多晶硅隧道压阻模型*

基于陷阱模型,分析了多晶硅能带结构和导电机理,给出了解释隧道压阻效应的等效电路,说明了构成多晶硅压阻效应的内在因素以及隧道压阻效应在其中的作用。综合晶界区域和晶粒中性区两方面压阻效应建立了新的压阻模型——隧道压阻模型。结果表明,掺杂浓度在1020cm-3以上,复合晶界的压阻系数不但大于晶粒中性区的压阻系数,而且随掺杂浓度增加而增大,从而揭示了多晶硅纳米薄膜在重掺杂情况下出现应变因子随掺杂浓增加而增大的重要实验现象的内在机理。     

掺杂浓度对多晶硅纳米薄膜应变系数的影响

为有效利用多晶硅纳米薄膜研制MEMS压阻器件,本文对LPCVD多晶硅纳米薄膜应变系数与掺硼浓度的关系进行了研究,并利用扫描电镜和X射线衍射实验分析了薄膜的结构特点.结果表明:在重掺杂情况下,纳米薄膜的应变系数明显大于相同掺杂浓度下单晶硅的应变系数,而且掺杂浓度在2.5×1020cm-3左右时,应变系数具有随掺杂浓度升高而增大的趋势.对这种实验结果依据隧道效应原理进行了理论解释,提出了多晶硅压阻特性的修正模型.     

掺杂浓度对多晶硅纳米薄膜应变系数的影响

为有效利用多晶硅纳米薄膜研制MEMS压阻器件,本文对LPCVD多晶硅纳米薄膜应变系数与掺硼浓度的关系进行了研究,并利用扫描电镜和X射线衍射实验分析了薄膜的结构特点.结果表明:在重掺杂情况下,纳米薄膜的应变系数明显大于相同掺杂浓度下单晶硅的应变系数,而且掺杂浓度在2.5×1020cm-3左右时,应变系数具有随掺杂浓度升高而增大的趋势.对这种实验结果依据隧道效应原理进行了理论解释,提出了多晶硅压阻特性的修正模型.     

多晶硅薄膜的高温压阻效应

利用LPCVD制备重掺杂多晶硅薄膜,在0～560℃温度范围内对薄膜的压阻效应进行研究,同时对多晶硅薄膜应变系数随温度的变化,以及薄膜的淀积温度与薄膜厚度对应变系数的影响进行了相关的实验研究.结果表明,利用多晶硅材料制作的压敏电阻,其最高工作温度可以达到560℃以上.     

多晶硅薄膜的高温压阻效应

利用LPCVD制备重掺杂多晶硅薄膜,在0～560℃温度范围内对薄膜的压阻效应进行研究,同时对多晶硅薄膜应变系数随温度的变化,以及薄膜的淀积温度与薄膜厚度对应变系数的影响进行了相关的实验研究.结果表明,利用多晶硅材料制作的压敏电阻,其最高工作温度可以达到560℃以上.     

硼掺杂多晶硅薄膜电阻率的温度特性

本文研究了用于制作压阻传感器的硼掺杂ＬＰＣＶＤ多晶硅薄膜电阻率的温度特性．在室温～４５０℃较高温度范围，实验发现电阻率与温度的关系中存在一个极小值，理论分析表明极小值所对应的温度正比于晶界势垒高度，理论分析与实验结果相符合．通过对影响薄膜电阻率温度特性诸因素的分析讨论，提出了减小多晶硅薄膜电阻温度系数的最佳途径．     

多晶硅薄膜压阻系数的理论研究

利用应力退耦模型,分别对多晶硅薄膜晶粒中性区和晶界势垒区的压阻系数进行了理论分析,并推导出多晶硅压阻系数的表达式.实验结果表明,利用文中推导出的理论公式所获得的计算值与实验测量结果基本符合,所给出的有关多晶硅压阻系数的理论结果可以作为多晶硅特性分析的理论依据.     

多晶硅薄膜压阻系数的理论研究

利用应力退耦模型,分别对多晶硅薄膜晶粒中性区和晶界势垒区的压阻系数进行了理论分析,并推导出多晶硅压阻系数的表达式.实验结果表明,利用文中推导出的理论公式所获得的计算值与实验测量结果基本符合,所给出的有关多晶硅压阻系数的理论结果可以作为多晶硅特性分析的理论依据.     

