超级化学镀铜方法填充微道沟的基础研究

【作者】 王旭；

【导师】 王增林；

【作者基本信息】 陕西师范大学 ， 无机化学， 2011， 博士

【摘要】 金属铜由于其具有较低的电阻率和较高的抗电迁移能力,已被广泛地应用于超大规模集成电路的大马士革铜互联线工艺中。其铜互联线工艺的微孔和道沟的完全填充是通过超级电镀技术来实现的。随着集成电路芯片中铜互联线宽度迅速减小,均匀铜种子层很难获得,而使得电镀铜填充变得越来越困难。超级化学镀铜具有化学镀铜和超级填充的双重特点,无需种子层,能够实现无空洞完全填充,从而受到广泛关注。本文在乙醛酸作为还原剂的化学镀铜溶液中,通过对大量的抑制剂、加速剂的单独、协同加入对化学铜溶液超级填充的影响,实现了体系的超级化学铜填充。研究、总结了超级化学铜填充实现的方法,并通过电化学方法对其形成超级化学填充的机理进行探究。本论文首先选择了较大的大分子量的添加剂,研究添加剂的单独加入对化学铜溶液沉积速率的影响。发现分子量为3100的PPG-PEG-PPG三段聚醚(简称PEP-3100),对化学镀铜沉积速率具有较强的抑制作用。没有添加任何添加剂的化学镀铜沉积速率是8.2μm/h,当PEP-3100的浓度仅为1.0 mg/L时,化学镀铜的沉积速率降低至2.1μm/h。当化学铜溶液中PEP-3100浓度为1.0 mg/L,研究其添加对不同宽度微道沟的化学镀铜填充的影响。断面SEM图结果表明宽度100-380 nm、深度430nm的道沟均被化学铜完全填充。线性扫描伏安法测定结果进一步证明PEP-3100对抑制化学镀铜的沉积速率有较大的影响；作为对比,研究了添加EPE-8000(1.0 mg/L)作为抑制剂的化学镀铜溶液对微道勾填充能力的影响,发现EPE-8000对深径比较小的道勾能有效填充,而对深径比较大的微道勾,填充时底部容易出现了空洞。本论文的重要内容为设计、实现完全的超级化学填充体系。在对超级电镀铜沉积速率研究的基础上,我们设计出了实现完全超级化学铜沉积的方案。即通过加速剂加速底部化学铜的沉积,通过抑制剂和加速剂的协同作用,共同抑制化学铜在道沟口部和表面的沉积,从而实现化学铜对微孔和道沟的完全填充。在大量添加剂研究实验的基础上,我们发现单独添加SPS对化学镀铜沉积速率有加速作用；虽然PEG-4000单独加入对化学铜有抑制作用,而SPS和PEG-4000的共同加入,极大的抑制了化学铜的沉积速率。利用SPS分子量小,水溶性好,具有较高的扩散系数,能均匀分散在溶液中,而PEG-4000具有较大的分子量和低的扩散系数,从而使PEG-4000在道勾内部形成一定的浓度梯度的特点,使得PEG-4000在微孔表面和口部具有较大的浓度,微孔底部浓度很小。利用SPS和PEG-4000的协同作用,我们成功的实现了超级化学镀铜的完美填充。线性扫描伏安曲线表明,PEG和SPS混合添加对铜离子的还原和乙醛酸的氧化都有抑制作用。但添加添加剂SPS和PEG沉积的铜膜电阻率较大,不利于超大规模集成电路的应用。JGB在低浓度时具有加速化学镀铜沉积速率的作用,而在高浓度时对化学沉积速率具有抑制作用。在化学镀铜溶液中同时加入JGB和EPE-8000(分子量大约为8000),对化学镀铜沉积速率具有协同抑制作用。利用EPE-8000有较小的扩散系数,在道勾中形成一定的浓度梯度和JGB分子量较小的特点,EPE-8000抑制道沟口部、表面的化学镀铜沉积速率和JGB加速微道沟底部的化学镀铜沉积速率的协同作用,实现了超级化学镀铜的完美填充。化学镀铜填充道沟断面SEM图表明,宽度从130到520 nm,深度450到770 nm的道沟都能被完美填充。线性扫描伏安法和混合电位理论研究显示,单独添加JGB能加速乙醛酸的氧化,而当单独添加三段聚醚EPE-8000时能抑制乙醛酸的氧化。当JGB和EPE-8000混合添加时,能协调抑制了乙醛酸的氧化。大分子的抑制剂具有较低的扩散系数,小分子的加速剂具有较高的扩散系数,往化学铜溶液中添加小分子的加速剂和大分子的抑制剂,利用抑制剂对道沟口部、表面的化学镀铜的沉积速率具有抑制作用和加速剂对道沟底部的化学铜的沉积速率加速的作用,从而能够实现超级化学铜的完美填充。利用该实验原理,通过实验设计,利用小分子的JGB、SPS作为加速剂,利用大分子的聚合物PEP-3100、PEG-4000作为抑制剂,利用大分子聚合物PEP-3100、PEG-4000、EPE-8000和JGB对微道沟底部的化学镀铜沉积速率的协同抑制作用,同样能实现完美的超级化学镀铜的完美填充。利用该实验原理不仅可用于超级化学镀铜填充体系,也可以用于其他超级化学镀填充体系。更多还原

