Abstract:
A substrate processing apparatus comprises a substrate transfer chamber; a plurality of substrate processing chambers disposed on a first side wall of the substrate transfer chamber and stacked in the vertical direction; a plurality of first gate valves, each being disposed between each of the substrate processing chambers and the substrate transfer chamber; a substrate accommodating chamber disposed on a second side wall of the substrate transfer chamber; a substrate transfer device, disposed within the substrate transfer chamber, for transferring the substrate under reduced pressure between the substrate processing chambers and the substrate accommodating chamber; an elevator disposed outside the substrate transfer chamber and comprising a stationary portion and an elevating portion which is vertically movable with respect to the stationary portion; a rigid connecting member capable of moving through a through-hole formed in a predetermined face of the substrate transfer chamber, the rigid connecting member mechanically connecting the elevating portion and the substrate transfer device through the through-hole; and a sealing member for establishing a hermetic vacuum seal between the predetermined surface and the connecting member which penetrates through the through-hole.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a substrate processing apparatus, and particularly to a semiconductor wafer processing apparatus. 
     2. Description of the Related Art 
     Conventionally, in order to reduce the area occupied by a semiconductor wafer processing apparatus, a semiconductor wafer processing apparatus as shown in FIG. 1 (Refer to Japanese Patent Application Laid-Open No. 5-152215.) is proposed. 
     In a semiconductor wafer processing apparatus 2000 of FIG. 1, a plurality of reaction chambers 204 are arranged in layers perpendicular to an installation floor, thereby reducing the floor area occupied by the semiconductor wafer processing apparatus 2000. 
     In the semiconductor wafer processing apparatus 2000, a wafer transfer robot 202 and a robot elevator 201 for hoisting and lowering the robot 202 are disposed within a wafer transfer chamber 205. The robot elevator 201 hoists and lowers the wafer transfer robot 202 so as to load a semiconductor wafer into or unload from a reaction chamber 204 through a gate valve 203. 
     As described above, in the conventional semiconductor wafer processing apparatus 2000, since the robot elevator 201 is disposed within the wafer transfer chamber 205, the interior of the wafer transfer chamber 205 is contaminated and consequently the interior of the reaction chamber 204 is contaminated, resulting in contamination of a wafer processed by the semiconductor wafer processing apparatus 2000 and thus introducing a problem of poor yield in production of semiconductor devices. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is a main object of the present invention to provide a substrate processing apparatus capable of preventing the interior thereof from being contaminated due to a elevator or the like. 
     According to the present invention, there is provided a substrate processing apparatus, comprising: 
     a substrate transfer chamber which can be depressurized; 
     a plurality of substrate processing chambers disposed on a first side wall of the substrate transfer chamber, the plurality of substrate processing chambers being stacked in the vertical direction; 
     a plurality of first valves, each being disposed between each of the substrate processing chambers and the substrate transfer chamber, and each of the plurality of the first valves being capable of providing hermetic vacuum isolation between each of the substrate processing chambers and the substrate transfer chamber when closed and allowing a substrate to pass therethrough when opened; a substrate accommodating chamber disposed on a second side wall of the substrate transfer chamber; 
     a substrate transfer device disposed within the substrate transfer chamber and being capable of transferring the substrate under reduced pressure between the substrate processing chambers and the substrate accommodating chamber; 
     elevating means disposed outside the substrate transfer chamber and comprising a stationary portion and an elevating portion which is vertically movable with respect to the stationary portion; 
     a rigid connecting member capable of moving through a through-hole formed in a predetermined face of the substrate transfer chamber, the rigid connecting member mechanically connecting the elevating portion and the substrate transfer device through the through-hole; and 
     a sealing member for establishing a hermetic vacuum seal between the predetermined face and the connecting member which penetrates through the through-hole. 
     In the present invention, since the elevating means is disposed outside the substrate transfer chamber, the interior of the substrate transfer chamber can be prevented from being otherwise contaminated due to the presence of the elevating means, thereby preventing substrates from being contaminated. 
     Since the elevating portion of the elevating means and the substrate transfer device are mechanically connected, through the through-hole, by the rigid connecting member which can move through the through-hole formed in the predetermined face of the substrate transfer chamber, even though the elevating means is disposed outside the substrate transfer chamber, the substrate transfer device can be reliably elevated and lowered by the elevating means. 
     In order to connect the elevating portion and the substrate transfer device via a predetermined face of the substrate transfer chamber such that the substrate transfer device goes up/down as the elevating portion goes up/down, the elevating portion and the substrate transfer device may be magnetically coupled. In this case, there is no need for forming a through-hole in a predetermined face of the substrate transfer chamber, but the predetermined face may be made of material which allows the transmission of magnetic lines of force, thereby magnetically connecting the elevating portion and the substrate transfer device which are isolated from each other by the face. 
     Since there is disposed the sealing member for establishing a hermetic vacuum seal between the predetermined face of the substrate transfer chamber and the connecting member which penetrates through the through-hole formed in the predetermined face, even though the through-hole is formed in the predetermined face of the substrate transfer chamber and the substrate transfer device is adapted by the rigid connecting member to go up/down as the elevating portion goes up/down, the substrate transfer chamber can be hermetically vacuum-sealed and can be depressurized. 
     Further, since the plurality of substrate processing chambers are disposed on the first side wall of the substrate transfer chamber and are stacked in the vertical direction, the area occupied by the substrate processing chambers can be reduced within a clean room. Also, the number of sides of the substrate transfer chamber can be reduced thereby to reduce the size of the substrate transfer chamber, resulting in a reduction in the area occupied by the substrate transfer chamber. Thus, the substrate processing apparatus occupies less area within the clean room. 
     As the number of sides of the substrate transfer chamber is reduced, the cost of manufacture of the substrate transfer chamber can be reduced, and the required multidirectional maintenance space can also be reduced. Further, in the case where the substrate transfer chamber is connected to another substrate transfer chamber or the like, the distance over which a connection is made between the substrate transfer chamber and another substrate transfer chamber or the like can be reduced. This allows a substrate to be transferred between the substrate transfer chamber and another substrate transfer chamber or the like without providing a substrate transfer device at a connecting section therebetween; thus the substrate processing apparatus can accordingly be made simpler in structure and manufactured at lower cost. 
     Since there are provided the plurality of first valves, each being located between each of the substrate processing chambers and the substrate transfer chamber, and each of the plurality of the first valves is capable of providing hermetic vacuum isolation between each of the substrate processing chambers and the substrate transfer chamber when closed and allowing a substrate to pass therethrough when opened, each substrate processing chamber and the substrate transfer chamber can be maintained under vacuum independently of each other, and also a substrate can move between each substrate processing chamber and the substrate transfer chamber. This first valve is preferably a gate valve. 
     A substrate is preferably a semiconductor wafer. In this case, the substrate processing apparatus functions as a semiconductor wafer processing apparatus. 
     A substrate may also be a glass substrate for use in a liquid crystal display device. 
     In the substrate processing chamber, there are preferably performed processes including: the deposition of various films, including insulating films, metal wiring films, polycrystalline silicon films, and amorphous silicon films, by various CVD (Chemical Vapor Deposition) methods such as a plasma enhanced CVD method, a hot wall CVD method, a photo assisted CVD method and the like; etching; heat treatment such as annealing and the like; epitaxial growth; and diffusion. 
     The substrate transfer device is preferably a substrate transfer device for transferring a substrate in a horizontal direction, more preferably an articulated robot. 
