SiC Device Dual Protective Films Prevent Moisture Intrusion

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Solution Overview

Problem

Conventional silicon carbide semiconductor devices face reliability issues in high-temperature high-humidity environments due to moisture intrusion and mobile ions, leading to threshold voltage drops and drain-source leakage, particularly in the termination region where the silicon nitride film can crack and allow leakage currents.

Innovation Solution

A silicon carbide semiconductor device with a novel protection structure featuring a first protective film of silicon nitride and a second protective film of organic material, where the silicon nitride film covers the inner-circumferential upper source electrode and upper gate electrode, and the organic film covers the rings and outer-circumferential upper source electrodes, preventing moisture intrusion and mobile ion accumulation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a single protective film structure is used, then the device structure is simple, but moisture can intrude through cracks in the silicon nitride film causing reliability degradation

Engineering Contradiction:

Improvereliability in high-temperature high-humidity environmentVSAvoidprotective film structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The protective film is divided into two separate films: a first protective film (silicon nitride) and a second protective film (organic material). The first protective film provides moisture barrier functionality, while the second protective film seals the outer circumference to prevent moisture intrusion at the edges. This segmentation allows each film to perform its specific function optimally without the limitations of a single-film structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the device are provided with different protective film configurations. The first protective film covers the inner region including electrodes and semiconductor structures, while the second protective film specifically covers the outer circumference region. This local differentiation addresses the specific moisture intrusion risks at different locations - cracks in the inner region and edge exposure in the outer region.

Inventive Principle:

Principle #3Local quality

2Reliability

If the silicon nitride film covers the entire surface including outer circumference, then coverage is complete, but moisture can intrude through cracks and mobile ions accumulate

Engineering Contradiction:

Improveprevention of moisture intrusionVSAvoidmobile ion accumulation and leakage current

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The second protective film is extracted to specifically cover the outer circumference region, separating this protective function from the first protective film. This extraction prevents mobile ions from the first protective film from migrating to the outer circumference and causing leakage currents, while also preventing moisture intrusion at the exposed edges.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The second protective film acts as an intermediary layer between the external environment and the first protective film at the outer circumference region. It prevents direct contact between moisture and the first protective film, and also blocks mobile ions from reaching the semiconductor structures, thereby eliminating the harmful effects of ion accumulation.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If protective films cover all regions including pad regions, then protection is comprehensive, but electrical connection is blocked

Engineering Contradiction:

Improveprotection against moistureVSAvoidelectrical connection accessibility

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The protective films are selectively applied to cover specific regions (inner region with electrodes and outer circumference region) while leaving the pad region exposed. This local quality approach ensures that electrical connections at the pad region remain accessible for bonding and wiring, while all other regions receive comprehensive moisture protection.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS20180151719A1Silicon carbide semiconductor device

Publication Date: 2018.05.31 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

AI summary

A silicon carbide semiconductor device includes a first conductivity type silicon carbide substrate having an active region and a termination region surrounding the active region, a plurality of unit cells located in the active region, and a termination structure located in the termination region. Each unit cell is provided with a transistor structure. The termination structure includes the silicon carbide semiconductor layer, a second conductivity type second body region surrounding the active region, one or more second conductivity type rings surrounding the second body region, one or more outer-circumferential upper source electrodes surrounding the active region, and an upper gate electrode. The silicon carbide semiconductor device further includes a first protective film and a second protective film. The first protective film covers the inner-circumferential upper source electrode, the upper gate electrode, and an inner side surface of the one or more outer-circumferential upper source electrodes except for a pad region. The second protective film covers the first protective film and at least a part of the one or more second conductivity type rings.