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

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The ASE

The ICP-DRIE tool at Danchip: STS ASE - positioned in cleanroom B-1

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). Originally the main purpose of the ASE was etching of silicon using the Bosch process. However, after the acquisition of the DRIE-Pegasus the ASE now only serves as backup silicon dry etcher and is also used as a polymer etcher. From around December 2017 this machine will turn into a "dirty" machine meaning that samples with up to 4 cm2 of metal on the surface will be allowed to process. Extra gasses will be added to the machine during this summer to allow SiO2 and SiN etching. Using these gasses may affect the conditioning of the chamber and thereby the stability of the current processes. Any clean processes and sensitive processes should be moved to the DRIEs) during this autumn (2017).

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.

The user manual, quality control procedure and results, user APV(s), technical information and contact information can be found in LabManager:

Equipment info in LabManager

Process information

• Etch of Silicon using ASE
• Etch of polymers using ASE

An overview of the performance of the ASE and some process related parameters

Purpose	Dry etch of	Silicon Polymers such as polyimide, PDMS, PMMA, BCB and resists
Performance	Etch rates	Silicon: ~0-15 µm/min (depending on features size and etch load)
	Anisotropy	Good
Process parameter range	Process pressure	~0.1-95 mTorr
	Gas flows	SF6: 0-600 sccm O2: 0-100 sccm C4F8: 0-300 sccm CO2: 0-100 sccm Ar: 0-100 sccm
Substrates	Batch size	1 6" wafer per run 1 4" wafer per run 1 2" wafer per run Or several smaller pieces on a carrier wafer
	Substrate material allowed	Silicon wafers with layers of silicon oxide or silicon (oxy)nitride Quartz wafers
	Possible masking material	Photoresist/e-beam resist PolySilicon Silicon oxide or silicon (oxy)nitride Aluminium