Trapping device

Abstract: A trapping device is presented to improve production efficiency of vacuum processing devices. The trapping device comprises an exhaust path for evacuating process gas from a hermetic chamber through a vacuum pump; a regeneration path disposed adjacent to the exhaust path and comprising a regeneration means; not less than two trap sections communicable either with the exhaust path or with the regeneration path; and switching means for transposing the trap sections either to the exhaust path or to the regeneration path. A trapping operation and a regeneration operation can be performed concurrently respectively in the exhaust path and the regeneration path.

Description: Field of the Invention The present invention relates to a trapping device used in, for example, an evacuation system for evacuating a vacuum chamber in a semiconductor manufacturing apparatus. Description of the Related Art A conventional evacuation system will be described with reference to Figure 9. A vacuum chamber 101 is a processing chamber for processing semiconductor devices through processes such as etching or chemical vapor deposition (CVD). The processing chamber 101 is communicated with a vacuum pump 103 through a pipe 102. The vacuum pump 103 is used to raise the gas pressure of the spent gas from the processing chamber 101 to an atmospheric pressure, and in the past, oil-lubricated rotary pumps were common but modern pumps are mainly so-called dry pumps. When the degree of vacuum required in the processing chamber 101 is higher than the performance capability of the dry pump 103, an ultra-high vacuum pump such as a turbo-molecular pump is provided upstream of the dry pump. A gas scrubber 104 is provided in a downstream location of the vacuum pump 103, and depending on the characteristics of the exhaust gases, those gases which cannot be exhausted to the atmosphere directly, such as those that are poisonous or explosive, are treated in this device by such processes as adsorption, decomposition and absorption, and only the harmless gases are exhausted into the atmosphere. The pipe 102 is provided with valves in desired locations. In such conventional vacuum systems, if the reaction byproduct contains a substance having a high sublimation temperature, that substance will leave a solid residue in the process of pressure rise and, in some cases, precipitate in the vacuum pump to cause failure of the pump. For example, when aluminum is subjected to an etching process, using typical process gases such as BCl 3 , Cl 2 , the exhaust gas from the processing chamber 101 will contain a reaction byproduct AlCl 3 as well as residual gaseous BCl 3 and Cl 2 . Among these gases, AlCl 3 does not precipitate on the intake side of the vacuum pump where it has a low partial pressure, but while it is being pressurized to raise the partial pressure, it precipitates inside the vacuum pump and the solid particles adhere to the interior wall of the vacuum pump. This phenomenon is a cause of pump failure. Similar problems are encountered when byproducts such as (NH 4 ) 2 SiF 6 and NH 4 Cl are formed for producing SiN thin film by CVD. Conventional remedial approaches include: (1) The vacuum pump is heated to maintain the pump at a high temperature so that the exhaust gas would not precipitate solid particles inside the pump and is eliminated through the pump in a gaseous state. (2) A water-cooled trap is provided in an upstream location (intake side) of the vacuum pump so as to precipitate potential particles before they enter the vacuum pump. In the first approach, although it is effective in preventing precipitation inside the vacuum pump, precipitation can still occur in a gas scrubber disposed downstream of the vacuum pump, and the resulting blockages of the filtering layers presented a serious operational and maintenance problems. In the second approach, the system has to be shutdown for cleaning of the traps resulting that the system productivity is sacrificed. Therefore, it is desirable first to be able to trap potential particles in the spent exhaust gas and to regenerate the intercooler automatically without having to shut down the system. Such a system would assure long service life of the pump, provide protection for gas scrubbers and reduce time loss so that the operational reliability of the manufacturing system will be improved. It is further desirable that the system is able to reduce the cost of building and operating the trapping device. GB-A-1 044 889, DE-A-1 229 984 and DE-A-4 438 874 disclose various trap systems suitable for continuous operation. In accordance with the invention a trapping device as set forth in claim 1 is provided. Preferred embodiments are disclosed in the dependent claims. SUMMARY OF THE INVENTION It is an object of the present invention to provide a trapping device to enable trapping and regeneration operations to be performed concurrently in such a manner that the processing system can be controlled automatically without shutting down the system for trap regeneration. It is another object to provide a trapping device that can perform such trapping operations efficiently so as to raise the overall operational reliability by improving the service