10.1.5 Etching

In the etching process unwanted material is selectively removed from the surface of the wafer. Etching is a means of transferring the pattern of the photo resist to the wafer after the photolithographic step. Of course the etching chemicals are chosen so that they react with the unprotected parts of the wafer and do not affect the photo resist. Generally a single integrated circuit is exposed to several different etching processes. There are two kinds of etching, namely wet and dry etching.

10.1.5.1 Wet Etching

During wet etching which is also called chemical etching, liquid etching agents are applied to the wafer surface. Since the liquid etches in all directions, the patterned area is undercut. Thus wet etching is no longer used for pattern transfer in modern processes, although it is in use for unmasked etches of the entire wafer surface.

10.1.5.2 Dry Etching

Dry etching is directional which practically eliminates the problem of undercutting caused by wet etching. Dry etching techniques are sputter etching, ion beam etching, and plasma etching. Only directional dry etching techniques allow to create feature sizes below one micrometer in the wafer below the photo resist layer.