2005 Introduction to Microfabrication 1
1.1 Microfabrication disciplines Microfabrication technologies IC industry and related industries MEMS, solar cells, flat-panel displays, optelectronics In-plane dimension: ~1um (0.1~100um) Out of plane dimension: 10nm~1um (0.1nm~100um) 1947: Invention of transistor 1 2
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MEMS 1 m 1mm 10 m 20 mm CNT R e ρul UL = = µ ν 4
MEMS MEMS Interdisciplinary technology -TAS (micro Total Analysis Systems 5
Microelectronics / Optelectronic devices GaAs (III-V LED GaN, ZnO 6
Mechanical devices (~150GPa) Cantilever, Diaphragm structures Pressure sensors Resonators Gyroscopes Switches Micromachines : micro-sensors & actuators (Piezoelectric materials) (Shape memory alloy : SMA) Si 7
Nanotechnology electron-beam lithography: drawing and fabrication of nanometer-sized structure Atomic Force Microscopy (AFM): characterization and manipulation of atomic structure. Superlattices for optelectronics GaAs/ Al x Ga 1-x As nano-machines of biological cells (molecular motors) 8
1.2 Substrates Base materials for deposition and etching Very convenient for microfabrication: Si variety of sizes, shapes : ~300mm variety of resistivities: 1m~20k -cm stable insulator layer : SiO 2 smooth surface single crystal with various orientations cheap strong (but fragile) Other substrates quartz gallium arsenide (GaAs) sapphire, alumina (Al 2 O 3 ) glass metal 9
1.3 Materials crystalline structure Deposition process 1.4 Surface and Interface Structure multi-layered structure surface layer roughness reflectivity chemical stability interlayer: internal stress, adhesion 10
1.5 Process Microfabrication process 1. High temperature process Thermal oxidation dopant diffusion 2. Thin-film deposition 3. Patterning Photolithography» simple CMOS 6 steps; 0.18umCMOS 25 steps 4. Layer transfer and bonding microfluidic channel packaging of MEMS devices 11
MEMS MEMS (Frontend) (Backend) Frontend 1. 2. CVD 3. 4. 5. 6. 7. Backend 1. 2. 3. 4. 12
Si substrate Al thin film Si photoresist Al thin film Si Si photo mask Si Al thin film Si photoresist Al thin film Si 13
1.5.1 Arrhenius behaviour rate Ea = z( T )exp kt Many microfabrication processes show Arrheniustype dependence Etching Oxidation CVD 14
1.6 1.7 Lateral dimensions Device structure : 0.1~100um wire bonding, bump Microfluidics : capillaries, reservoirs Vertical dimension Aspect ratio 2:1 1um MEMS 10um 15
1.8 Devices 1.8.1 Volume devices Currents are generated and transported through the wafer Device structures extend through the wafer Power transistor, thyristror, radiation detector, solar cell 1.8.2 Surface devices Utilizing surface layer in the wafer IC, MOS, CCD» CMOS : only the top 5um layer is used 16
1.8.3 1.8.4 1.8.5 Thin-film devices Devices which are built by depositing and patterning thin films on wafers TFT (Thin Film Transistor) Surface micromechanical devices (switch, microfluidics) Membrane devices Devices on membrane structure Thermal isolation acoustic devices such as filter Stacked devices Devices which are made by layer transfer and bonding techniques vacuum cavity : pressure sensors, accelerometers, microfluidics : micropumps, microvalves, microchannels, 17
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1.9 MOS transistor MOS : metal-oxide-semiconductor MOS 19
1.10 Cleanliness and yield 20
HEPA high efficiency particular air 1ft 3 (30cm 3 ) 0.5um 10 class100=log(100*(100/30) 3 )=M3.5 21
1.11Industries The electronics industry is based on Si semiconductor devices 2002: 10 18 transistors were shipped, the cost was $10-7 a piece. 1968: 10 8 transistors, $1 a piece Device density : Moore s law 22
Moore s Law Gordon Moore: Former chairman of Intel IC 0.18 m Critical dimension (1/2) T/18 months DRAM (2) T/18 months 30nm 23
DRAM 24