While ProLIFT can be used to fill the PS pores prior to the application of photoresist in step I, it is not UV sensitive but can be removed by standard alkaline developer during the photoresist development step. This allows ProLIFT to be patterned in the same wet process that defines the photoresist but requires accurate timing of the development time. If the developing time is too short, exposed photoresist will be removed but ProLIFT residue will remain in the PS film slowing the RIE removal of PS, as shown in Figure 6a. Furthermore, any residual ProLIFT in the PS film once released is expected

to introduce stress in released microbeams, resulting in beam breakage (poor yield). On the other hand, if the developing time is too Androgen Receptor Antagonist long, the photoresist will be over developed, Selleck Tubastatin A causing a large side wall angle of the photoresist pattern, resulting in poorly defined PS structures as shown in Figure 6b. Worse, over developing can result in lift off of the patterned photoresist if it is not well attached to the PS film. Repeated experiments have shown the development time when using ProLIFT becomes a significant issue when patterning PS films above 1-μm thick, as they require a much longer developing time (>60 s) to remove all the ProLIFT in the PS films than typically required for photoresist development (approximately 30 s). Figure 6 Comparison of pore

fill techniques utilizing ProLIFT and SOG. Different techniques: (a) ProLIFT pore filling technique with short developing time, (b) ProLIFT pore filling technique with long developing time and (c) SOG pore filling technique. At three steps: (I) UV light exposure with photoresist patterning, (II) developing to remove exposed positive photoresist and (III) RIE and photoresist/pore filling material removal. On the contrary, SOG can be used to form a layer of SiO2

to fill the pores of PS at step I of Figure 6, which is not removed during the developing process at step II. This guarantees the accurate Orotidine 5′-phosphate decarboxylase control of developing time for the photoresist layer, resulting in well-patterned PS structures at step III, as shown in Figure 6c. Our tests showed a 10-s dip in 10% HF/DI is sufficient to remove all SOG in an exposed PS film (where there was no photoresist) up to 2.45-μm thick. The short dip resulted in an optical thickness change of less than 4.4%, suggesting the short dip had very little effect on the PS layer. In this work which used PS layers of 2.45-μm thickness, SOG as a pore filling layer was more advantageous than ProLIFT and was used as described. These results show a complete MEMS fabrication process using a single material system can be achieved using combination of anodization and electropolishing. No sacrificial layer was required to achieve release of the beams.