Dispatching system with dynamically forward loading (DFL) intensity to solve nonlinear wafer out problem

Abstract

Calculate the WIP.sub.i for a stage ST.sup.kk for each lot Li in a queue of lots being processed in a production line between the stage ST.sup.kk and an end point, where "i" is a positive integer representing the position of the lot Li in the queue, and where "kk" is a positive integer indicating the sequential position of the stage ST.sup.kk (location along the production line) from the beginning to the end of a predetermined portion of the production line. Calculate remaining scheduled cycle time (RCT.sub.i) for each lot Li. Calculate consumed scheduled cycle time (CST.sub.i) for each lot Li. Calculate (WIP.sub.i *RCT.sub.i) for each lot Li. Calculate (WIP*CST.sub.i) for each lot Li. Sum WIP.sub.i *RCT.sub.i for all lots Li of a stage. Sum WIP.sub.i *CST for all lots Li of a stage. Calculate the Index of Dynamic Forward Loading Intensity (I.sub.DFL) for each stage ST.sup.kk by dividing the (Sum WIP.sub.i *RCT.sub.i, for all lots of the stage) by the (Sum WIP.sub.i *CST.sub.i, for all lots of the stage) where kk is a positive integer indicating the location of the stage from the beginning to the end of the production line. Adjust the dispatching order of lots based on the rankings of the stages of the production I.sub.DFL line, with lowest I.sub.DFL ratings having priority.

Claims

Having thus described the invention, what is claimed as new and desirable to be secured by Letters Patent is as follows:

1. A method for determining an Index of Dynamic Forward Loading (I.sub.DFL) for a stage on a production line comprising:

calculate a Work In Process.sub.i (WIP.sub.i) for a stage ST.sup.kk for each lot Li in a queue of lots being processed in a production line between said stage ST.sup.kk and end point, where "i" is a positive integer representing the position of said lot Li in said queue, and where "kk" is a positive integer indicating the sequential position of the stage ST.sup.kk in a location along said production line from the beginning to the end of a predetermined portion of said production line,

calculate remaining scheduled cycle time (RCT.sub.i) for each lot Li,

calculate consumed scheduled cycle time (CST.sub.i) for each lot Li,

calculate WIP.sub.i *RCT.sub.i for each lot Li,

calculate WIP.sub.i *CST.sub.i for each lot Li,

summing WIP.sub.i *RCT.sub.i for all lots Li of a stage,

summing WIP.sub.i *CST.sub.i for all lots Li of a stage,

calculate an Index of Dynamic Forward Loading (I.sub.DFL) Intensity for each stage ST.sup.kk by dividing the Sum WIP.sub.i *RCT.sub.i, for all lots of the stage ST.sup.kk, by the Sum WIP.sub.i *CST.sub.i, for all lots of the stage ST.sup.kk, where kk is a positive integer indicating the location of the stage from the beginning to the end of said production line, and

adjust dispatching order of lots based on I.sub.DFL Intensity of all stages of the production line, with lowest I.sub.DFL Intensity having priority.

2. A method in accordance with claim 1 including determining I.sub.DFL in accordance with the equation as follows: ##EQU16##

Li=Lot "i"

i=1, 2 . . . n, where n is the number of the lot Li

N.sub.i =wafer quantity of lot Li

RCT.sub.i =Remaining scheduled Cycle Time for lot Li

CST.sub.i =Consumed Scheduled Cycle Time for lot Li.

3. A method in accordance with claim 1 including determining I.sub.DFL for two lots Li in accordance with the equations as follows: ##EQU17##

4. A system for determining an Index of Dynamic Forward Loading Intensity (I.sub.DFL) for a stage on a production line comprising:

means for calculating a Work in Process (WIP.sub.i) for a stage ST.sup.kk for each lot Li in a queue of lots being processed in a production line between said stage ST.sup.kk and end point, where "i" is a positive integer representing the position of said lot Li in said queue, and where "kk" is a positive integer indicating the sequential position of the stage ST.sup.kk location along said production line from the beginning to the end of a predetermined portion of said production line,

means for calculating the remaining scheduled cycle time (RCT.sub.i) for each lot Li,

