Abstract:
A system and method for recording and addressing out of control (OOC) events in a semiconductor processing line. The method includes steps of (a) opening OOC entries in an OOC database, and (b) working the OOC entries. Opening an OOC entry is performed in response to one or more OOC events in wafer lots being processed in the semiconductor processing line. A lot record addresses an isolated occurrence pertaining to one wafer lot. An issue record addresses a trend of repeated defects or failures. Opening an OOC entry in the OOC database preferably includes assigning and recording an “owner” responsible for addressing the OOC entry. Working the OOC entries includes opening activity records for the OOC entries, receiving user input on corrective measures, and recording the measures in the activity records. The method preferably also includes steps of (c) closing OOC entries after working the OOC entries, and (d) reassigning OOC entries if ownership is transferred for the entries. The system includes (a) a plurality of computer systems, including a plurality of entry terminals, (b) an OOC database coupled to the plurality of computer systems, (c) an OOC interface executing on one or more of the entry terminals and coupled to the OOC database, and (d) an OOC tracking program executing on one or more of the computer systems and coupled to the OOC database and to the OOC interface.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to the field of semiconductor processing and more particularly to tracking and addressing manufacturing issues in a semiconductor fabrication facility. 
     2. Description of the Related Art 
     Fabrication of an integrated circuit entails the sequencing of numerous processing operations. During the manufacture of an integrated circuit from a bare wafer, various layers of dielectric, polysilicon, and metal are deposited, doped, patterned, etched, and polished to form specific features of the circuit such as gates, interconnects, and contacts. The step in this manufacturing process must be performed with care, since successful completion of each step typically depends on meeting some strict requirements. For example, at some steps in a processing sequence, one or more processing tools are used to modify the wafer to produce the circuit features by exposing the wafer to chemical conditions that must be tightly controlled. The various reactant gasses and solutions must generally be introduced with their constituents in specified ranges of pressures and concentrations, and must be used in particular temperature ranges for controlled durations of time. The lithography steps that introduce patterns for various layers onto the wafer have strict tolerances on the mechanical positioning of the wafer and the optical elements of the lithography tools. The polishing steps typically have a combination of mechanical and chemical requirements for successful operation. Throughout the process, a high degree of cleanliness is required to prevent damage to the wafers, and in effect, a contamination-free environment is required in all steps of production. 
     Altogether, a semiconductor fabrication line has numerous criteria for the successful production of integrated circuits. When one or more of these criteria is not met, the adverse situation is often observed only by its resulting effects on the wafer. These effects may be apparent in sensitive test structures designed to indicate adverse events in the processing steps, and they may also appear as failed devices on the wafer. An important task in a typical fabrication facility is the recognition and correction of adverse events in the processing steps to prevent the waste of valuable raw materials and unfinished wafers. The adverse events include instances where the mechanical, chemical, thermal, or temporal criteria are not met in the various processing steps, situations where contaminants are inadvertently introduced to the process, and other undesired conditions. The adverse events can arise from equipment failures as well as from inappropriate actions on the part of facility personnel. A great deal of equipment and personnel time is dedicated to detecting and recording the processing errors and other adverse events, but unfortunately, the collected data are often not used as well as they can be. 
     One reason why diagnostic information is often not fully utilized is that in some cases a previous problem occurs again, but is not immediately recognized as something that has been previously addressed. Thus, time may be wasted “reinventing the wheel” while the correct cause and solution to the problem might be immediately available if the problem were recognized as an old issue. 
     Another issue is that even when problems are detected at an early stage in the fabrication facility, they are occasionally overlooked until they have a significant impact on the fabrication yield. This oversight often occurs from the lack of delegated responsibility to address the detected problem. 
     A third problem in the control of errors and other adverse events in the manufacturing process is the sheer volume of information collected about them. Sorting through the copious quantities of test data from a fabrication facility is a daunting task, even with the aid of statistical-analysis software. Much of the test data gathered is of little or no relevance when taken one piece at a time—early recognition of fabrication problems often depends on noting correlated deviations measured at different points in the process. The large amount of gathered data can greatly reduce the practicality of finding such independent corroborating measurements. 
     These and other problems arise in semiconductor manufacturing facilities trying to address processing errors and other adverse events in their early stages, before the underlying problems run further out of tolerance and cause large amounts of waste that could have been prevented by timely corrective action. 
