Patent Publication Number: US-6711454-B2

Title: System and method for scheduling the movement of wafers in a wafer-processing tool

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of patent application Ser. No. 09/844,582, filed Apr. 26, 2001 now U.S. Pat. No. 6,535,784 issued Mar. 18, 2003. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a system and method for processing wafers in a wafer-processing tool, and more particularly to scheduling the movement of wafers in the wafer-processing tool. 
     2. Description of the Related Art 
     Wafer-processing tools may be utilized in various stages of fabricating semiconductor devices from semiconductor wafers. Conventional wafer-processing tools typically include one or more processing stations or modules in which semiconductor wafers undergo various processing operations. For example, a wafer-processing tool can include a Chemical Vapor Deposition (CVD) module to form a film on the surface of the wafers. 
     Wafer-processing tools also typically include a control system to automate the processing of multiple wafers. However, conventional control systems for wafer-processing tools typically process the wafers in accordance with a predetermined program that specifies the order of operations to be performed in which the execution of one operation initiates the execution of another operation. These conventional systems, however, often need to be manually adjusted or reprogrammed to process different batches of wafers. This can be both time and cost prohibitive. 
     SUMMARY OF THE INVENTION 
     The present invention generally relates to a system and method for processing wafers in a wafer-processing tool. In one exemplary embodiment of the present invention, the wafer-processing tool includes a load module, a wafer-transfer unit, a process module, and a scheduler. In accordance with one aspect of the present invention, the scheduler is configured to generate a schedule for the movement of wafers in the wafer-processing tool based on the duration of the operations to be performed by the wafer-transfer unit and the process module in processing the wafers. 
    
    
     DESCRIPTION OF THE DRAWING FIGURES 
     The present invention can be best understood by reference to the following description taken in conjunction with the accompanying drawing figures, in which like parts may be referred to by like numerals: 
     FIG. 1 is a top view of a wafer-processing tool; 
     FIG. 2 is a flow chart of a schedule-generation process; 
     FIGS. 3 through 17 are block diagrams of exemplary schedules; 
     FIG. 18 is a top view of an alternative embodiment of a wafer-processing tool; 
     FIGS. 19 through 24 are block diagrams of exemplary schedules; 
     FIG. 25 is a top view of another alternative embodiment of a wafer-processing tool; 
     FIG. 26 is a block diagram of another exemplary schedule; 
     FIG. 27 is a top view of still another alternative embodiment of the wafer-processing tool; and 
     FIG. 28 is a block diagram of still another exemplary schedule. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description sets forth numerous specific details, such as specific configurations, parameters, and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present invention. 
     With reference to FIG. 1, a wafer-processing tool  100  is depicted. In accordance with one exemplary embodiment of the present invention, tool  100  includes a load module  102 , a wafer-transfer unit  104 , a wafer orienter  106 , a load-lock module  108 , a process module  116 , and a control module  118 . 
     In the present embodiment, load module  102  can be configured to receive wafer cassettes that hold multiple wafers. It should be recognized that load module  102  can be configured to receive various types of wafer cassettes. Additionally, for the sake of clarity, tool  100  is depicted in FIG. 1 as having one load module  102 . It should be recognized, however, that tool  100  can include any number of load modules  102 . 
     In the present embodiment, wafer-transfer unit  104  can be configured to pick-up and place wafers. Additionally, as will be described in greater detail below, wafer-transfer unit  104  can be configured to transport wafers between load module  102 , wafer orienter  106 , load-lock module  108 , and process module  116 . In one configuration of the present embodiment, wafer-transfer unit  104  can be configured as a two-arm robot. It should be recognized, however, that wafer-transfer unit  104  can include any suitable mechanism or device suitable for transporting wafers. Additionally, it should be recognized that tool  100  can include any number of wafer-transfer units  104 . 
     In the present embodiment, wafer orienter  106  can be configured to orient wafers. More particularly, in some applications, it can be desirable to orient the wafers before processing the wafers in process module  116 . For example, in one application, asymmetric wafers, such as slotted wafers, can be oriented by wafer orienter  106  such that they enter process module  116  with the same orientation. However, in some applications, the wafers may not need to be oriented. As such, tool  100  can be configured without a wafer orienter  106  or wafer orienter  106  may not be used. However, it should be recognized that tool  100  can also be configured with more than one wafer orienter  106 . 
     In the present embodiment, load-lock module  108  can be configured to transport wafers to and from process module  116 . In one configuration of the present embodiment, load-lock module  108  includes a first buffer  110 , a second buffer  114 , and a wafer-transfer unit  112  configured to transfer a wafer into and out of process module  116 . More particularly, in the present configuration, wafer-transfer unit  104  places a wafer to be processed onto first buffer  110 . Wafer-transfer unit  112  then transfers the wafer to be processed from first buffer  110  onto second buffer  114 . When process module  116  is ready, wafer-transfer unit  112  transfers the wafer to be processed from second buffer  114  into process module  116 . After the wafer is processed, wafer-transfer unit  112  transfers the wafer from process module  116  onto first buffer  110 . Wafer-transfer unit  104  then picks-up the processed wafer from first buffer  110 . It should be recognized, however, that tool  100  can be configured without a load-lock module  108 . Instead, wafer-transfer unit  104  can be configured to transport wafers directly to and from process module  116 . 
     In the present embodiment, process module  116  can be maintained at a pressure lower than the pressure within the remaining areas of tool  100 . In one preferred embodiment, process module  116  is maintained at a pressure below atmospheric pressure, while the remaining areas of tool  100  are maintained at atmospheric pressure. One advantage of maintaining process module  116  at a lower pressure relative to the other areas of tool  100  is that the flow of contaminants from process module  116  into tool  100  can be reduced or eliminated. 
     As such, in the present embodiment, load-lock module  108  can be configured to operate as an air lock between process module  116  and the remaining areas of tool  100 . More particularly, load-lock module  108  can be configured to be sealed, evacuated, and vented. In one configuration of the present embodiment, before transferring a wafer into or out of process module  116 , load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . Additionally, before wafer-transfer unit  104  places a wafer to be processed on first buffer  110  or picks-up a processed wafer from first buffer  110 , load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within the remaining areas of tool  100 . 
     In the present embodiment, process module  116  can be configured to perform any suitable wafer-processing operation, such as etching, chemical vapor deposition (CVD), sputtering, thermal oxidation, and the like. Additionally, it should be recognized that tool  100  can be configured with any number of process modules  116 . More particularly, as will be described below in conjunction with alternative embodiments and configurations, tool  100  can include multiple process modules  116  performing the same wafer-processing operation or different wafer-processing operations. 
     In the present embodiment, control module  118  can be configured to control tool  100 . More particularly, control module  118  can be configured to control the operations of load module  102 , wafer-transfer unit  104 , wafer orienter  106 , load-lock module  108 , and process module  118 . Control module  118  can include any suitable computer hardware, such as a processing unit, a data storage unit/medium, a user-interface unit, a data-input/output unit, and the like. Control module  118  can also include any suitable computer program. 
     Additionally, in accordance with one aspect of the present invention, control module  118  can include a scheduler configured to generate a schedule for the movement of wafers in tool  100 . Although the scheduler is depicted and described as being a part of control module  118 , the scheduler can also be configured as a separate unit having any suitable computer hardware and/or software. 
     Having thus described the various components of tool  100 , the processing of a wafer within tool  100  will be described below. The following description assumes that tool  100  is operating in a steady-state condition; meaning that there is already one or more wafers being processed somewhere in tool  100  before the unprocessed wafer is removed from load module  102 . In other words, the following description does not describe the processing of the first or the last wafer to be processed. Additionally, to assist in distinguishing between different wafers in tool  100 , in the following description, a number is assigned to each wafer. It should be recognized, however, that these numbers do not necessarily suggest any particular order or priority. 
     As alluded to above, wafers can be transported to and from tool  100  in wafer cassettes, which can be mounted on load module  102 . As such, to process a wafer in tool  100 , wafer-transfer unit  104  first removes an unprocessed wafer (wafer  1 ) from load module  102 . As described above, in one configuration, wafer-transfer unit  104  is configured as a two-arm robot. As such, wafer-transfer unit  104  picks-up the unprocessed wafer (wafer  1 ) from load module  102  and places a wafer (wafer  2 ) that has been previously processed into load module  102 . 
     Wafer-transfer unit  104  then transports the unprocessed wafer (wafer  1 ) to wafer orienter  106 . Wafer-transfer unit  104  removes a wafer that was previously oriented (wafer  3 ) from wafer orienter  106  and places the unprocessed wafer (wafer  1 ) onto wafer orienter  106 . However, as described above, it should be recognized that in some applications the wafer (wafer  1 ) is not oriented. 
     Wafer-transfer unit  104  then transports the oriented wafer (wafer  3 ) to load-lock module  108 . Wafer-transfer unit  104  removes a wafer (wafer  4 ) that was previously processed from first buffer  110  and places the oriented wafer (wafer  3 ) onto first buffer  110 . Wafer-transfer unit  112  then transfers the oriented wafer (wafer  3 ) onto second buffer  114 . As described above, prior to removing the processed wafer (wafer  4 ) from first buffer  110  and placing the oriented wafer (wafer  3 ) onto first buffer  110 , load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . 
     Wafer-transfer unit  112  then transfers the oriented wafer (wafer  3 ) on second buffer  114  into process module  116 . After process module  116  has completed processing the wafer (wafer  3 ), wafer-transfer unit  112  removes the processed wafer (wafer  3 ) from process module  116  and transfers it to first buffer  110 . As described above, prior to removing a wafer from process module  116  or placing a wafer into process module  116 , load-lock module  1108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . 
     As described above, wafer-transfer unit  104  picks-up the processed wafer (wafer  3 ) from first buffer  10  and returns it to load module  102 . Wafer-transfer unit  104  then picks-up another unprocessed wafer (wafer  5 ) from load module  102 . This process can be repeated to process any number of wafers within any number of wafer cassettes. 
     As described above, in accordance with one aspect of the present invention, control system  118  includes a scheduler configured to generate a schedule for the movement of wafers in tool  100 . Additionally, control system  118  can include a recipe that specifies processing parameters, such as temperature, pressure, time, chemistries, concentrations, and the like. Furthermore, different batches, group, or sets of wafers can be processed in tool  100  utilizing different recipes. For example, a recipe can specify duration for the processing time in process module  116 . For one batch of wafers, the recipe can specify one duration, such as 50 seconds. For another batch of wafers, the recipe can specify a duration, such as 100 seconds. As such, in accordance with one aspect of the present invention, the scheduler can generate a schedule for a batch of wafers to be processed using a recipe for that batch of wafers before processing that batch of wafers. 
     With reference now to FIG. 2, an exemplary schedule-generation process  200  for the scheduler is depicted. It should be recognized that each operation and combination of operations of process  200  and those described below can be stored in a computer-readable storage medium and can be implemented as instructions for a computer. It should also be recognized that each operation and combination of operations can also be implemented by special purpose hardware-based computer systems that perform the specified functions or operations, or combination of special purpose hardware and computer instructions. Additionally, as described earlier, the scheduler can be a component of control module  118  or a separate unit. 
     With continued reference to FIG. 2, in the present embodiment, in operation  202 , a limitation duration is determined. With reference again to FIG. 1, as described above, the processing of wafers in tool  100  can involve a number of operations. In the embodiment described above, these operations can be grouped into a processing cycle that includes operations to be performed by process module  116 , an LLM cycle that includes operations to be performed by load-lock module  108 , and a provide cycle that includes operations to be performed by wafer-transfer unit  104 . As will be described in greater detail below, the duration of each cycle can then be determined. The limitation duration can then be determined based on the duration of these cycles. However, it should be recognized that a schedule can be generated based on the duration of these cycles without determining a limitation duration. 
     With reference now to FIG. 3, an exemplary process cycle  300  is depicted. In the present embodiment, process cycle  300  includes operations to be performed by process module  116  (FIG.  1 ). More particularly, in operation  302 , with reference to FIG. 1, wafer-transfer unit  112  picks-up an unprocessed wafer from second buffer  114 . In operation  304  (FIG.  3 ), wafer-transfer unit  112  places the unprocessed wafer into process module  116 . In operation  306  (FIG.  3 ), the unprocessed wafer is processed in process module  116 . In operation  308  (FIG.  3 ), wafer-transfer unit  112  picks-up the processed wafer from process module  116 . In operation  310  (FIG.  3 ), wafer-transfer unit  112  places the processed wafer onto first buffer  110 . 
     For the sake of example, assume that operations  302 ,  304 ,  308 , and  310  each take about 5 seconds and operation  306  takes about 60 seconds. As such, in this example, process cycle  300  takes about 80 seconds. However, it should be recognized that operations  302 ,  304 ,  308 , and  310  need not take the same amount of time and can vary depending on the configuration of tool  100 . It should also be recognized that the duration of operation  306  can vary depending on the particular application. Additionally, it should be recognized that the duration of operations  302  through  310  can be calculated explicitly or determined empirically. 
     With reference now to FIG. 4, an exemplary LLM cycle  400  is depicted. In the present embodiment, LLM cycle  400  includes operations to be performed by load-lock module  108  (FIG.  1 ). More particularly, in operation  402 , with reference now to FIG. 1, load-lock module  108  is vented such that the pressure within load-lock module  108  is approximately equal to that of tool  100 . In operation  404  (FIG.  4 ), wafer-transfer unit  104  picks-up a processed wafer from first buffer  110 . In operation  406  (FIG.  4 ), wafer-transfer unit  104  places an unprocessed wafer onto first buffer  110 . In operation  408  (FIG.  4 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to that in process module  116 . In operation  410  (FIG.  4 ), wafer-transfer unit  112  picks-up the unprocessed wafer from first buffer  110 . In operation  412  (FIG.  4 ), wafer-transfer unit  112  places the unprocessed wafer onto second buffer  114 . As depicted in FIG. 4, in the present embodiment, operations  410  and  412  can be performed concurrently with operation  408 . 
     For the sake of example, assume that operations  402  and  408  each take about 20 seconds. Assume that operations  404 ,  406 ,  410 , and  412  each take about 5 seconds. As such, in this example, LLM cycle  400  takes about 50 seconds. However, it should be recognized that operations  402  and  408  need not take the same amount of time. Additionally, it should be recognized that operations  404 ,  406 ,  410 , and  412  need not take the same amount of time. Furthermore, the duration of operations  402  through  412  can vary depending on the particular application. Additionally, it should be recognized that the duration of operations  402  through  412  can be calculated explicitly or determined empirically. 
     With reference now to FIG. 5, an exemplary provide cycle  500  is depicted. In the present embodiment, provide cycle  500  includes operations to be performed by wafer-transfer unit  104 . More particularly, in operation  502 , with reference now to FIG. 1, wafer-transfer unit  104  picks-up a wafer to be processed from load module  102 . In operation  504  (FIG.  5 ), wafer-transfer unit  104  picks-up a wafer that has been previously oriented from wafer orienter  106 . In operation  506  (FIG.  5 ), wafer-transfer unit  104  places the wafer to be oriented onto wafer orienter  106 . In operation  404  (FIG.  5 ), wafer-transfer unit  104  picks-up a processed wafer from first buffer  110 . In operation  406  (FIG.  5 ), wafer-transfer unit  104  places an unprocessed wafer onto first buffer  110 . In operation  508  (FIG.  5 ), wafer-transfer unit  104  places the processed wafer into load module  102 . In operation  510  (FIG.  5 ), wafer orienter  106  orients a wafer. Additionally, as depicted in FIG. 5, in the present embodiment, operation  510  can be performed following operation  506  and concurrently with operations  404 ,  406 , and/or  508 . Furthermore, for the sake of clarity and completeness, operations  404  and  406  are shown in both provide cycle  500  and LLM cycle  400  (FIG.  4 ). However, it should be recognized that operations  404  and  406  are performed once, as either part of provide cycle  500  or LLM cycle  400  (FIG.  4 ), but not both. 
