超级化学镀微道沟填充的研究

【作者】 昝灵兴；

【导师】 王增林；

【作者基本信息】 陕西师范大学 ， 应用化学， 2012， 硕士

【摘要】 目前超大规模集成电路铜互连线工艺采用大马士革工艺,即先通过物理气相沉积(PVD)法形成防扩散层(如TaN、TiN、WN等)和铜种子层,利用超级电镀铜技术填充道沟或微孔,然后通过化学机械研磨(CMP)去除多余。然而,随着半导体技术的飞速发展,铜互连线的宽度变得越来越窄,超级电镀铜填充存在许多问题,因此人们试图用超级化学镀铜来实现半导体微孔填充。本论文在以甲醛作为还原剂的化学镀铜溶液中,研究了添加剂对化学镀铜溶液超级填充行为的影响,实现了超级化学铜填充。并且首次实现了在次磷酸钠作为还原剂的化学镀镍体系的超级化学镍填充。并通过电化学方法研究了各种添加剂对形成超级化学填充的作用机理。本论文的研究内容如下：首先,研究了在甲醛作为还原剂的化学镀铜溶液中添加2-MBT(2-锍基苯并噻唑)和PE-3650(平均分子量为3650的聚醚)对超级化学镀铜的影响。结果发现,单独添加2-MBT对化学镀铜沉积速率具有加速作用；单独添加PE-3650对化学镀铜沉积速率有微弱的抑制作用。然而,当2-MBT和PE-3650共同加入时急剧地降低了化学镀铜的沉积速率,出现了协同抑制作用。利用2-MBT分子量小,具有较高的扩散系数,能均匀分散在微孔或道沟的内外,而PE-3650具有较大的分子量,较低的扩散系数,从而使PE-3650在微孔或道沟内部形成一定的浓度梯度(从微孔或道沟底部向口部的浓度依次增大),使得2-MBT和PE-3650在微孔或道沟表面和口部出现协同抑制作用,而微孔或道沟底部几乎只有2-MBT的加速作用。本论文利用2-MBT和PE-3650的协同抑制作用,成功地实现了超级化学镀铜的完美填充。另外使用线性扫描伏安法和混合电位理论研究测定2-MBT、PE-3650的添加对铜离子的还原及甲醛的氧化电位的影响,合理的解释了各添加剂在化学镀铜溶液中的作用和实现超级化学铜填充的机理。本论文利用超级化学铜微孔填充的这种思路和方法,首次实现了超级化学镍填充。研究了在化学镀镍溶液中添加分子量在3000-5000的PAA(聚丙烯酸)对沉积速率和不同规格微道沟的超级化学镍填充的影响。结果表明,PAA对化学镍沉积有强的抑制作用,在没有添加任何添加剂时的化学镀镍沉积速率是5.51μm/h,当添加2.0mg/L的PAA时,化学镀镍的沉积速率降低至2.06μm/h。随着PAA浓度的进一步增大,虽然化学镀镍的沉积速率有所下降,但其降幅明显减小。因此,本论文选择往化学镀镍溶液中添加2.0mg/L的PAA,研究其对不同宽度微道沟的化学镍填充的影响。由填充道沟断的面图可知,宽度从80到280nm的道沟都实现了完全填充；线性扫描伏安法测定结果证明PAA通过抑制阴极和阳极反应,从而降低化学镀镍的沉积速率。最后,在甲醛为还原剂的化学镀铜体系中研究了添加一定量2-MBT对化学镀铜沉积速率、镀层表面形貌、沉积铜膜质量和结构的影响。研究结果表明：化学镀液温度在70℃和40℃加入1.5mg/L的2-MBT可以使化学镀铜沉积速率分别从7.91μm/h提高到10.2μm/h和2.86μm/h提高到5.24μm/h,是甲醛化学镀铜体系中比较良好的加速剂。使用线性扫描伏安法和混合电位理论说明了2-MBT对化学铜沉积的加速机理。通过SEM表明：镀层铜颗粒细小、分布均匀、颗粒间结合紧密。通过能谱和接触角测试分析表明：镀层铜膜纯度高、平整性好。另外通过XRD分析表明：镀层铜膜晶体生长良好。更多还原

