Abstract:
PFC is recycled from a gas mixture using adsorption technology and techniques. Two adsorption units each include an adsorbent having a selectivity by which the PFC is selectively adsorbed with respect to the other gas(es) that make up the mixture. The gas mixture is selectively supplied to one of the first and second adsorption units and a condition is created in the first adsorption unit so that the PFC is adsorbed in the first adsorption unit. Once the adsorbent is saturated in the first adsorption unit, a condition is created in the first adsorption unit that causes the PFC to be desorbed. At this time, the gas mixture is selectively supplied to the second adsorption unit, and a condition is created in the second adsorption unit so that the PFC is adsorbed. Once the adsorbent is saturated in the second adsorption unit, a condition is created in the second adsorption unit that causes the PFC to be desorbed. High-purity PFC gas can be obtained from the exhaust gas even if the gas mixture is exhaust gas of a semiconductor device manufacturing process having a low concentration of PFC.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method of and an apparatus for recycling perfluorocompounds. More particularly, the present invention relates to a method of and an apparatus for recycling perfluorocompounds using adsorption separation technology.  
         [0003]     2. Description of the Related Art  
         [0004]     Perfluorocompounds (PFCs) are widely used throughout the semiconductor device manufacturing industry. In particular, perfluorocompounds (PFCs) are used in chemical vapor deposition (CVD), etching, and chamber cleaning processes. For example, CF 4  or C 2 F 6  gas is widely used in the etching of semiconductor substrates. Most of these PFC gases are nonvolatile and thus are very stable. Also, the PFC gases have a long retention time in the atmosphere and absorb ultraviolet rays radiating from the Earth. Thus, the PFC gases have a very high global warming potential (GWP). Despite this, the use of PFCs is increasing in the semiconductor device manufacturing industry.  
         [0005]     Several techniques, though, have been developed to reduce PFC emissions. One method for preventing PFC gas from being emitted into the atmosphere is to burn the PFC component of gas being discharged from semiconductor device manufacturing equipment. This method decomposes PFC gas effectively and thus, prevents environmental pollution. However, hydrogen fluoride is generated as a byproduct of the combustion process. Therefore, this method has problems in terms of its duration and stability. Also, the combustion process requires fuel and oxygen. Thus, additional operational costs are incurred when the combustion method is incorporated into the overall manufacturing process. Another method of suppressing the discharge of PFC gas is a distillation method. However, it is difficult to separate PFC gas from the discharge gas using distillation because of the physical properties of PFC gas. In addition, distillation requires specialized equipment which, again, adds to the cost of the manufacturing process.  
       SUMMARY OF THE INVENTION  
       [0006]     Objects of the present invention are to provide a recycling method and apparatus in which high-purity PFC gas can be obtained from a gas mixture having a low-concentration of the PFC gas.  
         [0007]     Another object of the present invention is to provide a low cost and efficient way to handle exhaust gas containing a PFC gas without emitting the PFC gas into the atmosphere.  
         [0008]     Still another object of the present invention is to provide a semiconductor device manufacturing facility that curbs the emission of PFCs without the use of expensive auxiliary equipment.  
         [0009]     Still another object of the present invention is to provide a semiconductor device manufacturing facility that efficiently recycles PFCs used in the facility.  
         [0010]     According to one aspect of the present invention, PFC is recycled from an exhaust gas using adsorption and desorption cycles.  
         [0011]     According to another aspect of the present invention, an apparatus is provided in which the adsorption and desorption cycles can be executed simultaneously.  
         [0012]     The present invention provides a method of recycling a PFC in which initially a gas mixture including a PFC gas is selectively supplied to the first of first and second adsorption units each including an adsorbent. At this time, the PFC gas is adsorbed in the first adsorption unit. The PFC is desorbed in the first adsorption unit once the adsorbent is saturated. The gas mixture is also selectively supplied to and adsorbed in the second adsorption unit. The PFC gas is then desorbed in the second adsorption unit once the adsorbent of the second adsorption unit is saturated. Finally, the desorbed PFC gas is recollected.  
