SiC Passivation Structure for High-Field Oxidation and Hydrogen Drift
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Solution Overview
Problem
Silicon carbide-based semiconductor devices experience undesired oxidation and hydrogen-related drift at high electric fields, leading to performance degradation, particularly in high-voltage applications where conventional passivation techniques fail to withstand field strengths above 250 kV/cm.
Innovation Solution
A termination structure for silicon carbide-based semiconductor devices incorporating a thermally grown oxide layer, a sputtered non-stoichiometric silicon nitride layer to reduce hydrogen incorporation, and a sputtered stoichiometric silicon nitride layer for enhanced hydrogen barrier properties, along with a chemical vapor deposited environmental barrier layer for step coverage and crack prevention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional oxide passivation techniques are used, then surface passivation is achieved, but oxidation occurs at high electric fields leading to performance degradation
Solution Approach 1:
The passivation structure is divided into multiple functional layers: a first oxide layer for initial passivation, a nitrogen-containing dielectric layer as a barrier to prevent oxidation, and a second oxide layer for additional passivation. This segmented approach allows each layer to perform its specific function, with the nitrogen-containing layer specifically blocking oxygen diffusion to the silicon carbide surface under high electric field conditions.
Solution Approach 2:
The nitrogen-containing dielectric layer serves as an intermediary barrier between the oxide layers and the silicon carbide surface. This intermediate layer prevents direct contact between oxygen and silicon carbide, thereby preventing oxidation while still allowing the oxide layers to provide surface passivation. The intermediary layer is crucial for blocking oxidation pathways under high electric field stress.
2Reliability
If plasma enhanced chemical vapor deposition is used to form passivation structures, then passivation is achieved, but hydrogen incorporation occurs causing drift at high electric fields
Solution Approach 1:
The patent changes the compositional parameters of the dielectric layer by incorporating nitrogen and controlling the oxide-to-nitrogen ratio. By adjusting these parameters, the layer achieves low hydrogen content while maintaining effective passivation properties. The specific composition (with nitrogen content between 10-90 atomic percent) is optimized to prevent hydrogen incorporation and subsequent drift at high electric fields.
Solution Approach 2:
The passivation structure uses composite materials combining oxides with nitrogen-containing dielectrics. This composite approach creates a material with properties superior to either component alone: the oxide provides passivation while the nitrogen-containing portion provides hydrogen barrier properties and prevents drift, achieving both reliability and stability at high electric fields.
3Power
If higher voltage operation is implemented, then power handling capability increases, but electric field strength increases causing oxidation and performance degradation
Solution Approach 1:
The passivation structure is designed and applied in advance before the device operates at high voltages. The multi-layer structure with the nitrogen-containing barrier layer is pre-configured to prevent oxidation and drift that would occur during high-power operation. This preliminary protection allows the device to safely handle high voltages without suffering from field-induced degradation.
Solution Approach 2:
The nitrogen-containing dielectric layer creates an inert environment at the silicon carbide surface, preventing oxygen access and oxidation even under high electric field conditions. This inert barrier allows the device to operate at higher voltages and powers without the harmful effects of electric field-induced oxidation, maintaining performance stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed structure effectively prevents oxidation and hydrogen-related drift, maintaining device performance and blocking capacity even at high electric fields, such as those exceeding 500 kV/cm, by reducing parasitic capacitance and minimizing trapping.
Implementation Method 1
an oxide layer on at least some of the silicon carbide portions of the device for satisfying surface states and lowering interface density
Implementation Method 2
a non-stoichiometric layer of silicon nitride on said oxide layer for avoiding the incorporation of hydrogen and for reducing parasitic capacitance
Implementation Method 3
a chemical vapor deposited environmental barrier layer for step coverage and crack prevention
Data Source
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AI summary
An improved termination structure for high field semiconductor devices in silicon carbide is disclosed. The termination structure includes a silicon carbide-based device for high-field operation, an active region in the device, an edge termination passivation for the active region, in which the edge termination passivation includes, an oxide layer on at least some of the silicon carbide portions of the device for satisfying surface states and lowering interface density, a non-stoichiometric layer of silicon nitride on the oxide layer for avoiding the incorporation of hydrogen and for reducing parasitic capacitance and minimizing trapping, and, a stoichiometric layer of silicon nitride on the nonstoichiometric layer for encapsulating the. nonstoichiometric layer and the oxide layer.