Career: Silicon Etching: Gas-Surface Dynamics and Profile Evolution

摘要CTS-9623450这个项目讨论了非弹性散射和反应性散射在半导体蚀刻中的重要性。利用最近发明的具有平移能量的氟原子高超声速中性束，在3-25 eV范围内对硅的稳态腐蚀过程中的气体表面动力学进行了基础研究，并对硅中的亚微米特征进行了腐蚀研究，以了解中性束是如何腐蚀的。这项工作是基于轮廓演化建模和平移能量在3到18 eV之间的氟原子束的实验的最新结果。用氟化学方法(无侧壁沉积)在室温下对硅进行各向异性腐蚀，证明了这种束流的能力。这是可能的，因为在所使用的高平动能下发生直接反应。碰撞诱导脱附(CID)被认为是导致氟化硅在较高能量下从SiFx层脱附的速率增加的机制。在CID模式下快速去除SiF3产物可实现暴露表面的快速氟化，这提高了氟的利用率，进而导致热解吸未反应的氟原子通量的减少。减少分散到侧壁的氟显著改善各向异性。对未反应F原子和反应产物(SixFy)在刻蚀过程中离开SiFx层的能量和通量进行了基本测量。此外，在二氧化硅表面也进行了类似的测量。二氧化硅在今天的晶圆上无处不在(例如，作为硬掩膜、栅氧化物等)。而其表面的散射也会影响轮廓的演化。除了提高对气体表面动力学的基本理解外，这些测量还提供了相互作用的物理和化学描述，并被并入了轮廓演化的蒙特卡罗模拟器中。基于SiFx上详细的散射实验的初步计算表明，它捕捉到了轮廓特征，如所谓的“微沟槽”，即在刻蚀特征底部出现凹槽的现象。对该模型进行了改进，使其能够描述图形相关的刻蚀、三维效应和刻蚀表面的粗糙度。通过考虑微结构充电和离子偏转效应，轮廓模拟器的适用性得到了增强，使其能够与其他人开发的等离子体反应器模型相结合，为下一代超高密度半导体器件设计刻蚀工具。还进行了刻蚀实验以支持该模型，并验证了轮廓特性的预测。了解预测和观测偏离理想各向异性剖面的来源有望实现对最终剖面的控制。通过对MOS器件栅氧化层的电损伤研究，展示了该技术的潜力。最后，在技术完善的基础上，尝试制作量子受限和光子禁带结构。揭示了经典化学工程概念与现代电子材料加工技术之间的关系，使化学工程的研究与教学相结合。例如，在本科生的热力学课程中提供了一些特殊的主题，例如等离子体中的平衡和表面热力学，这些都是传统上不会涉及的。本科生实验室计划在诊断学方面有实践经验的介绍性等离子体实验。P.I.S实验室还为本科生提供了扩展的研究项目，以提高他们对实验科学的欣赏。在研究生层面，除了电子材料处理课程外，还计划开设一门关于表面光束改性的新课程，该课程基于这项拟议研究的结果和理解。*

ABSTRACT CTS-9623450 This project addresses the importance of inelastic and reactive scattering in the etching of semiconductors. Experiments are proposed with a recently invented hypersonic neutral beam of fluorine atoms with translational energies in the 3-25 eV regime for fundamental studies of the gas-surface dynamics occurring during steady-state etching of silicon and etching studies of submicron features in silicon in order to understand how neutral beams etch. The effort is based on recent results from profile evolution modeling and experiments with flourine atom beams with translational energies between 3 and 18 eV. Anisotropic etching of silicon at room temperature with fluorine chemistry (no sidewall deposition) is demonstrated as a proof of the capabilities of such beams. This has been possible because of direct reactions occurring at the high translational energies employed. Collision-induced desorption (CID) has been implicated as the mechanism responsible for the increased desorption rate of fluorinated silicon moieties from the SiFx layer at the higher energies. Rapid removal of the SiF3 product in the CID mode enables rapid fluorination of the exposed surface, which increases fluorine utilization and, in turn, results in a reduction of the thermally desorbing unreacted fluorine-atom flux. Reduction of scattered fluorine to the sidewalls dramatically improves anisotropy. Fundamental measurements of the energy and flux of unreacted F atoms and reaction products (SixFy) leaving the SiFx layer during etching are made. Moreover, similar measurements are performed on the silicon dioxide surface. Silicon dioxide is ubiquitous on today's wafers (e.g., as a hard mask, gate oxide, etc.) and scattering on its surface will also affect profile evolution. Besides improving fundamental understanding of gas-surface dynamics, these measurements provide for a description of the physics and chemistry of the interaction, which is incorporated into a Monte Carlo simulator of profile evolution. Preliminary calculations based on detailed scattering experiments on SiFx are shown to capture profile peculiarities such as the so-called "microtrenching", that is, the appearance of grooves at the bottom of etched features. The model is improved to describe pattern-dependent etching, three-dimensional effects, and the roughness appearing on etched surfaces. By including microstructure charging and ion deflection effects, the applicability of the profile simulator is enhanced, enabling its combination with plasma reactor models (developed by others) for designing the etch tools for the next generation of ultrahigh-density semiconductor devices. Etching experiments are also performed to support the model and verify predictions of profile peculiarities. Understanding the origin of predicted and observed deviations from the ideal anisotropic profile is expected to enable control over the final profile. Electrical damage studies on gate oxides of MOS devices are done as a demonstration of the potential of the technique. Finally, upon perfection of the technique, fabrication of quantum-confined and photonic bandgap structures is attempted. In order to integrate research with education in chemical engineering, the relation between classical chemical engineering concepts and modern electronic material processing techniques is exposed. As an example, special topics are offered in the undergraduate thermodynamics class, such as equilibrium in plasmas and surface thermodynamics, which are not traditionally covered. An introductory plasma experiment is planned for the undergraduate laboratory with hands-on experience in diagnostics. Extended research projects are also offered to undergraduates in the P.I.'s laboratory to enhance their appreciation of experimental science. At the graduate level, in addition to a course on electronic materials processing, plans are made to offer a new course on beam modification of surfaces, which is based on results and understanding obtained from this proposed research. ***