C.Y. Yue

Antistick postpassivation of high-aspect ratio silicon molds fabricated by deep-reactive ion etching

High-aspect ratio (HAR) silicon molds formed with deep-reactive ion etching (DRIE) technique are difficult to use as masters for replication, especially for replication of high-aspect ratio microstructures. Microstructures in silicon molds made by DRIE have high surface energy and wavy vertical side walls, both of which make demolding difficult. In the research reported here, microstructured silicon master molds were made with the DRIE technique; the mold microstructures were trenches with maximum depth and width of 146 /spl mu/m and 9.8 /spl mu/m, respectively. Silicone rubber replicas could not be successfully demolded from such a high aspect ratio (15) silicon master without further surface modification. A second similarly etched mold was plasma treated with C/sub 4/F/sub 8/ for 120 seconds after etching (postpassivated). This treatment was found to be successful; five faithful replicas in silicone rubber were successfully demolded from the postpassivated mold whereas the replica mold broke during demolding from the unpostpassivated master, leaving the master mold microstructure filled with silicone rubber. At higher aspect ratio of 18, the silicon mold had to be plasma treated with C/sub 4/F/sub 8/ for at least 400 s before five replicas could be demolded successfully. Post-passivation with C/sub 4/F/sub 8/ was found to reduce the root mean square sidewall roughness of the silicon master mold trenches by about halves. The nanotribology of the silicon surface was studied with atomic force microscopy. The friction coefficient of the silicon surface was found to be reduced six-fold by the postpassivation technique. XPS analyzes showed that when post-passivation timing was increased, concentration of C-F increased while that of C-CF decreased and the thickness of the fluorinated coating increased. These results show that postpassivation of silicon microstructures made by DRIE can be used to fabricate much higher aspect ratio molds that has heretofore been considered possible using this substrate material and fabrication technique.

Functionalization of carbon nanotubes by argon plasma-assisted ultraviolet grafting

We have demonstrated the functionalization of single-wall carbon nanotubes (SWNTs) by argon (Ar) plasma-assisted ultraviolet (UV) grafting of 1-vinylimidazole (VZ). The Ar plasma treatment generates defect sites at the tube ends and sidewalls, which act as the active sites for the subsequent UV grafting of VZ monomer. Atomic force microscopy analyses indicate that the original nanotube bundles exfoliate to individual tubes after the VZ grafting. By control of the deposited energy of Ar plasma treatment (200W) and treatment time (5min), no visible chopping of the functionalized SWNT was observed. This method may be extended to other vinyl monomers and offers another diverse way of sidewall functionalization of SWNT.

SUB-MICRON PATTERNING TITANIUM NITRIDE BY FOCUSED ION-BEAM TECHNIQUE

Titanium nitride (TiN) thin films have low electrical resistivity, good chemical and metallurgical stability, and exceptional mechanical properties. As such, we are interested in exploring TiN for use as mold material for micro-and nano replication. Focused ion beam (FIB) technique was successfully used to fabricate sub-micron sized pattern on a TiN/Si(100) wafer. This mask-free fabrication technique takes advantage of the kinetic precision of FIB; the energy of ions used was 40 KeV. The width and depth of each trench in the TiN mold are 390 nm and 280 nm respectively.