Abstract:
A method of manufacturing a semiconductor device includes first and second processes, the latter requiring more processing time. An apparatus for performing the semiconductor manufacturing process includes a first reactor, and a plurality of second reactors for each first reactor. A first group of wafers are subjected to the first process within the first reactor, and are then transferred into a second reactor as isolated from the outside air. The first group of wafers is subjected to the second process within the second reactor. At the same time, a second group of wafers are subjected to the first process within the first reactor. After the first process is completed, the second group of wafers is transferred into an unoccupied one of the second reactors as isolated from the outside air. There, the second group of wafers is subjected to the second process. Accordingly, process failures otherwise due to the exposure of the wafers are minimized, and productivity is high despite the difference in the processing times.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method of and apparatus for manufacturing semiconductor devices. More particularly, the present invention relates to a method of and apparatus for forming a film on a plurality of wafers.  
         [0003]     2. Description of the Related Art  
         [0004]     Generally, semiconductor devices are manufactured by repeatedly performing a series of processes, such as photolithography, etching, ion implantation, chemical and mechanical polishing and the like, on a wafer. The respective conditions under which these processes are performed must be optimized such that the semiconductor devices manufactured by the unit processes have enhanced functions and a minimal rate of failure. In addition, the time periods under which the respective processes are carried out should be optimized so as to enhance the productivity of the overall semiconductor device manufacturing process.  
         [0005]     The respective unit processes have been gradually improved in consideration of these goals. However, productivity still lags in many areas of the manufacturing process and the respective unit processes are still prone to failures having a certain root cause.  
         [0006]     For instance, the respective unit processes for manufacturing the semiconductor devices includes a batch type chemical vapor deposition process used to form respective films on a plurality of wafers at the same time. The batch type chemical vapor deposition process is carried out in a furnace maintained at a high temperature. Thus, a native oxide is frequently formed by the reaction of silicon at the upper surface of the wafer and oxygen. In other words, an undesired native oxide is grown on the surface of the wafer before the actual CVD process begins. Accordingly, a film is formed on the native oxide and not on the surface of the wafer, whereby a process failure will occur.  
         [0007]      FIG. 1  is a sectional view of a semiconductor device in which a native oxide has been formed on the surface of the wafer. As shown in the figure, an oxide film  12  is formed on a silicon substrate  10 . A contact hole is then formed to expose a portion of the silicon substrate  10  in which source or drain is formed, for example. Subsequently, a conductive film  16  is formed by chemical vapor deposition on the oxide film  12  to fill the contact hole and contact the exposed portion of the substrate  10 .  
         [0008]     However, as mentioned above, before the conductive film  16  can be formed, a native oxide  14  having a thickness of a few Å to a few hundred Å is formed on the surface exposed by the contact hole. This native oxide  14  is an insulating material formed between the underlying silicon substrate  10  and the conductive film  16 . Accordingly, contact resistance increases. This increase in the contact resistance results in a corresponding decrease in the operation speed of the semiconductor device and otherwise degrades the electrical properties and reliability of the device.  
         [0009]     Accordingly, the native oxide and organic foreign particles are removed prior to the chemical vapor deposition process. This removal of native oxide and organic foreign particles is generally carried out by a wet etch process in which the wafers are dipped in an etch solution in a separate wet etch apparatus. In other words, the native oxide is removed from surfaces of the wafers using chemicals, the chemicals are cleaned from the surfaces of the wafers, and the wafers are dried. Afterwards, the wafers are transferred into the furnace whereupon the chemical vapor deposition process is performed.  
         [0010]     In the method described above, even after the native oxide is removed, the silicon component of the wafer surface may again react with oxygen such that a new native oxide is grown on the surface of the wafer. To prevent this from occurring, the deposition process must be performed within a certain time after the native oxide has been first removed from the surface of the wafer. Otherwise, the new native oxide must be removed from the surface of the wafer.  
         [0011]     However, the mass production of semiconductor devices makes it very difficult to perform the deposition process directly after the wet etch process. Also, incorporating the wet etch process into the overall manufacturing process reduces the manufacturing rate because the wet etch process equipment and the deposition process equipment are separately operated.  
