Ar Implantation Research Articles

A density functional tight-binding based strategy for modeling ion bombardment and its application to Ar bombardment of silicon nitride

In many modern applications, it is important to understand mechanisms of non-equilibrium chemistry and physics that are driven by low energy ion bombardment of solid surfaces. However, the study of these processes has been challenging as it demands a relatively unique balance between chemical fidelity and computational cost. To this end, we have proposed and constructed a new, high-throughput simulation pipeline based on density functional tight binding simulations. Additionally, we have extended the parameter set pbc-0-3 with the addition of Ar, thereby enabling the simulation of Ar bombardment. This pipeline was then applied to study the structural and compositional evolution of silicon nitride (SiN) under Ar bombardment. We identified a possible rate limiting step of bombardment-driven sputtering of SiN and suggested underlying mechanisms of Si and N removal. Damage from the bombardment, including generation of surface defects and Ar implantation, are further discussed. These findings and the newly developed simulation framework will serve as a useful foundation for further research in processes driven by ion bombardment.

Comparative study on the second-harmonic generation of thermally poled fused silica by multi-energy boron and argon ion implantations

The second-order optical nonlinearity (SON) of thermally poled fused silica was shown for the first time to be significantly improved by the implantation of multi-energy boron (B) ions, and the outcomes were compared with those obtained from the implantation of multi-energy argon (Ar) ions. Second-harmonic (SH) signals in both samples grew roughly linearly as the poling temperature rose. Samples with Ar implants showed a greater increase in SH signal with rising poling temperature. A qualitative explanation for the formation of [Formula: see text] in poled samples can be found in a model of charge hopping and migration through defects. The diminished SH signal in the B-implanted sample is probably caused by the negative charge trapping layer, as well as by B[Formula: see text] and E[Formula: see text] center defects.

Critical method evaluation refutes the Ar 2p signal of implanted Ar for referencing X-ray photoelectron spectra

Correct binding energy (BE) spectra referencing of insulating samples remains the major challenge in modern XPS analyses. Ar 2p signal of implanted Ar is sometimes used for this purpose. The method relies upon the assumption that chemically inert species such as noble gas atoms would be ideally suited as other factors affecting core level peak positions (such as chemical bonding) can be excluded. Here, we present a systematic study on the Ar 2p referencing method applied to a wide range of thin film sample materials of metals, nitrides, carbides, and borides. All specimens exhibit a well-defined Fermi edge, which serves as an independent internal reference for Ar 2p spectra of in-situ implanted Ar. Ar 2p3/2 binding energy is shown to vary by as much as 5.1 eV between samples. This is more than typical chemical shifts of interest, which obviously disqualifies Ar 2p referencing. The BE of the Ar 2p peaks shows a strong correlation to the number of valence electrons available for screening, implying that the polarization energy has a major role for the observed large spread of Ar 2p3/2 BE values. In several cases of single-phase films, an additional Ar 2p doublet is observed with the Ar 2p3/2 BE referenced to the vacuum level higher than the gas phase value of 248.6 eV, which is tentatively assigned to the formation of Ar-N and Ar-C complexes stabilized by Van der Waals forces. Ar implantation into two-phase samples, exemplified here by phase-segregated NiCrC/a-C:H and nanocomposite c-TiN/SiNx thin films, leads to complex Ar 2p spectra, which further demonstrates unreliability of the referencing method. The firm conclusion of the study is that the Ar 2p3/2 peak from implanted Ar is not a remedy for the charge referencing problem.

Illuminating Trap Density Trends in Amorphous Oxide Semiconductors with Ultrabroadband Photoconduction

AbstractUnder varying growth and device processing conditions, ultrabroadband photoconduction (UBPC) reveals strongly evolving trends in the defect density of states (DoS) for amorphous oxide semiconductor thin‐film transistors (TFTs). Spanning the wide bandgap of amorphous InGaZnOx (a‐IGZO), UBPC identifies seven oxygen deep donor vacancy peaks that are independently confirmed by energetically matching to photoluminescence emission peaks. The subgap DoS from 15 different types of a‐IGZO TFTs all yield similar DoS, except only back‐channel etch TFTs can have a deep acceptor peak seen at 2.2 eV below the conduction band mobility edge. This deep acceptor is likely a zinc vacancy, evidenced by trap density which becomes 5‐6× larger when TFT wet‐etch methods are employed. Certain DoS peaks are strongly enhanced for TFTs with active channel processing damage caused from plasma exposure. While Ar implantation and He plasma processing damage are similar, Ar plasma yields more disorder showing a ≈2 × larger valence‐band Urbach energy, and two orders of magnitude increase in the deep oxygen vacancy trap density. Changing the growth conditions of a‐IGZO also impacts the DoS, with zinc‐rich TFTs showing much poorer electrical performance compared to 1:1:1 molar ratio a‐IGZO TFTs owing to the former having a ∼10 × larger oxygen vacancy trap density. Finally, hydrogen is found to behave as a donor in amorphous indium tin gallium zinc oxide TFTs.