【Abstract】 Copper is used widely for metal interconnection in ultralargescale integration (ULSI) owing to its low resistivity and high reliability against electromigration. Filling technology of micro-holes and micro-trenches for copper interconnection was completed by superfill plating. With shrinkage of copper interconnection width, Cu seed layer of uniformity is almost achievable, which results in becoming more difficult during electroplating. Superfilling of electroless copper has caught worldwide attention that it has the dual characteristics of electroless copper and superfilling, without seed layer, bottom-up fill without any void is achieved. In the article superfill of electroless copper is reached by adding to inhibitor, accelerator, synergy adding to influence bottom-up fill with glyoxylic acid as a reducing agent in solution of electroless copper. Technique of bottom-up fill is researched and summarized; the mechanism of superfill is explored by electrochemistry method.First of all, the effects of sole large molecular additives were studied to deposition rate of electroless copper. It was found that PEP-3100 (molecular weight 3100) had a strong inhibition for the electroless copper deposition. The deposition rate of the electroless copper was 8.2μm/h without any additive, when the PEP-3100 concentration was 1.0 mg/L, the deposition rate of electroless copper was decreased to 2.1μm/h. When the PEP-3100 concentration was 1.0 mg/L, the bottom-up filling behavior of the electroless copper bath for different trenches was investigated. The cross-section SEM observation indicated the trenches with different widths ranging from 100 to 380 nm and depth 430 nm were all filled completely by electroless copper. The inhibitions of PEP-3100 for both cathodic and the anodic reaction were demonstrated by linear sweep voltammetry (LSV) method. As a contrast, the bottom-up filling behavior of the electroless copper bath for different trenches was investigated by EPE-8000 as inhibitor, it is found that high aspect via trenches are all filled completely by electroless copper, but for the trenches with low aspect via, some voids appeared in the cross-section SEM images.Design and achievement of a complete bottom-up electroless copper filling is important contents in the article. On research basis of super-filling for electroless copper, we design the project of achievement of a complete bottom-up electroless copper filling, namely by increasing the deposition rate of electroless copper at bottom, by inhibiting the deposition rate of electroless copper on the surface with the synergy of inhibitor and accelerator, micro-holes and micro-trenches are all filled completely by electroless copper. It is found that an addition of SPS accelerate the deposition rate of electroless copper by number tests of additive; the deposition rates of electroless copper are inhibited by sole adding to PEG-4000, but an addition of SPS and PEG-4000 has a stronger inhibition for the electroless copper deposition. SPS has a small molecular weight and high diffusion rate, which caused it to distribute evenly in the solution, and PEG-4000 has a large molecular weight and low diffusion rate, which resulted in a concentration gradation of PEG-4000 in the submicrometer trenches and caused a lower concentration of PEG-4000 in the bottom than that at the opening and the surface of the trench. Bottom-up filling of trenches were all filled completely by synergy of SPS and PEG-4000. The effects of PEG and SPS on the behaviors of copper reduction and glyoxylic acid oxidation were investigated by linear sweep voltammetry (LSV) curve. But the resistance of copper film is high with an addition of SPS and PEG, which is not beneficial to apply for ULSI.Addition of SPS accelerates the copper deposition rate at a low concentration, inhibits the copper deposition rate at a high concentration. The synergy inhibition was found for the deposition rate of electroless copper with an addition of SPS and EPE-8000(molecular weight about 8000) in the plating bath. EPE-8000 has a low diffusion coefficient, which resulted in a concentration gradation in the submicrometer trenches, and JGB has a small molecular weight, so EPE-8000 inhibits the copper deposition rate at the opening and the surface of the trench, and JGB accelerates the copper deposition rate in the bottom of the trench, bottom-up filling of trenches were all filled completely by synergy of JGB and EPE-8000. The cross-section SEM observation indicated the trenches with different widths ranging from 130 to 520 nm and depth ranging from 450 to 770nm were all filled completely by electroless copper. Linear sweep voltammetry (LSV) method and mixed potential theory is the study to show that sole addition of JGB accelerates glyoxylic acid oxidation and sole addition of EPE-8000 inhibits glyoxylic acid oxidation, mixed addition of JGB and EPE-8000 synergistic inhibits glyoxylic acid oxidation.Large molecular inhibitor has low diffusion coefficient, small molecular accelerator has high diffusion coefficient. Bottom-up filling of trenches were all achieved completely with synergistic addition of inhibitor to inhibit the copper deposition rate at the opening and the surface of the trench and accelerator to accelerate deposition rate in the bottom of the trench. Using the experiment mechanism too, superfill of electroless copper is achieved completely by designing with synergistic inhibition that small molecular JGB as accelerator, which accelerates the copper deposition rate in the bottom of the trench, large molecular polymer PEP-3100, PEG-4000 as inhibitor, which inhibits the copper deposition rate at the opening and the surface of the trench. Not only superfill of electroless copper system but also superfill of electroless system is achieved completely by the experiment mechanism.更多还原