NH3 Plasma Nitridation Research Articles

Double nitridation of crystalline ZrO2/Al2O3 buffer gate stack with high capacitance, low leakage and improved thermal stability

The gate dielectric stack composed of crystalline ZrO2 and Al2O3 buffer layer treated with double nitridation was developed to reduce the capacitance equivalent thickness (CET), leakage current density (Jg), interfacial state density (Dit), and enhance thermal stability as well. A high dielectric constant of the gate stack was provided by the crystalline ZrO2 with tetragonal/cubic phase. The Jg and Dit were suppressed by the insertion of the Al2O3 buffer layer treated with remote NH3 plasma nitridation because of the deactivation of the oxygen vacancies and the well passivation of the Si dangling bonds. A further nitridation using remote N2 plasma on ZrO2 was carried out to reduce the CET and Jg by the enhancement of the dielectric constant and the deactivation of the grain boundaries and oxygen vacancies. Accordingly, a low CET of 1.09nm, Jg of 3.43×10−5A/cm2, and Dit of 3.35×1011cm−2eV−1 were achieved in the crystalline ZrO2/Al2O3 buffer gate stack treated with the double nitridation. The hysteresis was also minimized significantly by the post-deposition annealing at 800°C, which is attributed to the enhanced thermal stability. The results indicate that the crystalline high-K dielectrics/buffer layer with double nitridation treatments is a promising gate stack structure beneficial to the sub-nanometer CET scaling in the future.

Impact of <i>In Situ</i> NH<sub>3 </sub>Plasma Treatments on the Interface between HfLaO<sub>x</sub><i></i> Thin Film and InP Substrate

In situ NH3 plasma nitridation was utilized to passivate InP surface, HfLaOx film was grown by plasma enhanced atom layer deposition method, and the HfLaOx film remain amorphous after 500°C annealing. High-resolution transmission electron microscopy (HRTEM) images showed that in situ NH3 plasma nitridation process make the boundary between InP and HfLaOx smooth and sharp, and could suppress the formation of the interfacial layer. X-ray photoelectron spectra (XPS) results indicated In-N and P-N bonds were formed on the nitride InP surface. The electrical measurements indicated in situ NH3 plasma nitridation process reduced the hysteresis improved capacitance density and to 7 mV, a sharp transition from depletion to accumulation was observed, the interfacial density states (Dit) of the sample with nitridation was 1.67×1012 cm2 eV1, and the equivalent oxide thickness (EOT) was 0.6 nm. The leakage current was 1.5 mA/cm2 at Vg-Vfb=1V.

Properties of LaAlO3 thin film on GaAs(1 0 0) treated by in situ NH3 plasma

In this work, we deposited LaAlO3 film on n-type GaAs by plasma enhanced atomic layer deposition (PEALD). In situ NH3 plasma nitridation of the GaAs surface was introduced to control the interface prior to plasma enhanced atomic layer deposition of LaAlO3. The chemical bonding state of NH3 plasma treated GaAs surface were investigated by X-ray photoelectron spectroscopy (XPS), which indicate that NH3 plasma nitridation can suppress interfacial growth on GaAs substrate. Transmission electron microscopy (TEM) images show the interface between LaAlO3 and GaAs was smooth and there was not obvious interface layer observed. The capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurement indicate that the NH3 plasma nitridation improved the electrical properties of LaAlO3 films on GaAs substrate.

