Precise localization of contaminants in graphene with secondary ion mass spectrometry

Integration of graphene with the existing fabrication lines may be possible only if the growth process fulfills the high purity requirements of the front-end-of-line integration approaches. While many analytical techniques may provide information about the concentration of contaminants, their dimensional sensitivity is usually poor and thus it is not possible to assess which contaminants are located above/below graphene and which are incorporated into its structure. In this work, an optimized secondary ion mass spectrometry measurement procedure that combines excellent detection limits (0.8-2.9 ppm) and subnanometer depth resolution is presented. It confirms the presence of sodium and sulfur at the surface of the graphene layer, the formation of graphene-copper composite, and allows the detection of molybdenum and tungsten at the interface between graphene and the germanium substrate. Such precision may prove to be valuable for further optimization of the growth process of 2D materials.