Abstract:
A substrate processing equipment comprises two pod supporting stages and two independently operable pod door openers. Each pod supporting stage is capable of placing thereon a pod for containing substrates therein. Each pod door openers having means for permitting access to the substrates inside the pod placed on a corresponding pod supporting stage.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a semiconductor processing equipment; and, more particularly, to a device for moving doors of substrate carriers, e.g., for use in a semiconductor processing equipment such as a batch-type vertical apparatus for performing a diffusion or a CVD (chemical vapor deposition) process to form diffusion, dielectric or metallic layers on semiconductor wafers. 
     BACKGROUND OF THE INVENTION 
     In a semiconductor processing equipment such as a batch-type vertical apparatus for performing a diffusion or a CVD process, semiconductor wafers are loaded into and unloaded from the apparatus while being kept in cassettes. Two kinds of carriers have been conventionally used. One is a box-shaped cassette having a pair of openings on two opposite sides and the other is a box-shaped FOUP (front opening unified pod; hereinafter, pod) having an opening on one side thereof with a pod door removably mounted thereon. 
     In the semiconductor processing equipment using the pod as the carrier, the wafers can be kept protected from contaminations of ambient atmosphere while being transferred since the pod containing the wafers is airtightly closed. Accordingly, the degree of cleanliness required for a clean room of the semiconductor processing equipment may be lowered, which in turn reduces cost for the maintenance of the clean room. For such reasons, the pod is gaining popularity as the carrier in the semiconductor processing equipment recently. 
     The semiconductor processing equipment using the pod as the wafer carrier is provided with a pod door opener for remaining and restoring the pod door. One example of such conventional pod door opener is disclosed in U.S. Pat. No. 5,772,386, wherein the pod door opener is disposed on a wafer loading port and equipped with a closure capable of frictionally engaging with a door of the pod located on the wafer loading port. The pod can be uncovered by lowering down the closure while the closure engages with the door. 
     However, since the conventional semiconductor processing equipment is provided with only a single wafer loading port, the lead time required in preparing wafers for an actual process increases due to replacement of a pod on the wafer loading port with another, which in turn lengthens the overall processing time of the semiconductor manufacturing process, thereby reducing the throughput thereof. 
     Another equipment having a multi-stage pod door system is disclosed in U.S. Pat. No. 6,042,324. Since, however, the pod doors of the equipment are simultaneously opened as a single unit by a vertical actuator, the lead time may not be reduced and the height of the equipment increases. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide a semiconductor processing equipment capable of increasing the throughput thereof. 
     In accordance with one aspect of the present invention, there is provided a semiconductor processing equipment comprising: 
     a plurality of wafer loading ports for seating carriers containing a number of wafers, the wafer loading ports being vertically stacked; and 
     a same number of carrier door openers as the wafer loading ports for opening doors of the carriers while the carriers are disposed respectively on the wafer loading ports, the pod door openers being operated independently of each other, 
     wherein, while one carrier on one of the wafer loading ports is under wafer loading or unloading process, other carriers are prepared for the wafer loading or unloading process on other wafer loading ports. 
