Abstract:
Controlling stocker capacity in an automated facility and controlling monitor budgets by capped releases, capped FOUP supplies, and wafer reuse methodology. A Database is used to order, track, and reclaim test (monitor) wafers in the FAB. The database automatically controls the amount of FOUPs in the FAB as well as the amount of wafers released into the FAB each day. This database also interacts with the Control Center in helping to release monitor wafers in the FAB.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The invention relates broadly to semiconductor device fabrication and, more particularly, to techniques for controlling inventory of monitor wafers in an automated semiconductor factory (FAB). 
   2. Related Art 
   The following comments are adapted from an article entitled “Tracking the performance of photolithographic processes with excursion monitoring”, by Eric H. Bokclberg and Michael E. Pariseau, IBM Microelectronics. 
   In today&#39;s high-volume semiconductor fabs, photolithographic process steps (wafer prime, resist-apply, expose, bake, and develop) are performed in sequence hundreds of times on hundreds of wafers per day to produce well-defined photoresist patterns. In many cases, these litho process steps are combined into one tool, referred to as a photocluster, that links a resist-process track system with an exposure tool. Because lithography plays a critical role in creating device features throughout the semiconductor production operation, accurate, repeatable photocluster performance is vital, and the individual tools are typically monitored by means of numerous tool checks (inspection procedures designed to evaluate specific components of the process). Examples include resist-film-thickness and hot-plate temperature uniformity measurements on the track, and dose-uniformity and focus-control evaluations on the expose tool. Assessment of defect performance is limited to foreign material (FM) particulate inspections through subprocesses such as resist-apply, develop only, or dry-wafer handling. While the individual tool checks ensure that many of the most critical components of the litho process are within established specifications, they are unable to monitor the interactions between components, which can create out-of-spec conditions in the printed pattern even though individual tools are in spec. Consequently, the integrated litho process is also monitored through inspections and measurements of production wafers. In-line product parametric data are sorted by photocluster and displayed in tool-specific statistical process control (SPC) charts. When out-of-control trends are identified, operation of the problem tools is inhibited until the problem can be investigated and resolved. 
   As long as these inspections occur immediately after the litho process, and the products and levels processed on each tool are consistent from day to day (as in a large-volume, single-part-number fab), this approach to photo tool control works reasonably well. However, as fab product loading becomes more varied, with multiple part numbers and multiple levels being processed on each photo tool, trend identification becomes more difficult and individual photo tool excursions are not always immediately evident. Furthermore, when defect inspection is 1 or 2 days downstream of the photo operation and 3 days worth of data are needed to recognize a trend, thousands of wafers can be affected by a tool problem before it becomes apparent. 
   Detection of a tool problem in the back end of the line (BEOL) may take even longer because prior-level “noise” can obscure defects during in-line inspection, and photo process excursions may not be evident until electrical testing several weeks later. The time delays between when excursions occur and when they are actually detected are critical factors in maintaining wafer yields and device performance—for each day that a defect or dimensional problem remains undetected, hundreds of wafers can be affected. 
   One solution to this problem is to track each tool&#39;s defect and dimensional performance daily with an excursion monitor-a clean wafer that is processed with a unique resist pattern and then inspected for defects and critical dimensions. Because there are no influences from prior levels, the data plots for each monitor can clearly reveal problems that existed too briefly to be identified by in-line product measurements. 
   This article outlines the challenges faced in establishing a daily excursion monitor program and presents examples of process excursions that have been successfully identified. 
   The excursion monitor program that has been adopted by the IBM Microelectronics Division in Essex Junction, Vt., is a daily tool check that identifies photo-process equipment malfunctions and other process excursions as soon as they occur, minimizing product rework, scrap, and yield loss. The concept is simple: a clean wafer is fully processed through a photocluster to create a specially designed resist pattern. The monitor wafer is then inspected, defects are classified, and the resist critical dimension (CD) is measured using scanning electron microscopy (SEM). Defect and measurement data are plotted in tool-specific SPC charts to monitor each tool&#39;s performance and identify trends. Because the excursion monitor is intended to be processed, inspected, and measured in the same way that production wafers are, it has been designed for ease of manufacturability with simple, straightforward patterning that can be integrated within a normal sequence of production lots at any operation. 
