I was struggling for last couple of weeks by varying various parameters of DRIE like SF6 , C2F4 flow rate, platen power(5 to 10W), ICP power (1000~3000W), vacuum (20~25 mtorr) but in none of the case it is becoming black silicon. The surface is becoming rough but not as rough as black silicon should be. Our idea is to make superhydrophobic surface by black silicon approach. It would be nics if you share your experience whoever done this. Our machine is SPTS DRIE.
Thanks Dr. Ali for your response but we do not have cryogenic ICPRIE. However, if you suggest it may be helpful for future.
Thanks Dr. Ali. We do not have cryo DRIE. We are trying with normal DRIE. I will consult the recipe with you within couple days.
I suggest you read Henri Jansen's famous Black Silicon Method papers. He goes over the overall method as well as the details used in his etcher using SF6/O2/CHF3.
Title: The black silicon method:a universal method for determining the parameter setting of a fluorine-based reactive ion etcher in deep silicon trench etching with profile control
Authors: Henri Jansen, Meint de Boer, Rob Legtenberg and Miko Elwenspoek
Journal: J. Micromech. Microeng. 5 (1995) 115-120.
This is a great reference to have. We have used this to generate very nice etch profiles before the proliferation of DRIE tools. You can combine the two methods to reduce the scalloping of the sidewalls if you don't have access to newer (that is faster switching) DRIE tools.
Once you make the black (rough) Silicon you will still need to make it hydrophobic so finish the process with a C4F8 deposition step.
I got black silicon accidentally while using Oxford ICP-DRIE Plasmalab100.
The recipe Bosch-process was (0.8 um PECVD SiO2 mask on Si):
200 cycles
Dep step
Time [sec] 7
O2 [sccm] 0
C4F8 [sccm] 85
SF6 [sccm] 0
Temp [°C] 18
RF [W] 0
ICP [W] 1500
Etch step
Time [sec] 13
O2 [sccm] 5
C4F8 [sccm] 0
SF6 [sccm] 129
Temp [°C] 18
RF [W] 15
ICP [W] 1500
SEM analysis confirmed black silicon formation.
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