     For the sake of example, assume that operations  404 ,  406 , and  502  through  510  each take about 5 seconds. As described above, operation  510  can be performed concurrently with operations  404 ,  406 , and/or  508 . As such, in the present example, provide cycle  500  takes about 30 seconds. However, it should be recognized that operations  404 ,  406 , and  502  through  510  need not take the same amount of time. Additionally, the duration of these operations can vary depending on the particular application. Furthermore, the duration of these operations can be calculated explicitly or determined empirically. 
     In summary, in the example provided above, process cycle  300  (FIG. 3) takes about 80 seconds, LLM cycle  400  (FIG. 4) takes about 50 seconds, and provide cycle  500  (FIG. 5) takes about 30 seconds. As such, in the present example, the process cycle is determined to be the limitation duration. 
     With reference again to FIG. 2, having determined the limitation duration, in operation  204 , a schedule is generated based on the limitation duration. In the present example, with reference now to FIG. 6, an exemplary schedule  600  is generated. However, it should be recognized that the particular operations, order of operations, and duration of operations depicted in FIG.  6  and described herein can vary depending on the particular configuration of tool  100  and the particular application. As such, schedule  600  can also vary depending on the particular configuration of tool  100  and the particular application. For example, as noted earlier, tool  100  can be configured without load-lock module  108 . As such, the limitation duration can be determined based on process cycle  300  (FIG. 3) and provide cycle  500  (FIG.  5 ). Thus, schedule  600  can then be generated without LLM cycle  400  (FIG.  4 ). 
     However, in the present example, tool  100  is assumed to include a load-module  108 . Moreover, as described above, the duration of process cycle  300  (FIG.  3 ), LLM cycle  400  (FIG.  4 ), and provide cycle  500  (FIG. 5) are assumed to be 80 seconds, 50 seconds, and 30 seconds, respectively. As such, process cycle  300  (FIG. 3) is determined to be the limitation duration. Thus, in the present example, schedule  600  is generated based on process cycle  300  (FIG.  3 ), then LLM cycle  400  (FIG.  4 ), then provide cycle  500  (FIG.  5 ). As noted above, it should be recognized that the operation of determining a limitation duration can be omitted. Instead, schedule  600  can be generated based directly on the duration of process cycle  300  (FIG.  3 ), LLM cycle  400  (FIG.  4 ), and provide cycle  500  (FIG.  5 ). 
     In accordance with one aspect of the present invention, schedule  600  can be generated by aligning process cycle  300  (FIG.  3 ), LLM cycle  400  (FIG.  4 ), and provide cycle  500  (FIG.  5 ). As will be described below in connection with the description of various exemplary schedules, two cycles can be aligned utilizing operations that may be common between the two cycles or an operation in one cycle that precedes or follows an operation in another cycle. 
     Additionally, in accordance with another aspect of the present invention, the duration of the cycles can determine the order in which the cycles are aligned. Thus, the cycle that is determined to be limitation duration is the cycle to which the remaining cycles are aligned. 
     In the present example, as depicted in FIG. 6, LLM cycle  400  (FIG. 4) is aligned to process cycle  300  (FIG.  3 ), then provide cycle  500  (FIG. 5) is aligned to LLM cycle  400  (FIG.  4 ). More particularly, LLM cycle  400  (FIG. 4) is aligned to process cycle  300  (FIG. 3) such that operation  402 , which corresponds to load-lock module  108  (FIG. 1) being vented, follows operation  304 , which corresponds to wafer-transfer unit  112  (FIG. 1) placing a wafer into process module  116  (FIG.  1 ). Additionally, in the present example, provide cycle  500  (FIG. 5) is aligned to LLM cycle  400  (FIG. 4) such that operation  404 , which corresponds to wafer-transfer unit  104  picking-up a processed wafer from first buffer  110  (FIG.  1 ), follows the completion of operation  402 , which again corresponds to load-lock module  108  (FIG. 1) being vented. 
     However, as alluded to earlier, schedule  600  assumes that tool  100  is operating in a steady state, meaning that the wafer being processed in accordance with schedule  600  is not the first or the last wafer to be processed. Thus, in accordance with one aspect of the present invention, with reference to FIG. 7, schedule  600  can include a start schedule  700 . 
     More particularly, in one embodiment, start schedule  700  includes operations  702  through  722 . In operation  702 , with reference to FIG. 1, wafer-transfer unit  104  picks-up the first wafer from load module  102 . In operation  704  (FIG.  7 ), wafer-transfer unit  104  places the first wafer onto wafer orienter  106 . In operation  706  (FIG.  7 ), wafer-transfer unit  104  picks-up the second wafer from load module  102 . In operation  708 , wafer orienter  106  orients the first wafer. In operation  710  (FIG.  7 ), wafer-transfer unit  104  picks-up the first wafer from wafer orienter  106 . In operation  712  (FIG.  7 ), wafer-transfer unit  104  places the second wafer onto wafer orienter  106 . In operation  714  (FIG.  7 ), wafer-transfer unit  104  places the first wafer onto first buffer  110 . In operation  716  (FIG.  7 ), wafer-transfer unit  112  picks-up the first wafer from first buffer  110 . In operation  718  (FIG.  7 ), wafer-transfer unit  112  places the first wafer onto second buffer  114 . In operation  720  (FIG.  7 ), load-lock-module  108  is vented. In operation  722  (FIG.  7 ), load-lock module  108  is sealed and evacuated. Moreover, as depicted in FIG. 7, operation  720  is completed before commencing operation  714 , when the wafer is placed onto first buffer  110  (FIG.  1 ). Additionally, operation  722  begins after operation  714 , when the wafer is placed onto first buffer  110  (FIG.  1 ). 
     In accordance with another aspect of the present invention, with reference to FIG. 8, schedule  600  can also include an end schedule  800 . As will be described in greater detail below, end schedule  800  is generated such that the last wafer processed in tool  100  (FIG. 1) has the same thermal history as the previous wafers that were processed in tool  100  (FIG.  1 ). 
     As depicted in FIG. 8, in operations  802  to  826 , the next-to-last wafer is processed in process module  116  (FIG. 1) while the last wafer is picked-up from wafer orienter  106  (FIG. 1) and the second-to-last wafer is transported back to load module  102  (FIG.  1 ). More particularly, with reference to FIG. 1, in operation  802  (FIG.  8 ), wafer-transfer unit  112  picks-up the next-to-last wafer from second buffer  114 . In operation  804  (FIG.  8 ), wafer-transfer unit  112  places the next-to-last wafer into process module  116 . In operation  806  (FIG.  8 ), the next-to-last wafer is processed in process module  116 . In operation  808  (FIG.  8 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  810  (FIG.  8 ), wafer-transfer unit  104  picks-up the last wafer from wafer orienter  106 . In operation  812  (FIG.  8 ), wafer-transfer unit  104  picks-up the second-to-last wafer from first buffer  110 . Note that the second-to-last wafer was placed on first buffer  110  in operation  310  (FIG.  8 ). In operation  814  (FIG.  8 ), wafer-transfer unit  104  places the last wafer onto first buffer  110 . In operation  816  (FIG.  8 ), load-lock module  108  is evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  818  (FIG.  8 ), wafer-transfer unit  104  places the second-to-last wafer into load module  102 . In operation  820  (FIG.  8 ), wafer-transfer unit  112  picks-up the last wafer from first buffer  110 . In operation  822  (FIG.  8 ), wafer-transfer unit  112  places the last wafer onto second buffer  114 . In operation  824  (FIG.  8 ), wafer-transfer unit  112  picks-up the next-to-last wafer from process module  116 . In operation  826  (FIG.  8 ), wafer-transfer unit  112  places the next-to-last wafer onto first buffer  110 . 
     As depicted in FIG. 8, in operations  828  to  844 , the last wafer is processed in process module  116  (FIG. 1) while the next-to-last wafer is transported back to load module  102  (FIG.  1 ). More particularly, with reference to FIG. 1, in operation  828  (FIG.  8 ), wafer-transfer unit  112  picks-up the last wafer from second buffer  114 . In operation  830  (FIG.  8 ), wafer-transfer unit  112  places the last wafer into process module  116 . In operation  832  (FIG.  8 ), the last wafer is processed in process module  116 . In operation  834  (FIG.  8 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  836  (FIG.  8 ), wafer-transfer unit  104  picks-up the next-to-last wafer from first buffer  110 . Note that the next-last wafer was placed on first buffer  110  in operation  826  (FIG.  8 ). In operation  838  (FIG.  8 ), load-lock module  108  is evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  840  (FIG.  8 ), wafer-transfer unit  104  places the next-to-last wafer into load module  102 . In operation  842  (FIG.  8 ), wafer-transfer unit  112  picks-up the last wafer from process module  116 . In operation  844  (FIG.  8 ), wafer-transfer unit  112  places the last wafer onto first buffer  110 . 
     As depicted in FIG. 8, in operations  846  to  850 , the last wafer is transported back to load module  102  (FIG.  1 ). More particularly, with reference to FIG. 1, in operation  846  (FIG.  8 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  848  (FIG.  8 ), wafer-transfer unit  104  picks-up the last wafer from first buffer  110 . Note that the last wafer was placed on first buffer  110  in operation  844  (FIG.  8 ). In operation  850  (FIG.  8 ), wafer-transfer unit  104  places the last wafer into load module  102 . 
     Thus, in end schedule  600 , operations  818 ,  840 , and  850  (corresponding to wafer-transfer unit  104  (FIG. 1) returning the second-to-last wafer, the next-to-last wafer, and the last wafer to load module  102  (FIG.  1 ), respectively) occur at the same amount of time following processing of the wafers in process module  116  (FIG.  1 ). As such, as noted earlier, the heat histories for these wafers can be kept uniform. 
     In the above description, it was assumed that process cycle  300  (FIG. 3) was assumed to be the limitation duration. The following description provides examples of generating schedule  600  in applications where LLM cycle  400  (FIG. 4) or provide cycle  500  (FIG. 5) is determined to be the limitation duration. However, in most applications of the present invention, process cycle  300  (FIG. 3) is likely to be the limitation duration as operation  310  (FIG.  3 ), which corresponds to processing of the wafer within process module  116  (FIG.  1 ), likely has the longest duration. 
     With reference to FIG. 9, for the sake of example, assume that process cycle  300  now takes about 45 seconds to complete. More particularly, in process cycle  300 , operation  306  takes about 25 seconds. Also, assume that LLM cycle  400  (FIG. 4) and provide cycle  500  (FIG. 5) take about 50 seconds and about 30 seconds, respectively. Accordingly, in the present example, LLM cycle  400  (FIG. 4) is now the limitation duration. 
     With reference now to FIG. 10, a schedule  1000  can be generated utilizing LLM cycle  400  (FIG. 9) as the limitation duration. More particularly, as depicted in FIG. 10, process cycle  300  (as depicted in FIG. 9) is aligned to LLM cycle  400  (FIG.  4 ), then provide cycle  500  (FIG. 5) is aligned to LLM cycle  400  (FIG.  4 ). 
     In the present example, process cycle  300  (FIG. 9) is aligned to LLM cycle  400  (FIG. 4) such that operation  304 , which corresponds to wafer-transfer unit  112  (FIG. 1) placing a wafer into process module  116  (FIG. 1) precedes operation  402 , which corresponds to load-lock module  108  (FIG. 1) being vented. Additionally, in the present example, a wait operation  1002  is provided following operation  306  such that operation  308 , which corresponds to removing the processed wafer from process module  116  (FIG.  1 ), follows the completion of operation  408 , which corresponds to load-lock module  108  (FIG. 1) being sealed and evacuated. As such, in the present example, wait operation  1002  takes 25 seconds. However, it should be recognized that wait operation  1002  can be any appropriate duration to extend operation  306 . 
     In the present example, provide cycle  500  (FIG. 5) is then aligned to process cycle  300  (FIG. 9) such that operation  404 , which corresponds to wafer-transfer unit  104  picking-up a processed wafer from first buffer  110  (FIG. 1) follows the completion of operation  402 , which again corresponds to load-lock module  108  (FIG. 1) being vented. 
     However, schedule  1000  assumes that tool  100  (FIG. 1) is operating in a steady state, meaning that the wafer being processed in accordance with schedule  1000  is not the first or the last wafer to be processed. Thus, in accordance with one aspect of the present invention, with reference to FIG. 11, schedule  1000  can include a start schedule  1100 . 
     More particularly, in one embodiment, start schedule  1100  includes operations  1102  through  1122 . In operation  1102 , with reference to FIG. 1, wafer-transfer unit  104  picks-up the first wafer from load module  102 . In operation  1104  (FIG.  11 ), wafer-transfer unit  104  places the first wafer onto wafer orienter  106 . In operation  1106  (FIG.  11 ), wafer-transfer unit  104  picks-up the second wafer from load module  102 . In operation  1108  (FIG.  11 ), wafer orienter  106  orients the first wafer. In operation  1110  (FIG.  11 ), wafer-transfer unit  104  picks-up the first wafer from wafer orienter  106 . In operation  1112  (FIG.  11 ), wafer-transfer unit  104  places the second wafer onto wafer orienter  106 . In operation  1114  (FIG.  11 ), wafer-transfer unit  104  places the first wafer onto first buffer  110 . In operation  1116  (FIG.  11 ), wafer-transfer unit  112  picks-up the first Wafer from first buffer  110 . In operation  1118  (FIG.  11 ), wafer-transfer unit  112  places the first wafer onto second buffer  114 . In operation  1120  (FIG.  11 ), load-lock module  108  is vented. In operation  1122  (FIG.  11 ), load-lock module  108  is sealed and evacuated. Moreover, as depicted in FIG. 11, operation  1120  is completed before commencing operation  1114 , when the wafer is placed onto first buffer  110  (FIG.  1 ). Additionally, operation  1122  begins after operation  1114 , when the wafer is placed onto first buffer  110  (FIG.  1 ). 
     In accordance with another aspect of the present invention, with reference to FIG. 12, schedule  1000  can also include an end schedule  1200 . As will be described in greater detail below, end schedule  1200  is generated such that the last wafer processed in tool  100  (FIG. 1) has the same thermal history as the previous wafers that were processed in tool  100  (FIG.  1 ). 
