Defect-Free Imprinting of Enclosed Microstructures and Dense Pillar Arrays by Vacuum-Assisted Degassing in Ormocer Resists: Process Optimization and Demonstration for Microfluidic Devices

The direct imprinting of enclosed microstructures such as dense pillar arrays is limited by air entrapment within stamp cavities, which prevents complete filling and leads to defective structure formation. Here, we present a systematic investigation of vacuum-assisted imprinting as a strategy to overcome this limitation, using OrmoStamp working stamps to replicate arrays of micropillars with 20 μm diameter, 27 μm height, and 38 μm pitch into UV curable resists from the Ormocer family. By degassing the stamp-polymer assembly inside a desiccator under controlled vacuum prior to UV curing, air entrapment is effectively eliminated. Three degassing conditions are compareda strong pump, a weak pump, and passive degassing at ambient pressurealongside two curing protocols: ambient-cure and in situ vacuum-pressure. With passive degassing at ambient conditions, we obtain ∼85% of fully imprinted pillars in the array after 60 min. In contrast, with a strong pump, we achieve 100% pillar yield after just 10 min of degassing. The optimized process is demonstrated across three materialsOrmoStamp, Ormocomp, and the fluorine-free OrmoStamp FF. Qualitative evidence suggests that air removal proceeds primarily via bubble migration from the cavities. The practical impact of the optimization is demonstrated through two functional microfluidic applications: a deterministic lateral displacement device for micro-particle separation, and a chip with U-shaped hydrodynamic traps for particle capture, both of which require defect-free microstructures for functional operation.