Department of Electrical and Computer Engineering, University of Waterloo, 200 University Ave, West, Waterloo, ON N2L 3G1, Canada.
Nanoscale Res Lett. 2013 Sep 23;8(1):394. doi: 10.1186/1556-276X-8-394.
Polydimethylsiloxane (PDMS) is the most popular and versatile material for soft lithography due to its flexibility and easy fabrication by molding process. However, for nanoscale patterns, it is challenging to fill uncured PDMS into the holes or trenches on the master mold that is coated with a silane anti-adhesion layer needed for clean demolding. PDMS filling was previously found to be facilitated by diluting it with toluene or hexane, which was attributed to the great reduction of viscosity for diluted PDMS. Here, we suggest that the reason behind the improved filling for diluted PDMS is that the diluent solvent increases in situ the surface energy of the silane-treated mold and thus the wetting of PDMS to the mold surface. We treated the master mold surface (that was already coated with a silane anti-adhesion monolayer) with toluene or hexane, and found that the filling by undiluted PMDS into the nanoscale holes on the master mold was improved despite the high viscosity of the undiluted PDMS. A simple estimation based on capillary filing into a channel also gives a filling time on the millisecond scale, which implies that the viscosity of PMDS should not be the limiting factor. We achieved a hole filling down to sub-200-nm diameter that is smaller than those of the previous studies using regular Sylgard PDMS (not hard PDMS, Dow Corning Corporation, Midland, MI, USA). However, we are not able to explain using a simple argument based on wetting property why smaller, e.g., sub-100-nm holes, cannot be filled, for which we suggested a few possible factors for its explanation.
聚二甲基硅氧烷（PDMS）因其灵活性和通过模塑工艺易于制造而成为软光刻中最受欢迎和最通用的材料。然而，对于纳米级图案，将未固化的 PDMS 填充到涂有硅烷抗粘层的母模的孔或沟槽中是具有挑战性的，这是脱模所必需的。以前发现通过用甲苯或己烷稀释 PDMS 可以促进 PDMS 的填充，这归因于稀释 PDMS 的粘度大大降低。在这里，我们认为稀释 PDMS 填充性提高的原因是稀释剂溶剂原位增加了硅烷处理模具的表面能，从而提高了 PDMS 对模具表面的润湿性。我们用甲苯或己烷处理母模表面（已经涂有硅烷抗粘单层），发现尽管未稀释 PDMS 的粘度很高，但仍可以改善未稀释 PMDS 填充到母模上纳米级孔中的情况。基于毛细管填充到通道的简单估计也给出了毫秒级的填充时间，这意味着 PDMS 的粘度不应该是限制因素。我们实现了孔径填充到亚 200nm，这比使用常规 Sylgard PDMS（不是硬 PDMS，Dow Corning Corporation，Midland，MI，USA）的先前研究更小。然而，我们无法用基于润湿性的简单论据来解释为什么不能填充更小的，例如亚 100nm 的孔，对此我们提出了一些可能的解释因素。
