Micro-Technology Technology & Applications 19 August 2002. Ole Hansen MIC Topics in Microelectronics Outline • Applications - motivation • Micro-Technology – Silicon Starting Material – Microlithography – Pattern Transfer – Material Deposition – Material Modification 19 August 2002. Ole Hansen MIC Topics in Microelectronics 1 Applications of Micro-Technology • Electronics • Sensors & Actuators – IC’s: CMOS, Bipolar – Pressure sensors – Discrete devices – Accelerometers – Power Devices – Gyroscopes – Micro-probes (AFM) • Optoelectronics • Bio/chemical m-systems – Imaging: CCD, CMOS – mTAS – Lasers & LED’s – Cell-sorting – Photodetectors – DNA-chips – Solar Cells – PCR-reactors – Silica Wave-guides on – Katalytic reactors Si 19 August 2002. Ole Hansen MIC Topics in Microelectronics The start of the Silicon Age December 1947: Invention of the Bipolar Transistor Bardeen, Brattain & Shockley 19 August 2002. Ole Hansen MIC Topics in Microelectronics 2 IC’s from 1960 to 2002 Fairchild, Gordon Moore, 1960 First planar IC. 19 August 2002. Ole Hansen MIC Topics in Microelectronics IC Technology History Moore’s Law 19 August 2002. Ole Hansen MIC Topics in Microelectronics 3 Where is the Limit? IBM 1990: STM image STM modified surface, Xe on Silicon 19 August 2002. Ole Hansen MIC Topics in Microelectronics Expected future Si technology SIA roadmap 103 103 ] M [ p ] i h m c / n s [ r s o s 2 2 t e 10 10 s i n s k n c a i r h t t , ] r t i o Lithography b h GateLithography G t 1 1 [ d 10 GateOxide Thick. 10 i Memory Size e z w i e Transistors/chip S n Clockfreq. GHz i y r L o m e 100 100 M 1995 2000 2005 2010 2015 Year 19 August 2002. Ole Hansen MIC Topics in Microelectronics 4 MEMS Non-electronic Applications Comb drive resonator Fold-up mirror Microcantilevers in flowchannel Selective coating Piezoresistive strain gauge Mirror-array for image projection 19 August 2002. Ole Hansen MIC AFM-probes- Topics in Microelectronics Sharp tips on microcantilevers Why Silicon? Technological properties Physical properties • Abundant element ~28% • Appropriate bandgap ~1.1eV • Simple purification – High breakdown voltage • Good crystal quality – No deep traps • Strong & hard material, 7GPa – Indirect-high carrier lifetime • Controllable doping • Reasonable mobility • Good oxide SiO2 – Electrons 1400cm2/Vs – Diffusion mask 2 – Dense pin-hole free dielectric – Holes 500cm /Vs – Good adhesion – Surface passivation 19 August 2002. Ole Hansen MIC Topics in Microelectronics 5 Resistivity vs. doping density An ”Extrinsic” material Dopants: Donors: P, As, Sb Acceptors: B, Al, Ga 1 r = qmnn + qm p p 1 rn » qmn N D 1 r p » qm p N A 19 August 2002. Ole Hansen MIC Topics in Microelectronics Czochralsky Crystal Growth • Low cost • Large diameter crystals ~300mm • Low defect density • Low dislocation density <100/cm2 • High contamination from crucible – O~25ppm, C~5ppm • Heavy metal ~ 1ppb • Moderate resistivity <50Wcm • Moderate carrier lifetime 0.3ms 19 August 2002. Ole Hansen MIC Topics in Microelectronics 6 Heat Poly-Silicon Lumps – Melt it 19 August 2002. Ole Hansen MIC Topics in Microelectronics Molten Silicon 19 August 2002. Ole Hansen MIC Topics in Microelectronics 7 Dip Seed Crystal in the Melt 19 August 2002. Ole Hansen MIC Topics in Microelectronics Pull Seed Rapidly Necking – Eliminates Defects 19 August 2002. Ole Hansen MIC Topics in Microelectronics 8 Slow Pull to Final Diametre 19 August 2002. Ole Hansen MIC Topics in Microelectronics Control Pull Speed Keep Constant Diametre 19 August 2002. Ole Hansen MIC Topics in Microelectronics 9 Almost Finished Crystal Hanging in the Seed Crystal 19 August 2002. Ole Hansen MIC Topics in Microelectronics Chemical Mechanical Polishing CMP Slurry: KOH/H2O with 10nm Silica Particles (KFe(CN)/H2O with Alumina Particles) Semirigid Polishing pad: Global Planarization Etchrate: R=K*p*v 19 August 2002. Ole Hansen MIC Topics in Microelectronics 10 Basic Micro-Technology • Material Deposition • Photolithography • Pattern Transfer • Material Modification – Doping & anneal 19 August 2002. Ole Hansen MIC Topics in Microelectronics Photolithography & Pattern Transfer The Key Technology 19 August 2002. Ole Hansen MIC Topics in Microelectronics 11 Basic Optical Aligners Photoresist Exposure Systems l W » 0.6 Resolution :W » l·G NA l DOF » 2 19 August 2002. Ole Hansen MIC 2(NA ) Topics in Microelectronics Standing Wave Interference Monochromatic Illumination 19 August 2002. Ole Hansen MIC Topics in Microelectronics 12 Photoresists & Photosensitive Materials Photoresists Photosensitive structure removed after pattern transfer materials • Positive interlayer dielectrics & • Negative mechanical structures • Electrodeposited resists • Polyimides • SU-8 Epoxy Spin-on deposition • BCB Cyclotene •Simple process •Good