         [0013]     The steps may be repeated after the PFC gas is desorbed in the second adsorption unit. Also, the gas mixture may be selectively supplied to and adsorbed in the second adsorption unit while PFC gas is being desorbed in the first adsorption unit. Similarly, the gas mixture may be selectively supplied to and adsorbed in the first adsorption unit while PFC gas is being desorbed in the second adsorption unit. In addition, the first adsorption unit may be kept at room temperature and atmospheric pressure while the PFC gas is being adsorbed therein. Alternatively, a relatively low temperature and high pressure may be maintained in the first adsorption unit to facilitate the adsorption of the PFC gas. On the other hand, a relatively high temperature and low pressure are maintained in the first adsorption unit to facilitate the desorbing of the PFC gas. Likewise, the second adsorption unit may be kept at room temperature and atmospheric pressure while the PFC gas is being adsorbed therein. Alternatively, a relatively low temperature and high pressure may be maintained in the second adsorption unit to facilitate the adsorption of the PFC gas. On the other hand, a relatively high temperature and low pressure are maintained in the second adsorption unit to facilitate the desorbing of the PFC gas.  
         [0014]     Also, the first adsorption unit may be pressurized before the gas mixture containing the PFC gas is introduced into the first adsorption unit. Similarly, the second adsorption unit may be pressurized before the gas mixture containing the PFC gas is introduced into the second adsorption unit. To this end, the non-adsorbed gas in one adsorption unit may be supplied from that unit to the other unit in which the adsorption of PFC gas is about to take place.  
         [0015]     The present invention also provides a method of recycling perfluorocompound (PFC) in which a gas mixture containing PFC gas is supplied to a first adsorption unit and the PFC gas is adsorbed in the first adsorption unit, and the PFC gas is then desorbed in the first adsorption unit while the second adsorption unit is pressurized and the gas mixture is supplied to the second adsorption unit. Thus, PFC gas is adsorbed in the second unit while PFC gas is being desorbed in the first adsorption unit. Next, the PFC gas is desorbed in the second adsorption unit while the first adsorption unit is pressurized and the gas mixture is selectively supplied to the first adsorption unit. Thus, PFC gas is adsorbed in the first adsorption unit while PFC gas is being desorbed in the second adsorption unit.  
         [0016]     The first adsorption unit may be initially pressurized with nitrogen. Then, the second adsorption unit is pressurized by supplying it with the non-adsorbed gas from the first adsorption unit. Similarly, in subsequent cycles in which PFC gas is to be adsorbed in the first adsorption unit, the first adsorption unit is pressurized by supplying it with non-adsorbed gas from the second adsorption unit.  
         [0017]     The present invention also provide an adsorption apparatus for recycling a perfluorocompound (PFC), which includes first and second adsorption units, a first pipe to which inlets of the first and second adsorption units are commonly connected, valves disposed in-line between the first pipe and the inlets of the first and second adsorption units, respectively, second and third pipes respectively connected to outlets of the first and second adsorption units, valves disposed in-line with the second and third pipes, respectively, a fourth pipe interconnecting the first and second adsorption units, and a valve disposed in-line with the fourth pipe. The valves are movable to positions at which gas that is not adsorbed by an adsorbent of the first adsorption unit flows through the fourth pipe into the second adsorption unit, and to positions at which gas that is not adsorbed by an adsorbent of the second adsorption unit flows through the fourth pipe into the first adsorption unit the adsorption apparatus may also includes a storage tank connected to the second and third pipes for storing the PFC desorbed in the first and second adsorption units.  
         [0018]     The adsorbent may be silica gel, activated alumina, zeolite or activated carbon. Preferably, the adsorbent is activated carbon because activated carbon has a relatively great ability to adsorb PFCs.  
