Abstract
We investigated the room temperature growth of HfO2 layers on Si substrates by pulsed laser deposition under ultra-high vacuum conditions. The laser fluence (LF) during HfO2 layer growth was varied as a growth parameter in the experiments. X-ray photoemission spectroscopy (XPS) was used to observe the interface chemical states of the HfO2/Si samples produced by various LFs. The XPS results indicated that an interface Hf-silicate layer formed, even at room temperature, and that the thickness of this layer increased with increasing pulsed LF. Additionally, Hf-Si bonds were increasingly formed at the interface when the LF was more than 2 J/cm2. This bond formation process was related to decomposition of HfO2 to its atomic states of Hf and O by multiphoton photochemical processes for bandgap excitation of the HfO2 polycrystalline target. However, the Hf-Si bond content of the interface Hf-silicate layer is controllable under high LF conditions. The results presented here represent a practical contribution to the development of room temperature processing of Hf-compound based devices.
Highlights
Hafnium (Hf)-based compounds such as HfO2, Hf-silicate, and nitride Hf-silicate have been intensively studied as candidate materials to replace SiO2 in advanced metal-insulator-semiconductor field-effect transistors (MISFETs).[1,2,3,4,5,6,7] Hf-silicate is a most promising material because of its relatively high dielectric constant when compared with that of SiO2, wide band gap (Eg ∼6 eV), large (1.5 eV) conduction band offset to Si,[9] and low interface state density with Si (Dit = 1–6×10 11 cm 2eV 1).[4]
Houssa et al studied the effects of Hf content on negative bias temperature instability (NBTI) in nitride Hf-silicate gate stacks and found that NBTI is reduced in layers with Hf content of approximately 50 at.%
While Hf-silicate layers have been grown on Si substrates by several physical vapor deposition (PVD) techniques, such as sputtering,[4,13,14] and chemical vapor deposition methods such as atomic layer deposition (ALD),[6,15,16] these layer fabrication methods require high temperature processing above 600◦C for material growth, postdeposition annealing, or both
Summary
Room temperature formation of Hf-silicate layer by pulsed laser deposition with Hf-SiO ternary reaction control We report on a unique phenomenon in PLD growth, where a ternary reaction at the interface between a binary metal oxide film and the Si substrate is controllable via the LF magnitude at room temperature (RT).
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