     In accordance with another aspect of the present invention, there is provided a method for processing wafers for use in a method for processing substrates for use in a semiconductor processing equipment having at least two loading ports, a plurality of carriers each of which contains a portion of the substrates, a carrier shelf for storing the carriers, a reaction chamber and a boat for loading and unloading the substrates into and out of the reaction chamber, the method comprising the step of transferring the substrates between the carriers and the boat, wherein the transferring step includes the steps of: 
     conveying one carrier between the carrier shelf and one loading port; and 
     carrying the portion of the substrates contained in the carrier between the carrier and the boat, 
     wherein, while the carrier on the loading port is under the transferring step, another carrier is transferred between the carrier shelf and another loading port. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which: 
     FIG. 1 schematically shows a semiconductor processing equipment in accordance with the present invention; 
     FIG. 2 illustrates a perspective front view of a pod door opener; 
     FIG. 3 is a perspective view of the pod door opener with pods disposed on the wafer loading ports; 
     FIG. 4 describes a schematic perspective rear view of the pod door opener with some parts eliminated; 
     FIG. 5 represents a perspective view of the eliminated parts V in FIG. 4; 
     FIG. 6A shows a plan view of a mechanism for mapping with the arm retracted; 
     FIG. 6B shows a plan view of a mechanism for mapping with the arm in operation position; 
     FIG. 7 illustrates a sequence for wafer loading and unloading in accordance with a first preferred embodiment of the present invention; 
     FIG. 8 illustrates another sequence for wafer loading and unloading in accordance with a second preferred embodiment of the present invention; 
     FIG. 9 illustrates still another sequence for wafer loading and unloading in accordance with a third preferred embodiment of the present invention; and 
     FIG. 10 illustrates still another sequence for wafer loading and unloading in accordance with a fourth preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. 
     FIG. 1 shows a semiconductor processing equipment  1  having a batch-type vertical apparatus for performing, e.g., a diffusion or a CVD process. The semiconductor processing equipment  1  is provided with an airtightly sealed housing  2 . At an upper portion of the rear side of the housing  2 , a heater unit  3  is vertically installed and a process tube  4  is concentrically disposed within the heater unit  3 . The process tube  4  has a gas supply line  5  for supplying a process gas or a purge gas into the process tube  4 , and an exhaust line  6  for use in evacuating the process tube  4 . A boat elevator  7  is installed below the process tube  4  to move a boat  8  having a boat receptacle  8   a  up and down, thereby loading or unloading the boat  8  into or from the process tube  4 . A plurality of wafers  9  can be loaded in the boat  8  in such a manner that the centers of the wafers are vertically aligned while maintaining a predetermined distance between two neighboring wafers. 
     Formed on a front wall of the housing  2  is a pod load/unload opening (not shown) through which pods  10  can be loaded into or unloaded from the housing  2 . The pod load/unload opening can be open and closed by a shutter (not shown). In front of the pod load/unload opening, a pod stage  11  is provided for receiving multiple, e.g., two, pods at a time. 
     At the upper central portion of the semiconductor processing equipment  1 , a rotatable pod shelf  12  is arranged. The pod shelf  12  is capable of holding, e.g., eight pods  10 . The numbers of pods that the pod shelf  12  can support is not limited to eight but may be increased, e.g., up to sixteen. The pod shelf  12  has two vertically disposed swastika-shaped pod supporting plates, each being capable of holding, e.g., 4 pods simultaneously. The pod shelf  12  is uni-directionally rotatable in a horizontal plane on a pitch-by-pitch basis by a rotary actuator (not shown), e.g., a stepping motor. 
     Below the pod shelf  12 , there is provided a two pod openers  20  each of which includes a wafer loading port  13 , bulkhead  21  and a closure  40 . The wafer loading ports  13  through which the wafers are carried into or out of the pod  10  are vertically stacked. 
     Inside the housing  2 , a pod handler  14  is installed between the pod stage  11  and the pod shelf  12 . The pod handler  14  is adapted to transfer pods between the pod shelf  12  and the wafer loading ports  13  and between the pod shelf  12  and the pod stage  11 . Pod transfer may also be conducted between the pod stage  11  and the wafer loading ports  13 , if necessary. Moreover, a wafer carry assembly  15  is provided between the boat  8  and the wafer loading ports  13  to transfer wafers  9  therebetween. 
     Details of the pod opener  20  will now be described with reference to FIGS. 1 to  6 B. 