         [0019]     The present invention also provides a semiconductor manufacturing facility in which the adsorption apparatus is connected to the exhaust line of a reaction chamber of a processing apparatus in which substrates are processed using PFC gas.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     These and other objects, features and advantages of the invention will be better understood from the following detailed description of the preferred embodiments thereof made with reference to the accompanying drawings. In the drawings:  
         [0021]      FIG. 1  is a schematic diagram of an embodiment of a semiconductor device manufacturing facility including an adsorption apparatus according to the present invention;  
         [0022]      FIG. 2  is a flowchart of a method of recycling PFCs according to the present invention; and  
         [0023]      FIG. 3  is a schematic diagram of another embodiment of a semiconductor device manufacturing facility including an adsorption apparatus according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     Referring to  FIG. 1 , an adsorption apparatus  100  for recycling PFC gas according to the present invention includes at least two adsorption devices  110  and  120 , such as adsorption towers or adsorption beds. For the sake of simplicity, the present invention will be described hereinafter with respect to the adsorption devices  110  and  120  being adsorption towers.  
         [0025]     A reaction chamber  192  of a semiconductor device processing apparatus  190 , such as an etch apparatus, is connected to inlets of the two adsorption towers  110  and  120  through main gas feed pipe  102  and branch pipes  103  and  104 . More specifically, an exhaust line  194  extends between and connects the reaction chamber  192  and the main gas feed pipe  102 . Gas including PFC is introduced into the reaction chamber  192  through a gas supply line  191 . A semiconductor substrate W is processed in the reaction chamber  192  and gas is discharged from the reaction chamber through the exhaust line  194 . The gas thus flows into the main gas feed pipe  102 . The branch pipes  103  and  104  are commonly connected to the main gas feed pipe  102 , and are respectively connected to the adsorption towers  110  and  120 . Valves  101 ,  112  and  122  are disposed in the pipes  102 ,  103  and  104 , respectively. Each of the valves can be moved between open and closed positions to selectively allow and block the flow of gas through the pipe in which the valve is disposed. Thus, a mixture of gas discharged from the semiconductor device processing apparatus  190  is supplied to the first adsorption tower  110  or the second adsorption tower  120  through the pipe  103  or  104 , respectively, depending on whether valves  112  and  122  are open or closed. The exhaust gas contains PFC gas. For example, the exhaust gas includes excess CF 4  or C 2 F 6 , used as an etching gas in a process of etching a semiconductor substrate W.  
         [0026]     The adsorption towers  110  and  120  are filled with an adsorbent, such as silica gel, activated alumina, zeolite, or activated carbon that will adsorb PFC gas with a relatively high selectivity with respect to other gases that may make up the exhaust gas. Preferably, the adsorbent is activated carbon because among the above-mentioned adsorbents, activated carbon has the greatest ability to adsorb PFC gas. Therefore, PFC gas can adsorbed in the adsorption towers  110  and  120  until the adsorbent is saturated with the gas. Also, PFC will be adsorbed or desorbed by the adsorbent (e.g., activated carbon) depending on the pressure and temperature in the adsorption tower. Therefore, the apparatus also includes a first temperature regulating device  111  for controlling the temperature of the first adsorption tower  110 , and a second temperature regulating device  121  for controlling the temperature of the second adsorption tower  120 .  
         [0027]     The other component(s) of the exhaust gas, that is gas other than the PFC, is not adsorbed in the adsorption towers  110  and  120  but it is emitted into the atmosphere. Such gas will be referred to as non-adsorbed gas. Also, the adsorption towers  110  and  120  are connected to one another by a pipe  108 . A valve  113  is disposed in the pipe. The valve may be opened and closed to selectively place the adsorption towers  110  and  120  in communication with each other. Thus, the non-adsorbed gas can be discharged from one adsorption tower to the other through pipe  108 .  
