Stress Adjustment in Si3N4 Films by Ion Implantation
Si3N4 films deposited at 730° C by current CVD techniques have an intrinsic tensile stress of 1–1.5×1010 dynes/cm2. Stress relief by cracking of the nitride film could impair the reliability of integrated circuits that incorporate these films as a mobile ion barrier. Cracks that originate at the surface may be prevented by adjusting the stress at the surface to be neutral or compressive.
We have adjusted the stress in a thin surface layer of Si3N4 film, pyrolytically grown at 730° C, from its intrinsic tensile value of ~1.2×1010 dynes/cm2 to comparable compressive values by bombarding the surface with 1–6×1014 Ar/cm2 at 30 keV. The integrated stress (dynes/cm) in the film was measured by the optically-levered-laser technique. At a dose ≈4×1014 Ar/cm2, the integrated stress peaks at ≈-4×104 dynes/cm (compression). Assuming the damaged region is 250Å thick, this corresponds to a (compressive) stress of -1.5×1010 dynes/cm2. Very little change is seen at doses up to 6×1014 Ar/cm2.
The influence of annealing on the stress was compared between implanted and unimplanted wafers. The stress (tensile) in the unimplanted wafer was virtually unchanged during 30 minute anneals as high as 800°C. Significant annealing was observed in the ion induced stress at temperatures ≥ 600°C.
KeywordsFuse Silica Residual Tensile Stress Thin Surface Layer Nitride Film High Residual Tensile Stress
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