RC-IGBT Field Stop Layer Defect Control
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Solution Overview
Problem
Conventional field stop (FS) structure reverse conducting insulated gate bipolar transistors (RC-IGBTs) integrating IGBT and FWD on a single semiconductor substrate suffer from degraded reverse recovery characteristics due to defects in the FS layer, leading to increased leak current and electrical losses.
Innovation Solution
A method involving the introduction of selenium as a first-conductivity-type impurity, followed by light ion irradiation to form low-lifetime regions and subsequent heat treatment to reduce defect density and adjust carrier lifetime, forming a field stop layer with enhanced impurity concentration and donor conversion, thereby controlling carrier lifetime and reducing electrical losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional electron beam irradiation is used to form low-lifetime regions, then carrier lifetime is reduced, but defect density increases leading to degraded reverse recovery characteristics
Solution Approach 1:
The patent changes the irradiation method from electron beam to light ion (proton or helium ion) irradiation. This parameter change reduces defect density in the FS layer while still achieving the desired carrier lifetime reduction through controlled irradiation dose and energy selection
Solution Approach 2:
The patent replaces electron beam irradiation with light ion irradiation. This substitution uses ions with different physical properties (mass, charge, penetration depth) to achieve the same functional effect (carrier lifetime reduction) while minimizing harmful side effects (defect formation)
2Quantity of substance
If selenium is ion implanted to form field stop layer, then impurity concentration is increased, but defect density increases leading to increased leak current
Solution Approach 1:
The patent performs light ion irradiation before the final heat treatment step. This preliminary action creates controlled defects that facilitate selenium diffusion and activation while the subsequent heat treatment anneals out harmful defects, achieving high impurity concentration with minimal leak current
Solution Approach 2:
The patent optimizes the heat treatment parameters (temperature, time, atmosphere) following light ion irradiation to activate selenium impurities while annealing defects. By carefully controlling these parameters, high impurity concentration is achieved without generating excessive leak current
3Ease of manufacture
If wafer thickness is reduced to lower cost, then manufacturing cost decreases, but wafer cracking occurs during processing
Solution Approach 1:
The patent performs light ion irradiation and heat treatment on the thin wafer before final processing steps. This preliminary action strengthens the wafer structure through controlled defect formation and annealing, enabling thin wafer processing without cracking while maintaining cost advantages
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 method significantly reduces leak current and electrical losses, improves yield rate, and adjusts reverse recovery time, achieving better performance compared to conventional electron beam irradiation methods.
Implementation Method 1
introducing a first-conductivity-type impurity to a rear surface of the semiconductor substrate; performing first heat treating of heat treating and activating the first-conductivity-type impurity, and forming a field stop layer of the first conductivity type
Implementation Method 2
performing a first irradiation of irradiating light ions from the rear surface of semiconductor substrate and forming in the drift layer, a first low-lifetime region having carrier lifetime shorter than that of other regions; performing a second irradiation of irradiating the light ions from the rear surface of the semiconductor substrate and forming in the field stop layer, a second low-lifetime region
Implementation Method 3
performing first heat treating of heat treating and activating the first-conductivity-type impurity; performing second heat treating of reducing a defect density of defects generated in the field stop layer when the second irradiation is performed
Implementation Method 4
performing second heat treating of reducing a defect density of defects generated in the field stop layer
Data Source
AI summary
A method of manufacturing a semiconductor device having an insulated gate bipolar transistor portion and a freewheeling diode portion. The method includes introducing an impurity to a rear surface of a semiconductor substrate, performing first heat treating to activate the impurity to form a field stop layer, performing a first irradiation to irradiate light ions from the rear surface of semiconductor substrate to form, in the semiconductor substrate, a first low-lifetime region, performing a second irradiation to irradiate the light ions from the rear surface of the semiconductor substrate to form, in the field stop layer, a second low-lifetime region, and performing second heat treating to reduce a density of defects generated in the field stop layer when the second irradiation is performed. Each of the first and second low-lifetime regions has a carrier lifetime thereof shorter than that of any region of the semiconductor device other than the first and second low-lifetime regions.