Energy Ion Implantation Research Articles

Effect of rise-time patterns on dynamics of sheath expansion during plasma immersion ion implantation

Plasma immersion ion implantation (PIII) has been developed as a low_cost and efficient surface modification technique of irregularly-shaped objects. The effect of six pulse waves with different rise_time patterns on the spatio-temporal evolution of plasma sheath, energy and dose of ion implantation has been simulated by particle-in-cell modeling. Statistical results may be obtained through assuming the Boltzmann distribution of electrons, and solving Poisson and Newton equations for tracing each ion in the plasma sheath. The results show that rise_time pattern has a critical influence on the evolution of plasma sheath. There exists maximum thickness difference of plasma sheath for different waveforms. The acceleration of ions is non_uniform due to the non-uniformity of electrical field strength. The maximum gradient of electrical field appears near the edge of plasma sheath. The results also show that optimization of dose and energy of incident ions may be achieved through modification of rise_time pattern. The numerical simulation of sheath expansion can be effectively used to provide a scientific basis for optimizing the PIII process.

Selective Enhancement of SiO[sub 2] Etch Rate by Ar-Ion Implantation for Improved Etch Depth Control

Argon-ion implantation can be used to selectively and dramatically enhance the etch rate of a silicon dioxide film down to a precise depth, to allow for improved control of etch depth in a timed oxide etch process. An empirical model based on damage concentration,- fit to experimental data, is used to explain the correlation between the implantation conditions (dose, energy) and the etch-rate enhancement parameters. The model is shown to yield predictions of the etch rate enhancement consistent with the existing model based on nuclear deposited energy. The depth of etch-rate enhancement is determined primarily by the implant energy, whereas the etch-rate enhancement factor is controlled by the implant dose. Enhancement factors close to five were achieved with moderate-dose (2 × 10 14 /cm 2 ) Ar + implantation. Lower ion-implantation energy results in sharper transition between the etch-rate enhanced and the unaffected oxide region. This technique can be used to improve process uniformity in fabrication of three-dimensional semiconductor device structures such as bulk-Si FinFETs, for reduced variations in circuit performance.

Single-walled carbon nanotube growth from ion implanted Fe catalyst

The authors present experimental evidence that single-walled carbon nanotubes can be grown by chemical vapor deposition from ion implanted iron catalyst. They systematically characterize the effect of ion implantation dose and energy on the catalyst nanoparticles and nanotubes formed at 900°C. They also fabricate a micromachined silicon grid for direct transmission electron microscopy characterization of the as-grown nanotubes. This work opens up the possibility of controlling the origin of single-walled nanotubes at the nanometer scale and of integrating them into nonplanar three-dimensional device structures with precise dose control.

Structure and properties of tetrahedral amorphous carbon films implanted with Ti ion

In this paper the structures, mechanical properties and tribological characterization of the tetrahedral amorphous carbon films implanted with Ti ion with energy range from 2 keV to 12 keV using MEVVA implantation have been investigated. The structures of the Ti containing amorphous carbon film have been studied by X-ray photoelectron spectroscopes. The tetrahedral amorphous carbon transform to sp2-rich amorphous carbon during Ti ion implantation. The hardness and elastic modulus of the tetrahedral amorphous carbon films decreases with Ti ion implantation as a result of graphitization of sp3-rich amorphous carbon film. The compressive stress of tetrahedral amorphous carbon films implanted with Ti decreases with increase of ion implantation dose and energy. The friction coefficient of tetrahedral amorphous carbon film implanted with Ti increases with implantation dosage.