         [0012]     Moreover, a native oxide cannot be completely prevented from re-growing on the surface of the wafer even when the deposition process is performed within the time period called for, by the process recipe, after the native oxide is removed. A native oxide grows rapidly on the surface of the wafer while the wafer is loaded into the furnace because the reaction between oxygen and silicon occurs more actively occurs at the high temperature maintained in the furnace. Thus, it is very difficult to use wet etching to prevent a native oxide from residing on the surface of the wafer before the CVD process is initiated.  
         [0013]     Japanese Patent Laid Open Publication No. 4-188722 discloses a heat treatment apparatus aimed at removing the native oxide from a surface of a wafer and preventing the native oxide from re-growing on the surface. The heat treatment apparatus includes a furnace in which a film is deposited on a wafer, a dry etching chamber disposed to one side of the furnace, a loadlock chamber connecting the dry etch apparatus to the furnace, and a robot arm for loading or unloading the wafer into and from the furnace. In this apparatus, the deposition process is carried out after the native oxide is removed by dry etching and the wafer is loaded into the furnace via the loadlock chamber.  
         [0014]     However, this process requires a great deal of time because the apparatus uses a robot arm to transfer the wafers from the loadlock chamber. More specifically, the wafers are transferred by the robot arm into a boat in the dry etching chamber. The robot arm can transfer only a few sheets (approximately five sheets) of wafers at a time. Thus, the transfer operation must be performed a numbers of times to transfer the total number of sheets of wafers (25 sheets to one hundred sheets) of one batch. Once the dry etching is completed, the wafers disposed in the boat within the etching chamber are again transferred, this time to a boat within the furnace. After the deposition process is completed, the wafers are unloaded from a boat within the furnace and are transferred out of the furnace using the robot arm.  
       SUMMARY OF THE INVENTION  
       [0015]     An object of the present invention is to solve the above-described problems of the prior art.  
         [0016]     That is, one object of the present invention is to provide a method of manufacturing a semiconductor device that includes first and second processes requiring different processing times and yet is both highly productive and highly efficient. Likewise, an object of the present invention is to provide an apparatus capable of performing the semiconductor manufacturing process without producing devices prone to process failures and without the need for significant downtime.  
         [0017]     The apparatus of the present invention includes a first batch reactor in which the first process is performed, and at least two second reactors in which the second process requiring more time than the first process is performed. A loadlock chamber communicates with inlets of the first and second reactors so as to define a path along which the group of wafers can be transferred therebetween. The loadlock chamber is sealed from the outside air. A transfer module is provided in the loadlock chamber for transferring the wafers.  
         [0018]     The first reactor may comprises a dry etching module, whereas the second reactors may comprise furnaces of a chemical vapor deposition system.  
         [0019]     In the method of the present invention, a first group of wafers is transferred into the first reactor whereupon the first process, e.g., dry etching, is performed. Once the first process has been completed, the first group of wafers is transferred into one of the second reactors while in a state isolated from external air. The second process which requires more time than the first process, e.g., chemical vapor deposition, is performed on the first group of wafers within the second reactor, and at the same time a second group of wafers is transferred into the first reactor. Then, the first process is performed on the second group of wafers within the first reactor. Subsequently, the second group of wafers is transferred into one of the second reactors, that does not already contain a batch wafers, while the second group of wafers is isolated from the external air. There, the second process is performed on the second group of wafers during the same period of time that the second process is being completed on the first group of wafers. Once the second process is completed, the wafers are unloaded from the second reactors. The steps can be repeated with respect to the wafers.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments thereof made with reference to the attached drawings, of which:  
         [0021]      FIG. 1  is a sectional view of a semiconductor wafer on which a native oxide film has grown;  
         [0022]      FIG. 2  is a schematic longitudinal sectional view of a semiconductor processing apparatus according to the present invention;  
         [0023]      FIG. 3  is a schematic plan view of the semiconductor processing apparatus according to the present invention;  
         [0024]      FIG. 4  is a schematic perspective view of the semiconductor processing apparatus according to the present invention;  
         [0025]      FIG. 5  is a sectional view of a dry etch module of the apparatus; and  
         [0026]      FIG. 6  is a process flow chart illustrating a method of processing a semiconductor wafer in according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     The preferred embodiments of the present invention will hereinafter be described in detail with reference to accompanying drawings.  
