  10  at the exhaust position, and the regeneration passages  18  are connected to the continuous processing trap apparatus  10  at the regenerating positions. Reaction by-products in the exhaust gases discharged from the hermetically sealed chamber  12  are trapped by a trap unit  34   a  in the trap apparatus  10 . At the same time, another trap unit  34   b  which has trapped reaction by-products is cleaned by a liquid introduced through liquid supply and discharge lines  22  and dried by a drying gas introduced through drying gas lines  24 . Thus, the trap unit  34   b  is returned to an initial state. After cleaning and drying of the trap unit  34   b  is completed, the trap unit  34   b  is moved into the exhaust position across the exhaust passage  16  and starts to trap reaction by-products in the exhaust gases. The cleaning liquid for cleaning the trap unit comprises pure water, for example, and the drying gas for drying the trap unit comprises a pure N 2  gas, for example, for thereby keeping the interior of the trapping and regenerating casing  32  clean. 
   The trapping and regenerating casing  32  houses therein a shaft  36  on which the two trap units  34   a ,  34   b  are mounted for trapping reaction by-products by cooling the trap units  34   a ,  34   b  with a coolant such as water or liquid nitrogen. Three valve bodies  50  are disposed on the shaft  36  on both sides of the trap units  34   a ,  34   b  and between the trap units  34   a ,  34   b . Seals  52  are mounted in respective seal grooves formed in the outer circumferential surfaces of the valve bodies  50 . By the three valve bodies  50  and the inner wall surface of the trapping and regenerating casing  32 , the interior of the trapping and regenerating casing  32  is divided into two trapping and regenerating chambers  54  that are hermetically sealed by the seals  52 . 
   The cleaning liquid lines  22  have control valves  22   a ,  22   b , and the drying gas lines  24  have control valves  24   a ,  24   b . The cleaning liquid line  22  and the drying gas line  24  which are connected upstream of the trap apparatus  10  extend as two regeneration passages  18  to supply the cleaning liquid and the drying gas to the trap apparatus  10 . Further, the cleaning liquid line  22  and the drying gas line  24  which are connected downstream of the trap apparatus  10  extend as two regeneration passages  18  to discharge the cleaning liquid and the drying gas from the trap apparatus  10 . 
   According to this embodiment, when the trap apparatus  10  is in the position shown in  FIG. 1 , the left trap unit  34   b  is in the left regenerating position to be regenerated, and the right trap unit  34   a  is in the exhaust position to trap reaction by-products. Then, the shaft  36  is moved to displace the left trap unit  34   b  into the exhaust position to trap reaction by-products and also to displace the right trap unit  34   a  into the right regenerating position to be regenerated. In this manner, the trap apparatus  10  performs regenerating and trapping actions successively to continuously trap reaction by-products. The trap apparatus  10  can thus trap reaction by-products in the exhaust gases discharged from the hermetically sealed chamber  12  and be regenerated without the need to be shut off for regenerating the trap unit and to prepare a trap unit for replacement while the trap apparatus  10  is in operation for a long period of time. 
   The continuous processing trap apparatus  10  shown in  FIG. 1  will be described in specific detail below. As shown in  FIG. 2A , the continuous processing trap apparatus  10  has a substantially cylindrical trapping and regenerating casing  32  having opposite ends hermetically sealed by closing plates  30 , a shaft  36  extending axially through the trapping and regenerating casing  32 , a pair of trap units  34  mounted on the shaft  36  within the trapping and regenerating casing  32 , and an air cylinder (not shown) as an actuating device for axially moving the shaft  36  back and forth. The trapping and regenerating casing  32  has an inlet port  38  and an outlet port  40  which are connected to the exhaust passage  16 , cleaning liquid inlet ports  42  and cleaning liquid outlet ports  44  which are connected to the cleaning liquid lines  22 , and purge ports  46  and exhaust ports  48  which are connected to the drying gas lines  24 . 