Influence of Generated Defects by Ar Implantation on the Thermoelectric Properties of ScN.

Nowadays, making thermoelectric materials more efficient in energy conversion is still a challenge. In this work, to reduce the thermal conductivity and thus improve the overall thermoelectric performances, point and extended defects were generated in epitaxial 111-ScN thin films by implantation using argon ions. The films were investigated by structural, optical, electrical, and thermoelectric characterization methods. The results demonstrated that argon implantation leads to the formation of stable defects (up to 750 K operating temperature). These were identified as interstitial-type defect clusters and argon vacancy complexes. The insertion of these specific defects induces acceptor-type deep levels in the band gap, yielding a reduction in the free-carrier mobility. With a reduced electrical conductivity, the irradiated sample exhibited a higher Seebeck coefficient while maintaining the power factor of the film. The thermal conductivity is strongly reduced from 12 to 3 W·m–1·K–1 at 300 K, showing the influence of defects in increasing phonon scattering. Subsequent high-temperature annealing at 1573 K leads to the progressive evolution of these defects: the initial clusters of interstitials evolved to the benefit of smaller clusters and the formation of bubbles. Thus, the number of free carriers, the resistivity, and the Seebeck coefficient are almost restored but the mobility of the carriers remains low and a 30% drop in thermal conductivity is still effective (ktotal ∼ 8.5 W·m–1·K–1). This study shows that control defect engineering with defects introduced by irradiation using noble gases in a thermoelectric coating can be an attractive method to enhance the figure of merit of thermoelectric materials.

Heavy ion irradiation induced structural and magnetic modifications in Co/Alq3 bilayer

This article reports on the Ar+ ion irradiation induced modifications of Co/Alq3/Si-substrate bilayer thin film. Irradiation was carried out with 10 keV Ar+ ions at a fluence of 1 × 1016 ions/cm2. To study structural and magnetic modifications, x-ray reflectivity (XRR) and magneto-optical Kerr effect (MOKE) techniques, respectively have been utilized. XRR analysis reveals a significant reduction of electron density of the Co layer and enhancement of intermixing of Co and Alq3 at the Co/Alq3 interface after ion irradiation. MOKE measurements affirm that saturation magnetization reduces by a factor of about 3 due to irradiation without any detectable changes in the coercivity. XRR analysis and Monte Carlo simulation demonstrate the ion irradiation induced defects formation due to Ar implantation and enhancement of interface mixing between Co and Alq3 is the main cause of the reduction in saturation magnetization.

Ionic Bombardment to Tune the Electrochemical Properties of a Semiconductor.

