Handbook of Silicon Based MEMS Materials and Technologies

5.1.6. Chemical Etching

Lapping or grinding leaves residual mechanical damage on the wafer surface, and wafer edges have residual damage from both lapping and edge-grinding operations. This damage is removed, and wafer is cleaned from impurities coming from mechanical operations in the etching step. The amount of silicon removed depends on the damage depth from previous operations. For etching there are two choices, acidic etch or alkaline etch. Acidic etch can produce smooth surfaces and it is suitable for all wafer orientations and dopants, including very heavily doped silicon; but as an exothermic process, process control is a challenge. Also, the decomposition of chemicals in the acidic mixture makes it challenging to master. Dopant and ...