thickness control •Planarising process 19 August 2002. Ole Hansen MIC Topics in Microelectronics Pattern Transfer Etching: Film Deposition Lithography Etch Film Strip Resist MOULD Filling: Lithography Selective Deposition Strip Resist Lift-Off: Lithography Film Deposition Lift-Off CMP: Lithography&Etching Film Deposition Polish (CMP) 19 August 2002. Ole Hansen MIC Topics in Microelectronics 13 Pattern Transfer - Etching Important Parameters Anisotropy Perfect Anisotropy Anisotropic Perfect Isotropy Selectivity Mask Smask = Rfilm/Rmask Film Ssubstrate= Rfilm/Rsubstrate Substrate Selectivity & Anisotropy interaction Conformal Film / Step After Nominal Etch After 100% Over Etch 19 August 2002. Ole Hansen MIC Topics in Microelectronics Dry Etching Reactive Ion Etching- RIE Gas inlet, e.g SF6 -50V 0V F F Plasma Glow RF F F + F F F + F F Cathode Darkspace To Pump Pressure: 0.01-1Torr Etchant :e.g. Atomic Flourine Enhanced by ion bombardment Anisotropy : Sidewall passivation Selectivity: good to poor Gas additives: O:2 Increase F and Silicon etch rate Sidewall passivation - Anisotropy H:2 Decrease F and Silicon etch rate Selective oxide etch SF6+O2 Silicon etch 19 August 2002. Ole Hansen MIC Oxide mask Topics in Microelectronics 14 Wet Silicon Etching in Alcaline Solutions Crystallographic Anisotropy R111<<R100,R110 Boron Etchstop (N>5*1019/cm):3 R~N -4 Electrochemical Etchstop: Anodic Oxidation 54.7o (100) (111) (111) (111) (100) Boron Etch Stop p-type n-type (Positive Bias) Outer corners are attacked by the etch Electrochemical pn Etch Stop 19 August 2002. Ole Hansen MIC Topics in Microelectronics Thin Film Deposition Methods Native Films Physical Vapour deposition - PVD • Thermal Oxidation / Nitridation • Vacuum Evaporation Chemical Vapour Deposition - CVD • Molecular Beam Epitaxy – MBE • Vapour phase epitaxy - VPE • Sputtering – Reactive sputtering • Metals & Semiconductors III-V • Atmospheric pressure – APCVD Electrochemical deposition • Low pressure CVD – LPCVD • Electroplating, Electroless plating • Plasma enhanced CVD – PECVD • Metals • Semiconductors Spin-on deposition • Dielectrics • Dielectrics (Doped glasses) • Metals • Polymers (Photoresist) Wafer Bonding Liquid Phase Epitaxy – LPE • Anodic bonding (Silicon/PYREX) • Semiconductors III-V • Fusion bonding (Silicon/Silicon) 19 August 2002. Ole Hansen MIC Topics in Microelectronics 15 Thin Film Deposition Important Issues Step Coverage Perfect, Conformal Poor Step Coverage No Step Coverage (LPCVD PECVD PVD-evaporation) Trench Filling Perfect Fill Partial Fill Poor Fill Additionally: Growth temperature. Uniformity < 5%. Adhesion. Morphology, stoichiometry & density. Pinhole density < 1/cm2. Stress – built-in and thermal mismatch. 19 August 2002. Ole Hansen MIC Topics in Microelectronics Oxidation Furnaces O2 or H2O Diffusion SiO2 Reaction 800-1200oC Si+O2 ®SiO2 Si+ 2HO®SiO +2H N , O , H , H O, HCl 2 2 2 2 2 2 2 Silicon 2x4 Dummy-wafers 3 Test-wafers 15-190 Production-wafers Typical19 August 2002boat. -load Ole Hansen MIC Topics in Microelectronics 16 LOCOS: Local Oxidation • Silicon nitride mask Silicon Nitride • Low diffusivity of O2, H2O in Si3N4 • Slow oxidation of Si3N4 Oxide LOCal Oxidation of Silicon Silicon LOCOS • Reduced surface topography • Self aligned diffusions • Used in most modern processes • Needs a stress relieve oxide - Pad oxide – Eliminates slip lines in Si 19 August 2002. Ole Hansen MIC Topics in Microelectronics Epitaxy • Single Crystal Films on Single Crystal Substrates • Homo Epitaxy: Substrate & Film Identical – Si/Si, GaAs/GaAs etc. • Hetero Epitaxy: Substrate & Film Different – GaAlAs/GaAs, SiGe/Si Single Crystal Film Single Crystal Substrate 19 August 2002. Ole Hansen MIC Topics in Microelectronics 17 Vapour Phase Epitaxy – VPE The Horizontal Reactor •Indirectly Heated Cold Wall Reactor •Growth Temperature: 1000-1300oC •Pressure ~1Bar or less •Very high gasflow rates Other Si-Sources: •Low Si-compound Molar Fraction Silane: SiH 4 •Quite Low Wafer Throughput Chlorosilane: SiHxCly 19 August 2002. •HClOle Hansen used MIC for pre-epi etch/clean Topics in Microelectronics Elemental Steps in VPE/CVD 1. Convective Gas Phase Transport 2. Gas Phase Reactions: SiCl4+H2 « SiCl2+2HCl 3. Mass Transport to Surface (Diffusion) 4. Adsorption to surface (Desorption from Surface) 5. Chemical reaction on Surface 6. Diffusion on Surface 7. Lattice Incorporation 8. Product Desorption 9. Mass Transport from surface 1 2 9 8 5 3 4 5 6 7 19 August 2002. Ole Hansen MIC Topics in Microelectronics 18 Step Coverage &Trench Filling Important Parametres Source Material: • Flux intensity • Angular Distribution Source/sample: • Sticking coefficient Improved Coverage/Filling: • Surface Diffusivity High surface diffusivity • Surface Reaction Rate Low sticking coefficient