Title of Invention: SUBSTRATE PROCESSING APPARATUS AND SUBSTRATE PROCESSING METHOD Abstract: A substrate processing apparatus includes an indexer block and a processing block adjacent to the indexer block in a lateral direction of the indexer block. A plurality of processing block layers are stacked in an up-down direction in the processing block. The indexer block includes a container holding portion and a first transfer robot that transfers a substrate between the substrate container held by the container holding portion and the processing block. Each of the processing block layers includes a plurality of processing units, a substrate placing portion, a dummy-substrate housing portion, and a second transfer robot that transfers a substrate between the substrate placing portion and the plurality of processing units and that transfers a dummy substrate between the dummy-substrate housing portion and the plurality of processing units. Detailed Description: CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority based on Japanese Patent Application No. 2020-145033 filed on Aug. 28, 2020, the entire disclosure of which is incorporated herein by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for processing a substrate. Examples of substrates to be processed include semiconductor wafers, substrates for FPDs (flat panel displays) such as liquid crystal displays or organic EL (electroluminescence) displays, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, substrates for photomasks, ceramic substrates, and substrates for solar cells, etc. 2. Description of the Related Art A substrate processing apparatus that processes substrates, such as semiconductor wafers, is used in a manufacturing process of a semiconductor device. An example of such a substrate processing apparatus is disclosed by Japanese Patent Application Publication No. 2017-41506. This substrate processing apparatus includes a carrier holding portion that holds a carrier that houses a substrate, a plurality of processing units that process the substrate, a transfer unit that transfers the substrate between the carrier and the processing unit, and a control unit. When a non-use duration time of the processing unit reaches a predetermined time, a controller requests a host device to carry in a dummy carrier holding a dummy substrate. When the dummy carrier is carried into the carrier holding portion, the transfer unit transfers the dummy substrate from the dummy carrier to the processing unit. The processing unit is washed by use of the dummy substrate. The transfer unit includes an indexer robot and a main transfer robot, and a delivery unit is disposed between these robots. The indexer robot transfers a substrate between the carrier and the delivery unit. The main transfer robot transfers a substrate between the delivery unit and the processing unit. When the dummy carrier is placed at the carrier holding portion, the indexer robot takes a dummy substrate out of the dummy carrier, and transfers this dummy substrate to the delivery unit. This dummy substrate is transferred by the main transfer robot from the delivery unit to the processing unit. When a unit washing process using the dummy substrate is finished, the main transfer robot takes the dummy substrate out of the processing unit, and transfers the dummy substrate to the delivery unit. This dummy substrate is transferred by the indexer robot from the delivery unit to the dummy carrier. When all dummy substrates are housed in the dummy carrier, the dummy carrier is carried out of the carrier holding portion. SUMMARY OF THE INVENTION As thus described, the dummy substrate is introduced from the outside of the substrate processing apparatus, and is transferred to the processing unit through the same path as a product substrate, and is carried out of the processing unit, and is housed in the dummy carrier. Therefore, in order to transfer the dummy substrate, both the indexer robot and the main transfer robot are used, and the dummy substrate is transferred through the delivery unit. Therefore, interference in transfer occurs between the dummy substrate and the product substrate, and the transfer efficiency of the product substrate becomes worse, and, as a result, productivity enhancement is hindered. Particularly in a substrate processing apparatus configured to concurrently process many product substrates by increasing the number of processing units, the indexer robot and the main transfer robot each have a large transfer load, and its reduction holds the key to productivity enhancement. Additionally, the occupation of the carrier holding portion by the dummy carrier begins when the dummy carrier is carried therein. The occupation continues thereafter until a dummy substrate is housed in the carrier after finishing a processing operation in the processing unit which occurs after transferring the dummy substrate to the processing unit from the dummy carrier. Therefore, the carrier holding portion continues being occupied by the dummy carrier, and therefore a waiting time for the carry-in of a product substrate may occur. Therefore, likewise, from this viewpoint, productivity enhancement is hindered. Therefore, one preferred embodiment of the present invention provides a substrate processing apparatus and a substrate processing method capable of performing a processing operation by use of a dummy substrate in a processing unit while reducing influence on the transfer of a product substrate. One preferred embodiment of the present invention provides a substrate processing apparatus including an indexer block and a processing block that is adjacent to the indexer block in a lateral direction of the indexer block and in which a plurality of processing block layers are stacked in an up-down direction. The indexer block includes a container holding portion that holds a substrate container that houses a substrate and a first transfer mechanism that transfers a substrate between the substrate container held by the container holding portion and the processing block. Each of the processing block layers includes a plurality of processing units that perform substrate processing, a substrate placing portion that temporarily holds a substrate that is delivered between the first transfer mechanism and the processing block layer, a dummy-substrate