Secondary Ion Mass Spectrometry Protocols for Electrodeposited Copper Impurity Quantification
Dynamic SIMS protocols require cesium primary beams and oxygen flooding to accurately quantify trace sulfur, chlorine, and carbon in plated copper films.
Matrix Secondary Ion Yield
Meaning
Ratio of the number of secondary ions collected to the number of primary ions impacting the sample surface for a specific element within a given material. The matrix secondary ion yield is a fundamental parameter in mass spectrometry that dictates the sensitivity and detection limits of the analysis. It varies by several orders of magnitude depending on the chemical environment of the target atoms and the presence of electronegative or electropositive species.
This value determines whether a trace contaminant can be detected at the required parts per billion levels.
Chemical Influence
Enhancement of the signal occurs when oxygen or cesium is introduced to the surface during the sputtering process. While matrix secondary ion yield is high for electropositive elements in an oxygen-rich environment, it remains low for noble gases or stable metals. This variability necessitates the use of calibration standards that match the composition of the sample as closely as possible.
Quantification Difficulty
Differences in this yield between different layers of a sample can lead to significant errors if not properly corrected. Because the matrix secondary ion yield depends on the work function of the surface, any change in the alloy concentration can alter the measured signal intensity. Scientists use relative sensitivity factors to normalize these effects and produce accurate concentration profiles.
Instrument Selection
Laboratory managers choose specific primary ion sources and detection configurations to maximize the throughput of ions for the elements of interest. When the matrix secondary ion yield is insufficient, the signal to noise ratio degrades, making it impossible to distinguish the sample from the instrument background. Optimization of this yield is the primary task during the development of a new analytical method.