【作者】 王新建；

【导师】 吴建生； 董显平；

【作者基本信息】 上海交通大学 ， 材料学， 2009， 博士

【摘要】 随着集成电路制造工艺的发展,铜由于具有低的电阻率和较高的抗电迁移能力而逐渐取代了铝作为互连线材料。当互连线特征尺寸减小到0.5μm以下,相比于互连线材料本身的固有性能,互连线的微观结构对互连线的性能以及可靠性的影响越来越大。合金化作为一种常用的控制薄膜结构,改善薄膜性能的方法引起了越来越多的人的注意。铜合金薄膜的基础研究对预测和改善铜互连线特性,提高未来高性能硅基集成电路可靠性具有指导意义。本研究自制嵌镶组合铜合金靶材,优化制备参数,采用磁控溅射法在不同基底上制备Cu(Cr)和Cu(Zr)合金薄膜,研究Cr、Zr合金掺杂对溅射Cu薄膜微观组织结构及性能的影响。这些研究不仅为Cu(Cr)和Cu(Zr)合金薄膜在微电子领域的应用提供新的支持,而且对设计和开发适合电子材料用的高强度高导电铜合金薄膜具有指导意义。结合磁控溅射仪特点,自制Cu1-xMx(M=Cr, Zr)嵌镶组合靶材。通过溅射法分别制备不同合金含量的Cu1-xMx(M=Cr, Zr, x<0.05,原子百分比)薄膜。合金薄膜纯度高,成分可控;且制备工艺简单,能够随时调节合金含量,为不互溶铜合金薄膜的制备提供了一种设计思路。改变溅射气压P和靶材与基底之间的距离(镀距)D,研究了溅射参数P、D,合金掺杂以及退火温度对溅射铜薄膜织构的影响。铜薄膜(111)织构随溅射气压P和镀距D的增加先升高而后下降。在溅射气压为0.5 Pa,镀距为200 mm时,溅射铜薄膜具有最强的(111)织构,且晶粒细小,薄膜致密度和平整度高。硅基底铜薄膜最终的生长织构不仅与薄膜表面能(界面能)有关,而且与体系的应变能有关。Cr、Zr合金掺杂显著提高硅基底溅射铜薄膜的(111)织构,并且在一定范围内合金薄膜的(111)织构随退火温度的升高而升高。合金薄膜(111)织构的增强与薄膜晶粒的细化、界面能增大有关,同时它们也涉及到内应力的变化。系统研究退火过程中Cu(2.6 at.%Cr)合金薄膜的微观组织结构演变。Cu(Cr)薄膜中晶粒的明显长大发生在450℃左右,薄膜晶粒尺寸呈现双峰分布。退火后合金薄膜内并没有明显的Cr相析出,Cu(2.6 at.%Cr)薄膜的双峰晶粒尺寸分布与Cu晶粒的择优生长有关。薄膜横截面透射电镜结果表明,退火后的纯Cu薄膜呈现粗大的竹节状晶粒结构,薄膜在膜/基界面处发生明显的晶界沟槽化。相比之下,退火态Cu(2.6 at.%Cr)合金薄膜晶粒为细小柱状晶,薄膜结构符合典型的PVD薄膜结构区域模型(Structural Zone Model)。Cr掺杂显著阻碍了薄膜的晶粒长大,有效抑制了退火Cu薄膜的晶界沟槽化。相比于纯Cu薄膜,Cu(Cr)合金薄膜中{111}孪晶界密度显著增加,孪晶宽度和孪晶片间距明显减小,平均的孪晶片间距约为6 nm。统计结果表明Cu(Cr)合金薄膜的孪晶界密度约为18.6×108 m2/m3,是纯Cu薄膜的20倍。Cu(Cr)薄膜中高密度纳米孪晶的形成与薄膜内应力的增加以及薄膜<111>取向晶粒的择优生长有关。退火后Cu(2.6 at.%Cr)合金薄膜的硬度和弹性模量远高于纯Cu薄膜,而退火电阻率与纯Cu薄膜接近。考察磁控溅射硅基底Cu、Cu(Cr)以及Cu(Zr)合金薄膜在退火过程中的形貌以及微观组织结构演变后可知,500℃退火时,Cu膜在硅基底上发生团聚,薄膜与基底之间发生明显的扩散和反应。Cr掺杂细化了退火铜薄膜的晶粒,抑制了薄膜的晶界团聚,提高了硅基底Cu薄膜的热稳定性。相反,Zr掺杂加速了铜薄膜与硅基底的扩散与反应,降低了硅基底铜薄膜的热稳定性。Cu(Zr)薄膜低的热稳定性与Zr掺杂对硅基底表面的“净化效应”有关。Cu(Cr)薄膜的退火电阻率与纯Cu膜相近。而Cu(Zr)薄膜由于界面铜硅化合物的形成,电阻率急剧上升。与Si基底相反,SiO2基底上的Cu(Zr)薄膜退火时,Zr向薄膜/基底界面偏聚,形成有效的富Zr界面阻挡层,阻碍了薄膜与基底间的扩散,提高了薄膜的热稳定性。界面阻挡层的形成与二元铜合金体系中掺杂元素的种类和含量有着密切的关系。Cr合金掺杂显著提高Cu导线的抗电迁移性能。相同条件下,Cu(Cr)导线的电迁移寿命是Cu导线的10-100倍。Cu(Cr)合金导线的抗电迁移性能的提高与退火后合金元素在薄膜表面(界面)的富集、薄膜晶粒{111}纳米孪晶界密度的增加以及(111)织构的增强有关。更多还原