housing portion that houses a dummy substrate that is usable in the plurality of processing units, and a second transfer mechanism that transfers a substrate between the substrate placing portion and the plurality of processing units and that transfers a dummy substrate between the dummy-substrate housing portion and the plurality of processing units. According to this configuration, the processing block that is adjacent to the indexer block in the lateral direction of the indexer block is configured such that the plurality of processing block layers are stacked in the up-down direction. Each of the processing block layers is provided with the dummy-substrate housing portion that houses a dummy substrate. A dummy substrate can be housed in the processing block layer, and therefore it is possible to transfer the dummy substrate between the dummy-substrate housing portion and the processing unit without the participation of the first transfer mechanism when necessity to use a dummy substrate in the processing unit arises. Therefore, it is possible to reduce the transfer load of the first transfer mechanism, and therefore it is possible to perform processing that uses a dummy substrate while reducing influence on the transfer of a product substrate. Particularly, the transfer load of the first transfer mechanism that transfers a substrate is very heavy between the plurality of processing block layers respectively having the plurality of processing units and the container holding portion. Therefore, the transfer efficiency of a product substrate is raised by reducing the transfer load of the first transfer mechanism, hence making it possible to raise productivity. The second transfer mechanism of each of the processing block layers has the job of transferring a substrate in the processing block layer, and therefore its transfer load is smaller than the first transfer mechanism. Therefore, the fact that the second transfer mechanism has the job of transferring a dummy substrate in the processing block layer does not cause a critical problem from the viewpoint of productive efficiency. Additionally, the dummy-substrate housing portion is in the processing block layer, and therefore it is possible to transfer a dummy substrate between the dummy-substrate housing portion and the processing unit without being transferred via the substrate placing portion that is used to deliver a substrate between the first transfer mechanism and the processing block layer. Therefore, it is possible to reduce interference between the transfer of a dummy substrate and the transfer of a product substrate, and therefore it is possible to improve the transfer efficiency of the product substrate, hence making it possible to raise productivity. Additionally, unlike the example of Japanese Patent Application Publication No. 2017-41506, the container holding portion is never occupied by the dummy carrier that houses a dummy substrate for a long time. This makes it possible to reduce an event that a waiting time occurs in order to carry in the substrate container that houses a product substrate, thus making it possible to contribute to productivity enhancement. In one preferred embodiment of the present invention, in each processing block layer, the plurality of processing units are arranged along a transfer path along which a substrate is transferred by the second transfer mechanism on both sides of the transfer path, and are stacked in the up-down direction. According to this configuration, the arrangement of the plurality of processing units in the processing block layers is designed so that substrates can be efficiently transferred by the second transfer mechanism. This makes it possible to contribute to productivity enhancement. In one preferred embodiment of the present invention, the substrate placing portion is disposed between the first transfer mechanism and the second transfer mechanism, and the dummy-substrate housing portion is disposed between the first transfer mechanism and the second transfer mechanism. According to this configuration, the substrate placing portion is disposed between the first transfer mechanism and the second transfer mechanism, hence making it possible to efficiently transfer a substrate therebetween. Additionally, the dummy-substrate housing portion is disposed between the first transfer mechanism and the second transfer mechanism, and therefore it is possible to place the dummy-substrate housing portion at a position at which the dummy-substrate housing portion does not interfere with the transfer of a substrate by the first transfer mechanism or with the transfer of a substrate by the second transfer mechanism. Therefore, it is possible to hold a dummy substrate in the processing block layer while restraining or preventing the transfer of a product substrate from being affected. In one preferred embodiment of the present invention, the dummy-substrate housing portion is disposed at a height different from a height of the substrate placing portion. According to this configuration, it is possible to three-dimensionally dispose the dummy-substrate housing portion and the substrate placing portion, hence making it possible to appropriately dispose the dummy-substrate housing portion in the processing block layer while effectively using a space in the processing block layer. As a result, the arrangement of the dummy-substrate housing portion that does not obstruct the transfer of a product substrate is realized. In one preferred embodiment of the present invention, the dummy-substrate housing portion is disposed so as to lie over and (partly or wholly) cover, or (partly or wholly) overlap the substrate placing portion when viewed in plan. According to this configuration, it is possible to dispose the dummy-substrate housing portion so as to overlap the substrate placing portion in a plan view while using a space above or below the substrate placing portion. This makes it possible to realize the arrangement of the dummy-substrate housing portion that does not obstruct the transfer of a product substrate, and makes it possible to dispose the dummy-substrate housing portion while effectively using a space in the processing block layer. In detail, an arrangement in which the dummy-substrate housing portion overlaps the substrate placing portion in