Sputtering Behavior Research Articles

Sputtering Behavior of P3HT under Low-Energy Monoatomic Projectile Bombardment: Insights from Molecular Dynamics Simulations

Sputtering Behavior of P3HT under Low-Energy Monoatomic Projectile Bombardment: Insights from Molecular Dynamics Simulations

Deep neural network-based reduced-order modeling of ion–surface interactions combined with molecular dynamics simulation

With the advent of complex and sophisticated architectures in semiconductor device manufacturing, atomic-resolution accuracy and precision are commonly required for industrial plasma processing. This demands a comprehensive understanding of the plasma–material interactions—particularly for forming fine high-aspect ratio (HAR) feature patterns with sufficiently high yield in wafer-level processes. In particular, because the shape distortion in HAR pattern etching is attributed to the deviation of the energetic ion trajectory, the detailed ion–surface interactions need to be thoroughly investigated. In this study, molecular dynamics (MD) simulations were utilized to obtain a fundamental understanding of the collisional nature of accelerated Ar ions on the fluorinated Si surface that may appear on the sidewall of the HAR etched hole. High-fidelity data for ion–surface interaction features representing the energy and angle distributions (EADs) of sputtered atoms for varying degrees of surface F coverage and ion incident angles were obtained via extensive MD simulations. A deep learning-based reduced-order modeling (DL-ROM) framework was developed for efficiently predicting the characteristics of the ion–surface interactions. In the ROM framework, a conditional variational autoencoder (AE) was implemented to obtain regularized latent representations of the distributional data with the condition of the governing factors of the physical system. The proposed ROM framework accurately reproduced the MD simulation results and significantly outperformed various DL-ROMs, such as AE, sparse AE, contractive AE, denoising AE, and variational AE. From the inferred features of the sputtering yield and EADs of sputtered/scattered species, significant insights can be obtained regarding the ion interactions with the fluorinated surface. As the ion incident angle deviated from the glancing-angle range (incident angle >80°), diffuse reflection behavior was observed, which can substantially affect the ion transport in the HAR patterns. Moreover, it was hypothesized that a shift in sputtering characteristics occurs as the surface F coverage varies, based on the inferred EADs. This conjecture was confirmed through detailed MD simulations that demonstrated the fundamental relationship between surface atomic conformations and their sputtering behavior. Combined with additional atomistic-scale investigations, this framework can provide an efficient way to reveal various fundamental plasma–material interactions which are highly demanded for the future development of semiconductor device manufacturing.

Establishing a Best Practice for SDTrimSP Simulations of Solar Wind Ion Sputtering

Solar wind (SW) ion irradiation on airless bodies can play an important role in altering their surface properties and surrounding exosphere. Much of the ion sputtering data needed for exosphere studies come from binary collision approximation sputtering models such as TRansport of Ions in Matter and its more recent extension, SDTrimSP. These models predict the yield and energy distribution of sputtered atoms, along with the depth of deposition and damage of the substrate, all as a function of the incoming ion type, impact energy, and impact angle. Within SDTrimSP there are several user-specific inputs that have been applied differently in previous SW ion sputtering simulations. These parameters can influence the simulated behavior of both the target and sputtered atoms. Here, we have conducted a sensitivity study into the SDTrimSP parameters in order to determine a best practice for simulating SW ion impacts onto planetary surfaces. We demonstrate that ion sputtering behavior is highly sensitive to several important input parameters including the ion impact angle and energy distribution and the ejected atom surface binding energy. Furthermore, different parameters can still result in similarities in the total sputtering yield, potentially masking large differences in other sputtering-induced behaviors such as the elemental yield, surface concentration, and damage production. Therefore, it is important to consider more than just the overall sputtering behavior when quantifying the importance of different parameters. This study serves to establish a more consistent methodology for simulations of SW-induced ion sputtering on bodies such as Mercury and the Moon, allowing for more accurate comparisons between studies.

