Page 1112 - Basic Electrical Engineering

A monolithic circuit is a complete circuit having active and passive circuit
components and their interconnections made on a single chip (the word
monolithic is derived from a Greek word mono = single, lithic = stone or

piece). Integrated circuit technology has developed small scale integration to
very large scale integration. Small scale integration (SSI) has less than 12

gates on a single chip while very large scale integration (VLSI) has over 1000
gates in a single chip.

17.2 FABRICATION OF MONOLITHIC ICS

The fabrication of ICs involves a very special and sophisticated technology.
Here we will briefly mention only the steps involved. The steps are as

follows:

i. Wafer preparation: Wafer is a very thin surface of p-type silicon which provides the base or
substrate on which the circuit elements are grown or developed. Wafers are made by slicing a
p-type round silicon material of certain diameter. These wafers are polished to a mirror finish
surface.
ii. Epitaxial growth: On the p-type substrate an n-type layer is grown by placing the wafer in a
furnace in an atmosphere of phosphorous gas at 1200°C. Thus, an epitaxial layer of n-type
material is formed on the p-type wafer.
iii. Diffused isolation: A thin layer of silicon dioxide is formed on the n-type layer by oxidation
method, i.e., by oxidizing the wafer in dry oxygen. Next, a thin coating of a chemical, called
photoresist is made on the SiO layer.
2

Figure 17.2 IC packages of various types

Following these, use is made of a mask, ultraviolet exposure, etching,
scrubbing and diffusion. Thus, the monolithic process of IC fabrication
involves wafer preparation, epitaxial growth, diffused isolation, base and

emitter diffusion, etching, metallization (making of contacts and
interconnections), checking of circuitry, separating the wafer into individual