The laboratories in which ICs are manufactured today clearly must be clean facilities. It if artificially created clean environment that is suitable to increase the wafer yield. In clean rooms, quality of air, temperature and humidity are well regulated.

Particles that might deposit on silicon wafer and cause a defect may originate from many sources including people, machines, chemicals and process gases.

Unwanted Impurities must be kept below the ppm or ppb range and stray particles must be essentially eliminated. Modern IC factories employ a three tiered approach to control unwanted impurities:

Clean Rooms, Wafer Cleaning and Gettering

Clean rooms are classified according to the number and size of particles permitted per volume of air. Cleanliness of air is characterized by classes.

Class definition: Class X means that in each cubic foot of air in the factory, there are less than X total particles greater than 0.5 micrometer in size.

Example: A class 100 clean room maintains less than one hundred particles larger than 0.5 microns in each cubic foot of air space. A class 1000 clean room has less than 1000 such particles per cubic foot.

FED – STD 209E clean room standard:

Single dust particle of 20nm may damage the device or circuit. Building clean rooms is very expensive.

The air entering a clean room from outside is filtered to exclude dust, and the air inside is constantly re-circulated through High – Efficiency Particulate Air (HEPA) filters to remove internally generated contaminants.

Conditions like temperature, humidity, electrostatic discharge, pressure, vibration and magnetic field must also be controlled.

Before entering in clean room one must wear ‘bunny suits’ to cover their body and clothing.