     SUMMARY OF THE INVENTION 
     Presented herein is a method for recording and addressing out of control (OOC) events in a semiconductor manufacturing line. The method includes steps of (a) opening OOC entries, including lot records and issue records, in an OOC database, and (b) working the OOC entries. Opening an OOC entry is performed in response to one or more OOC events in wafer lots being processed in the manufacturing line. If an OOC event is an isolated occurrence pertaining to one wafer lot, a lot record is opened for the OOC event. If, however, the OOC event indicates a trend of repeated defects or failures, then an issue record is opened for the OOC event. Each issue record may be linked to one or more related lot records. Opening an OOC entry in the OOC database preferably includes assigning and recording an “owner” responsible for overseeing measures for addressing the OOC entry. 
     Working the OOC entries comprises (i) opening activity records in the OOC database, each of which is associated with an OOC entry and includes one or more corrective measures for the associated OOC entry, (ii) receiving user input on corrective measures for addressing the OOC events, and (iii) recording the measures in the activity records. Each activity record preferably indicates the status of corrective measures recorded therein. The method preferably also includes steps of (c) closing OOC entries after working the OOC entries, and (d) reassigning OOC entries if ownership is transferred for the entries. 
     This disclosure also describes a system for recording and addressing OOC events in a manufacturing line. The system comprises: (a) a plurality of computer systems, including a plurality of entry terminals for entering information on OOC events, (b) an OOC database coupled to the plurality of computer systems, (c) an OOC interface executing on one or more of the entry terminals and coupled to the OOC database, and (d) an OOC tracking program executing on one or more of the computer systems and coupled to the OOC database and to the OOC interface. 
     The OOC database is configured to store OOC entries and activity records for addressing the OOC entries. The OOC interface is operable to receive new OOC information, to receive measures for addressing OOC events, and to display information from the lot and issue records. The OOC tracking program is operable to open and modify OOC entries, including lot and issue records, in the OOC database. The OOC tracking program is preferably also operable to close OOC entries after the completion of all measures for addressing OOC events in all the activity records linked to the OOC entries. 
     Each OOC entry preferably has an ownership field, and the tracking program is operable to specify an owner of the OOC entry in the ownership field and to reassign the OOC entry to a new owner. 
     The disclosure further presents a computer-readable storage medium having program instructions recorded therein for recording and addressing OOC events in a manufacturing line 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which: 
     FIG. 1 shows a data structure for a database of out-of-control (OOC) events; 
     FIG. 2 is a flowchart for addressing OOC events; 
     FIG. 3 is an information-flow diagram for opening an OOC entry; 
     FIG. 4 is an information-flow diagram for working an OOC entry; 
     FIG. 5 is an information-flow diagram for closing an OOC entry; 
     FIG. 6 is an information-flow diagram for reassigning an OOC entry; 
     FIG. 7 is a view of an OOC interface screen with information sorted by entry date; 
     FIG. 8 is a view of an OOC interface screen with information sorted by analysis device; 
     FIG. 9 is a view of an OOC interface showing entry fields for a lot record; 
     FIG. 10 is a view of an OOC interface screen showing attachments in an OOC entry; 
     FIG. 11 is a view of an OOC interface screen with information relevant to tool studies; and 
     FIG. 12 is a view of an OOC interface screen showing summary information for a tool study. 
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Described herein is a system and method for maintaining a database for recording and for responding to manufacturing issues in a semiconductor fabrication facility. These manufacturing issues include concerns in the fabrication line, such as processing errors, tool malfunctions, impurities in the reagent gasses and other reactants, and other issues. In a preferred embodiment, the system and method are used to coordinate assessments and responses to out-of-control (OOC) events observed at monitoring points in the manufacturing process. 
     FIG. 1 shows the structure of a database for recording wafer defects and other OOC events. The OOC database holds OOC entries, which may be either lot records or issue records, that document wafer defects and other OOC events observed in the fabrication facility. The OOC database also has activity records, which indicate how the OOC events are to be addressed. The activity records are created in response to be OOC entries, and are associated with the OOC entries for which they were created. 
     Thus the OOC database comprises three types of entries: lot records (illustrated by L 1 -L 6  in the figure), issue records (I 1 - 13 ), and activity records (A 1 -A 5 ). Lot records store information on OOC events in a particular wafer lot. Issue records have information on broader concerns that may affect more than one wafer lot. Actions to be taken in response to these OOC entries are recorded in activity records. Starting from the root of the database shown in the figure, the top level comprises a number of issue records and lot records. Issue records I 1 , I 2 , and I 3 , and lot records L 5  and L 6  are top-level entries in the database. Lot records L 1  through L 4  are for lots affected by the issues listed in issue records I 1  through I 3 . 
