Semiconductor Buffer Layer Segmentation for Leakage and Field Control
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Solution Overview
Problem
Conventional IGBTs face challenges in maintaining a safe operating area during short circuit conditions due to high impurity concentrations in the deep low concentration buffer layer, leading to increased electric fields and leakage currents, with insufficient consideration for reverse bias safe operation areas and lacking specific dopant descriptions for buffer layers.
Innovation Solution
A semiconductor device with a drift layer, a MOSFET part, and two buffer layers, where the first buffer layer has a low impurity concentration and is formed by proton implantation, and the second buffer layer has a higher impurity concentration, formed by ion-implanting group V elements, to optimize impurity distribution and reduce leakage currents and electric fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the impurity concentration of the deep low concentration buffer layer is increased, then leakage current is reduced, but the electric field on the drift layer reverse side becomes too high during short circuit current interruption
Solution Approach 1:
The buffer layer is segmented into two distinct layers: a deep low concentration buffer layer and a shallow high concentration buffer layer. This segmentation allows each layer to perform its specific function - the deep layer reduces leakage current while the shallow layer limits the electric field during short circuit conditions, thereby resolving the contradiction between reducing leakage current and controlling electric field stress.
Solution Approach 2:
Different impurity concentrations are applied at different depths within the buffer region. The deep low concentration buffer layer has lower impurity concentration to reduce leakage current, while the shallow high concentration buffer layer has higher impurity concentration to limit electric field during short circuit. This local differentiation of properties resolves the contradiction by optimizing each region for its specific function.
2Stress or pressure
If the impurity concentration of the deep low concentration buffer layer is decreased, then the electric field during short circuit is reduced, but leakage current increases significantly
Solution Approach 1:
The buffer layer is divided into two functional segments: the deep low concentration layer controls electric field during short circuit, while the shallow high concentration layer suppresses leakage current. This segmentation resolves the contradiction by assigning different optimization goals to different layers rather than requiring a single layer to satisfy both conflicting requirements.
Solution Approach 2:
The invention applies different impurity concentrations at different depths: lower concentration in the deep region to control electric field stress, and higher concentration in the shallow region to suppress leakage current. This local quality differentiation allows simultaneous optimization of both parameters that are contradictory when using a uniform concentration.
3Object-generated harmful factors
If a shallow high concentration buffer layer is added, then leakage current is reduced to sufficiently small levels, but the device complexity increases
Solution Approach 1:
The invention merges the functions of leakage current suppression and electric field control into a single integrated buffer structure consisting of two layers. While this increases structural complexity compared to a single layer, it eliminates the need for separate structures or components, achieving functional integration that balances complexity with performance benefits.
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 solution effectively reduces leakage currents and maintains a high short circuit safe operating area while suppressing oscillations and electric field peaks, enhancing the reverse bias safe operation area and manufacturing efficiency.
Implementation Method 1
a first buffer layer formation step of forming a first buffer layer by ion-implanting protons to a first depth into a reverse side of the drift layer
Implementation Method 2
a second buffer layer formation step of forming a second buffer layer by ion-implanting group V elements to a second depth shallower than the first depth into a reverse side of the first buffer layer
Data Source
AI summary
A semiconductor device includes a drift layer formed of a first conductive type semiconductor material, a MOSFET part including a p-type base layer provided on a front surface of the drift layer, a first n-type buffer layer provided on a reverse side of the drift layer, and a second n-type buffer layer provided on a reverse side of the first n-type buffer layer and having a high impurity concentration. The first n-type buffer layer has a higher impurity concentration than the drift layer and has a total amount of electrically active impurities per unit area of 1.0×1012 cm−2 or less.