The effect of annealing on residual stress and dislocation propagation in silicon slices with damaged layer induced by scribing

The effect of annealing on residual stress and dislocation propagation in silicon slices with a damaged layer induced by diamond scribing, laser scribing and diamond blade cutting was studied by infra-red photoelastic measurements and dislocation pit observations. Residual stress and dislocation propagation both showed clear annealing temperature dependence at temperatures above 500° C, although the residual stress was greatly reduced by a small degree of dislocation propagation. The experimental results can be explained using the stress recovery theory by the model of the damaged layer with a mosaic crystal layer and a single crystal layer with micro-cracks and dislocations.     

Observation of the formation of electron irradiation induced secondary defects in Czochralski silicon

Electron irradiation and in situ observation of Czochralski silicon are carried out in a 2 MeV ultra-high voltage electron microscope at temperatures from room temperature to 400° C. Two kinds of irradiation-induced interstitial type secondary defects are found to be formed; (1) dislocation loops formed in the bulk of the specimen and (2) dislocation loops formed near the electron incident surface of the specimen. The experimental results show that supersaturation of interstitials occurs in the region near the electron incident surface of the specimen during irradiation. It is suggested that some vacancy clusters are formed by irradiation with a high electron flux.     

Effect of temperature on thermally induced defects in silicon

Deep level transient spectroscopy has been used to study thermally activated defects in silicon. It has been observed that different annealing temperatures activate different defects in silicon, which were lying on inactive sites before annealing. Two deep mid-gap levels at energy positions E _c −0.48 eV and E _c −0.55 eV were found to be introduced by different heat treatments. It is also noted that heat treatment at 1,250 °C suppresses the concentration of deep level at E _c −0.23 eV and enhances the concentration of deep level at E _c −0.25 eV, while heat treatment at 950 °C has an opposite effect. Annealing response of the level at E _c −0.48 eV is found different to the annealing response of the level at E _c −0.55 eV which suggests them two different levels.     

On the scribing and subsequent fracturing of silicon semiconductor wafers

The integrated circuits deposited on silicon wafers are often separated by scribing with a diamond tool followed by bending to produce fracture. Using a commercial scribing tool we find permanent deformation and three types of crack. The median crack which propagates downwards is the objective of the scribing process. Lateral cracks which form, apparently following plastic deformation, may lead to chipping on either side of the scribing tool. These cracks and also the chevron cracks which form on the surface are very similar to cracks observed in scratching glass. However, in silicon, because of its anisotropy, the chevron cracks may be a serious problem since they can guide the median crack out of the scribing direction onto a preferred cleavage plane. This aspect leads to a brief discussion of the crystallography of silicon and recommendations for scribing configurations which should minimize undesired fracture. Finally, it is shown that the established methods of linear elastic fracture mechanics may be used to predict the maximum radius of curvature required to fracture a wafer containing a prescribed series of median cracks.     

Diffusion induced residual stress in comb-type microaccelerometer structure

This paper presents the effect of residual stresses due to deep boron diffusion on microaccelerometer structure. The microaccelerometer structure was simulated at various residual stresses using finite element method. The residual stress due to the diffusion process was estimated to be 450 MPa by using Raman spectroscopy. After fabricating the microaccelerometer structure, the deflection (~2 μm) of the moving comb fingers due to the stress was found to be in good agreement with the simulated value (2.1 μm). Sensitivity of the accelerometers was measured to be ~50 mV/g for 0–30 g range. In the initial range (0–5 g), the output of the accelerometers are depicting nonlinearity as anticipated from the simulated results.     

Photodeflection and photoacoustic microscopy of cracks and residual stresses induced by Vickers indentation in silicon nitride ceramic

The feasibility of using photodeflection and photoacoustic microscopy to detect subsurface lateral and vertical cracks, as well as residual internal stresses induced by Vickers indentation in silicon nitride ceramic has been investigated. It is shown that the normal component of the photodeflection signal can be used to detect lateral subsurface cracks and the tangential component to detect vertical cracks. It is established that the sensitivity of the photoacoustic method to residual internal stresses arises from the dependence of the elastic parameters or the coefficient of thermal expansion of the silicon nitride ceramic on the internal stresses. Pis’ma Zh. Tekh. Fiz. 23, 44–52 (March 12, 1997)     

Observation of the electrostatic defects induced by ionizing radiation in a liquid crystal

Defects generated by a flux of α particles in a nematic liquid crystal (NLC) have been observed in a polarization microscope. The observed objects are treated as electrostatic defects with a dipole character induced in the NLC. This phenomenon can be used for the creation of ionizing radiation detectors.     