life and lowering the capital and operation cost of the processing system. The object has been achieved in a trapping device as defined in claim 1 so that a trapping operation and a regeneration operation can be performed concurrently and respectively in both the exhaust path and the regeneration path. Accordingly, the trapping device eliminated the need for shutting down the system for exchanging the trap or the need to have spare traps so that the hermetic chamber can be operated continually without interruption. Coupled with a suitable exchange timing device, the processing system can be operated totally automatically. The hermetic chamber may be a semiconductor processing chamber, and as necessary, a gas scrubber can be provided for detoxifying or safening the spent gas. It is preferable that the vacuum pump be a dry type in which lubricant is not used in the evacuation passage to avoid contamination by diffusion of lubricant oil vapors. The not less than two trap sections may be connected to each other to move in a interlocking manner, or separated to be independently movable. The trap section may be housed in a trap chamber disposed in the evacuation path, and a regeneration chamber for accommodating another trap section may be provided in the regeneration path so that hermetic integrity of the system is maintained while switching the trap sections. The regeneration chamber may be provided with openings or ports to exhaust vaporized gaseous species. The not less than two trap sections may be disposed parallel to a flow direction of the spent gas. The trap sections are adapted to be moved in a linear manner. The not less than two trap sections may be disposed transversely to a flow direction of said exhaust path or a flow direction of said regeneration path. The trap section may be a temperature-controlled trap, and is cooled when communicating with said exhaust path and is heated when communicating with said regeneration path. The trap section may be transposed automatically according to a control signal indicating a trapped amount directly or indirectly. When the trap section is to function as a temperature-controlled trap, temperature may be controlled by flowing a thermal medium from an external source, such as cooled water or other coolant, or a liquid substance (e.g. liquid nitrogen) capable of utilizing vaporization heat thereof. Thermoelectric cooling based on Peltier elements or by Pulse-tube refrigerator can provide cooling without using a cooling medium. Similarly, regeneration operation may be performed using a thermal medium or electrical heating, thermoelectric heating or by natural phenomena. Released gases can be retrieved together with the thermal medium (usually gaseous) or retrieved separately, and in the latter case, a thermal medium path for regeneration medium is separately provided. The trap is constructed with one or more baffle plates so as to enhance contact between the spent gas and the trap section by providing tortuous paths and increased contact surface area. The trap section may be switched by using air cylinder. In this case, the drive may be operated by an air drive controller including solenoid valves and speed controllers, so that the controller may be regulated by a sequencer or by signals from a relay device. The trap sections may be operated totally automatically without any human intervention by selecting appropriate control methods, such as: switching the trap section when indicated by pressure sensors to detect the differential pressures between fore- and aft-trap locations; or more simply, they may be switched after a given period of operation of the trap sections. When there is only one regeneration path for one exhaust path, both devices are in use for the same duration, so it is desirable to arrange the two devices such that the regeneration capability is higher than the trap capability, because regeneration process generally needs a longer duration of time. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross sectional view of an embodiment of the trapping device of the present invention. Figure 2 is a schematic drawing of a vacuum system for use with the trapping device shown in Figure 1. Figures 3A & 3B are enlarged cross sectional views of the trap section shown in Figure 1. Figures 4A & 4B are enlarged cross sectional views of the trap section of another embodiment of the present invention. Figure 5 is a schematic drawing of the drive circuit for the air cylinder. Figure 6 is a cross sectional view of the trapping device after a switching operation. Figures 7A & 7B are cross sectional views of other examples showing sealing portions of the trapping device. Figure 8 is a cross sectional view of another example of the trapping device of the present invention. Figure 9 is a schematic drawing of a conventional vacuum system. DESCRIPTION OF THE PREFERRED EMBODIMENTS Several embodiments of the trapping device according to the present invention will be presented with reference to Figures 1-8. Figures 1 shows a first embodiment of the trapping device and Figure 2 shows an evacuation system using the trapping device. The system comprises a hermetic chamber 10 and a vacuum pump 12 communicated through an exhaust path 