Semiconductor Field Stop Layer for Energy Loss Reduction

Solution Overview

Problem

Semiconductor devices with thin wafers face energy loss issues due to increased leak current and reduced breakdown voltage, particularly when high oxygen impurity content is used, as the depletion layer easily reaches the back surface, leading to inefficient energy conversion.

Innovation Solution

A semiconductor device with a field stop layer having a higher impurity concentration than the drift layer, featuring a net carrier concentration profile with at least one peak and a hydrogen atom concentration profile with multiple peaks, which is formed under the same process conditions regardless of oxygen impurity content, effectively suppressing energy loss by creating a high resistivity region and improving productivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the semiconductor wafer is thinned to reduce resistance and energy loss, then energy loss is reduced, but breakdown voltage deteriorates and leak current increases

Engineering Contradiction:

Improveenergy lossVSAvoidbreakdown voltage

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent applies local quality by creating a buffer layer with specific impurity concentration (1×10^16 to 1×10^18 atoms/cm³) at the back surface region of the thinned wafer. This localized modification allows the depletion layer to be gently stopped at the buffer layer, preventing it from reaching the back surface and causing breakdown, while maintaining low resistance in the bulk drift layer for low energy loss.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the impurity concentration parameter by introducing a buffer layer with higher impurity concentration than the drift layer at the back surface. This parameter change creates a potential well that stops the depletion layer, allowing thin wafer design (low energy loss) while maintaining adequate breakdown voltage through the buffer layer's electrical properties.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If a buffer layer is formed to stop the depletion layer, then breakdown voltage is maintained, but manufacturing complexity increases

Engineering Contradiction:

Improvebreakdown voltageVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent merges the buffer layer formation with the existing field stop layer implantation process. By using the same ion implantation equipment and process flow to create both the field stop layer and buffer layer, the manufacturing complexity is minimized while achieving the required breakdown voltage maintenance through the combined structure.

Inventive Principle:

Principle #5Merging (Combining)

3Device complexity

If a field stop layer is formed using conventional methods, then the structure is simple, but energy loss deteriorates when high oxygen impurity content is used

Engineering Contradiction:

Improvestructure simplicityVSAvoidenergy loss

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent applies local quality by creating a buffer layer with specific impurity concentration (1×10^16 to 1×10^18 atoms/cm³) at the back surface region of the thinned wafer. This localized modification allows the depletion layer to be gently stopped at the buffer layer, preventing it from reaching the back surface and causing breakdown, while maintaining low resistance in the bulk drift layer for low energy loss.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the impurity concentration parameter by introducing a buffer layer with higher impurity concentration than the drift layer at the back surface. This parameter change creates a potential well that stops the depletion layer, allowing thin wafer design (low energy loss) while maintaining adequate breakdown voltage through the buffer layer's electrical properties.

Inventive Principle:

Principle #35Parameter changes

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 reduces energy loss and maintains consistent electrical properties across different oxygen and carbon impurity concentrations, enhancing the semiconductor device's performance and manufacturing efficiency.

Implementation Method 1

performing a heat treatment in which the first conductivity type impurities are diffused

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

performing a heat treatment in which the first conductivity type impurities are diffused

Methodology Applied

Scientific EffectHeat treatment: Heat Treatment

Data Source

PatentUS20240072124A1Semiconductor device, method of manufacturing semiconductor device, and power conversion device

Publication Date: 2024.02.29 MITSUBISHI ELECTRIC CORP

AI summary

Provided is a semiconductor device and a method of manufacturing a semiconductor device in which deterioration of energy loss is suppressed. The semiconductor device includes: a drift layer of a first conductivity type provided between a first main surface and a second main surface of a semiconductor substrate; and a field stop layer of the first conductivity type having an impurity concentration higher than that of the drift layer and provided between the drift layer and the second main surface. A net carrier concentration profile at room temperature of the field stop layer have at least one peak from the second main surface toward the first main surface. A hydrogen atom concentration profile of the field stop layer have at least two peaks from the second main surface toward the first main surface. The hydrogen atom concentration profile has more peaks than the net carrier concentration profile.