基于纳米二氧化硅浆料的化学机械抛光研究

Chemical Mechanical Polishing Research of Nano Silica Slurry

摘要:

化学机械抛光技术是当今时代能实现集成电路(IC)制造中晶圆表面全局平坦化的重要技术。集成电路芯片上各个功能元器件制作完成之后，需用金属导线按照特定的功能将其连接。金属铜具有低电阻率、高导热系数和优异的抗电迁移能力，是实现互连最为重要的金属材料。目前，主要采用双大马士革工艺实现芯片各元器件之间的铜导线互连，该工艺对每一层布线后铜的表面平整度有非常高的要求。因此，需采用合适的化学机械抛光技术对铜导线进行处理。研发了一款以纳米SiO₂为磨料的化学机械抛光液，可用于金属铜及其合金的化学机械抛光作业，浆料pH值在9—10之间且质量分数可调，研究了抛光液磨料含量和抛光工艺参数对其抛光铜片效果的影响。结果表明：抛光液中的纳米SiO₂磨粒原生粒径为(50±20) nm，比表面积为(50±10) m²·g^-1，粒径分布均匀，且能长时间保持稳定分布状态，经过约280 d的跟踪监测，浆料中SiO₂粒子中位粒径仅增大4.5%，浆料稳定性良好；抛光可实现单质铜表面亚纳米级精度，在抛光液磨料质量分数为25%、抛光加载压力为10 N、抛光头和抛光盘转速为150 r·min^-1且逆向旋转的工艺条件下，单质铜表面粗糙度最低，可达1.33 nm；单质铜的材料去除率最高可达160 nm·min^-1，能够满足IC制造过程中晶圆表面快速平坦化加工的需求。

Abstract:

Chemical Mechanical Polishing （CMP） is widely recognized as the sole method capable of achieving global planarization of wafer surfaces in contemporary integrated circuit （IC） manufacturing. Once the fabrication of various functional components on an IC chip is completed， they need to be interconnected using metal wires according to specific functions. Among these metals， copper stands out due to its low resistivity， high thermal conductivity， and excellent resistance to electromigration， making it the most crucial material for realizing interconnections. At present， the copper wire interconnection between the components of the chip is mainly completed by the double Damascus process， which has a very high requirement for the surface flatness of the copper after each layer of wiring. Therefore， it is necessary to use appropriate chemical mechanical polishing technology to polish the copper wire after each layer of wiring to achieve partial or comprehensive flatness. In this paper， a CMP slurry with nano silica as abrasive particles is independently developed， which can be used for chemical mechanical polishing of copper and its alloys. The pH value of the CMP slurry is between 9 and 10 and the concentration is adjustable. Through the exploration of the process parameters such as polishing pressure and polishing speed in the polishing process， the sub-nanometer accuracy of the elemental copper surface can be finally achieved. The surface roughness of polished copper can reach 1.33 nm by white light interferometer. In addition， the material removal rate of elemental copper can reach up to 160 nm·min^-1， which can meet the needs of rapid wafer surface flattening in the IC manufacturing process. The CMP slurry used nanometer SiO₂ abrasive particles with a native particle size of （50±20） nm， a specific surface area of （50±10） m²·g^-1， and a uniform size distribution in the slurry. It could maintain a stable size distribution for a long time， and after approximately 280 days of tracking monitoring， the median particle size of SiO₂ particles in the slurry only increased by 4.5%， indicating good stability of the slurry.