CHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEWIntroductionThe Integrated Circuit Laboratory (ICL) of the Xerox Palo Alto Research Center has beencreated to meet several long range goals of the corporation. A central activity of ICL is themanagement of a silicon device fabrication facility. This fabrication line will serve both as a quickturnaround facility supporting research in the design of electronic components implemented viaVery Large Scale Integration (VLSI) and as a VLSI fabrication process laboratory supportingresearch in the technology of making VLSI devices.The state-of-the-art integrated circuit processing to be performed in ICL requires asophisticated system for its control. The "clean room" environments used during integrated circuit(IC) fabrication preclude the use of dust creating paper--video displays with their associatedcomputers are much preferred. Support of design analysis and VLSI technical developmentrequires the capture and storage of large amounts of operational and test data. To fully realize thepotential of new techniques in IC processing, detailed and complicated "recipes" will be developedthat are best applied via direct computer control of IC processing equipment.Cholla will provide information handling facilities and computer control of silicon processingequipment. The facilities provided will include:1)A language for IC processing run specification and documentation.2)Computer assisted operation sequence control.3)Capture and storage of operational and test data.4)Computer control of equipment parameter setup and verification.5)Equipment status and performance reporting.6)File facility to provide stored information for analysis.Cholla will be designed and built by members of both the Computer Science Laboratory andthe Integrated Circuit Laboratory. This document will serve as a guide to the framework of thecomplete system. A major consideration in this design is proper phasing of the implementation. Itis not the intention of the designers to provide every possible feature within an initial system, butrather to provide a working system that will allow new features to be added as their utility becomesknown. Components and features of Cholla will be implemented as resources permit. Initialservices will be provided through modification of and additions to existing PARC hardware andsoftware. The Cholla design is such that further pieces of the system, e.g., data analysis, may beadded in a straightforward manner.Plan of this DocumentThere are several ways in which Cholla may be viewed. One may view it from the perspectiveof a process line operator, process researcher, hardware installer, software maintainer, etc. Each offpqGpqpqpqpqpq pqpq _r y[pN Y^ W]H U(N R*1 P2yN89@ LT&= JA GX EE CG AKMy?3+ <1y:Ay81-y51y3?y1)+y.9y,,, *g"= (2c %N #B" !E ^1, )R " rXyzp*1 E/7 =gZ  CHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW2these perspectives will be briefly touched on in this document, but not in as great detail as wouldbe expected by any particular perspective. More detailed information will be available in severalother documents, including a Cholla User's Manual and a Cholla Software Design Document.Cholla may also be viewed as a software system, a hardware system, or a PARC project.Distinctions between these perspectives are deliberately blurred in this document. This documentwill give a consistent overview of the entire project, and should be the first document to read foranyone interested in any aspect of Cholla.The remainder of this document will be concerned with introducing common terms and theirdefinitions, and with descriptions of system components, both hardware and software. As with anycomplex technology, there are numerous concepts that must be understood before one mayunderstand particular systems that deal with that technology. Thus, descriptions of the VLSIprocess line environment and of the computing environment in which Cholla will be implementedwill be given next, followed by descriptions of Cholla, which operates in those environments.The Process Line EnvironmentThe minute tolerances required during the VLSI fabrication process require very specializedequipment and skilled operators. The equipment employed includes furnaces, ion implanters, waferscrubbers, acid etchers, and sophisticated test equipment, to name just a few of the machinesinvolved. Impurities in the substances used can have such a disastrous effect on the end productthat most of this equipment is used within a clean room environment. A clean room is a restrictedaccess area in which dust is kept to a minimum to avoid contaminating wafers in progress in thefabrication process. In such an area, operators must wear protective clothing that minimizes thepossibility of dust entering the clean room environment. Paper, which creates a significant amountof dust, is prohibited in such an environment. Electronic systems that carry instructions tooperators and to machines are virtually required in these clean rooms.Silicon devices are constructed on wafers, small disks which are later broken apart into manyseparate, identical chips