Trench MOSFET Metal Gate Cap for Simpler Power Transistor Fabrication
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Solution Overview
Problem
Existing transistor devices for power applications, such as Si CoolMOS, Si Power MOSFETs, and Si IGBTs, face challenges in manufacturing simplicity and performance enhancement, particularly with the use of metal gate electrodes which require integration into the front-end of line process.
Innovation Solution
A transistor device structure featuring a semiconductor substrate with a metal gate electrode in a gate trench, encapsulated by an electrically insulating cap, and optionally including charge compensation structures like field plates, allowing for standard wet chemical cleaning processes and improved manufacturing feasibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal gate electrode is integrated into the front-end of line process, then device performance is improved, but manufacturing complexity increases
Solution Approach 1:
The gate electrode is segmented into two distinct parts: a metal gate electrode formed in the gate trench for performance enhancement, and a polysilicon gate electrode formed later in the process for manufacturing simplicity. This segmentation allows each material to serve its optimal function while simplifying the overall manufacturing process.
Solution Approach 2:
The metal gate electrode is formed preliminarily during the front-end of line process, before the polysilicon gate electrode is formed. This preliminary action ensures the metal gate is in place to enhance device performance from the outset, while the subsequent polysilicon formation simplifies the manufacturing process.
2Productivity
If a metal gate electrode is used, then switching performance is improved, but manufacturing simplicity is reduced
Solution Approach 1:
The gate structure is segmented into metal and polysilicon portions, allowing the metal gate to provide superior switching performance while the polysilicon gate can be formed using standard, simple manufacturing processes that are easier to implement.
Solution Approach 2:
The polysilicon gate electrode acts as an intermediary that bridges the gap between the metal gate electrode and the control electrode. This intermediary allows the use of metal for performance enhancement while maintaining manufacturing simplicity through standard polysilicon processing techniques.
3Reliability
If the metal gate electrode is exposed to electrical fields, then charge compensation is improved, but device ruggedness is reduced
Solution Approach 1:
The insulating cap serves as an intermediary layer between the metal gate electrode and the high electrical fields in the drift region. This intermediary protects the metal gate electrode from direct exposure to damaging electrical fields while still allowing it to perform its charge compensation function.
Solution Approach 2:
The insulating cap is formed beforehand to cushion and protect the metal gate electrode from the harsh electrical field environment. This protective layer is in place before the device operates, preventing field-induced damage to the metal gate electrode.
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 proposed structure simplifies the manufacturing of metal gate transistor devices, enables homogeneous switching across the chip, reduces switching losses, and enhances device ruggedness by encapsulating the metal gate electrode and reducing exposure to electrical fields.
Implementation Method 1
a gate dielectric lining the gate trench
Implementation Method 2
an electrically insulating cap arranged on the metal gate electrode and within the gate trench
Implementation Method 3
the lower dielectric layer is formed using a HDP (High Density Plasma) deposition process
Implementation Method 4
the upper dielectric layer comprises a TEOS layer, i.e. is deposited using a TEOS (Tetraethyl orthosilicate) process
Data Source
AI summary
In an embodiment, a transistor device a semiconductor substrate having a main surface, and a cell field including a plurality of transistor cells of a power transistor. The cell field further includes: a body region of a second conductivity type; a source region of a first conductivity type on or in the body region, the first conductivity type opposing the second conductivity type; a gate trench in the main surface of the semiconductor substrate; a gate dielectric lining the gate trench; a metal gate electrode arranged in the gate trench on the gate dielectric; and an electrically insulating cap arranged on the metal gate electrode. A method of fabricating a gate of the transistor device is also described.