         [0028]     Pipes  105  and  106  are connected to outlets of the adsorption towers  110  and  120 , respectively. The pipes  105  and  106  are commonly connected to a main collection pipe  107 . Valves  114 ,  124  and  132  are disposed in the pipes  105 ,  106  and  107 , respectively. Each of the valves can be moved between open and closed positions to selectively allow and block the flow of PFC gas through the pipe in which the valve is disposed. Thus, PFC gas desorbed in the first adsorption tower  110  flows through the pipes  105  and  107  when the valves  114  and  132  are opened. Likewise, PFC desorbed in the second adsorption tower  120  flows through the pipes  106  and  107  when the valves  124  and  132 . The main recollection pipe  107  is connected to a gas storage tank  130 . Therefore, the PFC gas desorbed in the first and second adsorption towers  110  and  120  may be recollected and stored in the storage tank  130 .  
         [0029]     The concentration of PFC gas is relatively low in the exhaust gas discharged during a typical semiconductor device manufacturing process, such as an etch process. Accordingly, the adsorption towers  110  and  120  can be pressurized to cause the adsorbent to more efficiently adsorb the PFC gas. To this end, a source of nitrogen (N 2 ) is connected to the adsorption towers  110  and  120 . The source of nitrogen (N 2 ) may be connected to the towers  110  and  120  through the main gas feed pipe  102 . Alternatively, the adsorption towers  110  and  120  can be pressurized using non-adsorbed gas that is fed through the pipe  108 .  
         [0030]     A method of recycling PFC gas using the apparatus of  FIG. 1  will now be described in more detail with reference to  FIG. 2 . At the start of the process, a PFC gas is introduced into a reaction chamber of a substrate processing apparatus. For example, CF 4  and/or C 2 F 6  is introduced into a reaction chamber  192  of an etch apparatus  190  as an etching gas. An excess amount of the PFC gas does not react with the substrate W in the reaction chamber  192 . Gas is discharged from the reaction chamber  192  during and after the etching process. This exhaust gas thus contains the excess PFC gas. The exhaust gas containing PFC gas, e.g., CF 4  and/or C 2 F 6 , is discharged from the reaction chamber  192  of the etch apparatus  190  to the pipe  102  via exhaust line  194 . The exhaust gas is first supplied to the first adsorption tower  110  by opening the valve  112  and closing the valve  122 .  
         [0031]     The PFC component of the exhaust gas has a relatively low concentration. Therefore, the first adsorption tower  110  may be pre-pressurized so that the adsorbent will adsorb the low concentration of PFC gas more effectively. Specifically, the first adsorption tower  110  may be pre-pressurized by introducing nitrogen gas into the first adsorption tower  110  through pipes  102  and  103 .  
         [0032]     The PFC component of the exhaust gas introduced into the first adsorption tower  110  will be adsorbed or desorbed by the adsorbent (preferably activated carbon) depending on the pressure and temperature in the adsorption tower. Specifically, in this type of separation process, the concentration of PFC gas in the adsorbent increases (adsorption) as the gas pressure increases and temperature decreases, and the concentration of PFC gas in the adsorbent decreases (desorption) when the gas pressure decreases and temperature increases.  
         [0033]     A condition is established in the first adsorption unit so that the gas comprising a PFC will be adsorbed by the adsorbent of the first adsorption unit. For example, the first adsorption unit may be maintained at room temperature and atmospheric pressure. However, alternatively, a relatively high pressure and low temperature condition is established in the first adsorption tower  110 . The exhaust gas is injected into the first adsorption tower  110  through branch pipe  103 . Therefore, the PFC component of the exhaust gas is selectively adsorbed by the adsorbent (e.g., activated carbon) in the first adsorption tower  110  (S 100 ). On the other hand, the non-adsorbed gas passes through the adsorption tower  110  to the second adsorption tower  120  through the pipe  108  to pre-pressurize the second adsorption tower  120 .  