Transient Ion Sheath in Pulsed Plasmas

In plasma-based ion implantation and deposition (PBII&D), the use of pulsed-plasma sources such as a shunting arc might have some advantages over a conventional plasma source used to produce high-density plasmas. It is desirable for a conformal implantation into the materials (targets) with complicated surfaces. In some cases, the pulsed plasmas may be surrounded by a vacuum region in the vessel, when the lifetime of each pulsed plasma is short compared with the plasma-expansion time. When a target is immersed in such isolated plasmas and a negative voltage pulse is applied for ion implantation, the ion-sheath potential may be different from what is expected in a plasma contacting the vacuum vessel of the ground potential. The ion-sheath potential, the difference between the plasma space potential and the target potential, determines the maximum energy of the implanted ions. A simplified one-dimensional model, in which the target is immersed in a plasma surrounded by a vacuum (or low density) region and an outside vessel of the ground potential, has been developed. It is shown that, when a negative high-voltage pulse is applied to the target for ion implantation, the resultant sheath potential can be substantially lower than the applied potential depending upon the ion current to the target and the distance of the plasma edge from the vessel wall. This effect on the ion current and implanted-ion energy distribution is discussed in this paper

Ultrafast dynamics of Ni+-irradiated and annealed GaInAs/InP multiple quantum wells

Carrier dynamics and optical activity of 10 MeV Ni+-irradiated and annealed GaInAs/InP quantum wells (QWs) have been studied using a time-resolved femtosecond up-conversion method. Quantitative results are obtained for a carrier capture time and a carrier lifetime (decay time) as a function of implantation dose. The carrier capture time decreases with the dose, while it is little affected by rapid thermal annealing (RTA). The capture time is 8 ps for the as-grown QW and 2 ps for the irradiated QW at the highest ion dose of 50 × 1010 ions cm−2. The carrier lifetime in the as-grown QW is long, 1.19 ns, but is only 3.7 ps after ion irradiation. RTA reduces the density of irradiation-induced defects and improves the optical activity. Other than the implantation dose, the lifetime also depends on the ion implantation energy (varied from 6 to 30 MeV at a fixed dose of 5 × 1010 ions cm −2): the higher the implantation energy, the longer the carrier lifetime. This is because the nuclear deposited energy decreases in the QW region with an increase in implantation energy. Hence, for an efficient defect production low-energy implantation (<10 MeV for Ni+) is preferred. The results obtained are compared with compressively strained GaInAs/GaAs QWs samples exposed to a similar dose and annealing conditions.

Reduction of strain and dislocation defects in GaN layers grown on Si substrate by MOCVD using a substrate defect engineering technique

AbstractWe report on the application of a new scheme of substrate engineering in Si (111) substrate to obtain high quality GaN layers on Si substrates. An ion implanted defective layer is formed in the Si substrate that partially, crystallographically and mechanically isolates the III‐Nitride layer and Si substrate which results in reduction of strain in the Nitride film. Nitrogen ion implantation energies of 60‐75 keV and ion doses of 1×1016 cm–2‐2×1016 cm–2 were applied to AlN buffer layers of 55 nm thick grown on Si (111). The experimental results show an increase in the crack separation of over 1 mm for 2 µm thick GaN film grown on implanted 55 nm AlN/Si complex substrate as seen under optical microscope. Moreover the GaN films grown on implanted AlN/Si substrate showed smoother surface morphology (RMS roughness of 0.41 nm) as compared to that grown on non‐implanted AlN/Si substrates (RMS roughness of 1.50 nm). Results of etch pit density and XRD measurements show significant reduction in dislocations in III‐Nitride layers. Our data shows a strong dependence of GaN quality on the implantation conditions. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A study of the influence of tunnel oxide thickness on the performance of flash memory based on ion‐beam synthesized silicon nanocrystals

AbstractIn this work, we have fabricated silicon nanocrystal (nc‐Si) based Flash memories with two different tunnel‐oxide thicknesses (3 and 7 nm). The nc‐Si is synthesized with very‐low energy ion implantation and subsequent thermal annealing. The endurance and retention characteristics of the memory devices are investigated. For the thick tunnel oxide (7 nm), a memory window of ∼0.5 V is achieved with the program/erase (P/E) operation at +12 V/–12 V for 1 ms; and for the thin tunnel oxide (3 nm), a memory window of ∼0.6 V can be obtained at +9 V/–9 V for 1 μs. For both oxide thicknesses, good endurance with a small threshold voltage drift after 105 P/E cycles is observed. For the thick and thin tunnel oxides, the device is expected to show ∼20% and ∼70% charge loss after 10 years, respectively. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Measurement of implanted helium particle transport by a flowing liquid lithium film

