【作者】 房振乾；

【导师】 胡明；

【作者基本信息】 天津大学 ， 微电子学与固体电子学， 2007， 博士

【摘要】 多孔硅(PS)具有大的体积表面比、高效率的发光特性,良好的化学稳定性以及与传统IC工艺的兼容性,使其在SOI技术,微电子机械系统(MEMS)技术以及微传感器技术等众多方面得到极大重视。近年来,随着MEMS技术的迅猛发展,作为一种新兴的牺牲层和绝热层材料,多孔硅以其优良的力学性能和绝热性能在制造化学微传感器、热微传感器、光电子器件以及太阳能电池等MEMS领域中得到广泛的应用。介孔硅(Meso-PS)作为多孔硅技术的一个分支,因其具有适中的孔径尺寸、孔隙率,良好的绝热特性、机械性能等特点在上述MEMS领域应用最为广泛。本论文采用双槽电化学腐蚀法制备介孔硅,主要针对MEMS中介孔硅材料的热学、力学和电学基本性质以及金属薄膜和半导体薄膜微温度传感器中基于介孔硅功能绝热层的绝热特性进行分析和研究。采用准确便捷且对样品无损伤的微拉曼光谱技术测量介孔硅的热导率,研究了实验条件及氧化后处理对其热导率的影响,并对实验测量的结果进行对比分析研究,得出介孔硅热导率随孔隙率及氧化后处理的变化规律。探讨了介孔硅的传热机理,基于有效介质理论,提出用于分析所制备介孔硅和氧化介孔硅热导率的理论模型,对影响所制备介孔硅和氧化介孔硅有效热导率的因素进行了理论分析,得出用于计算所制备介孔硅和氧化介孔硅有效热导率的理论计算公式,揭示了介孔硅层热导率与硅基底热导率间的巨大差异。研究分析表明理论计算与所获得的实验数据相一致,为今后利用介孔硅材料制作绝热层打下了良好的理论基础。由于介孔硅薄膜材料的尺度较小,传统的材料力学测试方法难以对其机械力学参数进行测量。纳米压痕技术具有操作简单、测量精度高、可以在很小的局部范围测试材料的力学性能等优点,在材料的微观力学性能研究方面得到了广泛的应用,逐渐成为微机械材料力学性能测量中应用最广的一种方法。通过纳米压痕技术研究了所制备介孔硅和氧化介孔硅的硬度和杨氏弹性模量随纳米压入深度的变化规律,比较了经不同温度处理的氧化介孔硅的力学性能差异。研究分析表明,所制备介孔硅的硬度和杨氏弹性模量随其孔隙率的增加而减小,经过不同温度的氧化后处理,氧化作用形成的二氧化硅包覆层可以明显提高其微观力学性能。在对介孔硅材料的热学和微机械力学性能的研究基础上,进一步探讨了所制备介孔硅及氧化介孔硅的电学性能。以金属半导体接触原理为基础,对铂金属薄膜与介孔硅所组成的金属—所制备介孔硅或氧化介孔硅—单晶硅微结构的纵向和横向接触特性进行分析和研究,得出其I-V特性随制备条件及氧化后处理的变化规律。研究发现,介孔硅层具有良好的电绝缘特性,介孔硅基微器件可以形成稳定的电接触。基于介孔硅的微结构的I-V特性主要由介孔硅层的电学特性所决定,表现出非整流的接触特性。基于介孔硅优良的绝热特性、良好的机械稳定性和电绝缘特性,对其在热微传感器中作为功能绝热层的应用作了进一步的研究。以具有正电阻温度系数(PTC)的铜金属薄膜和具有负电阻温度系数(NTC)的氧化钒薄膜为热敏元件对介孔硅功能结构层的绝热特性进行分析,并对相应热敏元件的电阻温度特性进行了研究。研究结果表明,基于介孔硅优良的绝热特性,热敏薄膜表现出良好的电阻温度特性,较高的灵敏度,可以应用于更加广泛的热敏感材料制作基于介孔硅功能绝热层的热微传感器,从而扩展了介孔硅功能绝热层的应用范围。更多还原