P型硅纳米板压阻特性的理论研究

考虑量子尺寸效应与自旋轨道耦合作用,从含有应变的6×6 Luttinger-Kohn哈密顿量出发,采用有限差分方法建立了p型硅纳米板的能带结构模型.基于硅纳米板压阻特性与其能带结构的相关性,采用改进的压阻理论定量分析了厚度、杂质浓度与温度对其压阻系数的影响.研究结果表明:量子尺寸效应强烈改变了硅纳米板的能带结构,是其压阻系数增大的主要因素,而自旋轨道耦合作用仅对含较高应变的硅纳米板的能带结构有较大影响;硅纳米板的压阻系数具有尺寸效应,随厚度减小而增大,随杂质浓度增加或温度升高而减小.在高简并条件下,硅纳米板的压阻系数与温度无关,完全由杂质浓度的大小控制;在非简并条件下,情况刚好相反.最后,利用施加应力前后空穴等能面形状的变化定性分析了硅纳米板压阻特性的起源.     

P型硅纳米板压阻特性的理论研究

考虑量子尺寸效应与自旋轨道耦合作用,从含有应变的6×6 Luttinger-Kohn哈密顿量出发,采用有限差分方法建立了p型硅纳米板的能带结构模型.基于硅纳米板压阻特性与其能带结构的相关性,采用改进的压阻理论定量分析了厚度、杂质浓度与温度对其压阻系数的影响.研究结果表明:量子尺寸效应强烈改变了硅纳米板的能带结构,是其压阻系数增大的主要因素,而自旋轨道耦合作用仅对含较高应变的硅纳米板的能带结构有较大影响;硅纳米板的压阻系数具有尺寸效应,随厚度减小而增大,随杂质浓度增加或温度升高而减小.在高简并条件下,硅纳米板的压阻系数与温度无关,完全由杂质浓度的大小控制;在非简并条件下,情况刚好相反.最后,利用施加应力前后空穴等能面形状的变化定性分析了硅纳米板压阻特性的起源.     

Tunnelling piezoresistive effect of grain boundary in polysilicon nano-films

The experiment results indicate that the gauge factor of highly boron doped polysilicon nanofilm is bigger than that of monocrystalline silicon with the same doping concentration, and increases with the grain size decreasing.To apply the unique properties reasonably in the fabrication of piezoresistive devices, it was expounded based on the analysis of energy band structure that the properties were caused by the tunnel current which varies with the strain change forming a tunnelling piezoresistive effect. Finally, a calculation method of piezoresistance coefficients around grain boundaries was presented, and then the experiment results of polysilicon nanofilms were explained theoretically.     

双势垒量子阱薄膜压阻效应实验研究

采用分子束外延方法在砷化镓衬底上生长了AlAs/GaAs双势垒量子阱薄膜结构。介绍了量子阱薄膜在单轴压力作用下的压阻实验,测试出薄膜在压力影响下的I-V曲线,并分析了量子阱薄膜压阻效应的成因。通过实验证实了量子阱薄膜具有较高灵敏度的压阻效应,其压阻灵敏度比目前常用的多晶硅的压阻灵敏度提高一个数量级。     

阵列式微机械悬臂梁的研制及其特性分析

在一个芯片上设计了六组不同规格的矩形压阻悬臂梁.采用ANSYS有限元分析系统对微压阻悬臂梁进行应力分析,并对压阻悬臂梁的噪声、灵敏度以及最小可探测位移进行了研究.选用多晶硅为压阻材料,以硅微机械加工技术为基础,完成了阵列式压阻悬臂梁的制备.通过测量器件的噪声和灵敏度,计算出在6V偏压和10 0 0Hz测量带宽下,多晶硅悬臂梁的最小可探测位移为1nm .     

