School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, 1205 W State Street, West Lafayette, IN 47907, USA.
Nanoscale. 2017 Feb 2;9(5):1827-1833. doi: 10.1039/c6nr07637h.
Graphene is a promising ultra-thin barrier against undesired mass transport, however, the high deposition temperatures or the defect inducing post-deposition transfer processes limit its widespread applicability. Herein we report on the successful blocking of copper (Cu) ion diffusion by large area multi-layer graphene (MLG) membranes deposited directly on silicon oxide (SiO) via low temperature plasma-enhanced chemical vapor deposition. The barrier strength of MLG is compared to evaporated tantalum (Ta) by applying positive bias-temperature stress (BTS) to Cu/barrier/SiO/Si test structures. After constant BTS of 4 × 10 V cm at 400 K for 50 min, the MLG barrier device exhibits a negligible flat band voltage shift in capacitance-voltage measurements and no discernible current peak in triangular voltage scans, whereas the Ta barrier allows significant Cu ion transport. Highly limited Cu ion diffusion through MLG suggests that lower energy diffusion paths, like grain boundaries and defects of individual graphene layers, do not align in the direction of an applied stress field. In general, the presented low-temperature direct growth MLG membranes can block undesirable diffusion in many applications, and are especially suitable as Cu diffusion barriers in integrated circuit chips, photovoltaic cells and flexible electronic devices.
石墨烯是一种很有前途的超薄阻挡层，可以阻止不需要的物质传输，然而，高沉积温度或导致沉积后转移过程的缺陷限制了其广泛应用。本文报告了通过低温等离子体增强化学气相沉积（PECVD）直接在氧化硅（SiO）上沉积大面积多层石墨烯（MLG）膜，成功阻止了铜（Cu）离子扩散。通过对 Cu/阻挡层/SiO/Si 测试结构施加正偏压-温度应力（BTS），将 MLG 的阻挡强度与蒸发的钽（Ta）进行了比较。在 400 K 下进行 50 分钟的 4×10 V cm 的恒定 BTS 后，在电容-电压测量中，MLG 阻挡器件的平带电压偏移可以忽略不计，在三角形电压扫描中没有可辨别的电流峰值，而 Ta 阻挡层则允许 Cu 离子的显著传输。Cu 离子通过 MLG 的扩散受到高度限制，这表明在施加的应力场方向上，能量较低的扩散路径，如晶粒边界和单个石墨烯层的缺陷，没有对齐。总的来说，所提出的低温直接生长 MLG 膜可以阻止许多应用中不需要的扩散，特别适合用作集成电路芯片、光伏电池和柔性电子设备中的 Cu 扩散阻挡层。
