Semi-quantitative analysis of trace elements by Secondary Ion Mass Spectrometry

Secondary Ion Mass Spectrometry (SIMS) offers a technique of surface specific analysis with an information depth as low as 1 nm. SIMS also has high sensitivity for most elements. It is a viable analysis technique to investigate superficial residues and contamination on the surfaces of components used in IC packaging, though quantification by SIMS is difficult except for the specific case of trace concentrations with calibration standards. The focus of this work is on routine semi-quantitative analysis of trace elements on surfaces using an automated bench-top SIMS instrument without calibration standards. The potential of SIMS in this role was investigated by evaluating the effectiveness of various cleaning processes for removal of a coating on a copper leadframe surface. The cleaning efficiency can be quantified by analysis of characteristic trace elements of the coating. The main characteristic elements in the coating were Cr, Na, Zn, Si, as well as S from cleaning process. By using SIMS, it was possible to (i) identify inorganic chemical compounds / elements present on the leadframe surface (ii) semiquantitatively estimate the relative concentrations of the elements of interest and (iii) obtain thickness measurements of the coating on the leadframe surface. The results from this study show that even in bench-top format, SIMS has the sensitivity to detect certain elements and offers a fast way to assess the relative concentrations of specific trace elements on a solid surface. This feedback can help manufacturing engineers to evaluate the effectiveness of a process and the influence of changing various parameters in process design of experiment.