means for calculating consumed scheduled cycle time (CST.sub.i) for each lot Li,

means for calculating WIP.sub.i *RCT.sub.i for each lot Li,

means for calculating WIP.sub.i *CST.sub.i for each lot Li,

means for summing WIP.sub.i *RCT.sub.i for all lots Li of a stage

means for summing WIP.sub.i *CST.sub.i for all lots Li of a stage,

means for calculating an Index of Dynamic Forward Loading (I.sub.DFL) Intensity for each stage ST.sup.kk by dividing the Sum WIP.sub.i *RCT.sub.i, for all lots of the stage ST.sup.kk by the Sum WIP.sub.i *CST.sub.i, for all lots of the stage ST.sup.kk, where kk is a positive integer indicating the location of the stage from the beginning to the end of said production line, and

means for adjusting dispatching order of lots based on I.sub.DFL Intensity of all stages of the production lines with lowest I.sub.DFL Intensity having priority.

5. A system in accordance with claim 4 including determining I.sub.DFL in accordance with the equation as follows: ##EQU18##

Li=Lot "i"

i=1, 2 . . . n, where n is the number of the lot Li

N.sub.i =wafer quantity of lot Li

RCT.sub.i =Remaining scheduled Cycle Time for lot Li

CST.sub.i =Consumed Scheduled Cycle Time for lot Li.

6. A system in accordance with claim 4 including determining I.sub.DFL for two lots Li in accordance with the equations as follows: ##EQU19##

7. A method for determining a rate of dispatching lots for a stage on a production line comprising:

determining a weighted loading of work for each of said lots between said stage and a succeeding location on said production line by calculating a ratio of weighted progress of said lots as a product of time from dispatching of each lot and as a product of time to completion for each lot to produce an Index of weighted progress for said stage, and

adjusting the rate of dispatching of said lots as a function of said Index.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to systems for controlling work flow in a manufacturing plant and more particularly to dispatching systems therefor.

2. Description of Related Art

Since the product mix and the process technology are complicated in a foundry comprising a semiconductor fabrication plant, different technologies are employed in different stages of the plant. Some of those stages can employ the same types of machines, i.e. equipment, for processing. Because of several factors, WIP (Work In Process) can easily pile up in a particular area on an occasional basis. For example, when one or more of the machines, in one or more of the stages, becomes unstable or where there is a resource arrangement bias that causes the production line to deteriorate into a non-linear status, losses result which comprise reduced wafer movement, increased cycle time, and delayed wafer delivery.

"Bottleneck Starvation Indicators for Shop Floor Control" IEEE TRANSACTIONS ON SEMICONDUCTOR MANUFACTURING; VOL. 1., No. 1, (FEBRUARY 1988) pages, 147-153.

U.S. Pat. No. 5,396,432 of Saka et al. shows a production system and method of operating thereof.

U.S. Pat. No. 5,751,580 of Chi describes a fuzzy logic method and system for adjustment of priority rating of WIP in a production line.

U.S. Pat. No. 5,768,133 of Chen et al., which is commonly assigned, shows a WIP/Move management tool for a semiconductor manufacturing plant and a method of operation thereof.

U.S. Pat. No. 5,818,716, that is commonly assigned, of Chin et al. describes a dynamic lot dispatching required turn rate factory control system and a method of operation thereof for a semiconductor plant.

U.S. Pat. No. 5,826,238 of Chen et al., which is also commonly assigned, describes a method and a system for a daily target generation and machine allocation with priority.

SUMMARY OF THE INVENTION

Characteristics influencing the distribution of WIP are as follows: 1. variable product type; 2. manpower arrangement; 3. machine available time; and 4. dispatching

Indexes that are driven by dispatching of lot of work are as follows: 1. cycle time; 2. OTD (on-time delivery); and 3. wafer movement

Index of Dynamic Forward Loading (I.sub.DFL)

1. Using the Lever Principle, the remaining cycle time and consumed cycle time are used to generate the "Dynamically Forward Loading (DFL) Index (I.sub.DFL). The Intensity of the DFL Index (I.sub.DFL) is referred to as ".alpha.". There is a judgement factor used in making decisions pertaining to dispatching which is enhanced by use of .alpha. and I.sub.DFL.