     As shown in FIG. 1, the semiconductor processing equipment in accordance with the present invention includes a vertically oriented bulkhead  21  which is used by both of the pod openers  20  in common. The wafer loading ports  13  are vertically provided on the front surface of the bulkhead  21  facing the pod stage  11  and the corresponding closures  40  are provided on the rear surface of the bulkhead  21  facing the wafer carry assembly  15  as shown in FIGS. 2 and 3. The bulkhead  21  has rectangular-shaped openings  22  through which pod doors  10   a  are coupled with the corresponding door openers  20 . The size of an opening  22  is larger than that of the pod door  10   a , which also has a rectangular shape, as shown in FIGS. 6A and 6B. The rectangular-shaped openings  22  are vertically provided in the bulkhead  21 . 
     As shown in FIG. 2, a support  23  for each of the wafer loading ports  13  is horizontally provided on the front surface of the bulkhead  21  below each opening  22 . The plan view of the support  23  is of a substantially square frame shape having some cutout portion at the distal end thereof away from the bulkhead  21 . A pair of parallel guide rails  24  are mounted on an upper plate of the support  23 , the rails  24  running normal to the front surface of the bulkhead  21 . A loading platform  27  is slidably mounted on the guide rails  24  through guide blocks  25 . The loading platform  27  can move toward and away from the opening  22 , i.e., in a to-and-fro direction, by an air cylinder  26  mounted on the upper plate of the support  23 . 
     The loading platform  27  also has a substantially square frame shape with some cutout portion at the distal end thereof away from the bulkhead  21 . On the upper surface of the loading platform  27 , vertically oriented alignment pins  28  provided at locations corresponding to, e.g., three corner points of an equilateral triangle. These pins are adapted to match with corresponding holes (not shown) formed at a bottom surface of the pod  10 . 
     As shown in FIG. 4, a guide rail  30  for each of the pod openers  20  is mounted on the rear surface of the bulkhead  21  below the corresponding opening  22 . The guide rail  30  is extended horizontally parallel to the rear surface of the bulkhead  21 , i.e., along the left-right direction. An angle-shaped slider  31  is slidably supported by the guide rail  30  and movable in the left-right direction. An air cylinder  32  is mounted on a vertical portion of the angle-shaped slider  31  along the left-right direction. An end portion of a piston rod  32   a  of the air cylinder  32  is anchored to the bulkhead  21 . The movement of the angle-shaped slider  31  is controlled by the retraction and extension of the air cylinder  32 . 
     As shown in FIG. 5, a pair of parallel guide rails  33  running along the to-and-fro direction are installed on an upper surface of a horizontal portion of the angle-shaped slider  31 . A back/forth slider  34  is slidably mounted on the guide rails  33 . The back/forth slider  34  has a guide hole  35  which extends in the left-right direction in one end portion along the left-right direction, e.g., a left end portion of the back/forth slider  34 . A bracket  36  is fixedly mounted on the left side portion of the angle-shaped slider  31  and a rotary actuator  37  is vertically mounted on the bracket  36 . A circularly moving guide pin  38  provided at an arm  37   a  of the rotary actuator  37  is slidably engaged with the guide hole  35 . Therefore, the back/forth slider  34  is driven to move toward and away from the bulkhead  21  linearly along the to-and-fro direction by the rotating movement of the rotary actuator  37 . 
     Mounted on the top surface of the back/forth slider  34  is a bracket  39 . A square-shaped closure  40  larger than the opening  22  is vertically fixed to the bracket  39 . The square-shaped closure  40  is movable in the to-and-fro direction by the movement of the back/forth slider  34  and in the left-right direction by the movement of the angle-shaped slider  31 . The front surface of the closure  40  facing toward the wafer loading ports  13  has a peripheral region and a central region thicker than the peripheral region. That is, the distance from the front surface at the central region (hereinafter, referred to as central front surface) to the rear surface of the closure  40  is greater than that for the front surface at the peripheral region (hereinafter, referred to as peripheral surface) of the closure  40 . The size of the central region of the front surface of the closure  40  is slightly smaller than the opening  22 , so that the central region can get into the opening  22 . 