【Abstract】 Due to its very large surface to volume ratio, intense visible photoluminescence, good chemical stability and easy compatibility with modern standard IC technology, porous silicon (PS) has received considerable attention in various fields such as silicon-on-insulator (SOI), micro-electro-mechanical-system (MEMS), micro-sensors technologies and so on. In recent years, with the rapid development of MEMS technologies, PS has been utilized as new kinds of sacrificial and thermal isolation materials. This very promising material has been an object of numerous MEMS applications in fabrication of chemical microsensors, thermal microsensors, optoelectronics and solar cell because of its excellent mechanical and thermal isolation properties. As a part of PS technologies, meso-PS has been effectively investigated in the above-mentioned MEMS applications for its moderate pore-size and porosity, excellent thermal isolation and mechanical properties.In this paper, meso-PS was prepared in a double-tank cell by using the electrochemical corrosion method. The thermal, mechanical and electrical properties of meso-PS in MEMS were investigated in detail. Besides, the thermal isolation properties of meso-PS as functional isolation layer used in metal film and semiconductor thermoresistors were also thoroughly analyzed.Thermal conductivity (TC) of meso-PS was measured using a direct non-contact and non-destuctive technique based on micro-Raman scattering spectroscopy. The affection of experimental conditions and post-oxidation process on its TC was studied. The comparison of measured data was also analyzed. TC values of meso-PS with respect to porosity and post-oxidation process were given. Theoretical models describing mechanisms of heat transfer in as-prepared and oxidized meso-PS based on the effective medium theory were brought forward. The factors affecting effective thermal conductivity (ETC) of as-prepared and oxidized meso-PS were analyzed theoretically, and the calculating formulas of ETC of as-prepared and oxidized meso-PS were given. The great difference between TC of meso-PS and that of silicon wafer was also revealed. It is shown that theoretical values are quite in good agreement with experimental data and this research has contributed to the construction of a systematic theoretical base for the usage of meso-PS as thermal isolation material in future. The characteristic dimensions of meso-PS films are so small that their mechanical parameters can not be measured by traditional mechanical testing methods. Due to its easy operation, high-resolution, characterization of mechanical behavior of materials in a very small region, nanoindentation technique has been widely adopted and used in the characterization of mechanical behavior of materials at small scales. For this reason, the method has become a primary technique for determining the mechanical properties of thin films and small structural features. The hardness and Young’s elastic modulus of as-prepared and oxidized meso-PS with respect to nanoindentation depth were thoroughly investigated using nanoindentation. The mechanical properties of oxidized meso-PS under various oxidized temperatures were also compared. The experimental results reveal that the hardness and Young’s elastic modulus of as-prepared meso-PS decrease with increasing porosities. SiO2 cladding layers are formed after post-oxidation process at different temperatures, and the mechanical properties of the films are distinctly improved.Based on the investigation of the thermal and mechanical properties of meso-PS, the electrical properties of as-prepared and oxidized meso-PS were deeply discussed. According to the theories of metal-semiconductor contacts, the longitudinal and transverse contact properties of Pt/as prepared or oxidized meso-PS/monocrystalline silicon microstructures were analyzed. Then their I-V characteristics with respect to preparation conditions and post-oxidation process were known. These results indicate that meso-PS layers have excellent electrical insulation properties and microdevices with meso-PS can obtain stable electrical contacts. I-V characteristics of meso-PS based microstructures exhibit nonrectifying contact properties and are mainly determined by the electrical properties of meso-PS layers.Owing to the favorable thermal isolation, mechanical stability and electrical insulation of meso-PS, its usage as thermal isolation layer in thermal microsensors was thoroughly studied. Taken Cu thin films exhibiting a positive temperature coefficient (PTC) characteristic and vanadium oxide thin films exhibiting a negative temperature coefficient (NTC) characteristic as thermal-sensitive devices, the analysis of thermal isolation properties of meso-PS functional structural layers were undergone. The resistance-temperature properties of corresponding thermal-sensitive devices were also investigated. It is found that these thermal sensitive films show fine resistance-temperature properties on account of the excellent thermal isolation of meso-PS. A wide range of materials can be utilized as thermal-sensitive materials in the fabrication of thermal microsensors with meso-PS functional structural layers, and consequently, the applications of meso-PS functional structure layers can be broadened.更多还原