According to the "lever principle", a lever is in a state of balance when the product of the right side force multiplied by the right side torque arm equals the left side force multiplied by the left side torque arm. Using an analogy to the "lever principle" and referring to FIG. 5, the elements are as follows:

Fulcrum of lever=Each specific lot/set of lots.

Force applied to right side Wafer quantity of each specific lot/set of lots.

Right side torque arm=Remaining scheduled cycle time counting back from the last stage, i.e. the QC-stage, to the current lot stage.

For example, referring again to FIG. 5, let us assume that there are two (2) lots remaining in production on the line. Those lots are L3 and L4. Let us use a predefined comparison at stage ST2. The fulcrum of the lever separates the right and left sides=L3+L4.

A=Force applied to the right side=wafer quantity of sets of lots L3+L4

B=Right side torque arm=Remaining scheduled cycle time counting from QC-stage to current lots L3+L4

C=Force applied to left side=wafer quantity of sets of lots L3+L4

D=Left side torque arm=Consumed scheduled cycle time counting from stage ST2 to current L3 and L4 stages

Thus, when ##EQU1##

the production system is balanced.

2. The I.sub.DFL Index immediately indicates any production dispatching bias caused by a factor such as an unstable machine or an inefficient deployment of manpower at each stage which would influence the scheduling and efficiency of the other stages in the manufacturing line.

A computer operated method is employed for determining the rate of dispatching lots for a stage on a production line. First, determine the weighted loading of work for each of the lots between the stage and a succeeding location on the production line by calculating a ratio of weighted progress of the lots as a product of time from dispatching of each lot and as a product of time to completion for each lot to produce an index for the stage. Then, adjust the rate of dispatching of the lots as a function of the Index.

In accordance with this invention the computer system calculates the WIP.sub.i for a stage ST.sup.kk for each lot Li in a queue of lots being processed in a production line between the stage ST.sup.kk and end point, where "i" is a positive integer representing the position of the lot Li in the queue, and where "kk" is a positive integer indicating the sequential position of the stage ST.sup.kk (location along the production line) from the beginning to the end of a predetermined portion of the production line. Calculate remaining scheduled cycle time (RCT.sub.i) for each lot Li. Calculate consumed scheduled cycle time (CST.sub.i) for each lot Li. Calculate (WIP.sub.i *RCT.sub.i) for each lot Li. Then, calculate (WIP*CST.sub.i) for each lot Li. Sum WIP.sub.i *RCT.sub.i for all lots Li of a stage. Sum WIP.sub.i *CST for all lots Li of a stage. Calculate the Index of Dynamic Forward Loading Intensity (I.sub.DFL) for each stage ST.sup.kk by dividing the (Sum WIP.sub.i *RCT.sub.i, for all lots of the stage) by the (Sum WIP.sub.i *CST.sub.i, for all lots of the stage) where kk is a positive integer indicating the location of the stage from the beginning to the end of the production line. Adjust the dispatching order of lots based on the rankings of the stages of the production I.sub.DFL line, with lowest I.sub.DFL ratings having priority.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects and advantages of this invention are explained and described below with reference to the accompanying drawings, in which:

FIG. 1 is an elementary schematic diagram of example of some of the factors involved in the system of this invention with a production line with a single stage and a single lot of work.

FIG. 2 shows a schematic diagram of the kind shown in FIG. 1 with a single stage and two lots of semiconductor wafers on a semiconductor production line.

FIG. 3A shows five lots all of which are at or near the first stage of a hypothetical production line and thus I.sub.DFL >>1.

In FIG. 3B, the five lots of FIG. 3A are distributed equally along the line between the first stage and the end of the hypothetical production line, so I.sub.DFL =1.

In FIG. 3C, the five lots of FIG. 3A are all at or near the end of the hypothetical production line and thus I.sub.DFL <<1.

FIG. 4 shows a fabrication line with four stages ST.sup.kk where kk=1, 2, 3 and 4.

FIG. 5 shows the implementation of Dynamic Forward Loading Intensity to the fabrication line of FIG. 4 with the same arrangement of four stages in the same locations as in FIG. 4, but with a different arrangement of the WIP which includes six lots.