     By such configuration, a peripheral front surface of the closure  40  can firmly abuts with the periphery of the opening  22  by moving forward the back/forth slider  34  against the bulkhead  21  and the opening  22  can be closed. 
     Further, as shown in FIGS. 5 to  6 A, a packing member  55 , e.g., an O-ring, may be provided around the peripheral surface of the closure  40  in order to air-tightly seal against the rear side wall of the bulkhead  21  around the opening  22  when the closure  40  abuts with the bulkhead  21 . Another packing member  56  may be provided on the peripheral region of the central front surface in order to seal against the pod door  10   a  lodged on the wafer loading port  13  when the closure  40  abuts with the bulkhead  21 . The packing member  56  serves to prevent potential contaminants on the door  10   a  of the pod  10  from entering into the processing area where the wafer carry assembly  15  is located. An additional packing member  54  may also be provided on the region of the front side wall of the bulkhead  21  around the opening  22  in order to seal against the door frame of the pod  10  when the pod  10  is arranged to move against the bulkhead  21 . 
     As shown in FIGS. 2 and 4, a pair of rotatable keys  41  are arranged on the left and the right sides of the central front surface of the closure  40 . The keys  41  are located along the horizontal centerline on the central front surface. Each key is coupled with a pulley  42  provided on the rear surface of the closure  40 . Both pulleys  42  are connected by a belt  43  which has a connection plate  44 . An air cylinder  45  is horizontally mounted above one of the pulleys  42  and a piston rod thereof is connected to the connection plate  44  such that extension and retraction of the air cylinder  45  can produce a reciprocating rotary motion of the pulleys  42 , thereby inducing the keys  41  to rotate. In addition, each key  41  includes a coupling member  41   a  at the end portion thereof for engaging with a locking mechanism (not shown) on the door  10   a  of the pod  10 . 
     As shown in FIG. 2, a pair of suction elements  46  capable of holding the pod door  10   a  by vacuum suction are diagonally provided on two corner regions of the central front surface of the closure  40 . Each suction element  46  has a suction pipe  47  and the suction pipe  47  is connected with an air exhaust/supply pipe (not shown). End portions of the suction pipes  47  are adapted to match with aligning holes in the pod door  10   a . Therefore, the suction pipes also act as supporting members for holding the pod door  10   a.    
     Referring to FIGS. 2,  4 ,  6 A and  6 B, on the front side wall of the bulkhead  21 , a rotary actuator  50  having a vertically oriented rotary shaft  50   a  is installed beside the opening  22 . A C-shaped arm  51  is provided to pass through an opening  52  in the bulkhead  21 . One end of the C-shaped arm  51  is connected to the rotary shaft  50   a  and a mapping device  53  for detecting the locations of wafers in the pod  10  is installed at the other end. The C-shaped arm  51  can be rotated in a horizontal plane. 
     In operation, the pods  10  are loaded onto the pod stage  11  through the pod load/unload opening and then transferred by the pod handler  14  to predetermined positions on the pod shelf  12  for temporary storage as shown in FIG.  1 . 
     FIG. 7 illustrates the pod transferring process between the pod shelf  12  and the wafer loading ports  13  and also the wafer transferring process between the pods on the wafer loading ports  13  and the wafer boat  8  in accordance with the first embodiment of the present invention. 
     The two pod openers  20  are arranged to close the openings  22  such that the packing member  55  seals against the rear side wall of the bulkhead  21 . One pod  10  is transferred from the pod shelf  12  to, e.g., the upper wafer loading port  13  by the pod handler  14  and disposed on the loading platform  27 . The three alignment pins  28  on the loading platform  27  engage with the corresponding three holes (not shown) formed under the pod  10  to thereby complete the alignment of the pod  10  on the loading platform  27 . 
