Paper TF+EM+NS+SS-ThA1
Comparison of Al₂O₃ Deposited via Prompt Inorganic Condensation vs. Atomic Layer Deposition

Thursday, October 31, 2013, 2:00 pm, Room 104 A

Due to the purge separated pulsing of precursor and oxidation gases combined with self-limiting surface reactions, atomic layer deposition (ALD) enables the synthesis of dense conformal thin films with atomic scale control. In terms of sustainable manufacturing however, ALD suffers from slow deposition rates, precursor waste, and the requirement of a vacuum system. Solution-based thin-film deposition methods are attractive because they allow for deposition at atmospheric pressure and with shorter processing times. However, traditional solution based approaches often involve organometallic sol-gels with bulky ligands. High temperature post deposition anneals are required to drive off these ligands resulting in a dramatic change in physical dimensions as the films are densified. The resulting films are thus often porous and exhibit poor electrical properties. More recently, a novel solution processing technique known as prompt inorganic condensation (PIC) enables the deposition of dense, smooth, high-quality films through the use of aqueous metal-inorganic precursors.

In this work we compare the electrical and physical properties of Al₂O₃ films produced by ALD and PIC. ALD of Al₂O₃ was performed using trimethyl-aluminum and H₂O at 300°C. PIC of Al₂O₃ was performed using an aqueous aluminum hydroxide nitrate solution at room temperature in atmosphere. Post deposition anneals were performed following PIC to convert the hydroxide to an oxide and densify the films. Al/Al₂O₃/Si MOS capacitors were used for electrical measurements. For 10 nm thick films, 300°C annealed PIC Al₂O₃ shows higher leakage, and lower breakdown strength than ALD Al₂O₃. After a 500°C anneal, the PIC Al₂O₃ shows lower leakage current density at fields >2.5 MV/cm and equivalent breakdown strength to ALD Al₂O₃. Conduction mechanisms will be discussed. Capacitance vs. voltage data showed that PIC films have a lower dielectric constant than ALD films and an anneal temperature dependent flat band voltage shift. X-ray reflectivity indicates that as-deposited PIC films have a low density which increases with increasing anneal temperature to approach that of the ALD films. Finally, X-ray photoelectron spectroscopy and transmission electron microscope data are used to examine the Al₂O₃/Si interfacial region. Differences in interfacial layer formation may explain the reduced leakage current observed in the lower density PIC films. Our results show that PIC is promising method for deposition of thin (~10 nm) Al₂O₃ films on silicon.