格雷：模拟集成电路课件2-1
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Chapter2Bipolar, MOS & BiCMOSIntegrated-Circuit Technology---Basic Processes in Integrated-Circuit Fabrication ---Typical Processes of Bipolar Integrated-Circuit ---Components in Bipolar Integrated Circuits---MOS Integrated-Circuit Fabrication---Components in MOS Technology---BiCMOS TechnologyBasic Processes in IC Fabrication Objective♦Introduced the fabrication of IC♦Describe the basic fabrication process steps Outline♦Integrated circuit fabrication♦Basic processing stepsSilicon IC Technologies Bipolar Bipolar/CMOS MOSJunction Isolated DielectricIsolatedOxideIsolatedSilicon-Germanium SiliconCMOS PMOS(Al Gate)NMOSSi GateAl GateSi GateAl GateIntegrated Circuit FabricationCompare of BJT and MOSFET Technologies ---Almost every comparison favors the BJT; However, a similar comparison made from a digital viewpoint would come up on the side of CMOS---Therefore, since large-volume technology will more likely be driven by digital demands, CMOS is a reasonable result as the technology of availability.---The potential for technology improvement for CMOS is greater than for BJT ( volume sales drives more research)---Performance generally increases with decreasing channel length, except when considering breakdown voltages and leakage current effectsBiCMOS may be the best compromise for the mixed signal system on a chipBasic Fabrication Process--Oxide growth--Thermal diffusion--Ion implantation--Deposition--Photolithography & Etching (--Epitaxy)9Oxidation9DiffusionHigh concentration low concentration9Diffusion9Ion ImplantationLower temperature processUseful for field-threshold adjustmentAnneal is requiredBetter repeatability (implant dose)9Deposition---Various materials are deposited on the silicon wafer Silicon nitride Si3N4 -> Local OxidationSilicon dioxide SiO2 -> Dielectric isolationAluminum -> Interconnects, MOS gates, inductorsPolysilicon->MOS gates, resistor, capacitors, fuses---Methods:Physical-Vapor Deposition (PVD)Vacuum steam deposition,Sputter depositionChemical-Vapor deposition (CVD)Atmospheric-pressure chemical-vapor deposition (APCVD) Low-pressure chemical-vapor deposition (LPCVD)Plasma-assisted chemical-vapor deposition (PECVD)9Photolithography & Etching9Positive Photoresist9Negative Photoresist9Etching9EpitaxySummary---Fabrication is the mean by which the circuit components, both active and passive, arebuilt as an integrated circuit.---Base process steps include:* Oxide grown* Thermal diffusion* Ion implantation* Deposition* Photolithography & Etching* Epitaxy---These steps are restricted to a physical area by the use of photolithography---The use of photolithography to apply a process to a certain area is called a masking step---The complexity of a process can be measured in the terms of the number of masking steps or masks required to implement the processBipolar TechnologyMajor Processing Steps for a Junction Isolation BJT TechnologyStart with a p substrate1. Implantation of the buried n+ layer;2. Grown of the epitaxial layer;3. p+ isolation diffusion;4. Base p-type diffusion;5. Emitter n+ diffusion;6. p+ ohmic contact;7. Contact etching;8. Meal deposition and etching;9. Passivation and boned pad opening;Implantation of the Buried Layer (Mask Step 1)Epitaxial Layer (No Mask Reqired)P+ isolation diffusion (Mask Step 2)Base p-type diffusion (Mask Step 3)Emitter n+ diffusion (Mask Step 4)P+ ohmic contact (Mask Step 5)Contact etching (Mask Step 6)Metal deposition and etching (Mask Step 7)Passivation(Mask Step 8)Typical Impurity Concentration Profile for the npn BJTSubstrate pnp BJTLateral pnp BJTModification to the Standard npn Technology•Dielectric isolation –Isolation of the transistor from the substrate using an oxide layer ( eliminate parasitic depletion capacitors Æhigh speed)•Superbeta transistors –Use a high thin base width to achieve higher values of β.•Double diffused pnp BJT –Double diffusion is used to build a vertical pnp transistor whose performance more closely approaches that of the npn BJT.•Use of smaller devices to reduce parasitic capacitances Æhigher doping densities to decrease depletion widths Ælower breakdown voltages.Summary☻The objective has been to give a physicalunderstanding of how the npn BJT is fabricated.☻The fabrication sequence for a typical npn BJT has been illustrated☻Methods of implementing other active devices in the npn BJT technology were shown☻Simple npn BJT technology chooses to emphasize the npn over pnp because the npn BJT performance is always superior to the pnp BJT performance. Thus, the philosophy in design is to use the npn where ever possible and incorporate the pnp only where it has to be usedPassive Components in Bipolar ICs * Resistors* Capacitors* High-Performance active Devices compatible with BJT technologyCross-Section of an NPN BJTAll passive components must be compatible with this structureIntegrated Circuit Resistorseohms/squar of units the has and y resistivit sheet a is where ) :e Ohms/squar min y resistivit where ) of terms inexpressed is sheet conductive a of Resistance s ρρρ(ΩWL ρW L )T ρ( R (ΩWTL A ρL R s ==⋅Ω===Base and Emitter Diffusion ResistorsBase Resistor:Sheet resistance≈100 to 200 Ω/sqEmitter Resistor:Sheet resistance≈2 to 10 Ω/sqEpitaxial Resistors Typical resistance is 2-5kΩ/sq.Epitaxial Pinched ResistorEpitaxial Pinched ResistorSheet Resistance is 4-10kΩ/sq;Voltage across the resistor is limited to 6V or less.PN Junction Capacitance Collector-Base Capacitance (Cµ)Capacitance values include thebottom plus side wall capacitance.Cµ≈1fF/µm2 (dependent on thereverse bias voltage)BE capacitance CS capacitanceMOS Capacitor StructureIntegrated Circuit ResistorsBJT diodesDielectric IsolationDielectric Isolation High speed circuitsCompatible High-Performance Transistors*Superbeta transistorsβ≈2000-5000Allow the emitter diffusion to almost reach the collector side of the base creating a very small base width. Reduce the breakdown voltage and Early voltage is degraded.*P-Channel MOS transistorUse the base diffusion to create the source and drain in an n-epitaxial island and thin oxide and metal to form the gate. *Double-diffused pnp transistorDiffuse a p collector into the n-epitaxial region along with a n-diffusion for the base and a heavily doped p diffusion for the emitter.Summary* Showed passive components that were compatible with bipolar technology* Capacitors use pn-junction and are depletion capacitors * Resistors include---Base/Emitter diffused---Epitaxial---Epitaxial pinched* Diodes---Base-Collector shorted diode is the best choice for most applications* Modification to the standard bipolar technology include ---Dielectric isolation---High-performance transistors。
