Oxygen Plasma System Recipes

Back to Dry Etching Recipes.

Ashers (Technics PEII)

CF4/O2 PEii

Gas is CF₄ / O₂ (88%/12%)

SiN Etching

• Pressure = 300mT–350mT
• Power = 100W
• Etch Rate ≈ 50-100 nm/min. Varies.
• Process notes: Make sure to PR-protect the underside, and the bevel/wafer edge, as the SiN can be removed in those areas as well if not covered by PR. You can coat the wafer bevel/edge using a swab, manually "painting" the bevel while the wafer is on a PR spinner vacuum chuck, and then the Brewer Lift-pin hotplate (Bay 7) to bake at ~100-110degC.

Chamber Clean after CF4 Etching

• Pressure = 300mT–350mT
• Power = 100W
• Time = 10min

O2 Ashing

O2; 300mT / 100W - on either Technics asher.

~15sec to make a surface hydrophilic, eg. before wet etching or applying photoreist.

~30-120sec to improve wirebonding pad metal prior to deposition of liftoff metal.

~1-5min to remove polymerized photoresist/scum after dry etching

~5-10min to strip ~0.5-1.0µm photoresist. Rotate wafer 180° halfway through etch. Optionally increase to 200W for faster etching.

Use glass slides to prevent wafers from sliding on platen.

Plasma Clean (Gasonics 2000)

Recipes are posted at the tool, with photoresist etch rates.

Plasma Clean (YES EcoClean)

Some negative photoresists (eg. UVN) do not strip well without ion bombardment (requiring Technics PEii or RIE/ICP instead). We believe that the UV exposure from plasma may increase hardening via crosslinking.

Recipe Temperature control is by the lift-pins , with hotplate at 200°C

N₂/O₂ Recipes

Recipe Names:

• "STD-N2-O2-180C-3kW-3min"
  • These recipes used to be named “180C-3kW-3min”, prior to 2023-09-15.
  • The new, Renamed recipes are identical, except have a 1x pump/purge added to the start of the cycle to improve repeatability.
• Variations: (underlined portion of filename above)
  • Temperature: 100C, 130C, 150C,180C
    • NOTE: some wafers will get hotter than the indicated temperature, due to optical absorption. See below for alternative recipes that avoid this.
  • Power: 3kW, 0.7kW
    • 3kW is very fast for full PR strip, but often increases substrate temperature significantly.
    • 0.7kW reduces substrate temperature, although exact values are not known.
  • Time: Various times are available, with strings such as "30sec", "1min", "3min" etc.
• Recipe screenshots

Recipe Characterization:

• Various Resists Etched at 150C-3kW
• SPR220-7 at 3kW various Temps with N2/O2 recipes

3kW recipes appear to gradually heat wafers beyond the hotplate temperature, and also expose the underside of the wafer. Very efficient cleaning of positive photoresists, but exact temperature is unknown and may increase with time.

N₂/O₂ effect on Gold contacts & Substrate Temperature

These Nitrogen-containing recipes, at both 3kW and 0.7kW, have a tendency to oxidize Gold, turning Gold contacts brown. We found that the optical emission of the N₂ plasma emits strongly in the visible, which is absorbed especially by Gold (especially Blue/UV optical absorption, that's why Gold looks yellow), causing additional heating of the surface, perhaps as much as 100°C hotter. If your devices contain gold contacts, or are very temperature sensitive, consider using our O2-only recipes below.

O₂-Only Recipes

O₂-only recipes do not oxidize gold contacts, and have been found to have stable/repeatable temperatures, and lower PR etch rates than N₂-O₂ recipes. See below for PR etch rates.

NOTE: The O2 plasma does not emit much light, because the plasma is remote. The tool is etching even if the porthole does not look brightly lit.

• Recipe Names: "STD-O2-100C-3kW-3min"
• Variations: (underlined portion of filename above)
  • Temperature: 100C, 130C, 150C, 180C
  • Power: 3kW
  • Time: Various times are available, with strings such as "30sec", "1min", "3min" up to "15min"
• Recipe Screenshots

O₂ Recipe Characterization

• O2 only recipes without N2 gas: SPR220-7 at 3kW various temperature
• Comparison of ash rate for O2-only vs O2/N2 mixture
• Gold surface oxidation (darkening) due to O2/N2 plasma; the need for O2 only recipes
• Note: Ruthenium layers will likely partially oxidize in these recipes, possibly turning brown.

Internal To Add: 
• PR Etch rates for each recipe

UV Ozone Reactor

The UV Ozone Reactor is used for two purposes:

• Etch away organic residue with no ion bombardment
• Oxidize surface (monolayers) of a substrate, which has been used for
  • Providing a wet-etchable sacrifical surface layer which is removed prior to deposition or regrowth
  • Controlled digital etching, by wet etching the oxide and then repeating the oxidation/etch cycle.

Plasma Activation (EVG 810)

O2 and N2 plasma activation recipes are available on this tool.

These are the qualified recipes provided by EVG and will not require adjustment of the RF Match:

• ExSitu_0.4mbar – 0.4mbar, N₂, 100/75W
• ExSitu_0.4mbar_Line2 – 0.4mbar, O₂, 100/75W
• ExSitu_0.8mbar – 0.8mbar, N₂, 100/75W
• ExSitu_0.8mbar_Line2 – 0.8mbar, O₂ 100/75W
• Dis 0.2mbar_Line2 – 0.2mbar, O₂, 125/75W