     FIG. 1  is a diagram illustrating the excursion monitor process flow. Reclaimed wafers to be used as excursion monitors are initially inspected for FM. They are then delivered to the photocluster, where they are coated with resist and developed using a standard production resist process, except that they are exposed using a reticle specifically designed for excursion monitoring. 
   The aforementioned article describes the process flow of the wafer as it pertains to the use in the FAB and at the process tools. 
   The present invention deals with the wafer prior to entering the FAB for processing and after the wafers are selected for reclaim (last step, upper left, in FIG.  1 )—namely, pre and post processing in the FAB. 
   A common problem with releasing monitor wafers into the FAB is staying within budget. There is also a problem with consistency in controlling the wafers while released in the FAB (releasing and getting the wafers off the floor). (“Controlling” a wafer is the process of releasing the correct part numbers to the FAB, reusing returned wafers in different process areas to reduce cost, and finally reclaiming wafers to an outside vendor. “Releasing” is the process of taking a raw wafer, placing it into a FOUP (Front Opening Universal Pod), and assigning to a wafer route so it can be used in the FAB.) 
   SUMMARY OF THE INVENTION 
   The problem being solved is controlling stocker capacity in an automated facility and controlling monitor budgets by capped releases, capped FOUP supplies, and wafer reuse methodology. 
   It is an object of the invention to tightly control the release of monitor wafer when at the same time controlling stocker supply in an automated factory. 
   Generally, the invention advantageously utilizes a Lotus Notes Database to order, track, and reclaim test (monitor) wafers in the FAB. (Any type of database having saving and manipulating files functionality could be used to implement this process.) This database automatically controls the amount of FOUPs in the FAB as well as the amount of wafers released into the FAB each day. This database also interacts with the Control Center in helping to release monitor wafers in the FAB. 
   “Reclaiming” is the act of taking the wafers out of service (after they are no longer needed) and sending to an outside vendor to be reworked for future use. 
   According to the invention, a method of controlling an inventory of monitor wafers in an automated semiconductor factory (FAB) comprises the steps of: 
   submitting a monitor wafer buy request by a process area (PA); 
   determining whether the PA is under budget; 
   if the PA is not under budget, canceling the transaction; 
   if the PA is under budget, determining the monitor wafer by the database (DF), and 
   releasing the request with either prime wafers, reclaimed wafers or reused wafers, as determined by the database (DF), 
   after the monitor wafers are used in the process areas (PA), returning the wafers to the control center (CC); 
   after returning the monitor wafers to the control center (CC), determining whether or not the monitor wafers can be reused. 
   According to the invention, a computerized method of controlling inventory of monitor wafers in an automated semiconductor factory (FAB) comprises providing a system having at least one computer, and on the at least one computer performing the following steps of manipulating and displaying files:
         displaying a view of MPC (Manufacturing Process Center) On Demand where technicians can view all the monitor wafers that need attention and where the technicians can program the database;   displaying a view of Control Center on Demand where Budget Control Files and stocker Control Files are displayed;   displaying a view of Budget Control Files which is the file that controls the amount of wafer monitors that a process area (PA) can purchase in a set period of time; and   displaying a view of Stocker Control File which is the file that controls the amount of Front Opening Universal Pods (FOUPs) that a process area can have in the FAB.       

   According to the invention, an article of manufacture comprises a computer usable medium having computer readable program code means embodied therein for controlling inventory of monitor wafers in an automated semiconductor factory, the computer readable program code means in said article of manufacture comprising computer readable program code means for causing a computer to effect the steps of the computerized method mentioned above. 

   
     BRIEF DESCRIPTIONS OF THE DRAWINGS 
     The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying figures (FIGS.). The figures are intended to be illustrative, not limiting. 
       FIG. 1  is a flowchart illustrating an exemplary excursion monitor process flow of the prior art. 
       FIG. 2  is a flowchart illustrating an embodiment of the operation of the Semiconductor Factory—Monitor Wafer Purchase and Controls Database of the present invention. 
       FIG. 3  is a diagram of a system having multiple networked computers for implementing the invention. 
       FIGS. 4–9  are drawings of screenshots, such as would be viewed (on computer monitors) by users of the system ( FIG. 3 ) implementing the invention, according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the description that follows, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by those skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. 
