Integrated circuits are formed on small silicon chips and can be categorized based on the number of logic gates as SSI, MSI, LSI, VLSI, or ULSI. The fabrication process involves growing layers on the silicon wafer through steps like epitaxial growth, oxidation, photolithography, diffusion, and metallization to connect components. Photolithography is a key step where a light-sensitive photo-resist is used to selectively expose and remove silicon dioxide, allowing impurities to be introduced to create different circuit components on the chip.

1. Integrated Circuits
The entire circuit is formed on very small (1mm X 1mm) silicon chip. Depending on the no. of
circuit components the ICs (Integrated Circuit) can be divided in different category. They are-
 SSI(Small Scale Integration) – logic gate ≤ 10
 MSI (Medium scale Integration) – logic gate ≤ 100
 LSI (Large scale Integration) – logic gate ≤ 1000
 VLSI (very large scale Integration) – logic gates > 1000
 ULSI (Ultra large scale Integration) logic gates > 1000000
The technology of fabrication IC is a very expensive and very vast. Here briefly we are
describing the process.The process starts with silicon wafer followed by the different steps. The
main steps of fabrication of Ices are,-
 Epitaxial growth: This is basically inserting n-Type or p-Type layer whenever
necessary. This involves cracking of silane.
 Oxidation: Oxidation process required to separate one region of the silicon chip from
other.
 Photo lithography: This is one of the main steps for fabrication of IC.The different
regions of silicon chips are selected photo lithographically and etched for fabricating
different regions with different components.
 Diffusion: Different impurities are doped to get different device structure.
 Metallization: It involves decomposition of metal films which inter-connect different
components on a chip to obtain circuit.

3. As mention earlier Photo lithography is the main step in fabricating. Issuing this process SiO2 of
some regions are removed deliberately to introduce some impurities. On the silicon chip, a thin
layer of SiO2 is first deposited over which a photo-sensitive emulsion called photo-resist is
coated. This has a property that exposed portion get polymerized and resist any chemical etching.
By this property desired portion can get polymerized and rest will be remaining same. The chip
is then dipped in solvent which dissolves the unpolymerised portion of the photo-resist. Now it is
exposed to chemical etchant which removes SiO2 leaving exposed Si surface beneath it through
which metallization can be carried out to get a device called circuit.