Growth behavior of atomic-layer-deposited Pb(Zr,Ti)O_x thin films on planar substrate and three-dimensional hole structures

Quaternary Pb(Zr,Ti)O_x (PZT) films were deposited at 240°C by a combination of liquid-injection atomic layer deposition (ALD) of binary PbO, TiO_x, and ZrO_x thin films. In preliminary work, binary ZrO_x films were deposited at 240°C by ALD. Two solutions of Zr(C₉H₁₅O₂)₄[Zr(DIBM) ₄] and Zr(C₁₁H₁₉O₂)₄ [Zr(DPM)₄] dissolved in ethylcyclohexane (ECH) were prepared, and it was found that the Zr(DIBM)₄ solution provides a three-times-higher deposition rate for the ZrO_x films than the Zr(DPM)₄ solution. We focused the study on the set of precursors which offers the highest degree of flexibility for adjusting the Zr(Zr+Ti) ratio in the PZT films: Pb(C₁₁H₁₉O₂)₂ [Pb(DPM)₂], Ti[OCH(CH₃)₂]₄ [Ti(Oi-Pr)₄], and Zr(DIBM)₄ dissolved in ECH, and water as the oxidant. This set of solutions contributed to increasing the Zr(Zr+Ti) ratio in the deposited PZT films to more than 0.2, which remained below 0.1 in the ALD-PZT using Pb(DPM)₂, Ti(Oi-Pr)₄, and Zr(DPM)₄. The Zr(Zr+Ti) ratio was further increased to 0.5 by modifying the sequence of the discrete-source gas pulses. A polarization-voltage hysteresis loop was observed for a 70 nm thick PZT film deposited on a planar substrate after postannealing for crystallization. To assess the feasibility of ALD as a tool for coating three-dimensional (3D) structures uniformly, PZT films were deposited on submicrometer 3D structures. As-deposited amorphous PZT films as well as crystallized PZT films were both free of any gradient in the cation composition over the structure. The present work reports interesting interactions on stacking different binary-oxide layers by ALD and demonstrates why the multiprecursor ALD process is a promising approach for uniformly coating 3D nanostructures with complex oxide materials.