远程等离子体氮化制备超薄界面层调制金属/锗接触势垒研究

The successful replacement of SiO2 by high k dielectrics greatly promotes the study of Ge devices. However, the direct contact for metal/Ge exhibits a strong Fermi-level pinning, which results in a too large contact resistivity for NMOSFET source/drain contact. Due to the difficulty of obtaining a high enough doping concentration for n-Ge, lowering the metal/Ge contact barrier becomes critical. With a successful attempt to lower the contact barrier, this project proposes a study on modulation of metal/Ge contact barrier by an ultrathin GeON interlayer fabricated by a remote plasma direct nitridation on GeOx/Ge. We have demonstrated that the GeON layer can not only effectively passivate the Ge surface, but also its thickness can be <1nm with a CBO<1eV to Ge, which theoretically allows a contact resistivity<1E-7 Ohm-cm2. This project will study the barrier modulation mechanism, the role of N atoms, the Ge out-diffusion behavior as well as the thermal stability of this contact system. With the study, we will build the barrier modulation model and identify the modulation mechanism, reveal the status and function of N in GeON layer, understand the Ge out-diffusion mechanism and suppress it, discover the thermal stability and effectively improve it. Finally, we will realize a contact resistivity <1E-7 Ohm-cm2 for metal/n-Ge contact.

高k栅介质成功取代二氧化硅极大促进了人们对锗器件的研制。但锗与金属直接接触显示出强烈的费米能级钉扎效应，导致NMOSFET源漏区接触电阻率过大。因很难获得高掺杂n型锗，降低金属/锗接触势垒成为关键。在降低势垒已取得初步成功基础上，本项目拟用远程等离子体直接氮化GeOx/Ge表面技术，制备超薄GeON中间层，开展金属/锗接触势垒调制研究。我们已证明该层不仅可为锗栅介质层提供良好钝化，且因厚度可以<1纳米、与锗导带偏移<1eV，理论上其又可实现<1E-7欧姆-平方厘米的较理想接触电阻率。项目拟研究GeON层调制接触势垒的机理、N在薄层中的作用、锗的外扩散机制和体系的热稳定性规律。通过研究揭示势垒调制机理，建立调制模型；明确N在超薄层中的存在形态和作用；掌握锗的外扩散机制并对其进行有效抑制；给出该体系的热稳定性规律，并有效增强之。最终在n型锗上实现接触电阻率<1E-7欧姆-平方厘米的金半接触。

围绕如何获得有效势垒调制和超低接触电阻率的核心目标，项目从实现方案与调制机理上进行了系统研究。项目1）开展了Ga在Si，SiGe，Ge中激活的系统性研究，在Ge上实现了5E-10 欧姆平方厘米的超低接触电阻率；2）提出了基于超薄Ti中间层的La/Ti/Si双层金属接触结构，不但实现了超低接触电阻率且热稳定性大幅提高；3）在SiGe衬底上利用TiN/Ti双层接触结构实现1E-9欧姆平方厘米的接触电阻率，且发现了高热稳定性接触要求Ti层厚度要适中；4）利用有机物界面层调制了Hg/n-Si肖特基接触，证明了偶极子效应的调制作用；5）利用TiN覆盖层技术降低了TiSix/Si功率二极管的肖特基势垒，降低了其无效功耗。