Performance of thin-film transistors on polysilicon films grown bylow-pressure chemical vapor deposition at various pressures

Defect properties of undoped low-pressure chemical-vapor-deposited (LPCVD) polysilicon films have been investigated by capacitance techniques on a simple metal-oxide-semiconductor (MOS) capacitor structure. The results show that the effective density of bulk and interface trap states is almost independent of the deposition pressure. After reducing the polysilicon film thickness by etching, although the grain size decreases due to the columnar mode of growth at low pressures, the trap states density reduces significantly. This finding could be explained by the hypothesis that, during the growth of the material, impurities are segregated at the film surface by fast diffusion through the grain boundaries. The transport properties of 0.5-μm-thick polysilicon films deposited at a pressure ranging from 100 to 0.5 mtorr were evaluated from measurements on thin-film transistors (TFTs). The results demonstrate that at high pressures the grain boundaries and at low pressures the polysilicon-SiO₂ interface roughness scattering are the main factors in determining the transistor performance     

堆叠式内存制造中炉管非选择性半球状多晶硅片数效应

随着动态随机存取存储器(内存)线宽的缩小,需要半球状多晶硅等新技术来增大电容。当前对选择性半球状多晶硅论述较多,非选择性半球状多晶硅则较少提到。文中讲述的是炉管非选择性半球状多晶硅在0.13μm堆叠式内存上的实际应用,侧重于解决片数效应。炉管非选择性半球状多晶硅的下电极阻值具有非常严重的片数效应,电容的下极板电阻从炉管底部向上增高,并随着产品片数的增加而增高,导致上部产品良率偏低,一个制程只能生产一批产品。通过对非选择性半球状多晶硅的制程原理及硬件构造进行分析,发现片数效应是由于籽晶沉积阶段的硅烷流量通常非常小,只有10～15标准毫升,它在硅片上的分布密度会随着产品的增多而沿气流方向减少,沿气流方向的硅片只好通过增加籽晶和迁移步骤的温度来拉起更多的基体硅进入半球体,相应的剩余基体硅就会变薄,这就导致了下电极阻值的增高。文章根据该发现,提出了炉管非选择性半球状多晶硅片数效应的解决方法。     

Modeling and optimization of monolithic polycrystalline silicon resistors

The processing parameters of monolithic polycrystalline silicon resistors are examined, and the effect of grain size on the sensitivity of polysilicon resistivity versus doping concentration is studied theoretically and experimentally. Because existing models for polysilicon do not accurately predict resistivity dependence on doping concentration as grain size increases above 600 Å, a modified trapping model for polysilicon with different grain sizes and under various applied biases is introduced. Good agreement between theory and experiments demonstrates that an increase in grain size from 230 to 1220 Å drastically reduces the sensitivity of polysilicon resistivity to doping levels by two orders of magnitude. Such an increase is achieved by modifications of the integrated-circuit processes. Design criteria for the optimization of monolithic polysilicon resistors have also been established based on resistivity control, thermal properties, and device geometry.     

多晶硅薄膜高温退火特性研究分析

利用原子力显微镜、二次离子质谱分析仪和探针,对多晶硅薄膜的高温退火特性进行了实验研究。研究结果表明,多晶硅薄膜退火时出现的第二次反退火阶段,其物理起因是由于注入杂质在薄膜中的再分布;而在更高退火温度下,多晶硅薄膜会出现晶粒再结晶和再结晶弛豫过程,这些过程都会影响多晶硅薄膜的薄层电阻。     

Influence of chemical corrosion on resistivity and 1/f noise of polysilicon gauges

New reliability problems rise for microsensors working in harsh environments: e.g., polycrystalline silicon piezoresistive gauges can be deteriorated in many applications, thus leading to a decrease of the sensor lifetime. In order to investigate these problems, polysilicon gauges highly doped with boron were processed, and accelerated corrosion tests were realized in different atmospheres. Two different runs were processed in order to distinguish the effect of corrosion on polysilicon only from the effect on the whole gauge. Electrical characterization of the gauges was then performed. The static characterization shows that only the thermal budget is responsible for the degradation of polysilicon resistivity. On the dynamic point of view, the 1/f noise developed by the gauges was found to be very sensitive to the kind of atmosphere and also to the thermal budget. Chlorine reveals to be very corrosive for polysilicon even at only 5% mixture with air or argon. Kinetics of the chemical reactions seems to be attainable from 1/f noise measurements.