     Preferably, the sealing member is formed of an elastic material and covers the rigid connecting member, which connects the elevating portion and the substrate transfer device, such that the connecting member can move within the sealing member and that one end of the sealing member is connected in a hermetically vacuum-sealed manner to the predetermined face of the substrate transfer chamber while the other end of the sealing member is connected in a hermetically vacuum-sealed manner to the connecting member. Since hermetic vacuum seal is maintained by the elastic material, the maintenance of hermetic vacuum seal is reliable and the movement of the connecting member can be handled independently of the maintenance of the hermetic vacuum seal, thereby ensuring the smooth, reliable movement of the connecting member. The description &#34;one end of the sealing member is connected in a hermetically vacuum-sealed manner to the predetermined face of the substrate transfer chamber&#34; encompasses both the case where one end of the sealing member is connected in a hermetically vacuum sealed manner directly to the predetermined face of the substrate transfer chamber, and the case where one end of the sealing member is connected in a hermetically vacuum-sealed manner indirectly to the predetermined face of the substrate transfer chamber via another member. Similarly, the description &#34;the other end of the sealing member is connected in a hermetically vacuum-sealed manner to the connecting member&#34; encompasses both the case where the other end of the sealing member is connected in a hermetically vacuum-sealed manner directly to the connecting member and the case where the other end of the sealing member is connected in a hermetically vacuum-sealed manner indirectly to the connecting member via another member. 
     The sealing member formed of an elastic material is preferably bellows, more preferably metallic bellows. 
     The sealing member may be an O-ring. By installing an O-ring between the through-hole and the connecting member, both the maintenance of hermetic vacuum seal and the movement of the connecting member can be ensured in a simple structure. 
     Preferably, the stationary portion of the elevating means is a screw shaft, and the elevating portion comprises a nut, thereby forming a ball screw by the screw shaft and the nut. The ball screw provides smaller friction and higher mechanical efficiency. 
     Preferably, the predetermined face of the substrate transfer chamber where the through-hole is formed is the bottom face of the substrate transfer chamber, and the ball screw is located under the substrate transfer chamber. This prevents the interior of the substrate transfer chamber from being contaminated with particles generated from the sealing member such as bellows. 
     This predetermined face of the substrate transfer chamber may be the top face of the substrate transfer chamber, and the ball screw may be located above the substrate transfer chamber. 
     Preferably, the substrate transfer device comprises a driving unit, a substrate transfer unit capable of moving in a substantially horizontal direction by the driving unit, and a driving unit container capable of providing hermetic vacuum isolation between the inside and outside of the driving unit container, and the driving unit is accommodated in the driving unit container, thereby maintaining the clean atmosphere within the substrate transfer chamber. 
     In this case, one end portion of the rigid connecting member is preferably connected to the driving unit container at the vicinity of an end portion thereof located closer to the substrate transfer unit. Thus, the height of the substrate processing apparatus as a whole can be reduced. 
     Preferably, in a case where the predetermined face of the substrate transfer chamber where the through-hole is formed is either the bottom face or the top face of the substrate transfer chamber, a projecting section whose shape corresponds to the driving unit container is projected from the bottom face when the predetermined face is the bottom face, or from the top face when the predetermined face is the top face, such that the projecting section is capable of accommodating the driving unit container therein. Since in order to accommodate the driving unit container, only the projecting section is projected from the wafer transfer chamber without increasing the entire size of the wafer transfer chamber, the volume of the wafer transfer chamber can be reduced, thereby reducing time required for evacuating the wafer transfer chamber. 
     Preferably, the predetermined face of the substrate transfer chamber is the bottom face of the substrate transfer chamber. 
     Preferably, a second valve is disposed between the substrate accommodating chamber and the substrate transfer chamber, and the second valve is capable of providing hermetic vacuum isolation between the substrate accommodating chamber and the substrate transfer chamber when closed and allowing a substrate to pass therethrough when opened, thereby allowing the substrate accommodating chamber to be depressurized independently of the substrate transfer chamber. 
     By allowing the substrate transfer chamber and the substrate accommodating chamber to be depressurized, the oxygen concentration therein can be reduced to a minimal level, thereby suppressing oxidation of a substrate in the substrate transfer chamber and the substrate accommodating chamber. 
     The second valve is disposed between the substrate transfer chamber and the substrate accommodating chamber, and the second valve is capable of providing hermetic vacuum isolation between the substrate transfer chamber and the substrate accommodating chamber when closed and allowing the substrate to pass therethrough when opened. Therefore the substrate transfer chamber and the substrate accommodating chamber can be maintained under vacuum independently of each other, and also a substrate can move between the substrate transfer chamber and the substrate accommodating chamber. This second valve is preferably a gate valve. 
     Further, the substrate processing apparatus according to the present invention preferably comprises an atmospheric pressure section located at a side which is different from the substrate transfer chamber&#39;s side with respect to the substrate accommodating chamber, and a third valve disposed between the substrate accommodating chamber and the atmospheric pressure section, the third valve being capable of maintaining the substrate accommodating chamber under vacuum in isolation from the atmospheric pressure section when closed and allowing a substrate to pass therethrough when opened. 
     Thus, the substrate accommodating chamber can be maintained under vacuum in isolation from the atmospheric pressure section, and also a substrate can move between the substrate accommodating chamber and the atmospheric pressure section. 
     As described above, since the second and third valves are disposed at the substrate accommodating chamber and the substrate accommodating chamber can be depressurized independently of the substrate transfer chamber, the substrate accommodating chamber can function as a load-lock chamber when a substrate is transferred between the atmospheric pressure section and the substrate transfer chamber maintained under reduced pressure. 
     Preferably, heat resistant first substrate holding means is disposed within the substrate accommodating chamber, whereby the substrate accommodating chamber can be used as a substrate cooling chamber for cooling a high-temperature substrate which has been processed in the substrate processing chamber. 
     The heat resistant first substrate holding means is preferably a heat resistant substrate holder made of quartz, glass, ceramics, or metal, whereby even when the substrate accommodating chamber is maintained under vacuum, impurities such as outgass are not generated from the substrate holder, thereby maintaining clean the atmosphere within the substrate accommodating chamber. Ceramics are preferably sintered SiC, or sintered SiC coated with SiO 2  by CVD or the like. 
     As described above, since the substrate accommodating chamber can be used as a substrate cooling chamber and as a load-lock chamber, there is no need for providing a substrate cooling chamber and a cassette chamber on side walls of the substrate transfer chamber, and a cassette can be placed in the atmospheric pressure section. 
     Since the second valve is disposed between the substrate transfer chamber and the substrate accommodating chamber, the pressure of the substrate accommodating chamber can be restored to atmospheric pressure while the substrate transfer chamber is maintained under reduced pressure, and a substrate contained in the substrate accommodating chamber naturally cools down while the pressure of the substrate accommodating chamber is being restored to atmospheric pressure, so that the temperature of each substrate is lowered to a sufficient level before the substrate leaves the substrate accommodating chamber. Consequently, when the substrate is subsequently taken out into atmospheric environment, it can be prevented from being oxidized or contaminated by atmospheric environment. In this manner, a step of restoring pressure to atmospheric pressure and a step of cooling a substrate can be simultaneously performed within the substrate accommodating chamber, and subsequently the cooled substrate can be transferred under atmospheric pressure to a cassette. A cassette which contains substrates can then be delivered out from the substrate processing apparatus. 
     Preferably, a plurality of substrate accommodating chambers are disposed on the second side wall of the substrate transfer chamber, the plurality of the substrate accommodating chambers being stacked in the vertical direction, and there are disposed a plurality of fourth valves, each being located between each of the substrate accommodating chambers and the substrate transfer chamber and being capable of providing hermetic vacuum isolation between each of the substrate accommodating chambers and the substrate transfer chamber when closed and allowing the substrate to pass therethrough when opened, whereby the substrate accommodating chambers can be depressurized independently of one another and each of the substrate accommodating chambers can be depressurized independently of the substrate transfer chamber. This fourth valve is preferably a gate valve. 