14, two adjacent regeneration paths 16 disposed on the right and left of the exhaust path 14 and two trap sections 18 which are placed so as to be interchangeable by moving in a direction to traverse the exhaust path 14 and the regeneration path 16. The vacuum pump 12 is a single stage pump, but a multi-stage pump may also be used. A gas scrubber 20 is disposed downstream of the vacuum pump 12. A regeneration gas from a regeneration gas source (not shown) is supplied to the regeneration path 16 for vaporizing the trapped precipitates by heating and transporting the vaporized gas through a branch path and a three-way switching valve 22. The downstream side of the trapping device in the regeneration path 16 is provided with a gas scrubber 24, which may be omitted by sharing the gas scrubber 20. With reference to Figure 1, the trapping device includes a rectangular casing 26 traversing the exhaust path 14 and the regeneration path 16, a transposing shaft 28 transversely crossing the casing 26, and an air cylinder 30 as a drive means for producing a reciprocation motion along the transposing shaft 28. The casing 26 is divided into three spaces in the transverse direction by partition walls 32, into a central trap chamber 34 and two regeneration chambers 36 on both sides, and each chamber has a port connection 39, having a flange 38, to communicate with either the exhaust path 14 or the regeneration path 16. The transposing shaft 28 has three equally-spaced partition plates 40, made of a thermal insulating material, and a plurality of baffle plates 42 between the partition plates 40 are integrally fixed to the transposing shaft 28 by welding, for instance, to maintain a good thermal conduction therebetween. The partition walls 32 of the casing 26 are provided with a center opening 33, of a size to permit the baffle plates 42 to pass through but not the partition plates 40. A bellows 44 is provided between the two transverse end walls of the casing 26 and the countering two partition plates 40 respectively to maintain hermetic sealing between the regeneration path 16 and the external environment. The contact between the partition wall 32 and the partition plates 40 are made through an O-ring which is similar to the one shown in Figure 7 to maintain hermetic sealing between the trap chamber 34 and the regeneration chamber 36. The partition plate 40 is made of a highly thermal insulating material so as to prevent heat transfer between the trap chamber 34 and the regeneration chamber 36. As shown in Figure 3A, the transposing shaft 28 is a cylindrical element made of a good thermal conductivity material, and its interior space is closed off with a central partition plate 40. The transposing shaft 28 has an inner tubes 46 inserted from both ends of the transposing shaft 28 into the vicinity of the central partition plate 40, as shown in Figure 3B. The space between the two tubes constitutes a thermal medium passage 48 for a thermal medium to enter into the inner tube 46 and, upon hitting the central partition plate 40, to return through the outer space to the outer end of the shaft 28. A cooling medium such as liquid nitrogen, chilled air or chilled water is supplied from a supply hose 50, circulated through the thermal medium passage 48 and discharged from a discharge hose 52 connected to each end of the transposing shaft 28. Of the two thermal medium passages 48 connected to the ends of the transposing shaft 28, only one passage connected to the trap chamber 34 having the baffles 42 is used for delivering the cooling medium, and cooling medium is shut off from the other passage connected to the regeneration chamber 36 and may be used instead to deliver a heating medium. In this example, the hoses 50, 52 are connected to the end of an air cylinder, and therefore, it requires less space than a case of connecting them between the air cylinder 30 and the casing 26. Figure 5 shows the piping arrangement for delivering air pressure to the air cylinder 30. The air pressure from an air source is reduced in a regulator 52, and is used to operate the cylinder 30 to move the piston (not shown) forward or backward according to electromagnetic switching signals generated by a solenoid valve 54. The speed of the air cylinder 30 is regulated by a speed controller 56. The solenoid valve 54 is controlled by control signals from, for example, sequencer or relay, and in this case, it exchanges the traps after a predetermined period of time of operation of the trap. A temperature sensor 58 is provided in a suitable location at the baffles 42 in the trap section 18, and pressure sensors 60 are provided in fore- and aft-locations of the trap section 18 in the exhaust path 14. These sensors enable to indirectly monitor the trap performance based on temperatures and pressures. The temperature sensor 58 can also be used to control regeneration of feed material by differentiating separation parameters of the feed material from those of other precipitation products. Next, the trapping process using the trapping device will be described. When the trap is positioned as shown in Figure 1, a cooling medium such as liquid nitrogen, chilled air or chilled water is supplied from the supply hose 50 through the