Glassivation

Glassivation is a semiconductor wafer fabrication process that involves the deposition of the final passivating layer on top of the die to protect the die from mechanical damage and corrosion. As the name implies, this final layer is often composed of an amorphous insulating material, or glass.

Silicon nitride (Si₃N₄) is a common glassivating material because of its suitability for this purpose. Highly resistant to diffusion, it is almost impenetrable to moisture and ionic contaminants such as sodium (Na). It can also be deposited with a low residual compressive stress, making it less prone to delamination or cracking. Its interfacing with the underlying metal layers is also very conformal. Finally, it can be prepared with very low pinhole density. Since silicon nitride has a high dielectric constant, it is not popular as an interlayer dielectric for the simple reason that it results in a high inter-metal capacitance.

Silicon nitride can be deposited using plasma-enhanced chemical vapor deposition (PECVD) or low-pressure chemical vapor deposition (LPCVD), although the former is the technique of choice for glassivation purposes because it allows a lower processing temperature.

Figure 1. Example of an LPCVD system that can be used to deposit silicon nitride on substrates

Wafer Fab Links: Incoming Wafers; Epitaxy; Diffusion; Ion Implant; Polysilicon;

Dielectric; Lithography/Etch; Thin Films; Metallization; Glassivation; Probe/Trim

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