AlGaN Transistor Source Gate Distance Reduction
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Solution Overview
Problem
The existing metal lift-off processes for III-V compound semiconductor manufacturing result in high on-resistance and limited drain current due to a large distance between the source and gate in transistors, leading to contamination and process control issues.
Innovation Solution
A novel method and structure for forming III-V compound semiconductor transistors with a short distance between the ohmic source contact and the gate, allowing for an overhead source structure to be formed simultaneously, which reduces the surface electric field and improves breakdown voltage by minimizing the distance between the source and gate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If metal lift-off process is used to form metal structures, then metal deposition is achieved, but contamination and process control issues occur
Solution Approach 1:
The patent extracts the harmful wet etching step from the metal lift-off process by directly depositing metal contacts through openings in the passivation layer formed by selective etching of the AlGaN layer, eliminating contamination from batch etchants while maintaining metal structure formation capability
Solution Approach 2:
The patent introduces an intermediary approach by using selective AlGaN layer etching to create contact openings before metal deposition, serving as a mediator between the passivation layer and metal contact, thereby avoiding direct contact with contaminated batch etchants
2Reliability
If minimum photoresist is used for metal removal, then metal bridge prevention is achieved, but large distance between source and gate results in high on-resistance
Solution Approach 1:
The patent inverts the conventional approach by not using photoresist for metal deposition at all. Instead, it forms metal contacts directly through selectively etched openings in the AlGaN layer, eliminating the photoresist thickness constraint and enabling minimal source-gate distance for low on-resistance while preventing metal bridges through precise selective etching
3Reliability
If large distance between source and gate is maintained, then metal bridge is prevented, but on-resistance increases and drain current is limited
Solution Approach 1:
The patent inverts the conventional metal lift-off approach by directly depositing metal contacts through selectively etched AlGaN openings, eliminating the need for photoresist and enabling minimal source-gate distance that reduces on-resistance while maintaining reliable metal bridge prevention through precise selective etching control
Data Source
AI summary
A circuit structure includes a substrate, a III-V semiconductor compound over the substrate, a AlxGa(1-X)N (AlGaN) layer over the III-V semiconductor compound, a gate over the AlGaN layer, a passivation film over the gate and over a portion of the AlGaN layer, a source structure, and a drain structure on an opposite side of the gate from the source structure, wherein X ranges from 0.1 to 1. The source structure has a source contact portion and an overhead portion. The overhead portion is over at least a portion of the passivation film between the source contact portion and the gate. A distance between the source contact portion and the gate is less than a distance between the gate and the drain structure.