     By providing a plurality of substrate accommodating chambers on a side wall of the substrate transfer chamber, while a certain substrate accommodating chamber is used for cooling a substrate contained therein, another substrate accommodating chamber may be used for transferring a substrate to the substrate processing chamber, thereby saving time. 
     Since a plurality of substrate accommodating chambers are disposed on the second side wall of the substrate transfer chamber, such that the plurality of the substrate accommodating chambers are stacked in the vertical direction, the area occupied by the substrate accommodating chambers can be reduced within a clean room. Also, the number of sides of the substrate transfer chamber can be reduced thereby to reduce the size of the substrate transfer chamber, resulting in a reduction in the area occupied by the substrate transfer chamber. Thus, the substrate processing apparatus occupies less area within the clean room. 
     As the number of sides of the substrate transfer chamber is reduced, the cost of manufacture of the substrate transfer chamber is reduced, and the required multidirectional maintenance space is also reduced. Further, when a plurality of substrate processing apparatuses are disposed, the distance over which a connection is made between the substrate transfer chamber and another substrate transfer chamber or the like can be reduced. This allows a substrate to be transferred between the substrate transfer chamber and another substrate transfer chamber or the like without providing a substrate transfer device at a connecting section therebetween; thus the substrate processing apparatus can accordingly be made simpler in structure and manufactured at lower cost. Further, the maintenance space for one substrate processing apparatus does not interfere with that for another substrate processing apparatus; therefore a plurality of substrate processing apparatuses can be efficiently arranged. 
     Two kinds of substrate accommodating chambers, one for incoming substrates and the other for outgoing substrates, may be separately provided. This allows two kinds of substrate accommodating chambers to be alternately used, thereby saving time. 
     Preferably, there are further disposed cassette holding means located within the atmospheric pressure section, and substrate transfer means located within the atmospheric pressure section and capable of transferring a substrate between a cassette held by the cassette holding means and the substrate accommodating chamber. 
     By disposing within the atmospheric pressure section the cassette holding means and the substrate transfer means capable of transferring a substrate between a cassette held by the cassette holding means and the substrate accommodating chamber, the cassette holding means and the substrate transfer means can be made simpler in structure as compared with the case where they are disposed in a vacuum environment. 
     A cassette is preferably a cassette for carrying substrates in and/or carrying them out from the substrate processing apparatus. 
     Preferably, a housing is further provided for accommodating the substrate processing chamber, the substrate transfer chamber, the substrate accommodating chamber, the substrate transfer means, and the cassette holding means. By disposing the substrate transfer means and the cassette holding means within the housing, the surface of a substrate placed in a cassette and the surface of a substrate being transferred by the substrate transfer means can be maintained clean. 
     Preferably, the substrate processing apparatus of the present invention has the following structure. A housing is further provided for accommodating at least the substrate transfer chamber, the plurality of substrate processing chambers, and the substrate accommodating chamber. At least each part of each of the projecting section of the substrate transfer chamber, the elevating means and the connecting member is projected from the housing. Such a housing provides the following advantage in addition to a reduction in particles within the substrate processing apparatus. By projecting from the housing at least each part of each of the projecting section of the substrate transfer chamber, the elevating means and the connecting member, at least each part of each of the projecting section of the substrate transfer chamber, the elevating means and the connecting member can be projected downward from the floor of a clean room or upward from the ceiling of the clean room. As a result, the substrate transfer chamber, the plurality of substrate processing chambers arranged in layers, and the substrate accommodating chamber can be increased in height, thereby increasing their capacity of accommodating substrates and thus increasing the number of substrates to be processed at one time. 
     Preferably, the substrate processing apparatus of the present invention has the following structure. There are further provided first substrate holding means, disposed within the substrate accommodating chamber, for holding a substrate and second substrate holding means, disposed within the substrate processing chamber, for holding a substrate. The second substrate holding means can hold a plurality of substrates, the first substrate holding means can hold a plurality of substrates, and the pitch of substrates held by the first substrate holding means is substantially identical to that of substrates held by the second substrate holding means. 
     In this case, more preferably, the substrate transfer means can transfer a plurality of substrates at one time and can also change the pitch of the substrates. 
     Since the second substrate holding means disposed within the substrate processing chamber can hold a plurality of substrates, the substrates can be processed in the substrate processing chamber with an increased efficiency. 
     Since the first substrate holding means disposed within the substrate accommodating chamber can hold a plurality of substrates and the pitch of substrates held by the first substrate holding means is substantially identical to that of substrates held by the second substrate holding means, the structure of the substrate transfer device, disposed within the substrate transfer chamber, which can be depressurized, can be simplified. Preferably, the substrate transfer device can transfer a plurality of substrates at one time under reduced pressure. 
     By making the pitch of substrates held by the first substrate holding means substantially identical to that of substrates held by the second substrate holding means, even when the substrate transfer device adopts the structure capable of transferring a plurality of substrates at one time under reduced pressure, there is no need for changing the pitch of substrates while transferring substrates. As a result, the structure of the substrate transfer device becomes simple, and contamination of vacuum can be prevented. Further, since a plurality of substrates can be transferred at one time, the efficiency of transferring substrates increases. 
     By contrast, if the pitch of substrates is made variable under reduced pressure, the structure of a transfer device will become complicated, and more than twice as much cost and space will be required as compared with the use of the transfer device under atmospheric pressure. Moreover, due to an increase in the number of mechanisms, contaminants generated from a driving shaft and the like become more likely to scatter. This results in a failure to maintain a predetermined degree of vacuum and is likely to introduce a problem of particles and to cause contamination of a substrate. Since particles are generated, within the substrate transfer chamber, located adjacent to the substrate processing chamber, the effect of particles is particularly large. If in order to avoid such a problem, substrates are transferred one by one between the first substrate holding means and the second substrate holding means, throughput will deteriorate. If in order to improve throughput, the transferring speed of a substrate transfer device is increased, the number of operations per unit time of the substrate transfer device will increase, resulting in a decrease in service life of the apparatus and introduction of a problem of particles. 
     In order to concurrently process, for example, to concurrently deposit a film on a plurality of substrates within the substrate processing chamber, these substrates must be arranged not at the pitch of grooves in a cassette, but at a pitch which is determined in consideration of a gas flow and the like within the substrate processing chamber, so as to maintain uniformity of a film thickness and the like. Therefore, it is preferable that the pitch of substrates is changed from the pitch of the grooves of the cassette at a certain point of transfer of substrates. 
     In the present invention, the substrate transfer means preferably has a structure capable of transferring a plurality of substrates at one time and changing the pitch of these substrates. Since the substrate transfer means is used under atmospheric pressure, even when the pitch of substrates is made variable, the substrate transfer means is simpler in structure and can be manufactured at lower cost as compared with that for use under vacuum, and the generation of particles can be suppressed. 
     By adopting the above-mentioned method of transferring a plurality of substrates at one time while the pitch of substrates is variable during transfer under atmospheric pressure and fixed during transfer under reduced pressure, the cost of manufacture of transfer devices can be reduced, the size of the transfer devices can be reduced, and the generation of particles can be suppressed so as to provide a clean environment for transfer of substrates. Further, since a plurality of substrates are transferred at one time, throughput improves. Since the pitch of substrates is variable, the pitch can be changed so as to process substrates at high precision within the substrate processing chamber. 
     Preferably, the first substrate holding means can hold at least twice as many substrates as those to be processed at one time within each of the substrate processing chambers. 
     Preferably, the first substrate holding means can hold at least twice as many substrates as those to be held by the second substrate holding means, whereby the first substrate holding means can hold at least twice as many substrates as those to be processed at one time within each of the substrate processing chambers. 
     As a result, substrates can be efficiently transferred between the substrate processing chamber and a cassette, thereby improving throughput. 
