High-resolution X-ray diffraction as a tool to investigate the evolution of local stress in sub-micrometric Si lines isolated by periodic arrays of oxide-filled trenches

The periodic strain induced in mono-crystalline Si lines isolated by the Shallow Trench Isolation process is investigated by High-Resolution X-ray diffraction which is very sensitive to local strain and is non-destructive. The array periodicity gives rise to satellites in the reciprocal space around the Si Bragg peak, their envelope being directly linked to the local strain field. In the particular case of sub-micrometric arrays, the reciprocal space maps present a secondary diffraction peak caused by a homogeneous strain area in the middle of the Si lines. The secondary intensity relative position can be translated in transverse and perpendicular strain values, which allows a quantitative comparison of samples. We first compare two process flows to show the effect of top-layer deposition on Si strain. Then, the influence of geometrical variations is studied for the softer process. When considering a fixed period, the strain is getting higher for a lower Si line/SiO 2 trench width ratio. The trenches depths variation shows a few effects on the strain values; the decrease in strain with decrease in depth is only noticeable for the transverse value. Finally, the homogeneous strain values increase with decrease in period from 580 nm down to 200 nm. All these results confirm that most of the stress is applied to the Si-active areas by the trenches filled with SiO 2.