1 Batch Processing – Definition, Advantages, Disadvantages A sequence of one more steps (recipe) usually carried out in more than one vessel and in a defined order, yielding a finished productProduction amounts are usually smaller than for continuous processingRequires reduced inventories and shorter response timesFinal product quality must be satisfied with each batch (no blending)More emphasis on production scheduling in batch processing
2 Other Advantages Batch time can be adjusted to meet quality specs Repetition is conducive to continuous improvement in productSlow dynamics permit real-time calculationsGreater agility
4 Batch Processing Used in Manufacturing Electronic materialsSpecialty chemicalsMetalsCeramicsPolymersFood and agricultural materialsBiochemicalsMultiphase materials/blendsCoatingsComposites
5 Representative processing steps in a semiconductor wafer fab (Deposition, Patterning, Etching, Doping, etc)
6 Unit operations in microelectronics manufacturing are characterized by: Physical/chemical complexityInability to measure directly many process variablesHigh sensitivity to process changesMultiple inputs/multiple outputs
7 CD Variation Effects in Pattern Transfer WaferReticleStepperEtchCDDefectsEdge RoughnessProximity EffectsAberrationsLens HeatingFocusLevelingDosePowerPressureFlow ratesFlatnessReflectivityTopographyRefractive Index ThicknessUniformityViscosityContrastTemperatureUniformityTimeDelayTimeTemperatureDispense PatternRinseAminesHumidityPressureResistPEBDevelopEnvironment
9 Comparative Economics Revenue/Capital1Chemical & Petrochemical 22.4PharmaceuticalSemiconductorCapital productivity is a major driving force for semiconductors_______________1From 1997 US Census Bureau
10 Why Control Critical Dimension (CD)? Small changes in CD distribution = Large $ values lostHigher speedGate CD (nm)210230250270Zero Yield(High leakage)(Low conductance)3s = 12nm3s = 36nm290
11 Figure 19.1 The five levels of process control and optimization in manufacturing. Time scales are shown for each level.
12 Control Hierarchy in Batch Processing Sequential control to step the process through a recipeLogic control to deal with device interlocksWithin-the-batch control to make set point changes and reject disturbancesRun-to-run control to meet final quality constraintsBatch production control to maximize utilization of equipment and minimize cycle time
13 Batch Mixing Tank-Operations Sequence Introduce liquid A until level reaches LH2Close A valve, open B valve and start mixerWhen level reaches LXH2, stop flow of B and the mixer and open discharge valve (VN9)Discharge product until level reaches LL2, then close the discharge valve.
17 Within-the-Batch Control: Operational Challenges Time-varying process characteristics (no steady state)Nonlinear behaviorModel inaccuraciesOn-line sensors often not availableConstrained operationUnmeasured disturbancesIrreversible behavior
20 Run-to-Run (RtR) Control Keeps batch process product on target by using feedback to manipulate batch recipe for consecutive batchesRequired due to a lack of in situ, real-time measurements of product quality of interestExtremely useful where initial conditions or tool states are variable and unmeasurableSupervisory controller determines optimal setpoints for real-time control loops (typically PID)
21 RtR ControlPredominantly used in semiconductor and batch chemical industriesCan be viewed as discrete-time process (k, k+1, k+2 … vs. t)Good for treating drifting processes (e.g. reactor fouling)Run-to-run optimization can be performed using process modelIntegrates with fault detection
22 Use of RtR ControlExamples of events which can have slow dynamics or infrequent step changes- equipment aging- periodic machine maintenance- changes in feedforward signal- measure disturbance- major fault, such as instrumentationdegradation
23 Application: Resist etch process The incoming pattern is masked with linewidths greater than required.An additional step is added to the etch process which etches the resist pattern.The resist etch step trims the lines to the proper resist linewidth.The rest of the etch transfers the resulting mask pattern into the polysilicon, creating the poly gate structures.Linewidth
25 Reduction in STI Rework with RtR Fab 25 STI Rework Rate0.00%1.00%2.00%3.00%4.00%5.00%6.00%13579111315171921232527293133353739411998 Work WeekPercent ReworkManual Implementationof APC AlgorithmAutomated ImplementationStandard SPC ChartingProcess Control
26 Figure 22.19 Batch control system – a more detailed view
27 Characteristics of batch scheduling and planning problems (Pekny and Reklaitis) DETERMINEWhatProduct amounts: lot sizes, batchSizesWhenTiming of specific operations, runlengthsWhereSites, units, equipment itemsHowResource types and amountsGIVENProduct requirementsHorizon, demands, starting andEnding inventoriesOperational stepsPrecedence orderResource utilizationProduction facilitiesTypes, capacitiesResource limitationsTypes, amounts, rates
28 Welcome to the Real World! For a real lot in a real fab, there are:ReworksDifferent process equipment at previous stepsWIP ordering/processingEquipment/Consumable material changesRecipe changes/adjustmentsScheduled/Unscheduled maintenanceMultiple reticle instancesEngineering lots
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