Autonomous experimentation has emerged as an efficient approach to accelerate the pace of materials discovery. Although instruments for autonomous synthesis have become popular in molecular and polymer science, solution processing of hybrid materials and nanoparticles, examples of autonomous tools for physical vapor deposition are scarce yet important for the semiconductor industry. Here, we report the design and implementation of an autonomous workflow for sputter deposition of thin films with controlled composition, leveraging a highly automated sputtering reactor custom-controlled by Python, optical emission spectroscopy (OES), and a Bayesian optimization algorithm. We modeled film composition, measured by x-ray fluorescence, as a linear function of emission lines monitored during the co-sputtering from elemental Zn and Ti targets in N$_2$ atmosphere. A Bayesian control algorithm, informed by OES, navigates the space of sputtering power to fabricate films with user-defined composition, by minimizing the absolute error between desired and measured emission signals. We validated our approach by autonomously fabricating Zn$_x$Ti$_{1-x}$N$_y$ films with deviations from the targeted cation composition within relative 3.5 %, even for 15 nm thin films, demonstrating that the proposed approach can reliably synthesize thin films with specific composition and minimal human interference. Moreover, the proposed method can be extended to more difficult synthesis experiments where plasma intensity depends non-linearly on pressure, or the elemental sticking coefficients strongly depend on the substrate temperature.

翻译：自主实验已成为加速材料发现进程的高效方法。尽管自主合成仪器在分子与聚合物科学、杂化材料溶液加工及纳米颗粒领域已广泛普及，但用于物理气相沉积的自主工具实例仍十分稀缺，且对半导体行业至关重要。本文报道了一种用于溅射沉积成分可控薄膜的自主工作流设计与实现，该工作流依托由Python定制控制的高度自动化溅射反应器、光学发射光谱（OES）及贝叶斯优化算法。我们将X射线荧光测量的薄膜成分建模为在N₂气氛中从锌和钛元素靶材共溅射过程中监测到的发射光谱线的线性函数。基于OES信息驱动的贝叶斯控制算法通过最小化目标发射信号与实际测量信号的绝对误差，在溅射功率空间中导航以制备用户自定义成分的薄膜。我们通过自主制备ZnₓTi₁₋ₓNᵧ薄膜验证了该方法，即使对于15纳米超薄薄膜，其阳离子成分与目标值的偏差仍控制在相对误差3.5%以内，证明该方法可在最小化人工干预条件下可靠合成特定成分薄膜。此外，该方法可拓展至更复杂的合成实验场景，如等离子体强度与压力呈非线性关系，或元素附着系数强烈依赖于基底温度的情形。