   Three disk-shaped valve bodies  50  having an outside diameter slightly smaller than the inside diameter of the trapping and regenerating casing  32  are fixedly mounted on the shaft  36  on both sides of the trap units  34  and between the trap units  34 . Annular seals  52  are mounted in respective seal grooves formed in the outer circumferential surfaces of the valve bodies  50 . The annular seals  52  preferably comprise O-rings or cap seals. The annular seals  52  are of such a diameter that when they are placed in position between the trapping and regenerating casing  32  and the valve bodies  50 , they are compressed by the bottoms of the seal grooves and the inner circumferential surface of the trapping and regenerating casing  32 . When the seals  52  are intimately held against the inner circumferential surface of the trapping and regenerating casing  32 , they seal the gaps between the inner circumferential surface of the trapping and regenerating casing  32  and the outer circumferential surfaces of the valve bodies  50 . If the inner circumferential surface of the trapping and regenerating casing  32  is coated with a layer of Teflon or the like, the seals  52  are easily slidable on the inner circumferential surface of the trapping and regenerating casing  32 , and the casing  32  is resistant to chemicals. 
   Hermetically sealed trapping and regenerating chambers  54  having the trap units  34  therein are defined between the valve bodies  50  in the trapping and regenerating casing  32 . The trapping and regenerating chambers  54  serve as a trapping chamber, respectively when the trap units  34  are placed in the exhaust or trapping position connected to the exhaust passage  16 , and as a regenerating chamber when the trap units  34  are placed in the generating positions connected to the regeneration passages  18 . 
   Since the seals  52  are mounted on the outer circumferential surfaces of the valve bodies  50 , it is not necessary to provide members or portions projecting from the inner circumferential surface of the trapping and regenerating casing  32  to define the trapping position and the regenerating positions. Therefore, even if the outside diameter d 1  (see  FIG. 2B ) of the trap units  34  is substantially equal to the inside diameter d 2  of the trapping and regenerating casing  32 , the trap units  34  can smoothly move in the trapping and regenerating casing  32 . Because the gaps between the trap units  34  and the trapping and regenerating casing  32  are small, the proportion of any gases of the exhaust gases introduced into the trapping and regenerating casing  32  which flow past the trap units  34  out of contact with the trap units  34  is reduced, thus enhancing trapping efficiency. 
   Each of the trap units  34  comprises a plurality of baffle plates fixed to the shaft  36  by welding or the like, and is cooled by a cooling thermal medium of a liquid such as liquid nitrogen or cooled air or water that is introduced into the shaft  36 . Temperature sensors (not shown) are mounted on the trap units  34  at certain positions for detecting temperatures, and pressure sensors (not shown) are mounted in the exhaust passage  16  at the positions upstream and downstream of the trap unit  34  for detecting a differential pressure across the trap unit  34 . 
   Operation of the continuous processing trap apparatus having the above structure will be described below. When the right trap unit  34  is in the trapping position connected to the exhaust passage  16  and the corresponding trapping and regenerating chamber  54  serves as the trapping chamber, a cooling thermal medium is introduced into the shaft  36  to cool the trap unit  34 . Certain components of the exhaust gases flowing into the trapping and regenerating chamber  54  are brought into contact with the trap unit  34 , and deposited and trapped in the trap unit  34 . 
   Since the outside diameter d 1  of the trap unit  34  is close to the inside diameter d 2  of the trapping and regenerating casing  32 , the amount of any introduced exhaust gases flowing past the trap unit  34  out of contact with the trap unit  34  is small. Therefore, the trapping efficiency with respect to reaction by-products products in the exhaust gases is increased while keeping the conductance of the exhaust gases which does not affect the process in the hermetically sealed chamber  12  and the performance of the vacuum pump  14 . The inventors of the present application tested the trap apparatus  10  for a trapping efficiency with respect to NH 4 Cl, and confirmed that the trapping efficiency of 98% was achieved and the conductance was of such a value as not to cause any problem in the semiconductor fabrication apparatus. 
   When the trapping process is completed, the cooling of the trap unit  34  is stopped, and the air cylinder is actuated to axially move the shaft  36  for thereby moving the right trap unit  34  to the right regenerating position connected to the regeneration passage  18 . With the right trapping and regenerating chamber  54  being connected to the cleaning liquid line  22  and the drying gas line  24 , the cleaning liquid is introduced from the cleaning liquid inlet port  42  into the trapping and regenerating chamber  54 . The trapped reaction by-products are dissolved in the cleaning liquid and/or peeled off by the physical action of the cleaning liquid, carried away with the cleaning liquid, and discharged from the cleaning liquid outlet port  44 . After the cleaning of the trap unit  34  is completed, the drying gas such as the N 2  gas is introduced from the drying gas purge port  46  into the trapping and regenerating chamber  54  to dry the trap unit  34  and the trapping and regenerating chamber  54 , and then discharged from the exhaust port  48 . When the drying process is completed, the right trap unit  34  is returned to the trapping position connected to the exhaust passage  16  for a next trapping process. 
