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

在这项研究中，我们研究了新的绝缘材料作为纳米电子MOSFET和其他器件的栅极。在过去的30年里，MOSFET的尺寸已经大大缩小。由于器件的积极垂直缩放，栅氧化层的厚度已经变得非常小(几纳米)，现在通过这种极薄的栅氧化层的直接量子力学隧道已经成为一个主要的担忧来源，因为泄漏电流大得令人无法接受。因此，这项研究的主要目标是研究以Hafnium和Zirconium氧化物和铝酸盐为基础的高介电常数材料(High-k材料)，作为二氧化硅的潜在替代品。这种高k值材料将允许物理上更厚的介质材料用作栅极绝缘体，但实现相同的电容或驱动电流。通过使用高k材料，将有可能实现1 nm或更小的等效SiO_2厚度。由于更厚的绝缘层，门将不会受到量子力学隧道效应的影响，这有可能成为一个阻碍表演的因素。拟议的研究计划既使用脉冲激光沉积(PLD)，也使用HfO2和Al_2O_3的共同溅射。我们计划在这两种技术中同时使用低能离子轰击，以获得更高质量的栅绝缘体。将对电击穿和电容-电压特性进行系统研究。为了了解工艺参数对栅极堆叠的影响，以及了解微结构与电学特性之间的关系，将进行系统的微结构表征。目前，这些替代SiO_2的新材料体系存在许多尚未解决的问题。将二氧化硅的大部分关键优势映射到这些新的高k材料门中是极其困难的。纳米电子MOSFET的材料化学、物理结构、热稳定性、阈值电压稳定性、界面态密度、合适的导电栅电极、介质击穿特性、失效模式、可靠性、迁移率脱除和漏电场影响等问题是需要进一步研究的领域。

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.