The purpose of this work is to study in detail the effects of monoatomic and gas cluster ion beam (GCIB) on a semiconducting electrode (InP) thanks to the correlation between X-Ray Photoelectron Spectroscopy (XPS) and electrochemistry. Such approach allows estimating the overall change in the electrical, chemical and structural properties of the modified semiconductor (SC). Recent developments in ion sputtering source enable a better control of the perturbations induced at the surface of the material. Furthermore, anodic dissolution will be presented as a tool to recover the initial characteristics of the modified electrode. The interaction of ions with matter and especially surfaces has been an active topic for both fundamental and applied research over the past decades and is still relevant today. Thanks to ion bombardments, various types of surfaces can be chemically, mechanically, optically or electrically modified. However, the understanding of the inherent phenomena and physical/chemical mechanisms involved remains incomplete. When ions, whose energy range between 1 and 10 000 eV, interact with a surface, many processes can occur and the energy distribution (dissipation) could differ markedly from one material to another. Nevertheless, whatever the source of modifications considered, the common fundamental question is the nature of the effects induced by the perturbation and its evaluation (area, depth). The consequences of ion bombardment on the surface of a SC may have repercussions: formation of ordered nanostructures via low-energy ion-beam irradiation as a bottom-up nano-manufacturing technique; ion implantation for SC device technology; optical lithography using ion beam or even functionalization of 2D materials. This topic has gained specific interest in the field of surface analysis where depth-profiling is required (e.g. XPS, Auger Spectroscopy or Secondary Ion Mass Spectroscopy). In contrast with monoatomic ions (e.g. Ar+), cluster ions (e.g. Arn +) do not penetrate deeply into target materials. Therefore, the energy of their impact is dissipated within the first few nanometers of the surface, resulting in low sputtering yields and minimal surface damage. However, the effects of these new generations of GCIB are not yet fully understood. The strong originality of our approach is to investigate the surface modifications induced not only by UHV characterization technique (XPS) but also with the use of solid/liquid interface electrochemical response for which SC have specific behavior. These efficient and quantitative tools provide relevant information on the modification performed at the SC surface: metallization, amorphization, preferential sputtering. The high number of parameters that govern the interfacial electrochemistry of the SC/electrolyte system (band bending, SC doping level, double layer capacitance, space charge layer, SC electrical impedance, photopotential) make this approach pertinent and sensitive to evaluate the perturbation amplitude. An example is given on the figure where the metallization of an InP electrode can be observed in vacuum after successive Arn + etching sequences by the shift of the Fermi level (XPS valence band region) and in solution by the narrowing of the depletion region and the flattening of the Mott-Schottky plot. In addition, a very important characteristic of SC interfacial electrochemistry is its availability to generate in situ anodic dissolution at nanoscale. Thereby, it represents an accurate and quantitative tool to estimate the thickness of the modified region. Moreover, using well-controlled dissolution, the initial properties can be retrieved. These results are compared to those obtained after annealing under UHV. Thus, the electrochemical responses will be associated directly to surface chemical information such as: loss of stoichiometry, Ar implantation, shift of the Fermi Energy level position, photo-peak broadening. Figure 1

Deuterium retention in dense and disordered nanostructured tungsten coatings

A systematic and attentive comparison of the deuterium (D) retention in tungsten (W) coatings with different nano-crystalline structures after the plasma exposure in comparison with polycrystalline tungsten (PCW) is presented. While a wide database is available for PCW, only a few data about the D retention in coatings with different structures exist. The D retention in W coatings produced by three different deposition techniques on different substrates was studied with respect to the influence of (a) coating crystallite size, (b) coating thickness, (c) specimen temperature during D plasma exposure, (d) presence of argon (Ar) used as working gas during the coating deposition and (e) substrate material. It is shown that the variation of the processing parameters, such as temperature, deposition rate, Ar implantation, etc. even within one deposition method results in different grain size distributions and structure of coating and has a significant effect on the D retention. It is revealed that the substrate material and the presence of Ar in a coating play a minor role in the D retention in the coating. It is shown that both the D concentration and the D retention in coatings drastically increase with decreasing the grain size. Consequently, in the case of using of W coating as a protective layer of a structural material, a compromise in the development of nanostructured tungsten films is necessary to keep the hydrogen isotope concentration at an acceptable level.

Fabrication of high-quality strain relaxed SiGe(1 1 0) films by controlling defects via ion implantation

We investigate effects of ion implantation on strain relaxation of SiGe(110) layers grown on Si(110) substrates. Ar+ or Si+ ion implantation is carried out before or after the SiGe growth. It is found that the strain relaxation of the SiGe(110) film is largely enhanced due to implantation-induced defects both for Ar and Si implantation. Particularly, the sample with Si implantation after the SiGe growth allows large strain relaxation and smaller surface roughness than Ar implantation. As a result, a 50-nm-thick Si0.79Ge0.21 or Si0.77Ge0.23(110) buffer layer with almost full relaxation and rms surface roughness below 0.5nm was obtained. It is, therefore, expected that high-mobility strained Si/Ge(110) channels can be realized on the SiGe(110) relaxed buffer layers fabricated by Si implantation. It is also demonstrated that the local introduction of the implantation defects allows controlling of lateral strain states and dislocation generation, opening new concepts of engineering of both strain and surface orientation.

