Structural analysis of graphene-capped copper by spectroscopic ellipsometry for humidity reliability assessment

The reliability of graphene-capped copper (Gr/Cu) against humidity is assessed by spectroscopic ellipsometry (SE). Changes in the volume fraction of crystalline Gr in single-layer graphene (SLG) and tri-layer graphene (TLG), and also Cu-oxide thicknesses under the Gr cap were characterized by SE before and after humidity reliability testing. It was found that TLG has a higher moisture resistance than SLG with less change in the crystalline Gr volume fraction and thickness than that of SLG, and this leads to the reduction in Cu-oxide thickness and the uniformity under the Gr cap. The results were consistent with the analysis results by X-ray photoelectron spectroscopy and Raman spectroscopy excluding variations due to differences in analysis areas of each method. Since detailed structural changes, such as Gr quality and thickness, can be evaluated non-destructively, SE is considered to be a promising method for the detailed analysis of Gr/Cu structures.