Field Stop IGBT Back-Side Dopant Activation Without High-Heat Annealing
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Solution Overview
Problem
Existing vertical insulated-gate bipolar transistor (IGBT) devices face challenges in reducing forward collector-emitter voltage drop and switching losses due to high carrier modulation in the N base of the PNP BJT, which degrades the safe operation area and increases the risk of latch-up during load short circuits, particularly due to limitations in controlling doping concentrations and activating impurities without high-temperature processes that can damage front-side structures.
Innovation Solution
The solution involves forming and activating P-type hole injection regions on the top surface of the substrate before epitaxial drift region growth, allowing for controlled dopant concentrations without the need for high-temperature back-side laser or furnace annealing, thereby integrating a Fast Recovery Diode with the IGBT to eliminate external FRD requirements and enhance switching performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature back-side laser or furnace annealing is used to activate implanted boron impurities, then dopant activation is achieved, but front-side structures are damaged
Solution Approach 1:
The patent performs dopant implantation and activation on the back side of the wafer before front-side processing. By completing the boron implantation and low-temperature activation early in the process flow, the need for subsequent high-temperature back-side annealing is eliminated, protecting front-side structures from thermal damage
Solution Approach 2:
The patent introduces a low-temperature activation process as an intermediary step that achieves dopant activation without requiring the high temperatures that would damage front-side structures. This intermediate approach allows activation at temperatures compatible with front-side structure integrity
2Reliability
If doping concentration of P-type hole injection region is increased to improve carrier injection, then injection efficiency improves, but doping control becomes difficult
Solution Approach 1:
The patent establishes the P-type hole injection region with controlled doping concentration through preliminary ion implantation before epitaxial growth. By setting the dopant concentration early in the process with precise ion implantation dosing, subsequent processing steps do not alter the doping level, ensuring both high injection efficiency and precise doping control
Solution Approach 2:
The patent optimizes the boron implantation dose and energy parameters to achieve the desired doping concentration range (1×10^19 to 1×10^21 atoms/cm³) that provides sufficient hole injection while maintaining manufacturing control. The specific parameter selection balances injection efficiency with dopant distribution precision
3Strength
If thick drift region is used to withstand high voltage, then voltage blocking capability improves, but forward voltage drop increases
Solution Approach 1:
The patent introduces a field stop layer with higher doping concentration (1×10^16 to 1×10^18 atoms/cm³) localized between the drift region and collector. This local quality change allows the drift region to maintain its thickness for voltage blocking while the field stop layer provides enhanced field management, reducing the on-state voltage drop without compromising voltage withstand capability
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 approach enables the fabrication of field stop IGBTs with reduced forward voltage drop and improved switching speed, while maintaining robustness and reliability by avoiding high-temperature processes that could damage front-side structures, thus optimizing the safe operation area and load handling capabilities.
Implementation Method 1
the back side of a wafer may be ground and ion implanted with phosphorous or hydrogen to form an N field stop region and with boron to form a P-type hole injection region
Implementation Method 2
A dopant activation process (e.g., annealing) is generally required to remove defects formed during ion implantation and to activate implanted phosphorous impurities to become N-type dopants and implanted boron impurities to become P-type dopants in crystalline silicon
Data Source
AI summary
A field stop insulated gate bipolar transistor (IGBT) fabricated without back-side laser dopant activation or any process temperatures over 450° C. after fabrication of front-side IGBT structures provides activated injection regions with controlled dopant concentrations. Injection regions may be formed on or in a substrate by epitaxial growth or ion implants and diffusion before growth of N field stop and drift layers and front-side fabrication of IGBT active cells. Back-side material removal can expose the injection region(s) for electrical connection to back-side metal. Alternatively, after front-side fabrication of IGBT active cells, back-side material removal can expose the field stop layer (or injection regions) and sputtering using a silicon target with a well-controlled doping concentration can form hole or electron injection regions with well-controlled doping concentration.