     As depicted in FIG. 12, in operations  1202  to  1226 , the next-to-last wafer is processed in process module  116  (FIG. 1) while the last wafer is picked-up from wafer orienter  106  (FIG. 1) and the second-to-last wafer is transported back to load module  102  (FIG.  1 ). More particularly, with reference to FIG. 1, in operation  1202  (FIG.  12 ), wafer-transfer unit  112  picks-up the next-to-last wafer from second buffer  114 . In operation  1204  (FIG.  12 ), wafer-transfer unit  112  places the next-to-last wafer into process module  116 . In operation  1206  (FIG.  12 ), the next-to-last wafer is processed in process module  116 . In operation  1002  (FIG.  12 ), the next-to-last wafer waits in process module  116 . In operation  1208  (FIG.  12 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  1210  (FIG.  12 ), wafer-transfer unit  104  picks-up the last wafer from wafer orienter  106 . In operation  1212  (FIG.  12 ), wafer-transfer unit  104  picks-up the second-to-last wafer from first buffer  110 . Note that the second-to-last wafer was placed on first buffer  110  in operation  310  (FIG.  12 ). In operation  1214  (FIG.  12 ), wafer-transfer unit  104  places the last wafer onto first buffer  110 . In operation  1216  (FIG.  12 ), load-lock module  108  is evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  1218  (FIG.  12 ), wafer-transfer unit  104  places the second-to-last wafer into load module  102 . In operation  1220  (FIG.  12 ), wafer-transfer unit  112  picks-up the last wafer from first buffer  110 . In operation  1222  (FIG.  12 ), wafer-transfer unit  112  places the last wafer onto second buffer  114 . In operation  1224  (FIG.  12 ), wafer-transfer unit  112  picks-up the next-to-last wafer from process module  116 . In operation  1226  (FIG.  12 ), wafer-transfer unit  112  places the next-to-last wafer onto first buffer  110 . 
     As depicted in FIG. 12, in operations  1228  to  1244 , the last wafer is processed in process module  116  (FIG. 1) while the next-to-last wafer is transported back to load module  102  (FIG.  1 ). More particularly, with reference to FIG. 1, in operation  1228  (FIG.  12 ), wafer-transfer unit  112  picks-up the last wafer from second buffer  114 . In operation  1230  (FIG.  12 ), wafer-transfer unit  112  places the last wafer into process module  116 . In operation  1232  (FIG.  12 ), the last wafer is processed in process module  116 . In operation  1002  (FIG.  12 ), the last wafer waits in process module  116 . In operation  1234  (FIG.  12 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  1236  (FIG.  12 ), wafer-transfer unit  104  picks-up the next-to-last wafer from first buffer  110 . Note that the next-last wafer was placed on first buffer  110  in operation  1226  (FIG.  12 ). In operation  1238  (FIG.  12 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  1240  (FIG.  12 ), wafer-transfer unit  104  places the next-to-last wafer into load module  102 . In operation  1242  (FIG.  12 ), wafer-transfer unit  112  picks-up the last wafer from process module  116 . In operation  1244  (FIG.  12 ), wafer-transfer unit  112  places the last wafer onto first buffer  110 . 
     As depicted in FIG. 12, in operations  1246  to  1250 , the last wafer is transported back to load module  102  (FIG.  1 ). More particularly, with reference to FIG. 1, in operation  1246  (FIG.  12 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  1248  (FIG.  12 ), wafer-transfer unit  104  picks-up the last wafer from first buffer  110 . Note that the last wafer was placed on first buffer  110  in operation  1244  (FIG.  12 ). In operation  1250  (FIG.  12 ), wafer-transfer unit  104  places the last wafer into load module  102 . 
     Thus, in end schedule  1200 , operations  1218 ,  1240 , and  1250  (corresponding to wafer-transfer unit  104  (FIG. 1) returning the second-to-last wafer, the next-to-last wafer, and the last wafer to load module  102  (FIG.  1 ), respectively) occur at the same amount of time following processing of the wafers in process module  116  (FIG.  1 ). As such, as noted earlier, the uniformity of the heat histories for these wafers can be maintained. 
     In the example provided above, process cycle  300  (FIG. 9) had a shorter duration than LLM cycle  400  (FIG.  4 ). It should be recognized, however, that operation  306  can be followed by an appropriate wait operation  1002  in applications where process cycle  300  (FIG. 9) is equal to or longer than LLM cycle  400  (FIG.  4 ). For example, assume that operation  306  takes about 30 seconds. As such, process cycle  300  (FIG. 9) now takes about 50 seconds. Although the duration of process cycle  300  (FIG. 9) is now equal to the duration of LLM cycle  400  (FIG.  4 ), operation  306  is preferably followed by wait operation  1002  such that operation  308  is performed after the completion of operation  408 . In this example, waiting operation  1002  would be for about 20 seconds. 
     With reference now to FIG. 13, for the sake of example, assume that provide cycle  500  now takes about 90 seconds to complete. More particularly, in provide cycle  500 , operations  502  and  508  each take about 35 seconds to complete. Also, assume that process cycle  300  (FIG. 3) and LLM cycle  400  (FIG. 4) take about 70 seconds and about 50 seconds, respectively. Accordingly, in the present example, provide cycle  500  is now determined to be the limitation duration. 
     With reference now to FIG. 14, a schedule  1400  can be generated utilizing provide cycle  500  (as depicted in FIG. 13) as the limitation duration. More particularly, as depicted in FIG. 14, process cycle  300  (FIG. 3) is aligned to provide cycle  500  (FIG.  13 ), then LLM cycle  400  (FIG. 4) is aligned to provide cycle  500  (FIG. 13) and process cycle  300  (FIG.  3 ). 
     In the present example, process cycle  300  (FIG. 3) is aligned to provide cycle  500  (FIG. 13) such that operation  502 , which corresponds to wafer-transfer unit  104  (FIG. 1) picking-up a wafer from load module  102  (FIG.  1 ), begins at the same time as operation  302 , which corresponds to wafer-transfer unit  112  (FIG. 1) picking-up a wafer from second-buffer  114  (FIG.  1 ). In the present example, LLM cycle  400  (FIG. 4) is also aligned to process cycle  300  (FIG. 3) such that operation  402 , which corresponds to load-lock module  108  (FIG. 1) being vented, follows operation  304 , which corresponds to wafer-transfer unit  112  (FIG. 1) placing a wafer into process module  116  (FIG.  1 ). 
     Additionally, in the present example, LLM cycle  400  (FIG. 4) is aligned to provide cycle  500  (FIG. 13) such that operation  404 , which corresponds to wafer-transfer unit  104  (FIG. 1) placing a wafer onto first buffer  110  (FIG.  1 ), of LLM cycle  400  (FIG. 4) aligns with operation  404  of provide cycle  500  (FIG.  13 ). As such, in the present example, a wait operation  1402  is provided following operation  402 , which corresponds to load-lock module  108  (FIG. 1) being vented. In the present example, wait operation  1402  takes about 15 seconds. However, it should be recognized that wait operation  1402  can be any appropriate duration. 
     Furthermore, in the present example, a wait operation  1404  is provided following operation  306  such that operation  308 , which corresponds to wafer-transfer unit  112  (FIG. 1) picking-up the processed wafer from process module  116  (FIG.  1 ), follows the completion of operation  408 , which corresponds to load-lock module  108  (FIG. 1) being evacuated. In the present example, wait operation  1404  takes about 5 seconds. However, it should be recognized that wait operation  1404  can be any appropriate duration. 
     However, schedule  1400  assumes that tool  100  (FIG. 1) is operating in steady state; meaning that the wafer being processed in accordance with schedule  1400  is not the first or the last wafer to be processed. Thus, in accordance with one aspect of the present invention, with reference to FIG. 15, schedule  1400  can include a start schedule  1500 . 
     More particularly, in one embodiment, start schedule  1500  includes operations  1502  through  1522 . In operation  1502 , with reference to FIG. 1, wafer-transfer unit  104  picks-up the first wafer from load module  102 . In operation  1504  (FIG.  15 ), wafer-transfer unit  104  places the first wafer onto wafer orienter  106 . In operation  1506  (FIG.  15 ), wafer-transfer unit  104  picks-up the second wafer from load module  102 . In operation  1508  (FIG.  15 ), wafer orienter  106  orients the first wafer. In operation  1510  (FIG.  15 ), wafer-transfer unit  104  picks-up the first wafer from wafer orienter  106 . In operation  1512  (FIG.  15 ), wafer-transfer unit  104  places the second wafer onto wafer orienter  106 . In operation  1514  (FIG.  15 ), wafer-transfer unit  104  places the first wafer onto first buffer  110 . In operation  1516  (FIG.  15 ), wafer-transfer unit  112  picks-up the first wafer from first buffer  110 . In operation  1518  (FIG.  15 ), wafer-transfer unit  112  places the first wafer onto second buffer  114 . In operation  1520  (FIG.  15 ), load-lock module  108  is vented. In operation  1522  (FIG.  15 ), load-lock module  108  is sealed and evacuated. Moreover, as depicted in FIG. 15, operation  1520  is completed before commencing operation  1514 , when the wafer is placed onto first buffer  110  (FIG.  1 ). Additionally, operation  1522  begins after operation  1514 , when the wafer is placed onto first buffer  110  (FIG.  1 ). 
     In accordance with another aspect of the present invention, with reference to FIG. 16, schedule  1400  can also include an end schedule  1600 . As will be described in greater detail below, end schedule  1600  is generated such that the last wafer processed in tool  100  (FIG. 1) has the same thermal history as the previous wafers that were processed in tool  100  (FIG.  1 ). 
     As depicted in FIG. 16, in operations  1602  to  1626 , the next-to-last wafer is processed in process module  116  (FIG. 1) while the last wafer is picked-up from wafer orienter  106  (FIG. 1) and the second-to-last wafer is transported back to load module  102  (FIG.  1 ). More particularly, with reference to FIG. 1, in operation  1602  (FIG.  16 ), wafer-transfer unit  112  picks-up the next-to-last wafer from second buffer  114 . In operation  1604  (FIG.  16 ), wafer-transfer unit  112  places the next-to-last wafer into process module  116 . In operation  1606  (FIG.  16 ), the next-to-last wafer is processed in process module  116 . In operation  1404  (FIG.  16 ), the next-to-last wafer waits in process module  116 . In operation  1608  (FIG.  16 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  1610  (FIG.  16 ), wafer-transfer unit  104  picks-up the last wafer from wafer orienter  106 . In operation  1612  (FIG.  16 ), wafer-transfer unit  104  picks-up the second-to-last wafer from first buffer  110 . Note that the second-to-last wafer was placed on first buffer  110  in operation  310  (FIG.  16 ). Also note that wait operation  1402  (FIG. 16) extends operation  1608  (FIG. 16) until wafer-transfer unit  104  is in position to pick-up the second-to-last wafer from first buffer  110 . In operation  1614  (FIG.  16 ), wafer-transfer unit  104  places the last wafer onto first buffer  110 . In operation  1616  (FIG.  16 ), load-lock module  108  is evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116  and less than the pressure within tool  100 . In operation  1618  (FIG.  16 ), wafer-transfer unit  104  places the second-to-last wafer into load module  102 . In operation  1620  (FIG.  16 ), wafer-transfer unit  112  picks-up the last wafer from first buffer  110 . In operation  1622  (FIG.  16 ), wafer-transfer unit  112  places the last wafer onto second buffer  114 . In operation  1624  (FIG.  16 ), wafer-transfer unit  112  picks-up the next-to-last wafer from process module  116 . In operation  1626  (FIG.  16 ), wafer-transfer unit  112  places the next-to-last wafer onto first buffer  110 . 
     As depicted in FIG. 16, in operations  1628  to  1644 , the last wafer is processed in process module  116  (FIG. 1) while the next-to-last wafer is transported back to load module  102  (FIG.  1 ). More particularly, with reference to FIG. 1, in operation  1628  (FIG.  16 ), wafer-transfer unit  112  picks-up the last wafer from second buffer  114 . In operation  1630  (FIG.  16 ), wafer-transfer unit  112  places the last wafer into process module  116 . In operation  1632  (FIG.  16 ), the last wafer is processed in process module  116 . In operation  1404  (FIG.  16 ), the next-to-last wafer waits in process module  116 . In operation  1634  (FIG.  16 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  1636  (FIG.  16 ), wafer-transfer unit  104  picks-up the next-to-last wafer from first buffer  110 . Note that the next-last wafer was placed on first buffer  110  in operation  1626  (FIG.  16 ). Also note that wait operation  1402  (FIG. 16) extends operation  1634  (FIG. 16) until wafer-transfer unit  104  is in position to pick-up the next-to-last wafer from first buffer  110 . In operation  1638  (FIG.  16 ), load-lock module  108  is evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  1640  (FIG.  16 ), wafer-transfer unit  104  places the next-to-last wafer into load module  102 . In operation  1642  (FIG.  16 ), wafer-transfer unit  112  picks-up the last wafer from process module  116 . In operation  1644  (FIG.  16 ), wafer-transfer unit  112  places the last wafer onto first buffer  110 . 
     As depicted in FIG. 16, in operations  1646  to  1650 , the last wafer is transported back to load module  102  (FIG.  1 ). More particularly, with reference to FIG. 1, in operation  1646  (FIG.  16 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  1648  (FIG.  16 ), wafer-transfer unit  104  picks-up the last wafer from first buffer  110 . Note that the last wafer was placed on first buffer  110  in operation  1644  (FIG.  16 ). In operation  1650  (FIG.  16 ), wafer-transfer unit  104  places the last wafer into load module  102 . 
     Thus, in end schedule  1600 , operations  1618 ,  1640 , and  1650  (corresponding to wafer-transfer unit  104  (FIG. 1) returning the second-to-last wafer, the next-to-last wafer, and the last wafer to load module  102  (FIG.  1 ), respectively) occur at the same amount of time following processing of the wafers in process module  116  (FIG.  1 ). As such, as noted earlier, the uniformity of the heat histories for these wafers can be maintained. 
     In the example provided above, provide cycle  500  (FIG. 13) had a longer duration than process cycle  300  (FIG.  3 ). It should be recognized, however, that operation  402  can be followed by an appropriate wait operation  1402  in applications where provide cycle  500  (FIG. 13) is equal to or shorter than process cycle  300  (FIG.  3 ). For example, with reference to FIG. 17, assume that operation  502  and  508  now each take about 25 seconds. As such, process cycle  300  (FIG. 3) is longer in duration than provide cycle  500  (FIG.  13 ). However, operation  402  is preferably followed by wait operation  1402  such that wafer-transfer unit  104  (FIG. 1) is in position to perform operation  404 . In this example, wait operation  1402  would be for about 5 seconds. 
     With reference again to FIG. 2, having thus developed a schedule based on the limitation duration, in operation  206 , the schedule is then executed. As described above, with reference again to FIG. 1, in one exemplary embodiment, tool  100  can include a control module  118  having appropriate computer hardware and software configured to execute the schedule. 
     In accordance with one aspect of the present invention, the execution of a schedule can be event-driven, timer-driven, or a combination of event and timer driven. As will be described below, one of these modes of executing a schedule can be preferred depending on the particular schedule to be executed. 
     In event-driven execution, the operations of a schedule are executed in response to the execution of another operation. For example, with reference to FIG. 6, in schedule  600 , the execution of operation  402  can be triggered by the completion of operation  304 . More particularly, with reference to FIG. 1, when wafer-transfer unit  112  has placed a wafer in process module  116  (operation  304  in FIG.  6 ), load-lock module  108  then begins to be vented (operation  402  in FIG.  6 ). In one exemplary embodiment, sensors can be provided in load-lock module  108  and/or process module  116  to signal control module  118  when wafer-transfer unit  112  has completed placing the wafer in process module  116 . Control module  118  can then send an appropriate control signal to load-lock module  108  to begin ventilating. 
