Predictive Semiconductor Lithography based on Theoretically-Informed Reaction-Diffusion Models

[1437878]最复杂的集成电路，如微处理器和存储芯片，都是通过一种叫做投影光刻的工艺制作的。在典型的光刻工艺中，硅片被涂上一层对辐射敏感的聚合物薄膜（“抗蚀剂”），并暴露在一种光的图案下。辐射触发了一种反应，产生了潜在的化学图像，并通过选择性地冲洗掉暴露（或未暴露）的材料来形成图案。工业应用需要高通量工艺，因此电阻必须对辐射高度敏感。这是通过称为“化学放大”的过程实现的。化学扩增（CA）抗蚀剂有两个主要成分：(i)具有酸不稳定保护基团的亲脂性聚合物；（ii）低浓度的光酸发生器（PAG）。将抗蚀剂暴露在辐射下会产生强酸-反离子催化剂，在中等温度下加热会促进酸催化的沿聚合物主链保护基团的分解。这种脱保护反应改变了聚合物的极性，以便在水基中发育。CA系统效率很高，因为抗蚀剂吸收的每个光子产生大约0.3-2个酸（取决于光子能量），每个催化剂可以裂解数百个键，因此低辐射剂量通过化学作用被“放大”。然而，优异的灵敏度是有代价的，因为酸在反应过程中的扩散会限制CA抗蚀剂的图案分辨率。虽然CA抗蚀剂已经研究了40多年，但目前还没有定量模型可以预测纳米级分辨率下反应的空间范围。这对半导体行业来说是一个越来越重要的障碍，因为目前的研究和开发工作的目标是10nm以下的特征尺寸。智力优势：本研究计划的目的是确定产生异常催化剂运输和催化剂失活的基本物理和化学。PI假设(i)催化剂的异常输运是由玻璃状聚合物薄膜中的动态非均质性引起的；(2)催化剂损失是酸催化副反应的标志。计划进行一系列实验来揭示这些效应。通过这项研究获得的知识将被开发成一种预测光刻工具，可以加速材料的开发和工艺优化。CA抗蚀剂的空间反应范围不能通过实验直接测量，因此需要将实验研究与预测纳米长度尺度上成分的模型相结合。本研究的智力价值在于开发了一种高效，定量和空间分辨的CA抗蚀剂反应扩散模型，该模型适用于广泛的加工条件，参数由实验研究确定。为了实现这一目标，该研究将采用最小的变量集，通过优化确定，同时结合玻璃状聚合物基质和酸性催化剂的潜在物理和化学。通过这项研究开发的框架将提供一种方法来调查尚未在实验室实验中实现的加工条件和配方。更广泛的影响：该研究项目的结果可能会立即影响下一代光刻的材料设计和工艺开发，因为预测模型减少或消除了迭代实验的需要。在建立了异常传输模型在广泛条件下的适用性之后，该方法的详细描述将通过出版物和演示文稿向公众提供，从而进一步发展光刻模拟，这仍然是工业应用中的瓶颈。参与本课程的学生将接受高分子物理与化学、计算方法和实验程序设计方面的培训。PI有让高中生和本科生参与实验室研究的记录，也通过美国国家科学基金会资助的休斯顿大学K-12营地参与社区外展活动。该计划的成果将被纳入PI的研究生课程“微电子化学处理”。

1437878 (Stein)The most sophisticated integrated circuits, such as microprocessors and memory chips, are patterned by a process called projection lithography. In a typical lithographic process, a silicon wafer is coated with a radiation-sensitive polymer film ("resist") and exposed to a pattern of light. Radiation triggers a reaction that generates the latent chemical image, and patterns are developed by selectively washing away the exposed (or un-exposed) material. Industrial applications require high-throughput processes, so the resists must be highly sensitive to radiation. This is achieved with a process termed "chemical amplification". Chemically-amplified (CA) resists have two principal components: (i) a lipophilic polymer with acid-labile protecting groups; and (ii) a low concentration of photoacid generator (PAG). Exposing the resist to radiation generates a strong acid-counterion catalyst, and heating at moderate temperature promotes the acid-catalyzed decomposition of protecting groups along the polymer backbone. This deprotection reaction changes the polymer polarity for development in an aqueous base. CA systems are highly efficient because each photon absorbed by the resist generates approximately 0.3-2 acids (depending on the photon energy), and each catalyst cleaves hundreds of bonds so a low radiation dose is "amplified" through chemistry. However, the excellent sensitivity of CA resists comes at a price, because acid diffusion during reaction will limit the pattern resolution of CA resists. While CA resists have been studied for more than 40 years, there are no quantitative models that predict the spatial extent-of-reaction with nanoscale resolution. This poses an increasingly important roadblock for the semiconductor industry, as current research and development efforts are targeting sub-10 nm feature sizes.Intellectual Merit:The aim of this research program is to identify the fundamental physics and chemistry that produce anomalous catalyst transport and catalyst deactivation. The PI hypothesizes that (i) anomalous catalyst transport is induced by dynamic heterogeneities in the glassy polymer films; and (ii) catalyst loss is a signature of acid-catalyzed side reactions. A series of experiments are planned that will reveal these effects. The knowledge acquired through this research will be developed into a predictive lithography tool that can accelerate materials development and process optimization. The spatial extent-of-reaction in CA resists cannot be directly measured with experiments, so experimental investigation needs to be coupled to models that predict composition at nanometer length scales. The intellectual merit of this research is the development of an efficient, quantitative, and spatially-resolved reaction-diffusion model for CA resists that is applicable in a wide range of processing conditions with parameters determined by experimental investigation. To achieve this goal, the study will employ a minimal set of variables to be determined through optimization while incorporating the underlying physics and chemistry of the glassy polymer matrix and acid catalyst. The framework developed through this research will offer a means to investigate processing conditions and formulations that have yet to be realized in laboratory experimentation.Broader Impacts :The outcomes of this research program may immediately impact materials design and process development for next-generation lithography, as predictive models reduce or eliminate the need for iterative experimentation. After establishing the applicability of the anomalous transport model over a wide range of conditions, detailed descriptions of the method will be available to the general public via publications and presentations, furthering the development of lithography simulation that remains a bottleneck in industrial applications. The students engaged by this program will receive training in polymer physics and chemistry, computational methods, and designing experimental procedures. The PI has a record of engaging high school students and undergraduate students in laboratory research, and also participates in community outreach through NSF-funded K-12 camps at the University of Houston. Outcomes of this program will be incorporated into the PI's graduate course "Chemical Processing for Microelectronics."