Meaning
Multilayer dielectric structures deposited on the surface of power semiconductor devices to manage electric field distribution and prevent environmental degradation. In the assembly of high-voltage transistors, these high power passivation stacks are used to minimize surface leakage currents and prevent premature voltage breakdown. The dielectric layers protect the active region from moisture ingress, mobile ionic contaminants and mechanical damage during subsequent packaging processes.
Stack Composition
Typical architectures utilize a sequence of thin films with contrasting physical properties, starting with a thin oxide layer at the semiconductor interface. This initial layer is followed by a thicker film that provides a barrier against moisture. The atomic layer deposition technique ensures uniform coverage over complex gate features.
Stress Management
Mechanical stress within the dielectric layers can introduce crystal defects in the underlying semiconductor substrate, leading to increased leakage. Thermal expansion mismatches between the dielectric materials and the semiconductor require careful balancing of layer thicknesses and deposition temperatures. By alternating compressive and tensile films within the stack, the net residual stress is kept within limits that prevent film cracking or wafer warping during thermal cycling.
Dielectric Breakdown
Voltage stress during operation places extreme electric fields across the passivation layers, especially near the gate edge and field plate terminations. The breakdown strength of the stacked materials must exceed the peak field concentration to prevent destructive dielectric puncture. Optimization of the deposition parameters, including precursor chemistry and plasma power, is necessary to achieve dense, defect-free dielectric films that can withstand continuous high-voltage operation.
If the deposition temperature is too low, the resulting film may contain residual hydroxyl groups that lower the dielectric strength, compromising the lifetime of the power transistor.