     Preferably, the first and second side walls of the substrate transfer chamber are opposed to each other so as to arrange on a substantially straight line the substrate processing chamber, the substrate transfer chamber, and the substrate accommodating chamber. This minimizes the number of sides of the substrate transfer chamber; for example, the substrate transfer chamber may assume a rectangular shape. 
     Preferably, the substrate transfer chamber has a rectangular shape as viewed from above, thereby reducing the size of the substrate transfer chamber and thus reducing the area occupied by the substrate transfer chamber. Thus, the substrate processing apparatus occupies less area within a clean room. By adopting the rectangular shape, the cost of manufacture of the substrate transfer chamber is reduced, and a required maintenance space is also reduced. Further, the distance over which a connection is made between the substrate transfer chamber and another substrate transfer chamber or the like can be reduced. This allows a substrate to be readily transferred between the substrate transfer chamber and another substrate transfer chamber or the like without providing a substrate transfer device at a connecting section therebetween; thus the substrate processing apparatus can accordingly be made simpler in structure and manufactured at lower cost. A plurality of substrate processing units, each having the structure such that the substrate processing chamber, the substrate transfer chamber, and the substrate accommodating chamber are arranged on a substantially straight line, can be readily arranged in parallel so that they occupy less area. 
     Preferably, the cassette holding means is located opposite to the substrate transfer chamber with respect to the substrate accommodating chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a cross sectional view for explaining a conventional semiconductor wafer processing apparatus; 
     FIG. 2 is a plan view for explaining a semiconductor wafer processing apparatus according to a first embodiment of the present invention; 
     FIG. 3 is a cross-sectional view taken along the line X--X in FIG. 2; 
     FIG. 4 is a schematic perspective view for explaining a wafer holder for use in the first through seventh embodiments of the present invention; 
     FIGS. 5A and 5B are schematic perspective views for explaining a wafer-transfer vacuum robot for use in the first through seventh embodiments of the present invention; 
     FIG. 6 is a schematic perspective view for explaining a cassette transfer and wafer transfer device for use in the first through seventh embodiments of the present invention; 
     FIG. 7A is a side view for explaining a pitch changing mechanism of the cassette transfer and wafer transfer device for use in the first through seventh embodiments of the present invention; 
     FIG. 7B is a rear view taken along the line Y--Y in FIG. 7A; 
     FIG. 8 is a schematic cross-sectional view for explaining the operation of transferring wafers in the semiconductor processing apparatus according to the first embodiment; 
     FIG. 9 is a cross-sectional view for explaining a semiconductor wafer processing apparatus according to a second embodiment of the present invention; 
     FIG. 10 is a cross-sectional view for explaining a semiconductor wafer processing apparatus according to a third embodiment of the present invention; 
     FIG. 11 is a plan view for explaining a semiconductor wafer processing apparatus according to a fourth embodiment of the present invention; 
     FIG. 12 is a plan view for explaining a semiconductor wafer processing apparatus according to a fifth embodiment of the present invention; 
     FIG. 13 is a plan view for explaining a semiconductor wafer processing apparatus according to a sixth embodiment of the present invention; and 
     FIG. 14 is a plan view for explaining a semiconductor wafer processing apparatus according to a seventh embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment: 
     FIG. 2 is a plan view for explaining a semiconductor wafer processing apparatus according to a first embodiment of the present invention. FIG. 3 shows a cross-sectional view taken along the line X--X in FIG. 2. 
     A semiconductor wafer processing apparatus 1 of the present embodiment is composed of a processing section 700, a transfer section 500, and a front section 100. 
     The processing section 700 is composed of a plurality of processing modules 701, each including a reaction chamber 70 and a gate valve 93. The transfer section 500 is composed of a transfer module 501, which includes a wafer transfer chamber 50 and a wafer-transfer vacuum robot 60. The front section 100 is composed of a plurality of load-lock modules 300 and an atmospheric pressure section 200. Each load-lock module 300 is composed of an wafer accommodating chamber 30, a gate valve 92, and a front door valve 91. In the atmospheric pressure section 200, there are disposed cassette shelves 11, each being used for mounting a cassette 10 thereon, and a cassette transfer and wafer transfer device 20. 
     The plurality of reaction chambers 70 are arranged in the vertical direction and connected to a wall 53 of the wafer transfer chamber 50. The gate valve 93 is disposed between each reaction chamber 70 and the wafer transfer chamber 50. Each reaction chamber 70 is adapted to be independently evacuated via an exhaust pipe 82. Within each reaction chamber 70 is placed a wafer boat 75 capable of carrying a plurality of (two in the present embodiment) semiconductor wafers 5 so as to process a plurality of wafers 5 at one time, thereby increasing the wafer processing efficiency. The pitch of wafers 5 carried in the wafer boat 75 is determined in consideration of a gas flow and the like within the reaction chamber 70; for example, when a process of depositing a film is to be performed within the reaction chamber 70, the pitch is determined so as to maintain the uniformity of film thickness within a predetermined range. 
     In the reaction chamber 70 there are performed processes including: the deposition of various films, including insulating films, metal wiring films, polycrystalline silicon films, and amorphous silicon films, by various kinds of CVD such as plasma enhanced CVD, hot wall CVD, photo assisted CVD, and the like; etching; heat treatment such as annealing and the like; epitaxial growth; diffusion. 
     Since the plurality of reaction chambers 70 are disposed in vertical layers on the wall 53 of the wafer transfer chamber 50, the area occupied by the reaction chambers 70 within a clean room can be reduced. Also, the number of sides of the wafer transfer chamber 50 can be reduced thereby to reduce the size of the wafer transfer chamber 50, resulting in a reduction in the area occupied by the wafer transfer chamber 50. Thus, the semiconductor wafer processing apparatus 1 occupies less area within the clean room. 
     As the number of sides of the wafer transfer chamber 50 is reduced, the cost of manufacture of the wafer transfer chamber 50 is reduced, and the required multidirectional maintenance space is also reduced. Further, in the case where another wafer transfer chamber is connected to the wafer transfer chamber 50, the distance between the wafer transfer chamber 50 and another wafer transfer chamber or the like can be reduced. This allows a wafer to be transferred between the wafer transfer chamber 50 and another wafer transfer chamber or the like without providing a wafer transfer device at a connecting section therebetween; thus the semiconductor wafer processing apparatus 1 can accordingly be made simpler in structure and manufactured at lower cost. 
     The plurality of wafer accommodating chambers 30 are disposed in vertical layers on a wall 54 of the wafer transfer chamber 50. The gate valve 92 is disposed between each wafer accommodating chamber 30 and the wafer transfer chamber 50. The front door valve 91 is disposed between each wafer accommodating chamber 30 and the atmospheric pressure section 200. Each wafer accommodating chamber 30 is adapted to be independently evacuated via exhaust pipes 83 and 81. 
     A wafer holder 40 is placed within the wafer accommodating chamber 30. FIG. 4 is a schematic perspective view for explaining the wafer holder 40. The wafer holder 40 has upper and lower disk-like column supporting plates 41 and 42 and two prismatic columns 43 and 44, which are held between the plates 41 and 42. A plurality of wafer supporting grooves 45 are formed in each of the columns 43 and 44, and the columns 43 and 44 stand such that respective grooves 45 face each other. The both ends of the grooves 45 are open so as to allow wafers to be loaded from both sides of the wafer holder 40 and to be unloaded to both sides thereof. The wafer holder 40 is made of quartz. 
     The pitch of the wafer supporting grooves 45 of the wafer holder 40, i.e. the pitch of wafers 5 held in the wafer holder 40 is made equal to that of wafers 5 mounted in the wafer boat 75 in the reaction chamber 70. The pitch of the wafer supporting grooves 45 of the wafer holder 40 is larger than that of grooves for holding wafers within the cassette 10. 