     The pod  10  provided on the loading platform  27  is moved toward the bulkhead  21  by the extension of the air cylinder  26  in such a manner that the respective packing members  54  and  56  are airtightly in contact with the pod door  10   a  and the pod frame therearound as shown in FIG.  6 A. The keys  41  and the suction pipes  47  of the closure  40  are also inserted in the key holes (not shown) and the aligning holes provided on the door  10   a , respectively. The pod transferring process described above is generally represented as a process “A” at the first stage in FIG.  7 . 
     After completing the pod transferring process “A”, a negative pressure is applied through the air exhaust/supply pipes  47  inside the suction elements  46  so that the suction elements  46  hold the door  10   a  by vacuum suction. Thereafter, the keys  41  are rotated by the air cylinder  45  so that the coupling members  41   a  unlock the door  10   a.    
     Next, the back/forth slider  34  is moved away from the bulkhead  21  by the rotary actuator  37  and then the angle-shaped slider  31  is moved away from the opening  22  by the air cylinder  32  so that the closure  40  holding the pod door  10   a  by the suction elements  46  is moved to a retreated position. By such movement of the closure  40 , the door  10   a  is separated from the pod  10  and the pod is opened as shown in FIG. 6B, thereby the wafers  9  loaded in the pod  10  is put under a condition that the wafer carry assembly  15  can access thereto. The pod door opening process described above is represented as a process “B” at the first stage in FIG.  7 . 
     Thereafter, as shown in FIG. 6B, the mapping device  53  is moved to the wafers inside the pod  10  through the opening  22  by the rotary actuator  50  and performs mapping by detecting the positions of the wafers, i.e., by identifying slots holding the wafers. After mapping is completed, the mapping apparatus  53  is returned to its initial position by the rotary actuator  50 . The mapping process described above is generally represented as a process “C” at the first stage in FIG.  7 . 
     Next, the wafers in the pod  10  on the wafer loading port  13  are transferred to the wafer boat  8  by the wafer transfer assembly  15 . The wafer transferring process described above is generally represented as a process “D” at the first stage in FIG.  7 . 
     While the wafer transferring process is performed at the first, e.g., the upper wafer loading port  13 , the pod transferring process “A”, the pod door opening process “B” and the mapping process “C” are sequentially carried out at the second, e.g., the lower wafer loading port  13 . the second wafer loading port  13  waits (process E) until the wafer transferring process “D” at the first wafer loading port  13  is completed. 
     Accordingly, upon the completion of the wafer transferring process “D” of the first wafer loading port  13  at the second stage, the wafer transferring process “D” can be started at the second wafer loading port  13  as shown in FIG. 7 (third stage). As a result, the wafer transferring operation can be alternatively performed by the wafer loading port  13  without interruption due to the replacement of the pods  10  and thus the system efficiency or the throughput of the semiconductor processing equipment can be improved. 
     During the third stage shown in FIG. 7, where the wafer transferring process “D” is carried out by the second wafer loading port  13 , a pod door closing process “E”, a pod changing process “A”, the pod door opening process “B”, the mapping process “C” and the waiting process “F” are sequentially carried out in that order, so that the wafer transferring process “D” can be started by the first wafer loading port  13  immediately after the completion of the process “D” at the second wafer loading port  13 . 
     The pod door closing process is carried out as follows. The closure  40  holding the pod door  10   a  is removed from the retreated position toward the opening  22  by the air cylinder  32  and then toward the empty pod  10  by the rotary actuator  37  to close the pod  10  by the pod door  10   a  thereafter, the keys  41  are rotated by the air cylinder  45  to actuate the locking mechanism of the pod door  10   a . After locking, the negative pressure inside the suction element  46  is removed by supplying a positive pressure through the pipe  47  and the closure  40 . The closure  40  remains in that position until the pod door opening process “B” is resumed. 
     The pod changing process “A” is carried out as follows. After the pod door  10   a  is restored on the empty pod  10  by the pod door closing process “E”, the loading platform  27  of the first wafer loading port holding the empty pod is moved away from the bulkhead  21  by the air cylinder  26 . The empty pod  10  is then stored back to the pod shelf  12  and a new pod holding wafer therein is transferred to the first wafer loading port. Thereafter, the newly supplied pod is provided to the closure  40  in an identical manner as in the pod transferring process “A”. The remaining process “B”, “C” and “F” are identical to those of the second stage. 
