Power Transistor Field Stop Region Proton Implantation
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Solution Overview
Problem
Power semiconductor transistors face challenges in optimizing electrical properties such as short circuit ruggedness, hot leakage current, and turn-off softness, particularly due to the limitations in the design and implementation of field stop regions within these devices.
Innovation Solution
A power semiconductor transistor design featuring a field stop region with a specific donor concentration profile, created through proton implantation at controlled angles and energies, which includes a first local maximum with a front width at half maximum that is smaller than the back width, optimizing the electric field distribution and switching behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a field stop region is created by proton implantation through the backside, then the electric field distribution is improved and short circuit ruggedness is enhanced, but the manufacturing precision and control of donor concentration profile are difficult to achieve
Solution Approach 1:
The patent applies parameter changes by systematically varying proton implantation parameters (energy, angle, dose) to achieve the desired donor concentration profile. Specifically, implantation energies of 100-800 keV and angles of 20-60 degrees are used to control the depth and distribution of donors, thereby resolving the contradiction between reliability improvement and manufacturing precision control.
Solution Approach 2:
The patent introduces angular dimensionality by performing proton implantation at oblique angles (20-60 degrees relative to the surface normal) rather than perpendicular incidence. This angular approach creates a controlled lateral distribution of donors that achieves the required concentration profile shape, transforming a one-dimensional depth control problem into a two-dimensional control problem involving both depth and lateral distribution.
2Reliability
If the field stop region has a steep donor concentration gradient, then the electric field drop is increased, but hot leakage current increases and turn-off softness deteriorates
Solution Approach 1:
The patent modifies the donor concentration gradient by adjusting proton implantation parameters to create a more gradual transition. The use of lower implantation energies (100-800 keV range) and oblique angles produces a broader, less steep concentration profile, which reduces hot carrier generation while maintaining adequate electric field control.
Solution Approach 2:
The patent applies local quality by creating spatially varying donor concentrations through angular implantation. The oblique incidence causes donors to be distributed differently at various lateral positions, creating local variations in concentration gradient that reduce peak fields and associated hot leakage while maintaining overall field control.
3Ease of manufacture
If proton implantation is performed at normal incidence, then the process is simple, but the donor concentration profile cannot achieve the required asymmetric shape with front width smaller than back width
Solution Approach 1:
The patent directly applies asymmetry by performing proton implantation at oblique angles (20-60 degrees) rather than normal incidence. This asymmetric approach creates the required asymmetric donor concentration profile where the front width (toward the drift region) is smaller than the back width (toward the backside), achieving the desired profile shape that controls electric field distribution effectively.
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 design enhances short circuit ruggedness, reduces hot leakage current, and improves turn-off softness by providing a laterally homogeneous donor concentration profile, preventing current filamentation and reducing the risk of latch-up, while tailoring the switching behavior of the transistor.
Implementation Method 1
creating a field stop region inside the semiconductor body by means of a at least one proton implantation step, wherein the implantation is carried out through the backside surface at an implantation angle with respect to a backside surface normal, the implantation angle being in the range from 20° to 60°. Further, the implantation is carried out at an implantation energy in the range from 100 keV to 800 keV
Data Source
AI summary
A power semiconductor transistor includes a semiconductor body having a front side and a backside with a backside surface. The semiconductor body includes a drift region of a first conductivity type and a field stop region of the first conductivity type. The field stop region is arranged between the drift region and the backside and includes, in a cross-section along a vertical direction from the backside to the front side, a concentration profile of donors of the first conductivity type that has: a first local maximum at a first distance from the backside surface, a front width at half maximum associated with the first local maximum, and a back width at half maximum associated with the first local maximum. The front width at half maximum is smaller than the back width at half maximum and amounts to at least 8% of the first distance.