Photolithographic Patterning of Colloidal Quantum Dots Enabled by Plasma‐Induced Ligand Polymerization

ABSTRACT

The ligands on the indium phosphide (InP) quantum dot (QD) are crossed‐linked through plasma‐induced ligand polymerization (PILP) by exposing the QD films to energetic Ar ions generated in an inductively coupled plasma (ICP). Following the PILP treatment, 3 um‐scale QD patterns were demonstrated using a photolithography process in this work. In the first step, the oleic acid (OA) ligands on InP QDs were cross‐linked by ions having energy in the range of 100–400 V in plasma. The cross‐linking OA was verified from C═C─H bond peak at 3006 cm ⁻¹ in Fourier‐transform infrared (FT‐IR) spectra. The energy dose required for cross‐linking was estimated from ion flux, bias voltage, and processing time. The energy dose of 5.9–6.6 J/cm ² was identified as appropriate dose range enabling cross‐linking of the ligands. In the second step, the photoresist (PR) was coated on the top of the cross‐linked QD films, and PR patterns were formed with UV exposure followed by PR development. In the final step, the unmasked QD regions were removed by ion sputter etching in an Ar plasma, and 3 µm‐scale patterns were demonstrated. This work demonstrates that PILP is an effective approach for microscale QD patterning.