2,2′-联吡啶对化学铜二元络合剂体系沉积过程的影响

Deposition Effect of 2,2′-dipyridyl in Dual-ligands Electroless Copper System

二元络合剂化学镀铜体系相较于一元络合体系,因增大了对沉积反应的调控空间而备受关注,稳定剂是二元体系的重要组分之一,当前关于稳定剂在二元络合体系中的作用规律系统性研究较少。本研究以2,2′-联吡啶为乙二胺四乙酸(EDTA)/四羟丙基乙二胺(THPED)化学镀铜二元络合体系为稳定剂,测试了体系的电化学特征和镀层结构的变化规律。基于活性离子的吸附差异,化学镀铜的二元络合体系混合电位分为诱导、过渡和稳定三个反应过程,发现2,2′-联吡啶使体系的混合电位值负向移动的趋势放缓。线性伏安法扫描数据表明,由于2,2′-联吡啶在反应电极表面的吸附,减缓了铜络离子的阴极还原反应,还原峰电流密度下降了34.3%,沉积反应受阴极还原步骤控制;镀层的沉积速率随2,2′-联吡啶浓度增加显著下降,同时由于强络合作用抑制了Cu+氧化,起到了稳定镀液的作用。通过SEM、EDS和XRD揭示,加入了2,2′-联吡啶后二元体系所制备的化学镀层呈均匀致密的菱形颗粒状,晶界面清晰分明,具有较高的纯度,以及明显的(220)晶面择优取向趋势,这与2,2′-联吡啶定向吸附在(111)、(200)生成方向抑制这二类晶面的生长,而在(220)生长方向吸附微弱从而抑制较少有关。

Compared with the single-ligand electroless copper system,the dual-ligands system was concerned about recently because it could increase the regulatory space for deposit reaction.2,2′-dipyridyl as a stabilizer was used for electroless copper plating in EDTA/THPED dual-ligands system.The electrochemical behavior and surface structure of copper layer were studied systematically.Mixed potential tests indicated that the overall process was divided into three districts that called as induction,transitional and stable region,2,2′-dipyridyl made fall-off trend of electrode potential to slowdown.2,2′-dipyridyl could retard cathodic polarization by linear sweep voltammetry test,the peak value of cathodic current density decreased 34.3%,which reduced obviously Cu deposition rate due to cathodic reaction was control step.Meanwhile,the decomposition time of electroless solution sharply increased and the reoxidation of Cu(I)ion was effectively inhibited in the presence of 2,2′-dipyridyl.Metallographic studies of copper layers with 2,2′-dipyridyl revealed that surface structures and fine particle distribution were uniform.The resultant product was high-purity without detectable metal oxide.Moreover,copper layers displayed that addition of 2,2′-dipyridyl favored the formation of the preferred orientation on the(220)lattice plane by X-ray diffraction,which was related to the directional adsorption of the stabilizer,i.e.preferential adsorption on the(111)and(200)crystal planes.There was no significant change in grain size with the addition of 2,2′-dipyridyl.