   The invention provides a technique for tightly controlling the release of monitor wafer while at the same time controlling stocker supply in an automated factory. 
     FIG. 2  is a flowchart illustrating an embodiment  200  of the operation of the Semiconductor Factory—Monitor Wafer Purchase and Controls Database of the present invention. Various steps are shown, in three categories: 
   Process Areas (PA) 
   Control Center (CC) 
   Database Function (DF) 
   In a first step  202  a monitor (referred to herein as monitor wafer or wafer) buy request is submitted by a process area (“PA”). Next, in a step  204 , it is determined whether the process area is under budget and, if not (i.e., the PA is over budget) the transaction is cancelled in a step  206  (this is a database function “DF”). See also FIGS.  5 , 6 , 7 . 
   If the PA is under budget (“yes” result in  204 ), in a step  208  the monitor type is determined by the database. And, the request is released with either prime wafers (step  210 ), reclaimed wafers (step  212 ) or reused wafers (step  214 ), as determined by the control center (“CC”). 
   In a next step  216 , the monitor wafers are being used in the process areas. See also  FIGS. 8 and 9 . 
   Then, after being used, the monitor wafers are returned to Manufacturing Processing Center (MPC). And in a step  218 , monitors wafers are selected for reclaim when they have reached the end of their useful life. See also  FIG. 9 . 
   Next, in a step  220 , it is determined whether the wafers can be reused. If not, they are sent for reclaim, step  222  (this is a control center (CC) function). If so (“yes” result of step  220 ), in a step  224 , the wafers are assigned to a reuse group (this is a database function (DF)). 
   Next, in a step  226 , the returned monitor wafers are reviewed by an MPC technician, and they are either sent for reclaim (step  228 ), sent for cleaning (step  230 ), or placed in reuse substock for future use (step  232 ). Wafers which are cleaned (step  230 ) also make it to the reuse substock for subsequent use (step  232 ) via a step  234  (Reclaim Group Assignments). 
   As shown in the flowchart, monitor wafers which have been placed in the reuse substock for future use make their way back into the system at step  208  as “reused” wafers. As shown by the step  222 ,  228  wafers which have been sent for reclaimed are effectively removed from the system. 
   The invention is suitably implemented as a software program running on one or more computers, in one or more physical locations.  FIG. 3  is a very generalized illustration of a system  300  one computer  310  (having a keyboard  312 , a mouse  314  and a monitor  316 ) upon which the program and relevant files are resident, and at least one other computer  320  (having a keyboard  322 , a mouse  324  and a monitor  326 ) connected in communication with the first computer via a wired or wireless network  330 . One of ordinary skill in the art to which the present invention most nearly pertains will readily understand how to implement the invention, as described both hereinabove and hereinbelow, based on the functional descriptions and examples set forth herein. For example, the software program can be implemented using Microsoft Windows operating system, and a graphical user interface (GUI) that many of us are well-accustomed to. The computer implementation is all rather straightforward and conventional, and requires no further description. 
     FIGS. 4–9  are representations of screenshots, such as would be displayed on computer monitors ( 316 ,  326 ) by users of the system implementing the invention, as described above. 
     FIG. 4  is a screenshot showing a view of MPC On Demand, according to the invention. This is where technicians can view all the monitors that need attention and where they can program the database. Generally, there is a main window  400  having seven individual, smaller windows  401 – 407 , each of which displays a list to a user. 
   A first window  401  displays a MPC Substock Queue which is where reuse monitor wafers available to be released are listed. A technician can review the available wafers. 
   A second window  402  displays a “MPC Tech Attention Queue” which is where returned monitor wafers waiting to be reviewed by a tech (technician) are listed. The technician can set parameters as to where they are sent. 
   A third window  403  displays a “MPC in Clean Queue” which is where monitor wafers that are good but require cleaning are listed. 
   Windows  404  through  407  contain control files. 
   The fourth window  404  displays “Reuse Routes” which is where monitor routes identified to release as reuse wafers are listed. The technician can set parameters to grade the wafers. 
   A fifth window  405  displays “Reclaim Routes” which is where wafer monitor routes identified to release as reclaim wafers are listed. 
   A sixth window  406  displays “Incoming Group Associations” which is where monitor routes identified to reuse groups are listed. The technician can program the group associations so that all of the wafers are in specific groups for particular uses. 