when the processing is complete. Usually several wafers are processedtogether and are carried in plastic cassettes, each of which can hold about two dozen wafers. Theentire process of fabricating these wafers usually requires on the order of one hundred individualsteps. Each step is performed at some machine on the fabrication line. These machines are capableof varying the steps they perform according to certain parameters. For instance, a furnace step mayvary in the length of time or particular temperature at which wafers are baked. Parameters areinput to the silicon processing equipment by means of dials manipulated by the operators ordirectly through electronic connections. The entire sequence of steps along with the particularparameters used to produce a silicon chip is called a process. A run consists of one or morecassettes of wafers with a certain set of designs applied to pattern those wafers carried through aparticular process.fpqGpqpqpqpqpq pqpqHYp _Z \*8 ZN Xw K VBH T Z Q*yOR MnF K9V I,1 FB D] =orXy: p%6 78) 5M 3a 1L-s p /_ ,N *\ (xG &CFy$#sp/ !sp=  sp5 oW :sp)5 7s p! 7( )2 fP 16spsp J  =\3CHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW3At several critical points in a run, measurements are made to insure that certain steps havebeen performed correctly and that the process is proceeding properly. Although most sections ofeach wafer are given the same pattern, that of the device being produced, some areas on each waferare used for test patterns which will be used in the testing phases. Some of these in situ testsperformed during processing are destructive to the wafer, and thus a run normally includes severalextra wafers that are carried through the process solely for this kind of testing.After the silicon processing has been completed, several parametric tests are performed on theremaining wafers to check that the devices have been produced successfully so far. Parametric testsare used primarily to check general electrical properties of the finished wafers and are reasonablyperformed at the silicon processing facility. Additionally, functional tests may be performed todetermine if the finished circuit properly performs the task for which it was designed. Functionaltesting is highly circuit dependant, and may sometimes be left to the circuit designer. After testingat the processing facility, the good wafers are broken into their individual chips which are thenbonded and packaged into their completed form, suitable for inclusion on a circuit board.At nearly every step in a run, information must be recorded on exactly how that step wasperformed. This information will later be consulted by process researchers to determine how toimprove the processes. As mentioned above, pencils, pens, etc. cannot be used in the processingenvironment. Electronic systems for recording such information are required.For a wide variety of reasons, not every section of a wafer that is destined to become a finishedchip will actually be fabricated properly. The percentage of good chips that are produced in a runis called the yield. One of the main goals of process researchers is to find processes that result inimproved yields. Flaws in circuit logic design (as opposed to flaws in circuit manufacture) thatresult in the silicon device not performing as desired are not the concern of the device maker, anddo not affect this yield measurement. To an electronic component designer, a silicon processing line is a place to which a design issubmitted and which returns packaged silicon chips that implement that design. Such a person isfor the most part unconcerned about the actual workings of the processing line or even with thedetails of the specific process used to create these chips. At a gross level, this designer is interestedin the general process used, such as NMOS or CMOS, as these choices restrict the particular logicdesign techniques that may be employed. The designer may be interested in properties of theprocess that affect the speed and power requirements of the resulting devices as well. However,beyond the choice of the general process and some general goals, the logic designer usually careslittle about the specific parameters used during the production of these chips.The component designer is concerned with the turnaround time required for the production ofthese chips. Typically, several iterations of the design process followed by device manufacture willbe required before a properly operating device is made. For these reasons, a quick turnaroundprocessing line is desirable for a research environment. The customers of the ICL processing linewill generally not be concerned with high volume production, but with fast, high quality, limitedproduction.fpqGpqpqpqpqpq pqpqHYpy_$8 \ R Z20 XwSsp VBH T RyQs p O^ Mn@# K9=s p I30 FM D6+ BespspFy@0D =K ;F 9My7\a 5'+8 2 spI 0\ .