FIG. 6A shows a graph of .alpha. which is the values of I.sub.DFL for various stages plotted as a function of location along a production line for stages SIN-2-PHO, POLY-1-PHO, POLY-2-PHO, and MET-1-PHO.

FIG. 6B shows a graph of I.sub.DFL another set of stages plotted as a function of location along a production line for stages SIN-2-PHO, POLY-1-PHO, POLY-2-PHO, and CONT-PHO.

FIG. 7 is a flow chart of a system provided in the computer control system of FIG. 8.

FIG. 8 shows a manufacturing plant which includes a central computer system and a fabrication plant with a shop floor where products, such as semiconductor chips, are being manufactured and a computer system for allocating fabrication plant resources in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The dispatching system of this invention provides Dynamic Forward Loading Intensity.

1. This system improves balance of the work load on the production line, while at the same time it prevents WIP (Work In Process) from piling up in some particular area on the production line, to achieve a linear rate of wafer output of the production line.

2 This system raises the resource (machine capacity) utilization and while it concomitantly reduces the cycle time.

3. This system raises the OTD (On Time Delivery) performance.

A Single Lot

FIG. 1 is an elementary schematic diagram of example of some factors involved in the system of this invention with a production line with a single stage and a single lot of work, e.g semiconductor wafers. The production line begins at first stage ST1 and ends at station QC. Single lot L1 is located between the first stage ST1 and the production line end QC. The Consumed Scheduled cycle Time (CST) B1 is marked between the current location and the Remaining scheduled Cycle Time (RCT) A1.

To generalize the diagram shown in FIG. 1, lot L1 on the production line is also referred to a Li where "i" is a positive integer applied to each stage of the line. In this case the lot is lot "1", so i=1. The symbol N.sub.i represents the number of wafers in lot "i" and in this case the specific symbol for N.sub.i when i=1 is N.sub.1. The value B.sub.i =CST.sub.i represents the time Consumed Scheduled cycle Time (CST) for the lot Li to reach the location shown in FIG. 1 is which in this case is B.sub.1 =CST.sub.1. The value A.sub.i =RCT.sub.i represents the time Remaining scheduled Cycle Time (RCT) for the lot Li to go from the location shown in FIG. 1 to the end of the line QC, which in this case is A.sub.1 =RCT.sub.1.

FIG. 2 shows a schematic diagram of the kind shown in FIG. 1 with a single stage and two lots of semiconductor wafers on a semiconductor production line. In FIG. 2, two lots L1 and L2 included quantities of N.sub.1 and N.sub.2 wafers each. Lot L2 is closer to stage ST1 because it was dispatched later than lot L1 which is closer to the end of the line QC. Thus the Consumed Scheduled cycle Time (CST) B1 of CST.sub.1 for lot L1 is larger than the Consumed Scheduled cycle Time B2=CST.sub.2 for lot L2. By the same token Remaining scheduled Cycle Time (RCT) A1=RCT.sub.1 for lot L1 is smaller than the Remaining scheduled Cycle Time A2=RCT.sub.2 for lot L2.

The I.sub.DFL Index (named the Index of Dynamic Forward Loading Intensity) is calculated based on the following:

1) Each stage along a production line has a Scheduled Cycle Time (SCT) which represents the time required to travel from the current stage to the last stage QC known as "QC-INSP".

2) Every lot "i" below the last stage has two separate periods, i,e. the stage period has two (2) sections which are 1) finished with a Consumed Scheduled cycle Time (CST) "B.sub.i " and 2) unfinished: Remaining Scheduled Cycle (RSC) time "A.sub.i ".

3) The I.sub.DFL Index of a stage is calculated as a summation of the products of {the unfinished or Remaining Scheduled Cycle time period (RCT.sub.i) of each lot "i"} times {the wafer quantity for the lot "i"} divided by the product of the {finished or Consumed Scheduled cycle Time period (CST.sub.i) of lots "i"} times {the wafer quantity for the lot "i"}.

Physical Meaning of Value of "I.sub.DFL "

I.sub.DFL >1: Lots for Stage ST.sup.kk are overloading below stage ST.sup.kk, so the flow rate should be decreased to be slower beyond stage ST.sup.kk. Thus lots should be pushed out from stage ST.sup.kk slowly, where kk is a positive integer indicating the sequential position of the stage ST.sup.kk (location along the production line) from the beginning to the end of a predetermined portion of the production line. Usually, the predetermined portion would include the entire production line.