         [0028]     First, the semiconductor processing apparatus according to the present invention will be described with reference to FIGS.  2  to  5 .  
         [0029]     The semiconductor processing apparatus includes a boat  100  for receiving a plurality of sheets of wafers. The boat  100  can receive 25 sheets to 100 sheets of wafers, constituting one process group or batch of wafers. The apparatus also includes a dry etch module  102  for performing a dry etch process on a batch of wafers. The dry etch module  102  removes native oxide from the surfaces of the wafers. The dry etch module  102  will now be described in detail with reference to  FIG. 5 .  
         [0030]     The dry etch module  102  comprises an etching chamber  104  having a volume capable of receiving the boat  100  on which the plurality of sheets of wafers are mounted. An inlet through which the boat  100  is introduced into the chamber  104  is disposed at a lower portion of the etching chamber  104 . An etch gas supply line  106  is connected to the etching chamber  104  for supplying an etch gas into the etching chamber  104 . A remote plasma generator  108  is connected with the etch gas supply line  106 . The remote plasma generator is a device that is well-known, per se, for exciting the etch gas that is introduced into the etching chamber  104  of the dry etch module.  
         [0031]     A first gas supply  110  is connected with the remote plasma generator  108 , and supplies the etch gas into the etching chamber  104  via the remote plasma generator  108 . A second gas supply  112  is connected to a line branched from the etch gas supply line  106  between the etching chamber  104  and the remote plasma generator  108 . Accordingly, gas supplied from the second etch gas supply  112  is supplied to the etching chamber  104  without passing the remote plasma generator  108 .  
         [0032]     A first distributing plate  114  having a plurality of holes  114   a  is disposed within the etching chamber  104 . The first distributing plate  114  is interposed between the side of the etching chamber  104  into which the etch gas supply line  106  enters and the region in the chamber dedicated to receive the boat  100 . Accordingly, the etch gas from the etch gas supply line  106  is supplied into the etching chamber  104  through the plurality of holes  114   a  formed in the distributing plate  114 . The sizes of the holes  144   a  in the first distributing plate  114  vary such that the etch gas is uniformly supplied into the region in the chamber dedicated to receive the boat  100 . Specifically, the holes in a first portion of the plate adjacent the location (outlet port) at which the etch gas supply line  106  opens into the chamber  104  are preferably smaller than those holes in a second portion of the plate that is remote (located further) from the outlet port of the etch gas supply line  106 .  
         [0033]     An exhaust system  116  is connected to the etching chamber  104  for exhausting etch gas that is supplied into the etching chamber but does not react with the wafers.  
         [0034]     A second distributing plate  118  having a plurality of holes  118   a  is disposed in the chamber  104 . The second distributing plate  118  is interposed between the side of the etching chamber  104  into which the exhaust system  116  opens and the region dedicated to receive the boat  100  in the etching chamber  104 . Accordingly, the non-reacted gas is exhausted to the exhaust system  116  through the plurality of holes  118   a  in the second distributing plate  118 . The sizes of the holes  118   a  in the second distributing plate  118  vary such that the non-reacted etch gas will be uniformly exhausted from the etch chamber  104 . That is, the holes  118   a  in a first portion of the plate adjacent to the exhaust system  116  are smaller than the holes that are in a second portion of the plate remote (located further) from the location (port) at which the exhaust system  116  opens into the chamber  104 .  
         [0035]     A temperature control device  120  for elevating or lowering the temperature of the wafers mounted in the boat  100  is disposed along the inner side portion of the etching chamber  104 . The wafers are preferably maintained at a temperature within a range of from about 15° C. to 30° C. while the native oxide is etched from the surfaces of the wafers. By-products are generated at the surfaces of the wafers a result of the dry etch process. The wafers must be heat-treated to detach and thus to remove these by-products from the surfaces of the wafers. Accordingly, the temperature control device  120  elevates the temperature within the etching chamber  104  after the etching process is performed.  
         [0036]     Next, the remainder of the semiconductor processing apparatus will be described with reference, again, to  FIGS. 2-4 .  
