HEMT Trench Passivation Structure for Current Collapse Reduction
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Solution Overview
Problem
Group III nitride semiconductor HEMT devices experience current collapse due to polarization effects causing drain current to decrease and dynamic on-resistance to increase, especially in high-frequency and high-voltage applications.
Innovation Solution
A method involving the formation of a heterojunction structure with a cap layer, passivation layers, and a P-type semiconductor layer on the trench inner wall, using specific etching techniques to minimize surface defects and enhance electron release back to the gate, thereby reducing current collapse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional HEMT device structure is used, then the device can operate as a high-frequency or high-voltage switching device, but current collapse occurs causing drain current to decrease and dynamic on-resistance to increase
Solution Approach 1:
The patent extracts and removes the harmful positively charged ionized donors from the barrier layer surface through selective etching processes. By creating a trench and removing the second passivation layer and part of the first passivation layer, the patent enables access to and removal of surface ionized donors that cause current collapse, while preserving the underlying heterojunction structure that provides high-power capability.
Solution Approach 2:
The patent converts the harmful polarization effect that creates surface ionized donors into a beneficial structure by using the same polarization-induced 2 DEG in the heterojunction interface to maintain channel conductivity, while simultaneously removing only the surface ionized donors through selective etching. This distinguishes between the useful bulk polarization effect and the harmful surface accumulation effect.
2Stability of the object's composition
If electrons migrate to the barrier layer surface to neutralize ionized donors, then the off-state electric field is managed, but the electrons cannot migrate back to the gate in time causing dynamic on-resistance to increase
Solution Approach 1:
The patent extracts the trapped electrons from the barrier layer surface by creating a trench structure and removing surface layers through selective etching. This allows trapped electrons to be removed from positions where they would otherwise migrate slowly back to the gate, thereby reducing the time delay in electron return and decreasing dynamic on-resistance.
3Ease of manufacture
If the cap layer is removed to access the heterojunction structure for etching, then the barrier layer surface can be treated, but the heterojunction structure may be damaged
Solution Approach 1:
The patent performs preliminary action by forming a trench structure and selectively removing the second passivation layer before attempting to access or treat the barrier layer surface. This preliminary trench formation provides controlled access pathways that enable subsequent surface treatment without requiring complete removal of the cap layer, thereby protecting the heterojunction structure integrity.
Solution Approach 2:
The patent uses the trench structure and selective passivation layer removal as an intermediary approach. Instead of directly removing the cap layer to access the barrier layer, the patent creates a controlled intermediate pathway through the passivation layers, allowing selective access to specific regions while maintaining overall structure protection.
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 method effectively reduces dynamic on-resistance by enhancing electron release to the gate, minimizing surface defects, and improving the stability of the heterojunction structure.
Implementation Method 1
the cap layer is used to protect the heterojunction structure during the wet etching
Implementation Method 2
a part of the second passivation layer is removed by dry etching
Implementation Method 3
a part of the first passivation layer is removed by wet etching
Implementation Method 4
The principle is that when an HEMT device is working in an off state, an electric field intensity on a side of a gate biased toward a drain reaches its maximum, so that electrons on the gate jump to a surface of the barrier layer under the action of an electric field force
Data Source
AI summary
The present application provides a semiconductor structure and a manufacturing method thereof. The semiconductor structure includes: a semiconductor substrate, a heterojunction structure, a cap layer, a first passivation layer and a second passivation layer disposed from bottom to up; a trench penetrating through the first passivation layer and the second passivation layer; and a P-type semiconductor layer located at least on an inner wall of the trench. After a part of the second passivation layer is dry etched to form the trench, the first passivation layer can be used for etching endpoint detection to avoid over etching. A part of the first passivation layer exposed by the trench of the second passivation layer can be removed by wet etching.