Abstract:
A method and computer program product for scheduling product lots through operations of a manufacturing line. The method including: selecting a set of sequential operations required to manufacture the lots; partitioning the product lots into designated lots and non-designated lots; and generating a release schedule for each of the non-designated lots into one or more operations of the set of sequential operations; generating a release schedule for each of the designated lots into each operation of set of sequential operations such that for each designated lot a total amount of time measured from completion of a first operation of the set of sequential operations through start of a last operation of the set of sequential operations does not exceed a target amount of time for the designated lots.

Description:
This application is a continuation of U.S. patent application Ser. No. 10/908,420 filed on May 11, 2005, now U.S. Pat. No. 7,477,958, issued Jan. 13, 2009. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of manufacturing facility control such as used in a semiconductor manufacturing facility; more specifically, it relates to a method and system for release to and product flow management of product in a manufacturing facility. 
     BACKGROUND OF THE INVENTION 
     Manufacturers, such as but not limited to semiconductor manufacturers, continually strive to increase yield and reduce cycle time in order to operate at the lowest possible cost. Conventional product release and product flow management methods address only logistic concerns such as cycle time and delivery schedule control. The problem of yield enhancement has been left to either improvements in tooling or establishment of simple process window/rework time windows. The ability to influence yield has otherwise been left un-addressed by product release and product flow management methods. 
     Therefore, there is a need for a method of release and product flow management for a manufacturing facility that allows for improved yield as well as cycle time and delivery schedule control. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention is a method for scheduling lots of product through operations in a manufacturing line, comprising: selecting a sequential subset of a set of sequential operations required to manufacture the lots; partitioning the lots of product into designated lots and non-designated lots; and generating a release schedule for each of the non-designated lots into one or more operations of the sequential subset of the set of sequential operations; generating a release schedule for each of the designated lots into each operation of the sequential subset of the set of sequential operations such that for each designated lot a total amount of time measured from completion of a first operation of the sequential subset of the set of sequential operations through start of a last operation of the sequential subset of the set of sequential operations does not exceed a target amount of time for the designated lots. 
     A second aspect of the present invention is a computer program product, comprising a computer usable medium having a computer readable program code embodied therein, the computer readable program code comprising an algorithm adapted to implement a method for scheduling lots of product through operations in a manufacturing line, the method comprising the steps of: selecting a sequential subset of a set of sequential operations required to manufacture the lots; partitioning the lots of product into designated lots and non-designated lots; generating a release schedule for each of the non-designated lots into one or more operations of the sequential subset of the set of sequential operations; and generating a release schedule for each of the designated lots into each operation of the sequential subset of the set of sequential operations such that for each designated lot a total amount of time measured from completion of a first operation of the sequential subset of the set of sequential operations through start of a last operation of the sequential subset of the set of sequential operations does not exceed a target amount of time for the designated lots. 
     A third aspect of the present invention is a system for scheduling lots of product through operations in a manufacturing line, comprising: a zone of control creation module for initializing a zone of control database for a zone of control of a manufacturing line, the zone of control comprising a sequential subset of a set of sequential operations required to manufacture the lots, the lots of product partitioned into designated and non-designated lots; a zone of control release module for planning a release schedule for the designated lots of the lots into each operation of the zone of control to meet a total amount of time target, the total amount of time target measured from completion of a first operation of the zone of control through start of a last operation of zone of control; a zone of control monitor module for updating the release schedule of the designated lots and release schedules of the non-designated lots into each operation of the zone of control; and a what next module for selecting a next lot from the designated and the non-designated lots to release into each operation of the zone of control. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  a diagram of a portion of a manufacturing line according to the present invention; 