a plan view may be an arrangement in which part or all of a dummy substrate housed in the dummy-substrate housing portion lies over and covers, or overlaps a substrate held by the substrate placing portion. In one preferred embodiment of the present invention, the plurality of processing block layers include a first processing block layer and a second processing block layer disposed above the first processing block layer. In the first processing block layer, the dummy-substrate housing portion is positioned below the substrate placing portion. In the second processing block layer, the dummy-substrate housing portion is positioned above the substrate placing portion. According to this configuration, in the first processing block layer (lower layer), the dummy-substrate housing portion is positioned below the substrate placing portion, and, in the second processing block layer (upper layer), the dummy-substrate housing portion is positioned above the substrate placing portion. Therefore, it is possible to reduce a difference in height between the substrate placing portion of the first processing block layer and the substrate placing portion of the second processing block layer. As a result, it is possible to shorten a substrate transfer stroke in the up-down direction by means of the first transfer mechanism, hence making it possible to reduce the transfer load of the first transfer mechanism. Therefore, it is possible to raise the transfer efficiency of a product substrate and to contribute to productivity enhancement. The plurality of processing block layers may have three or more processing block layers stacked in the up-down direction. In this case, the first processing block layer and the second processing block layer may be processing block layers that are adjacent to each other in the up-down direction, and may be configured such that another processing block layer is interposed therebetween. In one preferred embodiment of the present invention, the dummy-substrate housing portion of each processing block layer includes a plurality of dummy-substrate slots that are equal in number to the plurality of processing units included in the processing block layer. Each dummy-substrate slot is configured to hold a single dummy substrate. This configuration makes it possible to hold dummy substrates that are equal in number to the processing units in each processing block layer. Therefore, if necessity to carry a dummy substrate into any one of the processing units arises, it is possible to swiftly carry the dummy substrate into the processing unit by means of the second transfer mechanism. The first transfer mechanism does not participate in the carry-in of the dummy substrate, and therefore it is possible to restrain or prevent the transfer of a product substrate from being affected. In one preferred embodiment of the present invention, the plurality of processing units of each processing block layer are correlated with the plurality of dummy-substrate slots of the processing block layer in a one-to-one correspondence. The second transfer mechanism transfers a dummy substrate between the dummy-substrate slot and the processing unit that correspond to each other. According to this configuration, the plurality of dummy-substrate slots and the plurality of processing units in the processing block layer are correlated with each other in a one-to-one correspondence, and therefore it is possible to set a dummy substrate held by the dummy-substrate slot as a dummy substrate dedicated to a corresponding processing unit. As a result, the usage history of the dummy substrate is easily managed. In one preferred embodiment of the present invention, the substrate processing apparatus further includes a controller configured (programmed) to record a usage history of a dummy substrate housed in the dummy-substrate housing portion and to issue a warning based on the usage history of the dummy substrate when the dummy substrate reaches a usage limit. This configuration makes it possible to appropriately manage the usage situation of the dummy substrate and to issue a warning at an appropriate time. A user of the substrate processing apparatus can take countermeasures, such as dummy substrate replacement, against the warning. The dummy substrate is held in the substrate processing apparatus, hence making it possible to appropriately manage the usage situation of the dummy substrate by means of the controller included in the substrate processing apparatus. The usage history may include the number of uses of a dummy substrate. The controller may be communicably connected to a host computer. In this case, the controller may be configured (programmed) to transmit the warning to the host computer. In one preferred embodiment of the present invention, the substrate processing apparatus further includes a controller configured (programmed) to control the second transfer mechanism and the processing unit. When a dummy processing condition is satisfied, the controller controls the second transfer mechanism to transfer a dummy substrate from the dummy-substrate housing portion to the processing unit, and controls the processing unit to perform dummy processing. According to this configuration, when the dummy processing condition is satisfied, dummy processing in the processing unit is performed by the transfer of the dummy substrate in the processing block layer. Therefore, it is possible to realize dummy processing while restrain or preventing the transfer of a product substrate from being affected. In one preferred embodiment of the present invention, the dummy processing includes a maintenance process in which maintenance of the processing unit is performed. Preferably, the maintenance process includes at least one of a preparation process in which an environment is adjusted to process a substrate (product substrate) housed in the substrate container held by the container holding portion and a unit washing process in which an inside of the processing unit is washed and cleaned. For example, the maintenance process (e.g., unit washing process) may be performed under a dummy processing condition (maintenance execution condition, e.g., unit washing execution condition) that denotes that the number of substrates processed in the processing unit, which has been obtained by being