As-deposited HfO2 Films Research Articles

Characteristics of HfO2 thin films deposited by plasma-enhanced atomic layer deposition using O2 plasma and N2O plasma

The characteristics of HfO2 dielectrics deposited by the plasma-enhanced atomic layer deposition (PEALD) method using O2 and N2O plasmas were investigated. The deposited HfO2 films had a randomly oriented polycrystalline phase while the interfacial layers of the films were amorphous. During the PEALD process with N2O plasma, nitrogen was mainly incorporated into the interfacial region between the HfO2 film and the Si substrate. The nitrogen content of 2–3at.% in the interface was analyzed by Auger electron spectroscopy. The incorporated nitrogen at the interface effectively suppressed residual oxygen diffusion during subsequent annealing at 800°C in a N2 atmosphere. A thicker interfacial layer was observed in the as-deposited and annealed HfO2 film with O2 plasma than with N2O plasma. For HfO2 films prepared with the N2O plasma, where equivalent oxide thickness (EOT) increased from 1.43to1.56nm after annealing, the leakage current densities, measured at a gate bias voltage of ∣VG−VFB∣=2, increased from 3.5×10−8to4.8×10−8A∕cm2. For HfO2 films prepared with the O2 plasma, where EOT increased from 1.60to2.01nm after annealing, the leakage current densities decreased from 1.1×10−6to1.3×10−7A∕cm2. The film with O2 plasma had a higher amount of negative fixed oxide charges than the film with N2O plasma. N2O plasma improved the leakage current properties by allowing nitrogen incorporation at the interfacial region and less crystallization of HfO2 film.

Atomic Force Microscopic Nanolithography on Hafnium Oxide Thin Film Grown on Si(100)

As a high-dielectric-constant material, hafnium oxide is one of the promising gate oxides to replace SiO2 for future applications in microelectronics. By atomic force microscopy (AFM), we investigate the AFM-induced anodic oxidation on a hafnium oxide surface and compare the wet etching property of this local oxide with the as-deposited 3 nm HfO2 film in dilute HF solution. Oxide patterns can be reproducibly fabricated and their protruded feature mainly results from the local oxidation of the Si(100) substrate. The AFM-induced oxide pattern has a higher etch rate than the as-deposited HfO2 film due to a greater amount of oxygen.

Composition, structure, and electrical characteristics of HfO2 gate dielectrics grown using the remote- and direct-plasma atomic layer deposition methods

Hafnium oxide thin films were deposited using both the remote-plasma atomic layer deposition (RPALD) and direct-plasma atomic layer deposition (DPALD) methods. Metal-oxide semiconductor (MOS) capacitors and transistors were fabricated with HfO2 gate dielectric to examine their electrical characteristics. The as-deposited RPALD HfO2 layer exhibited an amorphous structure, while the DPALD HfO2 layer exhibited a polycrystalline structure. Medium-energy ion scattering measurement data indicate that the interfacial layer consisted of interfacial SiO2−x and silicate layers. This suggests that the change in stoichiometry with depth could be related to the energetic plasma beam used in the plasma ALD process, resulting in damage to the Si surface and an interaction between Hf and SiO2−x. The as-deposited RPALD HfO2 films had better interfacial layer characteristics, such as an effective fixed oxide charge density (Qf,eff) and interfacial roughness than the DPALD HfO2 films did. A MOS capacitor fabricated using the RPALD method exhibited an equivalent oxide thickness (EOT) of 1.8nm with a Qf,eff=−4.2×1011q∕cm2 (where q is the elementary charge, 1.6022×10−19C), whereas a MOS capacitor fabricated using the DPALD method had an EOT=2.0nm and a Qf,eff=−1.2×1013q∕cm2. At a power=0.6MV∕cm, the RPALD n-type metal-oxide semiconductor field-effect transistor (nMOSFET) showed μeff=168cm2∕Vs, which was 50% greater than the value of the DPALD nMOSFET (μeff=111cm2∕Vs). In the region where Vg-Vt=2.0V, the RPALD MOSFET drain current was about 30% higher than the DPALD MOSFET drain current. These improvements are believed to be due to the lower effective fixed charge density, and they minimize problems arising from plasma charging damage.

Characteristics of HfO2 thin films grown by plasma atomic layer deposition

The characteristics of HfO2 films grown on Si substrates using a tetrakis-diethyl-amino-hafnium precursor by the remote plasma atomic layer deposition (RPALD) and direct plasma ALD (DPALD) methods were investigated by physical and electrical measurement techniques. The as-deposited HfO2 layer from RPALD exhibits an amorphous structure, while the HfO2 layer from DPALD exhibits a clearly visible polycrystalline structure. Medium energy ion scattering measurement results indicate that the interfacial layer consists of the interfacial SiO2−x and silicate layers. These results suggested that the stoichiometric change in the depth direction could be related to the energetic reactant in a state of plasma used in the plasma ALD process, resulting in damage to the Si surface and interactions between Hf and SiO2−x. The as-deposited HfO2 films using RPALD have the better interfacial layer characteristics than those using DPALD. A metal-oxide-semiconductor capacitor fabricated using the RPALD method exhibits electrical characteristics such as equivalent oxide thickness (EOT) of 1.8 nm with an effective fixed oxide charge density (Qf,eff) of ∼4.2×1011q∕cm2 and that for DPALD has a EOT (2.0 nm), and Qf,eff(∼−1.2×1013q∕cm2).