Due to its low atomic number, low sputtering yield, high sputtered ion fraction and excellent thermal properties, liquid lithium has been proposed as a potential candidate for advanced plasma-facing components (PFC). Using a liquid material opens the possibility of a continuously flowing, self-regenerating plasma-facing surface with a small residence time. This would allow such component to handle very high heat loads that are expected. There are, however, multiple unanswered questions regarding how such a liquid PFC would interact with the plasma in the reactor. The issue of particle control is critical, and it can be a factor to determine the feasibility of these advanced concepts. Hydrogen and helium are important in this regard: hydrogen transport by a flowing PFC impacts the reactor fuel recycling regime and tritium inventory; helium transport can help quantify ash removal by the flowing PFC. The flowing liquid-metal retention experiment (FLIRE) was built at the University of Illinois to answer some of the questions regarding particle transport by flowing liquid films exposed to plasmas. Experimental results regarding helium transport by a flowing lithium film after irradiation with an energetic He ion beam are presented in this work. Retained fraction values up to 2% were measured for the experimental conditions, and the retention was found to increase linearly with implanted ion energy. A pure diffusion model was used to describe the helium transport by the Li film, and it was found that such model predicts a diffusion coefficient of (2.8 ± 0.6) × 10 −11 m 2/s, based on the experimental retention measurements. Preliminary evidence of long-term trapping of helium will also be presented.

Ti/AlNi/W Ohmic Contacts to P-Type SiC

AbstractImproved AlNi-based ohmic contacts to p-type 4H-SiC have been achieved using low energy ion (Al+) implantation, the addition of a thin Ti layer, and a novel two-step implant activation anneal process. Resistivities sometimes as low as 5×10−5 Ω-cm2 were reached by doping the surface region of lightly p-doped 4H-SiC epilayers via low energy Al+ implantation. Acceptor activation was achieved by annealing the samples with a 1400+1700°C two-step sequence in an Ar atmosphere, which also yielded improved surface morphology when implanted samples were capped with photo resist during the anneals. In this study, Ti/AlNi/W contacts on implanted layers were compared to Ti/AlNi/Au contacts. Even though the resistivities are higher than those of the Ti/AlNi/W system, the reduced anneal temperature, 650°C for Ti/AlNi/Au compared to 950°C for Ti/AlNi/W implies that Ti/AlNi/Au is a promising stacking configuration. Furthermore, the effects of a longer 30 minute anneal time at 600 − 700°C, in atmospheric pressure Ar ambients was observed. Namely, the 2 minute annealing cycle used for the Ti/AlNi/W study resulted in higher anneal temperatures before ohmic characteristics were seen. This same anneal time was not sufficient for the Ti/AlNi/Au samples, whereas increasing the cycle time to 30 minutes resulted in ohmic behavior at a much lower temperature. Increasing the anneal time however, had little or no impact on reducing the required anneal temperature of the Ti/AlNi/W.

Modifying residual stress and stress gradient in LPCVD Si 3N 4 film with ion implantation

This study presents a method for modifying residual stress in low-pressure chemical vapor deposition (LPCVD) Si 3N 4 films. Utilizing ion implantation technology, the residual stress and stress gradient in the Si 3N 4 film has been successfully modified with a wide adjustable range. Compressive stress is introduced by the ion implantation and offsets the intrinsic tensile stress in the film. Besides the distribution of the induced stress can modify the stress gradient in the film. An analytical model has been developed to describe the modifications. The dosage and energy of ion implantation can be controlled accurately, and therefore the presented method can modify stress level precisely. With this method, the mean residual stress in the Si 3N 4 film was adjusted from 1.2 GPa tensile to −0.1 GPa compressive continuously. Moreover, cantilever curling caused by the stress gradient was reduced efficiently, which demonstrates the modification of the stress gradient. The ion implantation slightly increased the film's etch rate in HF and KOH, and degrade the mechanical properties, hardness and elastic modulus, due to damage caused by atomic collision. Thermal annealing was used to recover the damage.