         FIG. 2  is a system diagram of a zone of control system according to the present invention; 
         FIG. 3A through 3E  illustrate the file structure of a the zone of control system of  FIG. 2 ; 
         FIG. 4  is a flowchart of a method of release and product flow management according to the present invention; 
         FIG. 5  is a flowchart of step  215  of  FIG. 4 ; 
         FIG. 6  is a flowchart of steps  220  and  225  of  FIG. 4 ; 
         FIG. 7  is a flowchart of step  305  of  FIG. 6 ; 
         FIG. 8  is a flowchart of step  315  of  FIG. 7  and step  445  of  FIG. 11 ; 
         FIG. 9  is a flowchart of step  230  of  FIG. 4 ; 
         FIG. 10  is a flowchart of steps  235  and  240  of  FIG. 4 ; 
         FIG. 11  is a flowchart of step  425  of  FIG. 10 ; 
         FIG. 12  is a flowchart of steps  435  of  FIGS. 10 and 480  of  FIG. 11 ; 
         FIG. 13  is a flowchart of step  245  of  FIG. 4 ; and 
         FIG. 14  is a schematic block diagram of a general-purpose computer for practicing the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a semiconductor environment it was discovered that yields on certain products increase if several distinct but sequential operations were performed within a given amount of time. This sequence of operations is called a yield management zone of control (ZOC), hereinafter ZOC. The tools are designated ZOC tools and a ZOC product to be yield managed is run in ZOC lots of one or more pieces through the ZOC tools in sequence. This effect is different from the time window effect affecting two sequential process steps where the first step can be repeated if a time limit expires. Though applicable to other conditions, the present invention was developed to address the condition of sequential multiple operations, each operation requiring a different fabrication tool and where there may be multiple operations within a tool, where there may be multiple tools for any particular operation, where rework may not be possible and/or where non-ZOC lots (those lots whose yields do not change significantly as a function of their cycle time) may share one or more of the ZOC tools. 
     For the purposes of the present invention, a lot may comprise a single piece (for example, a single wafer in a semiconductor manufacturing line) or a group of two or more pieces (for example, two or more wafers in a wafer lot in a semiconductor manufacturing line) not withstanding the fact, that in some tools pieces of the same lot may be processed together and in some tools pieces of the same lot may be processed sequentially (e.g. single wafer vs. batch tools). 
       FIG. 1  is a diagram of a portion of a manufacturing line according to the present invention. In  FIG. 1  a ZOC  100  contains multiple ZOC operations (operations are also known as manufacturing activities) from a first ZOC operation  105 A, a second ZOC operation  105 B, a third ZOC operation  105 C through a last ZOC operation  105 N. ZOC operation  105 A,  105 B,  105 C through  105 N operations may be expresses as ZOC operation  1 , ZOC operation  2 , ZOC operation  3  . . . through ZOC operation N. For exemplary purposes, ZOC operation  105 A includes process tools  110 A and  110 B, ZOC operation  105 B includes process tools  115 A,  115 B and  115 C, ZOC control  105 C includes process tools  120 A,  120 B and  120 C, and ZOC operation  105 N includes process tools  125 A and  125 B. Process tools  110 A and  110 B can both perform the same process, so a ZOC lot can be run on either of ZOC tools  110 A or  110 B in ZOC operation  105 A. Process tools  115 A,  115 B and  115 C can all perform the same process, so a ZOC lot can be run on any of ZOC tools  115 A,  115 B or  115 C in ZOC operation  105 B. Process tools  120 A,  120 B and  120 C can all perform the same process (or processes, i.e. are cluster tools), so a ZOC lot can be run on any of ZOC tools  120 A,  120 B or  120 C in ZOC  105 C. Process tools  125 A and  125 B can both perform the same process, so a ZOC lot can be run either of ZOC tools  125 A or  125 B in ZOC  105 N. While specific numbers of process tools are illustrated in  FIG. 1  for each ZOC operation, a given ZOC operation may include any number of ZOC tools from one up. Also, while all the ZOC operations are illustrated in proximity to one another, ZOC tools may be placed throughout a manufacturing line. 
     All ZOC tools  110 A,  110 B,  115 A,  115 B,  115 C,  120 A,  120 B,  120 C,  125 A and  125 C are illustrated as having load/unload (L/UL) stations  130  (which may include storage buffers) which are connected to an automated delivery system  135  and computer control/monitor stations  140  providing a link between ZOC tools and a manufacturing execution system (MES)  145 . The general function of an MES function is to schedule, release and track product lots to and through the tools of a manufacturing line by issuing specific execution instructions (lot movement instructions) to a floor control system. The function of MES  145  in relation to ZOC  100  is to issue specific lot movement and tool assignment instructions to the floor control system if not completely generated by then at least logically based on input from WNMs  185 A,  185 B through  185 N (see  FIG. 2 . 
