Influence of polymer additive molecular weight on surface and microstructural characteristics of electrodeposited copper

Abstract

Electrodeposition of copper was done with different molecular weight (MW) polyethylene glycol (PEG) as an additive in the plating bath. The adsorbed layer formed of PEG and chloride ion (Cl − ) in the presence of copper ions has a definite role in controlling the deposition mechanism and the coating characteristics. The adsorption behaviour and suppressor nature of PEG with different MW (200-20000) on the physicochemical and the surface morphological features of the copper deposit were characterized. The results reveal that depending on the adsorption capacity of the intermediate complex, the deposit properties show gradation. There is a range of morphology with particular grain structure for different MW PEG addition. Grain size and the roughness decreased with increase in PEG MW. The concentration of Cl − ion in the plating bath is also significant in determining the deposit mechanism of the bath as revealed from the shift in cathodic potential. The adsorbing power of the complex depends not only on PEG MW but also on Cl − ion concentration. XRD analysis of the copper deposit obtained with low MW PEG showed (220) as the major plane and with high MW PEG the prominent orientation was (111) and (200).

Effect of an Alkoxyliertes Beta Naphthol on Cu Electrodeposition for Application to Low‐Resistivity Cu Interconnects

“…Such columnar structures are often seen in electrodeposited Cu and Cu alloys . Figure (b) shows that the grain size was 28 ± 2 nm regardless of ABN concentration; this is in contrast with PEG, in which case grain size was considerably decreased upon addition of PEG …”

“…Although this equation does not provide quantitative information for thin films with preferred orientation, it is useful for qualitatively comparing grain sizes. In contrast to other organic additives, ABN did not significantly influence the crystal structure of Cu thin film over the concentration range 0–11.25 M. All thin films were grown in the highly oriented (111) direction. However, the size of the crystal grain is relatively small (28 nm on average), indicating that Cu thin films were grown with a columnar structure in the (111) growth direction instead of a single crystal.…”

“…Besides, as the reported size of trenches has decreased to as low as 20 nm, there has been an increasing need for effective large‐molecular‐weight additives working at low concentrations . However, the use of the well‐known high‐molecular‐weight polyethylene glycol (PEG), known as a suppressor, leads to an increase in the resistivity of Cu interconnects by reduction in grain size and by incorporation of impurities from a PEG‐chloride complex …”

Electrodeposited copper using direct and pulse currents from electrolytes containing low concentration of additives

“…Electrodeposition practitioners have used a variety of methods to control grain structure and orientation using non complexing aditives [17,20,47]. In this work we have examined the effect of a combination of additives, consisting of SPS (or MPS) and PEG which are known to adsorb on the surface of the electrode [25,48]. Normally the adsorbed compounds are extremely difficult to detect ex-situ due to their low concentration in the electrolyte; however, there is evidence that Cu deposition from a solution containing SPS and PEG can lead to incorporation of impurities along grain boundaries [43,48,49].…”

Surface Morphology and Stress in Electrodeposited Copper Nanofilms

“…5,[15][16][17] The use of these additives in electrodeposited copper thin films is also known to lead to smaller, more dense grains during film growth 18 . Additives are proposed to decrease surface diffusivity and reduce the number of vacant sites for adatom adsorption 19 .…”