IGBT Backside Field Stop Layer via Low-Temperature Laser Annealing
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Solution Overview
Problem
Conventional IGBT manufacturing processes require high-temperature thermal driving-in steps for field stop layers, which damage aluminum-based electrodes and complicate the manufacturing process, especially when forming backside field stop layers after protecting the front side electrode.
Innovation Solution
A low-temperature oxide method is employed to fabricate backside field stop layers in IGBTs, involving a multiple-recesses structure with amorphous silicon layers and laser annealing, allowing for the formation of field stop layers after the front side metal layer is formed, simplifying the process and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-temperature thermal driving-in step is used for field stop layer fabrication, then the field stop layer can be formed, but the aluminum-based electrode is damaged
Solution Approach 1:
The patent changes the temperature parameter from conventional high temperature (900°C) to low temperature (700-850°C) for the thermal driving-in step. This parameter change allows the field stop layer to be formed while preventing damage to the aluminum-based electrode, as the lower temperature is sufficient for dopant diffusion but below the damage threshold for the electrode material
Solution Approach 2:
The patent replaces the conventional high-temperature thermal process with a low-temperature thermal process combined with laser annealing. The laser annealing provides localized high energy to achieve the necessary dopant activation and diffusion without requiring overall high temperature treatment that would damage the electrode
2Object-affected harmful factors
If protection layer is used to protect front side electrode before backside field stop layer fabrication, then the electrode is protected, but the manufacture process becomes complicated
Solution Approach 1:
The patent performs the field stop layer fabrication on the backside of the substrate before forming the front side aluminum-based electrode. This preliminary action eliminates the need for protection layers during subsequent electrode formation processes, as the field stop layer is already in place and the electrode is formed last, avoiding any potential damage or complexity
Solution Approach 2:
The patent inverts the conventional sequence by fabricating the backside field stop layer before the front side electrode rather than after. This inversion of the process sequence eliminates the need for protection layers and simplifies the overall manufacturing process, as each step can proceed without protecting previously formed structures
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
This method simplifies the manufacturing process, reduces costs, and enables the formation of multiple field stop layers with varying impurity concentrations, thereby enhancing breakdown voltage.
Implementation Method 1
laser annealing the first conductive type amorphous silicon layers in the multiple-recesses structure to form a plurality of backside field stop layers
Data Source
AI summary
A low-temperature oxide method is used for manufacturing backside field stop layer of IGBT and first fabricates front elements and front metal layer on a first face of a first conductive type substrate. A multiple-recesses structure is formed on a back side of the first conductive type substrate. Each of the recess in the multiple-recesses structure has first conductive type implanted patterns on exterior sides thereof and the multiple-recesses structure has a first conductive type implanted layer on bottom thereof. A plurality of first conductive type polysilicon layers are deposited into the multiple-recesses structure and respectively corresponding to the first conductive type implanted patterns. A second conductive type impurity layer is formed on the bottom of the first conductive type substrate and laser annealing is conducted to form backside field stop layer for IGBT.