         [0034]     The exhaust gas is fed into the first adsorption tower  110  until the adsorbent is saturated with the PFC gas (S 110 ). Then, the PFC gas is desorbed (S 120 ) by establishing a condition in the first adsorption tower  110 , that is, a low pressure (e.g., close to a vacuum level) and high temperature condition (e.g., 100° C.), under which the absorbent will give up PFC gas. At this time, the valves  114  and  132  are opened. As a result, the desorbed PFC gas flows through the pipe  105  so as to be recollected. The recollected PFC gas may be stored in the storage tank  130 .  
         [0035]     In addition, the valve  122  is opened while desorption is taking place in the first adsorption tower  110 . Accordingly, the exhaust gas is supplied to the second adsorption tower  120  through the pipe  104 . As a result, the PFC component of the exhaust gas is adsorbed in the second adsorption tower  120  (S 200 ). To this end, the condition that was established in the first adsorption tower  110  to facilitate the adsorption of PFC gas by the adsorbent, e.g., a high pressure and low temperature condition, is established in the second adsorption tower  120 . Also, if the second adsorption tower is pre-pressurized by the non-adsorbed gas flowing from the first adsorption tower  110 , the PFC gas is adsorbed more effectively.  
         [0036]     The exhaust gas is fed into the second adsorption tower  120  until the adsorbent in the second adsorption tower  120  is saturated (S 210 ). At this time, the conditions under which PFC is desorbed from the adsorbent are established in the second adsorption tower  120  (S 220 ). That is, again, a low pressure and high temperature condition is established in the second adsorption tower  120 . Then, the PFC gas flows through the pipe  106  and is recollected, e.g., is stored in the storage tank  130  along with PFC gas desorbed in the first adsorption tower  110 . The valve  112  is opened while the desorption is taking place in the second adsorption tower  120  so that the exhaust gas is introduced into the first adsorption tower  110 , whereby another cycle in which PFC gas is adsorbed in the first adsorption tower  110  takes place.  
         [0037]     Also, during the time in which the PFC gas is being adsorbed in the second adsorption tower  120  (S 200 ), the non-adsorbed gas in the second adsorption tower  120  is introduced into the first adsorption tower  110  through the pipe  108 . In this way, the first adsorption tower  110  is pre-pressurized. That is, the first adsorption tower  110  is initially pressurized by supplying nitrogen gas into the first adsorption tower  10 ; then, for each cycle after that in which adsorption is to take place in the first adsorption tower  110 , the first adsorption tower  110  is pre-pressurized with non-adsorbed gas from the second adsorption tower  120 .  
         [0038]     As is clear from the description above, PFC gas is efficiently recollected because the adsorption/desorption processes are continuously and simultaneously taking place. Specifically, after the initial adsorption process, adsorption is always taking place in one of the first and second adsorption towers  110  and  120  while desorption is taking place in the other of the first and second adsorption towers  110  and  120 . The recollected gas may contain a slight amount of gas other than pure PFC gas. In this case, the recollected gas is again supplied to the first adsorption tower and the second adsorption tower, and the adsorption and desorption processes are repeated on the recollected gas. Consequently, PFC gas of a higher purity can be obtained. To this end, an adsorption apparatus as shown in  FIG. 3  may be used.  
         [0039]     Referring to  FIG. 3 , the adsorption apparatus  200  includes two adsorption towers  210  and  220 , a main exhaust gas feed pipe  202  connected to the reaction chamber  292  of a processing apparatus  290  of semiconductor device manufacturing equipment so as to receive exhaust gas discharged from the reaction chamber, and branch pipes  203 ,  204 . A temperature regulating device  211  controls the temperature of the first adsorption tower  210 . Likewise, a second temperature regulating device  221  controls the temperature of the second adsorption tower  220 .  