     One advantage of event-driven execution is that it can utilize less computer resources, such as processing time, memory space, and the like. Additionally, when the capability of wafer-transfer unit  104  is the time limitation, then event-driven execution can be faster than timer-driven execution. For example, schedule  1400  depicted in FIG. 14 can be executed utilizing event-driven execution rather than timer-drive execution. 
     In timer-driven execution, the operations of a schedule are executed at predetermined time settings or intervals. For example, with reference again to FIG. 6, in schedule  600 , operations  304  and  402  can be executed at specific time settings, such as 5 seconds and 10 seconds, respectively. Alternatively, operation  404  can be executed 5 seconds after operation  304 . As such, control module  118  can include a timing mechanism. 
     One advantage of timer-driven execution is that it can provide greater uniformity in the thermal histories of the wafers. As such, when the capability of wafer-transfer unit  104  is not the time limitation, then timer-driven execution is preferred over strictly event-driven execution. For example, schedule  600  depicted in FIG. 6 can be executed utilizing timer-driven execution rather than event-driven execution. 
     As noted above, another alternative is a combination of event-driven and timer-driven execution in which some operations are event-driven executed and others are timer-driven executed. For example, with reference again to FIG. 6, in schedule  600 , the execution of operations  402 , and  502  can be timer-driven, while the execution of the remaining operations of schedule  600  are event-driven. 
     More particularly, operation  302  can be triggered by the completion of operation  310  from a previous execution of schedule  600 . Thus, with reference to FIG. 1, wafer-transfer unit  112  picks-up an unprocessed wafer from second buffer  114  after having placed a previously processed wafer onto first buffer  110 . 
     With reference again to FIG. 6, operation  402  is executed at a specified time setting or interval. As depicted in FIG. 6, assume that operation  402  executes  10  seconds from the time that schedule  600  first begins to execute. Operation  404  then executes when operation  402  is completed. Thus, with reference to FIG. 1, load-lock module  108  begins to ventilate 10 seconds into the execution of schedule  600 . However, wafer-transfer unit  104  picks-up the processed wafer from first buffer  110  only after load-lock module  108  has completed ventilating. 
     One advantage of combining event-driven and timer-driven execution is that greater uniformity in heat history can be maintained while utilizing less computer resources. As such, schedule  600  depicted in FIG. 6 is preferably executed utilizing a combination of event-driven and timer-driven execution. 
     With reference to FIG. 1, thus far the generation of schedules for the processing of wafers has been described in conjunction with tool  100  having one load-lock module  108  and process module  116 . However, as alluded to earlier, tool  100  can be configured with any number of load-lock modules  108  and process modules  116 . As will be illustrated below in connection with alternative exemplary embodiments, the schedule-generation process depicted in FIG.  2  and described above for tool  100  having one load-lock module  108  and process module  116  can be utilized to generate schedules for tool  100  having multiple load-lock modules  108  and process modules  116 . 
     With reference to FIG. 18, in one alternative embodiment, tool  100  is shown having an additional load-lock module  1808  and process module  1816 . It should be recognized that process modules  116  and  1816  can perform the same or different wafer-processing operations. Additionally, process modules  116  and  1816  can operate in parallel or in series. As will be described in greater detail below, when process modules  116  and  1816  operate in parallel, a wafer is processed in either process module  116  or process module  1816 . In contrast, when process modules  116  and  1816  operate in series, a wafer is processed in both process module  116  and process module  1816 . 
     For the sake of convenience and clarity, assume that process cycle  300  (FIG. 3) depicts the process cycle for process module  116  and process module  1816 . Similarly, assume that LLM cycle  400  (FIG. 4) and provide cycle  500  depict the LLM cycle and provide cycle for process module  116  and process module  1816 . However, it should be recognized that process modules  116  and  1816  can have different process cycles, LLM cycles, and/or provide cycles. Additionally, as described above, the duration of these cycles can be calculated explicitly or determined empirically. 
     As described above, with reference to FIG. 2, schedule-generation process  200  can be utilized to generate a schedule for the movement of wafers in tool  100  having process modules  116  (FIG. 18) and  1816  (FIG.  18 ). For the sake of example, now assume that process modules  116  (FIG. 18) and  1816  (FIG. 18) operate in parallel. Thus, a wafer is processed in either process module  116  (FIG. 18) or  1816  (FIG. 18) but not in both. 
     As depicted in FIG. 2, in operation  202 , a limitation duration is determined. As noted above, in the present example, process modules  116  and  1816  are assumed to have process, LLM, and provide cycles as depicted in FIGS. 3,  4 , and  5 , respectively. As such, as described in conjunction with an earlier embodiment of the present invention, process cycle  300  (FIG. 3) is determined to be the limitation duration. 
     In operation  202 , a schedule is generated based on the limitation duration. With reference now to FIG. 19, an exemplary schedule  1900  is depicted for scheduling the processing of wafers in tool  100  (FIG. 18) having process modules  116  (FIG. 18) and  1816  (FIG.  18 ). However, it should be recognized that the particular operations, order of operations, and duration of operations depicted in FIG.  19  and described herein can vary depending on the particular configuration of tool  100  (FIG. 18) and the particular application. As such, schedule  1900  can also vary depending on the particular configuration of tool  100  (FIG. 18) can the particular application. 
     The various operations of schedule  1900  will be described in greater detail below. It should be recognized that a number of wafers are located in tool  100  at any given time. As such, for the sake of clarity, the following description includes numbers in parenthesis to aid in identifying the wafers being processed in tool  100 . As such, these numbers are provided to assist in distinguishing one wafer from another and not necessarily to suggest any particular order or priority. 
     In the present example, with reference to FIG.  18  and with regard to process module  116 , in operation  1902  (FIG.  19 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  1 ) from second buffer  114 . In operation  1904  (FIG.  19 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  1 ) into process module  116 . In operation  1906  (FIG.  19 ), the wafer (wafer  1 ) is processed in process module  116 . In operation  1908  (FIG.  19 ), wafer-transfer unit  112  picks-up the processed wafer (wafer  1 ) from process module  116 . In operation  1910  (FIG.  19 ), wafer-transfer unit  112  places the processed wafer (wafer  1 ) onto first buffer  110 . 
     In operation  1912  (FIG.  19 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  1920  (FIG.  19 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  2 ) from load module  102 . In operation  1922  (FIG.  19 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  3 ) from wafer orienter  106 . In operation  1924  (FIG.  19 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto wafer orienter  106 . In operation  1944  (FIG.  19 ), the wafer (wafer  2 ) is oriented. In operation  1926  (FIG.  19 ), wafer-transfer unit  104  picks-up from first buffer  110  a wafer (wafer  4 ) that was processed in process module  116  in an earlier process cycle. In operation  1928  (FIG.  19 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  3 ) onto first buffer  110 . In operation  1914  (FIG.  19 ), load-lock-module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure with process module  116 . In operation  1916  (FIG.  19 ), wafer-transfer unit  112  picks-up the unprocessed wafer (wafer  3 ) from first buffer  110 . In operation  1918  (FIG.  19 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  3 ) onto second buffer  114 . In operation  1930  (FIG.  19 ), wafer-transfer unit  104  places the processed wafer (wafer  4 ) into load module  102 . 
     With regard now to process module  1816 , in operation  1956  (FIG.  19 ), wafer-transfer unit  1812  picks-up an unprocessed wafer (wafer  5 ) from second buffer  1814 . In operation  1958  (FIG.  19 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  5 ) in process module  1816 . In operation  1960  (FIG.  19 ), the wafer (wafer  5 ) is processed in process module  1816 . In operation  1962  (FIG.  19 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  5 ) from process module  1816 . In operation  1964  (FIG.  19 ), wafer-transfer unit  1812  places the processed wafer (wafer  5 ) onto first buffer  1810 . 
     In operation  1952  (FIG.  19 ), load-lock modules  1808  is vented such that the pressure within load-lock module  1808  is equal to the pressure within tool  100 . In operation  1932  (FIG.  19 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  6 ) from load module  102 . In operation  1934  (FIG.  19 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  2 ) from wafer orienter  106 . In operation  1936  (FIG.  19 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  6 ) onto wafer orienter  106 . In operation  1946  (FIG.  19 ), the wafer (wafer  6 ) is oriented. In operation  1938  (FIG.  19 ), wafer-transfer unit  104  picks-up from first buffer  1810  a wafer (wafer  7 ) that was processed in process module  1816  in an earlier process cycle. In operation  1940  (FIG.  19 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto first buffer  1810 . In operation  1954  (FIG.  19 ), load-lock module  1808  is sealed and evacuated such that the pressure within load-lock module  1808  is equal to the pressure within process module  1816 . In operation  1948  (FIG.  19 ), wafer-transfer unit  1812  picks-up the unprocessed wafer (wafer  2 ) from first buffer  1810 . In operation  1950  (FIG.  19 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  2 ) onto second buffer  1814 . In operation  1942  (FIG.  19 ), wafer-transfer unit  104  places the processed wafer (wafer  7 ) into load module  102 . 
     With reference again to FIG. 19, operations  1980  through  1992  are associated with the beginning of another process cycle for process module  116 . More particularly, with reference again to FIG. 18, in operation  1980  (FIG.  19 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  2 ) from second buffer  114 . In operation  1982  (FIG.  19 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  2 ) into process module  116 . In operation  1984  (FIG.  19 ), the wafer (wafer  2 ) is processed in process module  116 . In operation  1988  (FIG.  19 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  8 ) from load module  102 . In operation  1990  (FIG.  19 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  6 ) from wafer orienter  106 . In operation  1992  (FIG.  19 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  8 ) onto wafer orienter  106 . 
     With reference again to FIG. 19, operations  1970  through  1976  are associated with the completion of a previous process cycle for process module  1816 . More particularly, with reference again to FIG. 18, in operation  1970  (FIG.  19 ), a wafer (wafer  7 ) is processed in process module  1816 . In operation  1972  (FIG.  19 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  7 ) from process module  1816 . In operation  1974  (FIG.  19 ), wafer-transfer unit  1812  places the processed wafer (wafer  7 ) onto first buffer  1810 . In operation  1976 , load-lock module  1808  is in the process of being sealed and evacuated. 
     Schedule  1900  assumes that tool  100  is operating in a steady state; meaning that the wafer being processed in accordance with schedule  1900  is not the first or the last wafer to be processed. Thus, in accordance with one aspect of the present invention, with reference to FIG. 20, schedule  1900  can include a start schedule  2000 . 
     More particularly, in one embodiment, start schedule  2000  includes operations  2002  through  20104 . In operation  2002 , with reference to FIG.  18  and with regard to process module  116 , wafer-transfer unit  104  picks-up the first wafer from load module  102 . In operation  2004  (FIG.  20 ), wafer-transfer unit  104  places the first wafer onto wafer orienter  106 . In operation  2006  (FIG.  20 ), wafer-transfer unit  104  picks-up the second wafer from load module  102 . In operation  20   32  (FIG.  20 ), wafer orienter  106  orients the first wafer. In operation  2008  (FIG.  20 ), wafer-transfer unit  104  picks-up the first wafer from wafer orienter  106 . In operation  2010  (FIG.  20 ), wafer-transfer unit  104  places the second wafer onto wafer orienter  106 . In operation  2022  (FIG.  20 ), load-lock module  108  is vented. In operation  2012  (FIG.  20 ), wafer-transfer unit  104  places the first wafer onto first buffer  110 . In operation  2024  (FIG.  20 ), load-lock module  108  is sealed and evacuated. In operation  2026  (FIG.  20 ), wafer-transfer unit  112  picks-up the first wafer from first buffer  110 . In operation  2028  (FIG.  20 ), wafer-transfer unit  112  places the first wafer onto second buffer  114 . In operation  2036  (FIG.  20 ), wafer-transfer unit  112  picks-up the first wafer from second buffer  114 . In operation  2038  (FIG.  20 ), wafer-transfer unit  112  places the first wafer in process module  116 . In operation  2040  (FIG.  20 ), the first wafer is processed in process module  116 . In operation  2042  (FIG.  20 ), wafer-transfer unit  112  picks-up the first wafer from process module  116 . In operation  2044  (FIG.  20 ), wafer-transfer unit  112  places the first wafer onto first buffer  110 . 
     With regard to process module  1816 , in operation  2014  (FIG.  20 ), wafer-transfer unit  104  picks-up the third wafer from load module  102 . In operation  2016  (FIG.  20 ), wafer-transfer unit  104  picks-up the second wafer from wafer orienter  106 . In operation  2018  (FIG.  20 ), wafer-transfer unit  104  places the third wafer onto wafer orienter  106 . In operation  2030  (FIG.  20 ), wafer orienter  106  orients the third wafer. In operation  2034  (FIG.  20 ), load-lock module  1808  is vented. In operation  2020  (FIG.  20 ), wafer-transfer unit  104  places the second wafer onto first buffer  1810 . In operation  2094  (FIG.  20 ), load-lock module  1808  is sealed and evacuated. In operation  2072  (FIG.  20 ), wafer-transfer unit  1812  picks-up the second wafer from first buffer  1810 . In operation  2074  (FIG.  20 ), wafer-transfer unit  1812  places the second wafer onto second buffer  1814 . In operation  2096  (FIG.  20 ), wafer-transfer unit  1812  picks-up the first wafer from second buffer  1814 . In operation  2098  (FIG.  20 ), wafer-transfer unit  1812  places the first wafer in process module  1816 . In operation  20104  (FIG.  20 ), the second wafer is processed in process module  1816 . 
     With reference to FIG. 20, note that operation  20104  continues as operation  1970  in schedule  1900 . As such, with reference again to FIG. 18, in operation  1972  (FIG.  20 ), wafer-transfer unit  1812  picks-up the second wafer from process module  1816 . In operation  1974  (FIG.  20 ), wafer-transfer unit  1812  places the second wafer onto first buffer  1810 . 
     With regard again to process module  116 , in operation  2050  (FIG.  20 ), wafer-transfer unit  104  picks-up the fourth wafer from load module  102 . In operation  2052  (FIG.  20 ), wafer-transfer unit  104  picks-up the third wafer from wafer orienter  106 . In operation  2054  (FIG.  20 ), wafer-transfer unit  104  places the fourth wafer onto wafer orienter  106 . In operation  2076  (FIG.  20 ), wafer orienter  106  orients the fourth wafer. In operation  2046  (FIG.  20 ), load-lock module  108  is vented. In operation  2056  (FIG.  20 ), wafer-transfer unit  104  places the third wafer onto first buffer  110 . In operation  2048  (FIG.  20 ), the load-lock module  108  is sealed and evacuated. In operation  2078  (FIG.  20 ), wafer-transfer unit  112  picks-up the third wafer from first buffer  110 . In operation  2080  (FIG.  20 ), wafer-transfer unit  112  places the third wafer onto second buffer  114 . In operation  1902  (FIG.  20 ), wafer-transfer unit  112  picks-up the third wafer from second buffer  114 . In operation  1904  (FIG.  20 ), wafer-transfer unit  112  places the third wafer into process module  116 . In operation  1906  (FIG.  20 ), the third wafer is processed in process module  116 . 