+8 ,S&y*^ '$< %I #;/ !JC '5 M S vOyAE  E ^ R m S 8 2 =g]DCHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW4Thus, there are many requirements placed on the operators of the processing line and on theprocess researchers. Each run through the line will be different in many ways, with varyingprocesses and designs. Process researchers must be able to gather and analyze informationregarding the performance of the line and to quickly change its operation. Operators must be ableto apply varying processes to their individual runs without reducing quality.Two ways of using operators on a silicon processing line are possible. These are called thespecialist and the modelmaker approaches. In the specialist approach, each operator is used forspecific steps only, similar to the traditional operation of an assembly line. This approach maywork well for high volume production lines, where the process applied never varies. On the otherhand, the modelmaker approach allows an operator to carry a single run through every step in itsprocess. This approach is considered to be preferable in a highly variable processing environmentas in the ICL, and it may well instill more pride in craftsmanship of individual runs. Althoughthere may be specialists operating a few of the machines at the ICL, it is primarily the modelmakerapproach that will be employed in the ICL processing line.Another aspect of the processing facility is its rapidly changing nature. Silicon devicefabrication technology is currently changing constantly, as new processes are discovered that providedenser packing of components on a chip with better yields. The equipment used on the ICLprocessing line will change frequently, with the associated requirement that a system used for itscontrol be able to adapt to these rapid changes.Life History of a RunTo better understand the requirements of a system to control the ICL processing line, thefollowing model of a run's history is given.Before a run begins, several events will have taken place. A circuit designer will have prepareda cicuit layout using various Computer Aided Design (CAD) tools. This will result in a set ofmasks, patterns to be applied to the silicon wafers at different steps in the fabrication process.These masks will be applied to form the different layers of silicon which together will implementthe designer's device. Most likely, the designer will have simulated the performance of this device,but real testing will await the actual delivery of the finished chips. (The CAD systems are not apart of Cholla; they are being built outside of this project.)When a design in the form of a mask set is ready, the next step is to select the process to beused to produce the silicon wafers. Usually a process researcher will make the decision as toprecisely which process to use, although the circuit designer may participate in this decision. Aprocess definition will be entered into Cholla, along with additional information such as testprograms, mask set, packaging requirements, and cicuit designer identification. A process definitionincludes all details regarding the processing steps for the run. These details cover which machinesfpqGpqpqpqpqpq pqpqHYpy_W \A Z+/ Xw] VBMyT X Qs ps pC O/2 Mn=$ K900 IV FE DX Be:y@0A =?& ;I 9b 7\0 01rXy,p*/ *,y(x3. &CA $sp P !C e o&< :>yB ,2 P fY 1?& U J =ZU$CHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW5will be used in which sequence and all parameters to be used at each step. Some steps will beperformed under direct computer control; in these cases, the recipes (programs) for interacting witheach piece of equipment thus controlled will be specified. The total information entered regardingthese steps and parameters thus constitutes the run definition.The run definition is then entered into a priority queue of pending runs. The manager of theprocessing line will make the decisions regarding when a run will begin. Among other things, anoperator will be assigned this run when it is activated. When the run is activated, it enters the setof active runs. While in either the pending or active run sets, this run's status (current step number,etc.) may be monitored by the processing line manager.After being activated, the run is in the hands of its operator. Its wafers will be taken from stepto step by this operator, who will perform all or nearly all actions. These actions include thebuilding up of new layers of silicon on the wafers as well as the in situ tests. Cholla will beconsulted by the operator for exact instructions at each step. All steps will require information tobe input back into Cholla regarding its performance. Such information as the time at which thestep began and ended will be entered by Cholla automatically. Other information specific to eachstep will be entered by the operator. Some steps will have direct control of input to the processingequipment from Cholla. Additionally, Cholla may receive results for some steps directly from theprocessing equipment. At each step, the process line manager may query Cholla to find out thestatus of this run.When the wafers have been completed, they are transferred to the parametric testers. Thesteps to be performed for such testing are also listed in the run definition held by Cholla. A largeamount of information will typically be generated during the test phase. This information too willbe stored by Cholla. Packaging and possibly more testing