SiC MOSFET Base Surface Exposure for Threshold Voltage Stability
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Solution Overview
Problem
Conventional MOSFETs using silicon carbide as a material face significant challenges in stabilizing threshold voltage, leading to variations in electrical characteristics, with existing solutions failing to identify the underlying cause of these variations.
Innovation Solution
A semiconductor device with a silicon carbide substrate having an off-angle main surface and an ohmic electrode where the base surface is exposed at the contact interface, utilizing a TiAlSi or NiSi alloy for the ohmic electrode, and controlling the length of the base surface to ensure stable contact, thereby mitigating variations in threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an ohmic electrode is formed on a silicon carbide substrate without exposing the base surface, then the manufacturing process is simpler, but the threshold voltage varies significantly
Solution Approach 1:
The patent applies local quality by exposing the base surface at specific locations within the contact interface region. This selective exposure creates different surface conditions in different areas: the base surface provides stable electrical contact where needed, while other areas maintain the original substrate structure. This localized modification resolves the contradiction by improving threshold voltage stability without requiring complete structural redesign.
Solution Approach 2:
The patent implements preliminary action by pre-exposing the base surface before forming the ohmic electrode. This preparatory step ensures that the contact interface has the optimal structure in advance, preventing threshold voltage variation from the outset. The base surface exposure is performed as a preliminary treatment that establishes stable electrical characteristics before the electrode formation process completes.
2Reliability
If the base surface is exposed at the contact interface, then threshold voltage stability improves, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by controlling the exposure depth and area of the base surface within specific ranges. By defining quantitative parameters for the base surface exposure (depth, area, location), the patent transforms a qualitative structural requirement into controllable manufacturing parameters. This resolves the contradiction by providing clear specification limits that guide manufacturing precision while achieving the desired electrical stability.
3Manufacturing precision
If conventional MOSFET structures are used without base surface exposure, then the device structure is simpler, but electrical characteristic variation cannot be sufficiently suppressed
Solution Approach 1:
The patent applies local quality by modifying only the contact interface region where base surface exposure is performed, while leaving the rest of the MOSFET structure conventional. This localized approach improves electrical characteristic control at the critical contact interface without requiring complex changes throughout the entire device structure, thus resolving the contradiction between manufacturing precision and device complexity.
Data Source
AI summary
A MOSFET includes a silicon carbide substrate including a main surface having an off angle with respect to a {0001} plane and a source electrode formed in contact with the main surface. A base surface is exposed at at least a part of a contact interface of the silicon carbide substrate with the source electrode. With such a construction, the MOSFET achieves suppressed variation in threshold voltage.