         [0037]     The semiconductor processing apparatus includes a plurality of furnaces  122  each having a volume sufficient to receive the boat  100 , and each for forming films on a plurality of wafers mounted on the boat  100 . The furnaces  122  each have an inlet, though which the boat  100  is introduced, at a lower portion of the furnace  122 .  
         [0038]     The batch type of chemical vapor deposition process that is carried out in each of the furnaces  122  generally requires a process time that is two to three times greater than the time required to carry out the process of removing native oxide in the dry etch module  102 . Thus, the number of furnaces  122  depends on the time required to carry out the etch process. Specifically, the number of the furnaces  122  is such that a ratio of the etch process time to the deposition process time is equal to or less than a ratio of one etch module to the number of furnaces. The present embodiment comprises two furnaces  122 , namely a first furnace  122   a  and a second furnace  122   b.  Also, the number of boats  100  depends on the number of the furnaces  122 . In particular, the number of boats  100  is equal to or greater than the number of the furnaces  122 , so that the chemical vapor deposition processes can be simultaneously carried out in the furnaces  122 .  
         [0039]     The semiconductor process apparatus also includes a loadlock chamber  124  communicating with the inlet of each of the furnaces  122  and the inlet of the dry etch module  102 . The loadlock chamber  124  is sealed from the outer environment.  
         [0040]     A nitrogen gas supply part  124   a  is connected to one side of the loadlock chamber  124  for supplying nitrogen gas into the chamber. An exhaust pump  124   b  is also connected to the loadlock chamber  124  for exhausting gas from the loadlock chamber  124 . Nitrogen gas is continuously supplied into the loadlock chamber  124  by the nitrogen gas supply part  124   a  while the gas within the loadlock chamber  124  is partially exhausted, such the loadlock chamber  124  is filled only with the nitrogen gas after a certain period of time. Although gas flows from the loadlock chamber  124 , the small flow of gas hardly influences the process, and yet the loadlock chamber  124  is easy to maintain. Alternatively, a vacuum pump may be connected to one side of the loadlock chamber  124 . The vacuum pump maintains a vacuum inside the loadlock chamber  124  to thereby prevent air from residing in the loadlock chamber.  
         [0041]     A transfer module  130  is disposed within the loadlock chamber  124 . The transfer module  130  functions to mount one group of wafers on the boat  100  and transfer the wafer-laden boat  100  into the dry etch module  102  and the furnaces  122   a,    122   b.  To this end, the transfer module  130  includes a boat standby support  130   a  on which the boat containing a plurality of wafers stands by. Also, the transfer module  130  includes a wafer transfer device  130   c  for mounting several sheets of wafers into the boat  100  at the boat standby support  130   a.  The wafer transfer device  130   c  is controlled to load the wafers, that are to be processed, into the boat  100 , and to unload the wafers, that have undergone the deposition process, from the boat  100 . The wafer transfer device  130   c  can transfer about five sheets of wafers into the boat  100  once.  
         [0042]     Still further, the transfer module  130  includes a first boat changer  130   b  for transferring the wafer-laden boat  100  from the boat standby support  130   a  to a position adjacent the inlet of the dry etch module  102  or the inlet of one of the furnaces  122 . The first boat changer  130   b  horizontally is capable of being rotated in a horizontal plane and is capable of being translated forward and backward while the boat  100  is disposed on an upper surface thereof. The first boat changer  130   b  is controlled to first transfer the boat  100  from the standby support  130   a  to a position adjacent the inlet of the dry etch module  102 . After the wafers in the boat  100  are etched in the dry etch module  102 , the first boat changer  130   b  moves from a position adjacent the inlet of the dry etch module  102  to a position adjacent the inlet of one of the furnaces  122 . Accordingly, the dry etch module  102  and the furnaces  122  are arranged to minimize the path along which the boat  100  is to be moved by the first boat changer  130   b.    
         [0043]     Thus when there are two furnaces  122  as in the present embodiment, the dry etch module  102  is arranged between the first furnace  122   a  and the second furnace  122   b  so as to minimize the path along which the boat  100  must be moved during each transfer operation. Also, each of the furnaces  122  and the dry etch module  102  are preferably spaced from each other by a distance no greater than the rotational radius of the first boat changer  130   b  such that the above-mentioned transfer operation can be carried out simply by rotationally driving the first boat changer  130   b.    
