Hi Adem,

In fact, it is not suprising. The best way to reah your goal will beTo use an oxyde hardmask . Furthermore , before to go on on this subject) I need to know the technique You use : is it cryogenic one or Bosch one?

Regards Mahomed

Adem, if you have a photo of the destroyed pillar, it Can help to oriente you .

Thanks Mohamed, I am using Bosch process. 

Thanks

Adem, The keys to succesfully etch your pillars with a adequate aspect ratio are : 

first an etching mask that can survive the process so a hard mask made of oxide or aluminium

then a proper cooling of you wafer, it means efficient clamping to extract heat. 

finally a recipe that produces vertical walls. you have to tune the duration of each etching and passivation steps to obtain a scalloping effect in accordance with you requirements. 

Hi Adem,

Ok for Bosch process...Now When you say, the "pillar were destroyed", what do you see exactly? ...pillar "cuted and collapsing with piece of pillar remaining on the bottom" or pillar "entirely etched from top living only some kind of sharp needle"?

Regards

Actually it was both. Pillars lying on the surface, and no pillars, very few pillars standing.  I think it is the etch rate that is causing the problems. 

Thanks for the answers.

Without  a  photo  it  is  not  easy  to  oriente  you . What is the thickness of you photo resist ? did you cure  it? Do you see some scallopingon remaining top pillar? The top pillar is it larger or thinner than  bottom  pillar  ?  What  is  the  gaz  ratio  of  c4f8  and  sf6 ?  What  is  the  source  power  and  bias  voltage ?  Do  you  set  the  same  pressure  for  the  two  gases ?  Regards

you can use simple photoresist (2-3micron thick) as a masking layer and do the Bosch process based DRIE to achieve this kind micro pillars. We have already demonstrated this (please see "Fabrication of High Density Silicon Microprobe Array" by S Dutta, I Yadav, P Kumar, R Pal, Physics of Semiconductor Devices, 483-485, (DOI:10.1007/978-3-319-03002-9_121). The trick is you have to use less etch and deposition power during the DRIE. moreover keep the backside cooling temp at 10 deg C