Reactive Ion Etching

The computer controlled, turbo pumped RIE system is used to etch features anisotropically (i.e. etching occurs only in the vertical direction with minimal undercutting of the etch mask). Etch gases are admitted into the chamber at low pressure and a radio frequency signal is passed through them. This breaks up the gas molecules and creates a plasma of reactive chemical species that react with the material being etched (substrate). Gases are chosen that will react with the substrate to produce volatile compounds which are then removed from the etch chamber by vacuum pumps. The RF signal is applied to the process gases in a manner that causes a voltage difference between the substrate and the plasma. This voltage accelerates the reactive etch species towards the substrate and causes etching to occur mainly in the vertical direction. As an additional feature a laser etch monitor is installed. Typical materials that are etched are GaAs, AlGaAs, Si, SiN, SiO, Ti, photoresist, and polyimides.

Etch Gases: Argon, Oxygen, SF6, SiCl4 and Cl2
Excitation frequency: 13.56 MHz
Sample size limited to 15 cm diameter
Masking materials include: metals, photoresist, SiO, SiN
Typical etch rates are:
GaAs/AlGaAs 300nm/min (SiCl4)
SiNx 150 nm/min (SF6)
SiOx 30 nm/min (SF6)
Ti 200 nm/min (SF6)