     With regard again to process module  1816 , in operation  2058  (FIG.  20 ), wafer-transfer unit  104  picks-up the fifth wafer from load module  102 . In operation  2060  (FIG.  20 ), wafer-transfer unit  104  picks-up the fourth wafer from wafer orienter  106 . In operation  2062  (FIG.  20 ), wafer-transfer unit  104  places the fifth wafer onto wafer orienter  106 . In operation  2082  (FIG.  20 ), wafer orienter  106  orients the fifth wafer. In operation  20100  (FIG.  20 ), load-lock module  1808  is vented. In operation  2068  (FIG.  20 ), wafer-transfer unit  104  places the fourth wafer onto first buffer  1810 . In operation  20102  (FIG.  20 ), load-lock module  1808  is sealed and evacuated. 
     With reference to FIG. 20, note that operation  20102  continues as operation  1976  in schedule  1900 . With reference again to FIG. 18, in operation  2090  (FIG.  20 ), wafer-transfer unit  1812  picks-up the fourth wafer from first buffer  1810 . In operation  2092  (FIG.  20 ), wafer-transfer unit  1812  places the fourth wafer onto second buffer  1814 . In operation  1956  (FIG.  20 ), wafer-transfer unit  1812  picks-up the fourth wafer from second buffer  1814 . In operation  1958  (FIG.  20 ), wafer-transfer unit  1812  places the fourth wafer into process module  1816 . In operation  1960  (FIG.  20 ), the fourth wafer is processed in process module  1816 . 
     In accordance with another aspect of the present invention, with reference to FIG. 21, schedule  1900  can also include an end schedule  2100 . As will be described in greater detail below, end schedule  2100  is generated such that the last wafer processed in tool  100  (FIG. 18) has the same thermal history as the previous wafers that were processed in tool  100  (FIG.  18 ). 
     With regard to process module  116  (FIG.  18 ), as depicted in FIG. 21, the fourth-to-last wafer is processed in operation  1984 . With reference to FIG. 18, in operation  2102  (FIG.  21 ), wafer-transfer unit  112  picks-up the fourth-to-last wafer from process module  116 . In operation  2104  (FIG.  21 ), wafer-transfer unit  112  places the fourth-to-last wafer onto first buffer  110 . 
     In operation  1988  (FIG.  21 ), wafer-transfer unit  104  picks-up the last wafer from load module  102 . In operation  1990  (FIG.  21 ), wafer-transfer unit  104  picks-up the second-to-last wafer from wafer orienter  106 . In operation  1992  (FIG.  21 ), wafer-transfer unit  104  places the last wafer onto wafer orienter  106 . In operation  2122  (FIG.  21 ), wafer orienter  106  orients the last wafer. In operation  2106  ( 21 ), wafer-transfer unit  104  places the second-to-last wafer onto first buffer  110 . In operation  2108  (FIG.  21 ), wafer-transfer unit  104  picks-up the sixth-to-last wafer from first buffer  110 . In operation  2112  (FIG.  21 ), wafer-transfer unit places the sixth-to-last wafer in load module  102 . In operation  2110  (FIG.  21 ), load-lock module  108  is sealed and evacuated. In operation  2192  (FIG.  21 ), wafer-transfer unit  112  picks-up the second-to-last wafer from first buffer  110 . In operation  2194  (FIG.  21 ), wafer-transfer unit  112  places the second-to-last wafer onto second buffer  114 . 
     With regard to process module  1816 , in operation  2132  (FIG.  21 ), wafer-transfer unit  1812  picks-up the third-to-last wafer from second buffer  1814 . In operation  2134  (FIG.  21 ), wafer-transfer unit  1812  places the third-to-last wafer in process module  1816 . In operation  2136  (FIG.  21 ), the third-to-last wafer is processed in process module  1816 . In operation  2164  (FIG.  21 ), wafer-transfer unit  1812  picks-up the third-to-last wafer from process module  1816 . In operation  2166  (FIG.  21 ), wafer-transfer unit  1812  places the third-to-last wafer onto first buffer  1810 . 
     In operation  2114  (FIG.  21 ), wafer-transfer unit  104  picks-up the last wafer from wafer orienter  106 . In operation  2124  (FIG.  21 ), load-lock module  1808  is vented. In operation  2116  (FIG.  21 ), wafer-transfer unit  104  picks-up the fifth-to-last wafer from first buffer  1810 . Note that the fifth-to-last wafer was removed from process module  1816  in operation  1962  (FIG. 21) and placed on first buffer  1810  in operation  1964  (FIG.  21 ). In operation  2118  (FIG.  21 ), wafer-transfer unit  104  places the last wafer onto first buffer  1810 . In operation  2120  (FIG.  21 ), wafer-transfer unit  104  places the fifth-to-last wafer in load module  102 . In operation  2130  (FIG.  21 ), load-lock module  1808  is sealed and evacuated. In operation  2126  (FIG.  21 ), wafer-transfer unit  1812  picks-up the last wafer from first buffer  1810 . In operation  2128  (FIG.  21 ), wafer-transfer unit  1812  places the last wafer onto second buffer  1814 . 
     With regard to process module  116 , in operation  2138  (FIG.  21 ), wafer-transfer unit  112  picks-up the second-to-last wafer from second buffer  114 . In operation  2140  (FIG.  21 ), wafer-transfer unit  112  places the second-to-last wafer in process module  116 . In operation  2142  (FIG.  21 ), the second-to-last wafer is processed in process module  116 . In operation  2144  (FIG.  21 ), wafer-transfer unit  112  picks-up the second-to-last wafer from process module  116 . In operation  2146  (FIG.  21 ), wafer-transfer unit  112  places the second-to-last wafer onto first buffer  110 . 
     In operation  2148  (FIG.  21 ), load-lock module  108  is vented. In operation  2150  (FIG.  21 ), wafer-transfer unit  104  picks-up the fourth-to-last wafer from first buffer  110 . In operation  2154  (FIG.  21 ), wafer-transfer unit  104  places the fourth-to-last wafer in load module  102 . In operation  2152  (FIG.  21 ), load-lock module  108  is sealed and evacuated. 
     With regard to process module  1816 , in operation  2168  (FIG.  21 ), wafer-transfer unit  1812  picks-up the last wafer from second buffer  1814 . In operation  2170  (FIG.  21 ), wafer-transfer unit  1812  places the last wafer into process module  1816 . In operation  2172  (FIG.  21 ), the last wafer is processed in process module  1816 . In operation  2174  (FIG.  21 ), wafer-transfer unit  1812  picks-up the last wafer from process module  1816 . In operation  2176  (FIG.  21 ), wafer-transfer unit  1812  places the last wafer onto first buffer  1810 . 
     In operation  2160  (FIG.  21 ), load-lock module  1808  is vented. In operation  2156  (FIG.  21 ), wafer-transfer unit  104  picks-up the third-to-last wafer from first buffer  1810 . In operation  2158  (FIG.  21 ), wafer-transfer unit  104  places the third-to-last wafer in load module  102 . In operation  2162  (FIG.  21 ), load-lock module  1808  is sealed and evacuated. 
     With regard again to process module  116 , in operation  2186  (FIG.  21 ), load-lock module  108  is vented. In operation  2188  (FIG.  21 ), wafer-transfer unit  104  picks-up the second-to-last wafer from first buffer  110 . In operation  2190  (FIG.  21 ), wafer-transfer unit  104  places the second-to-last wafer in load module  102 . 
     With regard again to process module  1816 , in operation  2178  (FIG.  21 ), load-lock module  1808  is vented. In operation  2180  (FIG.  21 ), wafer-transfer unit  1804  picks-up the last wafer from first buffer  1810 . In operation  2182  (FIG.  21 ), wafer-transfer unit  104  places the last wafer in load module  102 . 
     Thus, in end schedule  2100 , operations  2112 ,  2120 ,  2154 ,  2158 ,  2190 , and  2182  (corresponding to wafer-transfer unit  104  (FIG. 18) returning the sixth-to-last wafer, the fifth-to-last wafer, the fourth-to-last wafer, the third-to-last wafer, the second-to-last wafer, and the last wafer, respectively, to load module  102  (FIG.  18 )) occur at the same amount of time following the processing of the wafers in process modules  116  (FIG. 18) and  1816  (FIG.  18 ). As such, as alluded to earlier, the uniformity of the heat histories of these wafers can be maintained. 
     With reference again to FIG. 2, having developed a schedule based on the limitation duration, in operation  206 , the schedule is then executed. As described in greater detail above, with reference again to FIG. 1, in one exemplary embodiment, tool  100  can include a control module  118  having suitable hardware and software configured to execute the schedule. Alternatively, the scheduler can be configured as a separate unit having suitable hardware and software configured to execute the schedule. 
     With reference to FIG. 18, in the above description, the duration of the wafer-processing operation in process modules  116  and  1816  were assumed to be the same. Additionally, as described above, the schedule for process modules  116  and  1816  were generated together. It should be recognized, however, that the duration of the wafer-processing operations in process modules  116  and  1816  can vary depending on the particular application. It should also be recognized that a schedule that utilizes either process module  116  or  1816  can already be running on tool  100  when a schedule that utilizes both process modules  116  and  1816  is to be generated and executed on tool  100 . 
     For the sake of example, assume that the duration of the process cycles in process modules  116  and  1816  are now about 80 seconds and about 110 seconds, respectively. However, it should be recognized that the duration of the process cycle for process module  116  can be longer than that in process module  1816 . 
     For the sake of example, assume also that schedule  600  (FIG. 6) has already been generated and running for process module  116  when a schedule that utilizes both process modules  116  and  1816  is to be generated and executed. However, it should be recognized that process module  1816  can be operating when process module  116  is to be utilized. 
     Now assume that the process cycle in process module  1816  is preferred over that in process module  116 . For example, in some applications, it may be more desirable to quickly process wafers in process module  1816  than to maintain uniformity of the heat histories of the wafers being processed in process module  116 . In such applications, as described below, a wait period is provided between the process cycles of the process module  116  having the shorter process cycle. 
     For example, with reference now to FIG. 22, in a schedule  2200 , the process cycle for process module  1816  (FIG. 18) is assumed to be preferred, and the duration of the process cycles for process modules  116  (FIG. 18) and  1816  (FIG. 18) are about 80 seconds and about 110 seconds, respectively. As such, in schedule  2200 , a wait period is provided between process cycles in process module  116  (FIG. 18) that is equal to the difference in duration of the process cycles in process module  1816  (FIG. 18) and process module  116  (FIG.  18 ), which in this example is about 30 seconds. 
     The various operations of schedule  2200  will now be described in greater detail below. It should be recognized that a number of wafers are located in tool  100  (FIG. 18) at any given time. As such, for the sake of clarity, the following description includes numbers in parenthesis to aid in identifying the wafers being processed in tool  100  (FIG.  18 ). As such, these numbers are provided to assist in distinguishing one wafer from another and not necessarily to suggest any particular order or priority. 
     In the present example, with reference to FIG.  18  and with regard to process module  116 , in operation  2202  (FIG.  22 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  1 ) from second buffer  114 . In operation  2204  (FIG.  22 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  1 ) into process module  116 . In operation  2206  (FIG.  22 ), the wafer (wafer  1 ) is processed in process module  116 . In operation  2208  (FIG.  22 ), wafer-transfer unit  112  picks-up the processed wafer (wafer  1 ) from process module  116 . In operation  2210  (FIG.  22 ), wafer-transfer unit  112  places the processed wafer (wafer  1 ) onto first buffer  110 . 
     In operation  2212  (FIG.  22 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  2220  (FIG.  22 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  2 ) from load module  102 . In operation  2222  (FIG.  22 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  3 ) from wafer orienter  106 . In operation  2224  (FIG.  22 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto wafer orienter  106 . In operation  2244  (FIG.  22 ), the wafer (wafer  2 ) is oriented. In operation  2226  (FIG.  22 ), wafer-transfer unit  104  picks-up from first buffer  110  a wafer (wafer  4 ) that was processed in process module  116  in an earlier process cycle. In operation  2228  (FIG.  22 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  3 ) onto first buffer  110 . In operation  2214  (FIG.  22 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  2216  (FIG.  22 ), wafer-transfer unit  112  picks-up the unprocessed wafer (wafer  3 ) from first buffer  110 . In operation  2218  (FIG.  22 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  3 ) onto second buffer  114 . In operation  2230  (FIG.  22 ), wafer-transfer unit  104  places the processed wafer (wafer  4 ) into load module  102 . 
     With regard now to process module  1816 , in operation  2256  (FIG.  22 ), wafer-transfer unit  1812  picks-up an unprocessed wafer (wafer  5 ) from second buffer  1814 . In operation  2258  (FIG.  22 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  5 ) in process module  1816 . In operation  2260  (FIG.  22 ), the wafer (wafer  5 ) is processed in process module  1816 . In operation  2262  (FIG.  22 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  5 ) from process module  1816 . In operation  2264  (FIG.  22 ), wafer-transfer unit  1812  places the processed wafer (wafer  5 ) onto first buffer  1810 . 
     In operation  2252  (FIG.  22 ), load-lock modules  1808  is vented such that the pressure within load-lock module  1808  is equal to the pressure within tool  100 . In operation  2232  (FIG.  22 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  6 ) from load module  102 . In operation  2234  (FIG.  22 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  2 ) from wafer orienter  106 . In operation  2236  (FIG.  22 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  6 ) onto wafer orienter  106 . In operation  2246  (FIG.  22 ), the wafer (wafer  6 ) is oriented. In operation  2238  (FIG.  22 ), wafer-transfer unit  104  picks-up from first buffer  1810  a wafer (wafer  7 ) that was processed in process module  1816  in an earlier process cycle. In operation  2240  (FIG.  22 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto first buffer  1810 . In operation  2254  (FIG.  22 ), load-lock module  1808  is sealed and evacuated such that the pressure within load-lock module  1808  is equal to the pressure within process module  1816 . In operation  2248  (FIG.  22 ), wafer-transfer unit  1812  picks-up the unprocessed wafer (wafer  2 ) from first buffer  1810 . In operation  2250  (FIG.  22 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  2 ) onto second buffer  1814 . In operation  2242  (FIG.  22 ), wafer-transfer unit  104  places the processed wafer (wafer  7 ) into load module  102 . 
     With reference again to FIG. 22, operations  2280  through  2292  are associated with the beginning of another process cycle for process module  116 . More particularly, with reference again to FIG. 18, in operation  2280  (FIG.  22 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  2 ) from second buffer  114 . In operation  2282  (FIG.  22 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  2 ) into process module  116 . In operation  2284  (FIG.  22 ), the wafer (wafer  2 ) is processed in process module  116 . In operation  2286  (FIG.  22 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  2288  (FIG.  22 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  8 ) from load module  102 . In operation  2290  (FIG.  22 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  6 ) from wafer orienter  106 . In operation  2292  (FIG.  22 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  8 ) onto wafer orienter  106 . 
     With reference again to FIG. 22, operations  2270  through  2274  are associated with the completion of a previous process cycle for process module  1816 . More particularly, with reference again to FIG. 18, in operation  2270  (FIG.  22 ), a wafer (wafer  7 ) is processed in process module  1816 . In operation  2272  (FIG.  22 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  7 ) from process module  1816 . In operation  2274  (FIG.  22 ), wafer-transfer unit  1812  places the processed wafer (wafer  7 ) onto first buffer  1810 . 
