SiC Super Junction Device Trench Impurity Injection
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Solution Overview
Problem
The manufacturing of SiC semiconductor devices faces challenges in achieving effective super junction structures due to difficulties in SiC regrowth related to off-angle issues and high impurity diffusion, leading to increased time and cost, especially when using multi-epitaxial growth methods.
Innovation Solution
A method involving the formation of trenches in a SiC semiconductor layer, where second conductivity type impurities are injected onto the inner surface to create column regions, allowing for controlled impurity distribution and the formation of a super junction structure with an insulating film, which improves withstand voltage and reduces capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-epitaxial growth method is used to form super junction structure in SiC, then super junction structure can be formed, but manufacturing time and cost increase significantly
Solution Approach 1:
The manufacturing process is segmented into distinct steps: first forming trenches in the SiC semiconductor layer, then selectively injecting second conductivity type impurities onto the inner surfaces of these trenches. This segmentation allows the super junction structure to be formed more efficiently compared to the multi-epitaxial growth method, reducing manufacturing time while achieving the same structural outcome.
Solution Approach 2:
Trenches are formed in advance before impurity injection. This preliminary action creates predefined pathways and surfaces that guide the subsequent impurity injection process, enabling faster and more controlled formation of the super junction structure compared to forming it through multiple epitaxial growth cycles.
2Reliability
If second conductivity type SiC is embedded in trench to form super junction structure, then structure can be formed, but SiC regrowth is difficult due to off angle issues
Solution Approach 1:
Instead of embedding second conductivity type SiC material into trenches and attempting regrowth (which fails due to off-angle issues), the invention inverts the approach: trenches are formed first, then second conductivity type impurities are injected onto the trench inner surfaces. This inversion eliminates the regrowth problem entirely while achieving the desired super junction structure.
Solution Approach 2:
The mechanical process of embedding and regrowing SiC material is replaced with a chemical/diffusion-based impurity injection process. This substitution avoids the mechanical regrowth difficulties associated with off-angle trenches, as impurities can be deposited and activated without requiring epitaxial regrowth.
3Reliability
If impurities are injected into SiC layer, then super junction structure can be formed, but impurity diffusion is limited due to high density of SiC
Solution Approach 1:
Impurities are injected specifically onto the inner surfaces of trenches, creating localized high-concentration regions exactly where needed. The trench structure confines the impurity injection to specific locations, ensuring precise spatial control of the super junction structure formation despite SiC's low impurity diffusion characteristics.
Solution Approach 2:
The trench structure serves as an intermediary that facilitates impurity injection. By providing defined inner surfaces and confined spaces, the trenches act as a mediator that overcomes SiC's low impurity diffusion, enabling precise impurity placement through surface injection and subsequent activation processes.
4Reliability
If number of epitaxial layers is increased to compensate for low impurity diffusion, then super junction structure can be formed, but manufacturing complexity and cost increase
Solution Approach 1:
The invention extracts the impurity injection process from the epitaxial growth process itself. Instead of forming multiple epitaxial layers with impurities incorporated during growth, the method separates these functions: a single epitaxial layer is formed, then impurities are injected separately into trenches. This extraction eliminates the need for multiple complex epitaxial growth cycles.
Solution Approach 2:
The invention changes the process parameters from multiple epitaxial growth cycles to a single growth cycle followed by impurity injection. This parameter change (from multi-step growth to single-step growth plus post-processing) reduces manufacturing complexity while achieving the same super junction structure, leveraging SiC's low diffusion property as an advantage for precise impurity placement rather than a disadvantage.
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
This approach enables the simple and cost-effective production of semiconductor devices with enhanced withstand voltage and reduced capacitance, while preventing impurity diffusion and ensuring accurate concentration profiles, thereby effectively addressing the challenges of SiC semiconductor manufacturing.
Implementation Method 1
a step of forming a second conductivity type column region along the inner surface of each trench by injecting second conductivity type impurities onto the inner surface of the trench
Implementation Method 2
A pn junction is formed along the depth direction of the trench at the interface between the second conductivity type column region formed as described above and the first conductivity type column region. Then, a depletion layer is formed in a direction orthogonal to the depth direction of the trench from the interface (pn junction).
Data Source
AI summary
This semiconductor device includes: a semiconductor layer that is formed of first conductivity-type SiC; a plurality of trenches that are formed in the semiconductor layer; second conductivity-type column regions that are formed along the inner surfaces of the trenches; a first conductivity-type column region that is disposed between the adjacent second conductivity-type column regions; and insulating films that are embedded in the trenches. The semiconductor device is capable of improving a withstand voltage by means of a super junction structure. The semiconductor device may also include an electric field attenuation section for attenuating electric field intensity of a surface section of the first conductivity-type column region.