Trench Semiconductor Layout for Hole Extraction and Low Tail Current
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Solution Overview
Problem
Conventional semiconductor devices with both transistors and diodes on the same chip face inefficiencies in hole extraction during turn-off, leading to increased tail current and reduced withstand capability, due to the accumulation of holes between the transistor and diode regions.
Innovation Solution
The semiconductor device incorporates a semiconductor substrate with specific conductivity regions and trench structures, including dummy trench portions and accumulation regions, to enhance carrier injection and reduce hole accumulation, allowing efficient hole extraction during turn-off. This design features a boundary mesa portion with a higher concentration contact region and the absence of accumulation regions in certain areas to facilitate efficient hole extraction and reduce tail current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional semiconductor device with both transistor and diode regions is used, then the device can perform both switching and freewheeling functions, but holes accumulate between the regions causing increased tail current and reduced withstand capability
Solution Approach 1:
The semiconductor substrate is divided into distinct transistor region, diode region, and buffer region with different doping concentrations. This segmentation creates spatial separation of functions, allowing holes to be managed in dedicated buffer zones rather than accumulating in the diode region, thereby reducing tail current while maintaining withstand capability.
Solution Approach 2:
Different regions of the semiconductor substrate are assigned different doping concentrations (first, second, and third conductivity types with varying concentrations). The buffer region has a specific doping concentration between that of the transistor and diode regions, creating local quality variations that facilitate controlled hole extraction and prevent harmful accumulation.
2Area of stationary object
If the diode region is positioned adjacent to the transistor region, then the device structure is compact, but holes flow into the diode region during turn-off increasing tail current
Solution Approach 1:
A buffer region with intermediate doping concentration is introduced between the transistor region and diode region. This intermediary zone acts as a transition area that facilitates controlled hole extraction during turn-off, preventing holes from directly flowing into the diode region while maintaining the compact adjacent structure.
3Power
If accumulation regions are provided in all mesa portions, then carrier injection is enhanced, but hole extraction efficiency decreases during turn-off
Solution Approach 1:
Accumulation regions are selectively provided only in mesa portions of the transistor region, not in the diode region or buffer region. This local differentiation allows enhanced carrier injection where needed (transistor region) while maintaining efficient hole extraction pathways in other regions, resolving the contradiction between injection efficiency and extraction efficiency.
Data Source
AI summary
A semiconductor device includes a semiconductor substrate having a first conductivity type drift region and a second conductivity type base region above the drift region, trench portions at an upper surface of the semiconductor substrate arrayed parallel to one another, each of them penetrating the base region, and mesa portions between respective trench portions. Among the mesa portions, at least one mesa portion includes a first conductivity type first semiconductor region having a higher concentration than the drift region, a second conductivity type second semiconductor region having a higher concentration than the base region, and a first conductivity type accumulation region between the base and drift regions and has a higher concentration than the drift region. The drift region does not extend above the accumulation region. In a longitudinal direction of the trench portions, the accumulation region extends beyond an end portion of the first semiconductor region.