     The wafer loading processes are repeated until the described number of wafers are loaded from the pods  10  to the wafer boat  8 . After transferring the described number of wafers, the last two empty pods may be removed to the pod shelf  12  or stayed on the wafer loading ports  13 . Alternatively, only one empty port  13  may remain at the one wafer loading port  13 . The number of wafers which the wafer boat  8  can hold for one batch process is, e.g., 100 to 150, which is several times greater than that of wafers which one pod can contain therein, e.g., 25. 
     After the predetermined number of unprocessed wafers are loaded on the wafer boat  8 , the boat elevator  7  lifts the wafer boat  8  into the process tube  4 . When the wafer boat  8  is introduced into the process tube  4 , a lower end opening of the process tube  4  is hermetically sealed by the boat receptacle  8   a.    
     Next, the process tube  4  is evacuated through the exhaust pipe  6  to reduce the pressure therein down to a predetermined vacuum level. Thereafter, a desired wafer process, e.g., a diffusion or a CVD process, is carried out on the loaded wafers by controlling temperatures at desired levels by using the heater unit  3  while supplying predetermined process gases into the process tube  4  through the gas supply line  5 . 
     After a predetermined processing time has elapsed, the wafer boat  8  holding processed wafers is discharged from the process tube  4  and returned to its initial position. During the period in which the wafer boat  8  is loaded into and unloaded from the process tube  4  and the wafers are processed in the process tube  4 , either one or both of the pods  10  may be prepared at the corresponding wafer loading ports  13  in order to receive the processed wafers. 
     Thereafter, the wafer transfer assembly  15  transfers a portion of the processed wafers held in the wafer boat  8  to one empty pod  10  disposed on, e.g., the first wafer loading port  13  (upper loading port) with the door  10   a  opened. This process corresponds to the wafer transferring process “D” at the second stage shown in FIG.  7 . After completing the wafer transferring process “D” at one wafer loading port, the same process is carried out at the other wafer loading port with the door thereof being opened. This process corresponds to the process “D” at the third stage in FIG.  7 . 
     While the wafer loading process “D” is carried out at the second wafer loading port, the pod door closing process “E”, the pod changing process “A”, the pod door opening process “B” and the waiting process “F” are carried out at the first wafer loading port as in the third stage of FIG.  7 . The mapping process “C” is not performed because the processed wafers are transferred into an empty pod at this time. 
     The process “E”, “A”, “B” and “F” are identical to those described with respect to the wafer loading process from the pods  10  to the wafer boat  8 , excepting that the pod changing process “A” represents the process transferring a pod containing the processed wafers to the pod shelf  12  from a wafer loading port and moving an empty pod from the pod shelf  12  to the wafer loading port  13 . 
     In case all the empty pods have been transferred from the wafer loading ports  13  to the pod shelf  12  after loading all the wafers onto the boat  8 , the processed wafer unloading process can be accomplished as follows. First, one empty pod is transferred from the pod shelf  12  to one of the wafer loading ports and the pod door  10   a  thereof is opened. These correspond to the process “A” and “B” of the first stage in FIG.  7 . The timing of the processes “A” and “B” can be controlled such that the wafer transferring process “D” at the second stage can be started immediately after completing the pod door opening process “B” at the first stage. Of course, the mapping process “C” is omitted at the first stage because the pod is empty. 
     Thereafter at the second stage, the wafer transferring process “D” is carried out at the first wafer loading port  12 , while the process “A”, “B” and “F” are sequentially performed at the second wafer loading port. Then, the process at the third stage can be carried out as described above. 
     The processes are repeated until transferring all the processed wafers from the wafer boat  8  to the empty pods, which in turn are returned to the pod shelf  12 . 
