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

The ASE

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.

The two standard silicon etch recipes

Two recipes have been optimized for the ASE. Their specification is on a 10 % etch load wafer with trenches.

• Shallolr: The shallow etch process will etch a 2 $\mu$m opening down to make a 20 $\mu$m trench.
• Deepetch: The deep etch process will etch a 50 $\mu$m opening down to make a 300 $\mu$m trench.

The shallolr recipe

Common parameters		Multiplexed parameters
Parameter	Setting	Parameter	Etch	Passivation
Temperature	10oC	SF6 Flow	260 sccm	0 sccm
No. of cycles	31	O2 Flow	26 sccm	0 sccm
Process time	5:56 mins	C4F4 Flow	0 sccm	120 sccm
APC mode	manual	RF coil	2800 W	1000 W
APC setting	86.8 %	RF Platen	16 W	0 W
		Cycle time	6.5 s	5 s

The deepetch recipe

Common parameters		Multiplexed parameters
Parameter	Setting	Parameter	Etch	Passivation
Temperature	20oC	SF6 Flow	230 sccm	0 sccm
No. of cycles	250	O2 Flow	23 sccm	0 sccm
Process time	54:10 mins	C4F4 Flow	0 sccm	120 sccm
APC mode	manual	RF coil	2800 W	1000 W
APC setting	87.7 %	RF Platen	19 W	0 W
		Cycle time	8 s	5 s