     The number of the wafer supporting grooves 45 of the wafer holder 40, i.e. the number of wafers 5 which the wafer holder 40 can hold is at least twice the number of wafers 5 which the wafer boat 75 within the reaction chamber 70 can carry, i.e. at least twice the number of wafers 5 which can be processed at one time within the reaction chamber 70. Thus, the wafers 5 can be efficiently transferred between the reaction chamber 70 and the cassette 10, resulting in improved throughput. 
     Since the wafer holder 40 is made of quartz, even when the wafer accommodating chamber 30 is maintained under vacuum, impurities are not outgassed from the wafer holder 40, thereby maintaining clean the atmosphere within the wafer accommodating chamber 30. 
     Since the wafer holder 40 is made of quartz and thus has excellent heat resistance, the high-temperature wafer 5 which has been processed in the reaction chamber 70 can be cooled while being held in the wafer holder 40. The wafer holder 40 can thus be used for cooling wafers 5, so that the wafer accommodating chamber 30 functions as a wafer cooling chamber. Accordingly, there is no need for providing a separate cooling chamber on a side wall of the wafer transfer chamber 50 in order to cool the high-temperature wafer 5 which has been processed in the reaction chamber 70, whereby the area occupied by the semiconductor wafer processing apparatus 1 within a clean room can be reduced by the area which would otherwise be occupied by the cooling chamber. Also, the number of sides of the wafer transfer chamber 50 can be reduced thereby to reduce the size of the wafer transfer chamber 50, resulting in a reduction in the area occupied by the wafer transfer chamber 50. Thus, the semiconductor wafer processing apparatus 1 occupies less area within the clean room. Further, the cost of manufacture of the wafer transfer chamber 50 can be reduced. 
     Since the wafer holder 40 temporarily accommodates wafers 5 on the way of transfer from the cassette 10 to the wafer processing chamber 70, temporarily accommodates wafers 5 on the way of transfer from the wafer processing chamber 70 to the cassette 10, or temporarily accommodates wafers 5 on the way of transfer from the cassette 10 to the wafer processing chamber 70 as well as wafers 5 on the way of transfer from the wafer processing chamber 70 to the cassette 10, there is no need for providing a cassette chamber for accommodating the cassette 10 on a side wall of the wafer transfer chamber 50. As a result, the number of chambers to be disposed on side walls of the wall transfer chamber 50 is reduced, and the area occupied by the wafer processing apparatus 1 within a clean room can be reduced accordingly. Further, the number of sides of the wafer transfer chamber 50 is reduced, and the size of the wafer transfer chamber 50 is reduced accordingly, resulting in a decrease in the area occupied by the wafer transfer chamber 50. This also reduces the area occupied by the semiconductor wafer processing apparatus 1 within the clean room. Further, the cost of manufacture of the wafer transfer chamber 50 is reduced. 
     In the present embodiment, since the plurality of wafer accommodating chambers 30 are disposed on the wall 54 of the wafer transfer chamber 50, while a certain wafer accommodating chamber 30 is used for cooling wafers 5, another wafer accommodating chamber 30 may be used for transferring wafers 5 to the reaction chamber 70, thereby saving time. Also, two kinds of the wafer accommodating chambers 30, one for incoming wafers 5 and the other for outgoing wafers 5, may be separately provided. This allows two kinds of the wafer accommodating chambers 30 to be alternately used, thereby saving time. Further, a certain wafer accommodating chamber 30 may be used for monitor wafers, and another wafer accommodating chamber 30 may be used for process wafers which will become actual products. 
     Since the plurality of wafer accommodating chambers 30 are disposed in vertical layers on the wall 54 of the wafer transfer chamber 50, the area occupied by the wafer accommodating chambers 30 within a clean room can be reduced. Also, the number of sides of the wafer transfer chamber 50 can be reduced thereby to reduce the size of the wafer transfer chamber 50, resulting in a reduction in the area occupied by the wafer transfer chamber 50. Thus, the semiconductor wafer processing apparatus 1 occupies less area within the clean room. Further, the cost of manufacture of the wafer transfer chamber 50 is reduced. 
     Since the gate valve 92 is disposed between the wafer transfer chamber 50 and the wafer accommodating chamber 30, the pressure of the wafer accommodating chamber 30 can be restored to atmospheric pressure while the wafer transfer chamber 50 is maintained under reduced pressure. Therefore, each wafer 5 contained in the wafer accommodating chamber 30 cools naturally while the pressure of the wafer accommodating chamber 30 is being restored to atmospheric pressure, so that the temperature of each wafer 5 is lowered to a sufficient level before the wafer 5 leaves the wafer accommodating chamber 30. Accordingly, even when the wafers 5 are subsequently taken out into atmospheric environment, the wafers 5 are prevented from being oxidized or contaminated by atmospheric environment. In this manner, a step of restoring pressure to atmospheric pressure and a step of cooling wafers 5 are simultaneously performed within the wafer accommodating chamber 30, and subsequently the cooled wafers 5 are transferred under atmospheric pressure to the cassette 10. The cassette 10 which contains the wafers 5 is then delivered out from the wafer processing apparatus 1. 
     In the present embodiment, the cassette transfer and wafer transfer device 20, not the wafer-transfer vacuum robot 60 disposed within the wafer transfer chamber 50, is used for transferring wafers 5 between the wafer accommodating chamber 30 and the cassettes 10, thereby reducing time required for transferring wafers 5. Also, in the present embodiment, since the cassette transfer and wafer transfer device 20 is disposed within the atmospheric pressure section 200, the cassette transfer and wafer transfer device 20 can be made simpler in structure as compared with the case where it is disposed in a vacuum atmosphere. 
     The wafer transfer chamber 50 is adapted to be evacuated via the exhaust pipes 84 and 81. Also, the plurality of reaction chambers 70, the wafer transfer chamber 50, and the plurality of wafer accommodating chambers 30 are adapted to be evacuated independently of one another. 
     Since the wafer transfer chamber 50 and the wafer accommodating chamber 30 can be depressurized, the oxygen concentration therein can be reduced to an ultimate level, thereby suppressing oxidation of wafers 5 in the wafer transfer chamber 50 and in the wafer accommodating chamber 30. 
     Since the reaction chambers 70 can be independently evacuated, each of the reaction chambers 70 can function as a reaction chamber for processing wafers 5 under reduced pressure. Further, after the reaction chamber 70 is depressurized, the atmosphere therein can be replaced with a predetermined atmospheric gas, thereby establishing a highly pure gaseous atmosphere therein. 
     In the present embodiment, the plurality of reaction chambers 70 are all used for processing wafers 5 under reduced pressure. However, the plurality of reaction chambers 70 may all be used for processing wafers 5 under atmospheric pressure, or at least one of these reaction chambers 70 may be used for processing wafers 5 under atmospheric pressure while the remaining reaction chambers 70 may be used for processing wafers 5 under reduced pressure. 
     The wafer-transfer vacuum robot 60 is disposed within the wafer transfer chamber 50. FIGS. 5A and 5B are schematic perspective views for explaining the wafer-transfer vacuum robot 60. The wafer-transfer vacuum robot 60 is an articulated robot and is composed of arms 63, 65, and 67, each swingable in a corresponding horizontal plane, and rotational axles 62, 64, and 66 for swinging the respective arms. The robot 60 also include a two-axis driving unit 69 for rotating the rotational axle 62, a gear mechanism (not shown) for transmitting the rotation of the rotational axle 62 to the rotational axles 64 and 66, and a driving unit container 61 for accommodating the driving unit 69. The tip of the arm 67 is formed into a wafer mounting arm 68 for mounting wafers 5 thereon. As the rotational axle 62 rotates, the arms 63, 65, and 67 swing in the corresponding horizontal planes, thereby moving wafers 5 mounted on the wafer mounting arm 68 in a horizontal direction. 
