氮化镓等离子体原子选择刻蚀抛光方法研究

氮化镓是一种具有优异电学性能的宽禁带半导体材料，在无线通信、固态照明、功率电子等领域拥有广阔的应用前景。为了实现氮化镓基器件的优异性能，需要得到表面光滑且无亚表面损伤的氮化镓晶圆。传统的氮化镓晶圆抛光方法无法同时兼顾表面质量和材料去除速率，因此，实现氮化镓晶圆的高效率无损伤抛光成为目前亟待解决的问题。等离子体原子选择刻蚀技术可以根据表面成键状态不同的原子间化学反应活化能的差异，而对其进行有选择的去除。作为一种非接触式的加工方法，等离子体原子选择刻蚀技术具有很高的材料去除速率，且不会向材料内部引入应力与损伤。本文在深入研究等离子体原子选择刻蚀机理与工艺的基础上，探究了实现原子选择刻蚀的关键因素，以及表面氧化物的抑制与去除策略，以期实现氮化镓晶圆的高效率无损伤抛光。本文的主要研究内容总结如下。
(1) 研究了基于磨粒的加工方法对氮化镓表面及亚表面质量的影响规律，研磨所形成的亚表面损伤层会损害材料的光学性能。通过比较有无亚表面损伤层对后续晶圆抛光过程的影响，证明了亚表面损伤层的存在是制约氮化镓抛光工艺效率的关键因素。
(2) 建立了大气电感耦合等离子体的多物理场仿真模型。研究了等离子体工艺参数对样品表面温度以及近表面样品表面流速分布的影响规律。通过等离子体刻蚀实验验证了仿真模型的可靠性，为大气等离子体加工提供了工艺指导。
(3) 研究了各项工艺参数对等离子体刻蚀氮化镓的影响规律，揭示了等离子体温度与活性粒子浓度是实现等离子体原子选择刻蚀的关键性因素。基于等离子体原子选择刻蚀技术实现了氮化镓的表面抛光，实现了93 μm/min的材料去除速率。氮化镓在抛光后具有良好的亚表面晶体结构，表明等离子体原子选择刻蚀是一种非破坏性的加工方法。
(4) 研究了大气电感耦合等离子体刻蚀GaN的热影响机制，揭示了氮化镓在高温下的分解机制以及材料缺陷在热刻蚀中的演变规律。分析了等离子体原子选择刻蚀中样品边缘塌陷的形成原因，并阐明了等离子体原子选择刻蚀中活性粒子刻蚀与热分解的协同作用机制。
(5) 分析了等离子体刻蚀后表面氧化物的形成原因，并提出了有效的氧化物抑制与去除策略。采用了降低炬管并持续通入冷却气体的方法，成功地抑制了表面氧化物的生长，使得表面氧化层的厚度降低至4 nm，表面粗糙度降低至Sa 0.55 nm。
本文对等离子体原子选择刻蚀抛光氮化镓的机理与关键技术进行了研究，揭示了实现氮化镓的等离子体原子选择刻蚀的关键因素，成功实现了氮化镓晶片的高效率无损伤抛光。本论文的研究结果将丰富和完善氮化镓晶圆抛光的理论基础与技术手段，推动氮化镓在半导体等高新技术领域的工程应用。

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