Semiconductor Buffer Layer Structure for Low-Leakage High Breakdown Voltage
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Solution Overview
Problem
Semiconductor devices with high breakdown voltage suffer from increased crystal defects due to proton implantation, leading to reduced minority carrier concentration and increased leakage current, causing high surge voltage and oscillation during switching operations.
Innovation Solution
A semiconductor device with multiple n-type buffer layers formed by proton implantation, where the peak carrier concentration of the closest buffer layer is deeper than 15 μm, and the carrier concentration between buffer layers is calculated to ensure a flat distribution, reducing crystal defects and enhancing minority carrier storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If proton implantation is performed to form n-type buffer layer, then breakdown voltage is improved, but crystal defects increase leading to increased leakage current
Solution Approach 1:
The patent divides the n-type buffer layer into multiple regions with different impurity concentrations. By forming a first n-type buffer layer with higher impurity concentration and a second n-type buffer layer with lower impurity concentration, the structure segments the single buffer layer into functional zones that collectively suppress leakage current while maintaining high breakdown voltage.
Solution Approach 2:
The patent applies local quality by creating regions with different impurity concentrations within the n-type buffer layer. The first n-type buffer layer has a higher impurity concentration than the second n-type buffer layer, allowing each region to perform its specific function: the higher concentration region suppresses leakage, while the lower concentration region maintains breakdown voltage.
2Strength
If proton implantation is performed to form n-type buffer layer, then breakdown voltage is improved, but minority carrier concentration decreases causing oscillation during switching
Solution Approach 1:
The patent segments the n-type buffer layer into multiple regions with different impurity concentrations to balance breakdown voltage and minority carrier storage. The first n-type buffer layer with higher impurity concentration suppresses leakage, while the second n-type buffer layer with lower impurity concentration maintains minority carrier concentration for stable switching.
Solution Approach 2:
The patent changes the impurity concentration parameter across different regions of the n-type buffer layer. By creating a gradient from higher to lower impurity concentration, the structure optimizes both breakdown voltage and minority carrier storage capacity, preventing oscillation during switching operations.
3Strength
If n-type buffer layer with higher impurity concentration is formed, then depletion layer spreading is suppressed, but manufacturing complexity increases
Solution Approach 1:
The patent segments the n-type buffer layer formation process into two distinct implantation steps: first forming a buffer layer with higher impurity concentration, then forming a buffer layer with lower impurity concentration. This segmentation allows precise control of electrical characteristics while managing manufacturing complexity through systematic process design.
Solution Approach 2:
The patent performs preliminary proton implantation to form the first n-type buffer layer with higher impurity concentration before forming the second n-type buffer layer with lower impurity concentration. This preliminary action establishes the foundation for suppressing depletion layer spreading, which then guides subsequent processing steps.
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 suppresses depletion layer spreading, ensures high breakdown voltage, reduces generation loss, and minimizes voltage and current oscillation during switching, thereby reducing leakage current and thermal runaway risks.
Implementation Method 1
a method has been known which forms a hydrogen-related donor using the implantation of hydrogen (H) ions (protons) which have a long range at a relatively low acceleration voltage
Implementation Method 2
When protons are implanted into the n-type silicon substrate 51 (for example, a bulk substrate (wafer) formed by a floating zone (FZ) method) including an oxygen (O) atom, a hydrogen (H) atom and the oxygen (O) atom are combined with a vacancy (V) defect which occurs due to the implantation to generate a composite defect. As a result, a vacancy-oxide-hydrogen (VOH) defect occurs. The VOH defect becomes a donor (hydrogen-related donor) which supplies an electron.
Implementation Method 3
An activation process for increasing the donor concentration of the VOH defect can be implemented by low-temperature annealing (heat treatment) which is performed at a temperature of about 380° C.
Data Source
AI summary
A semiconductor device is disclosed in which proton implantation is performed a plurality of times to form a plurality of n-type buffer layers in an n-type drift layer at different depths from a rear surface of a substrate. The depth of the n-type buffer layer, which is provided at the deepest position from the rear surface of the substrate, from the rear surface of the substrate is more than 15 μm. The temperature of a heat treatment which is performed in order to change a proton into a donor and to recover a crystal defect after the proton implantation is equal to or higher than 400° C. In a carrier concentration distribution of the n-type buffer layer, a width from the peak position of carrier concentration to an anode is more than a width from the peak position to a cathode.