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 vapour deposition are scarce yet important for the semiconductor industry. Here, we report the design and implementation of an autonomous instrument for sputter deposition of thin films with controlled composition, leveraging a highly automated sputtering reactor custom-controlled by Python, optical emission spectroscopy (OES), and 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途径。尽管自主合成仪器在分子与聚合物科学、杂化材料与纳米颗粒的溶液加工领域已得到广泛应用，但面向物理气相沉积的自主化工具实例仍较为稀缺，然而此类工具对半导体工业至关重要。本文报道了一种用于可控组分薄膜溅射沉积的自主仪器设计与实现，该仪器基于由Python自定义控制的高度自动化溅射反应腔室、光学发射光谱（OES）与贝叶斯优化算法。我们将通过X射线荧光光谱测量的薄膜组分建模为N₂气氛中从元素Zn与Ti靶材共溅射过程中监测发射谱线的线性函数。基于OES信息的贝叶斯控制算法通过最小化目标发射信号与实测信号间的绝对误差，在溅射功率参数空间中导航，以制备用户定义组分的薄膜。我们通过自主制备ZnₓTi₁₋ₓNᵧ薄膜验证了该方法，即使在15 nm超薄薄膜中，其实际阳离子组分与目标值的偏差仍可控制在相对3.5%以内，证明该方法能够以最小人工干预可靠合成特定组分的薄膜。此外，所提出方法可推广至等离子体强度与压力呈非线性关系，或元素粘附系数强烈依赖于衬底温度等更复杂的合成实验场景。