添加剂及热处理对钴互连镀层电性能的影响机理研究

Effects of Additives and Heat Treatment on the Electrical Properties of Cobalt Interconnect Plating

随着芯片互连尺寸缩小至10 nm节点以下,钴(Co)凭借其短电子自由程、优异的抗电迁移和扩散阻挡性能,被提出作为替代铜的新一代互连材料。抑制剂的加入可以实现Co互连的电沉积超填充,但同时会造成Co电阻率的增加。热处理是改善电性能的常用手段,然而抑制剂和热处理对Co电性能的共同影响及机理有待研究。为研究其共同影响机理,评估了丁二酮肟(DMG)、聚乙烯亚胺(PEI)和2-巯基-5-苯并咪唑磺酸(MBIS)三种抑制剂的电化学行为,电沉积制备了抑制剂作用下的Co镀层,表征了热处理前后Co的晶体结构、晶粒尺寸和杂质变化。结果表明镀层方阻随着抑制剂浓度的增加而增大。0.02 wt.%DMG、0.0015 wt.%PEI和0.002 wt.%MBIS具有相似的抑制能力,对应镀层具有HCP晶体结构和相似的晶粒尺寸,且300℃热处理后未发生明显变化,镀层的初始方阻和300℃热处理后方阻下降率的大小关系均为0.02 wt.%DMG>0.0015 wt.%PEI>0.002 wt.%MBIS,造成该大小差异的主要原因分别是镀层初始杂质含量和热处理后杂质下降量的不同。此研究为业界选择最佳的添加剂及热处理工艺,以生产具备优越电性能的Co互连线提供了一定的理论支持。

As on-chip interconnect dimension shrinks below 10 nm node,cobalt(Co)is proposed to replace copper as the interconnect material due to its short electron mean free path,super electromigration resistance and excellent diffusion barrier properties.Superconformal Co filling can be achieved by electrodeposition with suppressors,which will simultaneously cause the resistivity increase.Heat treatment is usually carried out to improve the electrical properties.However,little attention has been paid to the combined effect mechanism of suppressors and heat treatment on the electrical properties of Co.To study the combine effect mechanism,electrochemical behaviors of three suppressors,dimethylglyoxime(DMG),polyethyleneimine(PEI)and 2-mercapto-5-benzimidazolesulfonic acid(MBIS)are evaluated,Co coatings are prepared by electrodeposition with these suppressors,and the crystal structure,grain size and impurities change of Co coatings before and after annealing are characterized.The results showed that the sheet resistance of Co increased with the increase of the suppressor concentration.0.02 wt.%DMG,0.0015 wt.%PEI and 0.002 wt.%MBIS have similar inhibition abilities.The corresponding three Co coatings have HCP crystal structure and similar grain sizes,and they did not significantly change after annealing at 300℃.The initial sheet resistances and sheet resistances drop rates of three Co coatings after annealing at 300℃are both 0.02 wt.%DMG>0.0015 wt.%PEI>0.002 wt.%MBIS.These differences were mainly caused by the differences of the initial impurities contents and the impurities decrease after annealing respectively.This research can provide theoretical support for selecting the suitable additives and annealing processes to produce Co interconnects with super electrical properties.