【作者】 何志巍；

【导师】 王印月；

【作者基本信息】 兰州大学 ， 凝聚态物理， 2006， 博士

【摘要】 自从1947年晶体管发明以及1958年第一个集成电路诞生以来,以硅基集成电路为核心的微电子技术取得了飞速发展,传统热生长法生长的SiO₂作为金属互连线间的绝缘介质,已远远不能满足需求,以此为背景的低介电常数材料成为当今微电子领域的研究热点。通过对各种候选材料物性及制备方法的综合分析,本文选取以溶胶-凝胶法为基础的介电常数低、与现有工艺兼容的纳米多孔SiO₂作为研究对象,系统地研究了其制备、微结构、化学键和电学等方面性质,获得了许多新的突破,并提出一种掺氟的新方法。 第一、用溶胶一凝胶法结合旋涂技术,制备纳米多孔SiO₂薄膜。首次利用两次改性解决了薄膜容易开裂的问题,并比较性地研究了溶胶、凝胶以及薄膜的性质。SEM和AFM表明,薄膜内孔径在70-80 nm,已形成较好的三维网络结构。FTIR指出,两次改性及正己烷清洗明显改善了薄膜的结构和电学性质,其介电常数约为2.0,漏电流密度仅为1.5×10^-7A/cm²,击穿场强高达1.9 MV/cm。 第二、以表面活性剂为模板,结合溶胶-凝胶法,得到孔径小（10-20 nm）、分布均匀、且结构坚固的纳米多孔SiO₂薄膜。FTIR表明,模板对表面改性过程有一引导作用,源于模板的双极性基团及由此产生的加溶现象,这一发现在国际上尚属首次。450℃退火样品的SEM显示,薄膜内去除模板后可形成相应孔洞。-CH₃基团的氧化分解在氮气气氛下得到遏制,提高了薄膜憎水性和热稳定性。其介电常数和漏电流密度在退火后分别为1.66和6.6×10^-8A/cm²,当电场强度增大到2.5 MV/cm时,仍没有观察到击穿现象。 第三、首次将氢氟酸（HF）作为催化剂引入到溶胶-凝胶中,实现氟元素的掺杂,制备出具有超低介电常数、性能优良的纳米多孔SiO₂:F薄膜,成功地将氟元素的掺杂理念与第三类降低介电常数的方法结合。该方法作为一种薄膜制备技术具有设备简单,工艺容易控制,掺杂方便等特点,进一步拓宽了溶胶-凝胶法在制备超低介电常数材料方面的应用潜力。 HF浓度过大或过小都可能导致氟元素引入量降低,最合适的配比为HF/H₂O=1/5。FTIR中出现了Si-F键,表明氟元素的引入。其介电常数可降到1.5左右,漏电流密度较用HCl作催化剂的SiO₂薄膜降低近一个数量级,遵循Schottky发更多还原

【Abstract】 Since the first integrated circuit was invented in 1958, the Si-based microelectronic technology has been developing very quickly. Completely in consistent with the prediction of the so-called "Moore’s Law", the transistor feature size is scaling down to a very small value. The conventional thermal grown SiO₂, as the insulating layer, is not applicable, because of the resistance-capacitance delay, cross-talk noise and power dissipation. Based on the detailed analysis of the properties and deposition methods for the candidates, we focus our research on the sol-gel derived nanoporous SiO₂ thin film, which has low dielectric constant, and compatibility with existent ULSI technology. To the best of our knowledge, we systematically and comparatively studied the properties of the film, such as preparation, microstructure, chemical bond state and electricity, and achieved many new breakthroughs. Moreover, we bring forward a new method to adulterate fluorine.1. Through sol-gel method with spin-on technology, we deposited nanoporous SiO₂ thin film. For the first time, we solve the question about the film surface crack through the spinning modification. The results of SEM and AFM indicate that the pore size is between 70-80 nm, and there is almost not collapse in the network structure. The FTIR analysis confirm role of the twice modification and n-hexane washing. The dielectric constant is 2.0, the leakage current density is 1.5×10^-7 A/cm², and the break down field is 1.9 MV/cm.2. In order to reduce the pore size and size distribution, we used the template method to prepare SiO₂ thin film. SEM pictures show that the pore size is in the range of 10-20 nm, and the framework is stronger than that prepared by conventional sol-gel method. For the first time, we find that the template has the homing function to the surface modification due to the two polar bonds. Comparing with the annealing in air atmosphere, the protection of nitrogen atmosphere can prevent the decomposition of the -CH3 bond, leadingto the better hydrophobicity and stability. The dielectric constant is 1.66, the leakage current density is 6.6x10"8 A/cm2, and we did not find the break down phenomenon even when the electric field increases to the value of 2,5 MV/cm.3. For the first time, we introduced the fluorine into the SiC>2 thin film by sol-gel method, and prepared the ultra-low k nanoporous SiO2:F film with good properties. As one of the methods to prepare thin film, this method possesses many virtues, such as simple equipment, easy to be controlled, convenient adulteration, and so on, which further widened the potentiality of sol-gel method.In our experiment, we deposited the SiO2:F thin film using the hydrofluoric acid （HF） as the catalyst. The concentration of the HF is very important, and the best ratio is that HF/ H2O=1/5. The existent of the Si-F bond in the FTIR spectra can confirm the introduction of the fluorine. There is only one kind leakage current emission mechanism in the SiC^F film, that is Schottky emission. The pore size is about 1-10 nm in the film. The relationship between the porosity and the dielectric constant belongs to the Rayleigh model, which indicates that most of the pore is closed and isolated, and be more useful in the ULSI.更多还原