Low-energy Nitrogen Implantation Research Articles

Bonding, retention and thermal stability of shallow nitrogen in diamond (100) by low-energy nitrogen implantation

We investigate the sub-surface bonding, retention, and thermal stability of nitrogen in diamond (100) implanted with 200 and 800 eV N2+ at room temperature (RT) and 600 °C at an ion dose of 3.4×1014 ions/cm2. Upon 200 eV N2+ implantation at RT and 600 °C, nitrogen is incorporated in the diamond lattice mainly in a C-N/C=N bond bonding configuration alongside a small CN(nitrile-like) component. 800 eV N2+ implantation at both RT and 600 °C, the implanted nitrogen can occupy multiple bonding configurations, including C-N/C=N and CN(nitrile-like) bonds. Implantation at 600 °C resulted in higher thermal stability of the implanted nitrogen compared to RT implantation due to dynamic annealing assisted defect curing and desorption of weekly bonded species (possibly nitrogen bonded to defects) during the high temperature implantation. The long-range order of the N2+ implanted diamond surfaces was also investigated using low-energy electron diffraction measurements.

Lithographically engineered shallow nitrogen-vacancy centers in diamond for external nuclear spin sensing

The simultaneous control of the number and position of negatively charged nitrogen-vacancy (NV) centers in diamond was achieved. While single near-surface NV centers are known to exhibit outstanding capabilities in external spin sensing, trade-off relationships among the accuracy of the number and position, and the coherence of NV centers have made the use of such engineered NV centers difficult. Namely, low-energy nitrogen implantation with lithographic techniques enables the nanoscale position control but results in degradation of the creation yield and the coherence property. In this paper, we show that low-energy nitrogen ion implantation to a 12C (99.95%)-enriched homoepitaxial diamond layer using nanomask is applicable to create shallow NV centers with a sufficiently long coherence time for external spin sensing, at a high creation yield. Furthermore, the NV centers were arranged in a regular array so that 40% lattice sites contain single NV centers. The XY8-k measurements using the individual NV centers reveal that the created NV centers have depths from 2 to 12 nm, which is comparable to the stopping range of nitrogen ions implanted at 2.5 keV. We show that the position-controlled NV centers are capable of external spin sensing with a ultra-high spatial resolution.

Investigation of Coherence Time of a Nitrogen-Vacancy Center in Diamond Created by a Low-Energy Nitrogen Implantation

A nitrogen-vacancy (NV) center in diamond has been investigated extensively because of its promising spin and optical properties for applications to nanoscale magnetic sensing and magnetic resonance of magnetic elements outside the diamond. For those applications, a long decoherence time and positioning of an NV center on the diamond surface are desired. Here, we report the creation of NV centers near the diamond surface using a 3 keV nitrogen implantation and the coherence property of the created NV center.

Temperature dependent retention characteristics of ion-beam modified SONOS memories

In this work, we report on the structural and electrical properties of oxide–nitride–oxide (ONO) structures that were formed by low-energy silicon or nitrogen implantation into oxide–nitride stacks. In particular ON stacks (2.5nm/6nm) were formed on n-type Si substrates, further implanted with 1keV Si or N to a fluence of 1016 ions/cm2, and finally wet oxidized at 850°C for 15min. TEM imaging showed that the thickness of the blocking oxide layer, formed during wet oxidation, strongly depends on the implanted species. Charging characteristics revealed that Si implanted stacks can trap either electrons or holes resulting to a memory window as large as 8.5V. In turn N implanted stacks can trap only electrons with a corresponding memory window of 4V. Room-temperature charge retention measurements showed that the electron loss rate is faster in samples implanted with Si (∼0.32V/decade) compared to N-samples (∼0.1V/decade). The 10-year extrapolated memory windows were 1.7 and 2.5V for Si and N-implanted devices, respectively. Retention measurements within the temperature range of 25–150°C indicate that the Si implanted stacks exhibit a thermally activated retention, while N-samples showed a temperature independent behavior. These results are mainly attributed to the different nature of traps generated by ion implantation and wet oxidation processing.

Hydrogenation and dehydrogenation of nitrogen-doped graphene investigated by X-ray photoelectron spectroscopy

We studied the hydrogenation and dehydrogenation of nitrogen-doped graphene (NDG) by in situ high-resolution X-ray photoelectron spectroscopy (XPS) and temperature-programmed XPS (TPXPS). Nitrogen-doped graphene was prepared by low energy nitrogen implantation in pristine graphene on Ni(111). Hydrogenation of NDG was performed by exposure to atomic hydrogen. Upon hydrogenation the XP spectra in the C 1s region reveal one new peak, shifted to lower binding energies as compared to graphene, which is associated with newly formed CH groups. In the N 1s region two new peaks, shifted to higher binding energies are observed; these are associated with hydrogenated pyridinic and graphitic nitrogen. TPXPS spectra reveal a different thermal stability of the two hydrogenated nitrogen species, while the C–H groups of graphene show no significant changes compared to undoped hydrogenated graphene.