The Effect of Low Energy Ion Implantation on MoS2

The use of ultra low energy ion implantation is investigated as a doping method for MoS2. 200 eV Cl and Ar implants at doses between 1 × 1013 and 1 × 1015 cm−2 were introduced into exfoliated MoS2 flakes. XPS results for Cl implants show a decrease in core peak binding energies for Mo3d and S2p with increasing dose, implying a p-doping effect. Implantation of MoS2 device channel regions is shown to reduce the channel's conductivity. However, isolated implantation of the contact region with low doses (1 × 1013 cm−2) of Cl and Ar are shown to improve output characteristics by linearizing the IDS-VDS curves and by increasing current through the device. Cl was shown to be more effective than Ar at increasing the current, implying there is a potential chemical effect as well as damage effect. For higher doses (≥ 1 × 1014 cm−2), the current through the device is reduced with increasing dose for both implant species. This report presents the as-implanted, unannealed results. Post-implantation anneals may be necessary to activate the dopants and fully realize the potential of this doping method.

Reversible metal-insulator transition of Ar-irradiatedLaAlO3/SrTiO3interfaces

The conducting state of a quasi-two-dimensional electron gas (q2DEG), formed at the heterointerface between the two wide-bandgap insulators LaAlO3 (LAO) and SrTiO3, can be made completely insulating by low-energy, 150-eV, Ar+ irradiation. The metallic behavior of the interface can be recovered by high-temperature oxygen annealing. The electrical transport properties of the recovered q2DEG are exactly the same as before the irradiation. Microstructural investigations confirm that the transition is not due to physical etching or crystal lattice distortion of the LAO film below its critical thickness. They also reveal a correlation between electrical state, LAO film surface amorphization, and argon ion implantation. The experimental results are in agreement with density functional theory calculations of Ar implantation and migration in the LAO film. This suggests that the metal-insulator transition may be caused by charge trapping in the defect amorphous layer created during the ion irradiation.

Self-Heating in GaN Transistors Designed for High-Power Operation

DC and transient self-heating effects are investigated in normally off AlGaN/GaN transistors designed for a high-power operation. Electrical and optical methods are combined with thermal simulations; 2-μs-long voltage pulses dissipating about 4.5 W/mm are applied on four different transistor structures combining GaN or AlGaN buffer on an n-type SiC substrate with or without Ar implantation. Transistors with only 5% Al mass fraction in the buffer show almost a threefold increase in the transient self-heating if compared with devices on the GaN buffer. On the other hand, 2-μs-long pulses were found not to be long enough for the Ar-implanted SiC substrate to influence the device self-heating unless AlGaN composition changes. In the dc mode, however, both the buffer composition and Ar implantation significantly influence the self-heating effect with the highest temperature rise for the transistor having the AlGaN buffer grown on the Ar-implanted SiC. We point on possible tradeoffs between the transistor high-power design and the device thermal resistance.

Suppressing light reflection from polycrystalline silicon thin films through surface texturing and silver nanostructures

This work demonstrates a novel method combining ion implantation and silver nanostructures for suppressing light reflection from polycrystalline silicon thin films. Samples were implanted with 20-keV hydrogen ions to a dose of 1017/cm2, and some of them received an additional argon ion implant to a dose of 5 × 1015 /cm2 at an energy between 30 and 300 keV. Compared to the case with a single H implant, the processing involved both H and Ar implants and post-implantation annealing has created a much higher degree of surface texturing, leading to a more dramatic reduction of light reflection from polycrystalline Si films over a broadband range between 300 and 1200 nm, e.g., optical reflection from the air/Si interface in the AM1.5 sunlight condition decreasing from ∼30% with an untextured surface to below 5% for a highly textured surface after post-implantation annealing at 1000 °C. Formation of Ag nanostructures on these ion beam processed surfaces further reduces light reflection, and surface texturing is expected to have the benefit of diminishing light absorption losses within large-size (>100 nm) Ag nanoparticles, yielding an increased light trapping efficiency within Si as opposed to the case with Ag nanostructures on a smooth surface. A discussion of the effects of surface textures and Ag nanoparticles on light trapping within Si thin films is also presented with the aid of computer simulations.

