Low-temperature solderless Cu–Cu bonding is an important technology for advanced packaging, such as fine-pitch 3-D packaging and heterogeneous integration. In this study, we prepared an oxidation-free Cu surface using an optimized N ₂ plasma process in a two-step Ar/N ₂ plasma treatment based on the design of the experiment method, to improve direct Cu–Cu bonding quality at 260 °C. The N ₂ plasma treatment process was optimized using the Minitab optimizer with chemical state results obtained by X-ray photoelectron spectroscopy (XPS) analysis. The Cu surface treated under the two-step Ar/N ₂ plasma with optimized N ₂ plasma conditions not only formed Cu nitride well, but the surface remained without further oxidation for at least one week at room temperature. The Cu–Cu bonding was performed at the low bonding temperature of 260 °C and low bonding pressure of 0.9 MPa for 1 hour, and the bonded interface was evaluated using scanning acoustic tomography (SAT) and field emission scanning electron microscope (FE-SEM) images. We measured shear strength to estimate the bonding interface quality of the oxidation-free Cu–Cu bonding specimen. A maximum shear strength of 62.6 MPa was obtained. Our bonding results demonstrated remarkably improved Cu–Cu bonding quality compared with other previous Cu–Cu joint studies that used Sn, Cu/Ag nanoparticles, or Cu composites.

中文翻译：

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低温（260°C）无焊点Cu-Cu键合用于小间距3-D封装和异构集成

低温无锡Cu–Cu粘合是用于高级封装（例如小间距3-D封装和异构集成）的一项重要技术。在这项研究中，我们根据实验方法的设计，使用经过优化的N ₂等离子体工艺，在两步Ar / N ₂等离子体处理中制备了无氧化的Cu表面 ，以改善260°C时Cu-Cu的直接键合质量C。使用Minitab优化器优化了N ₂等离子体处理过程，并通过X射线光电子能谱（XPS）分析获得了化学状态结果。经过优化的N ₂在两步式Ar / N ₂等离子体 下处理的Cu表面 等离子体条件不仅能很好地形成氮化铜，而且在室温下至少一周还没有进一步氧化就保留了表面。Cu-Cu键合在260°C的低键合温度和0.9 MPa的低键合压力下进行1小时，并使用扫描声层析成像（SAT）和场发射扫描电子显微镜（FE-SEM）评估了键合界面） 图片。我们测量了剪切强度，以估计无氧化铜-铜粘结试样的粘结界面质量。获得的最大剪切强度为62.6 MPa。与其他先前使用Sn，Cu / Ag纳米颗粒或Cu复合材料的Cu-Cu联合研究相比，我们的结合结果表明Cu-Cu结合质量得到了显着改善。