Piezoresistive Silicon Diaphragm Doping and Strain Gauge Adhesion Defect Modes
Optimal piezoresistive stability requires heavy surface boron doping above 2e19 cm-3 combined with plasma-activated silane coupling to prevent delamination.
Silicon Nitride Barrier
Inorganic Shield
A protective dielectric film prevents the diffusion of moisture and mobile ionic contaminants into the sensitive active layers of a semiconductor device. The silicon nitride barrier is deposited as a final passivation layer because of its dense amorphous structure, which is highly resistant to chemical penetration. This robust film is particularly effective at blocking sodium ions and water molecules that would otherwise degrade the electrical characteristics of the transistors.
Deposition Process
Chemical vapor deposition techniques use precursor gases such as silane and ammonia to deposit the silicon nitride film at temperatures below four hundred degrees Celsius. This low-temperature deposition is necessary to prevent the melting of existing metal interconnects on the wafer. The resulting film is highly amorphous, which eliminates grain boundaries that could act as fast diffusion pathways for contaminants.
The thickness and refractive index of the deposited film are monitored using ellipsometry.
Chemical Resistance
This dielectric barrier also protects the underlying aluminum or copper traces from mechanical damage and oxidation during subsequent packaging steps. In-line testing verifies the integrity of the film by checking for pinholes or microcracks that could compromise its barrier performance. A continuous, defect-free barrier is essential for devices operating in harsh, non-hermetic environments.
Mechanical Strain
High intrinsic tensile or compressive stress within the deposited nitride film can cause cracking of the underlying dielectrics or film delamination. The deposition parameters must be adjusted to balance this internal stress while maintaining high density.