     Two sets of the arm 67 and the wafer mounting arm 68 are disposed. The distance between the wafer mounting arms 68 is made equal to the pitch of the wafer supporting grooves 45 of the wafer holder 40 and the pitch of wafers 5 mounted in the wafer boat 75 contained in the reaction chamber 70. Accordingly, there is no need for changing the pitch of wafers 5 on the way of transfer between the wafer holder 40 and the reaction chamber 70. Thus, although the wafer-transfer vacuum robot 60 can transfer two wafers 5 at one time using the two wafer mounting arms 68, the structure of the wafer-transfer vacuum robot 60 can be simplified, and contamination of a vacuum atmosphere can be prevented. Further, since two wafers 5 can be transferred at one time, the wafer transferring efficiency increases. 
     The driving unit container 61 has a hermetically sealed structure. Since the driving unit is accommodated in this hermetically sealed container 61, the atmosphere within the wafer transfer chamber 50 can be maintained clean. 
     A projecting section 52 whose shape corresponds to that of the driving unit container 61 is projected from a bottom 56 of the wafer transfer chamber 50 so as to accommodate the driving unit container 61. Since in order to accommodate the driving unit container 61, only the projecting section 52 is projected from the wafer transfer chamber 50, the volume of the wafer transfer chamber 50 can be reduced, thereby reducing time required for evacuating the wafer transfer chamber 50. 
     A through-hole 57 is formed in the bottom 56 of the wafer transfer chamber 50. A screw shaft 561 is vertically disposed outside and under the wafer transfer chamber 50. A motor 566 is disposed on the upper portion of the screw shaft 561 so as to rotate the screw shaft 561. A nut 565 is attached to the screw shaft 561, thereby forming a ball screw by the nut 565 and the screw shaft 561. A lifting base 564 is fixed to the nut 565. One end of a support bar 563 for supporting the wafer-transfer vacuum robot 60 is fixed onto the lifting base 564 such that the support bar 563 stands upright on the lifting base 564. Another end of the support bar 563 is fixed to the upper end portion of the driving unit container 61 of the wafer-transfer vacuum robot 60. The support bar 563 is made of stainless steel. Metal bellows 562 is disposed so as to cover the support bar 563 and such that one end of the bellows 562 is fixed in a hermetically sealed manner onto the bottom 56 so as to surround the through-hole 57 while the other end of the bellows 562 is fixed in a hermetically sealed manner onto the top face of the lifting base 564. 
     As the screw shaft 561 is rotated by the motor 566, the nut 565 goes up and down, and the lifting base 564 fixed to the nut 565 goes up and down accordingly. As the lifting base 564 goes up and down, the support bar 563, which is fixed perpendicularly onto the lifting base 564, for supporting the wafer-transfer vacuum robot 60 goes up and down, and the wafer-transfer vacuum robot 60 attached to the support bar 563 goes up and down accordingly. 
     The present embodiment uses the ball screw 560 composed of screw shaft 561 and the nut 565, thereby reducing friction and increasing mechanical efficiency. Since the ball screw 560 is disposed outside the wafer transfer chamber 50, the interior of the wafer transfer chamber 50 can be prevented from being contaminated, thereby preventing wafers 5 from being contaminated. Further, since the ball screw 560 is located under the bottom 56 of the wafer transfer chamber 50, the interior of the wafer transfer chamber 50 can be prevented from being contaminated with particles generated from the bellows 562. 
     Since the wafer-transfer vacuum robot 60 is mechanically connected to the lifting base 564 via the rigid stainless-steel support bar 563 for supporting the wafer-transfer vacuum robot 60, the wafer-transfer vacuum robot 60 goes up and down reliably as the lifting base 564 goes up and down. 
     The support bar 563 for supporting the wafer-transfer vacuum robot 60 is covered with the bellows 562 such that one end of the bellows 562 is fixed in a hermetically sealed manner onto the bottom 56 of the wafer transfer chamber 50 so as to surround the through-hole 57 while the other end of the bellows 562 is fixed in a hermetically sealed manner onto the top face of the lifting base 564. The bellows 562, therefore, maintains reliably the wafer transfer chamber 50 in a hermetically sealed state, thereby allowing the wafer transfer chamber 50 to be evacuated. Also, since the movement of the support bar 563 for supporting the wafer-transfer vacuum robot 60 is isolated from the maintenance of hermetic seal, the support bar 563 moves smoothly and reliably. 
     Further, since an end of the support bar 563 for supporting the wafer-transfer vacuum robot 60 is fixed onto the upper end portion of the driving unit container 61 of the wafer-transfer vacuum robot 60, the height of the wafer transfer chamber 50 can be reduced, and accordingly the height of the entire semiconductor wafer processing apparatus 1 can be reduced. 
     The entire semiconductor wafer processing apparatus 1 is accommodated in a housing 900. A filter (not shown) and a fan (not shown) are disposed on the ceiling of the housing 900 corresponding to the front section 100 so as to produce a downflow into the housing 900. Cassette shelves 11 for mounting the cassettes 10 thereon are disposed within and attached to the housing 900. The cassette shelves 11 are disposed substantially opposite to the wafer transfer chamber 50 with respect to the wafer accommodating chamber 30. Three cassette shelves 11 are arranged in each of horizontal planes located at two different positions in the vertical direction. That is, a first set of three cassette shelves 11 are arranged at the same height, and a second set of three cassette shelves 11 are disposed above the first set of cassette shelves 11. As a result of providing the cassette shelves 11 within the housing 900, the surfaces of wafers 5 carried in the cassette 10 can be maintained clean. Also, since a plurality of cassettes 11 are provided, cassettes 11 can be arranged for each of a plurality of kinds of processing. Moreover, it is possible to dispose a cassette which holds wafers for monitoring and a cassette which holds dummy wafers. 
     A cassette IN/OUT opening 13 is provided at the lower portion of the front panel 901 of the housing 900. A cassette stage 12 is disposed within the housing 900 at the substantially same height as that of the cassette IN/OUT opening 13. The cassette 10 carried into the housing 900 through the cassette IN/OUT opening 13 is temporarily held on the cassette stage 12, and also the cassette 10 which contains the processed wafers 5 is temporarily held on the cassette stage 12 before it is delivered out from the housing 900. 
     The cassette stage 12 is located under the cassette shelves 11 so as to prevent the wafers 5 contained in the cassette 10 placed on the cassette shelf 11 from being affected by particles which enter the housing 900 from outside through the cassette IN/OUT opening 13 when the cassette 10 enters/leaves the housing 900. 
     Between the wafer accommodating chamber 30 and the cassette shelves 11 is disposed the cassette transfer and wafer transfer device 20 which can load the cassette 10 onto and unload from the cassette shelf 11 and which can transfer wafers 5 between the cassette 10 and the wafer accommodating chamber 30. The cassette transfer and wafer transfer device 20 has a ball screw composed of a screw shaft 29 and a nut (not shown). As the screw shaft 29 rotates, the cassette transfer and wafer transfer device 20 goes up and down accordingly. Since the cassette transfer and wafer transfer device 20 is provided within the housing 900, the surfaces of wafers 5 being transferred thereby can be maintained clean. 
     FIG. 6 is a schematic perspective view for explaining the cassette transfer and wafer transfer device 20. 
     A cassette transfer device 21 and a wafer transfer device 23 are disposed on bases 25 and 26 and can independently perform parallel displacement in the direction of a corresponding arrow. The cassette transfer device 21 has a cassette transfer arm 22 and transfers the cassette 10 which is mounted on a cassette holder 27 attached to an end of the cassette transfer arm 22. The wafer transfer device 23 has a plurality of tweezers 24, each carrying wafers 5 by mounting wafers 5 thereon. 
