Power Transistor Epitaxial Expansion Layer Conductivity
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Solution Overview
Problem
The conductivity of n-trench MOSFETs is negatively affected in forward operation due to high field strengths, and setting the doping concentration for expansion layers is problematic, which compromises the transistor's performance.
Innovation Solution
A method involving the application of a first epitaxial layer with a specific doping concentration to create an expansion layer inside the semiconductor substrate, combined with trench structure formation using a silicon dioxide hard mask and precise doping techniques, enhances conductivity while ensuring high blocking strength and reducing feedback capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If deep-reaching, highly-doped p-regions are used to protect the gate oxide from high field strengths, then blocking strength is improved, but conductivity in forward operation deteriorates
Solution Approach 1:
The patent applies different doping concentrations at different depths: highly-doped p-regions at shallow depths for blocking strength, and an expansion layer with lower doping concentration at greater depths for improved conductivity. This spatial differentiation of doping quality resolves the contradiction between blocking strength and forward operation conductivity.
Solution Approach 2:
The patent changes the doping concentration parameter with depth, creating an expansion layer where the doping concentration is lower than in the highly-doped p-regions but higher than in the drift region. This parameter gradient optimizes both blocking strength and conductivity by having high doping where needed for protection and lower doping where it would harm forward operation.
2Reliability
If expansion layers are added to improve conductivity in forward operation, then conductivity is improved, but manufacturing complexity increases due to problematic doping concentration setting
Solution Approach 1:
The expansion layer is formed during the preliminary epitaxial growth stage, before trench formation and subsequent processing steps. By incorporating the expansion layer in the initial epitaxial layer with predetermined doping concentration, the patent avoids the complexity of later doping operations and simplifies the overall manufacturing process.
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 achieves high conductivity in forward operation with maintained blocking strength and reduced feedback capacitance, allowing for efficient power transistor performance.
Implementation Method 1
applying a first epitaxial layer having a first doping concentration to a front side of a semiconductor substrate
Implementation Method 2
the expansion layer is produced with the aid of implantation of dopants
Implementation Method 3
the hard mask is elevated after structuring and is reduced with the aid of dry etching
Data Source
AI summary
A method for manufacturing a power transistor. The method includes: applying a first epitaxial layer including a first doping concentration to a front side of a semiconductor substrate, producing an expansion layer, which is situated inside the first epitaxial layer, producing various implanted areas starting from the front side of the semiconductor substrate, producing a trench structure starting from the front side of the semiconductor substrate, producing first isolation areas in the surroundings of the trench structure, producing transistor heads, and applying metal layers.