seam

A seam is a discontinuity or weak boundary that forms where two growth fronts of a deposited film meet inside a feature, potentially causing reliability issues. **Formation**: During conformal or bottom-up gap fill, film grows from opposing sidewalls. When the two growth fronts merge at the center, the interface may not bond perfectly. **Location**: Typically along the centerline of filled trenches or vias. Can extend the full height of the feature. **Characteristics**: Weak bonding, incorporated impurities, or voids along the meeting plane. May be visible in TEM cross-sections. **Impact**: Seams can act as diffusion paths for moisture or chemicals. Weak mechanical interface. Can cause reliability failures under electrical or thermal stress. **Tungsten fill**: W CVD commonly shows seams in contact/via fill. **ALD seams**: Even highly conformal ALD can produce seams due to imperfect bonding at the meeting plane. **Mitigation**: Bottom-up fill (selective deposition) avoids opposing growth fronts. Flow chemistry optimization to improve surface mobility and bonding. **Post-treatment**: Annealing can partially heal seams by promoting atomic diffusion. **Inspection**: TEM imaging, electrical testing for reliability, chemical decoration to reveal seam paths.