counted, reaches a set value (or that the number of substrates processed therein exceeds a set value). Either additionally or alternatively, the maintenance process (e.g., preparation process or unit washing process) may be performed under a dummy processing condition (maintenance execution condition) that denotes that a duration time of a non-use state (non-use duration time) during which the processing unit is not used for substrate processing, which has been obtained by being measured, reaches a set value (or that a duration time of a non-use state exceeds a set value). One preferred embodiment of the present invention provides a substrate processing method that is executed in a substrate processing apparatus including an indexer block that has a container holding portion that holds a substrate container that houses a substrate and a first transfer mechanism that transfers a substrate between the substrate container held by the container holding portion and a processing block; and the processing block that is adjacent to the indexer block in a lateral direction of the indexer block and in which a plurality of processing block layers are stacked in an up-down direction. Each processing block layer includes a plurality of processing units that perform substrate processing, a substrate placing portion that temporarily holds a substrate that is delivered between the first transfer mechanism and the processing block layer, a dummy-substrate housing portion that houses a dummy substrate that is usable in the plurality of processing units, and a second transfer mechanism that transfers a substrate between the substrate placing portion and the plurality of processing units and that transfers a dummy substrate between the dummy-substrate housing portion and the plurality of processing units. The substrate processing method allows the substrate processing apparatus to execute a dummy substrate carrying-in step in which, in each processing block layer, the second transfer mechanism carries a dummy substrate housed in the dummy-substrate housing portion in the processing block layer into any one of the plurality of processing units in the processing block layer, a dummy processing step in which dummy processing that uses the dummy substrate carried into any one of the plurality of processing units is performed in the processing unit, a step in which, after finishing the dummy processing, the second transfer mechanism takes the dummy substrate out of the processing unit, and transfers the dummy substrate to the dummy-substrate housing portion, a step in which the second transfer mechanism carries a substrate placed in the substrate placing portion of the processing block layer into any one of the plurality of processing units of the processing block layer, and a step in which the substrate carried into any one of the plurality of processing units is processed in the processing unit. According to this method, it is possible to perform processing that uses the dummy substrate in the processing unit of each processing block layer while reducing the transfer load of the first transfer mechanism. As a result, it is possible to improve productive efficiency. In one preferred embodiment of the present invention, the dummy substrate carrying-in step is executed in parallel with or prior to a substrate carry-in step in which the first transfer mechanism takes a substrate out of the substrate container, and carries this substrate into the substrate placing portion of one of the plurality of processing block layers. According to this method, it is possible to allow the first transfer mechanism to carry a product substrate into the processing block layer, and, on the other hand, to carry a dummy substrate into the processing unit in each processing block layer. The first transfer mechanism is not required to participate in the carry-in of the dummy substrate, and therefore it is possible to transfer the dummy substrate in the processing block layer without waiting for the transfer of a substrate by means of the first transfer mechanism or in parallel with the transfer of the substrate. Therefore, it is possible to reduce the transfer load of the first transfer mechanism, and, in addition to this, it is possible to swiftly transfer a dummy substrate to the processing unit in the processing block layer. In one preferred embodiment of the present invention, the dummy processing step is executed in parallel with or prior to the substrate carry-in step. As described above, the first transfer mechanism is not required to participate in the transfer of a dummy substrate in the processing block layer, and therefore it is possible to start dummy processing in the processing unit without waiting for the transfer of a substrate by means of the first transfer mechanism or in parallel with the transfer of the substrate. Therefore, it is possible to reduce the transfer load of the first transfer mechanism, and, in addition to this, it is possible to swiftly start dummy processing in the processing block layer. The aforementioned or yet other objects, features, and effects of the present invention will be clarified by the following description of preferred embodiments given below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustrative plan view showing an internal configuration of a substrate processing apparatus according to a preferred embodiment of the present invention. FIG. 2 is an illustrative longitudinal sectional view seen from line II-II of FIG. 1. FIG. 3 is an illustrative transverse sectional view seen from line III-III of FIG. 1. FIG. 4 is an illustrative elevational view showing an internal configuration of a processing block seen from direction IV of FIG. 1. FIG. 5 is a view shown to describe a configuration example of a substrate placing portion. FIG. 6 is a view shown to describe a configuration example of a dummy-substrate housing portion. FIG. 7 is an illustrative cross-sectional view shown to describe a configuration example of a processing unit. FIG. 8 is a block diagram shown to describe a configuration relative to the control of the substrate processing apparatus. FIG. 9 is a flowchart shown to describe the operation of a controller relative to dummy processing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an illustrative plan view showing an internal