| 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.
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