thermal medium passage 48 to the trap section 18 positioned in the trap chamber 34 to cool the baffles 42 through the transposing shaft 28. Therefore, certain elements of the exhaust gas are precipitated in the trap chamber 34 and adheres to the baffles 42. After a certain period of trap operation, the air cylinder 30 is activated, which changes the position of the trap section from that shown in Figure 1 to that shown in Figure 6. The trap section 18 regenerated in the regeneration chamber 36 is transposed to the trap chamber 34, and the trap section 18 located in the trap chamber 36 is transposed to the other regeneration chamber 36 so that trapping and regeneration operations are carried out in respective chambers 34, 36. In carrying out the processes presented above, because the partition plate 40 is made of a thermal insulating material to thermally isolate the trap chamber 34 and the regeneration chamber 36, there is little loss of thermal energy, and trapping and regeneration operations can be carried out quite efficiently. Also, because the regeneration chamber 36 and the transposing shaft 28 are hermetically sealed with the bellows 44, thermal energy loss as well as loss of processing efficiency caused by heat transfer between the chamber 38 and the external environment are minimized. This arrangement assures stable trapping and regeneration operations as well as prevention of infiltration of contaminating elements into the exhaust path 14. Figure 4 shows another way of cooling the baffles in the trapping device shown in Figure 1. The space between the transposing shaft 28 and the inner tube 46 is provided with a cooling device 62 based on a thermoelectric cooling device (Peltier device). A radiation tube 72 is provided between the transposing shaft 28 and the inner tube 46, and the radiation plates 68 of the cooling device 62 is attached to the radiation tube 72, and the cooling plates 66 are attached to the transposing shaft 28 with a spacer 74 made of a highly thermally conductive material such as indium. Within the same space as the cooling device, a heater 64 for regeneration process is also provided. In this embodiment, the cooling device 62 using the thermoelectric elements 70 is activated when the trap section 18 is located in a trap position, and the heat medium passage 48 is provided with a cooling gas such as nitrogen, whereas heater 64 is activated when the trap section 18 is located in a regeneration position. Since the thermoelectric element can provide cooling and heating only by supplying electric energy, the trap system is made simple, installation cost is low and maintenance is easy. Operation is uncomplicated involving relatively simple cooling and on/off temperature control, for example. Also, the cooling/heating effects can be reversed by reversing the polarity of D.C. electricity source, therefore, the heater 64 can be eliminated by employing polarity switching on the power supply. Alternative sealing methods are shown in Figures 7A and 7B. In Figure 7A, the peripheral region of the opening section 33 of the partition wall 32 is made into a tapered surface 76, and an elastic packing 78 is provided on the partition plate 40 to seal against the tapered surface 76. A hermetic sealing is produced by the action of the tapered surface 76 bearing against the elastic packing 78. If the durability of the sealing parts is important, a harder substance such as a metallic packing may be used. Figure 7B shows a type of sealing provided by a stepped section 80 formed on the periphery of the opening section 33 with an intervening O-ring 74 to for enhancing the sealing effect. Temperature sensor 58 provided in the trap section 18 and pressure sensor 60 provided in the exhaust path 16 allow monitoring of operating conditions inside the trap chamber so that, should an abnormal condition develops, a warning signal can be released to take quick remedial steps. For example, an abnormal increase in the temperature of the trap section 18 or an increase in the pressure difference would indicate an increase in thermal load due to the deposition of precipitates. Such a warning can be dealt with, for example, by exchanging the trap even before its allotted time is expired. Of course, such warning signals may be used for basis for switching the trap sections 18. In accordance with the invention, the trap sections are interchanged by a linear movement within the casing 26. Figure 8 shows another embodiment of the invention having a plurality of trap sections 18 arranged in series in the exhaust direction. In this case, a regeneration path 16 is arranged in parallel downstream of the exhaust path 14. The casing extends in the exhaust direction and is provided with a plurality of transposing shafts (two in the drawing) to produce a reciprocating motion by air cylinder. One transposing shaft is assigned to each trap section 18, and each trap section 18 can be independently transferred to either a trap chamber 34 or a regeneration chamber 36. Although this system operates in the same way as the previous apparatus by interchanging the trap section 18 to either the trap chamber 34 or the regeneration chamber 36, this system is advantageous because only one regeneration path