Fatigue damage evolution in silicon films for micromechanical applications

In this paper we examine the conditions for surface topography evolution and crack growth/fracture during the cyclic actuation of polysilicon microelectromechanical systems (MEMS) structures. The surface topography evolution that occurs during cyclic fatigue is shown to be stressassisted and may be predicted by linear perturbation analyses. The conditions for crack growth (due to pre-existing or nucleated cracks) are also examined within the framework of linear elastic fracture mechanics. Within this framework, we consider pre-existing cracks in the topical SiO₂ layer that forms on the Si substrate in the absence of passivation. The thickening of the SiO₂ that is normally observed during cyclic actuation of Si MEMS structures is shown to increase the possibility of stable crack growth by stress corrosion cracking prior to the onset of unstable crack growth in the SiO₂ and Si layers. Finally, the implications of the results are discussed for the prediction of fatigue damage in silicon MEMS structures.     

油田用水基纳米聚硅增注剂的制备及其性能研究

以超疏水的纳米聚硅乳液为前躯体,选用复配的表面活性剂,将超疏水的纳米聚硅核均匀分散在水中,制备了水基纳米聚硅乳液.该乳液分散性和稳定性较好,可以完全用水取代柴油作携带介质将纳米聚硅材料带入井下.模拟岩芯驱替试验表明岩芯经水基纳米聚硅乳液处理后,水的流速平均从0.250 mL/m in增加到0.475mL/m in,增加了90.0%,增注效果十分显著.岩芯的X射线光电子能谱分析显示,纳米聚硅和表面活性剂能吸附在岩石表面上,改变岩石表面的润湿性,提高水相相对渗透率.     

The behaviour of mosaic blocks and electrical properties of polysilicon under ion implantation

Abstract

The change in microstrains ε, block sizes L and in the temperature dependences of conductivity of polysilicon with the grain size 30-40nm at N⁺, Ne⁺, P⁺ ion irradiation has been studied. It is shown that ε increases while L practically is not changing up to amorphization. The change in conductivity is governed by an increase in the density of states near the Fermi level and depends both on the damage rate for the given ions and their chemical activity.     

Metallation of poly(1-trimethylsilyl-1-prop-1-yne) and poly(vinyltrimethylsilane) with superbases

The pathway and degree of metallation of polymers were studied depending on the the conditions (temperature, concentration, nature, and component ratio) of metallation of poly(1-trimethylsilylprop-1-yne) (PTMSP) and poly(vinyltrimethylsilane) (PVTMS) by superbases, viz., BuⁿLi and Bu^sLi, in combination with potassium tert-pentyl oxide (Pe^tOK). For the BuⁿLi—Pe^tOK system (1 : 3), the yield of modified PTMSP reached 90%. In the case of PTMSP, only the Me groups at the double bonds and at the Si atoms undergo metallation, whereas only the Me groups at the Si atoms are metallated in PVTMS. The kinetics of metallation with the BuⁿLi—Pe^tOK system was studied.     

纳米晶粒多晶Si薄膜的低压化学气相沉积

利用低压化学气相沉积(LPCVD)方法,以充Ar的SiH4作为反应气体源,在覆盖有热生长SiO2层的p-(100)Si衬底上制备了具有均匀分布的纳米晶粒多晶Si膜(nc-poly-Si).采用扫描电子显微镜(SEM)、原子力显微镜(AFM)和拉曼谱等检测手段,测量和分析了沉积膜层的表面形貌、晶粒尺寸与密度分布等结构特征.结果表明,nc-poly-v膜中Si晶粒的尺寸大小和密度分布强烈依赖于衬底温度、SiH4浓度与反应气压等工艺参数.典型实验条件下生长的Si纳米晶粒形状为半球状,晶粒尺寸约为40nm,密度分布约为4.0×1010cm-2和膜层厚度约为200nm.膜层的沉积机理分析指出,衬底表面上Si原子基团的吸附、迁移、成核与融合等热力学过程支配着nc-poly-Si膜的生长.     

Microstructure and electrical characterization based on AFM of very high-doped polysilicon grains

In this work, we demonstrate that atomic force microscopy allows topography measurement as well as the local electrical properties of very high-doped polysilicon film prior to any subsequent annealing. AFM and TEM observations showed the columnar microstructure of the polysilicon layer. The electrical effect of this microstructure was characterized using SCM, KFM and C-AFM. Each electric mode gives additional information on the local properties of the polysilicon layer.     

西门子反应器中硅棒热电行为数值模拟与分析

改良西门子法制备多晶硅过程中,化学气相沉积所需能量全部由电流加热硅棒提供.本文考虑多晶硅还原炉中辐射和对流热量传递形式,耦合频率控制的焦耳电加热方程,建立了12对棒多晶硅还原炉热场-电磁场耦合模型,并通过工业数据验证了其模拟结果的合理性.分析了硅棒半径、交流电频率以及反应器壁发射率对西门子还原炉内、外硅棒内部温度及电流密度分布的影响.结果表明:当硅棒半径增长到所用交流电频率引起的趋肤深度时,交流电趋肤效应开始显著影响硅棒内部温度梯度;交流电频率的增大,硅棒内部温度梯度逐渐减小;反应器壁发射率增加,低频时硅棒内部温差增大,而高频时发射率对硅棒内部温度分布影响不再显著.     

THE SURFACE EFFECT ON THE TENSILE STRENGTH OF MICROMACHINED POLYSILICON FILMS FOR MEMS

In order to accomplish reliable mechanical design of MEMS, the influences of surface roughness and octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) on the mechanical properties of micromachined polysilicon films for MEMS are investigated. Surface effect on the fracture properties of micromachined polysilicon films is evaluated with a new microtensile testing method using a magnet-coil force actuator. Statistical analysis of the surface roughness effects on the tensile strength predicated the surface roughness characterization of polysilicon films being tested and the direct relation of the mechanical properties with the surface roughness features. The fracture strength decreases with the increase of the surface roughness. The octadecyltrichlorosilane self-assembled monolayers coating leads to an increase of the average fracture strength up to 32.46%. Surface roughness and the hydrophobic properties of specimen when coated with OTS films are the two main factors influencing the tensile strength of micromachined polysilicon films for MEMS.