集成电路铜互连中钽硅氮扩散阻挡层的制备及其阻挡特性研究

【作者】 刘正；

【导师】 周继承；

【作者基本信息】 中南大学 ， 电子科学与技术， 2008， 硕士

【摘要】 随着集成电路集成度的提高以及特征尺寸的不断下降,传统的Al金属化布线已经不能满足器件发展要求。Cu由于具有低电阻率和高抗电迁移能力可作为Al的替代材料。但Cu与介质层的粘附性差,且铜易扩散进入硅与二氧化硅成为深能级杂质,并且在较低的温度下就会形成铜与硅的化合物,从而影响器件的可靠性。因此,需要在Cu与Si之间加入扩散阻挡层来有效地阻挡Cu向Si中扩散,同时改善Cu膜与基体的结合能力。在综合分析比较了各类阻挡层制备方法、性能特征的基础上,本文采用双靶磁控反应溅射法在p型Si（111）衬底上制备出了不同Si、N含量的Ta-Si-N和Cu/Ta-Si-N的纳米薄膜,并对薄膜样品进行了快速热退火（RTA）。用四探针电阻测试仪（FPP）、原子力显微镜（AFM）、X射线衍射（XRD）、扫描电镜（SEM）、EDS能谱等分析测试方法对各样品的方块电阻、表面形貌、晶体结构、成分等特性进行了表征分析。实验结果表明,Si、N掺杂有利于改善Ta基阻挡层的阻挡性能。Si的掺入能有效抑制钽的氮化物结晶,且随着Si含量的升高,Ta-Si-N阻挡层的非晶化程度提高;而通过向Ta-Si薄膜中掺入N则能有效抑制钽的硅化物结晶,使沉积态的阻挡层由纳米晶转变成非晶态。Ta-Si-N阻挡层的阻挡性能与Si靶溅射功率和N₂/（N₂+Ar）流量比密切相关。固定N₂/（N₂+Ar）流量比时,Si靶溅射功率应存在一最优值,使阻挡性能达到最好。当Si靶功率过大或过小时,阻挡性能较差。在固定Si靶溅射功率的情况下,阻挡性能随N₂/（N₂+Ar）流量比的上升而有所改善,但当薄膜中氮含量大于50%时,阻挡性能改善并不明显。Ta-Si-N阻挡层的失效主要是由Cu扩散引起。其主要失效机制为:Cu通过阻挡层中的晶界扩散,或直接通过阻挡层的非晶结构扩散入Si中,并与Si反应生成Cu₃Si。Ta-Si-N薄膜的结晶温度高,Cu/Ta-Si-N/Si薄膜体系的界面稳定性好,Cu膜与Ta-Si-N阻挡层之间的粘附性好,没有发生Cu膜脱落的现象。更多还原

【Abstract】 With the development of integrated circuit （IC） and increase in the degree of integration, the feature size is shrinking and traditional Al metallization cannot satisfy the requirement of electrical device. To reduce the interconnection delay, Cu metallization is taking the place of traditional Al interconnection due to its lower resistivity and superior resistance to electromigration. However, adhesion of Cu to Si substrate is poor. In addition, Cu atoms are quite mobile and can diffuse into Si easily, leading to formation of Cu-Si compounds. Cu atoms act as deep level impurities, affecting the reliability of devices. Therefore, it is inevitable to add diffusion barrier between Si and Cu.On the basis of a comparative study of the diffusion barriers on their fabrication methods and characteristics, Ta-Si-N thin films and Cu/Ta-Si-N thin films were deposited on p-type Si（111） substrates by dual-targets magnetron reactive sputtering. Then rapid thermal annealing （RTA） was performed on the samples. The sheet resistance, surface morphology, crystalline structures and chemical composition of the films were characterized by four-point probe （FPP） sheet resistance measurement, atomic force microscopy （AFM）, scanning electron microscope （SEM）, X-ray diffraction method （XRD） and energy disperse spectroscopy （EDS）, respectively.The experiment shows that when doped with Si and N, the barrier property of Ta-based thin films is improved. When doped with Si, the crystallization of Ta nitrides can be suppressed effectively. And when Si content gets higher, the degree of amorphism is increased. The as-deposited Ta-Si thin-film is nano-crystalline. When doped with N, the as-deposited thin-film becomes amorphous which means the N addition can suppress the crystallization of Ta silicides effectively. The diffusion barrier property of Ta-Si-N has much to do with Si sputtering power and N₂/（N₂+Ar）. When the N₂/（N₂+Ar） flow rate is fixed, there is an optimal value of the Si target sputtering power and it can make the Ta-Si-N barrier possess the best barrier property and the barrier performance is degraded when Si content is too high or too low. And the diffusion barrier property of Ta-Si-N barrier is improved with the N₂/（N₂+Ar） increasing, but not evidently when N content beyond 50%.The failure of the barriers is mainly attributed to the Cu diffusion. Cu atoms diffuse through grain boundaries of the barriers or diffuse the amorphous structure of Ta-Si-N layers directly, and react with Si to form the Cu₃Si phase.The crystallization temperature of Ta-Si-N thin films is high and the interfacial stability of Cu/Ta-Si-N/Si structures is good. Also, the adhension of Cu with Ta-Si-N is strong, and no Cu film falling is observed.更多还原