Damage In Silicon Research Articles

Dislocation slip mechanism and prediction method during the ultra-precision grinding process of monocrystalline silicon

Prediction of dislocation depth during ultra-precision grinding of monocrystalline silicon is a major challenge. To provide atomistic perspective, a single grain scratching molecular dynamics (MD) model of monocrystalline silicon is established to analyze the initiation and slip mechanism of dislocation. The simulation results show that the initiation of dislocations depends on the normal scratching force, and the dislocation length decreases with the decrease of scratching force and the increase of scratching velocity. Besides, the active slip system was identified by calculating Schmid factor, and the slip stress τ(111)[110],p (i.e. Peierls stress) of 2 GPa for ±1/2[110] dislocation on (1 1‾ 1) plane was obtained. Furthermore, a prediction model for dislocation depth was established based on the analysis of shear stress τ(111)[110]. Finally, a set of nano-scratch experiments were carried out, and the depth and slip direction of dislocation that close to the predicted were obtained by TEM method. This study provides a new method for predicting and controlling dislocation damage of monocrystalline silicon during ultra-precision grinding.

UV Laser Copper Pad Surface Exposure for Laser Direct Structuring (LDS) of Interconnection

Microelectronics market demands strong miniaturization and high-quality packages solutions; therefore, companies and researchers start thinking about alternative methods to create more flexible and performing interconnections which are able to reduce package dimensions. Laser direct structuring (LDS) technology creates a conductive pattern on MID (Moulded Interconnected Device) with the combination of laser layout structuring and electroplating bath. LDS can be applied to leadframe based IC packages to realize interconnections in alternative to standard wires connection. Feasibility study on copper (Cu) pad covered by moulding compound is conducted varying laser parameters as power, frequency and scanning speed to obtain a 80μm diameter via on die. Die via is connected through a trace with a 200μm diameter via on lead to realize the interconnection path, filled with copper after plating process. UV 355nm wavelength laser is used to obtain a complete exposition of Cu surface without silicon damage. Visual inspection with optical microscope and SEM analysis method are performed to evaluate the integrity of metal pads and interconnection layout.

Improved machinability of single crystal silicon by applying in-situ laser-vibration hybrid assisted diamond cutting

Single crystal silicon is an important optical material used widely in the infrared systems. The surface quality and subsurface damage of silicon seriously affect the service performance. In this study, an in-situ laser-vibration hybrid assisted diamond cutting technology is proposed. The properties of cutting device were tested as experimental parameters. A series of grooving experiments were carried out with different cutting methods and the microlenses on silicon were successfully fabricated based on better manufacturing parameters. The surface morphology and subsurface damage was investigated from sin-wave structure manufacturing. Experimental results show that in-situ laser-vibration hybrid assisted diamond cutting effectively improves surface quality and inhibits subsurface lattice distortion. Compared with conventional diamond cutting, the depth of brittle transition increases by about 10 times with 1075 nm. Under the same cutting parameters, the formation of surface cracks of microlenses and sin-wave structure are significantly inhibited by applying in-situ laser-vibration hybrid assisted diamond cutting. This new technology is an effective and promising method for ultra-precision machining silicon.

Study of irradiation damage in silicon at different scales

In this work we focus on the simulation of radiation effects on silicon under proton irradiation at different scales. Two models of the Monte Carlo displacement damage calculation method in the Particle and Heavy Ion Transport code System (PHITS) were first used: the Torrens displacements per atom (NRT-DPA) model and a thermal recombination corrected dpa (arc-DPA), the prediction result of the final arc-DPA model is about 1/3 lower than the traditional NRT-DPA model; we also compared the difference between the two calculated values at the same dose of irradiation. When presenting a molecular dynamics study of the generation and evolution of silicon defects under irradiation, we simulated a 10 keV displacement cascade at room temperature. By post-processing the simulation results, the changes in the distribution and number of defects, as well as the evolution of defect clusters, were analyzed, where both the number of point defects and vacancy clusters show a tendency to increase and then decrease. Finally, first-principles were used to simulate and analyze the energy band structures, DOS, effective mass, the dielectric function, reflection and transmission spectra of silicon after introduction of defects. In order to obtain more accurate value of the bandgap, the HSE06 hybridization generalization is used so that the bandgap is not underestimated, while the clear bandgap facilitates fine analysis of the band structures of the defect states. We found that although the width of the energy band is reduced, which will lead to a increase of intrinsic carrier concentration. At the same time, the effective mass of the electron and hole are greatly reduced, which ultimately leads to a reduction of carrier mobility, and this will finally cause series of performance degradations.

