Impact of active dimension on junction leakages of a Ti-salicide process integrated with shallow-trench isolation

Abstract

We observed that the active line dimension bounded by shallow trench isolations (STI) affects the junction leakages significantly. The diodes with high STI peripheral to area ratio were found to be sensitive line dimension is shrinked to <EQ 0.25 micrometers , we observed that the junction characteristics are degraded and the junction leakages increase by > 1 order. Cross-sectional transmission electron microscopy on the silicided p+ active lines of different widths showed a bowing-up of the silicide film for narrower lines. The unique silicide film profile is caused by more Si consumption along the center of the narrow lines which in turn draws the silicide film closer to the junction. Junction delineation using Wright etch technique revealed a similar bowed junction profile near the STI edge implying an effectively shallower junction. We believe that the uneven Si consumption is aggravated by the overlapping stress from the trench sidewalls which forms a highly stressed region especially in the narrow active lines. Relieving some sidewall stress by allowing some STI trench oxide recess actually helps to modulate the Si consumption from the center to the edge of the active lines which result in more even silicidation and lower junction leakage.