         [0044]     The transfer module  130  also includes a boat elevator  130   d  operable to raise and lower the boat  100 . The boat elevator  130   d  is controlled to raise a boat  100  that has been transferred to a location adjacent the inlet of a furnace  122  or the inlet  104   a  of the dry etch module  102  by the first boat changer  130   b,  and to thereby load the boat  100  into the dry etch module  102  or the furnace  122 . In this embodiment, a respective boat elevator  130   d  is provided for each of the dry etch module  102  and the furnaces  122 , whereby boat elevators  130   d  load the boat into the dry etch module  102  and the furnaces  122 , respectively.  
         [0045]     A cooling station  132  ( FIG. 3 ) is disposed within the loadlock chamber  124  for reducing the temperature of the boat  100  on which the wafers are mounted. A second boat changer  130   e  is disposed between the cooling station  132  and the boat standby support  130   a  for transferring the boat  100  from the boat standby support  130   a  to the cooling station  132 .  
         [0046]     Accordingly, the boat  100  containing wafers which have undergone the deposition process may be transferred by the second boat changer  130   e  from the boat standby support  130   a  to the cooling station  132 . Then, the temperature of the wafers, and the temperature of the boat  100  containing the wafers are lowered in the cooling station  132 , Subsequently, the boat  100  is transferred to the boat standby support  130   a  by the second boat changer  130   e.  Finally, the wafers are transferred to the outside of the loadlock chamber  124  by the wafer transfer device  130   c.    
         [0047]     As described above, the semiconductor device processing apparatus is furnished with multiple furnaces  122  for each dry etch module  102  in consideration of the fact that the deposition process requires more time than the etch process. Accordingly, there is no down-time and thus, the semiconductor manufacturing process is performed with a high degree of productivity. Also, the re-growing of the native oxide is prevented because the deposition process is performed directly after the native oxide removing process without having exposed the wafer to the outside air.  
         [0048]     Next, the semiconductor device manufacturing process will be described in specific detail with reference to the flow chart of  FIG. 6 .  
         [0049]     A first group of wafers is loaded onto the first boat (step S 10 ). The first boat can accommodate 25 to 100 sheets of wafers. Specifically, the first boat while empty is placed in a standby position on the boat standby support  130   a.  Then, the wafer transfer device  130   c  transfers multiple sheets of wafers onto the first boat. The wafer transfer device  130   c  can transfer about five sheets of wafers at a time and so, the transfer operation is repeated, if necessary, until a desired number of wafers are loaded.  
         [0050]     The first boat is then transferred into the dry etch module  102  (step S 12 ). Specifically, the first boat is transferred by the first boat changer  130   b  from the standby position to a position adjacent the inlet  104   a  of the dry etch module  102 . The first boat is then raised by the boat elevator  130   d  into the etching chamber  104 .  
         [0051]     Then, the first group of wafers is dry-etched in the dry etch module  102  to remove native oxide from the surfaces of the wafers (step S 14 ). Initially, the temperature of the etching chamber  104  is maintained at a temperature of about 15-30° C. In this state, an etch gas is supplied into the etching chamber  104 . The etch gas includes a reaction gas comprising a fluorine-containing compound capable of etching oxides with ease, and a carrier gas for carrying the reaction gas. The carrier gas dissociates the fluorine atoms from the reaction gas to form fluorine radicals in order to perform the etch process. For example, NF 3  can be used as the reaction gas, and excited nitrogen gas, excited hydrogen gas or a mixture thereof can be used as the carrier gas. The fluorine radicals are bonded (reacted) with the silicon of the native oxide (SiO 2 ) formed on the wafer to form an etch product such as SiF.  
         [0052]     Subsequently, the temperature in the etching chamber  104  and thus, the surface temperature of the first group of wafers, is raised until the etch product attached to the surface of the wafers is vaporized. In particular, the temperature of the etching chamber  104  is raised to about 150-300° C., whereupon the etch product is vaporized, and the vaporized etch product is exhausted to the outside of the etching chamber  104 .  