configuration of a substrate processing apparatus according to a preferred embodiment of the present invention. FIG. 2 is an illustrative longitudinal sectional view seen from line II-II of FIG. 1. FIG. 3 is an illustrative transverse sectional view seen from line III-III of FIG. 1. FIG. 4 is an illustrative elevational view showing a partial internal configuration seen from direction IV of FIG. 1. The substrate processing apparatus 1 includes an indexer block 2 and a processing block 3 adjacent to the indexer block 2 in a lateral direction (first horizontal direction X) of the indexer block 2. The indexer block 2 includes a plurality of (in the present preferred embodiment, four) carrier holding portions (load ports) 25 and an indexer robot 26. For convenience, in some situations, the side of the carrier holding portion 25 is hereinafter defined as a front side with respect to the first horizontal direction X, and the other side opposite to the front side is hereinafter defined as a rear side with respect thereto. The plurality of carrier holding portions 25 are arranged along a second horizontal direction Y perpendicular to the first horizontal direction X. Each of the carrier holding portions 25 is configured to accept and hold a carrier C that is automatically transferred by an automatic carrier transferring mechanism installed in a factory. Each of the carrier holding portions 25 is configured to hold a single carrier C. The carrier C is a substrate container that houses a to-be-processed substrate (product substrate) W. An example of the carrier C is a FOUP (Front Opening Unified Pod). The carrier C is configured to hold a plurality of substrates W (for example, twenty-five substrates) in a stacked state. More specifically, the carrier C is configured to hold a plurality of substrates W in a horizontal posture in a stacked state along an up-down direction Z when the carrier C is held by the carrier holding portion 25. The carrier holding portion 25 is an example of a container holding portion that holds the carrier C that is a substrate container. The substrate W is, for example, a semiconductor wafer. The indexer robot 26 is an example of a first transferring mechanism. The indexer robot 26 is configured to access a carrier C held by each of the plurality of carrier holding portions 25, and to carry a substrate W in/out, and transfers the substrate W between the carrier holding portion 25 and the processing block 3. In the present preferred embodiment, the indexer robot 26 is an articulated-arm robot including an articulated arm 27. In detail, the indexer robot 26 includes an articulated arm 27 formed by connecting a plurality of arms 28 together, one or more hands 29 joined to a front end of the articulated arm 27, and a base portion 30 that moves upwardly and downwardly while supporting the articulated arm 27. The plurality of arms 28 and the hands 29 that are constituents of the articulated arm 27 are swingable around a perpendicular swing axis that is set at each base end portion, and are provided with individual actuators (typically, electric motors), not shown, that are used to swing each arm 28 and each hand 29. The processing block 3 includes a plurality of processing block layers BL and BU stacked together in the up-down direction Z. In the present preferred embodiment, the processing block 3 includes a processing block layer of a first layer (lower layer) (which is hereinafter referred to as a “first processing block layer BL”) and a processing block layer of a second layer (upper layer) stacked thereabove (which is hereinafter referred to as a “second processing block layer BU”). Hereinafter, when a distinction is drawn between constituents of the first processing block layer BL and constituents of the second processing block layer BU, a reference sign whose end has the letter “L” is used for the constituents of the first processing block layer BL, whereas a reference sign whose end has the letter “U” is used for the constituents of the second processing block layer BU. The same applies to reference signs of the accompanying drawings. An internal configuration of the first processing block layer BL and an internal configuration of the second processing block layer BU in a plan view are substantially identical with each other. Therefore, it should be noted that the configuration (arrangement in a plan view) of the first processing block layer BL is represented by replacing the letter “U” of the end of a reference sign with the letter “L” and by reading it as the letter “L” in FIG. 1. The first processing block layer BL includes a plurality of (in the present preferred embodiment, twelve) processing units 11L to 13L, 21L to 23L, 31L to 33L, and 41L to 43L (note that the processing units of the first processing block layer BL are hereinafter referred to generically as the “processing units 11L to 43L” if necessary), a substrate placing portion 6L, a dummy-substrate housing portion 7L, and a main transfer robot 8L. The plurality of processing units 11L to 43L perform an operation to process a substrate W. In the present preferred embodiment, each of the processing units 11L to 43L is a single-substrate-processing type processing unit that processes substrates W one by one. The substrate placing portion 6L is a unit that provides a temporary substrate-storage space in which a substrate W, which is delivered between the indexer robot 26 and the first processing block layer BL, is temporarily held. The dummy-substrate housing portion 7L is a unit to hold a dummy substrate DW, which can be used in the processing units 11L to 43L, inside the substrate processing apparatus 1, and provides a waiting place for the dummy substrate DW. The main transfer robot 8L is an example of a second transferring mechanism that transfers a substrate W between the substrate placing portion 6L and the processing units 11L to 43L and that transfers a dummy substrate DW between the dummy-substrate housing portion 7L and the processing units 11L to 43L. The dummy substrate DW is a substrate that is identical with the substrate W in shape (e.g., circle) and in size. The dummy substrate DW is not used to manufacture a real product unlike a product substrate W that is supplied from the carrier C. The dummy substrate DW is introduced into and is used in the