     ZOC tools may be manual tools and not connected to delivery system  135  (e.g. human operators may move ZOC lots from ZOC tool to ZOC tool). ZOC tools need not be directly linked connected to MES  145  (e.g. human operators may receive and record ZOC lot/tool information from MES terminals distributed through a manufacturing line. 
       FIG. 2  is a system diagram of a zone of control system according to the present invention. In  FIG. 2 , a ZOC system  150  includes a ZOC creation module (ZOC CM)  155  and an associated ZOC CM file  160 , a ZOC game plan release module (ZOC GPRM)  165  and an associated ZOC GPRM file  170 , a ZOC game plan monitor module (ZOC GPMM)  175  and an associated ZOC GPMM file  180 , and a set of what next modules (WNM)  185 A,  185 B through  185 N (for corresponding ZOC operations, 1, 2 through N) and a corresponding WNM file ( 190 ). ZOC system  150  further includes a ZOC lot tracking file  195 . ZOC CM  155 , ZOC GPRM  165  and ZOC GPMM  175  all generate output that is stored in and/or can be retrieved from ZOC lot tracking file  195 . It should be noted that the file system comprising ZOC CM file  160 , ZOC GPRM file  170 , ZOC GPMM file  180 , WNM file  190  and ZOC lot tracking file  195  may be replaced by other file systems or data storage systems as known in the art. ZOC CM  155  can issue instructions and/or send data to ZOC GPRM  165 , ZOC GPRM  165  can issues instructions and/or send data to ZOC WNM  185 A (first ZOC operation) and ZOC GPMM  175  can issues instructions and/or send data to ZOC WNMs  185 B through  185 N. MES  145  (see  FIG. 1 ) and associated MES file  200  are not part of ZOC system  150  but MES  145  can issue instructions to and/or send data to ZOC CM  155 , ZOC GPRM  165  and ZOC GPRM  175  and can issue instructions to and/or send data to and/or receive data from WNM  185 A,  185 B through  185 N. ZOC GPMM  175  can issue a critical action report  205  and an alert report  210  as required. 
     Briefly, ZOC CM  155  creates a file that defines a ZOC that MES  145  may utilize to schedule and route ZOC and non-ZOC lots through ZOC system  150 . ZOC GPRM  165  generates a release schedule/tool assignment to the first of ZOC operation  105 A of ZOC  100  (see  FIG. 1 ) that will meet the yield window time restraint of the ZOC. ZOC GPMM  175  generates and updates ZOC lot priorities for the second through nth last operation of respective ZOC operations  105 B,  105 C through  105 N of ZOC  100  (see  FIG. 1 ) that will meet the yield window time restraint of the ZOC. WNM  185 A,  185 B through  185 N identify ZOC and non-ZOC lots for the tools of their respective ZOC operations, prioritize the ZOC and non-ZOC lots according to pre-defined rules, and assign the ZOC and non-ZOC lots according to predefined algorithms. WNM  185 A,  185 B through  185 N operate in real time. 
     ZOC system  150  generates, track and modifies ZOC lot schedules in the ZOC so ZOC lots start and finish through ZOC operations within a target time window that prevents delay related yield degradation, taking into account that there may be several ZOC lots and several non-ZOC lots that will use the same tools and schedules for all lots must be met. 
       FIG. 3A through 3E  illustrate the file structure of the zone of control system of  FIG. 2 . In  FIG. 3A , ZOC CM file  160  includes a ZOC operations file, a ZOC tool file, a ZOC lot ID file, a ZOC allowable delay time file, a ZOC knowledge base file, a ZOC required cycle time file and a non-ZOC lot ID file. The ZOC operations file lists the manufacturing operations for the ZOC. The ZOC tool file lists tools that perform the operations of the ZOC. The ZOC lot ID file list the lots that are to be processed as part of the ZOC. The ZOC allowable delay time file gives maximum delay times between operations in the ZOC. The ZOC knowledge base file includes specific processing related schedule information, for example, for how many pieces could mask cleaning be delayed if a ZOC required a masking operation using a mask scheduled for cleaning. The ZOC required cycle time file gives the maximum delay between the first and last operation of the ZOC. The non-ZOC lot ID file lists non-ZOC lots that will be run on the ZOC tools. 