ReaxFF molecular dynamics simulation of single-crystalline silicon plasma polishing and subsurface damage removal

Recently, plasma etching has become one of the most promising polishing methods due to its low cost and environmental friendliness. In this study, the mechanism and parametric influence of plasma etching were investigated using ReaxFF-based molecular dynamics (RBMD) simulation, allowing the characterization of the process of F atom etching of monocrystalline silicon and the removal of subsurface defects from an atomic perspective. We simulated the process of F-atom etching and the mechanism of F-atom removal of the subsurface damage of single-crystalline silicon. The simulation results indicate that SiF4 generated by monocrystalline silicon under the action of F atoms gradually generated SiF5- groups and detached from the substrate as the reaction time increases. Simultaneously, under the action of F atoms, Si atoms gradually filled the subsurface defects, achieving damage removal. In addition, the incident angle can be increased in the plasma polishing process to reduce the thickness of the amorphous deformation layer and improve the surface quality.

Dual-wavelength femtosecond laser-induced single-shot damage and ablation of silicon

An experimental and theoretical study of laser-induced damage and ablation of silicon by two individual femtosecond pulses of different wavelengths, 1030 and 515 nm, is performed to address the physical mechanisms of dual-wavelength ablation and reveal possibilities for increasing the ablation efficiency. The produced craters and damaged areas are analyzed as a function of laser fluence and time separation between the pulses and are compared with monochromatic irradiation. The order of pulses is demonstrated to be essential in bi-color ablation with higher material removal rates when a shorter-wavelength pulse arrives first at the surface. Simulations based on the two-temperature model show that the visible pulse is profitable for the generation of the electron-hole plasma while the delayed IR pulse is efficiently absorbed in the plasma enhancing energy coupling to the target. At long delays of 30–100 ps, the dual-wavelength ablation is found to be particularly strong with formation of deep smooth craters. This is explained by the expansion of a hot liquid layer produced by the first pulse with a drastic decrease in the surface reflectivity at this timescale. The results provide insight into the processes of dual-wavelength laser ablation offering a better control of the energy deposition into material.

Effect of annealing on focused ion beam induced surface damages in silicon analyzed by micro-Raman spectroscopy

In this paper, we describe Raman spectroscopic study for evaluating the influence of vacuum annealing on the surface modification of the focused ion beam (FIB) induced damaged layer on a single crystalline Si (c-Si) substrate. The damaged layer consisting of amorphous silicon (a-Si) with implanted Ga ions is formed after irradiating FIB onto the c-Si surface. After vacuum annealing at 700 °C for 10 s, the Raman spectrum peak of poly crystalline Si (p-Si) appears. With increasing annealing time, the spectral parameters, peak shift, peak intensity, and full width at half maximum (FWHM), for p-Si and c-Si change. Through the comparison between the phase fraction of a-Si, p-Si, and c-Si in the FIB damaged layer and the mechanical properties of the FIB-processed Si nanowires obtained in the quasistatic tensile testing, a recovery of the damaged layer by annealing is discussed.

Study of surface damage in silicon by irradiation with focused rubidium ions using a cold-atom ion source

Cold-atom ion sources have been developed and commercialized as alternative sources for focused ion beams (FIBs). So far, applications and related research have not been widely reported. In this paper, a prototype rubidium FIB is used to study the irradiation damage of 8.5 keV beam energy Rb+ ions on silicon to examine the suitability of rubidium for nanomachining applications. Transmission electron microscopy combined with energy dispersive x-ray spectroscopy is applied to silicon samples irradiated by different doses of rubidium ions. The experimental results show a duplex damage layer consisting of an outer layer of oxidation without Rb and an inner layer containing Rb mostly at the interface to the underlying Si substrate. The steady-state damage layer is measured to be 23.2(±0.3) nm thick with a rubidium staining level of 7(±1) atomic percentage.