【Abstract】 As the development of the manufacture techniques for integrated circuits, Cu has replaced Al as the interconnect material owing to its low resistivity and high electromigration resistance. However, microstructure control is becoming increasingly important as interconnect line-widths decrease below 0.5μm, because performance and reliability become more critically affected by specific microstructure than by average bulk properties. Much attention has been paid to the method of alloying, which could both control the microstructure and improve the properties of thin films. The basic researches of Cu alloy films play an important role in predicting the performance of Cu interconnects, optimizing the damascene technology and enhancing the reliability of Si-ICs.In this study, Cu(Cr) and Cu(Zr) films were deposited by magnetron sputtering by using the mosaic structure target with optimizing parameters. Effects of the Cr and Zr dopants on the microstructure and properties of Cu films were investigated. The research results could provide a guideline not only for the expanded application of Cu(Cr) and Cu(Zr) alloy films, but also for the design and the developmentof Cu alloy films with high strength and electrical conductivity.The Cu1-xMx(M=Cr, Zr) alloy targets with the mosaic structure were originally designed and manufactured. Cu1-xMx(M=Cr, Zr, x<0.05, at.%) alloy films with different thickness and composition were deposited on Si(100) substrates by using our mosaic structure target. The composition of alloy films with high purity is in control. Results presented here provide a new method for magnetron sputtering Cu film contain insoluble substances.Effects of the sputtering pressure P, the distance between the target and the substrate D, the alloying dopant and the annealing temperature on the texture and morphology of films were investigated. The (111) texture, as the increase of D and P, increases first and decreases subsequently. When the P is 0.5 Pa and the D is 200 mm, the films have the strongest (111) texture and the fine morphology. The texture of sputtered films is determined by both the surface energy and the strain energy of the system. In a certain range of temperature, Cr or Zr dopant increases the (111) texture of Cu films, which is related with the refinement of grains in alloy films and the increase of internal stress of alloy films.Evident grain growth in Cu(2.6 at.%Cr) alloy films occurs at the temperature above 450℃. After annealing at 450℃, Cu(Cr) alloy films exhibit a bimodal grain size distribution with fine grains. Annealing at higher temperatures results in an abnormal grain growth. No evident Cr precipitates are found in Cu(Cr) alloy films after annealing. The bimodal grain size distribution is considered to be ascribed to the growth of favorably oriented grains.Cross-section TEM images show that the annealed Cu films exhibit a‘bamboo’grain structure, and grain boundary grooves have formed at the film/substrate interface. By contrast, a typical columnar structure can be seen in Cu(Cr) alloy films, which is in good agreement with the structure zone model. Cr dopant inhibits the grain growth and the grooving process in annealed Cu films. Moreover, an extremely high density of {111} twin boundary is found in Cu(Cr) alloy films, in which the estimated twin spacing and twin lamella are about 6 nm. The twin boundary density in Cu(Cr) films is about 18.6×108 m2/m3, which is 20 times as much as that of annealed Cu films. The formation of nano-twin is related with the internal stress and the preferential <111>-orientated grain growth. As a result, the hardness and young’s modulus of alloy films increase markedly, without degrading the conductivity much after annealing.After annealing at 500℃, Cu films agglomerate on Si(100) substrates because of the significant grain growth. However, Cr dopant refines the grains, inhibits the agglomeration and enhances the thermal stability of Cu films on Si(100) substrates. In contrast, Zr dopant accelerates the diffusion and reaction between the Cu film and the Si(100) substrate and degrades the thermal stability of Cu films, which are related with the‘purifying effect’of Zr. As a result, the final resistivity of Cu(Cr) films is approached to that of Cu films, while the resistivity of Cu(Zr) films increases sharply after annealing.On the contrary, for the Cu(Zr) films on SiO2 substrates, Zr segregates at the film/substrate interface, thus, an effective Zr-rich layer at the interface is formed, which inhibits the diffusion between the film and the substrate. As a result, the thermal stability and adhesion between the film and the substrate are improved. The formation of the interfacial barrier layer is depended on the alloying element and its content in alloy films.Cr dopant improves the electromigration resistance remarkably. The electromigration lifetimes of Cu(Cr) lines are 10-100 times longer than those of Cu lines. The improvement of electromigration resistance of Cu(Cr) alloy lines is related with the segregation of Cr on the film surface, the increase of {111} twin boundaries density and the Cu(111) texture of alloy lines.更多还原