Production of Nitrogen-Doped Graphene by Low-Energy Nitrogen Implantation

Nitrogen doping of graphene is a suitable route to tune the electronic structure of graphene, leading to n-type conductive materials. Herein, we report a simple way to insert nitrogen atoms into graphene by low-energy nitrogen bombardment, forming nitrogen-doped graphene. The formation of nitrogen-doped graphene is investigated with high resolution X-ray photoelectron spectroscopy, allowing to determine the doping level and to identify two different carbon–nitrogen species. By application of different ion implantation energies and times, we demonstrate that a doping level of up to 0.05 monolayers is achievable and that the branching ratio of the two nitrogen species can be varied.

Surface modification of stainless steel drills using plasma-immersion nitrogen ion implantation

Better protective and functional coatings on dental drills are increasingly demanded for their desired mechanical, tribological or chemical properties. We have studied the surface modification of steel dental drills, with an aim to increasing both their cutting life and corrosion resistance in dentistry using low-energy plasma-immersion nitrogen implantation over different temperature ranges. The temperature of the drills was controlled by varying the implantation voltage. Following implantation, tests showed that the microhardness of the nitrided drill surfaces was approximately one order higher than that of untreated drills and the corrosion tolerance was found to increase with growing temperature of the plasma-immersion process.

Oxidation of very low energy nitrogen-implanted strained-silicon

In the present work we perform a systematic study of oxidation of very low energy nitrogen-implanted strained-silicon in terms of oxide growth, structural characterization of the implanted strained-silicon substrate and electrical properties of the ultra thin oxides as a function of the substrate strain level. Low energy (3 keV) nitrogen (N 2 +) implantation was performed in strained-Si/SiGe/Si substrates of various strain levels and oxidations were carried out for different times at 850 °C. It has been found that nitrogen implantation efficiently blocks silicon oxidation, independently of the strain level of the substrate. TEM analysis revealed the full absence of extended defects in the strained-silicon substrate after the thermal treatments. The grown oxides exhibit very good electrical properties in terms of interface trap densities and leakage currents.

Composition of tantalum nitride thin films grown by low-energy nitrogen implantation: a factor analysis study of the Ta 4 f XPS core level

Tantalum nitride thin films have been grown by in situ nitrogen implantation of metallic tantalum at room temperature over the energy range of 0.5–5 keV. X-ray photoelectron spectroscopy and factor analysis (FA) have been used to characterize the chemical composition of the films. The number of the different Ta–N phases formed during nitrogen implantation, as well as their spectral shapes and concentrations, have been obtained using principal component analysis and iterative target transformation factor analysis, without any prior assumptions. According to FA results, the composition of the tantalum nitride films depends on both the ion dose and the ion energy, and is mainly formed by a mixture of metallic tantalum, β-TaN0.05 , γ-Ta2N and cubic/hexagonal TaN phases. The kinetics of tantalum nitridation is characterized by two stages. In the first stage, the formation of β-TaN0.05 species leads to a strong attenuation of the metallic tantalum signal. During the second stage, β-TaN0.05 transforms into γ-Ta2N and cubic/hexagonal TaN species. For intermediate ion doses, the concentration of γ-Ta2N reaches a maximum, subsequently decreasing because of its transformation into cubic/hexagonal TaN phases with increasing ion dose up to saturation. At saturation, the films are mainly composed of a mixture of γ-Ta2N and cubic/hexagonal TaN phases, but small Ta0 and β-TaN0.05 signals are also observed. They should be attributed to preferential sputtering of nitrogen and/or to the limited thickness of the film. Comparison of the experimental nitrogen concentration with that obtained using TRIDYN simulations suggests that, in addition to nitrogen implantation and atomic mixing, other mechanisms, like ion beam enhanced diffusion or the chemical reactivity of the tantalum substrate towards nitrogen, should also be taken into account at higher ion-beam energies.