Topography of high-speed steel substrates sputter cleaned by an Ar/Ti cathodic arc plasma

Hard coated high-speed steels are often used for tooling applications and consist of three different microstructural constituents: a martensitic matrix, M6C and MC carbides. The behavior of these three during the various tool manufacturing steps has a detrimental effect on the final tool performance. The focus of the current work is the surface topography change due to variation of the substrate bias voltage applied during the Ar/Ti arc plasma sputter cleaning process which changed the sputtering behavior of the high-speed steel's microstructural constituents and the appearance of droplets on the sputtered surface. The surface topography was characterized by laser confocal and scanning electron microscopy. Furthermore, microstructural analysis was carried out on cross-section lamellae prepared by a focus ion beam technique and analyzed by transmission electron microscopy. At each of the three investigated substrate bias voltages (Ub) of −600, −800 and −1000 V during the Ar/Ti arc plasma sputter cleaning process, the mentioned microstructural constituents behaved differently. At an Ub threshold of −600 V, sputter erosion starts at M6C carbides in an inhomogeneous material erosion pattern. At −800 V, a homogeneous sputter behavior was established for the entire sample. M6C carbides showed the highest sputter erosion rate, on MC carbides Ti deposition occurred instead of sputter erosion, and the martensitic matrix was smoothened, as peaks and exposed features were sputtered preferentially. As of Ub = −1000 V, the sputter erosion behavior of the martensitic matrix changed and exposed features were preserved. The reason for this change was identified to be Ti+ ion implantation indicated by Monte Carlo simulations and the associated increase of the matrix' cohesive strength, calculated using Density Functional Theory. The published results in this study will help to further utilize Ar/Ti arc plasma sputter cleaning processes for intentional surface topography design.

Comprehensive effect of grain size and original target morphology on sputtering behavior of magnetron sputtering target

In this paper, the etching morphology, surface roughness, target voltage, and light emission line intensity of the copper target were investigated using a closed-field unbalanced magnetron sputtering system equipped with optical emission spectroscopy monitor (OEM). The results show that the morphology of the sputtering zone, the target voltage value, the surface roughness, and the OEM value are significantly correlated with the grain size of the target. After sputtering, the original target's morphology dramatically influences the surface roughness and OEM value.

Sputtering Behavior of Rough, Polycrystalline Mercury Analogs

The solar wind continuously impacts on rocky bodies in space, eroding their surface, thereby contributing significantly to the exosphere formations. The BepiColombo mission to Mercury will investigate the Hermean exosphere, which makes an understanding of the precise formation processes crucial for evaluation of the acquired data. We therefore developed an experimental setup with two microbalances that allows us to compare the sputter behavior of deposited thin solid layers with that of real mineral samples in the form of pressed powder. In addition, this technique is used to study the angular distribution of the sputtered particles. Using 4 keV He+ and 2 keV Ar+ ions, the sputter behavior of pellets of the minerals enstatite (MgSiO3) and wollastonite (CaSiO3) is studied, because these minerals represent analogs for the surface of the planet Mercury or the Moon. Pellets of powdered enstatite show significantly lower sputter yields than thin amorphous enstatite films prepared by pulsed laser deposition. 3D simulations of sputtering based on surface topography data from atomic force microscopy show that the observed reduction can be explained by the much rougher pellet surface alone. We therefore conclude that sputter yields from amorphous thin films can be applied to surfaces of celestial bodies exposed to ion irradiation, provided the effects of surface roughness, as encountered in realistic materials in space, are adequately accounted for. This also implies that taking surface roughness into account is important for modeling of the interaction of the solar wind with the surface of Mercury.