     FIG. 7A is a side view for explaining the pitch changing mechanism of the cassette transfer and wafer transfer device, and FIG. 7B is a rear view taken along the line Y--Y in FIG. 7A. 
     In the present embodiment, the wafer transfer device 23 has five tweezers 241-245. The tweezer 241 is integral with a block 260. Nuts 232, 233, 234, and 235 are fixed to the tweezers 242, 243, 244 and 245, respectively. The nuts 232 and 234 are in screw-engagement with a screw shaft 210, thereby forming ball screws, respectively. The nuts 233 and 235 are in screw-engagement with a screw shaft 211, thereby forming ball screws, respectively. The upper ends of the screw shafts 210 and 211 are connected to a motor 220 via an unillustrated gear mechanism. The lower ends of the screw shafts 210 and 211 are rotatably supported by the block 250. Between the block 250 and the block 260 is disposed a nut 270, which is in screw-engagement with a screw shaft 280. The nut 270 and the screw shaft 280 constitute a ball screw. When the screw shaft 280 is rotated, the nut 270 moves in a horizontal direction accordingly so as to move the tweezers 241-245 rightward and leftward in FIG. 7A. 
     A thread of a certain pitch is formed in an area 212 of the screw shaft 210 in which the nut 232 is engaged with the screw shaft 210, while a thread having a pitch double the pitch in the area 212 is formed in an area 213 of the screw shaft 210 in which the nut 233 is engaged with the screw shaft 210. A thread having a pitch three times the pitch in the area 212 is formed in an area 214 of the screw shaft 210 in which the nut 234 is engaged with the screw shaft 210, while a thread having a pitch four times the pitch in the area 212 is formed in an area 215 of the screw shaft 210 in which the nut 235 is engaged with the screw shaft 210. No relative movement in the vertical direction occurs between the blocks 250 and 260. When the screw shafts 210 and 211 are rotated by the motor 220, the nut 232 is raised by a predetermined distance relative to the blocks 250 and 260, which are stationary. Further, the nut 233 is raised over a distance double the distance over which the nut 232 is raised, the nut 234 is raised over a distance three times the distance over which the nut 232 is raised, and the nut 235 is raised over a distance four times the distance over which the nut 232 is raised. As a result, the tweezer 241 is not raised, the tweezer 242 is raised over a predetermined distance, the tweezer 243 is raised over a distance double the raised distance of the tweezer 242, the tweezer 244 is raised over a distance three times the raised distance of the tweezer 242, and the tweezer 245 is raised over a distance four times the raised distance of the tweezer 242. As a result, the pitch of the tweezers 241-245 can be changed uniformly. 
     FIG. 8 is a schematic cross-sectional view for explaining the operation of transferring wafers 5 in the semiconductor processing apparatus 1 according to the first embodiment. The operation for transferring and processing wafers 5 will be described with reference to FIGS. 2-8. 
     The cassette 10 which has been carried into the housing 900 of the semiconductor wafer processing device 1 through the cassette IN/OUT opening 13 is first placed on the cassette stage 12. Then, the cassette 10 is transferred onto the cassette holder 27 attached to the end of the cassette transfer arm 22 of the cassette transfer and wafer transfer device 20. The cassette transfer and wafer transfer device 20 carries the cassette 10 to the upper portion of the housing 900 and then transfers it onto the cassette shelf 11. Next, the cassette transfer device 21 moves leftward, and the wafer transfer device 23 then moves rightward so that the wafers 5 in the cassette 10 are mounted onto the tweezers 24. At this time, the pitch of the tweezers 24 is set to be equal to the pitch of the grooves of the cassette 10. 
     Subsequently, the wafer transfer device 23 is retracted and rotated by 180 degrees. Next, the pitch of the tweezers 24 is changed such that the pitch of the tweezers 24 becomes equal to the pitch of the wafer supporting grooves 45 of the wafer holder 40. Subsequently, the tweezers 24 are moved leftward so as to load wafers 5 into wafer holder 40 within the wafer accommodating chamber 30. In the present embodiment, five wafers 5 are transferred at once from the cassettes 10 to the wafer holder 40 by the cassette transfer and wafer transfer device 20. When the wafers 5 are transferred into the wafer accommodating chamber 30 by the cassette transfer and wafer transfer device 20, the gate valve 92 is closed, while the front door valve 91 is opened. 
     After the wafer holder 40 in the wafer accommodating chamber 30 is loaded with the wafers 5, the front door valve 91 is closed, and the wafer accommodating chamber 30 is evacuated. 
     After the evacuation, the gate valve 92 is opened. The wafer transfer chamber 50 has been evacuated in advance. 
     Subsequently, the wafers 5 are held by the wafer mounting arms 68 of the wafer-transfer vacuum robot 60 in the evacuated wafer transfer chamber 50, and are transferred from the wafer holder 40 within the wafer accommodating chamber 30 to the wafer boat 75 within the reaction chamber 70. At this time, the gate valve 93 is open, and the reaction chamber 70 has already been evacuated. Since the pitch of the wafer supporting grooves 45 of the wafer holder 40 is equal to the pitch of the wafers 5 loaded on the wafer boat 75, the pitch of the wafer mounting arms 68 of the wafer-transfer vacuum robot 60 is not changed and is maintained constant. In the present embodiment, two wafers are transferred at a time from the wafer holder 40 to the wafer boat 75 by the wafer-transfer vacuum robot 60. 
     After the transfer operation, the gate valve 93 is closed, and a predetermined atmosphere is created in the reaction chamber 70. Subsequently, the two wafers 5 loaded onto the wafer boat 75 in the reaction chamber 70 are simultaneously subjected to a predetermined processing such as film forming processing. 
     Upon completion of the predetermined processing, the reaction chamber 70 is evacuated, and the gate valve 93 is opened. The wafers 5 are transferred to the wafer holder 40 within the evacuated wafer accommodating chamber 30 by the wafer-transfer vacuum robot 60. At this time, the pitch of the wafer carrying arms 68 of the wafer-transfer vacuum robot 60 is not changed and is maintained constant. Two wafers are transferred at a time. 
     Subsequently, the gate valve 92 is closed, and atmospheric pressure is created in the wafer accommodating chamber 30 using nitride or the like, and the wafers 5 are cooled until the temperature of each wafer reaches a predetermined temperature. 
     Subsequently, the front door valve 91 is opened, and the wafers 5 are transferred into the cassette 10 by the wafer transfer device 23 of the cassette transfer and wafer transfer device 20. At this time, the pitch of the tweezers 24 is changed from a pitch corresponding to the pitch of the wafer supporting grooves 45 of the wafer holder 40 to a pitch corresponding to the pitch of the grooves of the cassette 10. 
     When a predetermined number of wafers 5 are transferred into the cassette 10, the cassette 10 is transferred to the cassette stage 12 by the cassette transfer device 21. The cassette 10 is then taken out through the cassette IN/OUT opening 13. 
     As described above, since two wafers are simultaneously treated in the reaction chamber 70, wafers can be processed with an improved efficiency. Since the pitch of the wafer supporting grooves 45 of the wafer holder 40 is equal to the pitch of wafers held on the wafer boat 75, it is not necessary to change the pitch of wafer mounting arms 68 of the wafer-transfer vacuum robot 60. Therefore, the structure of the wafer-transfer vacuum robot 60 can be simplified and the vacuum created in the wafer transfer chamber 50 is prevented from being contaminated. Since two wafers 5 can be transferred at a time, the efficiency of wafer transfer can be increased. 
     Although the pitch of wafers 5 is changed by the cassette transfer and wafer transfer device 20, the cassette transfer and wafer transfer device 20 is used under the atmospheric pressure. Therefore, even when the pitch of wafers 5 is changed, the cassette transfer and wafer transfer device 20 can have a simpler structure and can be manufactured at lower cost compared to the case in which the pitch of wafers 5 is changed in a vacuum. In addition, the generation of particles can be suppressed. 
