直拉硅单晶中氢行为的研究进展

总结了氢对直拉硅(CZ)单晶中缺陷影响的研究进展,主要介绍了氢促进氧扩散、热施主和氧沉淀生成,以及高温氢气退火促进直拉硅片空洞型缺陷消除的机理,其中氢促进硅中氧的扩散被认为是氢对直拉硅中的缺陷产生影响的主要原因.     

快速热处理对直拉硅单晶在模拟CMOS热处理工艺时氧沉淀的影响

本文研究了快速热处理工艺(RTP)在模拟的CMOS热处理工艺中对直拉硅单晶中氧沉淀和洁净区(DZ)的影响.研究表明:在模拟的CMOS热处理工艺之前,应用快速热处理(1250℃,50s)代替常规炉处理(1200℃,2h)消除直拉硅单晶热历史,可以更有效地消融原生氧沉淀.经过CMOS热处理工艺后,硅片的表面存在宽度约为20μm的洁净区(DZ),同时其体内有较高密度的体缺陷(BMD).     

直拉硅单晶中氧的轴向均匀性控制

本文从气氛、热场、坩锅材料、埚位、埚转、晶转、变参数拉晶等几个方面的论述了ＣＺ硅单晶初始氧浓度和氧的轴向均匀性的控制方法,着重研究了变参数拉晶对氧的轴向均匀性控制的影响。     

直拉硅单晶中氧的轴向均匀性控制

本文从气氛、热场、坩锅材料、埚位、埚转、晶转、变参数拉晶等几个方面论述了 CZ硅单晶初始氧浓度和氧的轴向均匀性的控制方法 ,着重研究了变参数拉晶对氧的轴向均匀性控制的影响。     

送风速度对室内气流分布影响的数值模拟

以某一典型的空调房间为研究目标,利用计算流体动力学（CFD）,研究在低温送风条件下,室内气流组织的分布状况。通过建立合理的数学模型进行数值模拟,运用试验手段验证了模拟结果的可靠性,得到几种送风速度下的室内气流速度场与温度场的计算结果,经过分析,确定该空调室的送风速度范围为（0．2—3）m／s,最佳值为2m／s。     

生长工艺对生长室内温度分布影响的数值模拟

为给实验研究晶体生长工艺提供必要的理论指导,以氢气和氧气的燃烧为基础,研究了焰熔法生长金红石单晶体过程中生长室内的温度分布特征,分析了H_2和O_2流量、喷嘴尺寸对温度分布的影响.研究表明:适合金红石单晶体生长的最佳燃烧器为内O_2、中H_2和外O_2的三管结构;随着H_2流量增加,生长室轴心线上和径向温度逐渐增大,H_2流量增加2 L/min,中心最高温度平均升高160℃,位置向下移动约2.5 mm;随着内、外O_2流量增加,生长室轴心线上和径向温度逐渐降低,与内O_2的影响相比,外O_2对中心温度影响较小,而对径向温度的影响较大;随着内O_2喷嘴孔径的增加,生长室轴心线上最高温度逐渐增大,而位置逐渐向喷嘴方向移动,而外O_2和H_2喷嘴孔径对轴心线上最高温度的影响非常小.     

电子辐照对直拉硅中氧沉淀的影响

主要研究了1.5MeV、剂量为3.5×1017e/cm2的电子辐照后的直拉硅经后续高温热处理,其体内氧沉淀的变化情况以及清洁区的形成.结果表明,电子辐照促进了直拉硅中氧沉淀的生成,而且经过快速热处理再加上高温一步退火,电子辐照后的直拉硅内形成一定宽度的清洁区,而且清洁区的宽度随快速热处理温度的升高而变窄.     

切割拉槽中深孔孔内分段爆破数值模拟

针对大冶铁矿切割井上部难以施工至设计高度从而影响立槽高度问题,考虑在切割巷的拉槽中深孔采用孔内分段爆破方案,以使得切割立槽高度达到设计高度,并解决悬顶的安全问题。为分析切割拉槽中深孔孔内分段爆破效果,基于ANSYS/LS-DYNA有限元数值模拟软件,对孔内分段装药和不分段装药两种不同装药结构下中深孔爆破切割立槽处应力变化、损伤区域进行模拟计算研究。结果表明：越靠近模型中部,应力波的叠加作用越强,其有效应力更加集中,所产生的损伤破碎面积更大。在矽卡岩区域内,两种不同装药结构的爆破方式在切割立槽处产生的有效应力大小高于矽卡岩的破坏强度,均能在切割立槽处造成较大面积的损伤破碎。在磁铁矿区域内,分段装药爆破后产生的爆破高度更高,在切割立槽处所产生的有效应力更大,产生的破碎面积更广。结合大冶铁矿现场实际爆破试验,孔内分段爆破后可顺利将悬顶安全处理,使得切割立槽达到设计高度,解决了后期施工生产的难题。     

