Supporting data for “Microstructure and orientation control of electro-deposited copper and its application in advanced electronic packaging”

In advanced IC packaging, chip stacking has emerged as a promising technology to overcome the physical limitations imposed by Moore's Law while continuing to achieve higher interconnect density and compact form factors. The electroplated copper used for connections in these packages has varying demands for structural stability across different procedures. For instance, in redistribution layer (RDL) applications, the width and pitch of RDLs for device connections continue to shrink, with some high-end RDLs potentially featuring lines as narrow as 2 μm. This places greater demands on the stability of copper structures to resist thermal migration and electromigration. To satisfy these needs, a composite Cu structure that combines fine grains and nanotwins was successfully developed, providing enhanced super filling capabilities and improved structural stability. This structure can effectively resist surface damage even after extended periods, offering a promising solution for achieving finer RDL in advanced packaging technologies. Furthermore, it exhibits an EM lifetime 2.9 times longer than its coarse-grain RDLs counterpart.Conversely, for bonding applications that connect vertical dies, it is essential to use electroplated copper with lower structural stability to minimize the thermal budget of Cu-Cu direct bonding and decrease potential damage to temperature-sensitive device. To satisfy these needs, a unique composite Cu structure is developed by incorporating a nanograin structure into the (111)-oriented coherent nanotwinned copper. This metastable composite structure remains stable at room temperature, ensuring its durability throughout long fabrication processes after electroplating, and then undergoes grain growth upon exposure to higher temperatures during bonding. The nanograin-enriched area of the composite copper undergoes substantial grain growth and facilitates atomic movement with adjacent nanotwins, enabling the growth of grains across the bonding interface to enhance the bonding quality. Successful Cu-Cu direct bonding can be achieved at a low thermal budget of 170 °C for 30 minutes, resulting in improved mechanical and electrical performance as evaluated by mechanical shear tests, electromigration tests, and thermal cycling tests.To further reduced the thermal budget of bonding process, then a super unstable nanograin copper structure specifically aims for Cu-Cu bonding at temperatures below 100 °C, or even at room temperature. This super unstable nanograin copper structure exhibits rapid self-annealing behavior, undergoing complete recrystallization at room temperature within 250 minutes or at 60°C within just 5 minutes. The driving force for grain growth can be attributed to the large excess energy stored in the high-angle grain boundaries (HAGBs) and dislocations. The calculated activation energy for the coarsening of super unstable copper grains is approximately 0.57 eV/atom, which is significantly lower than those reported for nanograin coppers using the same differential scanning calorimetry method.

在高级集成电路封装领域，芯片堆叠技术已崭露头角，成为突破摩尔定律物理限制、持续实现更高互连密度和紧凑型外形尺寸的可行技术。在这些封装中使用的电镀铜连接材料，对于结构稳定性的要求因不同工艺而异。例如，在再分布层（RDL）应用中，用于设备连接的RDL的宽度和间距持续减小，一些高端RDL的线条宽度可能窄至2微米。这要求铜结构具备更高的稳定性以抵御热迁移和电迁移。为满足这些需求，一种结合了细晶粒和纳米孪晶的复合铜结构成功研发，该结构提供了增强的超填充能力和改进的结构稳定性。该结构即便在长期使用后仍能有效抵抗表面损伤，为在先进封装技术中实现更精细的RDL提供了有希望的解决方案。此外，该结构的电迁移寿命比其粗晶粒RDL对应物高出2.9倍。相反，对于连接垂直晶圆的粘合应用，使用结构稳定性较低的电镀铜至关重要，以降低Cu-Cu直接粘合的热预算并减少对温度敏感器件的潜在损害。为满足这些需求，通过将纳米晶结构引入（111）取向的相干纳米孪晶铜中，开发了一种独特的复合铜结构。这种亚稳态复合结构在室温下保持稳定，确保电镀后在长期制造过程中的耐用性，并在粘合过程中暴露于较高温度时发生晶粒生长。复合铜中的纳米晶富集区域经历显著的晶粒生长，并促进与相邻纳米孪晶的原子迁移，从而在粘合界面促进晶粒生长，提高粘合质量。在170°C的低温热预算下，经过30分钟的Cu-Cu直接粘合成功实现，并通过机械剪切测试、电迁移测试和热循环测试评估，提高了机械和电气性能。为进一步降低粘合过程的热预算，一种针对在低于100°C或室温下Cu-Cu粘合的超级不稳定纳米晶铜结构被专门开发。这种超级不稳定纳米晶铜结构表现出快速的自修复行为，在室温下250分钟内或60°C下仅需5分钟即可完成完全再结晶。晶粒生长的驱动力可归因于高角度晶界（HAGBs）和位错中储存的大量过剩能量。对于超不稳定铜晶粒粗化的计算活化能约为0.57 eV/atom，这显著低于使用相同差示扫描量热法测量的纳米晶铜的活化能。