Mechanical effect of abrasives on silicon surface in chemo-mechanical grinding

To obtain high-quality surfaces and subsurfaces of ground silicon wafers, chemo-mechanical grinding (CMG) for silicon has been developed by inducing chemical reactions into grinding. Chemical reactions between abrasives and silicon during CMG process have been proved in previous studies. The mechanical effect of abrasives in CMG process is not fully understood. To investigate abrasives’ mechanical effect on material removal and subsurface damage of silicon in CMG process, silicon nanoscratching experiments with CeO2 indenter under a progressive normal load were conducted, and microtopographies of scratch surface and subsurface were observed. For comparison, silicon nanoscratching experiments with diamond indenter were also conducted. Finite element models of silicon nanoscratching with CeO2 and diamond indenters were built to investigate the relationship between stress distribution and damage evolution of silicon. Experimental investigations and simulation results indicate that no obvious material removal of silicon or serious subsurface damage is generated by CeO2 indenter's mechanical action because the wear of CeO2 indenter leads to the release of the stress on silicon. Material removal of silicon during CMG process relies on chemical reactions between soft abrasives and silicon other than stress on silicon generated by soft abrasives.

Influence of ionizing radiation on the parameters of p-channel MOS transistors

The results of experimental studies of the influence of gamma radiation Co60 on the basic parameters of silicon epitaxial-planar p-channel MOSFET transistors under different electrical modes are presented. Transistors were manufactured according to radiation-resistant DMOS technology with design standards of 1.4 μm. As a result of transistor studies, it was established that the values of all basic parameters after the radiation dose D = 106 rads (SiO2) in active electrical irradiation modes remained within the limits of the performance criteria; the parameter, most sensitive to influence of a dose of irradiation by gamma-quanta is the threshold voltage; in the passive electrical irradiation mode the transistor’s radiations resistance in all parameters corresponds to a dose of 2,8·106 rads (SiO2). A sufficiently high radiation resistance of the studied p-channel MOSFETs makes it possible to recommend them for use in aviation and space equipment. The different degrees of radiation degradation of the studied parameters during irradiation are due to their dependence either on the effects of ionization in the layers of sub-gate and insulating dielectrics, or structural damage in the bulk silicon of the transistor active regions. The high radiation resistance of the studied p-channel MOSFETs allows recommending them for use in aviation and space equipment.

A machine-learning interatomic potential to understand primary radiation damage of silicon

Harsh radiation environments cause displacement damages in semiconductor components, resulting in performance degradation. Molecular simulations provide a unique approach to study the dynamic processes of radiation-induced defect production, clustering, and evolution to design and reinforce novel semiconductor components. In this paper, we developed a more efficient machine learning (ML) potential with DFT accuracy to investigate the radiation damage in silicon material. The accuracy of the potential was verified by comparing the static properties, defect formation energy, and threshold displacement energy with experiments and DFT data. By simulating the excitation of a single PKA we found that with the ML potential PKA has an impact over a larger spatial area compared to the empirical potentials. Finally, by simulating multiple PKA excitations in sequence, we found that the first several excited PKAs produce an amorphous region. For the later excited PKAs, the energies are dissipated when they cross through the amorphous region, resulting in a 36% decrease in newly generated defects.

Three-temperature modeling of laser-induced damage process in silicon

Laser excitation in silicon from femto- to pico-second time scales is studied. We assume the three-temperature model which describes the dynamics of the distinct quasi-temperatures for electrons, holes, and lattice. Numerical results for damage threshold reproduce the experimental results not only quantitatively, but qualitatively as well, showing dependence on laser pulse duration. Comparison with experimental data suggests that electron emission and thermal melting are both responsible for damage in silicon. We found that electron–phonon relaxation time has a significant effect on pulse duration dependence of electron emission.

Silicon and mechanical damage increase polyphenols and vitexin in Passiflora incarnata L.