边坡坡度对路堤周围积雪分布影响规律的数值模拟研究

道路风吹雪灾害是雪灾害地区重要的灾害类型,对交通出行等造成很大威胁。该文以二维路堤为研究对象,通过Fluent软件对不同边坡坡度下的路堤进行流场模拟,得到了不同边坡坡度下路堤周围的风速和壁面剪切速度,进而从雪颗粒运动机理上分析边坡坡度对路堤周围积雪分布的影响。结果表明:路堤周围的流场与路堤表面的剪切速度有很好的对应关系;较缓的迎风边坡可减少路堤周围的积雪,在风吹雪灾害频发的地区进行道路建设时建议选取小边坡坡度的路堤;研究结果可为路堤的工程建设提供参考。     

原料对碳化硅单晶生长的影响

研究了具有立方结构的碳化硅(β-SiC)粉料在单晶生长过程中的物相变化及对生长晶体均匀性、缺陷等的影响。实验发现,在晶体生长过程中原料的晶型转变和Si、C挥发不一致造成晶体沿生长方向存在一个Si/C摩尔比的最大值。晶体中的针孔等缺陷的形成与原料中的杂质和气相组分偏离Si/C=1摩尔比有关,并通过电子探针得到证实。     

Impurity microsegregation due to periodic changes in the temperature and pulling rate of crystal grown by the Stepanov method

A mathematical model is proposed to describe the behavior of a doping impurity concentration in a crystal grown by the Stepanov method from a melt and subjected to periodic changes in its pulling rate and temperature of the thermal node. Various modes of these effects are discussed. The results obtained are given by graphs that characterize their influence on concentration distribution.Notation V pulling rate of the crystal - V _c crystallization rate - V _l velocity of melt motion - h(t) position of the crystallization front at the timet - H(t) dimensionless height of the crystallization front - l ₀ initial length of the crystal - R(t) crystal radius - k _j (j=l, s) thermal conductivities of the melt and the crystal - c _pj (j=l, s) specific heats of the melt and the crystal - _j (j=l,s) densities of the melt and the crystal - H _f latent heat of melting - ₀ angle of growth - coefficient of surface tension - T _m melting point - T _j (j=l, s) temperatures of the melt and the crystal - T ₀ temperature of the melt at the shaper outlet at the initial moment of time - l ^* length of the capillary channel - C _l impurity concentration in the melt,k ₀, coefficient of impurity distribution - b radius of the capillary channel Institute of Solid-State Physics, Russian Academy of Sciences, Chernogolovka, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, pp. 486–493, May–June, 1995.     

The effect of carbon on oxygen precipitation in high carbon CZ silicon crystals

To clarify the role of carbon impurities in the formation of oxygen precipitates, the behavior of CZ silicon wafers with varying carbon concentrations from 0.2 ppm to 2 ppm were studied under different heat treatment conditions. It is found that the rate of reduction in interstitial oxygen is not a function of carbon concentration as reported previously for both the cases of medium and low temperature annealing. Under medium temperature (1050°C) annealing no carbon reduction was detected, even though the reduction in interstitial oxygen can be very large, while with low temperature (750°C) annealing, oxygen reduction is always associated with the carbon reduction, but is not dependent on carbon concentration alone. A heterogenous precipitation model is presented to explain the observed phenomena.     

Vacancies in as-grown CZ silicon crystals observed by low-temperature ultrasonic measurements

By means of the low-temperature ultrasonic measurement, we try to observe the elastic softening due to the vacancies in as-grown silicon crystals grown by the Czochralski (CZ) method. We prepared a high-resistivity CZ silicon crystal ingot comprising the following defect-regions: the void region, the region of ring-like oxidation stacking fault, the Pv-region, the Pi-region, and the region of the dislocation clusters. Both of the elastic constants C ₄₄(T) and [C ₁₁(T) ? C ₁₂(T)]/2 measured for the samples taken from the Pv-region exhibit the softening of the type C _Γ(T) = C _Γ ⁽⁰⁾ [1 ? Δ_JT/(T ? Θ)] which was also found in our previous study for the non-doped FZ silicon and attributed to the neutral vacancy. No response of the softening to the applied magnetic field is found, as in our previous case of the non-doped FZ silicon. The observed softenings are attributed to the triply degenerate T ₂ states of the vacancy accommodating two electrons with anti parallel spins. The samples in the Pi-region exhibit no such softening, confirming that the origin of the softening is the vacancies. A qualitative explanation is given to the measured distribution of the vacancy concentration.     

Simulation of the depolarization effect in porous silicon

We describe a radiative transfer (RT) equation for the simulation of optical scattering effects in a nanostructured semiconductor for spectroscopic ellipsometry (SE). As an example, we chose porous silicon (PS), whose pores are considered to act as light scatterers. We examined the effects of pore radius, slab thickness, and incident angle. The volume scattering effect in the internal morphology of the PS generates incoherent light, leading to depolarization. By simulating the four Stokes parameters through the RT equation, we could theoretically assess the degree of polarization that is essential for SE measurements of some nanostructured semiconductors.     

