Nanoscale selective area atomic layer deposition of TiO2 using e-beam patterned polymers

Abstract

Here, we report nano-patterning of TiO₂ via area selective atomic layer deposition (AS-ALD) using an e-beam patterned growth inhibition polymer. Poly(methylmethacrylate) (PMMA), polyvinylpyrrolidone (PVP), and octafluorocyclobutane (C₄F₈) were the polymeric materials studied where PMMA and PVP were deposited using spin coating and C₄F₈ was grown using inductively coupled plasma (ICP) polymerization. TiO₂ was grown at 150 °C using tetrakis(dimethylamido) titanium (TDMAT) and H₂O as titanium and oxygen precursors, respectively. Contact angle, scanning electron microscopy (SEM), spectroscopic ellipsometry, and X-ray photoelectron spectroscopy (XPS) measurements were performed to investigate the blocking/inhibition effectiveness of polymer layers for AS-ALD of TiO₂. TiO₂ was grown with different numbers of growth cycles (maximum = 1200 cycles) on PMMA, PVP, and C₄F₈ coated substrates, where PMMA revealed complete growth inhibition up to the maximum number of growth cycles. On the other hand, PVP was able to block TiO₂ growth up to 300 growth cycles only, whereas C₄F₈ showed no TiO₂-growth blocking capability. Finally, mm-, μm-, and nm-scale patterned selective deposition of TiO₂ was demonstrated exploiting a PMMA masking layer that has been patterned using e-beam lithography. SEM, energy-dispersive X-ray spectroscopy (EDX) line scan, EDX elemental mapping, and XPS line scan measurements cumulatively confirmed the self-aligned deposition of TiO₂ features. The results presented for the first time demonstrate the feasibility of achieving self-aligned TiO₂ deposition via TDMAT/H₂O precursor combination and e-beam patterned PMMA blocking layers with a complete inhibition for >50 nm-thick films.