Analysis on Via-hole Filling Rrocess in Multilayred LSI Interconnection

随着大规模集成电路（LSI）技术的进步，要求进一步缩小尺寸，多层结构已经得到了热烈的研究。层间互连的形成过程是实现该结构的关键问题之一。通过表面扩散将导体金属填满过孔的回流法是一种很有前途的方法，但具体过程尚未明确。本文采用有限差分法求解表面扩散微分方程，分别对二维模型（充入槽内）和轴对称模型（充入圆柱内）进行了数值模拟。结果表明，当长径比（深度/半宽）或（深度/半径）大于3时，沟槽或圆柱体均无法实现完美填充。为方便读者，在地图上说明了完美充填的可行条件。讨论了充填时间与通孔尺寸和纵横比密切相关的问题。分析了不完全充填过程，并在此基础上提出了改进的过孔形状。采用分子动力学方法，在恒温条件下，在原子水平上详细模拟了扩散过程。

As recent advances on LSI (large scale integrated circuit) technology requires further reduction of the size, multilayred structure has been intensely investigated. The forming process of interconnection between the layrs is one of the key issues in order to accomplish the structure. The reflow, in which the via-hole is filled with the conductor metal by the surface diffusion, is a promising method though the detail in the process has not been clarified yet. In this study, the process is numerically simulated for a two-dimensional model (filling into a groove) and an axi-symmetrical one (filling into a circular cylinder) solving the differential equation of surface diffusion by a finite dellevence method. The results show that the perfect filling can not be achieved for the groove or the cylinder with the aspect ratio, (depth/half width) or (depth/radius), larger than 3. Feasible conditions for the perfect filling are illustrated in a map for reader's convenience. The time for the filling, which is strongly dependent on the size and aspect ratio of via-hole, is discussed. Moreover, the process in incomplete filling is analyzed and the modified shape of via-hole is proposed on the basis of the simulation. The diffusion process is simurated in atomic level in detail using molecular dynamics under constant tempelature.