     As described above, since the wafer transfer assembly  15  can transfer the processed wafers from the wafer boat  8  to the pods  10  continuously without having to wait for the replacement of the pods  10  on the wafer loading ports  13 , the throughput of semiconductor processing equipment  1  can be substantially increased. 
     The pods  10  containing the processed wafers are temporarily stored in the pod shelf  12  and then transferred to the pod stage  11  by the pod handler  14 . Next, the pods on the pod stage  11  are transferred through the pod load/unload opening (not shown) to another equipment for a subsequent process and new pods containing unprocessed wafers are charged on the pod stage  11 . 
     The processes of transferring pods between the pod shelf  12  and the pod stage  11  and charging and discharging pods into and from the semiconductor processing equipment  1  can be carried out while wafers are being processed in the process tube  4  and transferred between the wafer boat  8  and the pods  10  on the wafer loading ports  13 . As a result, the total process time of the semiconductor processing equipment  1  can be reduced. 
     Referring to FIGS. 8 to  10 , there are illustrated wafer transferring sequences in accordance with further preferred embodiments of the present invention. In the sequences shown FIGS. 8 to  10 , wafer mapping is completed at least for the pods containing wafers required for one batch process before the continuous wafer loading process begins for that batch process, e.g., by transferring the corresponding pods from the pod stage  11  to the wafer loading ports  13  in order to carry out the mapping and then moving them to pod shelf  12 . Therefore, the process sequences in FIGS. 8 to  10  will be described by assuming that the wafer mapping has been completed for the pods stored on the pod shelf  12  containing wafers needed for one batch process. The processes identified as reference numerals “A” to “F” and “A” in FIGS. 8 to  10  are basically identical to those of FIG.  7 . 
     The wafer transferring sequence in accordance with the second embodiment of the present invention will be described with reference to FIG.  8 . At the first stage of the sequence for transferring unprocessed wafers to the wafer boat  8 , a first pod containing unprocessed wafers is transferred from the pod shelf  12  to a first wafer loading port (process “A”) and the door of the first pod is opened (process “B”). 
     Immediately thereafter at the second stage, wafer transferring from the first pod to the wafer boat  8  (process “D”) starts and, at the same time, a second pod containing the unprocessed wafers are transferred to a second wafer loading port (process “A”) and waits until the wafer transferring process “D” at the first wafer loading port is completed (process “F”). 
     At the third stage, the door of the second pod is opened (process “B”) and the wafers therein are transferred to the boat  8  (process “D”) and the door is restored on the empty first pod (process “E”), which is then replaced with another pod carrying unprocessed wafer (process “A”), the new pod remaining at the first wafer loading port until the wafer loading process at the second wafer loading port is completed (process “F”). The processes described in connection with the third stage are alternately carried out until all the required wafers for one batch process are transferred to the wafer boat  8 . 
     As described above in the second embodiment of the present invention, the pod transferring process “A” and the pod changing process “A” for one wafer loading port are carried out during the wafer transferring process “D” at the other wafer loading port; and the pod door opening process “B” for one wafer loading port and the pod door closing process “E” for the other wafer loading port are simultaneously conducted. 
     The process sequence of the second embodiment for transferring processed wafers to empty pods is identical to that for transferring unprocessed wafers to the wafer boat  8 , excepting that the pod changing process “A” in the process sequence for transferring processed wafers represents the process of transferring a pod containing the processed wafers from a wafer loading port to the pod shelf  12  and then moving an empty pod from the pod shelf  12  to that wafer loading port. The process “A” of transferring a first empty wafer to one of the wafer loading ports is controlled in such a manner that the wafer transferring from the boat to the first empty pod can be conducted immediately after completing the opening of the door of the first pod. 
