Atomic layer deposition of binary and ternary lead and bismuth thin films

Jenni Harjuoja
Abstract & Cover

This thesis describes the deposition of binary lead oxide and ternary lead titanate, lead zirconate, bismuth silicate, and bismuth titanate films by atomic layer deposition (ALD) and characterization of structural, compositional and surface properties of the films. The first part of the thesis reviews the principles of the ALD technique and the relevant literature on perovskite oxides and films and the deposition of lead and bismuth films by ALD, and the second part summarizes the experimental work reported in the five appended publications. On the basis of the binary lead oxide depositions, the Ph4Pb/O3 process was chosen for the ternary oxide studies. Careful optimization of the pulsing ratio of the binary oxides allowed processing of stoichiometric perovskite PbTiO3 and PbZrO3 thin films. Crystalline PbTiO3 on Si(100) was detected after annealing at 600 °C. In the case of lead zirconate, the perovskite phase (PbZrO3) was obtained on SrTiO3(100) after annealing at 600 °C. In both cases, a slight excess of lead enhanced the crystallinity. Roughness values were nevertheless higher than values obtained in binary processes. A new bimetallic precursor Bi(CH2SiMe3)3 was introduced for the deposition of bismuth silicate. With ozone as oxidizing agent, ALD-window for Bi-Si-O thin film growth was found at 250-350 °C. The Si to Bi atomic ratio in this region was about 2. Addition of a second bismuth precursor, BiPh3, increased the bismuth content. Combination of the BiPh3/O3 process and the Ti(O-i-Pr)4/H2O process allowed successful deposition of bismuth titanate. Good control of the film stoichiometry was achieved at the deposition temperature of 250 °C. Both as-deposited ternary bismuth oxides were amorphous. After annealing at 600 °C, the a-axis-oriented Bi2SiO5 phase was detected. Higher annealing temperatures were necessary for bismuth titanate. The most textured film of Bi4Ti3O12 was obtained in N2 atmosphere at annealing temperature of 1000 °C. Roughness values of the thin films were reasonable, being in the range of 0.3-1.3 nm. 

Source of Information
FinALD40 exhibition material,
Helsinki University of Technology, Department of Chemical Technology, Laboratory of Inorganic and Analytical Chemistry
(Espoo, Finland)
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