Improvement of Capacitance Equivalent Thickness, Leakage Current, and Interfacial State Density Based on Crystallized High-K Dielectrics/Nitrided Buffer Layer Gate Stacks

The gate stack composed of tetragonal/cubic ZrO2 high-K dielectrics and nitrided Al2O3 buffer layer was investigated to reduce the capacitance equivalent thickness (CET), leakage current density (Jg), and interfacial state density (Dit). The high-K tetragonal/cubic phase of ZrO2 was formed by post metallization annealing at a low temperature of 450°C. The Jg was suppressed by the insertion of the Al2O3 buffer layer between ZrO2 and Si. The remote NH3 plasma nitridation on the Al2O3 buffer layer further leads to the deactivation of the oxygen vacancies and the well passivation of the Si dangling bonds. Accordingly, a suppressed Jg of 8.12 × 10−6 A/cm2 and Dit of 2.77 × 1011 cm−2 eV−1 were achieved in the crystallized ZrO2/nitrided Al2O3 gate stack with a low CET of 1.2 nm. The gate stack was also optically probed through the photoluminescence from Si, revealing that the hydrogen passivation and depassivation effects caused by the remote NH3 plasma treatment are highly correlated with the Dit. The results indicate that the crystallized high-K dielectrics/nitrided buffer layer is a promising gate stack structure to improve the electrical characteristics in the advanced metal-oxide-semiconductor devices.

Effect of hydrogen participation on the improvement in electrical characteristics of HfO2 gate dielectrics by post-deposition remote N2, N2/H2, and NH3 plasma treatments

The structural and electrical characteristics of hafnium oxide (HfO2) gate dielectrics treated by a variety of post-deposition nitridation processes, including remote N2, N2/H2 and NH3 plasma, are presented by the x-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy and electrical measurements. The XPS measurement reveals that the nitrogen content in the HfO2 thin film treated by remote nitrogen and hydrogen plasma is higher than that treated only by remote nitrogen plasma, suggesting that the hydrogen has the capability to facilitate nitrogen dissociation. An ultra-thin interfacial layer (IL) thickness (∼0.3 nm), a high dielectric constant (20), an acceptable gate leakage current density (∼9 × 10−6 A cm−2), and a low capacitance equivalent thickness (1.9 nm) of the HfO2 gate dielectric were achieved by the post-deposition remote NH3 plasma nitridation treatment. However, an IL layer as thick as 1.5 nm was observed in the sample treated only by remote N2 plasma. The results indicate that the participation of hydrogen in the nitridation process is a promising way to improve the electrical properties of HfO2 gate dielectrics.

Tetragonal $\hbox{ZrO}_{2}/\hbox{Al}_{2}\hbox{O}_{3}$ Stack as High-$\kappa$ Gate Dielectric for Si-Based MOS Devices

Abstract-The combination of tetragonal ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (t-ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) and amorphous Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> was explored as the gate dielectric for Si-based MOS devices. Because of the absence of a ZrSiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> and/or ZrSi interfacial layer, the thermally stable t-ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /Si stack is more eligible than the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /t-ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si stack for the gate dielectric since it demonstrates larger capacitance, smaller hysteresis, better frequency dispersion, lower leakage current, and more robust reliability. By employing additional NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> plasma nitridation to well passivate the grain boundaries of the t-ZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> film, without compromising its κ-value, a greatly reduced leakage current of 2.9 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> can be achieved at gate bias of flatband voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fb</sub> )-1 V with an effective oxide thickness of 1.64 nm, which paves a new way to develop a high-performance crystalline gate dielectric for advanced MOS devices.

Selective emitter solar cell formation by NH3 plasma nitridation and single diffusion

A new and simple process for fabricating a selective emitter solar cell has been proposed. Lightly and heavily doped emitters could be concurrently formed after a single POCl3 diffusion step through the selective formation of SiNx, which serves as the diffusion barrier and can be grown by NH3 plasma nitridation of the Si surface. The desired phosphorus depth profile for the lightly and heavily doped region verifies the eligibility of this process. From the electrical characterization, the selective emitter solar cell fabricated by this process manifests a higher absolute conversion efficiency than a conventional one by 0.5%. It is the enhanced response to the short wavelength light and the reduced surface recombination that causes the considerable improvement in conversion efficiency which is beneficial to further hold the competitive advantage for solar cell manufacturers. Most importantly, the proposed process can be fully integrated into the conventional solar cell process in a mass-production laboratory.