The cosmic-ray induced sputtering process on icy grains

ABSTRACT In molecular cloud cores, the cosmic ray (CR) induced sputtering via CR ion-icy grain collision is one of the desorption processes for ice molecules from mantles around dust grains. The efficiency of this process depends on the incident CR ion properties as well as the physicochemical character of the ice mantle. Our main objective is the examination of the sputtering efficiency for H2O and CO ices found in molecular cloud cores. In the calculation routine, we consider a multidimensional parameter space that consists of 30 CR ion types, 5 different CR ion energy flux distributions, 2 separate ice mantle components (pure H2O and CO), 3 ice formation states, and 2 sputtering regimes (linear and quadratic). We find that the sputtering behaviour of H2O and CO ices is dominated by the quadratic regime rather than the linear regime, especially for CO sputtering. The sputtering rate coefficients for H2O and CO ices show distinct variations with respect to the adopted CR ion energy flux as well as the grain-size-dependent mantle depth. The maximum radius of the cylindrical latent region is quite sensitive to the effective electronic stopping power. The track radii for CO ice are much bigger than H2O ice values. In contrast to the H2O mantle, even relatively light CR ions (Z ≥ 4) may lead to a track formation within the CO mantle, depending on Se,eff. We suggest that the latent track formation threshold can be assumed as a separator between the linear and the quadratic regimes for sputtering.

Ion irradiation-induced sputtering and surface modification of BN films prepared by a reactive plasma-assisted coating technique

Boron nitride (BN) films with a wide variety of nano-network structures (sp 2 and sp 3 bonds) were prepared using a reactive plasma-assisted coating technique, and their sputtering behavior was investigated. Fourier transform infrared spectroscopy (FTIR) and nanoindentation analyses confirmed the presence of sp 2- and sp 3-bonded phases. Subsequently, the thickness change after plasma exposure was studied for various BN films. The sputtered depth of the prepared BN films after plasma exposure was shallower than that of the SiO2 films. While no clear change was observed in the FTIR spectra, the leakage current and dielectric constant changed significantly owing to the surface modification during plasma exposure. The modified layer underneath the sputtered surface contained local defects that acted as carrier trapping or hopping sites. Sputtering behavior analysis, in combination with electrical measurements, is a useful methodology for designing a wide variety of BN films.

The influence of aluminum nanoparticles on the laser ablation characteristics of hydroxylamine nitrate-based liquid propellants

Hydroxylamine nitrate is a nontoxic green energetic propellant that has a high energy density and wide application prospects in the field of aerospace propulsion. Here, the laser ablation and propulsion properties of hydroxylamine nitrate-based propellants doped with aluminum nanoparticles were studied. The results showed a significant improvement in the laser absorption properties of hydroxylamine nitrate doped with aluminum nanoparticles. The maximum absorption rate increased by more than 80%, while the absorption depth decreased considerably with a minimum of 277 μm. The sputtering behavior also weakened during laser ablation, and the impulse of hydroxylamine nitrate could be enhanced by doping aluminum nanoparticles. With the 0.7wt% mass fraction of aluminum nanoparticles, a maximum impulse bit of 57.55 μN·s at 90 mJ laser energy. This is led to a maximum energy conversion efficiency of 218.1% and an enhancement of the kinetic energy of the hydroxylamine nitrate-based propellant of 56% with laser energy of 25 mJ. Compared with ordinary liquid propellants, doped samples have better propulsion performance.

Analytical model for the sputtering of rough surfaces

The sputtering yields of solids under ion bombardment are highly sensitive to the roughness of their surfaces. Understanding how sputtering is exactly affected by different surface morphologies is relevant especially for plasma-wall interaction in fusion reactors and space weathering of planetary surfaces. We present an analytical model that allows to calculate sputtering yields of random gaussian rough surfaces under arbitrary angles of incidence, taking into account local incidence angles, shadowing and redeposition of sputtered materials. Sputtering yields of a rough surface can then be calculated with the sputtering yield’s dependence on the ion incidence angle for a flat surface and a single statistical parameter, which characterizes the surface roughness. The model supports previous findings that the mean surface inclination angle δm is a well-suited parameter to describe the sputtering behavior of rough surfaces. Comparisons of the results to previous experiments and numerical simulations for various cases are presented, showing that the model allows to quantitatively reproduce sputtering yields of different samples over a wide range of roughness regimes.

