【作者】 黎德育；

【导师】 李宁；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2013， 博士

【摘要】 铜具有电阻率低，抗电迁移性强的优点，作为IC互连接材料已经得到了越来越广泛的应用。伴随而来的问题是传统的化学机械抛光工艺已经不能满足铜的抛光精度，从而提出了铜的电化学机械抛光工艺。磷酸体系是铜电化学抛光最为常用的抛光溶液，而铜在磷酸体系抛光中的电化学反应历程尚不明确，对于其中的一些粘度调节剂、添加剂等的研究尚需完善。为了明确铜在电化学抛光中的电化学行为，采用旋转盘环电极，对铜在磷酸溶液中的阳极溶解的中间产物进行研究。发现在环电极上在-0.26V及-0.04V处出现两个电流峰，分别对应了盘电极在阳极极化过程中活性溶解区的Cu生成Cu⁺反应和钝化区的Cu生成Cu₂O的反应。在活化区及钝化区中间产物均受到扩散的影响。铜在阳极极化的不同电位区间的电化学阻抗谱的解析表明了Cu⁺离子的产生不仅引起了-0.275V附近的感抗弧的出现，同时还引起了0V附近电位区域的负电阻容抗弧的出现。阻抗-时间（R_s-t）和阻抗-电位（R_s-E）曲线的测试结果表明，R_s-t和R_s-E曲线能够表征铜磷酸界面粘膜层及氧化物层的形成。在R_s-E曲线中可以分为六个区域。其中活性溶解区铜表面不生成铜氧化物、R_s的变化主要由粘膜层变化引起。在活性溶解与钝化过渡区，粘膜层的变化及铜氧化物的生成共同引起R_s的变化，此时生成的铜氧化物为n型半导体特性。在钝化区，电化学反应受配体扩散控制，此时电流密度不变，R_s主要由铜氧化物的增厚引起。电位达到0.6V时铜氧化物开始转呈p型半导体特性，R_s也开始上升。磷酸浓度与阳极极化电位的增加，有利于微观整平，对宏观的整平能力也有加强作用；当磷酸的浓度为55wt%，阳极极化电位为0.2V时，铜的抛光表面粗糙度最低，效果最好。磷酸浓度的增加有利于铜的阳极钝化，使得钝化电流下降，抛光过程中的欧姆电阻增加。随着磷酸浓度的升高，形成的氧化膜的载流子密度和平带电位下降；载流子密度下降反应了膜的金属过剩程度下降。对铜电极施加了50g/cm²及200g/cm²的压力的稳定电位时间曲线及Tafel曲线表明，在压力的作用下，电极的旋转更多地影响了阴极过程，而且铜的腐蚀溶解速度与转速符合Levich关系；在稳定电位下，在磷酸溶液中的腐蚀受阴极扩散控制，力的施加有助于阴极去极化过程，有利于氧在抛光液中的扩散，从而使得腐蚀加快。研究表面活性剂SDS、PEG、PVP对铜的电化学抛光的影响发现，SDS的加入对铜在磷酸水溶液中的电化学阳极溶解的全过程起到了有效的抑制作用。在活化区和钝化区，SDS在铜表面的吸附对铜的阳极溶解起到了抑制作用；在氧气析出初始阶段所生成的细小致密气泡层覆盖了铜电极表面，从而抑制了铜在这个电位区间的溶解速率，提高了对铜的溶出抑制率。表明SDS是一种有效的提高其平坦化率的添加剂。PEG及PVP在氧气析出区也出现了对铜的抑制效果。此外还研究了缓蚀剂BTA、TTA对铜的电化学抛光的影响，发现BTA在磷酸体系中稳定电位附近对铜具有非常好的抑制效果，抑制效率一度达80%；在钝化区，BTA的缓蚀作用随电位的增加逐渐下降。BTA对铜的抛光起到良好的效果，而TTA对铜的缓蚀及抛光效果比BTA差。更多还原