High-resolution Rutherford backscattering spectrometry study on process dependent elemental depth profile change of hafnium silicate on silicon

Process characterization of HfSiO(N)/SiO(N) films was performed by nondestructive elemental depth profile analysis using high-resolution Rutherford backscattering spectrometry. As-grown atomic layer deposition HfSiO film (2 nm) was found not to be uniform but to have a gradient near the top surface with Si concentration higher than the bulk. Regardless of native oxide removal, HfSiO grown on HF-last Si results in an almost identical interfacial SiOx thickness with that of HfSiO grown on chemical oxide. Dependence of interfacial layer on oxygen transport behavior during high-temperature annealing was also investigated. Whereas only the upward oxygen outdiffusion from the HfSiO layer was observed for the films deposited on HF-last Si and SiON, downward oxygen transport to the bottom interfacial layer was also observed when HfSiO film was deposited on chemical oxide. This result indicates that the bonding properties of chemical oxide are different from those of SiO2 and that chemical oxide can accommodate oxygen ions. Finally, thermal stability of nitrogen in HfSiO introduced by NH3 annealing and plasma nitridation was compared. Nitrogen desorption by spike anneal was only observed for HfSiON film with nitrogen introduced by plasma nitridation process.

Programming Speed Enhancement by NH3 Plasma Nitridation of Tunneling Oxide for Ge Nanocrystals Memory

The characteristics of Ge nanocrystals charge-storage memory stacks with plasma surface treatment of the tunneling oxide layer have been studied in this paper. The tunneling silicon oxide (TO) surface was nitrided by plasma treatment, which appears to modify the bonding type of the substrate surface and enhance the nucleation sites for Ge nanocrystals. The chemical bonding depth profile of the /TO layers and the Ge nanocrystals structure were examined by X-ray photoelectron spectroscopy and transmission electron microscopy, respectively. The trap charge densities were estimated to be as high as from hysteresis loop for sweep. The nitrided interface (oxynitride) between the trapping layer and the tunneling silicon oxide has a bandgap lower than the silicon oxide, which causes an asymmetric tunneling barrier under programming and erasing conditions. An effective thinner barrier under programming bias results in enhanced programming speed due to improved carrier injection efficiency. It was also observed that the nitrided interface reduces Ge diffusion into the TO layer, which is known to result in degradation of the properties of Ge nanocrystal-based memory devices.

Reoxidation after NH3 Plasma Nitridation for Multiple-Thickness Oxynitrides

A novel manufacturable multiple gate oxynitride thickness technology is proposed in this work. An ultrathin dielectric film (EOT=2.5 nm) of lower oxidation growth rate than conventional films was fabricated by NH3 plasma nitridation. Oxide thickness was reduced by about 80% for samples treated by NH3 plasma nitridation. However, the thickness limitation is 1.3 nm for NH3 plasma nitridation. This is believed to be due to nitrogen incorporated in the silicon surface to form a nitridelike thin film, which retarded oxide growth. The effects of NH3 plasma nitridation were systematically studied, and the rapid thermal N2O reoxidation of an NH3 plasma sample was also demonstrated in this work. This novel process improves the gate oxide reliability, decreases bulk trap densities, provides better SILC immunity, and produces less charge trapping and a higher Qbd.

