Internal Stress and Atomic Transportation in Thin Film and Line Structure

为了研究用于大规模集成电路技术的铝和铜材料在高温区域的原子迁移特性，对铝和铜薄膜的表面形貌进行了原位x射线热应力测量和光学和电子观察。通过射频溅射沉积在玻璃或Si衬底上的Al和Cu薄膜具有强的< 111 >优先取向。无论射频功率、氩气压力和溅射时间如何，沉积态的残余应力都是拉伸的。采用x射线衍射技术对试样在RT - 200℃、300℃和400℃加热和冷却循环下的原位热应力进行了测量。当温度升高到100℃时，薄膜中的拉伸应力几乎降低到零水平，此后各热循环中直至最高温度的应力水平没有明显变化。在冷却阶段，膜内的应力转变为拉伸，但在初始阶段增加幅度较小，在低温范围的最后阶段增加幅度较大。这是由于晶界扩散、表面扩散和体扩散的能力。另一方面，由于沉积在Al或Cu薄膜表面的保护膜对原子输运的限制，在热循环过程中，被AlN或TiN薄膜覆盖的薄膜的热应力变化较大。SEM和AFM观察表明，加热阶段和冷却阶段分别出现了小丘和空洞。此外，通过原位激光显微观察，在加热阶段观察到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.