Atomic Layer Deposition of Pb(Zr,Ti)Ox, Thin Films by a Combination of Binary Atomic Layer Deposition Processes

Abstract

After an evaluation of Zr precursor, quaternary Pb(Zr,Ti)O_x [PZT] films were prepared by a combination of binary atomic layer deposition (ALD) processes. ZrO_x films were deposited on Pt/TiO_x/SiO_x/Si substrates using liquid injection ALD. Zr(C₁₁H₁₉O₂)₄ [Zr(DPM)₄] dissolved in ethylcyclohexane (ECH) with a concentration of 0.1 M and water were used as precursor and oxidant, respectively. According to the Arrhenius plot for the deposition rate of ZrO_x films at various deposition temperatures, the Zr precursor appeared to start marked thermal decomposition at a deposition temperature of 360degC. Below this thermal decomposition temperature, a saturated deposition rate of ZrO_x films against input of Zr precursor was confirmed. The saturated deposition rate was about 5-6x10^-12 mol/cm²-cycle at a deposition temperature of 300degC. Subsequently, binary ALD processes of TiO_x and PbO films, whose self-regulated growth mode has been already confirmed, were combined with the ZrO_x process into multi-precursor ALD of PZT films. Ti(OC₃H₇)₂(C₁₁H₁₉O₂)₂ [Ti(Oi-Pr)₂(DPM)₂] and Pb(C₁₁H₁₉O₂)₂ [Pb(DPM)₂] dissolved in ECH with a concentration of 0.1 M were used for PZT film preparation as well as Zr(DPM)₄. Unit sequences described as 1times(Pb-O)-2times(Ti-O) -ntimes(Zr-O) were repeated to deposit PZT films at 240degC. In the PZT process, the deposition rates of all cations were higher than those in their binary processes. The Pb/(Zr+Ti) and Zr/(Zr+Ti) ratio was adjusted by repeating the number of Zr-O cycles in a sequence. As-deposited PZT films were amorphous. Crystalline PZT films were obtained after annealing at 650degC, and the PZT crystal showed a preferred (100)/(001) orientation.