Specific Process Knowledge/Etch/DRIE-Pegasus/Pegasus-2/ORE with Al2O3 mask

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By Maria Farinha @nanolab, Jan 2023

Important! The pressure settings used below may no longer be permitted, always check with the Dry etch group.

As stated by Nguyen et al., the SF6 and O2 fluxes are only separated after 4 s during the C-step. Shorter time steps than that do not execute the function of the clearing. After testing recipes with only 2 s of clearing and with no clear step, it was understood it could be eliminated, showing more depth as well as less undercut when going for shorter cycles. From then on, not CORE but ORE recipes were applied D/E = O/RE.
Moreover, during the E-step, the MFC (mass flow controller) presented a delay to read the pressure when compared with the power, creating unwanted bias. To fight it, the E-step was divided into E1 and E2. The E1 of only 2 s is enough to stabilize the pressure, and E2 the profile is etch correctly, without the unwanted bias.

CORE process graphics and recipes: a) unwanted DC bias during the E-step; b) E-step separated into two steps, E1 decreased the bias.

Pillars

Using patterned samples of 1 μm pillars with 50 nm of Al2O3. After the tests, approximately 20nm of Al2O3 were still intact.

1μm Pillar recipe from March 2022 - #244 = 122 min
Pillars with different etching times.
 Time (s) Pressure (valve control) O2 flow (SCCM) SF6 flow (SCCM) Platen power (W)
O-step 10 3% 200 0 40
R-step 10 100% 0 5 40
E1-step 2 4% 0 350 40
E2-step 7 4% 0 350 300

* Pillars profile effect when varying the etch time.


Holes

Using patterned samples of 1 μm holes with 50 nm of Al2O3. After the tests, approximately 20nm of Al2O3 were still intact.

1μm holes recipe from March 2022
17.6 μm holes profile.
 Time (s) Pressure O2 flow (SCCM) SF6 flow (SCCM) Platen power (W) Coil power (W)
O-step 10 220 mTorr 200 0 40 0
R-step 10 100% 0 40 40 0
E1-step 2 220 mTorr 0 1200 0 0
E2-step 1-5 220 mTorr 0 1200 1 2000

* For #288 cycles, 120 min, the profile depth reaches 17.6 μm. For #144 cycles, 60 min, the profile depth reaches 10.1 μm. Width variation presented in the pictures.


Nanoholes

200nm nanoholes recipe from March 2022
Time (s) Pressure (valve control) O2 flow (SCCM) SF6 flow (SCCM) Platen power (W)
O-step
R-step
E1-step
E2-step

Isotropic etch

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