Interface of soft X-ray multilayers

软X射线多层膜是极紫外光刻系统中的关键元件，其反射性能与热稳定性对光刻系统的发展有着重要的影响。本文围绕Mo/Si多层膜界面展开讨论，研究了不同条件下多层膜的界面质量，分析了界面扩散与界面化合物形成对多层膜的反射性能与热稳定性的影响。 本文首先将中心波长位于13.5nm处的反射率谱线与硬X射线小角反射谱线结合起来，建立四层模型并提出了多层膜界面精细结构的分析方法。通过TEM、XPS、AFM等辅助分析手段进一步验证了界面分析模型的合理性。基于该方法分析表明磁控溅射制备的Mo/Si多层膜的Mo-on-Si界面宽度比Si-on-Mo大0.2 nm左右，并结合XPS证明界面组成材料是MoSi2。 单层膜工艺调试是多层膜研制的基础，通过研究沉积速率对单层薄膜的沉积过程与组织形态的影响，发现沉积速率的控制是制备致密、光滑薄膜的关键因素。基于稳定的单层膜工艺建立了多层膜沉积速率标定方法，获得了致密、光滑的Mo/Si多层膜的工艺参数，并探索了两种组成材料不同沉积速率组合对Mo/Si多层膜界面结构的影响。结果表明，高的沉积速率会使靶材和基底累积更多的热量，促进了多层膜的界面扩散。但过高的沉积速率会导致界面宽度大，并降低多层膜的反射率与带宽。此外，岛状成核及高能量沉积粒子对成膜表面具有“刻蚀”效应，进而增大界面宽度。 通过在Mo/Si多层膜界面处插入碳（C）扩散阻隔层，研究了扩散阻隔层的厚度对Mo/Si多层膜在13.5nm处反射率的影响。结果表明，扩散阻隔层厚度的增加会降低反射率，同时会影响中心波长的漂移，界面粗糙度先减小后增大。 利用GIXRR测试曲线拟合讨论温度对Mo/Si多层膜周期厚度的影响发现，不添加扩散阻隔层时，Mo/Si多层膜的周期厚度随着温度的上升而减小。当温度达到400℃时，周期厚度急剧下降，当增大到600℃时小角衍射峰消失，表明界面已经模糊。添加扩散阻隔层后，温度从室温上升到400℃过程中周期厚度基本维持稳定。当温度上升到500℃时，周期有微弱的下降趋势，达到600摄氏度后周期厚度减小了0.2nm。结果表明，添加扩散阻隔层后，多层膜的热稳定性有明显的提高，该结论进一步通过XRD与TEM分析得到验证。Soft X-ray multilayers are the critical components for the next generation lithography system, in which the reflectance and thermal stability plays an important role in the further development of extreme ultraviolet lithography system. In this work, we investigate the interface diffusion and interface roughness of the soft x-ray multilayers, which directly influence the optical performance and thermal stability of the EUV mirrors. At first, the extreme ultraviolet reflectance and the x-ray reflectivity data are combined to extract the final interface structure of the Mo/Si multilayers with a four-layer model. Other characterizations such as TEM, XPS, AFM are made to verified the proposed film structure. Based on the model, we find that the Mo-on-Si interface is about 0.2 nm thicker than that of Si-on-Mo interface. The interfacial compound is found to be MoSi2. Since the technique process of single layer is the foundation of multilayer fabrication, the influence of deposited rate on the deposition process and morphology is investigate. The results indicate that the deposited rate is the critical factor to prepare the dense and smooth coatings. Based on the technique process of single layer, the deposited rate of multilayer is investigated and the technique parameters are obtained to prepare the dense and smooth multilayers. The higher deposited rate can widen the interface width and decrease the reflectance and reflective band of the multilayers. The influence of the thickness of diffusion barrier layer on the reflectance of multilayer at 13.5nm is investigated via inserting an interlayer such as carbon. When the thickness of barrier layer increases, the reflectance decreases and the peak location would shift. The interface roughness decrease first and then increase. With the model mentioned above, the influence of annealing temperature on the periodical thickness of multilayer are investigated. The periodical thickness will decrease with the annealing temperature when there is no barrier layer. At 400℃, the periodical thickness decreases rapidly. At 600℃, the peaks in the GIXRR curve disappear, which indicates the roughness of the interface. In contrast, the periodical thickness is rather stable when using carbon as a barrier layer. Only 0.2nm are observed to decrease when at 600℃. The results indicate that the diffusion barriers are beneficial to improve the thermal stability of the soft X-ray multilayer