Physical and electrical characterization of Hafnium oxide and Hafnium silicate sputtered films

Abstract

Hafnium oxides and hafnium silicate films were investigated as a possible replacement for the SiO2 gate dielectric. Hafnium oxide films were formed by reactive sputtering from a single Hf oxide target in a predominantly Ar atmosphere containing small additions of oxygen. Hafnium silicates were made by adding a He-diluted silane gas for Si incorporation. By changing the silane gas flow, different Si atomic concentrations were incorporated into the Hf oxide films. Depositions were performed with the substrate held at temperatures of 22 °C and 500 °C. The chemical composition of the films was determined with nuclear techniques. Optical reflectivity was used to measure the optical band gap. The film morphology was investigated by transmission electron microscopy (TEM) and the electrical properties were measured with capacitance–voltage and current–voltage measurements using aluminum gate capacitors. TEM and electrical measurement showed that a SiO2 interfacial layer of about 3 nm formed at the Si interface due to the oxidizing sputter ambient. This precluded the growth of Hf based high-K films with small equivalent thickness. After correction for the interfacial oxide layer, the dielectric constant was found to decrease from about 21 for Hf oxide to about 4–5 for the Hafnium silicates with low Hf content (3 at. % Hf and 32 at. % Si). The optical band gap was found to increase from 5.8 eV for Hf oxide to about 7 eV for the silicate films. After annealing at 1000 °C followed by a 300 °C postmetallization anneal, negligible flat band voltage shift were measured on hafnium silicate films and good interface passivation was observed. However, leakage currents increased due to the high temperature processing.

Electrical, structural, and chemical properties of HfO2 films formed by electron beam evaporation

“…Relatively thick SiO 2 IL formation during HfO 2 deposition using reactive sputtering in Ar/ O 2 ambient has already been observed previously. [26][27][28] In all studies, the IL thicknesses, 25, 28, and 32 Å, respectively, are very close to the IL thickness ͑30 Å͒ of the current work for HfO 2 films formed in O 2 ambient and with the ion assist on ͑samples C, 2, and 3͒. This indicates that in the presence of Ar/ O 2 plasma and in low temperature conditions ͓from 24°C ͑Ref.…”

“…The IL thickness is further increased ͑from 25 to 36 Å͒ when the substrate temperature is raised to 500°C. 26 Yamamoto et al, 27 however, managed to reduce the IL thickness by forming a Hf metal layer preventing oxidizing species from diffusing to the Si interface during the deposition. This Hf metal layer must be engineered to be entirely oxidized otherwise the presence of metallic Hf deteriorates the electrical properties.…”

Band alignment issues related to HfO2∕SiO2∕p-Si gate stacks

“…The literature consensus is that HfO 2 films have a gap of 5.6-6.0 eV, although the proof and methodology of this remains debated. [16][17][18][19][20] We obtain this value from our results by defining the edge as the 2 level of the Gaussian-modeled band tail states. Although there is no strong theoretical argument to include what we are calling band edge defect states in defining the "real" gap, they may be considered as contributing to an "effective" band gap (see Fig.…”

Morphology and crystallization kinetics in HfO2 thin films grown by atomic layer deposition

“…HfO 2 is compatible with polysilicon processing, [2][3][4][5][6] has a high dielectric constant of ϳ16 -25, 2,7-9 and has demonstrated very encouraging initial device characteristics. [10][11][12][13][14][15] The thermal stability of high-materials in direct contact with Si and SiO 2 has also emerged as a key issue in selecting suitable high-candidates. The thermal stability of HfO 2 films in contact with Si and SiO 2 has been studied for HfO 2 deposited by atomic layer deposition ͑ALD͒, 16 ion beam assisted deposition, 17 metalorganic chemical vapor deposition, 18 and jet vapor deposition ͑JVD͒.…”