| Because of its low resistivity and high reliability against electromigration, bottom-up copper filling is widely used in Ultra-Large Scale Integrated Circuits (ULSIs). However, with the rapid shrinkage in interconnection dimensions, it is difficult to fill the trenches and holes by electroplating, and so, electroless bottom-up copper filling is studied. In this paper, the effects additives were investigated on the bottom-up filling in the electroless plating, using formaldehyde as a reducing agent.The bottom-up copper filling for different sub-micrometer trenches was firstly achieved by electroless deposition technique using a triblock copolymer of PEG and PPG, ethylene oxide terminal blocks termed EPE, as an additive. Deposition rates of electroless copper bath with different concertrations of EPE-8000 were measured by weighting technique; It was found that EPE (molecular weight 8000) had a strong inhibition for the electroless copper deposition, the deposition rates decreased with the increases of EPE-8000 concentration, and when the EPE-8000 concentration was 1.0 mg/L, the deposition rate of electroless copper was decreased from 8.6 to 3.7μm/h, with the EPE-8000 concentration further increased, although the deposition rate of electroless copper decreased, but the decrease was significantly less than the beginning; The bottom-up filling behavior of electroless copper bath for different trenches was investigated in a plating bath containing 1.0 mg/L EPE-8000. The cross-section SEM observation indicated the trenches with different widths ranging from 110 to 640 nm were all filled completely by electroless copper. The inhibitions of EPE-8000 for both cathodic and the anodic reaction were demonstrated by linear sweep voltammetry (LSV) method.Bottom-up copper filling for different sub-micrometer trenches was also investigated by electroless deposition technique using PEG-PPG triblock copolymer with propylene oxide terminals termed PEP (Mw:3100). When the PEP-3100 concentrations changed from 0 mg/L to 1.5 mg/L, the deposition rate of electroless copper decreased from 8.6 to 5.0μm/h, and then decreased slowly as the PEP-3100 concentration became high. The bottom-up filling behavior of electroless copper bath for different trenches was investigated in a plating bath containing 1.5 mg/L PEP-3100. The cross-section SEM observation showed the trenches with different widths ranging from 175 to 290 nm were all filled completely by electroless copper, but for the trenches with the width of 105 nm, some voids appeared in the cross-section SEM images. This results indicated that the bottom-up filling capability of plating bath with an addition PEP-3100 was weaker than that with an addition of PEG-PPG triblock copolymer with ethylene oxide terminals termed EPE (Mw:8000). This was attributed to the inhibition of PEP-3100 was not strong than that of EPE-8000 and the diffusion coefficient of PEP-3100 was larger than that of EPE-8000, which resulted in a small ratio of deposition rate in the bottom and at the opening of trenches. The inhibitions of PEP-3100 for both cathodic and anodic reaction were demonstrated by linear sweep voltammetry (LSV) method. The contact angle measurement was employed to detect the wettability between the electroless copper plating solution and the sheer copper after the additives were added.The effects of the block copolymers with different structural units on bottom-up filling in the electroless plating were investigated further. The results of the deposition rates and the electrochemical showed that EPE had a stronger inhibition for the electroless copper deposition compared with the same molecular weight of PEG, PPG. The bottom-up filling behavior of electroless copper bath for trenches was investigated in a plating bath containing 2.0 mg/L different copolymers. The cross-section SEM observation indicated that some voids appeared in the cross-section SEM images whether with an addition of PEG-2000 or PPG-2000, but the trenches with the widths of 280 nm were filled completely by electroless copper with addition of EPE-200, without void and seam. The change of the absorption of EPE in the surface, for it had a relative special structure with both E0 and P0, which led to the concentration gradient in the trench.In this paper, another important a bottom-up filling of electroless copper was first designed and achieved, in which the deposition rates of electroless copper were inhibited at the surface of the substrate and accelerated in the bottom of the trench, using bis(3-sulfopropyl) disulfide (SPS) and polyethylene glycol (PEG) as additives. The cross-section SEM observation indicated that all trenches with different widths ranging from 100 to 290 nm were filled completely by electroless copper and no void was found. This was attributed to synergistic effect of three factors, addition SPS only in the bath accelerated Cu deposition markedly; addition bath SPS and PEG-4000 in the bath decreased Cu deposition sharply; the large molecular weight and lower diffusion coefficient of PEG-4000 resulted in concentration gradient of PEG-4000 in the trenches. The effects of PEG-4000 and SPS on the polarization behaviors of copper reduction and formaldehyde oxidation were investigated by linear sweep voltammetry (LSV) method and mixed potential theory.Finally, the adhesion improvement of ABS resin to electroless copper by H2SO4-MnO2 colloid with ultrasound-assisted treatment was studied, and the effects of the H2SO4 concentration and the ultrasound-assisted treatment (UAT) time on the surface roughness and adhesion strength were investigated. When the H2SO4 concentration was 11.8-12.7 mol/L, a good etching performance was obtained; With the UAT, many uniform cavities formed on the ABS surface, the average surface roughness (Ra) and maximum roughness (Rmax) of ABS substrates decreased from 386 and 397 nm to 278 and 285 nm, respectively, which were much lower than that etched by CrO3-H2SO4 colloid (420 and 510 nm, respectively); But the average adhesion strength increased from 1.29 to1.39 kN/m, which was close to that of chromic acid etching treatment (1.42 kN/m). The surface contact angle measurement indicated that the density of the polar groups on the ABS surface increased with the UAT time. The results indicated that surface etching with the UAT not only improved the uniformity of cavities, but also enhanced the oxidation rate of ABS resin, which resulted in a high adhesion strength and a low surface roughness. |
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