Manufacturing induced residual stress influence on the rolling contact fatigue life performance of lubricated silicon nitride bearing materials

Experimental results of the residual stress measurements on failed ceramic elements are presented in this paper. Residual stress measurements were performed through a small volume of irradiation. Residual stress relation to number of stress cycles, distance from induced ring crack, residual stress relation to contact path and measuring direction was studied. Residual stress measurements were performed on fatigue spall. A residual stress survey on the secondary cracks is also provided presented in this paper. Analysing the relationship of residual stress with rolling contact fatigue is an important study which will provide guidelines on the design process and manufacturing of these elements. Two compressive residual stress values of 213 and 228 MPa were recorded on either edge of the contact path, these values are higher compared to 84 MPa at the centre of the contact path. This phenomenon indicates that compressive residual stresses are relieved much faster during rolling contact fatigue at higher contact stress level. The spall depths in ceramic rolling contact bearing elements were found to be ranging from 100 to 148 μm. The variation of the compressive residual stress values is prominent at this depth. The decrease in the compressive residual stress values is registered in the spall region and demonstrates sub-surface damage in the region.     

Contemporary approaches to reducing weld induced residual stress

Abstract

Self-equilibrating residual stresses may occur in materials in the absence of external loading due to internal strain inhomogeneity. While favourable distributions of residual stress can bestow an object with the appearance of superior material properties, most welding processes leave behind residual stresses in particularly unfavourable patterns, causing a greater susceptibility to fracture based failure mechanisms and unintended deformation. Currently, heat treatment is the primary means of removing these stresses, but since the formation of residual stress is dependent upon many material and process factors, there are several other viable mechanisms (using thermal, mechanical or phase transformation effects) by which it may be modified. It is only now, using relevant advances in numerical and experimental methods, that these techniques are being fully explored. This article gives a brief introduction to weld induced residual stresses and reviews the current state of the art with regard to their reduction. Emphasis is placed on the recent development of unconventional techniques, and the mechanisms by which they act.     

Low-temperature radiation-stimulated gettering of impurities and defects in silicon by layers of porous silicon

Experimental results are presented for the low-temperature gettering of impurities and defects in semiconductor silicon wafers by layers of porous silicon followed by argon ion irradiation. It is shown that the gettering effect is caused by the simplest mobile point defects (vacancies) and elastic waves.     

表面粗糙度对喷丸残余应力场的影响

为定性研究表面粗糙度对喷丸残余应力场的影响,采用余弦曲线模拟靶材粗糙表面,建立喷丸二维有限元模型,采用ABAQUS/EXPLICIT求解器对喷丸过程进行数值模拟,研究了表面粗糙度喷丸残余应力场的影响规律,分析了同一粗糙度下弹丸尺寸和喷射速度对喷丸残余应力场的影响规律,并与表面理想光滑时的情况进行了对比.结果表明,表面粗糙度的增加使残余压应力区变浅变薄,甚至使靶材表面产生残余拉应力,不利于喷丸强化件抗疲劳性能的提高,喷丸件表面应尽可能光滑以改善喷丸效果.     

Measurement of Young''s modulus and residual stress of copper film electroplated on silicon wafer

The Young's modulus and residual stresses of electroplated copper film microbridges were measured. Special ceramic shaft structure was designed to solve the problem of getting the load-deflection curves of the microbridges from a nanoindentation system equipped with a normal Berkovich probe. Theoretical analysis of the load-deflection curves of the microbridges is proposed to evaluate the Young's modulus and residual stress of the copper films simultaneously. The calculated results based on the experimental measurements showed that the average Young's modulus and residual stress of the electroplated copper films are 115.2 GPa and 19.3 MPa, respectively, while the Young's modulus measured by the nanoindenter for the same copper film with silicon substrate is 110±1.67 GPa.     

