标题: | 高介电系数钛酸锶钡薄膜BaxSr1-xTiO3于动态随机存取记忆体电容器之研究 The Study of High Dielectric-Constant Barium Strontium Titanate (BaxSr1-xTiO3) for DRAM Storage Capacitors |
作者: | 赖明骏 Ming-Jiunn Lai 郑晃忠 Dr. Huang-Chung Cheng 电子研究所 |
关键字: | 钛酸锶钡;射频磁控平行溅镀系统;动态随机存取记忆体;Barium Strontium Titanate;RF magnetron co-sputter system;DRAM |
公开日期: | 1998 |
摘要: | 随着积体电路密度的增加与元件尺寸的缩小,动态随机存取记忆体的电容面积与操作电压亦随之减小,但为了维持一定的讯号/杂讯比而不产生错误的判读,其所储存的电荷必须保持一临界值,因此,我们必须在不增加储存单元投影面积的前提下有效地提升电容器的电容值。 根据基本电容公式,有三种提升电容器电容值的方法:增加电极板有效面积、缩减介电层厚度以及以高介电常数材料取代传统之介电层。但为增加电极板有效面积,随着电容需求日增,制程亦愈形困难;而介电层厚度缩减至某一程度,则会造成穿遂效应,形成极大的漏电流。因此,使用高介电常数材料必将是未来之趋势。 钛酸锶钡是近年来备受注意的材料,其提供了下列优点:高介电常数、低漏电流、长使用周期、优良的化性、热稳定性及低损耗因子等;而射频磁控溅镀法则为一普遍且成熟之镀膜技术。本论文研究即利用一多靶式射频磁控溅镀系统,成功地在低基板温度(T=300~350℃)沈积具高介电常数(er > 350),及低漏电(~ 10-8A/cm2)的钛酸锶钡薄膜,并针对不同之薄膜沈积条件,研究其薄膜电性与物性,并加以分析了解其物理机制;此外,快速退火方式亦被证实能有效提升阻障层抗氧化能力及对内扩散的阻挡能力。最后,我们研究不同电浆方式处理对钛酸锶钡薄膜的影响,结果显示适当的氧电浆处理能够改善负偏压漏电流特性,若配合适当沈积气体压力所沈积之薄膜,预期能获得最佳之结果。 With increasing the density of devices on ULSI, the minimum feature size is scaled down into deep-submicron regime. For DRAM capacitors, the cell areas and applied voltage are also rapidly shrinking, which lead to lower storage capacitance while the minimum value of capacitance should be maintained in order to achieve a reasonable signal-to-noise (S/N) ratio. According to the calculating equation for flat-type capacitor, there are three ways to increase the value of capacitance, including the decrease of dielectric thickness, the enlargement of the effective surface area of storage nodes, and the utilization of high dielectric constant materials. However, large tunneling current limits the shrinking of dielectric thickness and more complicated processes are needed with enlarging the effective surface area of storage nodes. Therefore, the utilization of high dielectric constant materials is the trend for Giga-bit scale DRAMs in the future. Barium Strontium Titanate (BaxSr1-xTiO3) is the most attractive material due to its high dielectric constant, low leakage current, TDDB over 10 years, good chemical and thermal stability, and low dissipation factor. And RF magnetron sputtering is a prevalent and mature technique for thin film deposition. In this thesis, a high dielectric constant (er > 350) and low leakage current (~10-8A/cm2) BST thin film was successfully deposited at low substrate temperature (T=300~350℃) by utilizing a RF magnetron co-sputter system. The physical and electrical properties of BST films deposited with different deposition parameters were also investigated in order to realize the associated mechanisms. Moreover, Rapid Thermal Annealing (RTA) was proved to enhance the resistance of barrier layers against inter-diffusion and being oxidized during BST deposition. Finally, BST films were treated with different plasma, and the results showed improved leakage current at negative bias. The optimum leakage characteristic at negative bias is expected in BST thin films deposited at proper gas pressure with O2 plasma post-treatments. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#NT870428046 http://hdl.handle.net/11536/64330 |
显示于类别: | Thesis |