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|When:||08/ 6/2014 3:00 PM - 4:00 PM|
|Description:||ALS/CXRO Seminar Series|
Ambient Pressure Photoelectron Spectroscopy at the MAX IV Laboratory and Real-time Characterization of the Atomic Layer Deposition of Metal Oxides
Ambient pressure X-ray photoelectron spectroscopy (APXPS) capabilities are quickly expanding at the MAX IV Laboratory in Lund, Sweden. The SPECIES beamline is currently finishing renovation at the MAX II storage ring, and a second APXPS endstation will come online with the new MAX IV storage ring in 2016. A brief overview of this instrumentation will be given followed by a presentation of an ongoing project to study the surface chemistry of the atomic layer deposition of metal oxides.
Thin films of high-κ metal oxides are of growing interest in the effort to reduce the size of electronic devices. Atomic layer deposition (ALD) is widely used to grow films of metal oxides as it allows for the controlled growth of a consistent film over small three-dimensional structures. Through alternating exposure between two molecular precursors, self-limiting growth of thin films by simple ligand displacement reactions is thought to be the principle mechanism. However, evidence is mounting that more complex surface chemistry exists and can influence the quality of the films. In an effort to increase the understanding of the reactions that take place during the ALD, we have studied the process in real-time during the deposition of HfO2 onto InAs and TiO2 on titania using ambient pressure X-ray photoelectron spectroscopy.
Tetrakis(dimethylamido) hafnium (TDMAH) and titanium tetraisoproxide (TTIP) were used as metal precursors while water was used as the oxygen source for both systems. Removal of the isoproxide ligands in TTIP happens via a ligand dissociation mechanism, but not all of the ligands are fully displaced during the hydrolysis reaction as seen in the C 1s spectra. In contrast, complete surface hydrolysis occurs in the HfO2 system. However, upon reaction of TDMAH with the surface, the amido ligands undergo more complex surface chemistry, as demonstrated by multiple peaks in the N 1s spectra. Temperature influences the species formed on the surface only during the HfO2 deposition. A transient species was detected in the Hf 4f spectra, showing electronic structure changes during the initial reaction of TDMAH with the surface. These results confirm the surface chemistry during ALD is more complex than the idealized process often envisioned.