Radiation hardness improvement of separation-by-implantation-of-oxygen/silicon-on-insulator material by nitrogen ion implantation

In our work, nitrogen ions were implanted into separation-by-implantation-of-oxygen (SIMOX) wafers to improve the radiation hardness of the SIMOX material. The experiments of secondary ion mass spectroscopy (SIMS) analysis showed that some nitrogen ions were distributed in the buried oxide layers and some others were collected at the Si/SiO2 interface after annealing. The results of electron paramagnetic resonance (EPR) suggested the density of the defects in the nitrided samples changed with different nitrogen ion implantation energies. Semiconductor-insulator-semiconductor (SIS) capacitors were made on the materials, and capacitance-voltage (C-V) measurements were carried out to confirm the results. The super total dose radiation tolerance of the materials was verified by the small increase of the drain leakage current of the metal-oxide-semiconductor field effect transistor with n-channel (NMOSFETs) fabricated on the materials before and after total dose irradiation. The optimum implantation energy was also determined.

Recent advances in nanoparticle memories

Nanoparticle memories have made their point during last years as a possible solution to overcome the scaling issue of electronic non-volatile memories. Ultimately, we are looking for nanoparticle memories to significantly decrease the voltage needed to write/erase the memory without compromising its retention characteristics. Several approaches have been reported for semiconductor nanoparticle formation using techniques such as chemical vapor deposition, molecular beam epitaxy or sputtering. In the present review emphasis is placed on a silicon nanoparticle memory resulting from low-energy ion implantation of silicon within a thin oxide layer and subsequent annealing. This process allows for the formation of a two-dimensional array of silicon nanoparticles within the gate oxide in one processing step making the process attractive for CMOS integration. Material issues related with ion implantation energy, dose and annealing ambient for optimum device performance are addressed. As an alternative to semiconductor nanoparticles, metallic nanoparticles have been investigated since they have the potential for more versatile engineering of energy barriers that would allow improved data retention for memory devices operating at low voltages. Processing approaches for metallic nanoparticle formation are addressed and corresponding memory device performance is discussed for the particular case of room temperature deposited metallic nanoparticles by chemical methods.

Structural properties of Ge-implanted SiO 2 layers and related MOS memory effects

Recently, the feasibility of using ion implantation of germanium and high temperature annealing to fabricate a near-interface nanocrystal (nc) layer into a silicon dioxide (SiO 2) on Si film has been demonstrated. In this work, the influence of ion implantation parameters on the nc layer formation in SiO 2 is studied. Transmission electron microscopy and Rutherford backscattering spectroscopy have been used to study the Ge-redistribution in the SiO 2 films. Depending on the ion implantation energy and dose, the formation of a bulk nc layer in addition to the desired near-interface layer can be observed. A maximum near-interface Ge-nc density of 1.7 × 10 12 cm −2 has been measured. Capacitance–voltage measurements have been used to study electrical properties of metal-oxide-semiconductor structures containing such implanted SiO 2 films. The results indicate a strong memory effect due to the presence of near-interface Ge-nc. As an example, flat-band shifts of 4.5 V have been obtained at a programming voltage of 7 V for 1 s. For the first time, long retention properties have been demonstrated on a memory structure containing a single near-interface Ge-nc layer.

The effect of ion implantation energy and dosage on the microstructure of the ion beam synthesized FeSi 2 in Si

Nanometer-sized β-FeSi 2 precipitates are formed in Si by ion beam synthesis (IBS). A systematic study is carried out to investigate the correlation among the implantation parameters, the microstructure, and the luminescence properties. On the one hand, we found additional orientation relationships (ORs) appear between the β-FeSi 2 and the Si with improved lattice coherence between the two, when the ion implantation energy is increased. On the other hand, the degree of preferential orientation deteriorates and leads to poor lattice coherence between the particles and Si matrix when the iron ion is overdosed. These microstructure changes lead to different luminescence properties (intensity, peak position and shape) of the β-FeSi 2 particles accordingly.

Simulation of a semitransparent conducting mesh electrode for plasma immersion ion implantation

Particle-in-cell simulations of plasma evolution in the vicinity of a mesh electrode that is semitransparent to ions are presented. Space-charge accumulation and ion focusing have an important effect on the ion trajectories and ion energy distribution inside the mesh. The results indicate that when such an electrode is used to assist plasma immersion ion implantation of insulating targets, the initial plasma conditions and mesh geometry are key factors in achieving optimum dose uniformity and implanted ion energy.

