【作者】 李世彬；

【导师】 吴志明；

【作者基本信息】 电子科技大学 ， 机械电子工程， 2008， 博士

【摘要】 氢化硅薄膜由于在红外成像传感器、太阳能电池及薄膜晶体管等微电子器件中有着广泛应用前景而备受关注。等离子体化学气相沉积技术制备氢化硅薄膜工艺条件成熟稳定而成为薄膜制备的首选方法。本论文通过改变PECVD工艺条件,制备了非晶、微晶和多形硅三种氢化硅薄膜。运用多种分析与测试方法,研究了氢化硅薄膜的微观结构、光学、电学和热学等物理特性。选定多形硅薄膜为微测辐射热计热敏层,并重点从光学和热学两方面对微测辐射热计结构进行了优化设计。在椭偏光谱仪中采用FB模型,拟合得到非晶硅薄膜的折射率和光学禁带宽度,证明非晶硅薄膜的折射率和光学禁带对衬底温度的依赖关系。同时工作气体压强对非晶硅薄膜的沉积速率、光学禁带和消光系数值也有显著影响。傅立叶红外光谱分析了在KBr衬底上沉积的非晶硅薄膜的官能团信息,说明衬底温度和气体压强变化影响了薄膜中的氢含量改变。以纯硅烷为反应气源时,采用X射线衍射、拉曼和傅立叶红外光谱表征说明随着气体压强的升高,等离子体沉积过程产物形态变化过程为:非晶硅(a-Si:H)→多形硅(pm-Si:H)→凝聚块(agglomeration)→粉末(powder)。在较高的射频功率密度下,采用高浓度氢稀释硅烷为反应气源时,沉积产物形态变化过程为:微晶硅(μc-Si:H)→多形硅(pm-Si:H)→凝聚块(agglomeration)→粉末(powder)。采用电极间热梯度理论和氢刻蚀模型分析了微晶与多形硅晶化机理的差异,证明微晶硅薄膜的体积晶化率随薄膜厚度的增加而增加,而多形硅的体积晶化率对薄膜厚度没有依赖关系。通过研究硼掺杂浓度与氢化硅薄膜电学特性关系表明硼掺杂降低了薄膜的电阻率和方阻值,同时也降低了薄膜的温度电阻系数。研究电阻对时间的依赖关系表明氢化硅电阻值随测试时间增大而增大,XPS测试结果表明薄膜的氧化增大了薄膜电阻。实验还证明氢化硅薄膜的晶化降低了电阻率和方阻值,光照和焦耳热作用改变薄膜的电阻。搭建了半导体噪声测试系统,对非晶、微晶和多形三种氢化硅薄膜的1/f噪声测试分析说明薄膜的晶化使得薄膜结构的有序度更高,晶化降低了薄膜的1/f噪声。采用基于傅立叶热传导定律为理论基础的静态法测试了不同衬底温度下制备非晶硅薄膜的热导率,结果表明薄膜的热导率随衬底温度升高而增大。同时薄膜中存在Si-H键合的震动模造成热量损失也导致薄膜热导率降低。研究不同厚度的非晶、微晶和多形硅三种氢化硅薄膜的热导率结果表明微晶硅薄膜的晶化增大了薄膜的热导率。微晶硅薄膜的表面和薄膜底部存在和晶化率梯度一样的热导率梯度,即表面的热导率高,而薄膜底部的热导率低。多形硅薄膜的热导率和微晶硅相近,多形硅薄膜的热导率增加一方面归因子纳米硅晶粒的存在,同时薄膜内高的氢含量增大了薄膜的致密度,也使得薄膜的热导率增大。首次将多形硅薄膜用作微测辐射热计温阻层,以光学和热学设计理论为基础优化设计了微测辐射热计微桥结构。根据光学导纳矩阵理论,用Matlab软件模拟了不同厚度氮化钛厚度和不同谐振腔高度膜系的红外吸收率,谐振腔高度e=2.5μm时,微测辐射热计红外吸收率高,并且红外吸收率随氮化钛薄膜厚度增加而增大。综合考虑了微桥热导、热响应时间常数以及额定辐射功率下的桥面温升情况下,确定当多形硅厚度为0.1μm时,桥腿长度为25μm,宽为1μm时热导值和热响应时间满足微测辐射热计设计要求。更多还原

