Real-Time In-Situ Chemical Sensing in GaN MOCVD for Advanced Process ControlINTRODUCTIONGaN-based Semiconductor TechnologyGaN Heterostructure DesignAPC ImplementationChemical Sensing in GaN MOCVDStrategy for Real-Time APC (Thickness)Process Variability is a ConcernReal-Time AlGaN Thickness MetrologyRun-to-Run Crystal Quality VariationReal-Time Crystal Quality PredictionImplications – Intrinsic ChemistryRun-to-Run PL Quality VariationReal-time PL Quality PredictionReal-time PL Quality PredictionPre-Process Contamination ControlReal-Time Fault DetectionReal-Time Fault DetectionCONCLUSIONSNov. 5, 2003 1Soon Cho_AVS 50th International Symposium (Baltimore)RealReal--Time InTime In--Situ Chemical Sensing in Situ Chemical Sensing in GaNGaNMOCVD MOCVD for Advanced Process Controlfor Advanced Process ControlMS-WeM2Univ. of MarylandUniv. of MarylandSoon Soon ChoCho, , Gary W. RubloffNorthrop Grumman Corp.Northrop Grumman Corp.Michael E. Aumer, Darren B. Thomson, Deborah P. PartlowNov. 5, 2003 2Soon Cho_AVS 50th International Symposium (Baltimore)INTRODUCTION• Advanced Process Control (APC) has become pervasive in Si ULSI manufacturing– Maintain process targets (wafer-to-wafer or real-time course correction)– Identify equipment faults (fault management)• In-situ chemical sensing is key APC enabler and driver– Quantitative metrology for course correction– Semi-quantitative sensing for fault detection and classification– Semi-quantitative sensing for process understanding• In-situ chemical sensors provide viable quantitative real-time metrology– Better than 1% precision in thickness control (W CVD)– 3 sensors – mass spec, acoustic, FTIR– Real-time end point control demonstrated (W CVD)– Multi-use: compatible with fault detection and process learning• Apply to GaN MOCVD for advanced electronic applicationsNov. 5, 2003 3Soon Cho_AVS 50th International Symposium (Baltimore)GaN-based Semiconductor TechnologyBenefitsBenefits::• Robust, high temperature operation• Larger bias voltage (high power)• Greater speed and bandwidth• Greater power dissipationCurrent Limitations:Current Limitations:• Poor product reproducibility• Process - product quality relationship largely unknown • Poor understanding of intrinsic chemistryHeterojunction Field Effect TransistorSourceDrainGate2DEG forms conducting channelCurrent modulation achieved with variation of gate voltageMonolithic Microwave Integrated CircuitHFET can play a role in:• Power amplifiers• Low noise amplifiers• Mixers• MultipliersNov. 5, 2003 4Soon Cho_AVS 50th International Symposium (Baltimore)GaN Heterostructure DesignCrystal QualityThickness (~100 nm desired)Thin: GaN crystal quality suffersThick: GaN cracksDesire pitted surface for stress relief in GaN layerCrystal QualityMaterial Quality (nbkg< 1014cm-3, even lower desired)Thickness (~1 um thick)4H-SiC(0001) substrateAlN nucleation layerGaN layerAlxGa1-xN capComposition (~30 to 35% AlN)High: breakdown suffersLow: 2DEG diminishedThickness (~20 to 25 nm)Thick: pinch-off voltage increasesThin: 2DEG diminishedAbrupt, high quality interfaces required for all layersCap layer thickness is directly related to transconductanceand the frequency of unit current gain1Tmfgd∝∝Nov. 5, 2003 5Soon Cho_AVS 50th International Symposium (Baltimore)APC ImplementationPLPL, Sheet Resistance, SIMSXRD, PLXRR (AlGaN), PL (GaN), SEM (AlN)Post-processcharacterizationCrystal QualityCompositionImpurities(C & O)Film ThicknessMetric4H-SiC(0001) substrateAlN nucleation layerGaN layerAlxGa1-xN capAPC:Early identification of process excursionsand equipment faultsUpstream acoustic sensing for TMA & TMGImpurities in gas phaseRatio of selected byproduct signals (e.g. Methane/Ethane)Time-integration of selected byproduct generation signals (e.g. methane, ethane)Real-time in-situ measurementPLPL, Sheet Resistance, SIMSXRD, PLXRR (AlGaN), PL (GaN), SEM (AlN)Post-processcharacterizationCrystal QualityCompositionImpurities(C & O)Film ThicknessMetricNov. 5, 2003 6Soon Cho_AVS 50th International Symposium (Baltimore)Pressure transductionto low pressure (mass spec)Inficon Composeracoustic sensorGaN MOCVDPROCESS CHAMBEREMF MOCVD SystemInficon Transpectormass spectrometerSENSORSChemical Sensing in GaN MOCVDProcessGas FlowSensorGas FlowNov. 5, 2003 7Soon Cho_AVS 50th International Symposium (Baltimore)Strategy for Real-Time APC (Thickness)SignalTime100 TorrPressureMultiplexing1E-5 TorrGas SamplingGas Sensing∫ (Signal) dt ≥ Target ?AcousticMassSpecGaN MOCVD ProcessReal-Time IntegrationTMA, TMG, NH3 ÎGaN, CH4, C2H650 TorrReal-Time End Point ControlProcess time as the primary control variable for film thicknessReal-time integrated sensor signalas the secondary control variableIn-Situ Metrology∫ (Signal) dtFilm ThicknessTARGETNov. 5, 2003 8Soon Cho_AVS 50th International Symposium (Baltimore)Process Variability is a Concern• < 25% of semi-insulating runs currently meet thickness target without RT process control• Plenty of sources of process variability – Showerhead design changes, usage– Liner #, usage– Spatial relationship bet. s/h & susceptor– Background impurities• Intentional fine tuning of process recipe is largely overwhelmed by such unintentional process variabilityÎ Significant thickness variation common; Multiple process adjustments and wafers needed to reach target • Real-time process- & wafer-state info requiredG286G287G288G289G290G295G308G346G347G351G357G359G370G379G380G382G383G386G387G400G401G406G409G412G413010020030040025-Mar26-Mar26-Mar26-Mar27-Mar3-Apr30-Apr18-Jul21-Jul24-Jul4-Aug6-Aug28-Aug11-Sep15-Sep17-Sep18-Sep24-Sep25-Sep10-Oct13-Oct17-Oct22-Oct27-Oct28-OctTarget 200-250A RangeAlGaN thickness (A)Run #G287 G288 G289 G2900150160170180190200Mar26Mar26Mar26Mar27Target = 200AControl capability 3A or 1.5%AlGaN thickness (A)Run #Nov. 5, 2003 9Soon Cho_AVS 50th International Symposium (Baltimore)0.01.0x10-21.5x10-22.0x10-22.5x10-23.0x10-23.5x10-20140160180200220240260G287G288G289G290G406G409G413Precision 3.1A or 1.45%Total drift 109A or 51.2%AlGaN thickness (A)Integrated Methane+Ethane signals (Amp-sec)Real-Time AlGaN Thickness Metrology• Goal = maintain target thickness• Metrology must be developed within the relevant local range of thickness variation (e.g. target ± 50A)• Metrology precision ~ 1.5% or 3A in