   Inasmuch as the trapping and regenerating chamber  54  is hermetically sealed by the seals  52  mounted on the outer circumferential surfaces of the valve bodies  50 , contaminants are prevented from entering the exhaust passage  16  and the regenerating passages  18  when the trap unit traps reaction by-products and is regenerated. 
   When the trap units  34  are stopped, the seals  52  are held in intimate contact with the inner circumferential surface of the casing, thus providing a sufficient sealing action. When the trap units  34  are being moved, the seals  52  are retracted into the valve bodies  50  to avoid friction caused by sliding motion and shocks caused when the seals  52  are moved past steps provided by the gas inlet and outlet ports, and the cleaning liquid and drying gas inlet and outlet ports. 
     FIGS. 3A and 3B  are illustrative of a mechanism for applying external forces to the valve body which supports the seal to project and retract the seal. The valve body  50  has a pair of disks  60 ,  62  movable toward and away from each other by the air cylinder (not shown) which moves the shaft  36  back and forth. The disk  60  has a tapered surface  60   a  on its outer circumferential edge, and the disk  62  also has a tapered surface  62   a  on its outer circumferential edge. These tapered surfaces  60   a ,  62   a  jointly provide a V-shaped cross section which spreads radially outwardly. The seal  52  is disposed so as to be in contact with the tapered surfaces  60   a ,  62   a.    
   When the disks  60 ,  62  are spaced away from each other, as shown in  FIG. 3A , the seal  52  is placed in a region surrounded by the tapered surfaces  60   a ,  62   a  and has an outer circumferential end slightly projecting radially outwardly from the outer circumferential edges of the disks  60 ,  62 . When the disks  60 ,  62  are moved toward each other, as shown in  FIG. 3B , the seal  52  is pressed by the tapered surfaces  60   a ,  62   a  and spread radially outwardly. The seal  52  is now held in close contact with the tapered surfaces  60   a ,  62   a  and the inner circumferential surface of the trapping and regenerating casing  32  in a triangular groove fashion, thus reliably sealing the gap therebetween. While only one seal  52  is shown in  FIGS. 3A and 3B , the same mechanism can be used with a double seal structure having two seals  52  on the outer circumferential surface of the valve body  50 . 
   The trap units  34  which are associated with the sealing mechanism shown in  FIGS. 3A and 3B  are switched around as described below. Before the air cylinder is actuated to move the shaft  36 , the disks  60 ,  62  of the valve body  50  are moved away from each other for thereby accommodating the seal  52  in the region surrounded by the tapered surfaces  60   a ,  62   a . After the movement of the trap units  34  by the shaft  36  is completed, the disks  60 ,  62  of the valve body  50  are moved toward each other for thereby pressing the seal  52  with the tapered surfaces  60   a ,  62   a  to bring the seal  52  into close contact with the tapered surfaces  60   a ,  62   a  and the inner circumferential surface of the trapping and regenerating casing  32 , thus sealing the gap therebetween. 
   By spreading the seal  52  radially outwardly into close contact with the inner circumferential surface of the trapping and regenerating casing  32 , the trapping and regenerating chamber  54  is sufficiently sealed when the valve body  52  is stopped (sealed). When the valve body  50  is moved, the seal  52  is radially contracted to reduce the projection thereof from the outer circumferential surface of the valve body  50 . The seal  52  is thus subject to reduced friction caused by sliding motion and also reduced shocks upon movement across steps at the inlet port  38 , the exhaust port  40 , the cleaning liquid inlet and outlet ports  42 ,  44 , and the drying gas purge and exhaust ports  46 ,  48 , and hence has increased durability. 
     FIG. 4  shows a trap apparatus which introduces a gas into the trapping and regenerating casing  32  to provide a device for applying an external force to the valve bodies  50 . As shown in  FIG. 4 , a pressurized gas G is introduced into the trapping and regenerating casing  32  from the pipe  42  or  46  connected thereto to push the valve bodies  50  for thereby radially spreading the seals  52 , e.g. O-rings with the mechanism described above. In the trapping and regenerating casing  32 , a vacuum is created in a chamber A, a pressure is developed in a chamber B, and a pressure near the atmospheric pressure or the regenerating liquid pressure or the drying gas (N 2 ) pressure is developed in a chamber C. These chambers A, B, C are hermetically sealed by the seals  52 . The gas G under pressure may be a pure N 2  gas to keep the interior of the trapping and regenerating casing  32  clean. 