I.sub.DFL =1: Line is balanced below stage ST.sup.kk, which is the ideal situation being pursued by this invention.

I.sub.DFL <1: Too few lots are loading below stage ST.sup.kk, so the flow rate should be increased to be faster beyond stage ST.sup.kk. In this case the wafers (lots) should be pushed out from the stage ST.sup.kk more rapidly.

In any case the number of lots being pushed out from the stage ST.sup.kk should be controlled accordingly.

Below is the formula for calculating the I.sub.DFL Index in accordance with the above paragraph for Stage STkk and lots Li. ##EQU2##

Li=Lot "i"

i=1, 2 . . . n, where n is the number of the lot Li

WIP.sub.i =wafer quantity of lot i

RCT.sub.i =Remaining scheduled Cycle Time for lot i

CST.sub.i =Consumed Scheduled Cycle Time for lot i

i=1, 2 . . . n, where n is the number of the lot

Note that each product has a Scheduled Cycle Time (SCT) defined for each FAB (FABrication plant).

In FIG. 3A, five lots L1 to L5 are all at or near the first stage ST1 of a hypothetical production line. The values of CST.sub.i for the lots L1 to L5 are very small and the values of RCT.sub.i are large so assuming all values of wafer quantities WIP.sub.i are identical, the ratios of RCT.sub.i to CST.sub.i are all very large and thus I.sub.DFL >>1.

In FIG. 3B, the five lots L1 to L5 are distributed equally along the line between the first stage ST1 and the end of the hypothetical production line QC. Thus, again assuming all values of wafer quantities WIP.sub.i are identical, and the values of RCT.sub.i and CST.sub.i are equally balanced, roughly as shown, then I.sub.DFL =1.

In FIG. 3C, the five lots L1 to L5 are all at or near the end of the line QC of the hypothetical production line. The values of CST.sub.i for the lots L1 to L5 are very large and the values of RCT.sub.i are small, so assuming all values of wafer quantities WIP.sub.i are identical, the ratios of RCT.sub.i to CST.sub.i are all very small and thus I.sub.DFL <<1.

At a given time and at a given stage on the production line, there may be many lots comprising WIP distributed along the production line. Thus, we sum up for all of those lots the Remaining Scheduled Cycle time period (RCT.sub.i) and Consumed Scheduled cycle Time period (CST.sub.i), respectively, and calculate the I.sub.DFL (Index of Dynamically Forward Loading).

The Intensity a of the DFL Index is the stage loading intensity.

Equation (1) is restated below for another symbol N.sub.i in place of WIP.sub.i which is a more efficient form of notation. ##EQU3##

Li=Lot "i"

i=1, 2 . . . n, where n is the number of the lot Li

N.sub.i =wafer quantity of lot Li

RCT.sub.i =Remaining scheduled Cycle Time for lot Li

CST.sub.i =Consumed Scheduled Cycle Time for lot Li

Referring to FIG. 1 again, the value of I.sub.DFL is being calculated for the stage "STkk " as follows: ##EQU4##

In this case, as can be seen in FIG. 1, there is only one lot Li which is lot L1 since in this case "i"=1. Thus the formula above is as follows in this case. ##EQU5##

RCT.sub.1 =Remaining scheduled cycle time for lot 1

CST.sub.1 =Consumed scheduled cycle time for lot 1

L1=Lot L1

N.sub.1 =Wafer quantity of lot L1 (No. of wafers in lot L1)

Referring to FIG. 2 again, equation (2) is rewritten for two lots L1 and L2.

kk Stage with Lots i=1 and 2

##EQU6##

Symbols A.sub.i and B.sub.i are defined as follows:

A.sub.i =RCT.sub.i . . . Remaining scheduled Cycle Time for lot i

B.sub.i =CST.sub.i . . . Consumed Scheduled cycle Time for lot i

Now substitute symbols A.sub.i and B.sub.i into equation (6) yielding the result as follows: ##EQU7##

FIG. 4 shows a fabrication line with four stages STkk where kk=1, 2, 3 and 4. Stage ST1 is located near to the beginning of the line and stage ST4 is nearer to the end of the line QC. Lots L1, L2, L3, L4, L5, L6, L7, L8 and L9 are distributed along the line. As can be seen lots L1 and L2 have passed stage ST4 and are progressing towards end QC. Lot L3 is between stages ST3 and ST4. Lots L4, L5, L6 and L7 have passed stage ST2 and are progressing towards stage ST3. Lots L8 and L9 are between stages ST1 and stage ST2.

