目的 以薄膜修饰Cu凸块和镀覆一定厚度Ag层的Cu基板分别作为键合偶的两端,在低温低压条件下实现了Cu-Cu键合互连,解决了键合过程中由于高温高压条件诱发的热冲击和缺陷问题,保证了敏感的薄芯片在封装中的可靠性。方法 以在Cu凸块上沉积出的平均高度约为2 μm,根部平均直径为500~800 nm的针锥状Cu晶薄膜和在Cu基板上沉积出的2 μm 厚度的多孔Ag片层为基础,在温度为200 ℃,压力为5 MPa 条件下,在空气氛围中键合25 min,实现Cu-Cu互连键合。利用扫描电子显微镜（SEM）、透射电子显微镜（TEM）等分析手段,对键合接触层的组织构架、化学组成及其性能展开了系统表征。结果 Cu凸块镀覆的修饰层为呈现针锥阵列结构的Cu晶层,针锥结构的高度和分布均匀一致,顶角角度偏小,具有明显的尖端效应。在Cu基板上镀覆的Ag层为均匀的多孔纳米Ag片结构,呈现出梭形纹理。在键合时,较硬的Cu针锥插入较软的Ag层中,且依然保持清晰的锥形轮廓,Cu晶微锥结构与Ag之间存在充分的原子尺寸的嵌入与键合,产生机械镶嵌效果。在最优参数条件下,键合界面的平均剪切强度为38.9 MPa,黏结界面非常致密基本无缝隙存在。结论 由于Cu晶表面修饰层的特殊形貌、片状Ag层的纳米尺寸效应和变形效应,键合在低温低压、空气氛围中完成,不需要超高真空、超平整表面以及复杂的后续热处理工艺条件以增加键合界面剪切强度,提高了封装的可靠性,该技术有望获得广泛的实际应用。
Abstract
A thin-film-modified Cu bump serves as one end of the bonding pair, while a Cu substrate coated with a specific thickness of Ag layer functions as the other end. Cu-Cu bonding interconnects are achieved under low-temperature and low-pressure conditions. This approach resolves thermal shock and defect issues induced by high-temperature and high-pressure bonding conditions, ensuring the reliability of sensitive thin chips during packaging. The work aims to introduce nanoscale structures and materials into the bonding process to explore a low-temperature, no-solder, no-flux insertion bonding method. Compared to other Cu-Ag bonding techniques, this bonding process can be completed at low temperatures and on flat surfaces due to the nanoscale characteristics of the Cu bump modification layer and the deformation effect of the porous Ag sheet.
The preparation of thin-film-modified Cu bumps was achieved by electroplating Cu columns and applying a chemical copper plating process to form a micrometer-thick film on patterned chips. This method was based on a needle-cone-shaped Cu crystal film deposited on the Cu bump with an average height of approximately 2 μm and an average root diameter of approximately 500-800 nm, and a 2 μm thick porous Ag layer deposited on the Cu substrate. Cu-Cu interconnect bonding was achieved by bonding for 25 minutes at 200 ℃ and 5 MPa pressure in an air atmosphere. The connection between the Cu micro-cone array structure on the Cu bump and the porous Ag layer was achieved. Upon completion of bonding, the average shear strength at the bonding interface was measured with a destructive shear test method. The cutting tool was pushed down on the Cu bump at a speed of 1.2 mm/min, with the tool sensor recording the maximum shear force. The microstructure, chemical composition, and related properties of the bonded contact layer was investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thickness of the coating was measured with an X-ray fluorescence thickness gauge.
The modified layer deposited on the Cu bump exhibited a Cu crystalline layer with a needle-cone array structure. The height and distribution of the needle-cone structure were uniform and consistent. The apex angles were relatively small, exhibiting a pronounced tip effect. The Ag layer deposited on the Cu substrate formed a uniform porous nano-Ag flake structure with a spindle-shaped texture. During bonding, the harder Cu needle cones penetrated the softer Ag layer while retaining their distinct conical profiles. Sufficient atomic-scale interlocking and bonding occurred between the Cu micro-cone structure and Ag, creating a mechanical interlocking effect. Under optimal parameter conditions, the average shear strength at the bonding interface reached 38.9 MPa, with an extremely dense bonding interface exhibiting virtually no gaps. Due to the unique morphology of the Cu crystal surface modification layer, the nanoscale effects of the flake-like Ag layer, and the deformation effects, bonding is achieved under low-temperature and low-pressure conditions in an air atmosphere. This method eliminates the need for ultra-high vacuum, ultra-flat surfaces, and complex subsequent heat treatment processes to enhance bonding interface shear strength, thereby improving package reliability. This technology holds promise for extensive practical applications.
关键词
Cu晶 /
Ag层 /
键合 /
电子封装 /
扩散
Key words
Cu crystal /
Ag layer /
bonding /
electronic packaging /
diffusion
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基金
智能制造现代产业学院专项经费（0220119）; 广东省教育科学规划项目高等教育专项（2023GXJK643）
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