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LIMA — Laser Induced Mass Analysis — was used to identify impurities captured in defect structures formed by three different backsurface damage systems. Analysis data indicate that a poly layer and wet sandblast damage provide greater getter efficiency than abrasive SVG backsurface damage.
In this study oxidized CZ and FZ silicon samples were evaluated. Impurities such as Na, K, Al, Cr, Cu as well as H, C, O and Cl could be identified in the backsurface structures and the oxide layer, but not in the silicon bulk beyond the getter related defects. The so identified gettered impurities were directly correlated to the defect density observed on the front surface, while also considering the impact of the interstitial oxygen concentration in the CZ wafer samples.
The LIMA technique uses a Nd:Yag laser to vaporize and ionize portions of the sample. The generated ions are then injected into a “time of flight” mass spectrometer, which displays a complete mass spectrum within microseconds. This capability to vaporize and characterize microvolumes of sample materials in relatively short times make this an attractive technique for bulk analysis.
gettering, laser ionization mass analysis, backsurface damage, evaporate, ionize, contaminants
Engineering Manager, Fab Process Materials Engineering, CQ and R at Signetics, Sunnyvale, CA