     In  FIG. 3B , ZOC GPRM file  180  includes a ZOC lot release file, which lists the ZOC earliest lot release date/time into the first operation of the ZOC. GPRM file  170  contains data pertinent to the first ZOC operation. 
     In  FIG. 3C , ZOC GPMM file  170  include a ZOC lot priority file, a ZOC lot alert file, a ZOC lot critical list file, a recover options file, and a non-ZOC lot priority file. GPMM file  170  contains data pertinent to the second through last ZOC operations. The ZOC lot priority file lists the current relative priorities of ZOC lots. The ZOC lot alert file lists ZOC lots that have scheduling problems jeopardizing the ZOC time window. The ZOC lot critical list file lists ZOC lots which require recovery actions be taken in order to meet the ZOC time window. The recover options file contains potential actions that may be selected to recover a ZOC lot on the critical list to the ZOC time window. The non-ZOC lot priority file lists the current relative priorities of non-ZOC lots. Several ZOC lots and non-ZOC lots may share the same priority or ZOC lots and non-ZOC lots may be ranked in priority in a single list depending upon the type of MES used. 
     In  FIG. 3D , WNM file  190  includes a dispatch list file which lists which of the ZOC and non-ZOC lots each ZOC operation are to be processed next and on which ZOC tool. 
     In  FIG. 3E , MES file  200  includes a routing file, a tool file, a work in progress (WIP) file and an acceptable delay file. The routing file lists all the operations each lot must be processed through in the entire manufacturing line. The tool file lists the tools and status available for each operation in the manufacturing line. The WIP file lists the present status of all lots in the manufacturing line in two categories, those lots available to run on each tool in each operation, and those lots either assigned to or already in each tool (or tool buffer) in each operation. The acceptable delay file lists the time windows that cannot be exceeded between two sequential operations (this is not the ZOC time window which is for the entire set of ZOC operations). 
       FIG. 4  is a flowchart of a method of release and product flow management according to the present invention. In step  215 , operations  1  through N (or last) are selected for inclusion in a ZOC of control and a ZOC control is created. Step  215  is illustrated in  FIG. 5  and described in further detail infra. In step  220  all ZOC lots available for processing through the first operation of the ZOC are identified and in step  225 , an earliest release date/time into the first ZOC operation is generated for all ZOC lots available for starting in the first ZOC operation. Potential release date/times into subsequent operations of the ZOC are generated by the process used to generate the release date/time into the first ZOC operation. Steps  220  and  225  are illustrated in  FIG. 6  and described in further detail infra. In step  230 , the specific ZOC and non-ZOC lots to dispatch next into the ZOC tools of the first ZOC operation are selected and dispatched though a MES. 
     In step  235  all ZOC lots available for processing through each operation of the second through last operations of the ZOC are identified and in step  240 , release date/times to the second through last ZOC operations is generated for all ZOC lots available for starting in each of the second through last ZOC operations. Steps  235  and  240  are illustrated in  FIG. 10  and described in further detail infra. In step  245 , the specific ZOC and non-ZOC lots to dispatch next into each ZOC tool of each of the second through last ZOC operation are selected and dispatched though a MES. 
     The process flow through steps  220 ,  225  and  230  occurs simultaneously with the process flow through steps  235 ,  240  and  245 . There are two process flows because there are specific differences on how scheduling through the first operation of a ZOC is handled compared to how scheduling is handled in subsequent operations of the ZOC. 
       FIG. 5  is a flowchart of step  215  of  FIG. 4 . In step  250  a ZOC is defined using data from MES file  200 . The ZOC of control is defined by the product type, first operation in the ZOC, the last operation in the ZOC and the maximum amount of time a lot of product this type is allowed to take from completing the first operation of the ZOC to entering the last operation of the ZOC. A ZOC control is a subset of sequential operations of the overall set of operations required to fabricate product of the product type. 