【Abstract】 At present, ultra large-scale integration (ULSI) copper interconnects are fabricated by the "Damascene" process, in which a layer of diffusion barrier (TaN, TiN, WN etc.) and a copper seed layer were deposited on surface of submicrometer trenches the substrates by physical vapor deposition, and then, the submicrometer trenches were filled with electrodeposited copper, last, the planarization was fabricated by the process of chemical mechanical polishing (CMP). However, with the rapid development of the semiconductor technology and the rapid shrinkage in interconnection dimensions, it is difficult to fill the trenches and holes by bottom up electroplating copper, and so, people try to achieve bottom-up copper filling with the electroless copper plating solution.In this paper, the effects additives on the bottom-up filling in the electroless plating were investigated, and bottom-up copper filling was achieved using formaldehyde as a reducing agent. And the bottom-up electroless nickel filling was first achieved, using sodium hypophosphite as a reducing agent. The formation mechanism of bottom-up copper or nickel filling in the electroless copper or nickel plating bath included of various additions were investigated by electrochemistry method.The content of this thesis is as follows:First of all, the effects of the additives of2-MBT and PE-3650on bottom-up copper filling were studied by the cross-sectional SEM observation. The results indicated the electroless copper deposition was accelerated by an addition of2-MBT alone at a low concentration, and the electroless copper deposition could be inhibited by an addition of PE-3650. However, the inhibition of PE-3650for electroless copper deposition became very strongly with an addition of2-MBT. Because of large molecular weight and low diffusion coefficient of PE-3650, the concentration gradient of PE-3650between the bottom and the surface of the trenches could be formed. On the other hand,2-MBT has small molecular weight and high diffusion coefficient, which caused it to distribute evenly between the bottom and the surface of the trench. And so, the deposition rates of electroless copper on the surface and the opening of trenches were synergy inhibited by the high PE-3650concentration combined with the2-MBT. While the deposition rates of electroless copper in the bottom of trenches was accelerated by very low PE-3650concentration combined with the2-MBT. This thesis completed bottom-up filling used the synergy effect of2-MBT and PE-3650on electroless copper deposition. The effects of2-MBT and PE-3650on the polarization behaviors of the electroless copper plating bath were investigated by the linear sweep voltammetry method and mixed potential theory, and the formation mechanism of the bottom-up copper filling in the electroless copper plating were explained reasonably.This thesis also achieved bottom-up nickel filling by means of the principle and method of bottom-up copper filling in the electroless copper plating. The deposition rate of the electroless nickel and bottom-up filling behavior for different sub-micrometer trenches were also investigated by electroless deposition solution with an addition of PAA (Mw:3000-5000). The result indicated that PAA had a strong inhibition for the electroless nickel deposition, and when the PAA concentration was increased from0to2.0mg/L, the deposition rate of electroless nickel decreased from5.51to2.06μm/h. With a further increase of the PAA concentration, the deposition rate of electroless nickel decreased slowly. Therefore, when PAA concentration was2.0mg/L in electroless nickel bath, the bottom-up filling behaviors of electroless nickel bath with different trenches were investigated, and the cross-section SEM observation indicated the trenches with different widths ranging from80to280nm were all filled completely by electroless nickel. The inhibitions of PAA for both cathodic and the anodic reaction were demonstrated by linear sweep voltammetry (LSV) method.Finally, the effects of2-MBT on deposition rate, surface morphology and the micro structure of deposited copper film were studied in the electroless copper plating solution. The results indicated that electroless copper deposition rate was significantly increased with an addition of1.5mg/L2-MBT, and the deposition rates of electroless copper bath at70℃and40℃were increased from7.91and2.86to10.2and5.24μm/h, respectively, which indicated that2-MBT was used as a good accelerating agent for electroless copper. The acceleration mechanism of2-MBT for electroless copper was studied by a combination of linear sweep voltammetry and mixed potential theory. Meanwhile, the SEM observation indicated the size of depsited copper film became more small and uniform. The Energy Dispersive X-Ray Spectroscopy (EDX) measurement indicated that the purity of the depsited copper was improved with an addition of2-MBT. The surface contact angle measurement indicated that the smooth of the depsited copper film surface was increased with an addition of2-MBT. In addition, the crystallography of depsited copper film in the plating bath containing2-MBT was characterized by X-ray diffraction. The results showed that crystallinity of depsited copper film was increased with an addition of2-MBT.更多还原