will also be performed. These steps, likethe other steps, are also controlled by Cholla. Finally, the packaged chips will be finished, with allinformation regarding their creation saved on the Cholla file store.Not directly involved with a particular run, but important to the process researchersnonetheless, is a large amount of general data. Such information as environmental factors, e.g.,clean room temperature and humidity, may be entered into Cholla's files. Other informationregarding materials used at different times, etc. may also be entered.The Computing EnvironmentThe ICL is a laboratory in the Xerox Palo Alto Research Center. At PARC a rich and uniquecomputing environment has been in place for some years. Key components of this computingenvironment are small, personal computers, linked to one another by means of a passivecommunication network called the Ethernet. The Ethernet, a simple length of coaxial cable, onwhich each conected computer may send and receive packets of information, makes distributedapplications possible.fpqGpqpqpqpqpq pqpqHYp _<" \S Z Y Xw0s pyVB! ,SC *B ''7 %I #>" !Jf rX s yLpB sp1 ,8 b =g[oCHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW7be stored locally (on a disk connected directly to a processor running a program that uses the file)or remotely (on a disk connected to some other processor in the network). Remote files offeradvantages in that information is sharable, i.e. it may be accessed from several different computers,and that information is stored in only one place, insuring that the information is always correct andcurrent. When a portion of a disk file is required by some computer in Cholla, a request is sent tothe File Store, which will return the specified portion or write upon the specified portion asrequested.With the File Store used in this manner, several separate computers may read the sameinformation at the same time. Only one computer may modify this information at any given time.The File Store machine will make sure that the information used throughout Cholla is consistentand checkpointed to reduce the possibility of disruption due to failure of any system component.The current candidate systems for the Cholla File Store are IFS (Interim File System) that is incurrent use in the Xerox Internet and the Juniper File System, an experimental filing system beingdeveloped at PARC. The choice of which file store to use depends on several factors, among whichare availability of suitable hardware for either system, availability of software usable in Cholla andmaintenance of such software. The other parts of Cholla are designed in such a way that eitherkind of file store will be compatible with Cholla.PrinterAn electronic Xerographic printer, probably a Dover or Penguin printer, is included in Cholla.The printer will be used by the scientists working in ICL in the ways that computer printers areusually used. In addition, the printer provides an important backup facility for the operation of theICL fabrication line. Standard procedures will include printing the run definitions for each activeand pending run at frequent intervals (say, once per day). In case of a system failure, the rundefinitions will be available, and the fabrication line will be able to proceed in a manual mode,much the same as it operates today.Eventually, a color printer (Puffin) may be added to the ICL computing environment. Outputfrom the CAD systems may be printed on this printer, providing better graphic indications thanblack and white printers can. No support for color printers is included in the initial Chollaimplementation. Such support may be added during later stages of the Cholla project.Process FollowersOperators on the fabrication line will use the computers indicated as "Process Followers" inFigure 1. These machines will read the run definitions as stored on the File Store, and will be usedfor input of results into the run definitions by the operators. When direct control of a piece ofprocess line equipment is provided, initiation of such control will be performed at a processfollower.fpqGpqpqpqpqpq pqpqHYp _&> \ =sp ZS Xwa VBT T V Q yO0% Mn'8 K9.1 I`yF] Db BeO @0V =_ ;2 6Bsy2p6( 0M . Y ,Td *X 'Q %#y#$7 !KV U U ]sXyp*2 '> Y o#: : =]CHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW8These process followers are redundant with one another in that all such workstations may beused by any operator interchangeably. Storage of the run definitions on the File Store makes thispossible. There will be several process follower workstations in the clean room. The number ofthese workstations required depends on the number of operators expected to be working at anygiven time, on the layout of the fabrication area, and on the expected congestion at any location inthe fabrication area. The general criterion for placement of process follower workstations is thatany operator should have convenient access to a workstation at any step in the fabrication process.As different areas of the fabrication line are separated by doors and large pieces of equipment, andmore than one operator is expected to be working in the same area at