     As described above, the pitch of wafers 5 is changed under the atmospheric pressure and is fixed under the reduced pressure, and a plurality of wafers 5 are transferred at a time. Therefore, the manufacturing cost of the transfer apparatus can be decreased, and the size of the transfer apparatus is prevented from increasing. In addition, the generation of particles is suppressed, so that wafers 5 can be transferred in a clean environment. Moreover, simultaneous transfer of a plurality of wafers 5 improves the throughput, and the capability of changing the pitch of wafers 5 makes it possible to change the pitch of wafers 5 so as to guarantee that wafer processing is performed highly accurately in the reaction chamber 70. 
     In the present embodiment, the walls 53 and 54 of the wafer transfer chamber 50 are opposed to each other so as to arrange on a substantially straight line the reaction chamber 70, the wafer transfer chamber 50, and the wafer accommodating chamber 30, and the wafer transfer chamber 50 has a rectangular shape as viewed from above. As the wafer transfer chamber 50 has a rectangular shape, the size of the wafer transfer chamber 50 can be reduced, and the area occupied by the wafer transfer chamber 50 can be reduced accordingly. Thus, the semiconductor wafer processing apparatus 1 occupies less area within a clean room. By adopting the rectangular shape, the cost of manufacture of the wafer transfer chamber 50 is reduced, and a required maintenance space is also reduced. Further, the distance over which a connection is made between the wafer transfer chamber 50 and another wafer transfer chamber or the like can be reduced. This allows the wafers 5 to be readily transferred between the wafer transfer chamber 50 and another wafer transfer chamber or the like without providing a wafer transfer device at a connecting section therebetween; thus the semiconductor wafer processing apparatus 1 can accordingly be made simpler in structure and manufactured at lower cost. A plurality of semiconductor wafer processing units, each having the structure such that the reaction chamber 70, the wafer transfer chamber 50, and the wafer accommodating chamber 30 are arranged on a substantially straight line, can be readily arranged in parallel so that they occupy less area. 
     Second Embodiment: 
     FIG. 9 is a cross-sectional view for explaining a semiconductor wafer processing apparatus according to a second embodiment of the present invention. The semiconductor wafer processing apparatus 1 of the present embodiment is the same as that of the first embodiment except that: the reactions chambers 70, the wafer transfer chamber 50, and the wafer accommodating chambers 30 are located at the lower portion of the housing 900; and the wafer-transfer vacuum robot 60, and the screw shaft 561 and the like for lifting/lowering the wafer-transfer vacuum robot 60 are located at the upper portion of the housing 900. 
     Third Embodiment: 
     FIG. 10 is a cross-sectional view for explaining a semiconductor wafer processing apparatus according to a third embodiment of the present invention. 
     According to the present embodiment, six reaction chambers 70 are arranged in the vertical direction on the wall 53 of the wafer transfer chamber 50, and four wafer accommodating chambers 30 are arranged in the vertical direction on the wall 54 of the wafer transfer chamber 50. Because of an increase in the number of the reaction chambers 70 as well as the wafer accommodating chambers 30, the height of the wafer chamber 50 is increased accordingly. In order to accommodate this many reaction chambers 70 and wafer accommodating chambers 30 within the housing 900, the projecting section 52 of the wafer transfer chamber 50, the screw shaft 561, the bellows 562, and the support bar 563 for supporting the wafer-transfer vacuum robot 60 are partially projected from the housing 900. Since these projecting portions can be projected downward from the floor of a clean room, the height of the wafer transfer chamber 50 can be increased, thereby allowing more reaction chambers 70 as well as more wafer accommodating chambers 30 to be arranged in the vertical direction. Thus, more wafers 5 can be processed within less area. 
     Fourth Embodiment: 
     FIG. 11 is a plan view for explaining a semiconductor wafer processing apparatus according to a fourth embodiment of the present invention. 
     In the present embodiment, semiconductor wafer processing units 2 and 2&#39; are disposed in parallel, the unit 2 (2&#39;) having the structure such that the reaction chamber 70 (70&#39;), the wafer transfer chamber 50 (50&#39;), the wafer accommodating chamber 30 (30&#39;), the cassette transfer and wafer transfer device 20 (20&#39;), and the cassette shelf 10 (10&#39;) are arranged on a substantially straight line. The semiconductor wafer processing units 2 and 2&#39; each having such a structure can be readily disposed in parallel, thereby reducing the area occupied by the entire apparatus composed of the units 2 and 2&#39;. 
     The wafer transfer chamber 50 (50&#39;) has a rectangular shape as viewed from above. Accordingly, the distance over which a connection is made between the wafer transfer chamber 50 and the wafer transfer chamber 50&#39; can be reduced. This allows a wafer to be readily transferred between the wafer transfer chamber 50 and the wafer transfer chamber 50&#39; without providing a wafer transfer device in an intermediate wafer transfer chamber 90, which serves as a connecting section between the chambers 50 and 50&#39;. Thus, the semiconductor wafer processing apparatus 1 can accordingly be made simpler in structure and manufactured at lower cost. The intermediate wafer holding chamber 90 can also be used as a cooling chamber for cooling a wafer or as a preheating chamber for preheating a wafer. 
     A space located between the reaction chamber 70 and the reaction chamber 70&#39; is large enough for use as a common maintenance space 3 for the semiconductor wafer processing units 2 and 2&#39;. 
     Fifth Embodiment: 
     FIG. 12 is a plan view for explaining a semiconductor wafer processing apparatus according to a fifth embodiment of the present invention. 
     In the present embodiment, a semiconductor wafer processing unit 6 according to the present invention, which has the structure such that the reaction chamber 70, the wafer transfer chamber 50, the wafer accommodating chamber 30, the cassette transfer and wafer transfer device 20, and the cassette shelf 10 are arranged on a substantially straight line, is connected to a semiconductor wafer processing unit 7, which includes a wafer transfer chamber 150 which is hexagon-shaped as viewed from above and on side walls of which cassette chambers 131 and 132, reaction chambers 171 and 172, and a wafer cooling chamber 142 are provided. 
     Since the wafer transfer chamber 50 is rectangle-shaped, it can be readily connected via the wall 51 thereof to a semiconductor wafer processing unit having a different shape. 
     Also, in the present embodiment, the distance over which a connection is made between the wafer transfer chamber 50 and the wafer transfer chamber 150 can be reduced. This allows a wafer to be readily transferred between the wafer transfer chamber 50 and the wafer transfer chamber 150 without providing a wafer transfer device in an intermediate wafer transfer chamber 90, which serves as a connecting section between the chambers 50 and 150. Thus, the semiconductor wafer processing apparatus as a whole can accordingly be made simpler in structure and manufactured at lower cost. The intermediate wafer transfer chamber 90 can also be used as a cooling chamber for cooling a wafer or as a preheating chamber for preheating a wafer. 
     Sixth Embodiment: 
     FIG. 13 is a plan view for explaining a semiconductor wafer processing apparatus according to a sixth embodiment of the present invention. 
     In the present embodiment, a wafer transfer chamber 55 is octagon-shaped as viewed from above, and the reaction chambers 70 are provided in layers on each of the seven side walls of the wafer transfer chamber 55. 
     Seventh Embodiment: 
     FIG. 14 is a plan view for explaining a semiconductor wafer processing apparatus according to a seventh embodiment of the present invention. 
     In the present embodiment, the wafer transfer chamber 55 of FIG. 13 from which reaction chambers 70a are removed is connected via an intermediate wafer transfer chamber 90 to the wafer transfer chamber 55 of FIG. 13 from which reaction chambers 70b are removed. The intermediate wafer transfer chamber 90 can also be used as a cooling chamber for cooling a wafer or as a preheating chamber for preheating a wafer.