Fig. 4 Organic Resist Results.
Top down SEM view of fluorine etched trenches in Si. The pattern was produced using e-beam lithography on 60-80 nm thick PMGI resist. The Si was then fluorine etched for 10 minutes at 200^oC. The areas that were not etched through are due to varying exposures of the e-beam.(See discussion below.)


In an effort to go to nanometer scale geometries (i.e. same high aspect ratios but nanometer size openings), we investigated etching Si using e-beam patterned photoresists as masks. Figure 4 shows a top down SEM view of some typical results using e-beam lithography on 60-80 nm thick PMGI resist. The Si was fluorine etched for 10 minutes. The areas that were not etched through are due to varying exposures of the e-beam.
The problem with this technique is that the fluorine etches most organic photoresists, and this limits the ultimate depth we could attain using this technique. Another problem with organic photoresists is their inability to withstand temperatures above about 150^oC. The inset table in Figure 2(a) shows etch rates and selectivities (compared to Si) of some more common photoresist materials.