processing units 11L to 43L in order to perform preprocessing (preparation processing) in which an internal environment of the processing units 11L to 43L is adjusted, unit washing in which the inside of the processing units 11L to 43L is washed and cleaned, and so on. Processing that uses the dummy substrate DW in this way is hereinafter referred to as “dummy processing.” The aforementioned preprocessing and the unit washing are a maintenance process performed to maintain the processing units 11L to 43L, and the dummy processing includes such a maintenance process. The plurality of processing units 11L to 43L are arranged at both sides of a transfer space 52L along the transfer space 52L that provides a transfer path 51L along which a substrate W is transferred by the main transfer robot 8L, and the processing units 11L to 43L face the transfer space 52L. The transfer space 52L has a predetermined width in the second horizontal direction Y in a plan view, and rectilinearly extends in a direction away from the indexer block 2 along the first horizontal direction X. The transfer space 52L has a height substantially equal to that of the first processing block layer BL with respect to the up-down direction Z. A first liquid supply portion 91, a first processing unit stack S1L, a first exhaust portion 101, a second liquid supply portion 92, a second processing unit stack S2L, and a second exhaust portion 102 are arranged along the transfer path 51L in order of increasing distance from the indexer block 2 on one side of the transfer space 52L in a plan view. A third exhaust portion 103, a third processing unit stack S3L, a third liquid supply portion 93, a fourth exhaust portion 104, a fourth processing unit stack S4L, and a fourth liquid supply portion 94 are arranged along the transfer path 51L in order of increasing distance from the indexer block 2 on the other side of the transfer space 52L. These are arranged so as to define the transfer space 52L having a substantially rectangular parallelepiped shape. The first to fourth processing unit stacks S1L, S2L, S3L, and S4L each include a plurality of processing units stacked together in the up-down direction Z (in the present preferred embodiment, three-stacked), i.e., the first to fourth processing unit stacks S1L, S2L, S3L, and S4L include processing units 11L to 13L, 21L to 23L, 31L to 33L, and 41L to 43L, respectively. The third processing unit stack S3L faces the first processing unit stack S1L with the transfer space 52L between the third processing unit stack S3L and the first processing unit stack S1L. The fourth processing unit stack S4L faces the second processing unit stack S2L with the transfer space 52L between the fourth processing unit stack S4L and the second processing unit stack S2L. Therefore, the plurality of processing units 31L to 33L that are constituents of the third processing unit stack S3L face the plurality of processing units 11L to 13L that are constituents of the first processing unit stack S1L with the transfer space 52L between the processing units 31L to 33L and the processing units 11L to 13L. Likewise, the plurality of processing units 41L to 43L that are constituents of the fourth processing unit stack S4L face the plurality of processing units 21L to 23L that are constituents of the second processing unit stack S2L with the transfer space 52L between the processing units 41L to 43L and the processing units 21L to 23L. In the present preferred embodiment, the first processing block layer BL includes twelve processing units 11L to 13L, 21L to 23L, 31L to 33L, and 41L to 43L, and these processing units are divided and disposed so that each of the four processing unit stacks S1L to S4L has three processing units. The transfer space 52L is partitioned from above by means of an intermediate partition wall 16 disposed at a position coinciding with the upper surface of each of the uppermost processing units 13L, 23L, 33L, and 43L of the respective processing unit stacks S1L to S4L, and is partitioned from below by means of a lower partition wall 15 disposed at a position coinciding with the lower surface of each of the lowermost processing units 11L, 21L, 31L, and 41L. All of the processing units 11L to 43L have a substrate carry-in/out opening 37 bored at a position facing the transfer space 52L. The main transfer robot 8L transfers a substrate W and a dummy substrate DW through the transfer space 52L, and carries the substrate W and the dummy substrate DW into/from each of the processing units 11L to 43L through the substrate carry-in/out opening 37. The substrate placing portion 6L is disposed between the indexer robot 26 and the main transfer robot 8L. More specifically, the substrate placing portion 6L is disposed at an end portion on the indexer-robot-26 side of the inside of the transfer space 52L in a plan view. In the present preferred embodiment, the substrate placing portion 6L is positioned between the first liquid supply portion 91 and the third exhaust portion 103. The substrate placing portion 6L is disposed at a height between the intermediate partition wall 16 and the lower partition wall 15 with respect to the up-down direction Z. In the present preferred embodiment, the substrate placing portion 6L is disposed so as to reach an approximately intermediate height within the height range from the intermediate partition wall 16 to an upper partition wall 17. The position in the up-down direction of the substrate placing portion 6L is required to fall within the height range accessible by the indexer robot 26 and to fall within the height range accessible by the main transfer robot 8L. The substrate placing portion 6L includes a not-yet-processed-substrate placing portion 61 on which a not-yet-processed substrate W is placed and an already-processed-substrate placing portion 62 on which an already-processed substrate W is placed. The not-yet-processed-substrate placing portion 61 and the already-processed-substrate placing portion 62 are stacked together in the up-down direction Z. Preferably, the already-processed-substrate placing portion 62 is disposed above the not-yet-processed-substrate placing portion 61. As shown in an enlarged view of FIG. 5 showing a configuration example, the not-yet-processed-substrate placing portion 61 and the already-processed-substrate