SiC Shielding Structure for Trench Gate Oxide Field Control
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Solution Overview
Problem
SiC power devices face challenges in achieving long-term reliability due to limitations in gate oxide shielding, particularly in trench-gate designs where field crowding and implantation energy constraints lead to inadequate shielding, affecting threshold voltage stability and increasing ON-resistance.
Innovation Solution
A shielding structure with a higher net doping concentration than the current-conduction region, where the shielding region's length to width ratio is between 1 to 10, effectively shields the gate oxide from electric fields, reducing the impact of trench width and n-type region width on electric field magnitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type buried implant is used for gate oxide shielding in trench-gate devices, then shielding is provided, but the implantation energy limitations result in a very limited depth of about only 500 nm below the gate trench bottom
Solution Approach 1:
The patent changes the doping concentration parameter of the shielding region, specifying a net doping concentration between 1×10^19 cm^-3 and 1×10^21 cm^-3. This high doping concentration enables effective shielding at the limited depth achievable by implantation, resolving the contradiction between shielding effectiveness and implantation depth limitations
Solution Approach 2:
The patent creates a localized highly doped region adjacent to the gate trench bottom with specific dimensional parameters (length L between 0.5-5 μm, width W between 0.1-1 μm, and L/W ratio between 1-10). This localized high-quality shielding region provides concentrated field control where it is most needed, achieving effective shielding within the constrained implantation depth
2Adaptability or versatility
If the width of the n-type region between neighboring p-type shielding regions is increased for dual-channel designs, then both gate trench sidewalls can be used as channel regions, but the electric field at the gate oxide becomes sensitive to trench depth and n-type region width
Solution Approach 1:
The patent specifies precise parameter ranges for the shielding region (doping concentration 1×10^19-1×10^21 cm^-3, length 0.5-5 μm, width 0.1-1 μm, L/W ratio 1-10) that stabilize the electric field distribution. These controlled parameters compensate for the increased n-type region width required for dual-channel operation, maintaining threshold voltage stability
Solution Approach 2:
The patent places the p-type shielding region in advance at the gate trench bottom before operation, creating a pre-configured field control structure. This preliminary shielding structure counteracts the field crowding effects that would otherwise occur in dual-channel designs with wider n-type regions, preventing threshold voltage instability before it occurs
3Reliability
If the lateral distance between the edge of the p-type shielding regions and each trench sidewall is reduced, then proper shielding is ensured, but the p-implantation tail comes close to the trench sidewalls and renders the channel doping sensitive to trench width
Solution Approach 1:
The patent optimizes the shielding region dimensions (length L: 0.5-5 μm, width W: 0.1-1 μm) and doping concentration (1×10^19-1×10^21 cm^-3) to achieve effective shielding while controlling the lateral extent. The L/W ratio constraint (1-10) ensures the shielding region extends sufficiently laterally to provide proper field control without creating an excessive implantation tail that would compromise threshold voltage precision
4Reliability
If a p-type implant below the trench is used for two-sided channel shielding, then shielding is provided, but the channel region must be interrupted which increases the ON-resistance
Solution Approach 1:
The patent creates a localized shielding region with specific dimensions (length L: 0.5-5 μm, width W: 0.1-1 μm) positioned adjacent to the gate trench bottom. This localized approach provides shielding exactly where the electric field is strongest, without requiring extensive implantation that would interrupt the channel region and increase ON-resistance
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 solution enhances gate oxide reliability by maintaining electric field penetration below critical levels, reducing ON-resistance, and stabilizing threshold voltage, while avoiding dielectric breakdown and implantation tail issues.
Implementation Method 1
a shielding region of a second conductivity type laterally adjacent to the current-conduction region and configured to at least partly shield the device structure from the electric field
Data Source
AI summary
A semiconductor device includes: a SiC substrate; a device structure in or on the SiC substrate and subject to an electric field during operation of the semiconductor device; a current-conduction region of a first conductivity type in the SiC substrate adjoining the device structure; and a shielding region of a second conductivity type laterally adjacent to the current-conduction region and configured to at least partly shield the device structure from the electric field. The shielding region has a higher net doping concentration than the current-conduction region, and has a length (L) measured from a first position which corresponds to a bottom of the device structure to a second position which corresponds to a bottom of the shielding region. The current-conduction region has a width (d) measured between opposing lateral sides of the current-conduction region, and L/d is in a range of 1 to 10.