【Abstract】 Hydrogenated silicon film attracts extensively attention due to its application on many kinds of microelectronic devices, such as infrared imaging system, solar cell and thin film transistor. Plasma enhanced chemical vapor deposition (PECVD) technique is the primary method which is used to prepare hydrogenated silicon film.In this dissertation, we changed the PECVD technique parameters, and deposited amorphous, microcrystalline and polymorphous silicon films. The microstructure, optical, electrical and thermal properties of hydrogenated silicon films were characterized by a series method. Polymorphous silicon film was selected to be thermal-resistance layer of micro-bolometer, and we optimized the structure of micro-bolometer through optical and thermal design.The refractive index and optical band gap of amorphous silicon were obtained by spectroscopy ellipsometry in FB model. The resuts demonstrate the value of refractive index and optical band gap of amorphous silicon film depends on substrates’ temperature. The variation of total gas pressure also influences the deposition rate, optical band gap and extinctive coefficient of amorphous silicon film. Fourier-transform infrared spectrometer (FTIR) was used to characterize the information of Si-H in silicon film deposited on KBr substrate. The effect of substrate temperature and total gas pressure on hydrogen content in silicon film was confirmed.With the increasing of pure silane total gas pressure, we use XRD, Raman and FTIR method to demonstrate the phase transition of the produce of PECVD process occurred as a formation of amorphous silicon→polymorphous silicon→agglomeration→powder formation. However, when using strong hydrogen dilution silane as source gas, the phase transition is microcrystalline silicon→polymorphous silicon→agglomeration→powder formation. The crystalline mechanism difference of microcrystalline and polymorphous silicon was investigated by thermal gradient theoretical and hydrogen etching model. The volume crystalline fraction of microcrystalline silicon increases with the increasing of film thickness, and there is no such relation in polymorphous silicon film. The resistivity, squared resistance and temperature coefficient of resistance in hydrogenated silicon film decrease with the increasing of boron doping concentration. The resistance of amorphous silicon increases with the increment of measurement time for the surface oxide. The crystalline in silicon film results in the decreasing of resistivity and squared resistance, and the resistance decreases with Joule effect and exposed in light. The measurement of 1/f noise in amorphous, microcrystalline and polymorphous silicon film was performanced with a self-design semiconductor system. The results demonstrate microcrystalline and polymorphous silicon films have low 1/f noise for their crystallization make them better ordered than amorphous silicon film.The thermal conductivity measurement results of silicon films show thermal conductivity of amorphous silicon increase with the increment of substrate temperature, and the vibrational bonds in silicon film were demonstrated to reduce the thermal conductivity. The crystalline in silicon films increases the thermal conductivity of hydrogenated silicon films. There is a thermal conductivity gradient in microcrystalline silicon film similar as the crystalline gradient. The thermal conductivity of polymorphous silicon is nearly silimar as that of microcrystalline silicon film. Both nanocrystal and high hydrogen content contribute to the increment of thermal conductivity in polymorphous silicon film.Polymorphous silicon film was used to thermal-resistance layer in micro-bolometer. According to optical admittance matrix theory, relation between sensing film thickness, resonant cavity height of microbolometer and infrared absorptivity was simulated using FEA (Finite Element Analysis) MatLab software. Optimal film thickness and resonant cavity height for high infrared absorptivity ranging from 3～5 to 8～14μm atmosphere window infrared bands were achieved, which provides reliable evidence to improve the sensitivity of microbolometer.更多还原