     FIG. 5  shows another mechanism for moving the valve bodies  50  of the trap apparatus. As shown in  FIG. 5 , a pressing mechanism is separate from the trapping and regenerating casing  32  and comprises a pair of cylinders  70   a ,  70   b  for moving the valve bodies  50 . The cylinders  70   a ,  70   b  comprise respective piston  72   a ,  72   b  movably disposed in respective casings  73  and having packings  71  on their outer circumferential surfaces, seals  74  mounted in the casings  73  in contact with the shaft  36  for hermetically sealing the casings  73 , and ports  76 ,  77  for introducing a compressed gas into and discharging the compressed gas from the cylinders  70   a ,  70   b . The shaft  36  connected to the trap units is used as a piston rod connected to the pistons  72   a ,  72   b.    
   For moving the valve bodies  50  to the left, a compressed gas G is introduced from the port  76  of the cylinder  70   a  into the cylinder  70   a , and discharged from the cylinder  70   a  through the port  77  of the cylinder  70   a . Similarly, a compressed gas G is introduced from the port  77  of the cylinder  70   b  into the cylinder  70   b , and discharged from the cylinder  70   b  through the port  76  of the cylinder  70   b . The pistons  72   a ,  72   b  are now moved to the left, and the valve bodies  50  fixedly mounted on the shaft  36  are moved to the left. While the valve bodies  50  are in motion, the gas is discharged from a chamber  78  in the cylinder  70   b  at a reduced rate controlled by a speed controller, for example, for thereby applying forces to spread the pistons  72   a ,  72   b  apart from each other to open the valve bodies  50  and thus retract the seals  52  such as O-rings. The valve bodies  50  can thus be moved with the seals  52  being retracted. The speed controller for controlling the rate of the compressed gas comprises a double solenoid valve assembly. For more reliable operation, the compressed gas may be supplied individually for each of the valve bodies. 
   After the completion of movement of the valve bodies  50 , a compressed gas is introduced into a chamber  79   b  in the cylinder  70   b  and a chamber  79   a  in the cylinder  70   a , thus pushing the pistons  72   a ,  72   b . Thus, the valves  50  are contracted to project the seals (e.g. O-rings)  52  radially outwardly to seal the gaps between the valve bodies  50  and the trapping and regenerating casing  32 . The mechanism shown in  FIG. 5  is operated similarly when the valve bodies  50  are moved to the right. The compressed gas used to move the valve bodies  50  and radially spread and contract the seals  52  is isolated from the trapping and regenerating casing  32  by the packings  74 . Since the cylinders  70   a ,  70   b  are separate from the trapping and regenerating casing  32 , the compressed gas used to move the valve bodies  50  and radially spread and contract the seals  52  does not affect the level of vacuum in the trapping and regenerating casing  32 . 
   The trap units may be moved in any of various fashions. For example, the shaft  36  may be axially moved back and forth by a motor or a separate cylinder. 
     FIG. 6  shows a trap apparatus having valve bodies with double seals. Specifically, each of the seals, e.g. O-rings on the valve bodies  50  comprises a pair of seals for an increased sealing capability. Depending on the process associated with the trap apparatus, the evacuating line needs to be heated to prevent reaction by-products to be trapped from being deposited in other regions than the trap units. In such an application, the double seals are effective to increase the heat insulating effect in the sealing portion. For example, the trapping and regenerating casing  32  is heated by a heater to prevent reaction by-products to be trapped by the trap unit  34   b  from being deposited in the trapping and regenerating casing  32 . At the same time, the trap unit  34   a  is in the regenerating position, and the cleaning liquid is applied thereto to cool the portion of the trapping and regenerating casing  32  surrounding the trap unit  34   a . The trap unit  34   b  is in the trapping position, and the temperature of the portion of the trapping and regenerating casing  32  surrounding the trap unit  34   b  cannot be lowered. The double seals on each of the valve bodies  50  are effective to provide an increased heat insulating effect for thereby keeping the seals  52  associated with the trap unit  34   b  in a heated state. 
