目的 为了应对GaN和Si之间巨大的晶格失配与热膨胀系数差异带来的界面应力与可靠性挑战,通过表面活化键合技术实现高质量的GaN/Si异质集成,并探究其微观键合机理与宏观性能的关联。方法 采用Ar原子束对GaN与Si晶圆表面进行活化预处理,随后进行直接键合与不同温度的退火处理。利用XPS、AFM、SAM、TEM以及EDX等表征方法对键合界面进行原子尺度的结构表征与元素分布分析,以揭示界面微观结构。结果 TEM分析表明,界面处形成了一层厚度均匀约为5 nm的非晶过渡层。EDX线扫描结果显示,Ga、Si、N、O等元素在该界面区域发生了明显的互扩散,扩散宽度约为8 nm。结合宏观测试,发现经500 ℃退火的样品平均键合强度最高,达到10.5 MPa,晶圆键合率超过90%。结论 界面非晶层与元素互扩散是表面活化键合工艺在原子尺度上的关键产物。非晶层起源于羟基化表面的脱水缩合反应（形成Si—O—Ga网络）,并作为高速扩散通道促进了元素互扩散。该成分渐变的非晶过渡层有效地弛豫了晶格与热失配应力,是实现高强度、高可靠性GaN/Si异质集成的核心微观结构。
Abstract
The heterogeneous integration of gallium nitride (GaN) with silicon (Si) substrates presents a transformative pathway for advancing next-generation high-power, high-frequency, and optoelectronic devices, leveraging the superior electronic properties of GaN and the mature, cost-effective manufacturing platform of Si. However, this integration is fundamentally challenged by a significant lattice mismatch and a substantial difference in coefficients of thermal expansion between the two materials. These inherent material incompatibilities induce severe interfacial thermo-mechanical stresses during post-bonding thermal processes, which can lead to wafer bowing, interface delamination, crack propagation, and ultimately, device failure. The work aims to systematically investigate the atomic-scale bonding mechanisms and interfacial microstructure evolution in GaN/Si heterostructures fabricated via SAB technology, thus elucidating how the SAB process mediates the formidable material disparities, correlating the nanoscale interfacial features with the macroscopic bonding quality and mechanical strength, and ultimately establishing a process-structure-property relationship that guides the fabrication of reliable heterogeneously integrated devices.
To achieve these objectives, 4-inch GaN and Si wafers were employed as the starting materials. The key innovation in sample preparation was the surface activation pretreatment. This involved exposing the mirror-polished GaN and Si surfaces to a beam of Ar ions in a vacuum environment. The wafers were then brought into intimate contact for pre-bonding at room temperature. A critical annealing step was performed in a controlled atmosphere furnace, with a particular focus on identifying the optimal temperature, which was determined to be 500 ℃ based on a series of parametric studies. The interfacial integrity and bonding rate were initially evaluated non-destructively through scanning acoustic microscopy (SAM). The core microstructural and chemical analysis was conducted via advanced transmission electron microscopy (TEM). Cross-sectional TEM lamellae were prepared via focused ion beam (FIB) milling. High-resolution TEM (HRTEM) imaging was used to resolve the atomic structure at the bonded interface. Complementary scanning TEM (STEM) mode coupled with energy-dispersive X-ray spectroscopy (EDS) was employed to perform precise line scans and elemental mapping across the interface, providing quantitative data on compositional gradients and interdiffusion profiles.
The SAM analysis showed that non-activated bonding samples exhibited poor bonding quality with large, contiguous un-bonded areas, while SAB-treated samples showed excellent bonding uniformity with only sporadic, point-like defects. Mechanical tests confirmed that the maximum bonding strength for samples annealed at 500 ℃ was 10.5 MPa. The TEM analysis revealed the nanoscale origin of this superior performance. At the heart of the GaN/Si interface, a distinct, continuous, and remarkably uniform amorphous interlayer with an average thickness of approximately 5 nm was consistently observed. This interlayer displayed no long-range crystallographic order, separating the single-crystal lattices of GaN and Si. The STEM-EDS line scans provided compelling evidence of active atomic intermixing. The intensity profiles for Ga and Si did not exhibit an abrupt step-function change at the nominal interface. Instead, they demonstrated a gradual transition over a width of 8 nm, indicating mutual interdiffusion. Furthermore, signals for oxygen (O) and nitrogen (N) were also present and intermingled within this interfacial zone. The oxygen signal peaked within the amorphous interlayer, confirming its role as a key constituent. This combination of an amorphous microstructure and elemental interdiffusion constituted the defining characteristic of the SAB-formed interface.
In conclusion, this work conclusively demonstrates that the formation of a nanoscale amorphous interlayer coupled with interfacial element interdiffusion is the fundamental mechanism responsible for successful, high-strength GaN/Si integration via surface-activated bonding. This work provides a comprehensive and coherent atomic-to-macroscopic understanding of SAB technology for GaN/Si integration. It is highlighted that the deliberate creation of a disordered, graded interfacial nanocomposite is the key to overcoming the challenges of heterogeneous integration, offering vital insights for the design and fabrication of robust wide-bandgap semiconductor devices on silicon platforms.
关键词
GaN/Si异质界面 /
界面应力 /
界面非晶层 /
元素互扩散 /
晶圆键合 /
表面活化 /
羟基化
Key words
GaN/Si heterojunction interface /
interfacial stress /
interfacial amorphous layer /
interdiffusion of elements /
wafer bonding /
surface activation /
hydroxylation
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基金
国家自然科学基金（62204050）; 江苏省高等学校基础科学研究面上项目（23KJB430036）; 无锡学院引进人才科研启动项目（2026r016）
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