Passiflora incarnata L. is a species of global pharmacological importance, has not been fully studied in the context of cultivation and management. It is known that silicon acts on abiotic stress and promotes phenols synthesis. The practice of mechanical damage is widely used in P. incarnata crops, and its interaction with silicon can have a significant influence on plant metabolism. Therefore, our objective was to investigate the effects of silicon and mechanical damage on photosynthesis, polyphenols and vitexin of P. incarnata. The experiment was conducted in a factorial design with SiO2 concentrations (0, 1, 2, 3 mM) and presence or absence of mechanical damage. It was found that mechanical damage improved photosynthetic performance at lower concentrations or absence of silicon. Moreover, this condition promoted an increasing in vitexin concentration when SiO2 was not provided. The application of 3 mM Si is recommended to increase polyphenols and vitexin, without harming dry mass of aerial part. The interaction between silicon and mechanical damage could be a tool to increase agronomic yield and commercial value of the P. incarnata crop.

Primary radiation damage in silicon from the viewpoint of a machine learning interatomic potential

Characterization of the primary damage is the starting point in describing and predicting the irradiation-induced damage in materials. So far, primary damage has been described by traditional interatomic potentials in molecular dynamics simulations. Here, we employ a Gaussian approximation machine-learning potential (GAP) to study the primary damage in silicon with close to ab initio precision level. We report detailed analysis of cascade simulations derived from our modified Si GAP, which has already shown its reliability for simulating radiation damage in silicon. Major differences in the picture of primary damage predicted by machine-learning potential compared to classical potentials are atomic mixing, defect state at the heat spike phase, defect clustering, and recrystallization rate. Atomic mixing is higher in the GAP description by a factor of two. GAP shows considerably higher number of coordination defects at the heat spike phase and the number of displaced atoms is noticeably greater in GAP. Surviving defects are dominantly isolated defects and small clusters, rather than large clusters, in GAP's prediction. The pattern by which the cascades are evolving is also different in GAP, having more expanded form compared to the locally compact form with classical potentials. Moreover, recovery of the generated defects at the heat spike phase take places with higher efficiency in GAP. We also provide the attributes of the new defect cluster that we had introduced in our previous study. A cluster of four defects, in which a central vacancy is surrounded by three split interstitials, where the surrounding atoms are all 4-folded bonded. The cluster shows higher occurrence in simulations with the GAP potential. The formation energy of the defect is 5.57 eV and it remains stable up to 700 K, at least for 30 ps. The Arrhenius equation predicts the lifetime of the cluster to be $0.0725\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{s}$ at room temperature.

Residual stress and thermal properties of rubber‐modified epoxy systems for semiconductor package

AbstractThe thermal and mechanical breakage of epoxy coating due to easy cracking, poor toughness, and large residual stress, occurring during curing and thermal aging process, is the key factor responsible for damage of silicon device on semiconductor elements. In this study, modified epoxy resins containing an imide ring and polybutadiene rubber‐modified epoxy resin used as the toughening agents were prepared to investigate the residual stress generated during the curing and thermal aging process. The curing process and the thermal properties of the modified epoxy systems were assessed by differential scanning calorimetry and rotational rheometry, dynamic thermomechanical analysis, thermomechanical analysis, and thermogravimetric analysis. A thin film stress analyzer was used to analyze the changes in thermal stress of the modified epoxy systems during curing and cyclic stress and compared with the data from theoretical calculation. The results show that, with the increase in content of the toughening agent, the toughness of the modified epoxy systems was significantly improved, and the curing and thermal cycle stresses could be simultaneously reduced. Besides, we also envision the extension of the comprehensive evaluation method for residual stress described in this study to enable the modification of epoxy coatings prepared using a toughening agent, in the near future.

Molecular dynamics simulation of silicon vacancy defects in silicon carbide by hydrogen ion implantation and subsequent annealing

Silicon vacancy defects in 4H-SiC are promising candidates for quantum technology. However, the fabrication of controlled atomistic defects in 4H-SiC is still a challenge. In this work, we used molecular dynamics (MD) simulations to study the mechanism of the evolution of silicon vacancy defects and damage during hydrogen ion implantation and subsequent annealing. By considering the electronic energy loss of hydrogen ions, the distribution of implanted hydrogen ions, and the atomic-scale mechanism of silicon vacancy defects and damage can be described more accurately. The results can observe the changing trend of silicon vacancy defects with the complete structure during the entire implantation and annealing process, and it is found that the local temperature generated by hydrogen ion implantation may affect the fluctuation of silicon vacancy defects. Besides, the yield of silicon vacancy defects can be improved by optimizing annealing conditions, and there is an optimal annealing temperature.