X-ray Photoelectron Spectroscopy Equipped with Gas Cluster Ion Beams for Evaluation of the Sputtering Behavior of Various Nanomaterials

The selection of ion-beam species and parameters for depth profiling requires experience to obtain accurate depth information and an efficient sputter rate on diverse samples. Sputter damage that causes changes in the chemical state and composition should be avoided. Monoatomic ion-beam sources are commonly utilized for the rapid sputtering of metals and inorganics, but sputter damage to highly oxidized metal oxides and organics is well-known. Cluster ion beams have become popular in recent years for soft materials because of their capability for low damage to organics, but sputter yields of metal and inorganic materials are very low. Currently, the material properties and structures of semiconductor devices have become more complicated because of rapid technical development. Thus, it is necessary to explore more sputtering methods for samples with hybrid architecture that contain metals/inorganics/organics together. Recently, gas cluster ion beams (GCIBs) with small cluster sizes were considered to be one of the methods with the advantages of both monatomic ion beams and conventional large-cluster GCIBs (>Ar2000+). A smaller-cluster GCIB results in higher energy per atom with a sputtering behavior similar to that of the monatomic ion beam and leads to enhancement of the sputter yield in metal and inorganic layers. However, the discussion of the cluster size selection for X-ray photoelectron spectroscopy (XPS) chemical state analysis during depth profiling is rather limited. In this work, a GCIB cluster measurement kit is developed and installed in an XPS system. The actual distribution of the cluster size of each GCIB setting can be measured before depth profiling. Depth profiling using GCIBs with a series of cluster sizes is performed to examine the sputter yield and evaluate the sputter effect on various organic, inorganic, and hybrid nanomaterials. The results also show the different sputtering behaviors of GCIBs with different cluster sizes (Ar500–2000+).

Research on sputtering behavior of three beams coaxial laser cladding powder based on the interaction of lasers and powder

During laser cladding, a mutual coupling effect exists among the powder, carrier gas, shielding gas, and laser beam. The key to optimizing the cladding process is determining the effective utilization of the powder and revealing the interaction mechanism of the laser and the powder. In this paper, a continuous-discrete phase coupling model of the interaction between 316L powder, carrier gas, and protective gas in laser cladding is established, which is based on a three-beam coaxial powder feeder. Quantitatively reveals the influence of working distance, carrier gas flow rate, and shielding gas flow rate on the state of powder aggregation and the external flow field of the powder nozzle during the cladding process. To improve the utilization rate of the powder, the cladding process parameters were optimized by the orthogonal test method. A custom program of laser heat source function was written to calculate the temperature rise of powder under the interaction of the laser and the powder. The relationship between powder temperature and cladding process parameters was established. The powder aggregation shape obtained by the numerical simulation was compared with the actual aggregation shape. The temperature of the powder particles at a fixed position was collected by a noncontact infrared thermometer DT-8856H and compared with the simulation results to verify the validity of the established model. The research in this paper can effectively reveal the powder participation and the interaction mechanism of the laser and the powder during laser cladding. It can provide a theoretical basis for optimizing the cladding process parameters throughout the cycle and improving the quality of the cladding layer.

Sputter yields of rough surfaces: Importance of the mean surface inclination angle from nano- to microscopic rough regimes

The roughness of a surface is known to have a strong influence on the sputtering process. Commonly used 1D Monte Carlo codes for calculating sputter yields show good agreement with experimental data only for comparably flat surfaces, whereas local ion incidence angles, shadowing and redeposition influence the sputter yields in both magnitude and angular dependence on rough surfaces. In the present work, we therefore investigated tungsten samples of largely different roughness, characterised by atomic force and confocal microscopy. A highly sensitive quartz crystal microbalance was used to determine sputter yields during ion irradiation. Low ion fluences were applied to ensure that the surface morphology did not change during irradiation. The results were used to benchmark our new ray-tracing simulation code SPRAY, which can take microscopy images without limitations in size as input. SPRAY was furthermore applied to perform systematic simulations for artificially roughened and computer-generated surfaces. A clear result was that the governing parameter for description of the sputtering behaviour is the mean value of the surface inclination angle distribution, rather than the commonly used root mean square roughness. Our simulations show that this parameter is universally applicable for a wide range of different surface structures.

