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We present measurements of mechanical stress in shallow trench isolation (STI) device structures using micro-Raman spectroscopy with ultraviolet (UV) excitation. UV (364 nm) light penetrates only 12 nm into silicon, probing the stress near the silicon surface. Following the evolution of stress from bare silicon to the finished STI structure, we experimentally identify the influence of sidewall oxide thickness, trench oxide densification and pre-gate (PG) oxide formation on the amount of mechanical stress introduced into the active area. Wet PG oxide formation with prior trench densification leads to a 60% higher stress than dry PG oxidation. Correlation of our stress data with TEM and electrical measurements reveal the formation of defects and an increase in leakage current by 3 orders of magnitude in narrow (0.3 /spl mu/m) trenches after wet PG oxidation.