Specific Process Knowledge/Etch/ASE (Advanced Silicon Etch)

The ASE

The ICP-DRIE tool at Danchip: STS ASE - positioned in cleanroom2

The ICP-DRIE (Inductively Coupled Plasma - Deep Reactive Ion Etcher) tool at Danchip is manufactured by STS and is called the ASE (Advanced Silicon Etcher). The main purpose of the ASE is etching of silicon using Bosch process.

The Bosch process: Etching of silicon

The Bosch process uses alternation between an etch cycle and a passivation cycle. Introducing a passivation step in an etch process is very beneficial for the control of the angle of the sidewalls in the etch process because it allows us to cover them with a protective layer that suppresses the isotropic etching. Combined with the high plasma density in the ICP chamber, the excellent sidewall control enables us to etch high aspect ratio structures in silicon with very high etch rates.

In the case of the silicon etching on the ASE, an etch phase with SF₆ and O₂ alternates with a passivation phase with C₄F₈.

A rough overview of the performance of the RIE´s and some process related parameters

Purpose	Dry etch of	Silicon Silicon oxide Silicon (oxy)nitride
Performance	Etch rates	Silicon: ~0.04-0.8 µm/min Silicon oxide:~0.02-0.15 µm/min Silicon (oxy)nitride:~0.02-? µm/min
.	Anisotropy	Can vary from isotropic to anisotropic with vertical sidewalls and on to a physical etch were the sidewalls are angled but without etching under the mask.
Process parameter range	Process pressure	~20-200 mTorr
.	Gas flows	SF$_{6}$: 0-130 sccm O$_{2}$: 0-100 sccm CHF$_{3}$: 0-100 sccm CF$_{4}$: 0-84 sccm H$_{2}$: ?sccm Ar: 0-145 sccm N$_{2}$: 0-100 sccm C$_{2}$F$_{6}$: 0-24 sccm
Substrates	Batch size	1 4" wafer per run 1 2" wafer per run Or several smaller pieces
.	Substrate material allowed	Silicon wafers with layers of silicon oxide or silicon (oxy)nitride Quartz wafers
.	Possible masking material	Photoresist/e-beam resist Silicon/PolySi Silicon oxide or silicon (oxy)nitride Aluminium Other metals if the coverage is <5% of the wafer area (ONLY PECVD3!)