FIG. 5 shows the implementation of Dynamically Forward Loading Intensity to the fabrication line of FIG. 4 with the same arrangement of four stages ST1, ST2, ST3 and ST4 in the same locations as in FIG. 4 but with a different arrangement of the WIP which includes six lots L1, L2, L3, L4, L5, and L6. Equation 5 has been rewritten to provide the calculation of I.sub.DFL.sup.2 for stage ST2 which involves the lots Li, L2, L3, L4 which are at or between stage ST2 and end QC.

Referring to FIG. 5 once more, the stage STkk=ST2 is being studied for the lots L1, L2, L3, L4. Lot L1 has traveled 8.5 units and is 3.5 units from the end QC along the 12 unit track from Stage ST2 to end QC. Lot L2 has traveled 6 units and is 6 units from the end QC. Lot L3 has traveled 2.5 units and remains 9.5 units from the end QC. The parameters for stage ST2 are as follows:

                TABLE I
                Lot L1      Lot L2      Lot L3      Lot L4
        Ai      A1 = 3.5    A2 = 6.0    A3 = 9.5    A4 = 11.0
        Bi      B1 = 8.5    B2 = 6.0    B3 = 2.5    B4 = 1.0
        N.sub.i  N.sub.1 = 20 N.sub.2 = 24 N.sub.3 = 6 N.sub.4 = 18

                         TABLE II
                         Lot L1             Lot L2
             Ai          A1 = 3.5           A2 = 1.0
             Bi          B1 = 3.5           B2 = 6.0
          N.sub.1        N.sub.1 = 20       N.sub.2 = 24
                                                    (11)
          ##EQU11##
                                                    (12)
          ##EQU12##
                                                    (13)
          ##EQU13##


    TABLE III
        Lot L1  Lot L2    Lot L3    Lot L4    Lot L5    Lot L6
    Ai  A1 =    A2 = 6.0  A3 = 9.5  A4 = 11.0 A5 = 12.5 A6 = 13.5
        3.5
    Bi  B1 =    B2 = 8.0  B3 = 4.5  B4 = 3.0  B5 = 4.5  B6 = 0.5
        10.5
    N.sub.i  N.sub.1 = 20 N.sub.2 = 24 N.sub.3 = 6 N.sub.4 = 18 N5 = 20   N6 =
     6.0
                                                      (14)
    ##EQU14##
                                                      (15)
    ##EQU15##

    TABLE IV
    STAGE      SIN-2-PHO   POLY-1-PHO    POLY-2-PHO    MET-1-PHO
    I.sub.DFL      1.6          0.7           1.0          1.2

    TABLE V
    STAGE      SIN-2-PHO   POLY-1-PHO    POLY-2-PHO    CONT-PHO
    I.sub.DFL      1.6          0.7           1.0          1.2

• Inventors
  Lo, Chiang-Chou; Hsu, Fang-Jen; Hsieh, Chao-Yu; Lin, Hsing-Chung;
• Assignee
  Taiwan Semiconductor Manufacturing Company (Hsin-Chu, TW)
• Published
  Oct-14-2003
• Current US Classes:
  700/100
  700/101
  705/8
• Application #
  428574
• International Classes
  G06F 019/00
• Field of Search
  700/13 700/14 700/28 700/32 700/46 700/100-103 700/108 700/121 705/8
• Examiner
  Von Buhr; Maria N.
• Agent
  Saile; George O., Ackerman; Stephen B., Jones, II; Graham S.
• US Patent References:
  5396432
  5446671
  5612886
  5721686
  5748478
  5751580
  5768133
  5818716
  5826238
  5838565
  5880960
  5889673