Influence of surface structure on D retention and erosion behaviours of RAFM steel with D-plasma exposure

As the first wall candidate material in the future fusion device, Reduced Activation Ferritic/Martensitic (RAFM) steel represented by CLF-1 steel was further investigated on the deuterium (D) erosion and retention behaviours. The influences of the surface conditions, including surface morphology, W-enriched structure and the original surface roughness, of the surface conditions including the sample temperature, W-enriched structure and the original surface roughness are mainly discussed. The results showed that with the increase of the sample temperature of CLF-1 steel during D-plasma exposure, the surface morphology changed obviously, and the grooves/pits formed by the erosion on the sample surface are deepened and the boundary becomes obvious. Then, the granular nanostructures appeared at the erosion edges and covered the grooves, eventually forming the nanoclusters structure on the surface. At the same time, TEM results showed that the thickness and content of W atoms on the surface increased. Under the combined action of the above surface conditions, both the sputtering rate and total D retention amount of CLF-1 steel decrease. Under the current experimental parameters, with the increase of the initial surface roughness, the sputtering morphology and the surface roughness of CLF-1 steel changed to different degrees after erosion of D, which eventually led to the slightly increase of the sputtering rate. The effect of incident D-plasma angle on the sputtering and redeposition behaviour of the material may explain this phenomenon. Besides, both the specific surface area of the contact plasma and the erosion behaviour of the material by D-plasma increased with the original surface roughness. The D releasing peak, thermal desorption temperature and total D retention amount of CLF-1 steel samples decrease with the original roughness of CLF-1 steel, which is mainly caused by the increase of D diffusion on the surface. At present, it can be found that the W-enriched surface behaviour induced by D-plasma exposure as well as the change of roughness and morphology lead to the decrease of the sputtering rate of RAFM steel with fluence, energy and sample temperature.

Persistent Sputtering Yield Reduction in Plasma-Infused Foams.

Aluminum microfoams are found to exhibit persistent sputtering yield reductions of 40%-80% compared to a flat aluminum surface under 100 to 300eV argon plasma bombardment. An analytical model reveals a strong dependency of the yield on the foam geometry and plasma sheath. For foam pore sizes near or larger than the sheath thickness, the plasma infuses the foam and transitions the plasma-surface interactions from superficial to volumetric phenomena. By defining a plasma infusion parameter, the sputtering behavior of foams is shown to be separated into the plasma-facing and plasma-infused regimes. While plasma infusion leads to a larger effective sputtering area, geometric recapture of ejected particles facilitates an overall reduction in yield. For a given level of plasma infusion, the reductions in normalized yield are more pronounced at lower ion energies since angular sputtering effects enable more effective geometric recapture of sputterants.

Sputtering of nanostructured tungsten and comparison to modelling with TRI3DYN

He-induced nanostructured tungsten (so-called W-fuzz) was bombarded with Ar ions under 60° and the dynamic erosion behaviour was experimentally investigated. By using a highly sensitive quartz-crystal-microbalance technique in a particle catcher configuration, the sputtered particles distribution of W-fuzz could be evaluated. In contrast to a flat sample, where sputtered particles are emitted primarily in forward direction, we find that W-fuzz samples emit sputtered particles preferably in backward direction (i.e. in the direction of the incident ion beam). After continuous Ar irradiation of a W-fuzz sample the distribution approaches that of a flat sample. In addition to experimental data we also show modelling results obtained with a state-of-the-art Monte-Carlo (MC) binary collision approximation (BCA) code TRI3DYN in full 3D. Surface morphology changes as monitored by SEM as well as the dynamic sputtering behaviour can be well reproduced by the full 3D MC-BCA code.

