Correlation of metallic contamination with gate disturb failure mechanism on EEPROM cell: data analysis and process robustness improvement for contamination free manufacturing

Due to device degradations, the metallic contamination is monitored in semiconductor manufacturing lines with analysis of the incoming products and in-line electrical characterization. Some intermittent gate disturb fallout was observed on flash memories, and investigation was carried on the cells of an EEPROM array. The failure analysis of the SCF (single cell fail), showed a hole at the corner of the active area, but was not able to localize precisely the involved process step. To understand the failure mechanism and confirm the root cause of the degradation, recreation experiments have been carried out aid the impact of the solvent, the metal type and the concentration has been demonstrated. The shape of the silicon pitting and its frequency in the silicon has been reproduced with copper in a hydrofluoric acid / ethylene glycol mixture, used in a pullback process step. Possible root causes of this metallic contamination are described in this study and the different assumption discussed: cross-contamination, incoming product, tool maintenance. It showed that the tubing between delivered bottles and the processing tool can accumulate metallic impurities which takes off for sometime, even with certified stainless steel tubing.