IC FABRICATION STEPS
• Wafer Preparation
• High purity Si. Single crystal.
• 10 – 30 cm in dia, 1 meter in length.
• Sliced, 400-600 micron thick. Surface then polished.
• Oxidation
• Oxygen, wet or dry, chemically reacts with Si => SiO2 at 1000-1200 deg.C
• At Si surface, thin SiO2 film, 0.1 – several micron thick.
• Diffusion
• Atoms move thru crystal lattice at 1000-1200 deg.C
• Doping such as n-well, pn junction, etc.
• As, P, B
• Ion Implantation
• Drive Ions into Si crystal by High voltage (100kV) ion accelerator, at room temp.
• Precise control of doping level.
• Depth of penetration well controlled.
• ex) NBL in BJT
• Chemical Vapor Deposition
• Chemical vapors reacts to form thin films.
• Ex) SiO2, Si3N4 .. at T< 500 deg.C
• Polycrystalline Silicon = polysilicon
• Metallization
• To form interconnects (wires), capacitor plates, …
• Aluminium
• Photolithography
• Photographic pattering of circuit on Si surface.
• Photoresist = photosensitive ‘polymeric’ material
• Packaging
• Chip (1-10mm) = 10-1B transistors; Wafer=several 100 chips
• Electrical testing Dicing the wafer into chips Packaging