Electrical, physical, and chemical characteristics of plasma-assisted chemical-vapor deposited semi-insulating a-SiN:H and their use as a resistive field shield for high voltage integrated circuits

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Abstract
The electrical, physical, and chemical characteristics of plasma‐assisted chemical‐vapor deposited semi‐insulating a‐SiN:H for use as a resistive field shield to passivate high voltage integrated circuits are summarized. The films were deposited onto the devices in a hot wall horizontal tube plasma reactor using NH3 and SiH4. The stoichiometry, refractive index, stress, structure, deposition rate, thermal stability, electrical properties, and sodium penetration resistance were determined. The chemical, physical, and mechanical properties of the film are controlled by the NH3/SiH4 flow ratio. The N/Si ratio decreased linearly from 1/2 at a 5/1 NH3/SiH4 flow ratio to 0.15/1 at a 1/2 NH3/SiH4 flow ratio. This decrease in nitrogen content manifests itself as an increase in the refractive index from 2.1 to 3.1. Using the random bonding model, we show that the bond strength decreases and effective bond length increases with decreasing N/Si ratio. The decrease in bond strength causes a decrease in the thermal stability of the film because hydrogen evolution is more easily achieved. The increase in bond length increases the magnitude of the compressive film stress. The electrical properties of the films are also controlled by the N/Si ratio. For example, the conductivity at 25 °C and 1 MV/cm increases from approximately 1×10−18(Ω cm)−1 to approximately 2×10−7(Ω cm)−1 when the N/Si ratio decreases from 1.1/1 to 0.15/1. The conductivity data are consistent with a Frenkel–Poole mechanism. SinSiN films with conductivities between 10−11 and 10−14 (Ω cm)−1 measured at 2.4×105 V/cm and 25 °C were successfully applied to high voltage ICs. These films did not affect the device yield, but did yield devices which were immune to surface ions. The average breakdown voltage of the high voltage devices passivated with semi‐insulating a‐SiN:H was increased by 20–40 V over those passivated with insulating a‐SiN:H.