Residual stress in nitride thin films: integrated experiments and development of a predictive model

非技术描述：氮化物薄膜用于各种各样的应用。一个例子是在钻头上涂上硬涂层以延长其使用寿命。这种涂层是通过从蒸汽中将原子沉积在工具表面上制成的，称为物理气相沉积。由于沉积过程不允许原子有时间进入其理想位置，因此所得薄膜通常具有大的应力。因此，该应力可导致膜破裂或分层而失效。本研究的目的是通过了解压力如何与潜在的物理过程相关来减少压力。通过使用影响应力的过程的数学模型，可以预测不同加工条件下的应力。 技术要求：这项工作的重点是理解和控制过渡金属氮化物薄膜中的应力。应力可以强烈地受到处理条件的影响，例如沉积物质的能量或膜生长的速率，但是对于应力降低如何发生还没有基本的理解。在这个项目中，在氮化物沉积过程中使用实时技术（基于晶片衬底中引起的曲率）进行应力测量。这些测量使得应力能够定量地与诸如生长速率和气体压力的处理参数相关。在生长之后，通过用聚焦离子束制作横截面并用电子显微镜测量晶粒结构来表征膜的微观结构。 这种表征使得能够确定应力对膜的晶粒尺寸和微观结构演变的依赖性。实验结果被用来完善和验证一个模型，该模型涉及的应力在膜中的底层过程。这个新模型结合了沉积原子的动力学和以前模型中没有包括的缺陷。这种方法能够更深入地了解应力的来源，薄膜生长者可以使用这种方法来预测不同材料系统在各种条件下的应力。该模型在研究人员的网站上提供给感兴趣的用户。工业和学术专业人士的短期课程描述了控制压力演变的机制。 学生（本科生和研究生）参加这项研究，以发展最先进的实验和建模技术的技能。 来自代表性不足群体的学生被招募参加这项研究，并促进他们在科学和工程领域发展职业的能力。

NON-TECHNICAL DESCRIPTION: Nitride thin films are used in a wide variety of applications. An example is the hard coating that is put on a tool bit to extend its lifetime. Such coatings are made by depositing atoms on the tool's surface from a vapor, referred to as physical vapor deposition. The resulting films often have large stress because the process of deposition does not allow the atoms time to get into their ideal positions. Consequently, this stress can lead to failure of the film either by cracking or delaminating. The goal of this research is to reduce the stress through understanding how the stress is related to the underlying physical processes. Through the use of a mathematical model of the processes affecting stress, it is possible to predict it for different processing conditions. TECHNICAL DETAILS: The focus of this work is to understand and control the stress in transition metal nitride thin films. Stress can be strongly affected by the processing conditions such as the energy of the deposited species or rate of film growth, but there is not a fundamental understanding of how stress reduction occurs. In this project, measurements of the stress are made during the nitride deposition using a real-time technique (based on the curvature induced in the wafer substrate). These measurements enable the stress to be quantitatively related to the processing parameters such as the growth rate and gas pressure. After growth, the film's microstructure is characterized by making a cross-section with a focused ion beam and measuring the grain structure with electron microscopy. This characterization enables the dependence of the stress on the film's grain size and microstructural evolution to be determined. The experimental results are used to refine and validate a model that relates the stress to the underlying processes in the film. This new model incorporates the kinetics of the deposited atoms and the defects that have not been included in previous models. This approach enables a deeper understanding of the origins of stress that can be used by thin film growers to predict the stress under various conditions for different materials systems. The model is made available to interested users on the researcher's website. A short course for industrial and academic professionals describes the mechanisms that control stress evolution. Students (at both the undergraduate and graduate level) participate in this research to develop skills in state-of-the-art experimental and modeling techniques. Students from underrepresented groups are recruited to participate in this research and promote their ability to develop careers in science and engineering.