   A seventh window  407  displays “Bypass Tech Review” which is monitor routes identified to automatically reclaim are listed. The technician can program the group associations so that bad wafers never reach the “Reuse Routes” shown in the fourth window  404 . 
     FIG. 5  is a screenshot showing a view of Control Center on Demand, according to the invention. 
   Generally, there is a main window  500 , smaller window  501  and a smaller window  502 . In window  501 , the technician can program the budget for the manufacturing area and display the “Budget Control Files”. In window  502 , the technician can control the number of FOUPs which hold the wafers and the number of stockers which hold the FOUPs are allowed in the process area. 
     FIG. 6  is a screenshot showing a view of Budget Control File, according to the invention. This is the file that controls the amount of wafer monitors that a process area (PA) can purchase in a set period of time, e.g., week. Wafer monitors cannot be ordered if the budget is exceeded unless a waiver is submitted (see  FIG. 8 ). Generally, there is a main window  600 , and a three areas  601 – 603  within the window. 
   A first area  601  displays a list of current wafer monitor releases for a period of time, such as a week. This provides a reporting tool. 
   A second area  602  displays type of wafer monitor released and where they are located. This provides a reporting tool. 
   A third area  603  displays wafer monitor budgets, by process sector or area. The technician is able to make adjustments or set the budgets for the number of wafer monitors used in each area. 
     FIG. 7  is a screenshot showing a view of Stocker Control File, according to the invention. This is the file that controls the amount of FOUPs that a process area can have in the FAB. Monitor orders are not permitted (are prohibited) if their FOUP supply exceeds their budget. Generally, there is a main window  700 , and a list  701  of stocker budgets by process area. Here the control center (CC) manager can adjust the stocker budgets by clicking at  702 . 
     FIG. 8  is a screenshot showing a view of Budget Increase Waiver form, according to the invention. This is where production managers can increase their budget if extra wafer monitors are needed, such as for unplanned maintenance. (refer to the “waiver” mentioned in the description of  FIG. 6 ). Generally, there is a main window  800 , and a number of GUI items  801 – 807 . Here is where production managers or technicians can increase their budget if extra wafer monitors are needed, such as for unplanned maintenance. 
   The production manager clicks on the button  801  to start the change order, and enters his name. 
   The production manager clicks on the button  802  to enter a reason for the budget change. 
   The production manager clicks on the button  803  to test the increase (or decrease) in the budget change. 
   The production manager clicks on the button  804  to select the project for which a budget change is being submitted. 
   The production manager clicks on the button  805  to enter the amount of monitor wafers by which the budget will be increased. 
   The production manager clicks on the button  806  to submit the budget adjustment. 
   The production manager clicks on the button  807  to exit the form. 
     FIG. 9  is a screenshot showing a view of Process Area Monitor Inventory, according to the invention. This is where users make their wafer buy request, and is used to buy additional wafers to add to inventory. Here can be seen the wafer monitor inventory available for process area (PA) to use. Generally, there is a main window  900 , including the following functions: 
   a button  901  for entering a wafer buy request which is used to buy additional wafers to add to inventory; 
   a button  902  for viewing the weekly wafer monitor budget; and 
   a button  903  for viewing the target number of FOUPs versus the actual number of FOUPs. 
   The present invention can be realized in a centralized fashion in one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system—or other apparatus adapted for carrying out the methods described herein—is suitable. A typical combination of hardware and software could be a general purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein. The present invention can also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which—when loaded in a computer system—is able to carry out these methods. 
   Computer program means or computer program in the present context mean any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after conversion to another language, code or notation and/or reproduction in a different material form. 
   It is noted that the foregoing has outlined some of the more pertinent objects and embodiments of the present invention. This invention may be used for many applications. Thus, although the description is made for particular arrangements and methods, the intent and concept of the invention is suitable and applicable to other arrangements and applications. It will be clear to those skilled in the art that other modifications to the disclosed embodiments can be effected without departing from the spirit and scope of the invention. The described embodiments ought to be construed to be merely illustrative of some of the more prominent features and applications of the invention. Other beneficial results can be realized by applying the disclosed invention in a different manner or modifying the invention in ways known to those familiar with the art. 
   Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, certain equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.) the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more features of the other embodiments as may be desired and advantageous for any given or particular application.