High permittivity (high-k) material gate for MOSFETs and other devices

在本研究中，我们研究了作为纳米电子mosfet和其他器件栅极的新型绝缘材料。在过去的30年里，mosfet的尺寸已经大幅缩小。由于器件的垂直缩放，栅极氧化物的厚度变得非常小（几纳米），现在通过这种极薄的栅极氧化物的直接量子力学隧穿已经成为一个主要的关注来源，因为泄漏电流大得令人无法接受。因此，本研究的主要目标是研究基于铪、锆氧化物和铝酸盐的高介电常数材料（高k材料），作为SiO2的潜在替代品。这种高k材料将允许使用物理上较厚的介电材料作为栅极绝缘体，但实现相同的电容或驱动电流。通过使用高k材料，可以实现1 nm甚至更小的等效SiO2厚度。由于较厚的绝缘体，该门不会受到量子力学隧道效应的影响，而量子力学隧道效应有可能成为引人注目的看点。提出的研究计划使用脉冲激光沉积（PLD）和HfO2和Al2O3的共溅射。我们计划在这两种技术中同时使用低能离子轰击来获得高质量的栅极绝缘体。系统地研究电击穿和电容对电压的特性。为了了解工艺参数对栅堆的影响以及微观结构与电特性之间的关系，将进行系统的微观结构表征。目前，在这些新兴的替代SiO2的材料体系中存在着许多尚未解决的问题。将SiO2的大多数关键优势映射到这些新的高k材料栅极中是极其困难的。纳米电子mosfet需要进一步研究的问题包括：材料化学、物理结构、热稳定性、阈值电压稳定性、界面态密度、合适的导电栅极、介电击穿特性、失效模式、可靠性、迁移率退化和漏场影响。

In this research we investigate new insulating materials to serve as gate of nanoelectronic MOSFETs and other devices. In the past 30 years, the size of MOSFETs has been scaled down quite dramatically. Due to aggressive vertical scaling of the devices, the thickness of the gate oxide has become extremely small (a few nanometers) and now the direct quantum mechanical tunnelling through this extremely thin gate oxide has become a major source of concern since the leakage currents are unacceptably large. The primary objective of this research is therefore to investigate higher permittivity materials (high-k materials), based on Hafnium and Zirconium oxides and aluminates, as potential replacements of SiO2. Such high-k  materials will permit a physically thicker dielectric material to be used as a gate insulator but realizing the same capacitance or drive current. By using high-k materials it would be possible to realize an equivalent SiO2 thickness of 1 nm or even less. Because of thicker insulator, the gate will not suffer from the quantum mechanical tunnelling which is threatening to become a show-stopper. The proposed research plans to use both pulsed laser deposition (PLD) and  the co-sputtering of HfO2 and Al2O3. We plan to use concurrent low energy ion bombardment in both techniques to achieve superior quality of the gate insulator. A systematic study of electrical breakdown and capacitance versus voltage characteristics would be conducted. Systematic microstructural characterizations would be carried out to understand the influence of process parameters on the gate stacks and to understand the relationship between microstructure and electrical characteristics. At present numerous unsolved problems exist in these new and emerging materials systems to replace SiO2. It had been extremely difficult to map most of the key advantages of  SiO2 into these new high-k materials gates. Some of the problem areas needing further study for nanoelectronic MOSFETs are: the materials chemistry, physical structure, themal stability, threshold voltage stability, interface state density, suitable conducting gate electrode, dielectric breakdown characteristics, failure modes, reliability, mobility degreadation, and drain field impact.