Pre-Amorphization and Low-Temperature Implantation for Efficient Activation of Implanted As in Ge(100)

1. IntroductionFormation of a low-resistance shallow n+/p junction is one of the key issues for enhanced performance of Ge n-channel MISFETs. In particular, for n-type dopants such as P and As, it is well-known that activated dopant concentration in Ge are saturated to be around 1018~1019 cm-3 after the annealing at 500 ºC [1]. In cumulative research knowledge on ion implantation into Si, the recrystallization process and dopant activation are strongly dependent on the substrate temperature during the implantation and the destruction of crystalline structure just after ion implantation is a crucial factor for dopant activation in the implanted layer [3]. In fact, it is also reported that pre-amorphous implantation (PAI) is effective to enhance amorphization and to form shallow junction on Si substrate [4].In this paper, the samples of the heavily As+ implanted Ge at different substrate temperatures during implantation and the samples of As+ implanted into pre-amorphized Ge by Ar or Xe implantation were prepared and the impact of these process conditions on the As+ion activation with annealing were studied systematically.2. Experimental ProcedureP-type Ge(100) wafers with a resistivity of 0.1-0.5 Ω∙cm were used in this study. After the removal of Ge surface native oxide by wet-chemical cleaning, a 7 nm-thick SiO2 layer was deposited by RF sputtering. And then, As+ ions were implanted into the wafers at different temperatures ranging from 400 to -50 ºC at 10keV with doses of 1x1015 and 5x1015 cm-2. TRIM simulation indicates the projected range (Rp) of around 8 nm from the sample surface. For some samples, Xe or Ar ion implantation prior to As+ implantation was performed to amorphize a Ge surface layer. The activation annealing was carried out at 600 ºC in N2ambient.3. Results and DiscussionFor the cases without pre-amophization, the crystallinity of Ge layer just after As+ ion implantation at a dose of 1x1015 cm-2 was evaluated by Raman scattering spectroscopy for the sample implanted at different temperatures. With decreasing substrate temperatures from 400 to -50 ºC, an increase in the broad amorphous Ge (a-Ge) peak at around 275 cm-1 and a decrease in the sharp crystalline Ge (c-Ge) peak at around 300 cm-1were clearly observable. This result indicates that the re-crystallization of Ge layer occurs partially during the ion-implantation even at the room temperature. To get a understanding of the As activation, chemical bonding features of As atoms for the samples implanted at room temperature (RT) and -50 ºC (dose: 5x1015 cm-2) were evaluated by using x-ray photoelectron spectroscopy (XPS) under monochromatized AlKα radiation (1486.6eV). It is found that, from the signal intensity ratio of As1+ component to the total (As1+/(As0++As1+)), the As activation ratio was estimated to be 11% for the sample at RT implantation and 16% for the sample at -50 ºC implantation. This result implies that advanced amorphization plays a role on the As activation with recrystallization. Thus, we have characterized the samples with pre-amorphizing implantation (PAI) and further advanced amorphization in the implanted layer was confirmed by Raman scattering spectroscopy and spectroscopic ellipsometry. Also, the sheet resistances measured by using a four-point probemethod for the samples after activation annealing at 600 ºC for 30sec show a marked decrease in sheet resistance for the sample with PAI (Fig. 1). The result indicates that PAI is quite effective for efficient activation of implanted As in Ge.4. AcknowledgmentsA part of this work was supported by Research Institute for Nano-device and Bio Systems (RNBS) and Natural Science Center for Basic Research and Development, Hiroshima University, Japan.

Implantation of high concentration noble gases in cubic zirconia and silicon carbide: A contrasted radiation tolerance

The modifications of the microstructure of yttria-stabilized cubic zirconia and silicon carbide single crystals implanted with high concentrations of noble gas ions and subsequently annealed at high temperature were characterized using RBS/C, XRD and TEM. It is found that the annealing behavior is strongly dependent on both the material and the implanted noble gases. Ar-implanted yttria-stabilized zirconia shows no significant microstructural modification upon annealing at 800°C, e.g. dislocations are still present and the size of the Ar bubbles does not evolve. This is in strong contrast with previous observations on helium-implanted zirconia, where the formation of bubbles and elongated fractures were observed. In the case of SiC, thermal annealing at 1000°C shows an enhanced damage recovery when He is implanted as compared to Ar implantation and the recrystallization of the matrix is accompanied with the release of noble gas atoms. This difference can be ascribed to different atomic radii, and thus mobility of implanted species.