     As noted earlier and as depicted in FIG. 22, the process cycles for process module  116  include a wait period that is equal to the difference in the duration of the process cycle for process module  1816  and process cycle for process module  116 . As depicted in FIG. 22, in the present example, the duration of the wait period is about 30 seconds. 
     With reference again to FIG. 18, now assume that the process cycle for process module  116  is preferred over the process cycle for process module  1816 . For example, in some applications, it may be desirable to maintain the thermal histories of the wafers that were being processed in process module  116 . In such applications, as described below, if the duration of the preferred process cycle is shorter than the other process cycle, then the preferred process cycle is repeated and a wait period is provided between the preferred process cycle and the other process cycle. 
     For example, with reference now to FIG. 23, in a schedule  2300 , the processing cycle for process module  116  (FIG. 18) is assumed to be preferred, and the duration of the process cycles for process modules  116  (FIG. 18) and  1816  (FIG. 18) are about 80 seconds and about 110 seconds, respectively. As such, in schedule  2300  the process cycle in process module  116  (FIG. 18) is repeated and a wait period is provided between process cycles in process module  1816  (FIG. 18) equal to the difference between twice the duration of the process cycle in process module  116  (FIG. 18) and the process cycle in process module  1816  (FIG.  18 ), which in this example is about 30 seconds. 
     The various operations of schedule  2300  will now be described in greater detail below. It should be recognized that a number of wafers are located in tool  100  (FIG. 18) at any given time. As such, for the sake of clarity, the following description includes numbers in parenthesis to aid in identifying the wafers being processed in tool  100  (FIG.  18 ). As such, these numbers are provided to assist in distinguishing one wafer from another and not necessarily to suggest any particular order or priority. 
     In the present example, with reference to FIG.  18  and with regard to process module  116 , in operation  2302  (FIG.  23 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  1 ) from second buffer  114 . In operation  2304  (FIG.  23 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  1 ) into process module  116 . In operation  2306  (FIG.  23 ), the wafer (wafer  1 ) is processed in process module  116 . In operation  2308  (FIG.  23 ), wafer-transfer unit  112  picks-up the processed wafer (wafer  1 ) from process module  116 . In operation  2310  (FIG.  23 ), wafer-transfer unit  112  places the processed wafer (wafer  1 ) onto first buffer  110 . 
     In operation  2312  (FIG.  23 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  2320  (FIG.  23 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  2 ) from load module  102 . In operation  2322  (FIG.  23 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  3 ) from wafer orienter  106 . In operation  2324  (FIG.  23 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto wafer orienter  106 . In operation  2344  (FIG.  23 ), the wafer (wafer  2 ) is oriented. In operation  2326  (FIG.  23 ), wafer-transfer unit  104  picks-up from first buffer  110  a wafer (wafer  4 ) that was processed in process module  116  in an earlier process cycle. In operation  2328  (FIG.  23 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  3 ) onto first buffer  110 . In operation  2314  (FIG.  23 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  2316  (FIG.  23 ), wafer-transfer unit  112  picks-up the unprocessed wafer (wafer  3 ) from first buffer  110 . In operation  2318  (FIG.  23 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  3 ) onto second buffer  114 . In operation  2330  (FIG.  23 ), wafer-transfer unit  104  places the processed wafer (wafer  4 ) into load module  102 . 
     With regard now to process module  1816 , in operation  2356  (FIG.  23 ), wafer-transfer unit  1812  picks-up an unprocessed wafer (wafer  5 ) from second buffer  1814 . In operation  2358  (FIG.  23 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  5 ) in process module  1816 . In operation  2360  (FIG.  23 ), the wafer (wafer  5 ) is processed in process module  1816 . In operation  2362  (FIG.  23 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  5 ) from process module  1816 . In operation  2364  (FIG.  23 ), wafer-transfer unit  1812  places the processed wafer (wafer  5 ) onto first buffer  1810 . 
     In operation  2352  (FIG.  23 ), load-lock modules  1808  is vented such that the pressure within load-lock module  1808  is equal to the pressure within tool  100 . In operation  2332  (FIG.  23 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  6 ) from load module  102 . In operation  2334  (FIG.  23 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  2 ) from wafer orienter  106 . In operation  2336  (FIG.  23 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  6 ) onto wafer orienter  106 . In operation  2346  (FIG.  23 ), the wafer (wafer  6 ) is oriented. In operation  2338  (FIG.  23 ), wafer-transfer unit  104  picks-up from first buffer  1810  a wafer (wafer  7 ) that was processed in process module  1816  in an earlier process cycle. In operation  2340  (FIG.  23 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto first buffer  1810 . In operation  2354  (FIG.  23 ), load-lock module  1808  is sealed and evacuated such that the pressure within load-lock module  1808  is equal to the pressure within process module  1816 . In operation  2348  (FIG.  23 ), wafer-transfer unit  1812  picks-up the unprocessed wafer (wafer  2 ) from first buffer  1810 . In operation  2350  (FIG.  23 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  2 ) onto second buffer  1814 . In operation  2342  (FIG.  23 ), wafer-transfer unit  104  places the processed wafer (wafer  7 ) into load module  102 . 
     With reference again to FIG. 23, operations  2380  through  23110  are associated with another process cycle for process module  116  (FIG.  18 ). More particularly, with reference again to FIG. 18, in operation  2380  (FIG.  23 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  3 ) from second buffer  114 . In operation  2382  (FIG.  23 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  3 ) into process module  116 . In operation  2384  (FIG.  23 ), the wafer (wafer  3 ) is processed in process module  116 . In operation  23100 , wafer-transfer unit  112  picks-up the processed wafer (wafer  3 ) from process module  116 . In operation  23102 , wafer-transfer unit  112  places the processed wafer (wafer  3 ) onto first buffer  110 . 
     Additionally, in operation  2386 , load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  2388  (FIG.  23 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  8 ) from load module  102 . In operation  2390  (FIG.  23 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  6 ) from wafer orienter  106 . In operation  2392  (FIG.  23 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  8 ) onto wafer orienter  106 . In operation  23110  (FIG.  23 ), the wafer (wafer  8 ) is oriented. In operation  2394  (FIG.  23 ), wafer-transfer unit  104  picks-up from first buffer  110  a wafer (wafer  1 ) that was processed in process module  116  in an earlier process cycle. In operation  2396  (FIG.  23 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  6 ) onto first buffer  110 . In operation  23104  (FIG.  23 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  23106  (FIG.  23 ), wafer-transfer unit  112  picks-up the unprocessed wafer (wafer  6 ) from first buffer  110 . In operation  23108  (FIG.  23 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  6 ) onto second buffer  114 . In operation  2398  (FIG.  23 ), wafer-transfer unit  104  places the processed wafer (wafer  1 ) into load module  102 . 
     As noted earlier and as depicted in FIG. 23, the process cycles for process module  1816  (FIG. 18) include a wait period that is equal to the difference in twice the duration of the process cycle for process module  116  (FIG. 18) and the duration of the process cycle for process module  1816  (FIG.  18 ). As depicted in FIG. 23, in the present example, the duration of the wait period is about 50 seconds. 
     With reference again to FIG. 18, as noted earlier, process modules  116  and  1816  of tool  100  can be configured to operate in series. For example, a wafer can be processed first in process module  116  then processed in process module  1816 . It should be recognized that the wafer can also be processed first in process module  1816  then processed in process module  116 . 
     With reference now to FIG. 24, an exemplary schedule  2400  is depicted for scheduling the serial processing of wafers in process modules  116  (FIG. 18) and  1816  (FIG.  18 ). More particularly, in the present example, wafers are first processed in process module  116  (FIG. 18) then processed in process module  1816  (FIG.  18 ). It should be recognized that the particular operations, order of operations, and duration of operations depicted in FIG.  24  and described herein can vary depending on the particular configuration of tool  100  (FIG. 18) and the particular application. As such, schedule  2400  can also vary depending on the particular configuration of tool  100  (FIG. 18) and the particular application. 
     The various operations of schedule  2400  will be described in greater detail below. It should be recognized that a number of wafers are located in tool  100  (FIG. 18) at any given time. As such, for the sake of clarity, the following description includes numbers in parenthesis to aid in identifying the wafers being processed in tool  100  (FIG.  18 ). As such, these numbers are provided to assist in distinguishing one wafer from another and not necessarily to suggest any particular order or priority. 
     In the present example, with reference to FIG.  18  and with regard to process module  116 , in operation  2402  (FIG.  24 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  1 ) from second buffer  114 . In operation  2404  (FIG.  24 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  1 ) into process module  116 . In operation  2406  (FIG.  24 ), the wafer (wafer  1 ) is processed in process module  116 . In operation  2408  (FIG.  24 ), wafer-transfer unit  112  picks-up the processed wafer (wafer  1 ) from process module  116 . In operation  2410  (FIG.  24 ), wafer-transfer unit  112  places the processed wafer (wafer  1 ) onto first buffer  110 . 
     In operation  2412  (FIG.  24 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  2420  (FIG.  24 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  2 ) from load module  102 . In operation  2422  (FIG.  24 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  3 ) from wafer orienter  106 . In operation  2424  (FIG.  24 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto wafer orienter  106 . In operation  2444  (FIG.  24 ), the wafer (wafer  2 ) is oriented. In operation  2426  (FIG.  24 ), wafer-transfer unit  104  picks-up from first buffer  110  a wafer (wafer  4 ) that was processed in process module  116  in an earlier process cycle. In operation  2428  (FIG.  24 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  3 ) onto first buffer  110 . In operation  2414  (FIG.  24 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  2416  (FIG.  24 ), wafer-transfer unit  112  picks-up the unprocessed wafer (wafer  3 ) from first buffer  110 . In operation  2418  (FIG.  24 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  3 ) onto second buffer  114 . 
     With regard now to process module  1816 , in operation  2456  (FIG.  24 ), wafer-transfer unit  1812  picks-up a wafer that was previously processed in process module  116  but not yet processed in process module  1816  (wafer  5 ) from second buffer  1814 . In operation  2458  (FIG.  24 ), wafer-transfer unit  1812  places this wafer (wafer  5 ) in process module  1816 . In operation  2460  (FIG.  24 ), the wafer (wafer  5 ) is processed in process module  1816 . In operation  2462  (FIG.  24 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  5 ) from process module  1816 . In operation  2464  (FIG.  24 ), wafer-transfer unit  1812  places the processed wafer (wafer  5 ) onto first buffer  1810 . 
     In operation  2452  (FIG.  24 ), load-lock modules  1808  is vented such that the pressure within load-lock module  1808  is equal to the pressure within tool  100 . In operation  2438  (FIG.  24 ), wafer-transfer unit  104  picks-up from first buffer  1810  a wafer (wafer  6 ) that was processed in process module  1816  in an earlier process cycle. In operation  2440  (FIG.  24 ), wafer-transfer unit  104  places the wafer that was earlier processed in process module  116  (wafer  4 ) onto first buffer  1810 . In operation  2454  (FIG.  24 ), load-lock module  1808  is sealed and evacuated such that the pressure within load-lock module  1808  is equal to the pressure within process module  1816 . In operation  2448  (FIG.  24 ), wafer-transfer unit  1812  picks-up the unprocessed wafer (wafer  4 ) from first buffer  1810 . In operation  2450  (FIG.  24 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  4 ) onto second buffer  1814 . In operation  2442  (FIG.  24 ), wafer-transfer unit  104  places the processed wafer (wafer  6 ) into load module  102 . 
     With reference again to FIG. 24, operations  2480  through  24110  are associated with another process cycle for process module  116  (FIG.  18 ). More particularly, with reference again to FIG. 18, in operation  2480  (FIG.  24 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  3 ) from second buffer  114 . In operation  2482  (FIG.  24 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  3 ) into process module  116 . In operation  2484  (FIG.  24 ), the wafer (wafer  3 ) is processed in process module  116 . In operation  24100 , wafer-transfer unit  112  picks-up the processed wafer (wafer  3 ) from process module  116 . In operation  24102 , wafer-transfer unit  112  places the processed wafer (wafer  3 ) onto first buffer  110 . 
     Additionally, in operation  2486 , load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  2488  (FIG.  24 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  7 ) from load module  102 . In operation  2490  (FIG.  24 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  2 ) from wafer orienter  106 . In operation  2492  (FIG.  24 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  7 ) onto wafer orienter  106 . In operation  24110  (FIG.  24 ), the wafer (wafer  7 ) is oriented. In operation  2494  (FIG.  24 ), wafer-transfer unit  104  picks-up from first buffer  110  a wafer (wafer  1 ) that was processed in process module  116  in an earlier process cycle. In operation  2496  (FIG.  24 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto first buffer  110 . In operation  24104  (FIG.  24 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  24106  (FIG.  24 ), wafer-transfer unit  112  picks-up the unprocessed wafer (wafer  2 ) from first buffer  110 . In operation  24108  (FIG.  24 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  2 ) onto second buffer  114 . 
     With reference again to FIG. 24, operations  24116  through  24128  are associated with another process cycle for process module  1816  (FIG.  18 ). More particularly, with reference again to FIG. 18, in operation  24116  (FIG.  24 ), wafer-transfer unit  1812  picks-up a wafer that was previously processed in process module  116  but not yet processed in process module  1816  (wafer  4 ) from second buffer  1814 . In operation  24118  (FIG.  24 ), wafer-transfer unit  1812  places this wafer (wafer  4 ) in process module  1816 . In operation  24120  (FIG.  24 ), the wafer (wafer  4 ) is processed in process module  1816 . 
     In operation  24122  (FIG.  24 ), load-lock modules  1808  is vented such that the pressure within load-lock module  1808  is equal to the pressure within tool  100 . In operation  24112  (FIG.  24 ), wafer-transfer unit  104  picks-up from first buffer  1810  a wafer (wafer  5 ) that was processed in process module  1816  in an earlier process cycle. In operation  24114  (FIG.  24 ), wafer-transfer unit  104  places the wafer that was earlier processed in process module  116  (wafer  1 ) onto first buffer  1810 . In operation  24124  (FIG.  24 ), load-lock module  1808  is sealed and evacuated such that the pressure within load-lock module  1808  is equal to the pressure within process module  1816 . In operation  24126  (FIG.  24 ), wafer-transfer unit  1812  picks-up the unprocessed wafer (wafer  1 ) from first buffer  1810 . In operation  24128  (FIG.  24 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  1 ) onto second buffer  1814 . In operation  2498  (FIG.  24 ), wafer-transfer unit  104  places the processed wafer (wafer  5 ) into load module  102 . 
     With reference again to FIG. 24, operations  2472  and  2474  are associated with the completion of previous process cycle for process module  1816  (FIG.  18 ). More particularly, with reference again to FIG. 18, in operation  2472  (FIG.  24 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  6 ) from process module  1816 . In operation  2474  (FIG.  24 ), wafer-transfer unit  1812  places the processed wafer (wafer  6 ) onto first buffer  1810 . 
     In the following description and related drawings figures, alternative embodiments of the present invention will be described and shown in connection with tool  100  (FIGS. 25 and 27) having  3  and  4  process modules. However, it should be recognized that tool  100  (FIGS. 25 and 27) can include any number of process modules. 
