面向LED图形化的大尺寸和非平整衬底整片纳米压印方法研究

LED图形化（即蓝宝石衬底和外延片的纳米图形化）是提高内量子效率和光提取效率、实现高亮度LED最有效技术途径之一。纳米压印因其高效、经济，被认为是LED图形化的优选工艺方法，为了满足工业产出率和低成本量产的需求，有必要实现大面积的整片（晶圆级）压印（而非常规的分区步进压印）。但将纳米压印工艺应用于LED图形化必须解决大面积快速填充、脱模和模具寿命问题，且要适应外延片翘曲和易碎的基材特点。本项目旨在发展一种基于氟聚合物基薄膜结构复合软模具和流体介电泳力驱动的整片晶圆纳米压印新方法。其创新性：采用低表面能氟聚合物软模具解决大面积脱模和寿命问题；以气动辅助压力实现软模具与非平整基材大面积共形接触和均匀施压；通过流体介电泳力实现大面积快速填充、且降低对外延片的应力。为此，项目将展开"流体介电泳力"驱动下聚合物流变填充行为和规律、整片纳米压印脱模过程中的界面物理特性和调控机理等方面研究。

Nano-structured LEDs, e.g., nano-patterned sapphire substrate (NPSS), photonic crystal, nanorod, nanowire, quantum dot, etc., have shown great potential for significant improving the internal quantum efficiency, light extraction efficiency and the directional far-field patterns, as well as implementing high-brightness LED manufacturing. Compared to other nanomanufacturing technologies, nanoimprint lithography (NIL) has been regarded as a promising method to mass produce various nanostructures for NanoLEDs with low cost and high throughput. Moreover, NanoLEDs are ideal applications for nanoimprint lithography due to their needs for sub-wavelenth structures over large-areas (wafer-level), with limited overlay and defect density requirements. Due to the non-flat LED wafer and substrate with warpage (bow) and bulge features, the particulate contamination commonly found on their surfaces, as well as other challenging issues (e.g., complex 3D convex patterns, high aspect ratio structures, difficulty to etch sapphire substrate for transferring patterns), the existing NIL processes cannot well satisfy the practical needs for high volume manufacture of NanoLEDs. This proposal presented a novel full-wafer scale NIL process which is based on a combination of the thin-film structured fluoropolymer mold and liquid dielectrophoresis (L-DEP). The thin-film structured fluoropolymer mold is used to carry out the demolding over large areas, and to extend the template lifetime. The gas-assisted imprinting method incorporating the soft mold is employed to ensure the large-area uniform contact on non-flat substrates. The liquid-dielectrophoresis force-driven UV-imprinting is utilized to implement the homogeneous and quick filling of liquid polymers over larger area patterns under low pressure condition. The goal of the project is to explore and develop a novel full wafer UV-NIL process which has the capability to implement the mass production of wafer-level nanopatterns on large-size and non-flat substrates at low cost and high throughput. It may provide a promising solution for LED nanopatterning, wafer level cameras, and other optical components. Moreover, some key issues including filling behavior based on the L-DEP, interface properties between the mold and the imprint polymer, and the structure and fabrication of the wafer-level composite mold, are also investigated in detail.