some times, severalworkstations are required. In the initial Cholla installation, the number of process followerworkstations in the clean room will be five.Equipment ControllerThis computer is responsible for the direct control of individual machines on the processingline. Several pieces of process line equipment are capable of receiving parameters electronically andof sending back results or of being monitored electronically. The Equipment Controller willinteract with such machines in the style appropriate for each machine.Many of the process line machines are capable of direct connections via an RS 232C interface.The RS 232C links will connect directly to another component of Cholla, the Data Line Scanner,which itself is connected to the Ethernet. The Equipment Controller will communicate with such aprocess machine via the Ethernet, through the Data Line Scanner machine and the connecting RS232C link (see Figure 1).The Data Line Scanner is an existing machine in the PARC network. It has the capability ofconnecting to up to 64 different RS 232C links. It is capable of processing the signals in and out ofthese links and of receiving and sending packets on the Ethernet, but not much more. The"smarts" involved in interacting with the process line machines will be contained therefore in theEquipment Controller.The Equipment Controller itself will have a Rushmore board for interfacing to IEEE 488 links.Several pieces of equipment on the ICL line (particularly test equipment) use this type of interface.Such machines will thus be directly connected to the Equipment Controller rather than indirectlyconnected through the Data Line Scanner.In the (distant) future, microcomputers containing Ethernet interfaces may be built. Suchmicrocomputers may be directly installed with process line equipment, allowing in essence a directconnection of the process line equipment to the Ethernet. Such an arrangement would be thesimplest form for interaction between Cholla and the process line machines as control informationcould be sent directly via the existing Etherent, bypassing the extra links required today.fpqGpqpqpqpqpq pqpqHYpy_X \W ZH Xw&6 VB=' T M QZ O.6 MnA K9@ I, CsXy@1pJ =` ;#9 9Fy7]] 5(*4 2A 0F .y,TC */7 'J %6, #y!K] R 00 (ywM B(:  T J [ \=XCHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW9Mail ServerAs Cholla is based primarily on the Laurel Message System, electronic mail offers a convenientmechanism for communication of information such as run definitions and auxiliary informationsuch as environmental measurements. The mail server will hold mailboxes for the Cholla systemand several of the process researchers at ICL. This component of Cholla will be taken as is fromthe Laurel group at PARC.There are several reasons for including a Mail Server in ICL. Although an IFS-type File Storeincludes a Mail Server within itself, the File Store performance can be adversely affected byrunning mail service concurrently with file service. The Juniper File Store does not include mailservice within itself. The electronic mail system that we use at Xerox is based on a transportmechanism that is the subject of research at PARC. As this mechanism evolves, its newest featureswill be available in the standard Mail Server supported by the Laurel group. Newer features of thismechanism will not become available in IFS mail servers. To remain compatible with this system, aseparate Mail Server is indicated.As newer features of Mail Servers become available, Cholla will be able to use them to providemore automated services of its own. For example, by using messages with special types, Cholla willbe able to include intelligent message readers that can add data to Cholla files automatically. Thecombination of standard Laurel with such message reading programs will provide a convenientinterface for the capture of various kinds of data, including environmental factors, materialsdeliveries, etc.The Mail Server is only one example of the leverage the Cholla gains from its association withthe computing network at PARC. As with the File Store, another existing PARC project, the MailServer offers substantial benefit to Cholla.Test Input WorkstationThis workstation is indicated in the schematic diagram of Figure 1 as the Process Follower inthe Test Equipment Area. It is identical in function to the process follower workstations in theclean room. This workstation will be used for instructions to the testers and for input of testresults.Process Manager WorkstationThis computer is essentially the same as a Process Researcher's workstation. The manager ofthe ICL processing line will use this workstation and will generally run special software for statusmonitoring, initiating runs, and for demonstrating the system to visitors. This workstation will becapable of running any Cholla user software including the process follower software that theoperators use.fpqGpqpqpqpqpq pqpqHYp _sX y[pJ Y2* W]W U(P RyPX N] LTF J&9 GE EL CS AK"y?S <1sp :@$ 8wA 6BM 4 y1M /G -n, 'sXy$pB "fH 1 T  xsXy)p*2 d H J U  ^ =g[CHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW10Process Researcher WorkstationsICL