         [0053]     Once the native oxide formed on the surfaces of the first group of wafers is removed, the first boat is transferred is elevated to the first furnace  122   a  (step S 16 ). The path along which the boat is transferred from the dry etch module  102  to the first furnace  122   a  is filled with nitrogen gas, or is maintained in a vacuum, to isolate the wafers loaded on the boat from outside air containing oxygen.  
         [0054]     Specifically, the first boat is lowered through the inlet  104   a  of the dry etch module by the boat elevator  130   d  and thus is transferred to the outside of the dry etch module  102 . Subsequently, the first boat is transferred by the first boat changer  130   b  to a position adjacent the inlet of the first furnace  122   a.  The transferred first boat is raised by the boat elevator  130   d  into the first furnace  122   a.    
         [0055]     Next, a chemical vapor deposition process is carried out in the first furnace  122   a  to form a film on the wafers mounted in the first boat. At the same time, a second group of wafers is loaded into the second boat (step S 18 ). The method of loading the second group of wafers into the second boat is identical to that of loading the first group of wafers into the first boat. Accordingly, a detailed description thereof will be omitted.  
         [0056]     The second boat is then transferred into the dry etch module  102  (step S 20 ). To this end, the second boat is first transferred to a position adjacent the inlet  104   a  of the dry etch module  102  by the first boat changer  130   b.  The second boat is then raised into the dry etch module  102  by the boat elevator  130   d  associated with the dry etch module  102 . Native oxide formed on the surfaces of the second group of wafers is dry-etched in the dry etch module  102  (step S 22 ).  
         [0057]     Once the native oxide formed on the surfaces of the wafers has been removed, the second boat is transferred to one of the furnaces  122  that does not already contain a wafer boat, i.e., the second furnace  122   b.  In this case, as well, the second boat is transferred from the dry etch module  102  to the furnace  122   b  while the wafers on the second boat remain isolated from the outside air (step S 24 ).  
         [0058]     A chemical vapor deposition process is then carried in the second furnace  122   b  to form a film on the wafers mounted on the second boat (step S 26 ).  
         [0059]     Again, the chemical vapor deposition process requires two or three times the amount of time as the preceding native oxide removing process because the native oxide formed on the surfaces of the wafers is relatively thin. In particular, the native oxide is only a few Å or a few hundred Å. Therefore, the series of processes (steps S 20  to S 26 ) from the process of removing the native oxide from the second group of wafers and the chemical vapor deposition process of forming a film on the wafers can be performed while the chemical vapor deposition process is performed with respect to the first group of wafers.  
         [0060]     Once the chemical vapor deposition process is completed on both groups of wafers, the boats on which the wafers are loaded are discharged from the respective furnaces  122  (step S 28 ). In particular, the first boat containing wafers on which the processes are first completed is discharged from the first furnace  122   a,  and then the second boat is discharged from the second furnace  122   b.    
         [0061]     Next, a cooling process may be performed to lower the temperature of the boats discharged from the furnaces  122  and the temperature of the wafers loaded in the boats. The cooling process is performed in the separate cooling station  132  that is furnished outside the furnaces  122 . To this end, a boat is transferred from the furnace  122  in which the deposition process has been performed to the boat standby support  130   a,  and the boat is then transferred form the boat standby part  130   a  to the cooling station  132  by the second boat changer  130   e.  Once the cooling process is completed, the boat is again transferred to the boat standby support  130   a  and the cooled wafers are transferred from the boat to the outside of the loadlock chamber  104  by the wafer transfer device  130   c.    
         [0062]     According to the semiconductor device processing method described above, the etch process (a preceding process) and the deposition process (the subsequent process) can be performed without delay. Accordingly, the processing method has a high degree of productivity. Also, a re-growing of the native oxide can be minimized because the deposition process is performed without the wafer having been exposed to outside air after the native oxide has been first removed form the wafer. Accordingly, when the deposition process forms a conductive film over a contact hole that exposes a surface of the wafer that was subjected to the etch process, minimal contact resistance occurs. The result is a semiconductor device having enhanced characteristics and reliability.  
         [0063]     Although the present invention has been described in detail with reference to the preferred embodiments thereof, various changes, substitutions and alterations thereto will be apparent to those skilled in the art that. All such changes, substitutions and alterations are seen to be within the true spirit and scope of the invention as defined by the appended claims.