is required so that the apparatus may be made more compact. It presents a flexibility that the number of trap sections 18 can be adjusted depending on the operational requirement of the system. For example, if the exhaust volume or precipitation volume increases suddenly, regeneration process can be stopped temporarily so that both trap sections can be placed in the trapping position. This advantage is multiplied by utilizing at least three trap sections. This is because the choice of placing the trap sections in either regeneration or trap position is significantly increased. The operational procedure of this system is different from the previous system in that the regeneration process is carried out by washing the trapping sections with a cleaning solution. The regeneration chamber 36 is provided with a cleaning solution supply pipe 16a opening at the upper portion and a cleaning solution discharge pipe 16b connected to the lower portion. In this embodiment, a plurality of supply pipes 16a are provided at corresponding locations to the trap sections 18. In this trapping device, in the state shown in Figure 8 after interchange of the trap sections 18, a suitable cleaning solution for dissolving the adhering substances is introduced through the inlet opening 16a and is discharged through the outlet 16b. As necessary, the process may be repeated, solution may be sprayed, ultrasonic cleaning may be applied or the cleaning chamber 36 may be filled with the cleaning solution. Or, the cleaning solution may be changed to another type to conduct additional cleaning steps or rinsing steps. To avoid infiltration of the cleaning solution into the vacuum pump and peripheral devices, the trap sections are dried with a drying gas. Such a regeneration apparatus based on cleaning solutions does not require to have the regeneration chamber 36 operate at elevated temperatures, therefore, measures to prevent heating affecting the performance of the trap chamber 34 can be minimized. Also, compared with the regeneration approach based on evaporating the precipitates, the regeneration capacity as well as processing speed are higher. Furthermore, compared with the evaporation approach, post-processing treatments are simpler, and especially, recycling of regenerated substances and storage are more convenient. Also, the configuration shown in Figure 8 has the washing chamber 36 disposed below the trap chamber 34, so that there is no danger of the cleaning solution seeping into the trap chamber 34, and therefore, this type of arrangement is most suitable for regeneration using solutions.

Claims: A trapping device comprising: a casing (26) divided by at least one partition wall (32) into a trap chamber (34) and a regeneration chamber (36), said trap chamber (34) being connected to an exhaust path (34) for trapping certain elements in said exhaust gas, and said regeneration chamber (36) being connected to a regeneration path (16) for vaporizing trapped precipitates; not less than two trap sections (18) being movable between said trap chamber (34) and said regeneration chamber (36); and switching means for a linear movement of said trap sections either to said trap chamber or to said regeneration chamber; wherein said trap sections (18) comprise a shaft portion (28) connected to said switching means and a baffle portion (42) fixed to said shaft portion (28). A trapping device according to claim 1, comprising two regeneration chambers (36) being located on both sides of said trap chamber (34). A trapping device according to claim 1 or 2, wherein said trap sections (18) are connected by said shaft portion (28). A trapping device according to one of the preceding claims, wherein said shaft portion (28) comprises a cooling means for cooling said baffle portion. A trapping device according to one of the preceding claims, wherein said shaft portion (28) comprises a heating means for heating said baffle portion. A trapping device according to one of the preceding claims, wherein a partition plate (40) is provided for operatively providing a sealing with said partition wall (32) between said trap chamber (34) and said regeneration chamber (36). A trapping device according to one of the preceding claims, wherein a flexible closure member (44) is provided for providing a sealing between said trap sections (18) and said casing (26). A trapping device according to one of the preceding claims, wherein a sensor means is provided for sensing an amount of trapped precipitates on said trap section (18), and a control means is provided for switching said trap sections (18) based on the output signals of said sensor means. A trapping device according to one of the preceding claims, wherein said exhaust path (14) is provided for evacuating process gas from a hermetic chamber through a vacuum pump. A trapping device according to one of the preceding claims, wherein said regeneration path (16) is disposed adjacent to said exhaust path (14).

Inventors: MATSUOKA YUJI, NOJI NOBUHARU, NOMURA NORIHIKO, SUGIURA TETSURO, MATSUOKA, YUJI, NOJI, NOBUHARU, NOMURA, NORIHIKO, SUGIURA, TETSURO
Applicants: EBARA CORP, EBARA CORPORATION
Application year: 1997
Main classification: B01D53
IPC codes: C23C16, B01D53, F25B21, F04B37