集成电路铜互连工艺中先进扩散阻挡层的研究

【作者】 谢琦；

【导师】 屈新萍；

【作者基本信息】 复旦大学 ， 微电子学与固体电子学， 2008， 博士

【摘要】 随着集成电路器件尺寸的持续缩小,互连延迟越来越成为制约集成电路发展的瓶颈问题。在32nm及以下技术节点,互连工艺中磁控溅射制备的Ta/TaN双层结构扩散阻挡层和铜籽晶层由于台阶覆盖特性不好将带来各种问题。为了降低互连线的电阻,必须在保证器件性能的同时,减小扩散阻挡层和籽晶层的厚度,而且两者必须在高深宽比结构中有非常好的台阶覆盖特性,因此迫切需要研究新型扩散阻挡层/黏附层材料和新型互连工艺,这是半导体发展路线图中提出的一个非常重要的挑战。采用新型扩散阻挡层/黏附层材料和新型淀积工艺有许多问题需要研究,包括新型扩散阻挡层和铜以及低介电常数介质之间的界面反应、新型原子层淀积（Atomic Layer Deposition,ALD）的工艺、ALD薄膜生长机理、表面化学、材料的物理性能和电学性能之间的关系等。对这些问题的研究不仅有科学价值,对未来的阻挡层发展方向提出的一些解决方案也有应用价值。基于以上问题本文围绕Cu互连扩散阻挡层“新材料”和“新工艺”两个主题,分成三个部分加以阐述:1:新型阻挡层材料W碳化物的研究实验比较了相同厚度的Ta/TaN双层结构和Ta或TaN单层结构扩散阻挡层性能,分析了Ta/TaN双层结构优越稳定性的原因,提出了Ta/TaN双层薄膜的微结构演变过程以及其阻挡层的失效机理。用共溅射方法制备了各种不同W/C比例的W_xC_y薄膜,比较了不同W_xC_y薄膜阻挡层的稳定性,利用在线激光散射（In-situ LLS）测试比较了Cu在各种W_xC_y薄膜上的团聚行为,利用Kissinger方程提取了Cu的团聚激活能（Ea）。研究了W碳化物扩散阻挡层对物理气相淀积Cu薄膜（厚度为100nm）形成孪晶的影响。实验表明在WC扩散阻挡层上无论是刚淀积的还是退火后的Cu薄膜都能形成纳米尺度孪晶,而在W阻挡层上没有类似现象。研究发现Cu在WC阻挡层上的界面能比在W阻挡层上的高很多,而界面能对于形成Cu孪晶非常关键。从动力学角度考虑界面上整个铜晶粒的扩散和旋转并提出Cu孪晶的形成机理。结合应力测试研究了Cu薄膜孪晶和团聚行为的联系,孪晶形成造成的应力梯度影响了空位的浓度分布和扩散行为,使得在退火过程中产生空洞。2:原子层淀积新工艺方法制备研究超薄TiO₂和TaN扩散阻挡层研究了用两种金属有机物先体TDMAT、Ti isopropoxide和三种反应源（H₂O气,H₂O等离子体以及O₂等离子体）制备超薄TiO₂薄膜。用密度函数理论（DFT）计算了原子反应过程,研究了先体脱附行为对TiO₂ALD生长模式及工艺窗口的影响。测试了不同工艺条件生长的TiO₂薄膜的结晶情况,分析了超薄TiO₂薄膜中C杂质含量对薄膜结晶的影响。研究了用PDMAT金属有机物先体和两种反应源（NH₃和N₂等离子体）制备TaN薄膜,比较不同反应源对ALD生长模式的影响。比较了不同工艺条件对ALD生长的TaN阻挡层稳定性的影响,证实低反应气体气压和长时间等离子体曝露可以优化淀积工艺。3.铜互连中新型籽晶层/黏附层的研究研究了物理气相淀积制备的Ru单层,Ru/TaN、Ru/WCN、Ru/TaCN双层结构扩散阻挡层性质,发现在Ru膜上的Cu薄膜在一定退火温度区间有氧化增强现象。发现Ru/TaCN比Ru/TaN双层结构具有更好的稳定性。研究了用等体子体增强原子层淀积方法制备Ru薄膜,使用的金属有机物先体是Ru（EtCp）₂,反应物为NH₃等离子体。研究了Ru分别在Si,TiN/Si和TaN/Si三种衬底上的ALD生长模式和薄膜性质。研究了受氧化的TaN衬底对Ru ALD生长的抑制影响。测试了ALD生长的Ru,Ru/TiN以及Ru/TaN等阻挡层的稳定性。初步研究了ALD Ru（7nm）/ALD TaN（5nm）双层结构在低k材料（k=2.5）上的性质。更多还原