A study on the surface structures and properties of Ni-free Zr-based bulk metallic glasses after Ar and Ca ion implantation

Ca or Ar implantation was performed on a Zr46Cu37.636Al8.364Ag8 (in atomic percent) bulk metallic glass (BMG) at 10 keV with a fluence of 8 × 1015 cm-2. The effects of ion implantation on the surface microstructure, nano-hardness, and corrosion behavior of the Zr-based BMG have been studied. The results showed that the BMG specimen maintained an amorphous structure after Ar or Ca ion implantation. The thermodynamic stabilities were altered by ion implantation, and the relaxation of an amorphous structure is shown. The surface nano-hardness and corrosion resistance were enhanced after ion implantation. The efficient improvement of the surface performance by ion implantation on BMGs was analyzed and discussed.

HfSiO Bulk Trap Density Controls the Initial $V_{\rm th}$ in nMOSFETs

The underlying physical mechanism of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> adjustment of nMOSFETs with HfSiO/TiN gate stack obtained by As and Ar implantation is investigated. It is experimentally proved that the trapped charge in the HfSiO bulk defects controls the initial <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> value in nMOSFETs. The reduction of the charged trap density in HfSiO by implant explains the tuned <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> values.

Diffusion and Gettering of Transition Metals in 4H-SiC

Diffusion of transition metals in 4H-SiC has been investigated by secondary ion mass spectroscopy using epilayers and substrates implanted with titanium (Ti), chromium (Cr), iron (Fe), or nickel (Ni). In the epilayers, Cr, Fe, and Ni atoms have diffused by argon (Ar) annealing at 1780°C for 30 min. In n+ substrates, the diffusivity of the metals is smaller than that in the epilayers, and only Ni has diffused by the annealing. By the Ar or helium implantation following the implantation of transition metals, diffusion of transition metals can be successfully suppressed.

A comparison of Ar ion implantation and swift heavy Xe ion irradiation effects on immiscible AlN/TiN multilayered nanostructures

We have compared the effects of 200keV 40Ar1+ ion implantation and 166MeV 132Xe27+ ion irradiation on immiscible (AlN/TiN)×5 multilayers grown on Si(100) wafers. The layers were deposited by reactive sputtering, individual layer thickness was ∼22nm (AlN) and ∼32nm (TiN), the stoichiometry Al:N∼45:55 and Ti:N∼50:50at%. Argon was implanted to 4×1016ionscm−2, and xenon to 5×1014ionscm−2. The projected Ar range is around mid depth of the multilayered structure, while swift Xe ions are buried deep into the Si substrate. Upon irradiation the structures remain essentially stable and unmixed; although in both cases we observed detectable effects. The use of wide range of irradiation parameters (Se/Sn=1.2–1.4, dpa=42–63 for Ar; and Se/Sn=249–258, dpa=0.03–0.05 for Xe) enabled to distinguish between the contribution of nuclear and electronic stopping. In case of Ar implantation both atomic collisions and electronic excitations contribute to the induced structural modifications, and in case of Xe only electronic excitations. It was deduced that electronic excitations generate local heating which influences lateral grain growth within individual layers, but no elemental redistribution. On the other hand, atomic collisions facilitate a low level of Ti migration into the under-stoichiometric AlN layers, in the vicinity of the implanted Ar ion range. Energy transfer and temperature distribution were evaluated and compared to the effects produced in the structures. The presented results can be interesting towards developing radiation tolerant materials.

SONOS memory devices with ion beam modified nitride layers

ABSTRACTIn this work we examine the development of ion beam modified oxide-nitride-oxide structures formed by low-energy (1 keV) implantation of Si, N and Ar ions (1x1016 ions/cm2) into oxide-nitride gate stacks and subsequent wet-oxidation to form the blocking oxide. Transmission electron microscopy indicates that the thickness of the blocking oxide layer is strongly affected by the implantation process going from 1 nm (non-implanted sample) to 4-5 nm (N and Ar implants) and 7.5 nm (Si implant). The Si implanted stacks exhibit the highest attainable memory window (∼ 8.5 V for a 1 ms pulse regime), which involve both electron and hole storage. In contrast the thinner blocking oxide that develops to the nitrogen and argon implanted stacks limits the memory window which is due only to electron trapping. Room temperature charge retention measurements of the programming state reveal that the electron loss rate is faster in samples implanted with Si than N, allowing for a memory window of 1.7 V and 2.5 V respectively after ten years extrapolation. This retention behavior is mainly attributed to the different nature of the traps generated in the implanted materials.