Internal Stress and Atomic Transportation in Thin Film and Line Structure

为了研究大规模集成电路(LSI)材料中铝和铜在高温区的原子迁移特性，采用原位X射线热应力测量和光学及电子显微镜观察了铝和铜薄膜的表面形貌。在所有情况下，沉积状态下的残余应力都是拉伸的，与射频功率、Ar气压和溅射时间无关。在RT-200℃、300℃和400℃的加热和冷却循环下，用X射线衍射法对试件进行了原位热应力测量。当温度升高到100℃时，薄膜中的拉应力几乎减小到零水平，此后在每个热循环中达到最高温度的应力水平没有显着变化。在冷却阶段，薄膜内的应力由拉应力转变为拉应力，但在低温范围的初始阶段，应力增幅较小，在低温范围的最后阶段，应力增加幅度较大。这是由于它具有晶界扩散、表面扩散和体扩散的能力。另一方面，由于沉积在Al或Cu膜表面的保护膜对原子输运的限制，AlN或TiN薄膜覆盖的薄膜在热循环过程中热应力变化较大。从扫描电子显微镜和原子力显微镜观察可以看出，加热阶段和冷却阶段分别形成了丘状和空洞。此外，通过激光原位显微镜观察了加热阶段表面粗糙度的变化和再结晶的出现。

In order to investigate the property of atomic migration in high temperature region of aluminum and copper for the materials used in LSI technology, in-situ X-ray thermal stress measurement and optical as well as electronic observations of surface morphology of Al and Cu films.Al and Cu films deposited on a glass or a Si substrate by RF sputtering had strong < 111 > preferred orientation. Residual stress in an as-deposited state was tensile in all the case regardless of the RF power, Ar gas pressure and sputtering time. An in-situ thermal stress measurement was made by X-ray diffraction technique on the specimens under the heating and cooling cycles between RT and 200℃, 300℃, and 400℃. The tensile stress in the films almost diminished to zero level by increasing temperature to 100℃ and after that there was no significant change in the stress level up to the maximum temperature in each thermal cycle. In the cooling stage, the stress in the film changed to tensile but the increasing rate was small in the initial stage and became large in the final stage of low temperature range. It is due to the ability of grain boundary diffusion, surface diffusion and body diffusion. On the other hand, the variation of the thermal stress in films covered by thin AlN or TiN film was large during the thermal cycles because of the constraining of the atomic transportation by the protective film deposited on the surface of Al or Cu film.From SEM and AFM observations, it was cleared that hillocks and voids develop in the heating stage and cooling stage, respectively. Furthermore, the change in surface roughness and the appearance of recrystallization were observed in the heating stage by the in-situ laser microscopic investigation.