placing portion 62 include boxes 63 and 64 that are open both toward the indexer-robot-26 side and toward the main-transfer-robot-8L side along the first horizontal direction X and substrate holding shelves 65 and 66 disposed inside the boxes 63 and 64. The substrate holding shelves 65 and 66 have a plurality of (for example, ten) substrate support members 67 and 68 arranged in the up-down direction Z. Each of the substrate support members 67 and 68 is configured to support a peripheral edge portion of a lower surface of a single substrate W from below and to hold this substrate W in a horizontal posture. This enables the not-yet-processed-substrate placing portion 61 and the already-processed-substrate placing portion 62 to hold the plurality of substrates W (for example, ten substrates) in a state in which the substrates W are stacked together on their substrate holding shelves 65 and 66, respectively, with intervals between the substrates W in the up-down direction Z in the horizontal posture. As shown in FIG. 2, a window 4L corresponding to the substrate placing portion 6L is formed so as to pass through a rear partition wall 2a of the indexer block 2 and a front partition wall 3a of the processing block 3, i.e., so as to pass through their adjoining partition walls. The indexer robot 26 can access the substrate placing portion 6L through the window 4L and carry a substrate W into/from the substrate placing portion 6L. The dummy-substrate housing portion 7L is disposed at a height different from that of the substrate placing portion 6L, and, in the present preferred embodiment, is disposed below the substrate placing portion 6L in the transfer space 52L. The dummy-substrate housing portion 7L is disposed so as to overlap the substrate placing portion 6L in a plan view. More specifically, when a substrate W is held by the substrate placing portion 6L and when a dummy substrate DW is held by the dummy-substrate housing portion 7L, the dummy-substrate housing portion 7L is disposed so that the substrate W and the dummy substrate DW overlap each other in a plan view. The overlapping of the substrate W and the dummy substrate DW in a plan view may be adjusted so that these substrates lie over and partly cover each other, or may be adjusted so that these substrates lie over and wholly cover each other, i.e., so that the dummy substrate DW lies over and covers substantially the entirety of the substrate W. The dummy-substrate housing portion 7L is disposed between the lower partition wall 15 and the intermediate partition wall 16, and is disposed in a height range that is accessible by the main transfer robot 8L. The rear partition wall 2a of the indexer block 2 and the front partition wall 3a of the processing block 3 are positioned, i.e., their adjoining partition walls are positioned on the front side of the dummy-substrate housing portion 7L, i.e., on the indexer-block-2 side. Each of these partition walls is not provided with a window corresponding to the dummy-substrate housing portion 7L. Therefore, in the present preferred embodiment, the indexer robot 26 cannot access the dummy-substrate housing portion 7L. As shown in an enlarged view of FIG. 6 showing a configuration example, the dummy-substrate housing portion 7L includes a dummy-substrate holding shelf 71. The configuration of the dummy-substrate holding shelf 71 may be substantially identical with those of the substrate holding shelves 65 and 66 of the substrate placing portion 6L. However, the number of dummy substrates DW that can be held by the dummy-substrate holding shelf 71 is not required to be equal to the number of substrates that can be held by the substrate holding shelves 65 and 66. In detail, the dummy-substrate holding shelf 71 has a plurality of (for example, twelve) dummy-substrate support members 72 arranged in the up-down direction. Each of the dummy-substrate support members 72 is configured to support a peripheral edge portion of a lower surface of a single dummy substrate DW from below and to hold this dummy substrate DW in a horizontal posture. The dummy-substrate housing portion 7L can hold a plurality of (for example, twelve) dummy substrates DW in a state in which the dummy substrates DW are stacked together on the dummy-substrate holding shelf 71 with intervals between the dummy substrates DW in the up-down direction Z in the horizontal posture. In detail, the dummy-substrate housing portion 7L has a plurality of slots (the number of which is identical with the number of processing units provided in the first processing block layer BL in the present preferred embodiment) stacked together in the up-down direction so as to house each dummy substrate DW in a horizontal posture (note that the slots are hereinafter referred to as “dummy-substrate slots DL1 to DL12”). A dummy-substrate sensor (not shown) may be provided for detecting the presence or absence of a dummy substrate DW in each of the dummy substrate slots DL1 to DL12. In the present preferred embodiment, the dummy-substrate housing portion 7L does not include a box that encloses dummy substrates DW housed therein, unlike the substrate placing portion 6L. Of course, such a box may be included. As shown in FIG. 2, the main transfer robot 8L is disposed in the transfer space 52L. The main transfer robot 8L includes a hand 81 that holds a single substrate in a horizontal posture and a hand driving mechanism 82 that drives the hand 81. A plurality of (for example, two) hands may be provided. The hand driving mechanism 82 is capable of moving the hand 81 in the horizontal directions X and Y and in the up-down direction Z, and is capable of turning the hand 81 around a vertical rotational axis. The hand driving mechanism 82 includes two support pillars 83, a vertical moving portion 84, a horizontal moving portion 85, a rotational portion 86, and a proceeding/receding portion 87. The hand 81 is joined to the proceeding/receding portion 87. If a plurality of hands 81 are provided, it is preferable to provide a plurality of proceeding/receding portions 87 corresponding to those hands 81. The two support pillars 83 are disposed with an interval between the support pillars 83 along the first horizontal direction X, and are respectively fixed to sidewalls of the transfer space 52L. The two support pillars 83 