Semiconductor Device With Broad Buffer Structure For Soft Recovery
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Solution Overview
Problem
Existing semiconductor diodes face challenges in achieving soft recovery characteristics with high-speed and low-loss performance, particularly in reducing reverse recovery current and suppressing kinked waveforms caused by leakage current, which affects the efficiency and reliability of power conversion systems.
Innovation Solution
A semiconductor device structure and manufacturing method that includes a semiconductor substrate with a broad buffer structure, where the impurity concentration is locally maximized in specific regions, and hydrogen ions are used for irradiation and heat treatment to control carrier lifetime and suppress leakage current, while maintaining high withstand voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If proton irradiation and heat treatment are used to form high-concentration N+ layer, then soft recovery characteristics are achieved, but leakage current increases causing kinked waveforms
Solution Approach 1:
The patent applies local quality by creating distinct regions with different impurity concentrations and lifetime characteristics within the drift layer. A high-concentration N+ layer is formed at a specific depth (5-20 μm from surface) through proton irradiation and heat treatment, while the surface region (0-5 μm) maintains lower concentration and longer lifetime. This spatial differentiation allows the N+ layer to provide soft recovery while the surface region controls leakage current, resolving the contradiction between these two requirements.
Solution Approach 2:
The drift layer is segmented into multiple functional regions: a surface region (0-5 μm) with longer carrier lifetime that suppresses leakage current, and a deeper N+ layer (5-20 μm) with higher impurity concentration that provides soft recovery characteristics. This segmentation allows each region to independently optimize its function, with the surface region preventing kinked waveforms and the N+ layer enabling soft recovery, thus resolving the contradiction.
2Speed
If carrier lifetime is reduced to achieve high-speed operation, then switching speed improves, but reverse recovery current increases
Solution Approach 1:
The patent uses local quality by assigning different lifetime characteristics to different depth regions. The surface region (0-5 μm) maintains longer carrier lifetime to limit reverse recovery current, while the deeper N+ layer (5-20 μm) has shorter lifetime for fast switching. This vertical gradient in lifetime properties allows the device to achieve high-speed operation without excessive reverse recovery current.
Solution Approach 2:
The patent segments the drift layer into a surface region with longer lifetime and a deeper region with shorter lifetime. The surface region acts as a buffer that prevents excessive reverse recovery current, while the deeper region enables fast switching. This segmentation resolves the contradiction between switching speed and reverse recovery current by distributing these opposing requirements to different spatial locations.
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 approach results in semiconductor devices with improved soft recovery characteristics, reduced reverse recovery current, and suppressed kinked waveforms, enhancing the efficiency and reliability of power conversion systems by optimizing carrier lifetime distribution and impurity concentration.
Implementation Method 1
an FZ (float zone) bulk wafer is irradiated with protons (H+) and heat treated to thereby provide hydrogen-related defect complex (HRDC), as donors near a projected range Rp inside the bulk
Implementation Method 2
heat treated to thereby provide hydrogen-related defect complex (HRDC), as donors near a projected range Rp inside the bulk
Implementation Method 3
the spreading of the space charge region is suppressed by the pinning effect of the space charge region (i.e., the phenomenon that expansion of the depletion layer is stopped at the buffer layer)
Data Source
AI summary
A semiconductor substrate and a method of its manufacture has a semiconductor substrate having a carbon concentration in a range of 6.0×1015 to 2.0×1017 atoms/cm3, both inclusively. One principal surface of the substrate is irradiated with protons and then heat-treated to thereby form a broad buffer structure, namely a region in a first semiconductor layer where a net impurity doping concentration is locally maximized. Due to the broad buffer structure, lifetime values are substantially equalized in a region extending from an interface between the first semiconductor layer and a second semiconductor layer formed on the first semiconductor layer to the region where the net impurity doping concentration is locally maximized. In addition, the local minimum of lifetime values of the first semiconductor layer becomes high. It is thus possible to provide a semiconductor device having soft recovery characteristics, in addition to high-speed and low-loss characteristics, while suppressing a kinked leakage current waveform.