Real-time monitoring of low temperature nucleation and growth processes during high power impulse magnetron sputtering

近年来，大功率脉冲磁控溅射技术不仅在研究领域受到越来越多的关注，而且在工业上也得到了广泛的应用。在HiPIMS中，为了保持目标的完整性，靶材被提供极短的极强脉冲，而平均功率与传统磁控溅射（MS）相当。这样的条件使电离溅射金属蒸气成为可能，并获得高于70%的电离分数，即比标准ms高约两个数量级。离子在等离子体电位或外部偏置电压下的加速，除其他外，允许沉积具有更高硬度、密度、折射率和电导率以及更好粘附性的薄膜。此外，离子和电子在衬底上复合时的高能量和局部热释放使得晶体相（包括亚稳相）在远低于热平衡定义的温度或传统质谱法获得的温度下沉积。同时，到达衬底的平均能量低于常规质谱法，这显著降低了衬底加热。因此，HiPIMS对于在聚合物和其他热敏基板上沉积高质量薄膜非常有趣，这些基板在沉积期间或之后不允许热处理。尽管对HiPIMS的兴趣迅速增长，但对其低温成核和生长过程知之甚少，也没有现场调查。在本联合提案中，我们的目标是了解热敏衬底在低温下HiPIMS过程中的薄膜形成，包括成核，生长，结晶和晶粒结构演变。我们的方法是基于同步加速器的掠入射小角x射线散射（GISAXS）实时监测，具有高时空分辨率。我们已经在亚毫秒尺度上展示了时间分辨率，这是HiPIMS中单脉冲的尺度。同时广角散射（GIWAXS）将允许现场测量相形成和转变过程。实时测量将辅以高分辨率电子显微镜、原子力显微镜、x射线光电子能谱、光学能谱和功能薄膜特性表征的结构研究。由于基础和技术的兴趣，我们将研究Au和Ag作为金属体系的沉积，以及TiO2和MoO3作为氧化物的沉积。在研究选定聚合物上更复杂的薄膜形成过程之前，我们将使用Si作为参考衬底。为了进行比较，我们计划进行传统的ms。针对有机光伏和光催化的目标应用，选择材料组合，并研究相关器件的溅射层性能。

During the last years, high power impulse magnetron sputtering (HiPIMS) got increasing attention not only in research but also in industry. In HiPIMS, the target is supplied with short extremely intense pulses while the average power is comparable to conventional magnetron sputtering (MS) in order to preserve the integrity of the target. Such conditions make it possible to ionize the sputtered metal vapor and to achieve ionized fractions above 70 %, i.e. about two orders of magnitude higher than in standard MS. The acceleration of the ions in the plasma potential or an external bias voltage, inter alia, permits deposition of films with higher hardness, density, refractive index, and conductivity as well as better adhesion. Moreover, the high energy per particle and the local heat release during recombination of ions and electrons on the substrate allow for deposition of crystalline phases, including metastable ones, at temperatures much lower than those defined by thermal equilibrium or obtained by conventional MS. At the same time, the average energy arriving at the substrate is lower than in normal MS, which markedly reduces substrate heating. Thus, HiPIMS is very interesting for deposition of high-quality films on polymers and other heat-sensitive substrates, which do not allow heat treatment during or after deposition. Despite the rapidly growing interest, little is known about the low temperature nucleation and growth processes during HiPIMS, and no in-situ investigations are available. In the present joint proposal, we aim at understanding film formation during HiPIMS on heat-sensitive substrates at low temperatures including nucleation, growth, crystallization, and grain structure evolution. Our approach is based on real-time monitoring with synchrotron-based grazing incidence small angle X-ray scattering (GISAXS) with high temporal and spatial resolution. We already demonstrated a time-resolution on the sub-ms scale, which is the scale of single pulses in HiPIMS. Simultaneous wide angel scattering (GIWAXS) will permit in-situ measurement of phase formation and transformation processes. The real-time measurements will be complemented by structural investigations with high-resolution electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, optical spectroscopy, and characterization of the functional thin film properties. Because of fundamental as well as technological interest, we will study the deposition of Au and Ag as metallic systems and of TiO2 and MoO3 as oxides. Prior to the investigation of the more complex film formation processes on selected polymers, we will use Si as a reference substrate. For comparison, we plan to perform conventional MS. The material combinations are select concerning target applications in organic photovoltaics and photocatalysis and related devices will be investigated with respect to the performance of the sputtered layers.