Effects of implantation energy and annealing temperature on the structural evolution of Ge+-implanted amorphous Si

High-resolution transmission electron microscopy in conjunction with autocorrelation function analysis have been applied to investigate the evolution of structural order in Ge+-preamorphized silicon layers. (001)Si wafers were preamorphized with 5 and 10keV Ge+ to a dose of 5×1015ions/cm2. A higher density of embedded nanocrystallites was found to be present in as-implanted amorphous Si layer for 10keV Ge+ than that for 5keV Ge+. The densities of embedded nanocrystallites in Ge+-preamorphized Si layer with 5 and 10keV Ge+ were found to diminish with annealing temperature first then increase. The effects of ion-implantation energy and annealing temperature on the structural evolution in Ge+-implanted amorphous Si are discussed in terms of ion-beam induced annealing and free energy change of the system. The depth dependence on the density of embedded nanocrystallites is attributed to the nonuniform distribution of Ge atoms.

Plasma-based ion implantation: a valuable technology for the elaboration of innovative materials and nanostructured thin films

Plasma-based ion implantation (PBII), invented in 1987, can now be considered as a mature technology for thin film modification. After a brief recapitulation of the principle and physics of PBII, its advantages and disadvantages, as compared to conventional ion beam implantation, are listed and discussed. The elaboration of thin films and the modification of their functional properties by PBII have already been achieved in many fields, such as microelectronics (plasma doping/PLAD), biomaterials (surgical implants, bio- and blood-compatible materials), plastics (grafting, surface adhesion) and metallurgy (hard coatings, tribology), to name a few. The major advantages of PBII processing lie, on the one hand, in its flexibility in terms of ion implantation energy (from 0 to 100 keV) and operating conditions (plasma density, collisional or non-collisional ion sheath), and, on the other hand, in the easy transferrability of processes from the laboratory to industry. The possibility of modifying the composition and physical nature of the films, or of drastically changing their physical properties over several orders of magnitude makes this technology very attractive for the elaboration of innovative materials, including metastable materials, and the realization of micro- or nanostructures. A review of the state of the art in these domains is presented and illustrated through a few selected examples. The perspectives opened up by PBII processing, as well as its limitations, are discussed.

Molecular Dynamics Calculation for Low-Energy Ion Implantation Process with Dynamic Annealing Effect

In this paper, we present a molecular dynamics (MD) study on a low-energy ion implantation process for nanoscale CMOS (Complementary Metal Oxide Semiconductor) processes. To model the profiles of interstitials and vacancies, the recoil interaction approximation (RIA) was employed, while the kinetic Monte Carlo (KMC) approach was used for modeling the dynamic annealing effect between cascades. The simulation results performed for as-implanted boron profiles were compared with the results of the binary collision approximation (BCA) calculation by UT-MARLOWE as well as with the experimental SIMS data. The simulation revealed that the dynamic annealing effect between cascades is essential for the accurate estimation of defect distribution as well as as-implanted ion distribution. The dynamic annealing effect was carefully investigated for a case of boron implantation with an ion implantation energy of 2 keV, doses of 1×1014 ions/cm2 and 1×1015 ions/cm2, and a dose rate of 1×1012 ions/cm2·s.

Concentration and ion-energy-independent annealing kinetics during ion-implanted-defect annealing

Nanocalorimetry revealed that the annealing kinetics of ion-implanted defects in polycrystalline Si is independent of ion fluence and implantation energy. Ion implantation of 30 keV Si−, 15 keV Si−, and 15 keV C− was performed at fluences ranging from 6×1011 to 1×1015atoms∕cm2, followed by temperature scans between 30 and 450 °C. The rate of heat release has the same shape for all fluences, featuring no peaks but rather a smooth, continuously increasing signal. This suggests that the heat release is dominated by the annealing of highly disordered zones generated by each implantation cascade. Such annealing depends primarily on the details of the damage zone–crystal interface kinetics, and not on the point defect concentration.