【Abstract】 With continuous scaling down of the devices, the material and process of interconnect technology also require corresponding innovation. In the 32nm and beyond technology node, many issues arise due to the poor conformality caused by relative thick sputtered Ta/TaN bi-layer and seed layer. In order to decrease the resistivity of interconnect lines as well as meet the performance requirement of the device, the need of decreasing barrier and seed layer thickness has increased, and also the aspect ratio of trench and via has increased. Therefore, researches on novel diffusion barrier/seed layer materials and process have attracted great attention. There are many issues need to be studied for using novel material for diffuision barriers/adhesion layer and novel deposition process, which includes interface reaction within Cu/diffusion barrier/Si or low k system, also atomic layer deposition （ALD） process and growth mechanism, surface chemistry and low k surface pretreatment.Based on "novel material" and "novel process" for the diffusion barrier, the main contents and results of this dissertation are summaried as follows.1: Novel diffusion barrerier material - W carbidesTa/TaN bi-layer structure and Ta or TaN single layer with same total thickness are compared as diffusion barrier. The reasons for super thermal stability of Ta/TaN bi-layer structure are analysed. The microstructure evolution and the failure mechanism for Ta/TaN bi-layer diffusion barriers are proposed.W_xC_y films with different W/C ratio are prepared by co-sputtering method. The stability of different W_xC_y films as diffusion barriers is compared. The agglomeration behavior of Cu on different W_xC_y films are characterized by in-situ laser light scattering （In-situ LLS） test. The Cu agglomeration activation energys （Ea） on diffirent W_xC_y films are derived by using Kissinger equation.The effects of W carbides diffusion barriers on the twinning formation of PVD sputtered Cu films （100nm） are studied. It is found that nano-scale twinning can be formed in the Cu films deposited on the WC diffusion barrier before or after annealing process, while there is no similar result for Cu on W barrier. It reveals that the interface energy for Cu on WC is much higher than that for Cu on W and it is critical for the formation of Cu twinning. The Cu twinning formation mechanism is proposed with consideration of the whole Cu grains diffusion and rotation. The correlation between Cu twinning and Cu agglomeration is studied by stress measurement. The stress gradient caused by twinning formation affacts the vacancy concentration distribution and diffusion behavior, which will cause the voids formation after annealing process.2: Research on atomic layer deposition of TiO₂ and TaN diffusion barriersUltra thin TiO₂ films prepared by two kinds of metal-organic precursors TDMAT, Ti isopropoxide and three kinds of reactants （H₂O vapor, H₂O plasma and O₂ plasma） are studied. The atomic reaction paths are calculated by using density functional theory （DFT）. The effects of precursors desorption on the TiO₂ ALD growth mode and process window are discussed. The crystallization behavior of the TiO₂ thin films with diffirent process conditions is studied. The effects of the C contents on the crystallization temperature for ultra thin TiO₂ films are analyzed.TaN films prepared by MO precursor PDMAT and two kinds reactants （NH₃ and N₂ plasma） are studied. The effects of diffirent reactants on the TaN ALD growth mode are discussed. The effects of different reactants on the stability of ALD growth TaN diffusion barriers are compared. It is revealed that the process can be optimized by using lower reactant gas vapour pressure and longer plasma exposure time.3: Novel seed/adhersion layer for Cu inteconnectRu single layer, Ru/TaN, Ru/WCN and Ru/TaCN bi-layer structure diffusion barriers prepared by physical vapor deposition are studied. The oxidation enhanced effect on Cu from under Ru layer is revealed.Plasma enhanced atomic layer deposition of Ru films prepared with MO precursor Ru（EtCp）2 and NH3 are studied. The growth mode and films properties of ALD Ru on three kinds of substrates including Si, TiN/Si and TaN/Si are compared. Results show that the surface properties of the TaN substrate are crutial to the nucleation for ALD Ru. The stability of ALD grown Ru, Ru/TiN and Ru/TaN barriers is tested. The Ru/TaN barrier can stand up annealing of 400℃/30min on Si substrate. However, results show that Cu has diffusied to the low k substrate for the ALD Ru（7nm）/ALD TaN（5nm） barriers on porous low k material （k=2.5）.更多还原