JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV VLSI DESIGN Previous Question Paper (December - 2020 - R16)

Integrated Circuit (IC) fabrication is a multi-step sequence of photographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material, typically silicon. The fundamental steps are as follows:

1. Wafer Preparation: High-purity silicon is grown into a cylindrical ingot (Czochralski process) and sliced into thin wafers, which are then polished to a mirror finish to provide a defect-free substrate.
2. Oxidation: A thin layer of silicon dioxide (SiO₂) is grown on the wafer surface, usually through thermal oxidation, to act as an insulating layer or a mask for subsequent doping.
3. Photolithography: This is the process of transferring a circuit pattern onto the wafer. It involves coating the wafer with a light-sensitive polymer called photoresist, exposing it to ultraviolet light through a photomask, and developing the resist to leave a specific pattern.
4. Etching: The exposed areas of the SiO₂ or other layers are removed using chemical etchants (wet etching) or reactive ion plasmas (dry etching) to expose the underlying silicon substrate according to the pattern defined by the photoresist.
5. Doping (Diffusion/Ion Implantation): Impurities (dopants like Boron or Phosphorus) are introduced into the silicon to change its electrical conductivity. Ion implantation is the modern standard, where high-energy ions are accelerated into the wafer surface.
6. Deposition: Various thin films, such as polysilicon, metal (aluminum or copper), or insulating dielectrics, are deposited onto the wafer using techniques like Chemical Vapor Deposition (CVD) or Physical Vapor Deposition (PVD/Sputtering).
7. Metallization: Interconnects are formed by depositing metal layers to create the electrical paths between individual components (transistors, resistors) on the chip.
8. Testing and Packaging: After fabrication, individual dies are tested for functionality. Functional dies are then diced from the wafer, mounted into protective packages, and wire-bonded to external pins for integration into electronic systems.