Wear reduction in AISI 630 martensitic stainless steel after energetic nitrogen ion implantation

A significant wear reduction by several orders of magnitude is the common result for austenitic stainless steels after energetic nitrogen implantation at medium temperatures around 380 °C. In contrast, martensitic stainless steels are rarely investigated. In this investigation, one steel grade, stainless steel AISI 630/DIN 1.4542, is treated using low energy nitrogen implantation at 380 and 600 °C, high voltage nitrogen plasma immersion ion implantation (PIII) and combined carbon/nitrogen PIII at 380 °C. Using PIII, an expanded martensitic lattice extending several micrometers into the sample was observed, whereas Fe 4N and CrN were formed after low energy implantation at 380 and 600 °C, respectively. All samples show a hardness of up to 2000 HV and a wear reduction by two orders of magnitude. Additional metallographic cross-sections confirm the microstructure derived from XRD data.

Characteristics of low-energy nitrogen ion-implanted oxide and NO-annealed gate dielectrics

In this work we assess the effect of low-energy nitrogen implantation for dual-gate oxide thickness formation. A comparison of transistor performance, 1/ f noise and oxide reliability is made between 3.5 nm thick oxides fabricated by nitrogen ion implantation followed by dry oxidation and a reference oxide grown by dry oxidation followed by annealing in nitric oxide (NO oxide). The results show that the ion-implanted samples have lower oxide charges, lower 1/ f noise, good reliability and sufficient boron penetration immunity.

Negative band gaps in dilute InNxSb1-x alloys.

A thin layer of InNSb has been fabricated by low energy nitrogen implantation in the near-surface region of InSb. X-ray photoelectron spectroscopy indicates that nitrogen occupies approximately 6% of the anion lattice sites. High-resolution electron-energy-loss spectroscopy of the conduction band electron plasma reveals the absence of a depletion layer for this alloy, thus indicating that the Fermi level is located below the valence band maximum (VBM). The plasma frequency for this alloy combined with the semiconductor statistics indicates that the Fermi level is located above the conduction band minimum (CBM). Consequently, the CBM is located below the VBM, indicating a negative band gap material has been formed. These measurements are consistent with k.p calculations for InN0.06Sb0.94 that predict a semimetallic band structure.

Low-energy high-flux nitriding of Ni and Ni20Cr substrates

The influence of a low-energy high-flux nitrogen implantation on the structure and hardness of Ni and NiCr 20 is examined. These implantation–diffusion experiments carried out at 475 and 450 °C, respectively, show that the nitriding process is very difficult for the pure Ni metal, whereas in the NiCr 20 substrate the formation of an expanded austenite γ N phase is identified by X-ray diffraction. Vickers microhardness indentation tests indicate an important hardening effect of the NiCr 20 substrate surface. The absence of any detectable nitridation effect in pure nickel substrates can be correlated with the low solubility of nitrogen. An increase in surface roughness and the presence of porosity is nevertheless observed by scanning electron microscopy and atomic force microscopy on both metallic substrates surfaces after the implantation process. This behaviour can be correlated with the sputtering effect produced by the very high implantation dose.

Influence of implantation energy on the electrical properties of ultrathin gate oxides grown on nitrogen implanted Si substrates

Metal–oxide–semiconductor tunnel diodes with gate oxides, in the range of 2.5–3.5 nm, grown either on 25 or 3 keV nitrogen-implanted Si substrates at (0.3 or 1) ×1015 cm−2 dose, respectively, are investigated. The dependence of N2+ ion implant energy on the electrical quality of the growing oxide layers is studied through capacitance, equivalent parallel conductance, and gate current measurements. Superior electrical characteristics in terms of interface state trap density, leakage current, and breakdown fields are found for oxides obtained through 3 keV nitrogen implants. These findings together with the full absence of any extended defect in the silicon substrate make the low-energy nitrogen implantation technique an attractive option for reproducible low-cost growth of nanometer-thick gate oxides.

Wear resistance after low-energy high-flux nitrogen implantation of AISI 304L stainless steel

Nitrogen implantation into 304L austenitic stainless steel has been carried out at 400 and 500 °C using a Kaufman-type ion source with an accelerating voltage of 1.2 kV and a current density of 1 mA/cm 2. For a processing time of 1 h (fluence ∼3.5×10 19 ions/cm 2) at 400 °C, a nitrided layer of f.c.c. expanded austenite of approximately 3.5 μm was formed. Thicker layers of approximately 6 μm were produced at 500 °C, but the formation of chromium nitride precipitates embedded in a b.c.c. ferritic matrix was observed. The hardness increased from 2.8 GPa for the untreated steel to approximately 15 GPa for implantation at 400 °C and to 18 GPa for implantation at 500 °C; in addition, a considerable reduction in the wear rate was observed. The durability of the wear improvement can be associated with the high hardness and significant thickness of the nitrided layers, as well as with the hardening mechanisms, which are different at both temperatures: a solid solution effect at 400 °C and a precipitation effect of chromium nitride at 500 °C.