will have a large community of process researchers. These researchers will use their ownpersonal computers, much the same as other researchers at PARC use personal computers. Processresearchers may run any software that is available, but will generally be interested in specificpackages for the tasks they are interested in. Included in the specialized software these machineswill run are CAD software and software for the analysis of Cholla data. Although the software thatis run by these researchers is not part of Cholla, the a large amount of Cholla data will be accessedthrough these workstations. We include these workstations in our inventory of components forcompleteness.Software ComponentsThe design of software is an iterative process. A design leads to implementation, which in turnprovides information that modifies the design. Of particular importance in this process is the speedperformance that is obtained by the software under construction. The performance of a softwaresystem is critical with regard to user acceptance, yet is difficult to predict on the basis of a designonly. Thus, the software design presented here is at a broad and general level. The Cholla systemwill function generally as outlined here, but its eventual implementation will undoubtedly beshaped by experience during its construction.When designing an ambitious system as Cholla, it is tempting to try to automate everyfunction. We have attempted to do the opposite--every function should be capable of beingperformed manually. We do this for two reasons. First, it will allow a gradual introduction of thesystem into the production environment. Instead of needing a large, complete set of automatedfunctions before any piece works properly, we will be able to bring the system up piece by piece.As time and resources permit, additional functions and more automation of existing functions canbe included in the system. Second, the system should not be so complicated that should a part of itfail, the entire fabrication line would effectively be shut down. Manual backup procedures will beavailable to overcome the temporary (or even permanent) failure of any piece of Cholla. Process and Test Data StorageUnderlying the entire software design is the design of the formats in which data is kept by thesystem. There are general requirements on this data that indicate proper means of storing all data.These requirements include:1)Flexibility: Data will be accessed by different means for different purposes. Some ofthese purposes are known today, e.g., access by process followers. Other purposes are notknown specifically today, e.g., retrieval for data analysis. This requirement suggests storingthe data in as general and unencoded form as possible.fpqGpqpqpqpqpq pqpqGp _sXy[p"; YV W](8 U(S RH PT NA LT E)rXyAp00 ?23 =p@ ;;Q 9J 6#: 4-y2g-( 02Z -M +=! )G '^` %)9+ "c X ;sXyp_ d y*0'V B 6 . D=]CHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW112)Robustness: Data should be stored in such a way that its integrity is preserved even in thepresence of software or hardware failures. Furthermore, should the data become damaged,it should be repairable using simple tools, such as a text editor.3)Access time: Certain applications, e.g., process following, require fast access to the data.Other applications, e.g., data analysis, may be able to cope with somewhat slower accesstime.To meet these requirements, data will generally be stored in the form of Laurel mail fileshaving a variety of structured, unique names. These files contain only text; therefore they may beread by a wide variety of existing programs. A special structure, the Laurel Table-of-Contents file(or TOC file) provides fast access to any message contained within such a file. In general,information will be stored as individual messages within Laurel mail files.Each message will conform to a simple kind of structure. The form : will be used for storage of parameters and results within messages. A table of formats for's specific to particular 's will be kept by Cholla and will be used to aid inthe extraction of data. In addition, range checking can be provided via this table along with format,so that Cholla can check input for conformance to expected norms.Test data is generally produced by special purpose equipment in specific formats. Such datawill be stored as separate files, with their own unique names. Messages in the run definition mailfiles that correspond to testing steps will have fields for the file name(s) of associated test data files.Through this simple technique, lengthy test output is associated with processing steps withoutdisturbing the mail file structure of the run definitions.The standard naming and directory functions provided by the File Store will be used to keeptrack of the collections of files associated with each run. By using appropriately constructed namesfor Cholla files, searches and access to data will be quite fast. We are consciously avoidingcomplicated database style storage as this tends to slow down even routine data access. WithCholla's simple formats for the storage of all data, other programs for