Low-Temperature Epitaxial Backside Field Stop Layer for IGBTs
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Solution Overview
Problem
Conventional IGBT manufacturing processes require high-temperature thermal driving-in steps that damage aluminum-based electrodes, complicating the process and increasing costs due to the need for protective layers before forming the backside field stop layer.
Innovation Solution
A low-temperature epitaxial method is developed to fabricate the backside field stop layer, involving the formation of conductive type impurity layers using plasma-enhanced chemical vapor deposition (PECVD) with temperatures below 600°C, allowing for the creation of multiple field stop layers with varying impurity concentrations after the front side metal layer is formed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature thermal driving-in step (900°C) is used to fabricate backside field stop layer, then field stop layer can be formed, but front side aluminum electrode is damaged
Solution Approach 1:
The patent changes the temperature parameter from conventional high-temperature (900°C) thermal driving-in to low-temperature (below 600°C) epitaxial growth. This parameter change enables field stop layer formation without damaging the aluminum electrode, as the lower temperature is compatible with the electrode material's thermal stability limits
Solution Approach 2:
The patent replaces the thermal driving-in mechanism with an epitaxial growth mechanism. Instead of using high-temperature thermal diffusion to form the field stop layer, the invention uses low-temperature epitaxial growth to deposit the layer with controlled impurity concentrations, thereby avoiding thermal damage to the aluminum electrode
2Object-affected harmful factors
If protection layer is added to protect front side during backside field stop layer fabrication, then aluminum electrode is protected, but manufacturing process becomes complicated
Solution Approach 1:
The patent performs the backside field stop layer fabrication before forming the front side aluminum electrode. By reversing the sequence of operations, the aluminum electrode is never present during high-temperature processing, eliminating the need for protection layers and simplifying the overall manufacturing process
Solution Approach 2:
The patent inverts the conventional process sequence by fabricating the backside field stop layer first (before front side electrode formation) rather than after. This inversion eliminates the contradiction between electrode protection and process complexity, as the electrode does not yet exist when backside processing occurs
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 enhances breakdown voltage by forming field stop layers with different impurity concentrations without damaging the front side metal layers, thereby improving the overall efficiency and performance of IGBTs.
Implementation Method 1
forming a plurality of second conductive type impurity layers on a back side of the first conductive type substrate by low-temperature epitaxial process
Data Source
AI summary
A low-temperature epitaxial method manufactures backside field stop layer of insulated gate bipolar transistor (IGBT) first provides a first conductive type substrate and fabricates front-side elements and front metal layer on a front side of the IGBT. A second conductive type impurity layer is formed on a back side of the first conductive type substrate by low-temperature epitaxial process and a collector metal layer is formed on bottom face of the first conductive type substrate.