Choelhwyi Bae

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 electric...

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 th...

Surface passivation of n-GaN by nitrided-thin-Ga2O3∕SiO2 and Si3N4 films

The electrical characteristics of n-GaN∕nitrided-thin-Ga2O3∕SiO2 and n-GaN∕Si3N4 metal-insulator-semiconductor (MIS) capacitors have been compared, and the work-function difference ϕms and effective dielectric-fixed charge density Qf,eff have been determined. Oxide samples showed lower interface trap level density Dit, lower leakage current, and better reproducibility compared to the nitride samples. The superior properties of the oxide samples are partially attributed to the nitrided-thin-Ga2O3 layer (∼0.6-nm-thick). ϕms and Qf,eff were determined, respectively, as 0.13V and 1.0×1012qcm−2 in oxide and 0.27V and −3.6×1011qcm−2 in nitride samples using flatband voltage versus dielectric thickness data. True dielectric-fixed charge density and location of the major amount of fixed charge are discussed based on Qf,eff, Dit, and spontaneous polarization of n-GaN.

Suppression of parasitic Si substrate oxidation in HfO2–ultrathin-Al2O3–Si structures prepared by atomic layer deposition

We investigated the effects of Al2O3 thickness on the suppression of parasitic substrate oxidation in HfO2–ultrathin-Al2O3–Si structures. The use of H2O as oxidizing agent in the atomic layer deposition (ALD) chemistry is considered key to preventing the formation of an SiOx interlayer during oxide deposition. An Al2O3 layer prepared with 10 cycles of atomic layer deposition (ALD, ∼0.74nm) effectively suppressed substrate oxidation during rapid thermal annealing in N2 for 10 s below 800 °C. Parasitic oxidation was observed at 600 °C for samples with only five cycles or without Al2O3. Ultrathin Al2O3 films can be relevant for the integration of HfO2 as gate dielectric in silicon technology.

Effects of N2 remote plasma nitridation on the structural and electrical characteristics of the HfO2 gate dielectrics grown using remote plasma atomic layer deposition methods

The characteristics of remote plasma atomic layer deposited HfO2 on Si, which has a very thin SiO2 interlayer with and without remote plasma nitridation (RPN), have been investigated. Small amounts of N atoms were successfully incorporated by RPN pretreatment, in which the dominant emission species were excited atomic nitrogen (N*) and excited molecular nitrogen (N2*), into a very thin SiO2 interlayer for the growth of HfO2 thin film. The thin (∼1.5nm) intermediate layer containing nitrogen, which was prepared by sequential O2 and N2 remote plasma treatment of the Si substrate, can effectively suppress growth of the unintentional interface layer. In addition, it enhances the thermal stability and the resistance to oxygen diffusion during rapid thermal annealing. The HfO2 film containing the remote plasma nitrided SiO2 interlayer annealed at 800°C showed a lower equivalent oxide thickness of ∼1.89nm and a lower leakage current density (3.78×10−7Acm−2 at ∣VG−VFB∣=2V) compared to a non-nitrided sample of the...

Electron trapping in metal-insulator-semiconductor structures on n-GaN with SiO2 and Si3N4 dielectrics

Electron trapping in Al-gate n-GaN∕nitrided-thin-Ga2O3∕SiO2 and n-GaN∕Si3N4 MIS capacitors was evaluated by capacitance-voltage (C–V) measurements. Significant positive flatband voltage shift (ΔVfb) was observed with increasing starting dc bias in the C–V measurements. For similar equivalent oxide thickness and under the same C–V measurement conditions, ΔVfb in the nitride was 3–10 times larger than in the oxide samples. It is suggested that flatband voltage shifts are due to border traps in SiO2 and to interface and bulk traps in Si3N4 samples.

Low-temperature preparation of GaN-SiO2 interfaces with low defect density. I. Two-step remote plasma-assisted oxidation-deposition process

In previous studies, device-quality Si-SiO2 interfaces and dielectric bulk films (SiO2) were prepared using a two-step process: (i) remote plasma-assisted oxidation (RPAO) to form a superficially interfacial oxide (∼0.6nm) and (ii) remote plasma-enhanced chemical vapor deposition (RPECVD) to deposit the oxide film. The same approach has been applied to the GaN-SiO2 system. Without an RPAO step, subcutaneous oxidation of GaN takes place during RPECVD deposition of SiO2, and on-line Auger electron spectroscopy indicates a ∼0.7-nm subcutaneous oxide. The quality of the interface and dielectric layer with/without RPAO process has been investigated by fabricated GaN metal-oxide-semiconductor capacitors. Compared to single-step SiO2 deposition, significantly reduced defect state densities are obtained at the GaN-SiO2 interface by independent control of GaN-GaOx interface formation by RPAO and SiO2 deposition by RPECVD.

Work-function difference between Al and n-GaN from Al-gated n-GaN/nitrided-thin-Ga2O3/SiO2 metal oxide semiconductor structures

In most previous reports on Al-gated n-GaN∕SiO2 metal–oxide–semiconductor (MOS) structures, the work–function difference between Al and n-GaN (ϕms) has been chosen as 0V by assuming that the work function of the Al gate and n‐GaN are both 4.1eV. In this letter, ϕms is determined as ∼0.1V using Al-gated n-GaN∕nitrided-thin-Ga2O3∕SiO2 MOS capacitors by measuring flatband voltage as a function of oxide thickness. Formation of an ultrathin (∼0.6-nm-thick) Ga2O3 layer on n-GaN prior to the deposition of SiO2 is important to prevent uncontrolled parasitic oxidation of then-GaN surface and possibly reduces the interface dipole between n-GaN and SiO2.

Ex situ growth of the c-axis preferred oriented SrBi2Ta2O9 thin films on Pt/Ti/SiO2/Si substrates

SrBi2Ta2O9 (SBT) thin films were deposited on (111) oriented Pt bottom electrodes using the rf magnetron sputtering method and then postannealed at 650–800 °C for 30 min in different oxygen atmospheres. The effect of Bi content on the c-axis preferred oriented growth was confirmed by the control of the Bi2O3 loss during the postannealing. With increasing Bi content in SBT thin films, the degree of the c-axis preferred orientation was enhanced. In addition, a bimodal grain size distribution due to the Sr deficiency in the SBT film was observed. It is suggested that the c-axis preferred oriented growth on Pt(111) bottom electrodes can be attributed to growth controlled by surface energy minimization.

Effect of Buffer Layer for HfO2 Gate Dielectrics Grown by Remote Plasma Atomic Layer Deposition

Three different buffer layers on a Si substrate were grown to investigate the interfacial layer effect during HfO 2 deposition and thermal annealing. The three different buffer layers were the very thin Al 2 O 3 , remote plasma nitridation (RPN)-treated Al 2 O 3 , and RPN-treated HfO 2 films. HfO 2 films were then grown on these three different buffer layers by a remote plasma atomic layer deposition method. The HfO 2 films with RPN-treated buffer layers retarded silicate formation or growth of an interfacial layer more effectively than those without RPN treatment. The HfO 2 films with an RPN-treated HfO 2 buffer layer showed the lowest effective oxide thickness and those with an RPN-treated buffer layer exhibited low leakage current density. The effective fixed-oxide charge density of the HfO 2 film with an RPN-treated HfO 2 buffer layer showed the lowest value of 3.60 X 10 11 /cm 2 compared to the other films. As the annealing temperature increased, the flatband voltage (V FB ) for the HfO 2 films was shifted and became close to the ideal V FB . The interface stability of HfO 2 with a nitrided buffer layer formed by RPN treatments resulted in the improvement of the electrical properties of HfO 2 films.