Processing outcomes of atomic force microscope tip-based nanomilling with different trajectories on single-crystal silicon

Atomic force microscope (AFM) tip-based nanomilling is an emerging technology for machining nanostructures with a high rate of material removal and slight tip wear. However, subsurface damage induced by nanomilling is poorly understood. In this study, we investigated nanomilling-induced subsurface damage of single-crystal silicon experimentally and with molecular dynamics simulations. We studied the effect of clockwise and anticlockwise trajectories on the nanochannel morphology. The clockwise trajectory resulted in a ‘U’-shaped nanochannel at a relatively low normal load. Transmission electron microscopy and Raman spectroscopy analysis of the nanochannel subsurface revealed atomic-scale defects, including dislocations, stacking faults, and amorphous silicon. Molecular dynamics simulations described the evolution of the phase transformation and subsurface damage. This work reveals the mechanism of subsurface damage of single-crystal silicon in nanomilling, which will facilitate the machining of nanostructures with minimal subsurface damage.

A synergistic model of stress and oxidation induced damage and failure in silicon carbide‐based ceramic matrix composites

AbstractA micromechanics‐based modeling approach that allows for the simultaneous consideration of deformation, damage, and oxidation associated with each constituent of silicon carbide (SiC)‐based ceramic matrix composites (CMC), including the fiber, fiber coating, and matrix, is described. Chemical kinetics models from the literature are combined with a progressive damage model. Rupture predictions of unnotched and notched stress‐hold (creep) specimens are compared with experimental measurements from a SiC/SiC CMC to assess the efficacy of the modeling approach. Techniques of improving creep rupture life are explored using the model.

The Influence of Crystal Orientation on Subsurface Damage of Mono-Crystalline Silicon by Bound-Abrasive Grinding.

Subsurface damage (SSD) produced in a grinding process will affect the performance and operational duration of single-crystal silicon. In order to reduce the subsurface damage depth generated during the grinding process by adjusting the process parameters (added), experiments were designed to investigate the influence of machining factors on SSD. This included crystal orientation, diamond grit size in the grinding wheel, peripheral speed of the grinding wheel, and feeding with the intention to optimize the parameters affecting SSD. Compared with isotropic materials such as glass, we considered the impact of grinding along different crystal directions <100> and <110> on subsurface damage depth (added). The Magnetorheological Finishing (MRF) spot technique was used to detect the depth of SSD. The results showed that the depth of SSD in silicon increased with the size of diamond grit. SSD can be reduced by either increasing the peripheral speed of the grinding wheel or decreasing the feeding rate of the grinding wheel in the <100> crystal orientation, if the same size of diamond grit was employed. In addition, we proposed a modified model around surface roughness and subsurface crack depth, which considered plastic and brittle deformation mechanisms and material properties of different crystal orientations. When the surface roughness (RZ) exceeded the brittle-plastic transition’s critical value RZC (RZC<100> > 1.5 μm, RZC<110> > 0.8 μm), cracks appeared on the subsurface. The experimental results were consistent with the predicted model, which could be used to predict the subsurface cracks by measuring the surface roughness. However, the model only gives the approximate range of subsurface defects, such as dislocations. The morphology and precise depth of plastic deformation subsurface defects, such as dislocations generated in the fine grinding stage, needed to be inspected by transmission electron microscopy (TEM), which were further studied.

Effects of grinding speeds on the subsurface damage of single crystal silicon based on molecular dynamics simulations

Understanding the damage mechanism of silicon under interfacial shear is vital as it can provide insights for the ultra-precision low damage machining. In this work, the nano-grinding process of single crystal silicon was studied by molecular dynamics (MD) simulations, the damage mechanism of single crystal silicon were analyzed in details under different grinding speeds. The results show that the maximum height of the grinding chip does not always increase with the increase of the grinding speed. When the speed exceeds 150 m/s, more atoms will flow to both sides of the groove. During grinding, the workpiece changes from cubic diamond structure to non-diamond structure and a small amount of hexagonal diamond structure. The Si-II phase was found in the subsurface damage layer. Residual stresses are mainly distributed in the subsurface damage layer (SDL) and do not always show compressive or tensile stresses as the depth increases. This investigation may shed light on the damage mechanism of silicon from an atomic perspective.