Specific Process Knowledge/Etch/Etching of Silicon Oxide/SiO2 etch using AOE/Standard recipe with resist mask/AOE SiO2 etch load dependency

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The etch rate dependency of the etch load

This page has been done by Berit Herstrøm @ DTU Nanolab (BGHE) if nothing else is stated

Etch load

Etch load is the percentage of the wafer surface that is exposed to the plasma. E.g. if you have a wafer with a surface of SiO2 where 95% of the surface is covered by photoresist (or another masking material that has a high selectivity to SiO2 with the used etcing recipe)the the etch load i 5%


Etch load effect of SiO2 etch with etch recipe SiO2_res and with photoresist as masking material

This work has been done by bghe@nanolab in February/Marts 2013

8 wafers with different etch load has been etched with the same recipe in the AOE: m_res_ny (now called SiO2_res 2019-06-26) for the same time and under that same conditions. This was done to isolate the etch load as a parameter to see how much that affects etch rate.

Samples

  • 100mm SSP Si wafers 525µm in thickness
  • 2.2 µm SiO2 grown in furnace: phospher drive-in, recipe Wet1100 for 10 hours
  • 1.4 µm photoresist
  • 5%-95% etch load - masks TRAVKA: 5%,10%,20%,35%,50%,65%,80% and 95%

AOE settings

Before each sample etch a 3 min TDESC clean was done to get the chamber in the same condition.

Parameter SiO2_res
Coil Power 1300W
Platen Power 200W
Platen temperature 0oC
He flow 174sccm
C4F8 flow 5sccm
H2 flow 4sccm
Pressure 4mTorr
Etch time 4min

Results

Ecth load: 5% 10% 20% 35% 50% 65% 80% 95% Comment
Etch rate 231±1.7nm/min 228±1.5nm/min 223±2.3nm/min 224±2.7nm/min 211±3.8nm/min 203±4.6nm/min 198±5.8nm/min 192±5.1nm/min "±" represents the non-uniformity over the wafer
Selectivity to resist 1: 2.9 2.8 2.7 2.5 2.4 2.3 2.0 2.0
Non-uniformity over a 100mm wafer - 1cm exclusion zone ±0.7% ±0.7% ±1.0% ±1.2% ±1.8% ±2.3% ±2.9% ±2.7%
By Berit Herstrøm @ DTU Nanolab

Conclusion

  • The etch rate decreases with etch load with aproximately 20%
  • The wafer non-uniformity increases with etch load going from less than ±1% to about ±3%
  • The selectivity to resist decreases with etch load from about 1:3 to about 1:2
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