In situ stress measurements during low-energy nitriding of stainless steel

Nitriding of austenitic stainless steel at moderate temperatures leads to the formation of a hard and wear-resistant surface layer of expanded austenite, characterised by an expansion of the lattice constant of up to 12%. This large expansion can be assumed to be accompanied by a corresponding high compressive stress parallel to the substrate at the interface between the implanted layer and the bulk substrate. In situ stress measurements using the beam bending method were performed to capacitively determine the curvature of thin samples, prepared from X5CrNi18.10 (DIN 1.4301, AISI 321), during low-energy nitrogen implantation. The thickness of the expanded austenite layer was derived afterwards from glow-discharge optical spectroscopy. Assuming an inversely parabolic growth rate for diffusion-limited growth, a rather high compressive stress of 1.4–1.5 GPa was reached after 90 s and stayed constant for 1 h. This value is near the plastic flow limit of stainless steel. Furthermore, while keeping the sample at 400 °C and switching off the nitrogen beam, the curvature of the sample almost instantaneously started to decrease exponentially by approximately 50% on a time scale of 15–30 min, indicating ongoing stress relaxation.

Dependence of ion beam induced nitrogen diffusion in aluminum on oxygen impurities

The diffusion of nitrogen in aluminum is investigated for three different methods of nitrogen implantation. Low energy nitrogen implantation (LEI) at 1 keV and plasma immersion ion implantation (PIII) with −30 kV pulses were performed in the temperature range from 250 to 500 °C, together with conventional ion implantation at room temperature with 100 keV N+ ions and subsequent annealing in vacuum at 440 or 485 °C. For the LEI samples a rather high diffusion leading to AlN layers of a few microns in less than 1 h was found, whereas a low diffusion coefficient was obtained for the PIII samples, exhibiting a sharp step near 350 °C. In contrast no diffusion was measured in the implanted and annealed samples. Several different factors are proposed to influence the observed diffusion: A competing path between the formation of AlN by trapping of N and N diffusion is responsible for the dependence of the layer thickness on the supply of nitrogen. The oxygen contamination drastically reduces the diffusion constant by occupying the surface sites and blocking the diffusion path. Finally, the phase transformation from c-AlN to h-AlN may cause the sudden onset of diffusion around 350 °C.

Effect of ion beam irradiation on metal silicon junctions

The effect of MeV and low energy nitrogen implantation on the electrical properties of metal semiconductor junctions is studied. It is found that MeV implantation has better contact performance is comparison to keV nitrogen implantation. The defects introduced due to MeV implantation have very little effect on contact formation.

Low energy nitrogen implantation into Si and SiO 2/Si

We report on N doses and profiles in Si and (ultra)thin SiO 2 films on Si nitrided by plasma or ion beam processing in the 3–1000 eV energy range. Accurate elemental quantification was performed by nuclear reaction analysis (NRA), and elemental profiling with subnanometer depth resolution was achieved by narrow nuclear resonance profiling (NNRP) or medium energy ion scattering (MEIS). Heavy and shallow nitrogen incorporation was observed up to 0.7 N/(N + O) and peak N concentrations at 2 nm and less from the sample surface. Device-quality films were produced with post-nitridation annealing in O 2, as indicated by C– V and I– V measurements.

High quality of ultra-thin silicon oxynitride films formed by low-energy nitrogen implantation into silicon with additional plasma or thermal oxidation

Silicon oxynitride (SiOxNy) insulators have been obtained by low-energy molecular nitrogen ion (N2+) implantation in Si substrates prior to thermal or high density O2 ECR (electron cyclotron resonance) or N2O RP (remote plasma) plasma oxidation at temperatures of 20°C and 350°C, respectively. Characterization by Fourier transform infrared (FTIR) analyses reveals the high structural quality and very low Si–N bond concentration of oxynitride films. The film thicknesses between 2.5 and 12 nm were found by ellipsometry using a fixed refractive index of 1.46. MOS capacitors, with Al electrodes and final sintering time at 420°C for 20–30 min in forming gas, were fabricated. A relative dielectric constant of 3.9 was adopted to extract the effective charge densities from capacitance–voltage (C–V) curves, resulting in values between 4×1010 and 6×1011 cm−2. Breakdown electric fields from 9–26 MV/cm were obtained from current–voltage (I–V) measurements. These results indicate that the obtained SiOxNy films are suitable gate insulators for metal-oxide-semiconductor (MOS) devices.