     FIG. 7  shows a trap apparatus with a seal monitoring mechanism. The seal monitoring mechanism detects a pressure variation in the space between the seals  52   a ,  52   b  of each of the double seals for thereby monitoring the sealing capability of the seals. The two seals  52   a ,  52   b , e.g. O-rings, of each of the double seals provide a hermetically sealed space  81  therebetween on the outer circumferential surface of the valve body. Seal monitoring pipes  83  are mounted on the trapping and regenerating casing  32  at the respective hermetically sealed spaces  81 . The seal monitoring pipes  83  are connected to a single pipe  84  which is connected to a pressure sensor  85 . When the seals  52   a ,  52   b  are radially spread to seal the gaps between the valve bodies  50  and the trapping and regenerating casing  32 , the pressure sensor  85  monitors variations in the pressures in the spaces  81 , i.e., a sealing capability. At this time, for monitoring the space  81  at the left end of the trapping and regenerating casing  32 , a valve  87  connected to the seal monitoring pipe  83  at the left end is opened, and for monitoring the space  81  at the right end of the trapping and regenerating casing  32 , a valve  88  connected to the seal monitoring pipe  83  at the right end is opened. In the illustrated embodiment, the three spaces  81  in the seals are simultaneously monitored by the single pressure sensor  85 . However, pressure sensors may be connected to the respective seal monitoring pipes  83  for individually monitoring the pressures in the seals. 
   The sealing capability of the seals may be monitored by creating a vacuum in the hermetically sealed spaces  81  with a vacuum pump  89  and detecting variations in the pressures in the hermetically sealed spaces  81  with the pressure sensor  85 . When the sealing process is not initiated by moving the valve bodies, a valve  90  connected to the vacuum pump  89  is closed to disable the seal monitoring mechanism. The vacuum pump  89  may be replaced with an ejector to maintain a low vacuum in the hermetically sealed spaces  81 , and variations in the pressures in the hermetically sealed spaces  81  may be monitored. The seal monitoring pipes  83  may be connected to the outlet port  40 , and the valve  90  may be opened at the time when no process is performed to evacuate the hermetically sealed spaces  81 , and then the valve  90  may be closed and the vacuum may be monitored by the pressure sensor  85 . 
     FIG. 8  shows a trap apparatus with a modified seal monitoring mechanism. In  FIG. 8 , the modified seal monitoring mechanism monitors the sealing capability of the double seals by detecting pressure variations with the pressure sensor  85  when the hermetically sealed spaces  81  between the seals are pressurized. A compressed gas such as an N 2  gas is introduced from a pipe  92  connected to the seal monitoring pipes  83  into the hermetically sealed spaces  81  between the seals to pressurize the hermetically sealed spaces  81 . Since the hermetically sealed spaces  81  are connected to the pressure sensor  85  by the seal monitoring pipes  83 , the sealing capability of the seals can be monitored by detecting pressure variations in the hermetically sealed spaces  81 . A mass flow meter  94  may be connected to the pipe  92  for monitoring a gas leakage to monitor the sealing capability of the double seals. Since the hermetically sealed spaces between the seals in the double seals are pressurized, the cleaning liquid can be used more safely in the regenerating system adjacent to the evacuating or trapping system. 
   Each of the trap units of the trap apparatus will be described in detail. The trap apparatus according to the present invention has a structure for increasing the trapping efficiency for adsorbing reaction by-products in the exhaust gases progressively toward the center of the trap unit. 
     FIGS. 9A and 9B  show a trap unit which has disk-shaped cooling bodies  103  disposed in a casing  101  and cooling fins  105  disposed between the disk-shaped cooling bodies  103 . Reaction by-products in the exhaust gases tend to be deposited or precipitated on cooling fins  105   a  near the inlet of the trap unit. Therefore, the cooling fins  105   a  are displaced inwardly to space a region, where the reaction by-products tend to be deposited, away from the inlet of the casing. Thus, the reaction by-products are precipitated in the region shifted into the inner side of the trap unit, and hence prevented from contacting the casing  101  or dropping off or damaging the interior of the casing  101  while the trap unit moves into a regenerating position. The trapped reaction by-products are also prevented from entering or engaging the seals while the trap unit moves into the regenerating position. 
     FIGS. 10A and 10B  show another modified trap unit. The trap unit has fins  105 ,  105   a  as reaction by-product trapping elements which have a temperature gradient for depositing more reaction by-products within the trap. The fins  105 ,  105   a  have such a temperature distribution that their temperature is progressively lower toward the inner position of the shaft  36 . The fins  105 ,  105   b  may be given a temperature gradient by mounting a cooling jacket  107  in a structural body  103  which supports the fins, and restricting the flow of a coolant into the inlet and outlet ports  42 ,  44  of the cooling jacket  107  within the inner coolant passage. The coolant is supplied through a pipe in the shaft  36  to the cooling jacket  107 . The fins  105 ,  105   a  are progressively thinner toward the inlet and outlet ports  42 ,  44 , as shown in  FIG. 10A . In this manner, the amount of reaction by-products trapped near the inlet port  42  is suppressed, and the trapping efficiency is increased by making the fins thicker toward the shaft  36 . 