     Generally speaking, lots that are associated with a particular issue are called “child lots”, and the corresponding issue is called a “parent issue.” A particular lot may be affected by more than one issue, as indicated by lot record L 2  in the figure, which is a child lot for issues I 1 , I 2 , and I 3 . Lot records L 5  and L 6  are examples of independent lot records, not associated with any parent issues. As illustrated in the figure, each activity record may be associated with a particular lot, as in the case of activity record A 4  associated with lot record L 1 . Alternatively, the activity records may address a larger issue that may affect more than one lot, as in the case of activity record A 1  associated with issue record I 1 . 
     A flow chart for one embodiment of a method for addressing OOC events is shown in FIG.  2 . Upon the occurrence of an OOC event  201 , an appropriate diagnostic tool or an analysis step notifies a user or of the problem in step  210 . At that point the user decides in step  220  whether or the OOC event should be entered as a new OOC entry in the OOC database. In another embodiment of the method, the decision in step  220  is performed by an automated monitoring system. If the OOC event has occurred in a new lot (that is, a lot not previously entered in the OOC database), or if the current OOC event has occurred in a prior lot (previously entered in the OOC database) but at new fabrication level in the process, an OOC entry is opened for the OOC event in step  230 . 
     During the opening, the OOC entry is assigned an “owner”—a person responsible for overseeing the resolution of the OOC entry. By designating an owner for each OOC entry, this method ensures that process control issues in the fabrication facility are addressed by responsible personnel. Ownership may be reassigned, that is, a new owner may be designated for an OOC entry, but new owners are duly notified of their new charges. This system of assigning and recording ownership provides several advantages. 
     Continuity: Ownership is always passed on to another owner, so someone always has responsibility for each OOC entry. 
     Historical reference: A record is maintained of prior owners, so a user may find out who has previous experience with the OOC entry. 
     A requirement of minimum entry by each owner: in a preferred embodiment of the method, each owner has to complete at least one corrective measure toward addressing the OOC entry. 
     Step  240  comprises procedures for working an OOC entry. In step  240 , diagnostic and corrective measures for an OOC entry are recorded in associated activity records, and are carried out to address the OOC events. The procedures for opening  230  and working  240  an OOC entry are described below in FIG.  3  and FIG.  4 . After an owner has concluded the delegated or assumed activities for the OOC entry, a determination is. made in step  245  of the disposition of the OOC entry. If all the required corrective measures in an activity record are completed, the activity record is closed in step  250 . Otherwise, the OOC entry is reassigned in step  270  to a new or previous owner for further working of the OOC entry. 
     In step  250  the OOC entry is closed after all the diagnostic and corrective measures for the OOC entry have been completed. Specifically, if the OOC record is a lot record, it is closed after all the activity records associated with the lot record are closed. If the OOC record is an issue record, it is closed after all of its associated activity records and lot records are closed, Conversely, in one embodiment of the method, dependent OOC entries may also be closed in response to closing an OOC entry on which they depend. If a lot or issue record is closed because the underlying concern has been addressed, all activity records and lot records subordinate to the lot or issue record are also closed. 
     Returning now to step  220 , if the OOC event is determined to be a repeated observation of a previously recorded OOC entry, then a new OOC entry is not opened for the OOC event. Instead, a decision is made in step  260  whether to continue a previously determined set of activities for the OOC entry, or to pass the OOC entry along to a new owner, for example, an operator who observed the new OOC event. If the OOC entry is not passed along then the new OOC event is preferably recorded in the OOC database and the OOC entry is worked in step  240  according to existing activity records. If the OOC entry is passed along, then in step  270  the OOC entry is reassigned to a new owner. The new owner is notified in step  275  of the ownership. Corrective activities under the new owner are preferably recorded in the OOC database. In an alternative embodiment of the method, reassignment of ownership relinquishes control of corrective actions for the OOC entry, and the corrective activities are not recorded in the OOC database. The procedure for reassigning an OOC entry  270  is described below in FIG.  5 . 