purposes not yet understoodcan easily be constructed to access the data stored by Cholla.The File Store must support remote access with multiple readers. Generally append access isall that is needed for writing, as new files will be built by appending rather than by writing inplace.Process DefinitionStandard process definitions will be stored in the form of Laurel mail files. A utility programwill be provided for the construction of such files from scratch or from existing mail files.Generally, a new process will be defined by slightly modifying an existing process. Such a newprocess will be stored as a completely separate mail file, so that each process definition can be easilyaccessed or compared.fpqGpqpqpqpqpq pqpqGpy_5'\ MZByXT PV<SyQE O` MK,8 KA HKyFB#DwX BBO @ %A =;+ ;Ay9nS 79c 50; 2^ 0:y.eK ,0] )E 'B %c #\>y!'A O  9sXyp:& E J K^  =];CHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW12Run definition will generally be accomplished via the message system. A designer will send amessage containing run related information to the process line manager. Such a message willgenerally include the name of a process definition file, the names of masks to be used with this run,identification of the designer, and any special instructions.The process line manager will create a run definition file as follows. First, a copy of theprocess definition file is made. This copy is the run definition. Next, the first message of the rundefinition is modified by inserting information from the designer's message. Note that thismodification process is essentially the same as that performed by the line operators using theProcess Following portion of Cholla. Finally, the run definition is stored on the File Store withappropriate names. This accomplishes the insertion of the run definition into the pending runsqueue. Activation of the run is performed using similar techniques of message modification andfile naming.Modification of a run definition after that run has become active is also possible. The generalstrategy is that steps which have already been performed are not modifiable, but the portion of therun definition which has not yet been performed is modifiable. The same utility program thatallows initial process definition will also allow run modification. We expect that such modificationswill be performed infrequently.Process FollowingThis is the part of Cholla that the operators will use as a normal part of their work. The stateof the run definition files in the File Store will mirror the actual state of the wafers in the run. Anoperator will log on to a Process Follower workstation and identify the particular run beingattended to. A Laurel-like display (see Figure 2) will show a range of steps surrounding the currentstep (or steps) in its table of contents area. Any step may be displayed in the displayed messagearea, and a current step may be displayed in the composed message area. The operator will readthe instructions for the current step and perform them. Any results that are required for this stepwill be entered into the step through the text editor and some will be checked automatically byCholla for consistency. Several fields will be filled in automatically, such as the time the step wasstarted, the time the step was finished, the operator's name, etc.An operator will be able to view the history of this run by selecting and displaying anymessage from the run definition. Steps already performed will have all result fields filled in.Steps not yet performed will have several blanks for insertion of result data. The operator will beable to get more specific information regarding a particular step by invoking an "Explain"command, which will display a detailed message regarding operation of a piece of equipment.Some steps may have automatic loading of parameters to and retrieval of results from processequipment. Starting, stopping, and interrupting equipment control will be accomplished through aset of commands given through the process followers. Such commands will have the effect offpqGpqpqpqpqpq pqpqGpy_E \F ZT Xw=yVB= T ^ QF OG Mn6, K9M I[ F yDQ Be X @0 O =S ; 6BsXy2pB 0h .K ,TJ *<& '_ %I #.1 !K,: By4$ U w); B%5  [yG W nL '>gZ$CHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW13transmitting information from the process follower through the equipment controller to thecontrolled equipment and back again to the process follower. The actual task of controllingprocessing equipment is performed by the Equipment Controller, leaving the process follower freeto perform other tasks while the controlled step is in progress.This direct control of IC processing equipment is purely an optimization of manual control.This functionality is provided to increase processing line throughput and reliability. It is not anessential feature of Cholla, and any direct control step may be performed manually.Status ReportingReporting the status of runs will be performed by examining the files in the file store. Specialdirectories and names of the files contained in those directories will be used to determine whichruns are in a particular status. To determine the detailed