     In step  255 , the ZOC is created using data from MES file  200 . Information is selected from MES file  200  that will be incorporated in the file that controls the ZOC. This information includes each operation, the tools for each operation, the raw process times for each tool in the ZOC, the average aggregate raw process time to complete all the operation in the ZOC and all lot types that need to be run through each tool of the ZOC. Creating a ZOC is essentially creation of a routing file. In step  260 , the ZOC is verified. Essentially, the ZOC routing file is compared to a subset of the overall routing file, the routing file of MES file  200 . If in step  265 , the ZOC does not verify then in step  270 , a human operator is notified that a ZOC creation error has occurred and the problem may be pointed out. If, in step  265 , the ZOC does verify then in step  275 , the various ZOC CM file are written to ZOC CM file  160  and in step  280 , ZOC lot tracking file  195  is created. The ZOC tracking file will include ZOC lot target date/time and ZOC lot complete estimated date/time data. 
       FIG. 6  is a flowchart of steps  220  and  225  of  FIG. 4 . This sequence of steps is creating ZOC release date/times for ZOC lots into the first ZOC operation and estimated complete date/times. In step  290  using the WIP file of MES file  200 , the lot IDs of all lots at the first ZOC operation are determined. In step  295 , using the ZOC Lot ID it is determined which of the lot IDs are ZOC lot IDs and in step  300 , the ZOC lot IDs are added to ZOC tracking file  195  and their information at the first ZOC operation. In step  305 , ZOC lot release date/times are generated and written to the ZOC lot release file of ZOC GPRM file  170  and ZOC lot complete target date/times are generated and written to ZOC lot tracking file  195  based on the ZOC lot release date/times and the ZOC required cycle time file of ZOC CM file  160 . At this point the ZOC lot complete target date/times are also the ZOC lot complete estimated date/times and the ZOC lot complete estimated date/times are written to ZOC tracking file  195 . Step  305  is illustrated in  FIG. 7  and described in further detail infra. From step  305 , the method proceeds to connector A of  FIG. 9 . 
       FIG. 7  is a flowchart of step  305  of  FIG. 6 . In step  310 , the lot with the earliest available release date/time into the ZOC tool is selected. In step  315 , ZOC lot predicted release and complete date/times for the first ZOC operation is generated using the earliest available release date/time and the ZOC lot ID file, the non-ZOC lot ID file and the ZOC required cycle time file of ZOC CM file  160 . Step  315  is illustrated in  FIG. 8  and described in further detail infra. In step  320 , a ZOC complete predicted date/time through all the ZOC operations is generated using a simulation model of the ZOC. In a first example, the simulation model is a stochastic simulation model (e.g. utilizes probabilities of processing events happening to schedule). In a second example, a deterministic model is used. In a third example, an analytic model is used. In either the first or third examples, the ZOC lot complete estimated date/time may be maximum likelihood point estimated date/time or range of values with an associated predictive probability density function. In any of the three examples, an additional time may be optionally added to the nominally calculated ZOC lot complete date/time in order to buffer against cycle time uncertainties. In step  325 , the ZOC lot complete predicted date/time is compared with the ZOC lot complete target date/time from ZOC tracking file  195 . If in step  330 , this window is not exceeded then in step  335  then the ZOC lot complete predicted date/time will be become the ZOC lot complete estimated date/time described supra and used in step  305  of  FIG. 6 . If in step  330 , this window is exceeded, then in step  340 , the ZOC release date/time is changed to a later date/time and the process loops back to step  315 . 
       FIG. 8  is a flowchart of step  315  of  FIG. 7  and step  445  of  FIG. 11 . In step  345 , the designated current ZOC operation is used to initialize the simulation model. In step  350 , using the ZOC lot ID file of ZOC CM file  160 , all ZOC lots at the current operation are identified. In step  355 , using the ZOC lot priority file and the non-ZOC lot priority file of ZOC GPMM file  180  and using the ZOC tool file (having tool logistics data) of ZOC CM file  160  the simulation model is run to generate a ZOC lot complete prediction date/time for each lot at the designated ZOC operation. In step  365  the ZOC lot complete predicted date/time becomes the ZOC lot complete estimated date/time and is written to ZOC lot tracking file  195 . 