Electrical characteristics of postdeposition annealed HfO2 on silicon

Electrical characteristics of ultrathin HfO2 films on p-type silicon (100) substrates were determined by capacitance-voltage and current density-voltage measurements. The as-deposited HfO2 films showed a dielectric constant of ∼22, a leakage current density of 5A∕cm2 and an interface state density of 6.5×1012cm2eV−1 at an equivalent oxide thickness (EOT) of 7.6Å due to the poor quality of HfO2∕Si interface. However, annealing in O2 and NH3 significantly reduced the interface state densities to 8.4×1011cm2eV−1 and 7.38×1011cm2eV−1, respectively, although the annealing increased the EOTs to 12.3Å and 11.3Å respectively, due to the growth of an additional interfacial layer. The forming gas anneal with either H2 or D2, however, significantly improved the quality of the HfO2∕Si interface without affecting the EOT. Postdeposition annealing in all chemistries decreased the leakage current densities by orders of magnitude at the same EOT compared to that of SiO2. The current transport mechanism in the as-deposed HfO2 sample is determined to be direct tunneling, and an Al∕HfO2 barrier height of 1.3eV and a HfO2∕Si barrier height of 1.4eV were obtained. The latter is in good agreement with the band offset determined by x-ray photoelectron spectroscopy analysis and ab initio calculations.

Correlation between scanning-probe-induced spots and fixed positive charges in thin HfO2 films

Scanning tunneling microscopy observations revealed unstable species that likely act as fixed positive charges in thin HfO2 films. The density of these species can be practically reduced by low-temperature postdeposition annealing (∼550°C). The results of various annealing conditions suggest that hydrogenous species created by the reaction of moisture with as-deposited HfO2 films causes this type of fixed positive charges in the films.

Study of HfO2 films deposited on strained Si1−xGex layers by atomic layer deposition

This paper focuses on the growth of HfO2 by atomic layer deposition (ALD) at 350°C on pseudomorphic Si1−xGex thin films (x=15% and 25%). Two different Si1−xGex surface preparations (chemical oxidation and HF “last” treatment) have been investigated to obtain the highest HfO2 film quality with the thinnest interfacial layer possible. The initial stages of the ALD growth on these different surfaces (i.e., hafnium adsorption and chlorine contamination) analyzed by total x-ray fluorescence show that HF last treated Si1−xGex surfaces are more convenient than chemically oxidized ones to grow high quality HfO2 layers. This result is confirmed by x-ray photoelectron spectroscopy investigations of the interfacial layer structure as a function of the surface treatment. As-deposited and annealed thin HfO2 layers (2.5, 3.5, 5, and 8nm) grown on HF last treated Si0.75Ge0.25 strained layers were analyzed by mercury probe. An equivalent oxide thickness as low as 0.7nm was obtained for a 2.5nm as-deposited HfO2 film. Mobility results show that a 22% mobility enhancement is obtained in the entire effective field range with HfO2∕SiGe compared to the HfO2∕Si reference.

Crystallisation kinetics and density profiles in ultra-thin hafnia films

Crystallisation onset temperatures as a function of chlorine contamination have been determined by grazing incidence diffraction on as-deposited ultra-thin HfO2 films grown by Atomic Layer Deposition. The onset temperatures are positively correlated with chlorine content, suggesting defect-hindered crystallisation kinetics. Density profiles have been deduced by reflectometry measurements and a model independent analysis scheme. It is shown that the HfO2/SiO2-Si interface is electronically denser than the bulk of the HfO2 film.

Interface of ultrathin HfO2 films deposited by UV-photo-CVD

We report in this article the deposition of ultra-thin HfO2 films on silicon substrate at 300–450 °C by photo-induced CVD using 222 nm excimer lamps. As-deposited films from 2.5 to 10 nm in thickness with refractive indices from 1.60 to 1.85 were grown. The deposition rate measured by ellipsometry was found to be 3 nm/min at a temperature of 400 °C. XRD showed that as-deposited HfO2 films were basically amorphous. Investigation of the interfacial layer by XPS and TEM reveals that thickness of the interfacial SiO2 layer slightly increases with the UV-annealing time and UV annealing can convert suboxide at interface into stoichiometric SiO2, leading to improved interfacial quality. Fourier transform infrared spectroscopy (FTIR), revealed that Hf–O absorption in the photo-CVD deposited HfO2 films is quite different at various deposition parameters. When compared to similar studies performed previously in zirconium, titanium and tantalum oxides, the interface layer of HfO2 is generally thinner than that of other materials. UV annealing can convert a suboxide at interface between the HfO2 and Si into stoichiometric SiO2, leading to improved interfacial quality. The thickness of the interface layer (silicon oxide or hafnium silicate) decreases with increasing thickness of the top HfO2 layers.

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

We report the effects of annealing on the morphology and crystallization kinetics for the high-κ gate dielectric replacement candidate hafnium oxide (HfO2). HfO2 films were grown by atomic layer deposition (ALD) on thermal and chemical SiO2 underlayers. High-sensitivity x-ray diffractometry shows that the as-deposited ALD HfO2 films on thermal oxide are polycrystalline, containing both monoclinic and either tetragonal or orthorhombic phases with an average grain size of ∼8.0 nm. Transmission electron microscopy shows a columnar grain structure. The monoclinic phase predominates as the annealing temperature and time increase, with the grain size reaching ∼11.0 nm after annealing at 900 °C for 24 h. The crystallized fraction of the film has a strong dependence on annealing temperature but not annealing time, indicating thermally activated grain growth. As-deposited ALD HfO2 films on chemical oxide underlayers are amorphous, but show strong signatures of ordering at a subnanometer level in Z-contrast scanning transmission electron microscopy and fluctuation electron microscopy. These films show the same crystallization kinetics as the films on thermal oxide upon annealing.