     FIG. 11  shows still another modified trap unit having fins  105  as reaction by-product trapping elements which are progressively thicker toward the center of the trap unit. The cooling temperature of the fins  105  is lowered at the inner side of the trap unit to deposit more reaction by-products toward the center of the trap unit. 
   In order to increase the trapping efficiency toward the center of the trap unit, the fins  105   a ,  105   b  at the inlet and outlet ports  42 ,  44  of the cooling jacket  107  may be made of ceramics of low thermal conductivity. The fins may be joined to the cooling jacket by welding or screws. Use of screws is preferable because of low thermal conductivity which is provided by the screws. Those fins  105  which are positioned at the center of the trap unit may be made of a material of high thermal conductivity, e.g. copper or SUS, for an increased trapping efficiency. Because copper has a corrosion resistance problem, it should preferably be plated with Ni by electroless plating. The cooling jacket should preferably be made of a material of high thermal conductivity as with the fins  105 . 
   If the cooling jacket  107  is positioned at the center of the trap unit, then it is easy to control the temperature distribution of the trap unit.  FIGS. 12A and 12B  show a coolant passage in the cooling jacket  107 . The cooling jacket  107  houses therein a coolant inlet pipe  108  and a coolant outlet pipe  109 . In order to increase the trapping efficiency toward the center of the trap unit, the rate of the coolant may be differed at the central portion of the cooling jacket  107  and at the ends of cooling jacket  107 . Specifically, the coolant passage in the cooling jacket  107  is designed to increase the rate of the coolant at the central portion of the cooling jacket  107  and reduce the rate of the coolant at the ends of cooling jacket  107 . Such a rate difference develops a temperature gradient in the cooling jacket such that the temperature is lower at the central portion of the cooling jacket  107  and is progressively higher toward the ends of cooling jacket  107 . A partition  110  may be employed to produce a coolant flow positively only at the central portion of the cooling jacket  107 . The partition  110  may have a plurality of holes formed therein to produce some flows at the ends, or may be free of any holes. 
     FIG. 13  shows another cooling jacket  107 . As shown in  FIG. 13 , the cooling jacket  107  has a coolant inlet pipe  111  and a coolant outlet pipe  112  at its central portion, a partition  113  surrounding the coolant inlet pipe  111  and the coolant outlet pipe  112 , and a coolant inlet pipe  115  and a coolant outlet pipe  116  disposed around the partition  113 . Fluids having different temperatures are supplied to flow through the inner coolant inlet pipe  111  and the outer coolant inlet pipe  115 . A structural body  103  which houses the coolant jacket  107  therein has a temperature gradient between the central portion and end thereof. As fins  105 ,  105   a  are fixed to the structural body  103 , the trapping efficiency is increased at the central portion of the trap unit. The coolant flowing through the cooling jacket  107  may comprise cooling water, a coolant (liquid nitrogen), or a fluid cooled by a Peltier device. The coolant may be in a gaseous phase. 
   Different fluids may be supplied to flow through the inner coolant inlet pipe  111  and the outer coolant inlet pipe  115 . It is preferable to cool the warm fluid discharged from the outlet pipes  112 ,  116  by way of a heat exchange with a chiller or the like, and circulate the cooled fluid back to the trap unit. 
   According to the present invention, as described above, the continuous processing trap apparatus is capable of maintaining a desired exhaust capability while keeping the conductance thereof, and also of increasing the trapping efficiency of reaction by-products in the exhaust gases. Since the continuous processing trap apparatus can reliably monitor the sealing capability, any unwanted trouble thereof in the evacuating line can be reduced, burden of periodical maintenance is lightened, and the overall downtime of the evacuating system can also be reduced. 
   As the trapping efficiency of reaction by-products in the exhaust gases is progressively higher toward the center of the trap unit, the reaction by-products are prevented from contacting the casing or dropping off or damaging the interior of the casing or entering (or engaging) the seals while the trap units are being moved into the trapping and regenerating positions. Therefore, the continuous processing trap apparatus is capable of performing stable trapping and regenerating operations. 
   Although certain preferred embodiments of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.