     With reference now to FIG. 25, tool  100  is depicted having load-lock modules  108 ,  1808 , and  2508 , and process modules  116 ,  1816 , and  2516 . With reference now to FIG. 26, an exemplary schedule  2600  is depicted for scheduling the processing of wafers in tool  100  depicted in FIG.  25 . However, it should be recognized that the particular operations, order of operations, and duration of operations depicted in FIG.  26  and described herein can vary depending on the particular configuration of tool  100  (FIG. 25) and the particular application. As such, schedule  2600  can also vary depending on the particular configuration of tool  100  (FIG. 25) can the particular application. 
     The various operations of schedule  2600  will be described in greater detail below. It should be recognized that a number of wafers are located in tool  100  (FIG. 25) at any given time. As such, for the sake of clarity, the following description includes numbers in parenthesis to aid in identifying the wafers being processed in tool  100  (FIG.  25 ). As such, these numbers are provided to assist in distinguishing one wafer from another and not necessarily to suggest any particular order or priority. 
     In the present example, with reference to FIG.  25  and with regard to process module  116 , in operation  2650  (FIG.  26 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  1 ) from second buffer  114 . In operation  2651  (FIG.  26 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  1 ) into process module  116 . In operation  2652  (FIG.  26 ), the wafer (wafer  1 ) is processed in process module  116 . In operation  2653  (FIG.  26 ), wafer-transfer unit  112  picks-up the processed wafer (wafer  1 ) from process module  116 . In operation  2654  (FIG.  26 ), wafer-transfer unit  112  places the processed wafer (wafer  1 ) onto first buffer  110 . 
     In operation  2655  (FIG.  26 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  2608  (FIG.  26 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  2 ) from load module  102 . In operation  2609  (FIG.  26 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  3 ) from wafer orienter  106 . In operation  2610  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto wafer orienter  106 . In operation  2638  (FIG.  26 ), wafer orienter  106  orients the wafer (wafer  2 ). In operation  2611  (FIG.  26 ), wafer-transfer unit  104  picks-up from first buffer  110  a wafer (wafer  4 ) that was processed in process module  116  in an earlier process cycle. In operation  2612  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  3 ) onto first buffer  110 . In operation  2656  (FIG.  26 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  2657  (FIG.  26 ), wafer-transfer unit  112  picks-up the unprocessed wafer (wafer  3 ) from first buffer  110 . In operation  2658  (FIG.  26 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  3 ) onto second buffer  114 . In operation  2613  (FIG.  26 ), wafer-transfer unit  104  places the processed wafer (wafer  4 ) into load module  102 . 
     With regard now to process module  1816 , in operation  2660  (FIG.  26 ), wafer-transfer unit  1812  picks-up an unprocessed wafer (wafer  5 ) from second buffer  1814 . In operation  2661  (FIG.  26 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  5 ) in process module  1816 . In operation  2662  (FIG.  26 ), the wafer (wafer  5 ) is processed in process module  1816 . In operation  2663  (FIG.  26 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  5 ) from process module  1816 . In operation  2664  (FIG.  26 ), wafer-transfer unit  1812  places the processed wafer (wafer  5 ) onto first buffer  1810 . 
     In operation  2665  (FIG.  26 ), load-lock module  1808  is vented such that the pressure within load-lock module  1808  is equal to the pressure within tool  100 . In operation  2614  (FIG.  26 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  6 ) from load module  102 . In operation  2615  (FIG.  26 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  2 ) from wafer orienter  106 . In operation  2616  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  6 ) onto wafer orienter  106 . In operation  2639  (FIG.  26 ), wafer orienter  106  orients the wafer (wafer  6 ). In operation  2617  (FIG.  26 ), wafer-transfer unit  104  picks-up from first buffer  1810  a wafer (wafer  7 ) that was processed in process module  1816  in an earlier process cycle. In operation  2618  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto first buffer  1810 . In operation  2666  (FIG.  26 ), load-lock module  1808  is sealed and evacuated such that the pressure within load-lock module  1808  is equal to the pressure within process module  1816 . In operation  2667  (FIG.  26 ), wafer-transfer unit  1812  picks-up the unprocessed wafer (wafer  2 ) from first buffer  1810 . In operation  2668  (FIG.  26 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  2 ) onto second buffer  1814 . In operation  2619  (FIG.  26 ), wafer-transfer unit  104  places the processed wafer (wafer  7 ) into load module  102 . 
     With regard now to process module  2516 , in operation  2670  (FIG.  26 ), wafer-transfer unit  2512  picks-up an unprocessed wafer (wafer  8 ) from second buffer  2514 . In operation  2671  (FIG.  26 ), wafer-transfer unit  2512  places the unprocessed wafer (wafer  8 ) in process module  2516 . In operation  2672  (FIG.  26 ), the wafer (wafer  8 ) is processed in process module  2516 . In operation  2673  (FIG.  26 ), wafer-transfer unit  2512  picks-up the processed wafer (wafer  8 ) from process module  2516 . In operation  2674  (FIG.  26 ), wafer-transfer unit  2512  places the processed wafer (wafer  8 ) onto first buffer  2510 . 
     In operation  2675  (FIG.  26 ), load-lock module  2508  is vented such that the pressure within load-lock module  2508  is equal to the pressure within tool  100 . In operation  2620  (FIG.  26 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  9 ) from load module  102 . In operation  2621  (FIG.  26 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  6 ) from wafer orienter  106 . In operation  2622  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  9 ) onto wafer orienter  106 . In operation  2640  (FIG.  26 ), wafer orienter  106  orients the wafer (wafer  9 ). In operation  2623  (FIG.  26 ), wafer-transfer unit  104  picks-up from first buffer  2510  a wafer (wafer  10 ) that was processed in process module  2516  in an earlier process cycle. In operation  2624  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  6 ) onto first buffer  2510 . In operation  2676  (FIG.  26 ), load-lock module  2508  is sealed and evacuated such that the pressure within load-lock module  2508  is equal to the pressure within process module  2516 . In operation  2677  (FIG.  26 ), wafer-transfer unit  2512  picks-up the unprocessed wafer (wafer  6 ) from first buffer  2510 . In operation  2678  (FIG.  26 ), wafer-transfer unit  2512  places the unprocessed wafer (wafer  6 ) onto second buffer  2514 . In operation  2625  (FIG.  26 ), wafer-transfer unit  104  places the processed wafer (wafer  10 ) into load module  102 . 
     With reference again to FIG. 26, operations  2680  through  2688  are associated with another process cycle for process module  116 . More particularly, with reference again to FIG. 25, in operation  2680  (FIG.  26 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  3 ) from second buffer  114 . In operation  2681  (FIG.  26 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  3 ) into process module  116 . In operation  2682  (FIG.  26 ), the wafer (wafer  3 ) is processed in process module  116 . In operation  2683  (FIG.  26 ), wafer-transfer unit  112  picks-up the processed wafer (wafer  3 ) from process module  116 . In operation  2684  (FIG.  26 ), wafer-transfer unit  112  places the processed wafer (wafer  3 ) onto first buffer  110 . 
     In operation  2685  (FIG.  26 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  2626  (FIG.  26 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  11 ) from load module  102 . In operation  2627  (FIG.  26 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  9 ) from wafer orienter  106 . In operation  2628  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  11 ) onto wafer orienter  106 . In operation  2641  (FIG.  26 ), wafer orienter  106  orients the wafer (wafer  11 ). In operation  2629  (FIG.  26 ), wafer-transfer unit  104  picks-up from first buffer  110  a wafer (wafer  1 ) that was processed in process module  116  in an earlier process cycle. In operation  2630  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  9 ), onto first buffer  110 . In operation  2686  (FIG.  26 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  2687  (FIG.  26 ), wafer-transfer unit  112  picks-up the unprocessed wafer (wafer  9 ) from first buffer  110 . In operation  2688  (FIG.  26 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  9 ) onto second buffer  114 . In operation  2631  (FIG.  26 ), wafer-transfer unit  104  places the processed wafer (wafer  1 ) into load module  102 . 
     With reference again to FIG. 26, operations  2690  through  2695  are associated with the beginning of another process cycle for process module  1816 . More particularly, with reference again to FIG. 25, in operation  2690  (FIG.  26 ), wafer-transfer unit  1812  picks-up an unprocessed wafer (wafer  2 ) from second buffer  1814 . In operation  2691  (FIG.  26 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  2 ) in process module  1816 . In operation  2692  (FIG.  26 ), the wafer (wafer  2 ) is processed in process module  1816 . 
     In operation  2695  (FIG.  26 ), load-lock module  1808  is vented such that the pressure within load-lock module  1808  is equal to the pressure within tool  100 . In operation  2632  (FIG.  26 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  12 ) from load module  102 . In operation  2633  (FIG.  26 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  11 ) from wafer orienter  106 . In operation  2634  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  12 ) onto wafer orienter  106 . In operation  2642  (FIG.  26 ), wafer orienter  106  orients the wafer (wafer  12 ). In operation  2635  (FIG.  26 ), wafer-transfer unit  104  picks-up from first buffer  1810  a wafer (wafer  5 ) that was processed in process module  1816  in an earlier process cycle. In operation  2636  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  11 ) onto first buffer  1810 . 
     With reference again to FIG. 26, operations  26100  through  26105  are associated with the beginning of another process cycle for process module  2516 . More particularly, with reference again to FIG. 25, in operation  26100  (FIG.  26 ), wafer-transfer unit  2512  picks-up an unprocessed wafer (wafer  6 ) from second buffer  2514 . In operation  26101  (FIG.  26 ), wafer-transfer unit  2512  places the unprocessed wafer (wafer  6 ) in process module  2516 . In operation  26102  (FIG.  26 ), the wafer (wafer  6 ) is processed in process module  2516 . In operation  26105  (FIG.  26 ), load-lock module  2508  is vented such that the pressure within load-lock module  2508  is equal to the pressure within tool  100 . 
     With reference again to FIG. 26, operations  26112  through  26118  are associated with the ending of a previous process cycle for process module  1816 . More particularly, with reference again to FIG. 18, in operation  26112 , the wafer (wafer  7 ) is processed in process module  1816 . In operation  26113  (FIG.  26 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  7 ) from process module  1816 . In operation  26114  (FIG.  26 ), wafer-transfer unit  1812  places the processed wafer (wafer  7 ) onto first buffer  1810 . In operation  26116  (FIG.  26 ), load-lock-module  1808  is sealed and evacuated such that the pressure within load-lock module  1808  is equal to the pressure within process module  1816 . In operation  26117  (FIG.  26 ), wafer-transfer unit  1812  picks-up an unprocessed wafer (wafer  5 ) from first buffer  1810 . In operation  26118  (FIG.  26 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  5 ) onto second buffer  1814 . In operation  2601  (FIG.  26 ), wafer-transfer unit  104  places a wafer (wafer  13 ) that was previously processed in process module  1816  in an earlier process cycle into load module  102 . 
     With reference again to FIG. 26, operations  26122  through  26128  are associated with the ending of a previous process cycle for process module  2516 . More particularly, with reference again to FIG. 25, in operation  26122  (FIG.  26 ), the wafer (wafer  10 ) is processed in process module  2516 . In operation  26123  (FIG.  26 ), wafer-transfer unit  2512  picks-up the processed wafer (wafer  10 ) from process module  2516 . In operation  26124  (FIG.  26 ), wafer-transfer unit  2512  places the processed wafer (wafer  10 ) onto first buffer  2510 . 
     In operation  2602  (FIG.  26 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  3 ) from load module  102 . In operation  2603  (FIG.  26 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  8 ) from wafer orienter  106 . In operation  2604  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  3 ) onto wafer orienter  106 . In operation  2637  (FIG.  26 ), wafer orienter  106  orients the wafer (wafer  3 ). In operation  2605  (FIG.  26 ), wafer-transfer unit  104  picks-up from first buffer  2510  a wafer (wafer  14 ) that was processed in process module  2516  in an earlier process cycle. In operation  2606  (FIG.  26 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  8 ) onto first buffer  2510 . In operation  26126  (FIG.  26 ), load-lock module  2508  is sealed and evacuated such that the pressure within load-lock module  2508  is equal to the pressure within process module  2516 . In operation  26127  (FIG.  26 ), wafer-transfer unit  2512  picks-up the unprocessed wafer (wafer  8 ) from first buffer  2510 . In operation  26128  (FIG.  26 ), wafer-transfer unit  2512  places the processed wafer (wafer  8 ) onto second buffer  2512 . In operation  2607  (FIG.  26 ), wafer-transfer unit  104  places the processed wafer (wafer  14 ) into load module  102 . 
     With reference now to FIG. 27, tool  100  is depicted having load-lock modules  108 ,  1808 ,  2508 , and  2708 , and process modules  116 ,  1816 ,  2516 , and  2716 . With reference now to FIG. 28, an exemplary schedule  2800  is depicted for scheduling the processing of wafers in tool  100  depicted in FIG.  27 . However, it should be recognized that the particular operations, order of operations, and duration of operations depicted in FIG.  28  and described herein can vary depending on the particular configuration of tool  100  (FIG. 27) and the particular application. As such, schedule  2800  can also vary depending on the particular configuration of tool  100  (FIG. 27) can the particular application. 
     The various operations of schedule  2800  will be described in greater detail below. It should be recognized that a number of wafers are located in tool  100  (FIG. 27) at any given time. As such, for the sake of clarity, the following description includes numbers in parenthesis to aid in identifying the wafers being processed in tool  100  (FIG.  27 ). As such, these numbers are provided to assist in distinguishing one wafer from another and not necessarily to suggest any particular order or priority. 
     In the present example, with reference to FIG.  27  and with regard to process module  116 , in operation  2860  (FIG.  28 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  1 ) from second buffer  114 . In operation  2861  (FIG.  28 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  1 ) into process module  116 . In operation  2862  (FIG.  28 ), the wafer (wafer  1 ) is processed in process module  116 . In operation  2863  (FIG.  28 ), wafer-transfer unit  112  picks-up the processed wafer (wafer  1 ) from process module  116 . In operation  2864  (FIG.  28 ), wafer-transfer unit  112  places the processed wafer (wafer  1 ) onto first buffer  110 . 
     In operation  2865  (FIG.  28 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  2814  (FIG.  28 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  2 ) from load module  102 . In operation  2815  (FIG.  28 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  3 ) from wafer orienter  106 . In operation  2816  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto wafer orienter  106 . In operation  2851  (FIG.  28 ), wafer orienter  106  orients the wafer (wafer  2 ). In operation  2817  (FIG.  28 ), wafer-transfer unit  104  picks-up from first buffer  110  a wafer (wafer  4 ) that was processed in process module  116  in an earlier process cycle. In operation  2818  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  3 ) onto first buffer  110 . In operation  2866  (FIG.  28 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock module  108  is equal to the pressure within process module  116 . In operation  2867  (FIG.  28 ), wafer-transfer unit  112  picks-up the unprocessed wafer (wafer  3 ) from first buffer  110 . In operation  2868  (FIG.  28 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  3 ) onto second buffer  114 . In operation  2819  (FIG.  28 ), wafer-transfer unit  104  places the processed wafer (wafer  4 ) into load module  102 . 