         [0040]     A semiconductor device processing apparatus  290  is connected to the adsorption apparatus. More specifically, an exhaust line  294  extends between and connects a reaction chamber  292  of the processing apparatus  290  and the main gas feed pipe  202 . Gas including PFC is introduced into the reaction chamber  292  through a gas supply line  291 . A semiconductor substrate W is processed in the reaction chamber  292  and gas is discharged from the reaction chamber through the exhaust line  294 . Thus, the discharged gas will flow to the main exhaust gas feed pipe  202 . The branch pipes  203 ,  204  are commonly connected to the main exhaust gas feed pipe  202  and are connected to the adsorption towers  210  and  220 , respectively.  
         [0041]     In addition, valves  212 ,  222  are disposed in-line in the branch pipes  203 ,  204 , respectively. The valves  212  and  222  are movable between open and closed positions to selectively allow and block the flow of gas to the adsorption towers  210  and  220 . That is, gas selectively flows through pipes  203  and  204  according to the positions of the valves  212  and  222 .  
         [0042]     Pipes  205  and  206  are connected to outlets of the adsorption towers  210  and  220 , respectively. Thus, PFC adsorbed and then desorbed in the adsorption towers  210  and  220  flows through pipes  205  and  206  so as to be recollected. The pipes  205  and  206  are connected in common to a main recollection pipe  207 . The main recollection pipe  207  is, in turn, connected to a gas storage tank  208 . Thus, the gas may be stored in the storage tank  208  as it is recollected.  
         [0043]     Furthermore, a return pipe  209  interconnects the pipes  205  and  206 . A valve  234  is disposed in the return pipe  209  to selectively allow and block the flow of gas through the pipe  209 . Also, valves  236  and  238  are disposed in the pipes  236  and  205 ,  206 , respectively, between the locations at which the return pipe  209  interconnects the pipes  205  and  206  and the locations at which the pipes  205  and  206  are connected to the main recollection pipe  207 . Thus, the valve  234  may be opened and the valves  236  and  238  may be closed so that the recollected gas flowing from one of the adsorption towers  210  and  220  may be returned to the other of the adsorption towers  210  and  220  through the return pipe  209 , whereupon the adsorption and desorption processes are repeated on the recollected gas. In addition, valves  214  and  224  are disposed in series in-line in a return pipe  240 . The valves  214  and  224  may be opened so that recollected gas flowing from one of the adsorption towers  210  and  222  may be returned to the other of the adsorption towers  210  and  22  through the return pipe  240 .  
         [0044]     Otherwise, the operation of the adsorption apparatus  200  is essentially the same as that described with reference to  FIG. 2 . For instance, the adsorption towers  210  and  220  are connected to one another by a pipe  208 . A valve  213  is disposed in the pipe. The valve may be opened and closed to selectively place the adsorption towers  110  and  120  in communication with each other. Thus, the non-adsorbed gas can be introduced from one of the adsorption towers  210  and  220  to the other of the adsorption towers  210  and  220  through the pipe  208  to pressurize the other of the adsorption towers  210  and  220 .  
         [0045]     According to the present invention, as described above, PFC gas can be separated from the exhaust gas of semiconductor device manufacturing equipment merely by controlling the pressure and temperature of an adsorption unit. Thus, the present invention provides an economical approach to handling exhaust gas of the type that typically has a low concentration of PFC gas, such as that of produced by semiconductor device manufacturing equipment. Also, the adsorption/desorption process itself is an effective way to separate out the PFC gas from the exhaust gas which typically contains a low concentration of the PFC gas. Moreover, PFC gas which is known to contribute to global warming is prevented from being emitted into the atmosphere. Also, the present invention recollects high purity PFC gas from the exhaust gas. Thus, its reuse is possible. Any non-adsorbed gas can be discharged with the use of a mass flow controller (MFC).  
         [0046]     Finally, although the present invention has been described above in connection with the preferred embodiments thereof, the present invention is not so limited. Rather, various modifications of the disclosed embodiments will be apparent to those skilled in the art that. Thus, modifications of the disclosed embodiments are seen to be within the true spirit and scope of the invention as defined by the appended claims.