SiC Passivation Anchorage Structure for Thermal Cycling Adhesion
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Solution Overview
Problem
The adhesion of polymeric passivation layers to silicon carbide (SiC) semiconductor bodies is compromised during thermal cycling due to mismatched coefficients of thermal expansion, leading to mechanical stresses and potential delamination, which can result in electrical discharges and damage to electronic devices, especially under high-voltage reverse-biasing conditions.
Innovation Solution
A manufacturing method that includes a semiconductor body with a passivation layer anchored by a protruding anchorage element, comprising a first portion with a maximum dimension and a second portion with a smaller dimension, extending into a cavity in the semiconductor body, to securely fix the passivation layer and prevent delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polymeric passivation layers are used to withstand high operating temperatures and electrical fields, then dielectric strength is improved, but adhesion to SiC deteriorates due to CTE mismatch
Solution Approach 1:
The patent introduces an intermediary anchorage element made of SiC that couples the polymeric passivation layer to the SiC semiconductor body. This mediator absorbs the CTE mismatch stress and provides a mechanical interlocking structure, allowing the use of high-dielectric-strength polymeric materials without adhesion failure during thermal cycling.
2Reliability
If thermal cycling is performed to test device reliability, then operational robustness is improved, but mechanical stresses at the interface increase leading to delamination
Solution Approach 1:
The anchorage element with its stepped geometry is designed beforehand to cushion and distribute the thermal expansion stresses that will occur during thermal cycling. The larger cross-sectional area at the SiC body interface provides a broader stress distribution area, preventing stress concentration and delamination during subsequent thermal cycling operations.
3Reliability
If the passivation layer is securely anchored to prevent delamination, then reliability under thermal cycling is improved, but device complexity increases
Solution Approach 1:
Instead of making the entire passivation structure complex, the patent applies local quality by creating a stepped anchorage element only at the critical interface region where the passivation layer meets the SiC body. The rest of the passivation layer maintains its simple planar structure, thus achieving improved adhesion without significant increase in overall device complexity.
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 anchorage element effectively prevents delamination of the passivation layer, ensuring high dielectric strength and electrical performance while reducing the risk of electrical discharges, thereby enhancing the reliability of SiC-based electronic devices under thermal cycling and reverse-biasing conditions.
Implementation Method 1
the high dielectric strength of the polymeric materials guarantees that the passivation layers will withstand high electrical fields, and consequently high potential differences across them, without undergoing electrical breakdown
Implementation Method 2
polymeric materials have high coefficients of thermal expansion (CTEs) (e.g., CTE=43e−6 l/K for the material polybenzobisoxazole—PIX), and this causes problems of adhesion of the passivation layer to the SiC, which has a lower coefficient of thermal expansion (CTE=3.8e−6 l/K)
Data Source
AI summary
A manufacturing method of an anchorage element of a passivation layer, comprising: forming, in a semiconductor body made of SiC and at a distance from a top surface of the semiconductor body, a first implanted region having, along a first axis, a first maximum dimension; forming, in the semiconductor body, a second implanted region, which is superimposed to the first implanted region and has, along the first axis, a second maximum dimension smaller than the first maximum dimension; carrying out a process of thermal oxidation of the first implanted region and second implanted region to form an oxidized region; removing said oxidized region to form a cavity; and forming, on the top surface, the passivation layer protruding into the cavity to form said anchorage element fixing the passivation layer to the semiconductor body.