Numerical and experimental study of the thermal stress of silicon induced by a millisecond laser

A spatial axisymmetric finite element model of single-crystal silicon irradiated by a 1064 nm millisecond laser is used to investigate the thermal stress damage induced by a millisecond laser. The transient temperature field and the thermal stress field for 2 ms laser irradiation with a laser fluence of 254 J/cm(2) are obtained. The numerical simulation results indicate that the hoop stresses along the r axis on the front surface are compressive stress within the laser spot and convert to tensile stress outside the laser spot, while the radial stresses along the r axis on the front surface and on the z axis are compressive stress. The temperature of the irradiated center is the highest temperature obtained, yet the stress is not always highest during laser irradiation. At the end of the laser irradiation, the maximal hoop stress is located at r=0.5 mm and the maximal radial stress is located at r=0.76 mm. The temperature measurement experiments are performed by IR pyrometer. The numerical result of the temperature field is consistent with the experimental result. The damage morphologies of silicon under the action of a 254 J/cm(2) laser are inspected by optical microscope. The cracks are observed initiating at r=0.5 mm and extending along the radial direction.     

Mathematical modeling of residual stress formation in electron beam remelting and refining of scrap silicon for the production of solar-grade silicon

A technique based on electron beam melting and refining has been used to refine N-type scrap silicon for the purpose of producing material suitable for photovoltaic applications. In this paper, the experimental setup and methodology are described and are presented together with the experimental results for three experiments. Temperature data obtained from embedded thermocouples for one of the experiments is presented. Neutron diffraction analysis was employed to measure the residual strain in the three castings. Finite element thermal and stress mathematical models are employed to predict the residual stress distribution.     

Process parameter effects on residual stress and phase purity after microlaser-assisted machining of silicon

Machining brittle materials, such as silicon, is expensive and often causes detrimental damage, but a relatively new technique, termed microlaser-assisted machining (micro-LAM), improves the efficacy of the machining process using traditional single point diamond turning with simultaneous laser assistance. Prior work shows it provides a smooth surface finish and reduces the likelihood of fracture by increasing the ductility of the material during the machining process. However, the quality of the finish and the utility of the machined silicon depends on having good phase purity and low residual stresses. Using Raman microspectroscopy and a wide range of micro-LAM machining parameters the current work has shown that the technique can give excellent results in terms of low residual stress, high phase purity, and good relative crystallinity. However, poor choice of process parameters can be very detrimental leading to high residual stresses (over 400?MPa) and multiple silicon phases being present.     

Role of machining defects and residual stress on the AISI 304 fatigue crack nucleation

Machining defects as rebuilt material and dislodgement were often induced by cutting of difficult to machining AISI 304 stainless steel. Their density increases with a decreasing of cutting speed. The effect of these defects on surface topography and residual stress was evaluated by roughness and X‐ray diffraction measurements coupled with numerical simulation. The role of the rebuilt material on the distribution of fatigue crack nucleation sites was investigated by scanning electron microscope examination of post fatigue samples loaded at different imposed strain amplitudes. The association of machining defects and fatigue crack nucleation sites was attributed to the contribution of additional tensile residual stresses induced by rebuilt material rather than local stress concentration. Moreover, the fatigue crack coalescence is promoted by increasing the rebuilt material density. When the machining defect density increases from 5 to 60 particles/mm², the fatigue life decreases from ?22% to ?65% with respect to the electropolished surface.     

Thermal and grinding induced residual stresses in a silicon carbide particle-reinforced aluminium metal matrix composite

The residual stresses in a silicon carbide particle-reinforced aluminium (SiC_p/Al) metal matrix composite (MMC) were measured using the X-ray diffraction method. The thermal residual stresses induced by annealing were found to be hydrostatic tension for the Al matrix and hydrostatic compression for the SiC reinforcement. After grinding treatment, the force equilibrium between these hydrostatic stresses was disturbed and compressive stresses were measured in both constituents. The effect of grinding extended into the bulk, and depth profiles of the residual stresses in both constituents were obtained by layer removal. The behaviour exhibited in these depth profiles is explained and their usefulness is indicated.