Распыление вольфрама ионами бериллия и неона

Sputtering yields for tungsten under Be and Ne ion bombardment as well as angular dependencies of the sputtering yields were calculated using molecular dynamics simulation. The results for Ne are in good agreement with experimental data. The obtained results for Be-W sputtering are needed to calculate the impurity influx into the plasma when the divertor material - tungsten - is bombarded with Be ions in ITER tokamak plasma. A model that explains the universal behavior of near-threshold sputtering yields for light ion-induced sputtering of tungsten was proposed.

Erosion of iron-tungsten model films by deuterium ion irradiation: a benchmark for TRI3DYN

The state-of-the-art 3D version of the Monte Carlo sputtering code TRI3DYN was benchmarked with experimental results obtained for iron-tungsten model films. The data which served for comparison concerned: (a) the mass removal rate for Fe-W films (with W) by prolonged deuterium ion bombardment at measured with the quartz crystal microbalance (QCM) technique as a function of ion fluence (up to a total fluence of ); (b) the change in surface morphology as measured by atomic force microscopy, and; (c) the change in elemental surface compositions as determined by different surface analytical techniques. Our benchmarking studies show that the code TRI3DYN is able to predict the outcome of the experiments, if the information about the initial surface morphology and elemental depth profile measurements of the sample are taken into account. It is not only the dynamical behaviour of the erosion yield with ion fluence that can be reproduced, but also the emerging surface pattern and the observed tungsten enrichment at the structured surface. The code provides a first insight into the reasons for the high influence of surface roughness at the scale on the sputtering behaviour of the plasma facing components (PFCs).

The sputter performance of an industrial-scale planar Mo-target over its lifetime: Target erosion and film properties

Magnetron sputter deposited Mo-based thin films are widely used as diffusion barriers and metallization layers for signal and data bus lines of flat panel displays or back electrodes of thin film solar cells. These films are deposited at large-scale from rectangular planar sputter targets, with the necessity of constant film thickness and properties over target usage. Within this work, a new 600 × 125 mm2 planar Mo-target was sputtered at a constant power of 3.5 kW until the erosion track reached 80% of the maximum useable target thickness. Every other 50 kWh, films were deposited onto a 9 × 5 matrix of (100) Si in different deposition modes (i.e. static and oscillation of the substrate carrier). By investigating the individual sample sets, the sputter behavior at different stages of target usage could be assessed. The sputter behavior changes with the progressing evolution of an erosion groove and affects thickness, stress and electrical resistivity of the films. In the beginning and end of target usage, films with low electrical resistivity and high tensile stresses are grown, whereas a medium target erosion leads to films with increased resistivity and lower tensile stresses. This time variance is attributed to two competing effects changing with proceeding target erosion, which affect the growth conditions of the films: (i) the increase of the reflection angle of Ar neutrals due to the evolution of an erosion groove, lowering the energy input into the growing film, and (ii) a rising number of Ar+ ions due to an increase of target current, directly affecting the overall number of reflected Ar neutrals, increasing the energy input into the growing film.

Numerical model of the radio-frequency magnetic presheath including wall impurities

Here, we present a numerical fluid plasma model able to capture the enhanced sputtering yield from the Faraday Screen and the Plasma-Facing Components of an Ion Cyclotron Resonance Heating antenna in a fusion machine. The model is a one-dimensional phase-resolved representation of a rectified radio frequency sheath in a magnetic field at an angle with respect to the material surface; the momentum transport of both ions and impurities is computed in the model. The sputtering behavior of the impurities coming off from the wall is obtained from the plasma-material interaction code Fractal-Tridyn. This study analyzes a range of magnetic angles and wave frequencies to parametrically investigate their effect on the energy-angle distributions of the impacting ions and sputtered impurities. Finally, an estimate of the impurity fluxes and of the gross-erosion rate is provided and compared with experimental data available in the literature.