【Abstract】 Copper with the low resistivity and high resistance to electric mobility hasbeen widely used as IC interconnecting material. Recently, theelectrochemical-mechanical polishing technology has been developed because thetraditional chemical-mechanical polishing process can not meet the strictrequirements on polishing quality. Although the solution based on phosphoric acidis generally used in the electropolishing of copper, however the mechanism ofpolishing using such solution is still unclear. Besides, the additives for adjusting theviscosity and other parameters need to be investigated further.The intermediate products from the copper/phosphoric acid solution in theanodic and the electrochemical behavior of copper are studied by rotating discelectrodes （RRDE）. Two current peaks on the ring electrode at0.26V and0.04Vare detected, which are corresponding to the reaction of Cu/Cu⁺in active dissolutionzone and Cu/Cu₂O in passivation, in the anodic polarization process of copper onthe disc electrode, and both of reactions are controlled by the diffusion process.The electrochemical characteristics of copper in different anode polarizationpotential zones are analysized by electrochemical impedance spectrum （EIS）. thatthe results illustrate that Cu⁺have not only caused the inductance of arc near0.275V, at the same time also caused a capacitive reactance arc consisting a negativeresistance near0V. The results of the ohm impedance-time （R_s-t） and ohmimpedance-potential （R_s-E） curves show that the two curves can characterize theformation of the viscous layer and oxide layer on the interface between copper andphosphate acid. The R_s-E curve can be divided into six regions. In activedissolution region, the changes of R_s is caused by generation of viscous phosphatefilm on the surface of copper not by generation of copper oxide. In transition regionbetween active dissolution and passivation, the change of R_sis caused by the changeof viscous phosphate film and the generation of copper oxide as a n typesemiconductor. In passivation region, the reaction is controlled by the diffusion ofthe ligand, and the current density remains unchanged. Therefore, R_sis mainlycaused by the thickening of copper oxide. When the copper oxide starts turing into ptype semiconductor at0.6V, R_sincreases faster. The larger anodic polarization potential and the higher concentration ofphosphoric acid would be advantageous to the leveling of microscopic andmacroscopic structures. The surface roughness of copper after electropolishing hasthe lowest value at0.2V and55wt%H3PO4. The passivation state will be enhanced,the passivation current will decline and the ohmic resistance will increase., Thecarrier density and flat potential of the oxide film of copper declined with theincrease in the concentration of phosphoric acid which indicates that the degree ofexcess of metal in copper oxide film decreases.In Tafel curve test, the different pressures of50g/cm²and200g/cm²areapplied on the copper electrode. It is found that the rotation of electrode greatlyinfluences the cathode process, and the corrosion rate of copper and the speed ofrotation are in line with Levich relations. These results illustrate that the corrosionin phosphoric acid solution is controlled by the diffusion of cathode process underthe stable potential and the applied force would be benefit to accelerating theprocess of cathode depolarization （the diffusion of oxygen in the solution） and thecorrosion.In this paper, the effects of surfactants including SDS, PEG and PVP on copperelectropolishing are investigated. The results show that the anodic dissolution of Cuin phosphoric acid solution at different applied potentials is inhibited when SDS isadded. In both active and passive potential regions, the inhibiting effect due to theadsorption of SDS on Cu is oberved. At high anodic potentials, O2is generated fromCu surface, and tiny O2bubbles aggregate on the whole electrode surface. Thecompact O2layers act as the physical barrier between Cu and electrolyte solutionpreventing Cu from further dissolution, which enhance the inhibiting efficiency.Therefore, SDS can be used as an additive in phosphoric acid electrolyte to achieveexcellent planarization efficiency for Cu electrochemical mechanical planarization.PEG and PVP also show a good inhibiting efficiency on copper in the zone ofoxygen evolution.The effects of inhibitors of BTA and TTA on copper electropolishing arestudied too. It is found that the corrosion inhibiting efficiency of BTA is80%nearopen potential and drop with the increase of potentials in the passivation region.BTA shows the better effect on copper electropolishing than that of TTA.更多还原