Reactive Ion Etching (RIE)
Equipment:
Reactive Ion Etcher (RIE)
SCHEDULER IS REQUIRED
Simple Recipes
- Silicon Etching
- Silicon Dioxide (SiO2)
- Silicon Nitride
- Polymer (photoresist)
Reactive Ion Etching (RIE) Etching Basics
A disadvantage of wet etching is the undercutting caused by the
isotropy of the etch. The purpose of dry etching is to create an anisotropic
etch - meaning that the etch is uni-directional. An anisotropic etch is critical
for high-fidelity pattern transfer.
RIE etching is one method of dry etching.
The figure below shows a diagram of a common RIE setup. An RIE
consists of two electrodes (1 and 4) that create an electric field (3) meant to
accelerate ions (2) toward the surface of the samples (5).
The area labeled (2) represents plasma that contains both
positively and negatively charged ions in equal quantities. These ions are
generated from the gas that is pumped into the chamber. At BYU we use O2 and CF4
gasses for our etches. In the Diagram CF4 has been pumped into the chamber,
making a plasma with many Fluorine (F-) Ions

The Fluorine ions are accelerated in the electric field. cause
them to collide into the surface of the sample. A hard mask is used to protect
certain areas from etching, exposing only the areas desired to be etched.
The figure below shows a photoresist mask on silicon dioxide.
The etching ions are accelerated into the etching region, where they combine
with silicon dioxide and then are dispersed. Because the electric field
accelerated ions toward the surface, the etching caused by these ions is much
more dominant than the etching of radicals - ions traveling in varied
directions, so the etching is anisotropic.

Listed below are
the etch chemistries used to etch various substrates.
Etch Chemistries of Different Etch Processes
Material Being Etched |
Etching Chemistry |
Deep Si trench |
HBr/NF3/O2/SF6 |
Shallow Si trench |
HBr/Cl2/O2 |
Poly Si |
HBr/Cl2/O2,
HBr/O2,
BCl3/Cl2,
SF6 |
Al |
BCl3/Cl2,
SiCl4/Cl2,
HBr/Cl2 |
AlSiCu |
BCl3/Cl2/N2 |
W |
SF6 only, NF3/Cl2 |
TiW |
SF6 only |
WSi2, TiSi2,
CoSi2 |
CCl2F2/NF3,
CF4/Cl2,
Cl2/N2/C2F6 |
Si02 |
CF4/O2, CF4/CHF3/Ar,
C2F6,
C3F8,C4F8/CO,
C5F8,
CH2F2 |
Si3N4 |
CF4/O2, CHF3/02,
CH2F2,
CH2CHF2 |
Table taken from Semiconductor Devices - Physics and Technology
by S.M. Sze. (pg. 440)