Hydrogen Embrittlement Suppressors for Nickel-Free Electroless Copper Baths

Abstract

The deposition of a nanovoid-free electroless copper layer is one of the main quality criteria of an electroless copper bath. Without certain additives known to contribute to copper bath stability, copper deposit thickness and color, crystal structure, suppression of nanovoiding, etc., the properties of the obtained copper layer are unpredictable and uncontrolled copper growth can be observed.Previous investigations have shown that nickel as an additive is one of the main drivers in suppressing hydrogen embrittlement (HE), one type ofnanovoiding, while other commonly used organic additives did not show any beneficial impact on suppressing HE.Presented herein are the results of a study carried out to investigate the impact of five different additives (A-E) on HE, surface morphology and epitaxy in a wide concentration range for a tartratebased, nickel-free electroless copper bath. To study the different effects of the additives on the deposited copper layer focused ion beam (FIB) and field emission scanning electron microscopy (FESEM) were utilized for examination. The present results clearly demonstrate that certain additives can reliably substitute nickel and overcome the HE phenomenon. Additive A is capable to suppress the nanovoiding while providing a thin, epitaxially grown and nanoscopically defect-free electroless copper layer with an optimal surface morphology for the subsequently plated electrolytic copper deposit. Additionally, the avoidance of the encapsulation of hydrogen during the copper deposition process results in a less nanopouros copper deposit, which minimizes the risk for delamination of the deposited copper.