Investigation of the interlayer characteristics of Ta2O5 thin films deposited on bare, N2O, and NH3 plasma nitridated Si substrates

Low-temperature N2O and NH3 plasma nitridations on Si surfaces are conducted to prevent the thermodynamic instability at the Ta2O5/Si interface. The surface and interface of the Ta2O5/Si systems, without or with nitridation, were examined by x-ray photoelectron spectroscopy (XPS), atomic force microscopy, transmission electron microscopy, and secondary ion mass spectrometry. Capacitance–voltage (C–V) measurements were carried out to investigate the electric/defect characteristics of the Ta2O5/Si systems. For the non-nitrided Si substrate XPS detects no surface oxide formed prior to Ta2O5 deposition. In contrast, NH3 plasma nitridation forms a nitrogen-rich SiOxNy layer, while N2O plasma nitridation produces an oxygen-rich SiOxNy layer on Si. C–V measurement reveals high densities of fixed charges, trapping sites, and interface states in the Ta2O5/non-nitrided Si sample, indicative that a defective interlayer was formed during Ta2O5 deposition. Ta2O5 on both nitrided systems exhibits a reduced amount of fixed charges and trapping sites. Nevertheless, NH3 plasma nitridation is not as effective as N2O plasma nitridation in diminishing the density of interface states. The different electric/defect characters between the NH3 and N2O nitrided systems are attributed to the further oxidation of the nitrogen-rich SiOxNy layer produced by NH3 plasma nitridation, which induces defects at the dielectric/Si interface. Effectiveness of the nitridation process, therefore, depends on the stability of the nitrided layer during deposition of Ta2O5.

Production of stable and metastable phases of zirconium nitrides by NH3 plasma nitridation and by double ion beam sputtering of zirconium films

Nitrided surfaces and nitrogen composition gradients in thin films exhibit interesting mechanical, electrical and optical properties. Metal, semiconductor or oxide surfaces can be transformed into a nitrided compound via interactions of nitrogen species issued from a plasma or an ion beam. The thermal activation is a key factor in both cases to ensure chemical reactions and short/long-range diffusion necessary to allow the growth of stable or metastable structures. In this work, we focus our attention on zirconium nitrides prepared under controlled temperature through reaction and diffusion, in Zr films, of low energy NHx species produced in NH3 plasma and through the implantation–diffusion of energetic N+2 ions during Zr deposition by using double ion beam sputtering. Zirconium nitrides show optical and electrical properties that depend on the conditions and on kinetics of the nitrogen take-up; the material exhibits a transition from the stable metallic ZrN to a metastable phase Zr3N4 that appears transparent and insulating. The influence of the energy of the nitriding species and of the temperature on nitride compositions and phases are addressed. A model using coupled implantation and thermal diffusion mechanisms is proposed to explain the phases produced. In relation with the described phenomena, a temperature-controlled plasma-immersion ion-implantation system is proposed for tailoring in-depth stable/metastable ceramic structures such as nitrides, oxides and carbides.

Constructive versus destructive effects of electron beam irradiation: an application to plasma nitridation of SiO2 thin films

Low energy (3–100 eV) electrons are shown to be efficient promoters of the superficial nitridation of thin (15 nm) SiO2 films using low pure NH3 pressures (⩽2 × 10−4 mbar) at ambient temperature. The ultrahigh vacuum experimental set-up permits us to uncouple two important effects both present in a thermally-assisted (700–950 °C) r.f. NH3 plasma nitridation process: the role played by low energy (3–5 eV) electrons and the temperature. It is found that the existence of charged particles near the sample surface must be taken into account in the plasma reaction process and that the main effect of thermal activation is to enhance the reaction and the diffusion of nitrogen species through the SiO2 layer down to the SiO2/Si interface.Auger sputter depth profiles of the plasma nitrided SiO2 films have been measured before and after bombardment with energetic electrons (1, 3, or 5 keV). Electron irradiation of the film induced a nitrogen depletion at the vacuum/dielectric interface and a nitrogen pile-up at the dielectric/silicon interface. Our results indicate that this phenomenon is a maximum for the lowest primary electron energy. This behavior can be understood on the basis of an electron-stimulated Si—N bond decomposition and the creation of positive nitrogen ions. The released nitrogen ions were found to either escape in vacuum or migrate through the dielectric layer and pile-up at the dielectric/silicon interface because of the existence inside the layer of a non-uniform electric field, in agreement with recent theoretical predictions.