       FIG. 9  is a flowchart of step  230  of  FIG. 4 . This sequence of steps is deciding the order of ZOC and non-ZOC lots into the first operation of the ZOC. In step  380 , using the ZOC lot release file from ZOC GPRM file  180  and the WIP files from MES file  200 , all lots available to run on the first operation of the ZOC are identified and for ZOC lots the release date/time resultant from the simulation model is read. In step  385 , all the lots, ZOC and non ZOC are ranked based lot priorities, tool throughputs in order to assign a tool and release date/time to the assigned tool based on local release algorithms. For example, if a lot has high priority but its earliest release time is not in the near future, the lot can be assigned a later release date/time that is no later than the release date/time from the simulation model. In step  390 , the tool assignment and release date/time is written to the dispatch list file of WNM file  190 . As steps  380  through  390  are being executed, steps  390  and  400  are also executed. In step  395 , the next lot to release is selected from the dispatch list file of WNM file  190  and in step  400  the MES sends an execute instruction to the floor control system. 
       FIG. 10  is a flowchart of steps  235  and  240  of  FIG. 4 . This sequence of steps is creating release date/times for ZOC lots into the second through N (or last) ZOC operations. In step  405  using the WIP files of MES file  200  all the ZOC lots at each ZOC operation from the second through the last are identified. In step  410  ZOC lots identified by the MES as on hold or inhibited are identified (they are flagged in the WIP files of MES file  200 ). A lot may be identified as on hold or inhibited because the lots processing may not continue for some technical process reason (e.g. the lots must be inspected or lot data analyzed prior to the lot continuing to the next operation). 
     In step  415 , it is determined if any ZOC lot is on hold or inhibited and is in jeopardy of not meeting its ZOC lot complete target date/time by comparing the ZOC lot&#39;s complete estimate to its corresponding ZOC lot complete target date/time. For all ZOC lots found to be in jeopardy, an alert report is issued in step  420  and written to the ZOC alert file of ZOC GPMM file  180 . Alert reports may or may not generate actions by a human operator. The method then proceeds to step  425 . For all ZOC lots found not to be in jeopardy the method immediately proceeds to step  425 . In step  425 , the estimated ZOC lot complete estimate is written to ZOC lot tracking file  195 . The operations of step  425  are similar to the operations performed in  FIG. 7  and described supra for the first operation of the ZOC, but are modified to account for effects only applicable to second through last ZOC operations. Step  425  is illustrated in  FIG. 11  and described in further detail infra. Next, in step  430 , it is determined if the recalculated ZOC lot complete estimated date/times for each ZOC lot meets its corresponding ZOC lot complete target date/time. If the ZOC lot complete estimated date/time meets its corresponding ZOC lot complete target date/time then the method proceeds to connector B of  FIG. 13 , otherwise the method proceeds to step  435  where a check for recovery actions is performed. Step  435  is illustrated in  FIG. 12  and described in further detail infra. 
       FIG. 11  is a flowchart of step  425  of  FIG. 10 . In step  440 , the lot with the earliest available release date/time into current operation under analysis is selected. In step  445 , ZOC lot predicted release and complete date/times for the current ZOC operation is generated using the earliest available release date/time and the ZOC lot ID file, the non-ZOC lot ID file and the ZOC required cycle time file of ZOC CM file  160 . Step  445  is illustrated in  FIG. 8  and was described in detail supra. In step  450 , a ZOC complete predicted date/time through all the ZOC operations is generated using the simulation model of the ZOC. In step  455 , the ZOC lot complete predicted date/time is compared with the ZOC lot complete target date/time from ZOC tracking file  195 . If in step  460 , this window is not exceeded then in step  465  the ZOC lot complete predicted date/time will be become the ZOC lot complete estimated date/time described supra and used in step  425  of  FIG. 10 . If in step  460 , this window is exceeded, then in step  470  it is determined if the ZOC lot is at a maximum priority. If the ZOC lot is at a maximum priority the method proceeds to step  475 , otherwise the method proceeds to step  480 . In step  475 , a check for recovery options is performed. Step  480  is illustrated in  FIG. 12  and described in detail infra. In step  480 , the ZOC release date/time is changed to a later date/time and the process loops back to step  445 . 
