A novel UV contact lithography process is presented to realize diffraction-limited dimensions in the patterning and lift-off of structures. The process involves a tri-layer stack comprising a bottom layer of lift-off resist (LOR), followed by a back anti-reflection coating (BARC), capped by a layer of I-line optimised photo resist (PR). This stack enables diffraction-limited exposure of PR in a contact mask aligner. The BARC layer decouples the development of the PR and LOR layers into independent process steps that may be optimised separately. It also strengthens structurally the lithographic stack, reducing the likelihood of PR collapse, particularly for small features in close proximity. Moreover, the process may be applied to transparent (e.g., SiO₂) or opaque (e.g., Si) substrates without change. We demonstrate the process by realising Au grating couplers aligned to underlying Au plasmonic waveguides on a multilayer substrate supporting Bloch long-range surface plasmons. The grating couplers consist of 16 unit cells arranged in a period of 980 nm, each unit cell comprising a 170 nm thick Au ridge and a duty cycle of ~50%. Physical and optical measurements are provided to validate the process.

提出了一种新颖的紫外线接触光刻工艺，以在结构的图案化和剥离过程中实现衍射极限尺寸。该工艺涉及三层堆叠，该三层堆叠包括抗剥离抗蚀剂（LOR）的底层，然后是背面抗反射涂层（BARC），并由一层I线优化的光致抗蚀剂（PR）覆盖。该叠层使接触掩模对准器中PR的衍射受限曝光成为可能。BARC层将PR和LOR层的开发分离为独立的工艺步骤，可以分别对其进行优化。它还在结构上增强了光刻堆栈，减少了PR塌陷的可能性，尤其是对于紧邻的小部件。而且，该工艺可以应用于透明的（例如，SiO ₂）或不透明（例如Si）基板，而不会发生变化。我们通过实现与支持Bloch远程表面等离子体激元的多层基板上的底层Au等离子体激元波导对准的Au光栅耦合器来演示该过程。光栅耦合器由以980 nm的周期排列的16个晶胞组成，每个晶胞包含170 nm厚的Au脊和〜50％的占空比。提供物理和光学测量以验证该过程。