Specific Process Knowledge/Etch/Etching of Silicon Oxide/SiO2 etch using AOE/Standard recipe with resist mask/Variations over SiO2 mres

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Experiments done with the TDESC electrode that we installed in 2010 (by Roy Cork and Berit Herstrøm @Nanolab)

After changing the electrode to the TDESC type we got a lot of issues with trenching during the acceptance test. After doing a lot of experiments and optimization it turned out that this was probably do to a bad resist profile. We used a negative resist and the problems were gone. Here I show some of the results we got during this optimization.

Conclusions

• Very important to have a good resist profile before etch.
• Trenching and rounded corners can be controlled with coil and platen power.
• H2 does not have much influence (expected to have influence on the SiO2:Si selectivity)
• C4F8 flow has a influence on the profile and on the aspect ratio dependent etch - keep it low.
• Pressure does not show much influence

• This is the resist mask profile before etching
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• Variation of Platen power at coil power 1300W, no H2 and C4F8 at 10sccm
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  Platen power 200W.
  Etch time 40min.
  Etch rate 243nm/min.
  Mask selectivity 3.9

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  Platen power 150W.
  Etch time 40min.
  Etch rate 216nm/min.
  Mask selectivity 4.3

• Variation of Platen power and He flow at coil power 1600W, no H2 and C4F8 at 10sccm
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  Platen power 200W.
  Etch time 25min.
  Etch rate 336nm/min.
  Mask selectivity 3.1

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  Platen power 150W.
  Etch time 25min.
  Etch rate 160nm/min.
  Mask selectivity 2.7

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  Platen power 200W.
  He flow 300sccm
  Etch time 25min.
  Etch rate 284nm/min.
  Mask selectivity 4.2

• Variation of Platen power and He flow at coil power 1000W, no H2 and C4F8 at 10sccm
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  Platen power 300W.
  Etch time 20min.
  Etch rate ?nm/min.
  Mask selectivity ?
  Still a little trenching

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  Platen power 200W.
  Etch time 20min.
  Etch rate 315nm/min.
  Mask selectivity 3.2
  still a little trenching

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  Platen power 150W.
  Etch time 30min.
  Etch rate 250nm/min.
  Mask selectivity 3.6
  No trenching, corner a bit rounded

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  Platen power 180W.
  Etch time 30min.
  Etch rate 280nm/min.
  Mask selectivity 2.8
  Very little trenching in the large opening and very little rounded corners in the small opening. A good compromise.

• Variation of He flow and pressure at coil power 1000W and platen power 180W (He: 174sccm - pressure: 4mTorr), no H2 and C4F8 at 10sccm
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  Etch time 30min.
  Etch rate 280nm/min.
  Mask selectivity 2.8

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  He flow 300sccm
  Etch time 30min.
  Etch rate 160nm/min.
  Mask selectivity 3.3

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  Pressure 2.3mTorr
  Etch time 30min.
  Etch rate 284nm/min.
  Mask selectivity 3.5

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  Pressure 6mTorr
  He flow 300sccm
  Etch time 30min.
  Etch rate ?nm/min.
  Mask selectivity ?

• Variation of C4F8 flow at coil power 1000W and platen power 180W, He: 300sccm, pressure: 4mTorr), no H2
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  C4F8 flow at 16sccm.
  Etch time 30min.
  Etch rate ?nm/min.
  Mask selectivity ?

• Negative mask
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  resist profile before etch

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  C4F8: 10sccm
  He: 300sccm
  H2: 8sccm
  Coil power: 1000W
  Platen power: 180W
  Etch time 35min.
  Etch rate ?nm/min.
  Mask selectivity ?

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  C4F8: 5sccm
  He: 174sccm
  H2: 4sccm
  Coil power: 1300W
  Platen power: 200W
  Etch time 30min.
  Etch rate ?nm/min.
  Mask selectivity ?