     With regard now to process module  1816 , in operation  2870  (FIG.  28 ), wafer-transfer unit  1812  picks-up an unprocessed wafer (wafer  5 ) from second buffer  1814 . In operation  2871  (FIG.  28 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  5 ) in process module  1816 . In operation  2872  (FIG.  28 ), the wafer (wafer  5 ) is processed in process module  1816 . In operation  2873  (FIG.  28 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  5 ) from process module  1816 . In operation  2874  (FIG.  28 ), wafer-transfer unit  1812  places the processed wafer (wafer  5 ) onto first buffer  1810 . 
     In operation  2875  (FIG.  28 ), load-lock module  1808  is vented such that the pressure within load-lock module  1808  is equal to the pressure within tool  100 . In operation  2820  (FIG.  28 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  6 ) from load module  102 . In operation  2821  (FIG.  28 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  2 ) from wafer orienter  106 . In operation  2822  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  6 ) onto wafer orienter  106 . In operation  2852  (FIG.  28 ), wafer orienter  106  orients the wafer (wafer  6 ). In operation  2823  (FIG.  28 ), wafer-transfer unit  104  picks-up from first buffer  1810  a wafer (wafer  7 ) that was processed in process module  1816  in an earlier process cycle. In operation  2824  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  2 ) onto first buffer  1810 . In operation  2876  (FIG.  28 ), load-lock module  1808  is sealed and evacuated such that the pressure within load-lock module  1808  is equal to the pressure within process module  1816 . In operation  2877  (FIG.  28 ), wafer-transfer unit  1812  picks-up the unprocessed wafer (wafer  2 ) from first buffer  1810 . In operation  2878  (FIG.  28 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  2 ) onto second buffer  1814 . In operation  2825  (FIG.  28 ), wafer-transfer unit  104  places the processed wafer (wafer  7 ) into load module  102 . 
     With regard now to process module  2516 , in operation  2880  (FIG.  28 ), wafer-transfer unit  2512  picks-up an unprocessed wafer (wafer  8 ) from second buffer  2514 . In operation  2881  (FIG.  28 ), wafer-transfer unit  2512  places the unprocessed wafer (wafer  8 ) in process module  2516 . In operation  2882  (FIG.  28 ), the wafer (wafer  8 ) is processed in process module  2516 . In operation  2883  (FIG.  28 ), wafer-transfer unit  2512  picks-up the processed wafer (wafer  8 ) from process module  2516 . In operation  2884  (FIG.  28 ), wafer-transfer unit  2512  places the processed wafer (wafer  8 ) onto first buffer  2510 . 
     In operation  2885  (FIG.  28 ), load-lock module  2508  is vented such that the pressure within load-lock module  2508  is equal to the pressure within tool  100 . In operation  2826  (FIG.  28 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  9 ) from load module  102 . In operation  2827  (FIG.  28 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  6 ) from wafer orienter  106 . In operation  2828  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  9 ) onto wafer orienter  106 . In operation  2853  (FIG.  28 ), wafer orienter  106  orients the wafer (wafer  9 ). In operation  2829  (FIG.  28 ), wafer-transfer unit  104  picks-up from first buffer  2510  a wafer (wafer  10 ) that was processed in process module  2516  in an earlier process cycle. In operation  2830  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  6 ) onto first buffer  2510 . In operation  2886  (FIG.  28 ), load-lock module  2508  is sealed and evacuated such that the pressure within load-lock module  2508  is equal to the pressure within process module  2516 . In operation  2887  (FIG.  28 ), wafer-transfer unit  2512  picks-up the unprocessed wafer (wafer  6 ) from first buffer  2510 . In operation  2888  (FIG.  28 ), wafer-transfer unit  2512  places the unprocessed wafer (wafer  6 ) onto second buffer  2514 . In operation  2831  (FIG.  28 ), wafer-transfer unit  104  places the processed wafer (wafer  10 ) into load module  102 . 
     With regard now to process module  2716 , in operation  2890  (FIG.  28 ), wafer-transfer unit  2712  picks-up an unprocessed wafer (wafer  11 ) from second buffer  2714 . In operation  2891  (FIG.  28 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  11 ) in process module  2716 . In operation  2892  (FIG.  28 ), the wafer (wafer  11 ) is processed in process module  2716 . In operation  2893  (FIG.  28 ), wafer-transfer unit  2712  picks-up the processed wafer (wafer  11 ) from process module  2716 . In operation  2894  (FIG.  28 ), wafer-transfer unit  2712  places the processed wafer (wafer  11 ) onto first buffer  2710 . 
     In operation  2895  (FIG.  28 ), load-lock module  2708  is vented such that the pressure within load-lock module  2708  is equal to the pressure within tool  100 . In operation  2832  (FIG.  28 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  12 ) from load module  102 . In operation  2833  (FIG.  28 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  9 ) from wafer orienter  106 . In operation  2834  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  12 ) onto wafer orienter  106 . In operation  2854  (FIG.  28 ), wafer orienter  106  orients the wafer (wafer  12 ). In operation  2835  (FIG.  28 ), wafer-transfer unit  104  picks-up from first buffer  2710  a wafer (wafer  13 ) that was processed in process module  2716  in an earlier process cycle. In operation  2836  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  9 ) onto first buffer  2710 . In operation  2896  (FIG.  28 ), load-lock module  2708  is sealed and evacuated such that the pressure within load-lock module  2708  is equal to the pressure within process module  2716 . In operation  2897  (FIG.  28 ), wafer-transfer unit  2712  picks-up the unprocessed wafer (wafer  9 ) from first buffer  2710 . In operation  2898  (FIG.  28 ), wafer-transfer unit  2712  places the unprocessed wafer (wafer  9 ) onto second buffer  2714 . In operation  2837  (FIG.  28 ), wafer-transfer unit  104  places the processed wafer (wafer  13 ) into load module  102 . 
     With reference again to FIG. 28, operations  28100  through  28108  are associated with another process cycle for process module  116 . More particularly, with reference again to FIG. 27, in operation  28100  (FIG.  28 ), wafer-transfer unit  112  picks-up an unprocessed wafer (wafer  3 ) from second buffer  114 . In operation  28101  (FIG.  28 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  3 ) into process module  116 . In operation  28102  (FIG.  28 ), the wafer (wafer  3 ) is processed in process module  116 . In operation  28103  (FIG.  28 ), wafer-transfer unit  112  picks-up the processed wafer (wafer  3 ) from process module  116 . In operation  28104  (FIG.  28 ), wafer-transfer unit  112  places the processed wafer (wafer  3 ) onto first buffer  110 . 
     In operation  28105  (FIG.  28 ), load-lock module  108  is vented such that the pressure within load-lock module  108  is equal to the pressure within tool  100 . In operation  2838  (FIG.  28 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  14 ) from load module  102 . In operation  2839  (FIG.  28 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  12 ) from wafer orienter  106 . In operation  2840  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  14 ) onto wafer orienter  106 . In operation  2855  (FIG.  28 ), wafer orienter  106  orients the wafer (wafer  14 ). In operation  2841  (FIG.  28 ), wafer-transfer unit  104  picks-up from first buffer  110  a wafer (wafer  1 ) that was processed in process module  116  in an earlier process cycle. In operation  2842  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  12 ) onto first buffer  110 . In operation  28106  (FIG.  28 ), load-lock module  108  is sealed and evacuated such that the pressure within load-lock-module  108  is equal to the pressure within process module  116 . In operation  28107  (FIG.  28 ), wafer-transfer unit  112  picks-up the unprocessed wafer (wafer  12 ) from first buffer  110 . In operation  28108  (FIG.  28 ), wafer-transfer unit  112  places the unprocessed wafer (wafer  12 ) onto second buffer  114 . In operation  2843  (FIG.  28 ), wafer-transfer unit  104  places the processed wafer (wafer  1 ) into load module  102 . 
     With reference again to FIG. 28, operations  28110  through  28115  are associated with the beginning of another process cycle for process module  1816 . More particularly, with reference again to FIG. 27, in operation  28110  (FIG.  28 ), wafer-transfer unit  1812  picks-up an unprocessed wafer (wafer  2 ) from second buffer  1814 . In operation  28111  (FIG.  28 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  2 ) in process module  1816 . In operation  28112  (FIG.  28 ), the wafer (wafer  2 ) is processed in process module  1816 . 
     In operation  28115  (FIG.  28 ), load-lock module  1808  is vented such that the pressure within load-lock module  1808  is equal to the pressure within tool  100 . In operation  2844  (FIG.  28 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  15 ) from load module  102 . In operation  2845  (FIG.  28 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  12 ) from wafer orienter  106 . In operation  2846  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  15 ) onto wafer orienter  106 . In operation  2856  (FIG.  28 ), wafer orienter  106  orients the wafer (wafer  15 ). In operation  2847  (FIG.  28 ), wafer-transfer unit  104  picks-up from first buffer  1810  a wafer (wafer  5 ) that was processed in process module  1816  in an earlier process cycle. In operation  2848  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  12 ) onto first buffer  1810 . 
     With reference again to FIG. 28, operations  28120  through  28125  are associated with the beginning of another process cycle for process module  2516 . More particularly, with reference again to FIG. 27, in operation  28120  (FIG.  28 ), wafer-transfer unit  2512  picks-up an unprocessed wafer (wafer  6 ) from second buffer  2514 . In operation  28121  (FIG.  28 ), wafer-transfer unit  2512  places the unprocessed wafer (wafer  6 ) in process module  2516 . In operation  28122  (FIG.  28 ), the wafer (wafer  6 ) is processed in process module  2516 . In operation  28125  (FIG.  28 ), load-lock module  2508  is vented such that the pressure within load-lock module  2508  is equal to the pressure within tool  100 . 
     With reference again to FIG. 28, operations  28130  through  28135  are associated with the beginning of another process cycle for process module  2716 . More particularly, with reference again to FIG. 27, in operation  28130  (FIG.  28 ), wafer-transfer unit  2712  picks-up an unprocessed wafer (wafer  9 ) from second buffer  2714 . In operation  28131  (FIG.  28 ), wafer-transfer unit  2712  places the unprocessed wafer (wafer  9 ) in process module  2716 . In operation  28132  (FIG.  28 ), the wafer (wafer  9 ) is processed in process module  2716 . In operation  28135  (FIG.  28 ), load-lock module  2708  is vented such that the pressure within load-lock module  2708  is equal to the pressure within tool  100 . 
     With reference again to FIG. 28, operations  28143  through  28148  are associated with the ending of a previous process cycle for process module  1816 . More particularly, with reference again to FIG. 27, in operation  28143  (FIG.  28 ), wafer-transfer unit  1812  picks-up the processed wafer (wafer  7 ) from process module  1816 . In operation  28144  (FIG.  28 ), wafer-transfer unit  1812  places the processed wafer (wafer  7 ) onto first buffer  1810 . In operation  28146  (FIG.  28 ), load-lock module  1808  is sealed and evacuated such that the pressure within load-lock module  1808  is equal to the pressure within process module  1816 . In operation  28147  (FIG.  28 ), wafer-transfer unit  1812  picks-up an unprocessed wafer (wafer  5 ) from first buffer  1810 . In operation  28148  (FIG.  28 ), wafer-transfer unit  1812  places the unprocessed wafer (wafer  5 ) onto second buffer  1814 . In operation  2801  (FIG.  28 ), wafer-transfer unit  104  places a wafer (wafer  16 ) that was previously processed in process module  1816  in an earlier process cycle into load module  102 . 
     With reference again to FIG. 28, operations  28152  through  28158  are associated with the ending of a previous process cycle for process module  2516 . More particularly, with reference again to FIG. 27, in operation  28152  (FIG.  28 ), the wafer (wafer  10 ) is processed in process module  2516 . In operation  28153  (FIG.  28 ), wafer-transfer unit  2512  picks-up the processed wafer (wafer  10 ) from process module  2516 . In operation  28154  (FIG.  28 ), wafer-transfer unit  2512  places the processed wafer (wafer  10 ) onto first buffer  2510 . 
     In operation  2802  (FIG.  28 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  11 ) from load module  102 . In operation  2803  (FIG.  28 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  8 ) from wafer orienter  106 . In operation  2804  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  11 ) onto wafer orienter  106 . In operation  2849  (FIG.  28 ), wafer orienter  106  orients the wafer (wafer  11 ). In operation  2805  (FIG.  28 ), wafer-transfer unit  104  picks-up from first buffer  2510  a wafer (wafer  17 ) that was processed in process module  2516  in an earlier process cycle. In operation  2806  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  8 ) onto first buffer  2510 . In operation  28156  (FIG.  28 ), load-lock module  2508  is sealed and evacuated such that the pressure within load lock module  2508  is equal to the pressure within process module  2516 . In operation  28157  (FIG.  28 ), wafer-transfer unit  2512  picks-up the unprocessed wafer (wafer  8 ) from first buffer  2510 . In operation  28158  (FIG.  28 ), wafer-transfer unit  2512  places the processed wafer (wafer  8 ) onto second buffer  2512 . In operation  2807  (FIG.  28 ), wafer-transfer unit  104  places the processed wafer (wafer  17 ) into load module  102 . 
     With reference again to FIG. 28, operations  28162  through  28168  are associated with the ending of a previous process cycle for process module  2716 . More particularly, with reference again to FIG. 27, in operation  28162  (FIG.  28 ), the wafer (wafer  13 ) is processed in process module  2716 . In operation  28163  (FIG.  28 ), wafer-transfer unit  2712  picks-up the processed wafer (wafer  13 ) from process module  2716 . In operation  28164  (FIG.  28 ), wafer-transfer unit  2712  places the processed wafer (wafer  13 ) onto first buffer  2710 . 
     In operation  2808  (FIG.  28 ), wafer-transfer unit  104  picks-up an unprocessed wafer (wafer  3 ) from load module  102 . In operation  2809  (FIG.  28 ), wafer-transfer unit  104  picks-up an oriented wafer (wafer  11 ) from wafer orienter  106 . In operation  2810  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  3 ) onto wafer orienter  106 . In operation  2850  (FIG.  28 ), wafer orienter  106  orients the wafer (wafer  3 ). In operation  2811  (FIG.  28 ), wafer-transfer unit  104  picks-up from first buffer  2710  a wafer (wafer  18 ) that was processed in process module  2716  in an earlier process cycle. In operation  2812  (FIG.  28 ), wafer-transfer unit  104  places the unprocessed wafer (wafer  11 ) onto first buffer  2710 . In operation  28166  (FIG.  28 ), load-lock module  2708  is sealed and evacuated such that the pressure within load lock module  2708  is equal to the pressure within process module  2716 . In operation  28167  (FIG.  28 ), wafer-transfer unit  2712  picks-up the unprocessed wafer (wafer  11 ) from first buffer  2710 . In operation  28168  (FIG.  28 ), wafer-transfer unit  2712  places the processed wafer (wafer  11 ) onto second buffer  2712 . In operation  2813  (FIG.  28 ), wafer-transfer unit  104  places the processed wafer (wafer  18 ) into load module  102 . 
     Although the present invention has been described in conjunction with particular embodiments illustrated in the appended drawing figures, various modifications can be made without departing from the spirit and scope of the invention. For example, tool  100  (FIG. 1) can include any number of load modules  102  (FIG.  1 ). Therefore, the present invention should not be construed as limited to the specific forms shown in the drawings and described above.