status of a particular run, that run's fileswill be found and examined to determine information such as current step number, etc.The current status of particular pieces of processing equipment, e.g., furnaces, will also beavailable. This service will be possible for equipment that is capable of being checked by theEquipment Controller. As more processing equipment is installed that allow this function, thescope of equipment status reporting will increase.The status reporting subsystem of Cholla will be a separate program that may be run on anyworkstation. Typically, this program will be run on the Process Line Manager's workstation, but adesigner wanting to know the status of a particular run will also be able to run this program. Theprogram will be designed to return the status as of the time that a status request is made. Byputting the status request in a loop so that it is done at regular intervals, the illusion of continuousmonitoring can be provided.Equipment ControlThe Equipment Control subsystem as outlined here is a rather ambitious part of the Chollasystem. This piece involves software for which we do not have much experience, and thus may notbe available in the first releases of Cholla. The overall Cholla design does accommodate this part,so that when it does become operational, it will mesh smoothly with the rest of Cholla.The Equipment Control subsystem will be capable of talking to various pieces of process lineequipment. This software will communicate with such equipment via RS 232C links (actually viathe Ethernet through the Data Line Scanner machine and its RS 232C links), IEEE 488 links ordirectly via the Ethernet. Continuous monitoring of equipment will not be provided. Instead, theEquipment Controller will send initial parameters to equipment, and it will poll the equipment forstatus and/or results. (Initially, it may not even poll, but just ask for results in response to specificcommands issued by an operator at a process follower workstation.)fpqGpqpqpqpqpq pqpqGp _> \H Z(8 Xw@yVB[ T !C QS LTsXyIpH FA DB& BfUy@15( =O ;P 92y7]-- 5(` 230 0U .,< ,T &sXy#pN !L` K Wy O x4* C*2 G D ^ oB (=gZCHOLLA: A COMPUTER ASSISTED SILICON PROCESSING LINE--OVERVIEW14Each separate piece of equipment that is capable of direct computer control has its ownparticular format for submission of parameters and return of results. Parameters for the control ofequipment will be contained in run definitions in a readable text form. These parameters will haveto be transformed into the particular sequences and codes expected by that piece of equipment. Aseparate, small device driver, or "recipe" will be developed for each piece of processing equipmentto be controlled this way. These recipes will be stored on the Equipment Controller (or perhaps onthe File Store) and will be referred to by name in the run definition step that calls for such directcontrol.Data Analysis InterfaceA significant goal of Cholla is to provide process researchers with information about runs thatmay be analyzed to provide insight into how to perform these processes better. The types ofanalyses that might be performed are limited only by one's imagination. In fact, limiting the typesof analyses to some fixed set of services would be extremely shortsighted. As a result, this portionof the system is left open ended.Rather than provide specific analysis programs, we will provide the raw data from which theanalyses can proceed. The format of the mail files used by Cholla will be published and strictlyadhered to. In addition, Cholla will provide a simple parser that will be capable of extractingspecified fields and values from the stored run definitions. We expect that process researchersthemselves will write software (or contract for software) that will perform the analyses that theyconsider appropriate. Since the data to be analyzed is stored in relatively simply structured files,analysis programs may be written in any language convenient to the process researcher. The parserwe provide will be a separate subsystem and return its results in a file, so problems of incompatiblelanguages will not arise. In fact, the parser will be quite simple, so that it would not be a majortask to translate it into some other convenient language.If analysis programs are to be run on a separate machine (say a VAX) then it would beworthwhile to have this parser translated so that it too could run in the same environment.Alternatively, one could perform analyses in a number of steps, running the parser on aworkstation, transferring the results to the analysis machine, and then running the analysis. If sucha separate machine is used, the main problem will be whether it can directly access the informationon the Cholla File Store. If so, then translating the parser and running it on the analysis machinewill be worthwhile. If not, the three step process described above should be used.fpqGpqpqpqpqpq pqpqGpy_D \.6 ZR XwE VBK T 8+ QR O JsXyFpM DS Bf40 @1R =!y;/, 9G 7]G 5(E 2"@ 0(= .Q ,TU *<( '9y%'. #4' !K G  ^ D \ wS 0=O TIMESROMAN  TIMESROMAN TIMESROMAN  TIMESROMAN    $ -5=EMU] fnvj/yw0 cholla.bravoBrotzUnknown