     FIG. 3 is an information-flow diagram describing one embodiment of the procedure  230  for opening an OOC entry. In this embodiment, information is transferred between a user  302 , a lot-tracking database  304 , a statistical process control (SPC) module  306 , an OOC interface  308 , and an OOC database  310 . In step  320 , the user logs information on a wafer lot into lot-tracking database  304 . An example of lot-tracking database  304  is the manufacturing software sold under the name WORKSTREAM™. The newly logged information is preferably then provided in step  325  to SPC module  306 , which returns statistical analysis data in step  330  to lot-tracking database  304 . Summary charts and graphical information are preferably then returned to the user in step  340 . If the summary charts indicate that any of the measurements are outside of prescribed tolerances, the user may then invoke in step  345  OOC interface  308  and record the OOC event in an OOC entry. OOC interface  308  is preferably a graphical user interface (GUI) that facilitates data entry by operators in the semiconductor fabrication environment. OOC interface  308  then performs an independent query  350  of the data in lot-tracking database  304 . OOC data received in step  355  from lot-tracking database  304  are recorded into the OOC entry, along with additional OOC information received in step  360  from the user. The OOC entry is then recorded in step  365  by OOC interface  308  into OOC database  310 . OOC database  310  is preferably an OOC database management system (DBMS). 
     In FIG. 4 is shown an information-flow diagram for an embodiment of step  240  (from FIG. 2) of working an OOC entry. (For clarity, elements that are the same as in preceding figures retain the same numerical labels here and in subsequent figures.) During the working of an OOC entry, information on the OOC entry, the status of corrective activities, and analysis information generated by the corrective activities are shared among the user  302 , OOC interface  308 , OOC database  310 , and a notification system  412 . In steps  420  and  425 , the user invokes OOC interface  308  and enters identifying information and other relevant data on the OOC entry. OOC interface  308  updates OOC database  310  in step  430 . In this step, information such as pattern distributions of defects and other OOC events, failure modes, testing conditions, and other data are recorded in OOC database  310 . This updating  430  may be either by manual entry through OOC interface  308 , or through an automated recordation, or through a combination of both. In steps  435  and  440  the user uses OOC interface  308  to create a new activity record for the OOC entry and to assign activities for the OOC entry to one or more owners. The activity records are written to OOC database  310  in step  445 , and the owners are notified in step  450  of the new activities through a notification system  412 . An example of notification system  412  is an automated email-paging network that sends an electronic mail to the owners&#39; pagers. Throughout this process, the user may receive stored information on the OOC entry through links  460  and  465 , in which stored information is provided from OOC database  310  to OOC interface  308 , and is made available from OOC interface  308  to the user. 
     One embodiment of the procedure for closing an OOC entry (step  250  in FIG. 2) is illustrated by the information-flow diagram in FIG.  5 . After the user  302  invokes OOC interface  308  in step  520  to indicate the completion of corrective measures in one or more activity records, OOC interface  308  updates OOC database  310  in step  525  to close the activity records. If this closing of activity records leaves no open activity records for a particular lot record, then the lot record is also closed by OOC interface  308 . And if the closing of other particular lot record leaves no open lot records for a particular issue record, then the issue record is also closed by OOC interface  308 . The closings of the records is confirmed for the user by OOC interface  308  in step  530 . 
     FIG. 6 illustrates one embodiment of the procedure for reassigning an OOC entry (step  270  from FIG.  2 ). As shown in this figure, the reassigning of an OOC entry comprises a transfer of information among an assignor  602 , OOC interface  308 , OOC database  310 , notification system  412 , and an assignee  604 . Assignor  602  invokes OOC interface  308  and delegates a lot record to a new owner, assignee  604 , in steps  620  and  625 . OOC interface  308  updates OOC database  310  in step  630  and notifies the new owner  604  through notification system  412  in steps  635  and  640 . Upon receiving notification of assignment as a new owner of an OOC entry, assignee  604  acknowledges the ownership by responding to OOC interface  308  in step  645 . OOC interface  308  then updates OOC database  310  with the confirmation of the new ownership in step  650 , and notifies assignor  602  through notification system  412  in steps  655  and  660 . 
