Discuss the process flow of Photolithography. Explain the type of photoresist used.

Photo lithography :- Photo lithography is the process of transferring geometric shapes on a mask to the surface of a silicon wafer. The steps involved in the photo lithogrophy process are wafer cleaning barrier layer formation photoresist applications soft baking, mask alignment, exposure and development and hard baking.

Example shown below uses oxidized silicon wafer and negative photoresist system.

In case of photolithography two types of photo-resist are used.

1. A Positive Photoresist :- It is a type of photoresist in which the portion of the photoresist that is exposed to light becomes soluble to the photoresist developer.

   Example; . Diazonaphthoquinone, novoloc (DQN) resist

2. A Negative Photoresist :- It is a type of photo resist in which the portion of the photoresist that is exposed to light becomes insoluble to the photorerist developer.

   Example: SU8, Kodak Thin Film Resist (KTFA)