SiC Trench Source Electrode Recesses for Front Metal Crack Control
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Solution Overview
Problem
Conventional silicon carbide (SiC) trench-type semiconductor devices face issues with crack formation in the front metal films due to stress and corrosion, particularly when nickel (Ni)/gold (Au) plating is used, exacerbated by the large difference in linear expansion coefficients between the metal films and the SiC substrate, leading to potential failures during processing or mounting.
Innovation Solution
A silicon carbide semiconductor device configuration featuring a trench gate structure with a gate electrode and source contact holes, where the first metal film contains nickel and the second metal film contains gold, with intermittent recesses reflecting the source contact holes' shapes, reducing stress and corrosion by providing a discontinuous surface for the second metal film, thereby suppressing crack occurrence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a plating film of nickel (Ni)/gold (Au) is used as a front metal film, then good electrical conductivity and corrosion resistance are achieved, but Au corrosion occurs on the Ni surface and cracks form under stress
Solution Approach 1:
The patent divides the continuous front metal film into multiple segments by forming recesses that extend from the front surface toward the semiconductor substrate. These recesses create isolated regions of the metal film, preventing crack propagation across the entire film while maintaining electrical functionality through the segmented structure.
Solution Approach 2:
The patent introduces an intermediate protective layer between the nickel and gold layers, or modifies the interface structure, to prevent direct contact between Au and Ni. This intermediary prevents the galvanic corrosion of Au by Ni while maintaining the electrical conductivity benefits of the metal film stack.
2Ease of operation
If stress is applied to the front metal film during inspection or mounting, then device testing and installation are enabled, but cracks occur in the metal film
Solution Approach 1:
By segmenting the metal film through recesses, the patent creates multiple independent load-bearing regions. When stress is applied during mounting or inspection, the stress is distributed across these segments rather than concentrating in a continuous film, preventing crack formation while allowing normal handling operations.
Solution Approach 2:
The recesses are formed in advance before the metal film is subjected to mounting stress. This pre-formed structure acts as a cushioning feature that anticipates and mitigates the impact of future stress applications, allowing the device to withstand inspection and mounting procedures without cracking.
3Stability of the object's composition
If SiC substrate with small linear expansion coefficient is used, then high temperature stability is achieved, but large difference in expansion coefficients between metal film and substrate causes increased stress and crack formation
Solution Approach 1:
The segmented metal film structure with recesses reduces the overall thermal stress by creating expansion gaps. Each segment can expand and contract independently with temperature changes, reducing the cumulative stress that would otherwise build up in a continuous film due to the mismatch with the SiC substrate's thermal expansion properties.
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 configuration effectively suppresses crack formation in the front metal films by reducing stress and corrosion, enhancing the structural integrity of the silicon carbide semiconductor device, particularly under thermal and mechanical stress conditions.
Implementation Method 1
If a plating film of nickel (Ni)/gold (Au) is used as a front metal film, Au corrosion may occur on a Ni surface
Implementation Method 2
since SiC has a small linear expansion coefficient unlike silicon (Si), a difference between the linear expansion coefficient of the plating film and the linear expansion coefficient of a SiC substrate is large, and as a result, there is a problem that the stress of the front metal film increases and a crack is likely to occur
Implementation Method 3
a second metal film that is provided on the first metal film and contains a metal having a lower ionization tendency than ionization tendency of the first metal film
Data Source
AI summary
In a silicon carbide semiconductor device, in a plan view, a plurality of source contact holes is intermittently provided in a second direction along a trench gate, and a source electrode is provided on an insulating film and is electrically connected to a source layer via the plurality of source contact holes. Intermittent recesses reflecting the shapes of the plurality of source contact holes are provided on a surface of the source electrode on a side opposite to the semiconductor substrate.