       FIG. 12  is a flowchart of steps  435  of  FIGS. 10 and 480  of  FIG. 11 . In step  485 , the ZOC lot is placed on the ZOC critical list and recorded in the ZOC critical list file of ZOC GPMM file  180 . In step  490 , options to recover are selected based on information in the knowledge base file of ZOC CM file  160  by a human. Any options found are written to the recover options file of ZOC GPMM file  180 . In step  495 , a critical action report is issued. Critical actions generally require approval/action by a human operator. 
       FIG. 13  is a flowchart of step  245  of  FIG. 4 . This sequence of steps is deciding the order of ZOC and non-ZOC lots into the second through last operations of the ZOC. In the following steps, lots at a particular ZOC operations are processed as a groups, and steps are repeated for each ZOC operation starting from the second ZOC operation. So, in step  500 , using the ZOC lot priority file from ZOC GPRM file  170 , the WIP files from MES file  200  and the recover options file from ZOC GPMM file  180 , all lots available to run on each of the second through last operations of the ZOC are identified and for ZOC lots the release date/time resultant from the simulation model is read. In step  505 , all the lots, ZOC and non ZOC are ranked based lot priorities, tool throughputs in order to assign a tool and release date/time to the assigned tool based on local release algorithms. For example, if a lot has high priority but its earliest release time is not in the near future, the lot can is assigned a later release date/time that is no later than the release date/time from the simulation model. Other actions, for example, tool assignment and release to the tool date/time can be changed by a human operator in response to information in the recover options file of ZOC GPMM files  180 . In step  510 , the tool assignment and release date/time is written to the dispatch list file of WNM file  190 . As steps  500  through  510  are being executed, steps  515  and  520  are also executed. In step  515 , the next lot to release is selected from the dispatch list file of WNM file  190  and in step  520  the MES sends an execute instruction to the floor control system. 
     Generally, the method described herein with respect to a method of release and product flow management is practiced with a general-purpose computer and the method may be coded as a set of instructions on removable or hard media for use by the general-purpose computer.  FIG. 14  is a schematic block diagram of a general-purpose computer for practicing the present invention. In  FIG. 14 , computer system  600  has at least one microprocessor or central processing unit (CPU)  605 . CPU  605  is interconnected via a system bus  610  to a random access memory (RAM)  615 , a read-only memory (ROM)  620 , an input/output (I/O) adapter  625  for a connecting a removable data and/or program storage device  630  and a mass data and/or program storage device  635 , a human interface adapter  640  for connecting a keyboard  645  and a mouse  650 , a port adapter  655  for connecting a data port  660  and a display adapter  665  for connecting a display device  670 . 
     ROM  620  contains the basic operating system for computer system  600 . The operating system may alternatively reside in RAM  615  or elsewhere as is known in the art. Examples of removable data and/or program storage device  630  include magnetic media such as floppy drives and tape drives and optical media such as CD ROM drives. Examples of mass data and/or program storage device  635  include hard disk drives and non-volatile memory such as flash memory. In addition to keyboard  645  and mouse  650 , other human input devices such as trackballs, writing tablets, pressure pads, microphones, light pens and position-sensing screen displays may be connected to human interface  640 . Examples of display devices include cathode-ray tubes (CRT) and liquid crystal displays (LCD). 
     A computer program with an appropriate application interface may be created by one of skill in the art and stored on the system or a data and/or program storage device to simplify the practicing of this invention. In operation, information for or the computer program created to run the present invention is loaded on the appropriate removable data and/or program storage device  630 , fed through data port  660  or typed in using keyboard  645 . 
     Thus the present invention provides a method of release and product flow management for a manufacturing facility that allows for improved yield as well as cycle time and delivery schedule control. 
     The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.