Nucleation, Growth, and Electrical Characterization of Al2O3 Thin Films Grown by Atomic Layer Deposition
Aponte Rivera, Fernando J.
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Materials with higher dielectric constant than SiO2 (~ .4.0), called as high-k materials, are of great demand for CMOS transistors and DRAM capacitors. Aluminum oxide (Al2O3) has many interesting properties, such as high dielectric constant (~9.7), high band gap (8.9 eV) and band offset (conduction band ~ 2.8eV, valence ~ 3.2 eV), high thermal and chemical stability, high dielectric strength (15 MV/cm), high radiation resistance, stable interface with Si, low bulk defect density, high crystallization temperature (~ 1200 C) and could be a potential candidate to replace SiO2 as a gate dielectric. Extensive work has been done on high-k metal oxides to reduce the leakage current and improve the gate capacitance. However, the lack of understanding of nucleation and growth mechanism of the ultra-thin films of Al2O3 on different surfaces is one the main bottle neck in achieving the low leakage. Atomic layer deposition (ALD) is one the state-of-the-art thin film growth technique know for layer-by-layer atomic growth. It is believe that the growth thin films by ALD will able meet the low leakage current requirement of micro- and nano-electronic devices. In the present study, in order to understand the growth mechanism (nucleation process and growth modes), structural, microsctructural, electrical, and dielectric properties of Al2O3 thin films by ALD, one set of thin films was grown with different pulse cycles on Si(111) substrates and another set of thin films of 100 nm thick was grown on different orientation of Si substrates, such as Si(100), Si(110), and Si (111). Structural, microstructural, electrical, and dielectric measurements were carried out using X-ray diffraction, X-ray photoelectron spectroscopy (XPS) atomic force microscopy (AFM), current-voltage characterization and dielectric measurements.X-ray diffraction studies showed the amorphous nature of thin films. AFM and XPS analysis revealed that the films grown with 1 and 2 pulsing cycles showed discrete nucleation and island-like growth, which is contrary to common perception that the pulsing one cycle will result the growth of one atomic layer. The current-voltage characteristics showed rectifying like behavior. The dielectric measurements that the films have low dielectric loss up to 1 MHz.