     FIG. 7 is representative view of a display generated by OOC interface  308 . This display shows OOC entries sorted according to the date on which they were received in OOC database  310 . As shown, the interface screen may be implemented in a GUI software package such as the one sold under the name OUTLOOK™. In other embodiments of OOC interface  308 , the OOC interface screen is created by dedicated software implemented specifically for OOC interface  308 . The OOC interface screen preferably lists the OOC entries stored in OOC database  310  and briefly displays information stored in the various fields of the each OOC entry. The display of OOC entries may preferably be sorted according to data contained in the various entry fields, such as: 
     the date the OOC entry was received in OOC database  310  (as shown in FIG.  7 ), 
     the total number of defects on a wafer, per unit area (TD defect density), 
     the number of additional defects accumulated on a wafer since a prior measurement, per unit area (AD defect density), 
     the type of defect being observed in a given TD/AD measurement (AD/TD major defect type) or 
     the “Quality Measure” (QM), which indicates the number of die with clusters of defects, 
     the posting date of the OOC entry, 
     the layer in which the OOC event was detected, 
     the lot identification number, 
     the pattern in which the defect was detected, or 
     the fabrication tool in which the OOC event occurred. 
     FIG. 8 is a representative view of an OOC interface screen showing OOC entries sorted by the device that observed the OOC events, and then by the layer in which the OOC events occurred. The GUI interface allows further information to be displayed when a particular OOC entry or field is selected by the user. 
     A representative view of an information-entry screen for OOC interface  308  is shown in FIG.  9 . In FIG. 9, OOC interface  308  provides entry fields in which a user may enter information about an OOC event to create a new OOC entry in OOC database  310 . Shown by way of example are a number of fields relevant to the OOC event, including: 
     the lot identification number, 
     the device on which the OOC event was detected (which type of memory, logic unit, or processor), 
     the layer of the wafer in which the OOC event was detected, 
     AD/TD defect densities, 
     AD/TD major defect type, 
     “large totals”—the total number or density of defects with a size greater than a cutoff size, 
     “large adders”—the number or density of additional defects with a size greater than a cutoff size accumulated since a prior measurement, 
     the quality measure, 
     the tool or tools used in processing the wafer lot prior to observation of the OOC event, 
     any previous history of similar OOC events, 
     any relevant observed pattern for the OOC event, 
     any known cause of failure for the tool, 
     corrective actions that were taken or other comments, 
     brief descriptions of any images taken of the wafer, 
     a list of any other lots of suspected to be affected by the same problem, 
     a list of any lots with which the OOC event may be followed up, 
     names of contact people consulted regarding the OOC event, 
     follow-up information on what happened to be wafer lot, 
     any extra scans or testing performance on the wafer lot, 
     any history of wafers that were scrapped as a result of the OOC event, 
     the estimated die-per-wafer loss resulting from the OOC event, 
     the initiator (the person who originally indicated he OOC disposition of the lot), and 
     updates, including results of any extra tests or monitoring of the lot, and an indication of whether or not the lot fabrication was completed. 
     The example information entry screen in FIG. 9 shows a selection tab for “attachments.” Selecting this tab provides a user with a view a shown in FIG. 10, which is a representative view of an entry screen for attachments to an OOC entry. As shown in the figure, additional documents or graphics may be inserted in this screen for association with the OOC entry. These attachments may include images of wafers displaying OOC defects, data files produced by analysis devices, or other relevant information for the OOC entry. In another embodiment, the information entry screen has another tab for a view where raw data may be entered. 
     It is noted that the methods and systems described herein may be used to record and address adverse events in the fabrication facility; their scope is not limited to OOC events. FIG. 11 shows how OOC interface  308  may be used to receive information for tool studies. Since OOC entries may be sorted according to the tool that led to an OOC event or other adverse event, information may be obtained on each tool regarding its history for causing adverse events. In various embodiments of OOC interface  308 , the attached information may be added manually (by the user) or automatically (by a tool that generates the attached information or pictures). Additionally, a user may choose between attaching either a copy of the additional information or a link to an appropriate file on in another database. 
     FIG. 12 is a view of a report screen summarizing information for a tool study. Information entered by a user may be presented in such a screen for rapid dissemination and analysis by other users. In this view, the report screen presents: 
     which tool is being studied, 
     the date of the report, 
     a recorded opinion of whether or not the study raises a new concern, 
     other tools used for comparison, 
     whether the tool under study was the “best” or “worst” in the comparison, 
     at which module in the fabrication line the study was performed, 
     the owner of the tool, 
     if the study is completed, the date it was closed, 
     whether the tool is at the front end, middle, or back end of the fabrication line (FEOL, MiDDOL, or BEOL), 
     whether or not the study is closed, 
     explanations of and comments on the study, and 
     relevant graphs and charts. 
     The sample report screen in FIG. 12 shows information largely entered by a user. In other-embodiments, some of this information and other information may be entered by automated reporting software.