     The sequence shown in FIG. 9 in accordance with the third embodiment of the present invention is identical to that of the second embodiment shown in FIG. 8, excepting that the pod door opening process “B” at one wafer loading port is conducted during the wafer transferring process “D” at the other wafer loading port in such a manner that the process “D” at one wafer loading port can be started upon the completion of the process “D” at the other wafer loading port. Also, the door closing process “E” at one wafer loading port and the wafer transferring process “D” at the other wafer loading port start simultaneously. 
     FIG. 10 illustrates a wafer transferring process in accordance with the fourth embodiment of the present invention. The process sequence shown in FIG. 10 is identical to that of the third embodiment shown in FIG. 9, excepting that the sequence of the waiting process “F” and the pod door opening process “B” is reversed at every stage. 
     Following advantages can be achieved in accordance with the present invention. 
     1) By vertically installing a pair of the pod door openers each of which is capable of independently opening and restoring the door of a pod on each wafer loading port, the wafer transferring process can be independently conducted at one wafer loading port while the other loading port is preparing for the subsequent wafer transferring process. As a result, the total process time can be considerably reduced and therefore the throughput of the semiconductor processing equipment can be increased. 
     2) By vertically arranging the wafer loading ports, the system efficiency can be improved without increasing the floor area or footprint of the semiconductor processing equipment. 
     3) The vertically arranged wafer loading ports eliminates the need for the left-right movement of the wafer carry assembly  15 , thereby simplifying the structure thereof and improving the system efficiency without increasing the width of the processing equipment. 
     4) The independently operable mapping devices provided to the respective wafer loading ports enables the mapping process at one wafer loading port and the wafer transferring process at the other to be conducted simultaneously. As a result, the loading time needed for the subsequent wafer transferring process can be eliminated and therefore the total process time of the semiconductor processing equipment can be considerably reduced, thereby increasing the system efficiency. 
     5) Simplified and small sized mapping device can be obtained by employing the rotary actuating mechanism therefor, wherein the rotary actuator is mounted on the front side wall of the bulkhead and the arm fixedly coupled thereto passes through the opening in the bulkhead and the mapping device is attached at the end of the arm, enabling the mapping device to approach the wafers in a pod by the rotation of the rotary actuator. 
     6) Any vertical component in the motion of the pod openers would result in the height increase thereof, which in turn makes the pod shelf located above the pod openers to be disposed at a higher position and increases the height of the semiconductor processing equipment. The increased number of vertically arranged pod openers would impose the multiplicative effect in the vertical position of the pod shelf and the height increase of the processing equipment itself. The higher vertical position of the pod shelf will entails the increase of the pod-transfer time, thereby decreasing the throughput of the equipment. 
     In contrast, the pod openers  20  in accordance with the present invention solely operate along horizontal directions and do not contribute at all to the height increase of the equipment and the pod-transfer time. Further, the pod shelf is arranged to receive two columns of pods along the width direction of the processing equipment, whereas only one column of wafer transferring ports is provided under the pod shelf. As a result, the purely transitional lateral motion of the pod openers can be accommodated by the reserved space under the pod shelf and, therefore, the system efficiency and the throughput can be improved without increasing the pod transfer time and sacrificing the floor area of the processing equipment. 
     It is to be appreciated that the configuration of the semiconductor processing equipment may be varied appropriately if necessary. 
     For instance, the number of the wafer loading ports is not limited to two but more than two wafer loading ports can be installed vertically of if the height increase can be accommodated. 
     In addition, in lieu of the rotary actuator for actuating the mapping device, another mechanism using an X-Y axis robot can be employed. Moreover, the mapping device can be omitted if so required. 
     Furthermore, the processing equipment can be of the type capable of processing other substrates, e.g., photo masks, printed circuit boards, liquid crystal panels, compact disks and magnetic disk, than the semiconductor wafers. 
     The processing equipment can be of the type adapted to perform, e.g., oxide formation, diffusion process and other types of heat treating process in place of the CVD. The present invention is also applicable to other types of semiconductor processing equipments than the batch type vertical processor. 
     While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.