extend along the up-down direction Z, and have a function serving as rails that guide the vertical movement of the vertical moving portion 84. The vertical moving portion 84 has the form of a rail that extends in the first horizontal direction X over the two support pillars 83 and both end portions of which are joined to the two support pillars 83. The vertical moving portion 84 is configured to move in the up-down direction with respect to the support pillar 83 while being guided by the two support pillars 83. The horizontal moving portion 85 is configured to be supported on the vertical moving portion 84 and to move in the first horizontal direction X with respect to the vertical moving portion 84 while being guided by the vertical moving portion 84. The rotational portion 86 is supported by the horizontal moving portion 85. The rotational portion 86 is configured to rotate around a vertical rotational axis on the horizontal moving portion 85. The proceeding/receding portion 87 is joined to the rotational portion 86. The proceeding/receding portion 87 proceeds or recedes in the horizontal direction with respect to the rotational axis, and, as a result, the hand 81 is allowed to proceed or recede in the horizontal direction. This configuration enables the main transfer robot 8L to deliver a substrate W between the substrate placing portion 6L and the main transfer robot 8L by allowing the hand 81 to access the substrate placing portion 6L. Additionally, this configuration enables the main transfer robot 8L to deliver a substrate W or a dummy substrate DW between an arbitrary one of the processing units 11L to 43L in the first processing block layer BL and the main transfer robot 8L by allowing the hand 81 to access the processing units 11L to 43L. Still additionally, this configuration enables the main transfer robot 8L to deliver a dummy substrate DW between the dummy-substrate housing portion 7L and the main transfer robot 8L by allowing the hand 81 to access the dummy-substrate housing portion 7L. Further, the main transfer robot 8L is enabled to transfer the substrates W, DW held by the hand 81 among the substrate placing portion 6L, the processing units 11L to 43L, and the dummy-substrate housing portion 7L in the first processing block layer BL. The second processing block layer BU is configured in substantially the same way as the first processing block layer BL, and therefore a repeated description will be hereinafter omitted as much as possible, and differences in configuration therebetween will be chiefly described. In the second processing block layer BU, a component having the same designation as in the first processing block layer BL is configured in substantially the same way. The second processing block layer BU includes a plurality of (in the present preferred embodiment, twelve) processing units 11U to 13U, 21U to 23U, 31U to 33U, and 41U to 43U (note that the processing units of the second processing block layer BU are hereinafter referred to generically as the “processing units 11U to 43U” if necessary), a substrate placing portion 6U, a dummy-substrate housing portion 7U, and a main transfer robot 8U. The first to fourth liquid supply portions 91 to 94 and the first to fourth exhaust portions 101 to 104 are disposed so as to extend in the up-down direction Z over the first and second processing block layers BL and BU. The plurality of processing units 11U to 43U in the second processing block layer BU are disposed in substantially the same way as the plurality of processing units 11L to 43L in the first processing block layer BL. The second processing block layer BU includes first to fourth processing unit stacks S1U to S4U, and these first to fourth processing unit stacks S1U to S4U each include a plurality of processing units stacked together in the up-down direction Z (in the present preferred embodiment, three-stacked), i.e., the first to fourth processing unit stacks S1U, S2U, S3U, and S4U include processing units 11U to 13U, 21U to 23U, 31U to 33U, and 41U to 43U, respectively. The first to fourth processing unit stacks S1U to S4U of the second processing block layer BU are disposed so as to overlap the first to fourth processing unit stacks S1L to S4L of the first processing block layer BL, respectively, in a plan view. The first processing unit stacks S1L and S1U of the first and second processing block layers BL and BU are stacked together in the up-down direction Z, thus forming a first tower T1 in which a plurality of processing units are stacked together (in the present preferred embodiment, six-stacked), i.e., forming a first tower T1 in which the processing units 11L, 12L, 13L, 11U, 12U, and 13U are stacked together. Likewise, the second processing unit stacks S2L and S2U of the first and second processing block layers BL and BU are stacked together in the up-down direction Z, thus forming a second tower T2 in which a plurality of processing units are stacked together (in the present preferred embodiment, six-stacked), i.e., forming a second tower T2 in which the processing units 21L, 22L, 23L, 21U, 22U, and 23U are stacked together. Additionally, the third processing unit stacks S3L and S3U of the first and second processing block layers BL and BU are stacked together in the up-down direction Z, thus forming a third tower T3 in which a plurality of processing units are stacked together (in the present preferred embodiment, six-stacked), i.e., forming a third tower T3 in which the processing units 31L, 32L, 33L, 31U, 32U, and 33U are stacked together. Additionally, likewise, the fourth processing unit stacks S4L and S4U of the first and second processing block layers BL and BU are stacked together in the up-down direction Z, thus forming a fourth tower T4 in which a plurality of processing units are stacked together (in the present preferred embodiment, six-stacked), i.e., forming a fourth tower T4 in which the processing units 41L, 42L, 43L, 41U, 42U, and 43U are stacked together. A transfer space 52U that is defined in the second processing block layer BU and that provides a transfer path 51U overlaps the transfer space 52L of the first processing block layer BL. The transfer space 52U in the second processing block layer BU is partitioned from below by means of
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