The influence of backgrinding on the fracture strength of 100 mm diameter (1 1 1) p-type silicon wafers

The influence of grinding geometry and damage depth on the fracture strength of 100 mm diameter (1 1 1) p-type silicon wafers has been studied. The fracture strengths were measured in a biaxial flexure test after the wafers were ground to 0.36 mm from 0.53 mm thick, in a grinding apparatus that produces a swath of swirls on the silicon wafer surfaces. Analysis of orientations of the swirl geometries and fracture probability was used to deduce the fracture strength relative to the crystallographic orientation of the wafers. Optical and scanning electron microscopy of bevelled, and cleaved and etched samples was used to measure the damage depths from selected locations on the wafers. The depth of damage and fracture strengths were correlated to the geometry of the backgrind swirl pattern and the relative position of the orientation flat. The damage depth was smaller when the swirl path was parallel or at 45° to the orientation flat as compared to the swirl paths at 90° and 135° orientations. As a result, the wafers ground in the former orientations had a higher fracture strength than those of the latter orientations (136 and 124 MPa versus 100 and 103 MPa, for the four orientations, respectively). This revised version was published online in November 2006 with corrections to the Cover Date.     

Factors determining the diameter of silicon carbide whiskers prepared by chemical vapor deposition

Since the whisker diameter is one of the important parameters for determining the characteristics of whisker-related systems, an understanding of the factors that affect its size is of great value for whisker preparation. In this study, chemical vapor deposition (CVD) of silicon carbide (SiC) whiskers using a gas mixture of methyltrichlorosilane and hydrogen has been conducted in a hot-wall reactor on graphite plates coated with Ni as a liquid-forming agent. The deposited SiC whiskers are then characterized by scanning electron microscopy (SEM) to determine their nucleation and growth behavior. Experimental results show that the diameter of SiC whiskers is determined by both the vapor—liquid—solid (VLS) mechanism and vapor—solid (VS) radial deposition, where the former is affected by the area of the solid—liquid interface from which the crystal precipitates and the latter by the thickening kinetics of vapor-deposited SiC on the lateral face. However, a comparison of the two factors indicates that an appropriate choice of the diameter of liquid droplets for VLS whisker growth is more effective than radial VS deposition for obtaining whiskers of desired diameters.     

Coupling effect of primary voids and secondary voids on the ductile fracture of heat-treatable aluminum alloys

Ductile fracture of commercial aluminum alloys is controlled not only by the primary voids but also by the secondary voids, which are respectively nucleated at cracked constituents and at decohered dispersoid. In this paper, experiment and modeling were carried out to study the combined effect of the two populations of voids on the ductile fracture in two kinds of heat-treatable aluminum alloys, i.e., Al-Cu-Mg alloys and Al-Mg-Si alloys. Different heat treatments were applied to the alloys to achieve various combinations of the two voids, which were subsequently related to the mechanical properties. A multiscale fracture model was proposed to describe quantitatively the relationships between parameters of the two voids and the ductility and fracture toughness of heat-treatable aluminum alloys. It is revealed experimentally and theoretically that the presence of secondary voids will reduce the ductile properties especially when the intervoid spacing is less than about 0.5 μm. All calculations are in good agreement with experimental results.     

Holographic-recording improvement in a bismuth silicon oxide crystal by the moving-grating technique

We investigate the enhancement of the diffraction efficiency of dynamic gratings recorded in a bismuth silicon oxide crystal at large modulation by the moving-grating technique. The optimum fringe velocity for maximum diffraction efficiency and the degree of enhancement of the diffraction efficiency at optimum fringe velocity are experimentally found to be dependent on the fringe modulation. We apply this technique to real-time incoherent correlation using bismuth silicon oxide. There are two main advantages in using moving gratings: First, the signal-to-noise ratio can be improved considerably because of the improved diffraction efficiency. Second, the resonant effect reduces the effect of environmental disturbances on the peak-correlation intensity, which is significant when the threshold detection level of the correlator is set.     

Reduction in the thermal conductivity of single crystalline silicon by phononic crystal patterning

Phononic crystals (PnCs) are the acoustic wave equivalent of photonic crystals, where a periodic array of scattering inclusions located in a homogeneous host material causes certain frequencies to be completely reflected by the structure. In conjunction with creating a phononic band gap, anomalous dispersion accompanied by a large reduction in phonon group velocities can lead to a massive reduction in silicon thermal conductivity. We measured the cross plane thermal conductivity of a series of single crystalline silicon PnCs using time domain thermoreflectance. The measured values are over an order of magnitude lower than those obtained for bulk Si (from 148 W m(-1) K(-1) to as low as 6.8 W m(-1) K(-1)). The measured thermal conductivity is much smaller than that predicted by only accounting for boundary scattering at the interfaces of the PnC lattice, indicating that coherent phononic effects are causing an additional reduction to the cross plane thermal conductivity.