STS Pegasus 4/Processes/LNF Switched Poly

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About this Process
STS Pegasus 4 Switched Poly 1 um.jpg
Process Details
Equipment STS Pegasus 4
Technology RIE
Material Silicon
Mask Materials PR, SiO2
Gases Used SF6, C4F8, O2

LNF Switched Poly is a Bosch-style switched process intended for shallow silicon and thin film poly- and amorphous silicon etches.

The STS Pegasus is not designed for polysilicon etching. There are other tools at the LNF specifically designed for this, including the LAM 9400 and the P5000 RIE. Please make a helpdesk ticket if you need assistance determining the correct tool or recipe for your process.


Follow the standard operating procedure.


Parameter Dep Etch
ICP Power 800 W 800 W
Bias Power 0 W 20 W
Bias Pulsing N/A 100 Hz 80%
Pressure 10 mTorr 10 mTorr
C4F8 Flow 150 sccm 120 sccm
SF6 Flow 0 sccm 200 sccm
Time 1 s 1.65 s
Chuck Temperature 20°C


Etch rate

Etch rate will vary with feature size and loading.

Material Etch Rate Uniformity
Silicon 0.4 µm/min ?%

Mask selectivity

Material Etch Rate Uniformity
SPR 220 110 Å/min 8%
Silicon dioxide 31 Å/min 18%
Silicon nitride 92 Å/min 13%
Low stress nitride 80 Å/min 12%

Etch profile

  • Undercut: 80-100 nm
  • Sidewall angle: 87-89° (loading dependent)
This recipe exhibits passivation breakthrough at the top corner of the feature (see image at top of page). This appears to go away for large open areas (isolated lines), but if this will be detrimental to your process, please consider another tool for polysilicon etches.


Etch length

This etch is designed for thin films and shallow etches (< 2 µm). It is not characterized for long processes.

Feature size

Due to passivation breakthrough at the surface, remaining features narrower than 1 µm will likely be etched away.

Open area