This thin fluorocarbon polymer limits the rate at which fluorine radicals

from the plasma reach the Si surface. In addition, it limits the rate of diffusion of volatile SiF y species into Si and, therefore, slows down the chemical see more etching. Concerning the etch rate in SF6/CHF3, it is lower compared with both SF6 and SF6/O2 gases. This is due to the fact that the F-atom density is barely higher in this mixture compared to the two other cases, thus retarding Si etching [23]. In Table 2, a comparison is made between the etch rate of a 100 × 100 μm2 Si area formed using a resist mask and the etch rate of Si through the PAA mask (pore diameter in the range of 35 to 45 nm). The thickness of the PAA mask was 400 nm. Several samples were considered, and the range of given values is an average of all measured values. As described

above, the etch rate is similar with SF6 and SF6/O2, while it is lower with SF6/CHF3. By increasing the PAA mask thickness from 400 to 500 nm, the etch rate in SF6/CHF3 was reduced from approximately 70 to 50 nm/min. Table 3 shows the feature etch depth on nanopatterned Si Selonsertib purchase surface for the three different PAA layer thicknesses and the three different etching times. The first learn more PAA layer was 390-nm thick, and no Al annealing was used before PAA formation. The two other layers were 400- and 560-nm thick, respectively, and an annealing step at 500°C for 30 min was applied to the Al film before anodization. We have observed that although the annealing resulted in a better adhesion of the PAA layer on the Si surface (no detachment even after 60 s of etch time), it also created an undulation of the PAA/Si interface, which led to etching inhomogeneities on the Si surface. In Glutathione peroxidase these two last cases, the etch depth varied from zero (non-etched areas) to the maximum value indicated in Table 3. In the case of the non-annealed sample, the etch depth was homogeneous in the whole film. The problem was that for an etching time above 40 s, the lateral etching of the Si film underneath the mask led to mask detachment. The maximum etch depth achieved in that case was around 45 nm. Table 3 Feature etch depth using SF 6

/CHF 3 PAA layer thickness (nm) Etching time (s) 20 40 60 390 (non-annealed) 32 nm 45 nm 20 nm (lower due to partially etched walls) 400 (annealed) 28 nm 45 nm 56 nm (maximum) (maximum) (maximum) 560 (annealed) 16 nm 23 nm 45 nm (maximum) (maximum) (maximum) Feature etch depth on nanopatterned Si surface through a PAA layer for three different PAA layer thicknesses and three different etching times. The first PAA layer was 390-nm thick, and no Al annealing was used before PAA formation. The two other layers were 400- and 560-nm thick, respectively, and an annealing step at 500°C for 30 min was applied to the Al film before anodization. Conclusions We investigated in detail the RIE of Si through a PAA mask for surface nanopatterning using SF6, SF6/O2, and SF6/CHF3 gases/gas mixtures.