Transistor Cell Body Implant for Wire-Bond Threshold Stability
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Solution Overview
Problem
Existing transistor devices experience threshold voltage drift due to wire bonding, particularly at the gate corners of the grid structure, leading to performance degradation and higher voltage variation, especially under bond wire attachment areas.
Innovation Solution
The solution involves locally increasing the depth and doping level of the body region in specific areas underneath the bond wire attachment areas, introducing a corner body implant to compensate for the threshold voltage drift and mitigate the effects of the two-dimensional electric field at the corners of the transistor cells, thereby achieving more uniform threshold voltage across the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wire bonding is performed on the transistor device, then electrical connections are established, but threshold voltage drift occurs particularly at gate corners leading to performance degradation
Solution Approach 1:
The patent applies preliminary anti-action by introducing a corner body implant before wire bonding to pre-compensate for the threshold voltage drift that will occur during subsequent wire bonding operations. The additional p-type doping at gate corners creates a counter-effect that offsets the negative threshold voltage drift caused by wire bonding, thereby maintaining threshold voltage stability throughout the device lifecycle.
Solution Approach 2:
The patent applies local quality by selectively increasing the p-type doping concentration specifically at the gate corner regions where threshold voltage drift occurs, rather than uniformly across the entire device. This localized corner body implant modifies only the critical areas underneath bond wire attachment points, maintaining uniform threshold voltage without affecting other regions of the transistor device.
2Reliability
If the body region depth and doping level are uniformly increased across all transistor cells, then threshold voltage uniformity improves, but device complexity and manufacturing complexity increase
Solution Approach 1:
The patent applies local quality by selectively increasing the p-type doping concentration specifically at the gate corner regions where threshold voltage drift occurs, rather than uniformly across the entire device. This localized corner body implant modifies only the critical areas underneath bond wire attachment points, maintaining uniform threshold voltage without affecting other regions of the transistor device.
Solution Approach 2:
The patent applies segmentation by dividing the transistor device into two distinct regions: a first area underneath bond wire attachment points where corner body implant is applied to compensate for threshold voltage drift, and a second area outside these regions where standard doping is maintained. This segmentation allows differential doping strategies to be applied to different functional zones, achieving overall uniformity while managing complexity.
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 approach results in reduced negative threshold voltage drift and higher voltage uniformity, maintaining performance comparable to SON packages with minimal impact on RON, even after long use, by locally tuning the threshold voltage within the transistor cells under the bond wire attachment areas.
Implementation Method 1
at least one of the depth and doping level of the body region is locally increased within the transistor cells located within one or more first areas of the first major surface of the semiconductor substrate
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
In an embodiment, a transistor device (10) comprises a semiconductor substrate (11) comprising a first major surface (12) and a plurality of transistor cells (14) formed in the semiconductor substrate (11). Each transistor cell (14) comprises a drift region (29) of a first conductivity type, a body region (30) of a second conductivity type arranged on the drift region (29), the second conductivity type opposing the first conductivity type, a source region (31) of the first conductivity type arranged on the body region (30), a columnar field plate trench (23) extending into the first major surface (12) of the semiconductor substrate (11) and comprising a field plate (26) and a gate trench structure (16) extending into the first major surface (12) of the semiconductor substrate (11) and comprising a gate electrode (18). A first metallization structure is arranged on the first major surface (12) that provides a first contact pad (33) for wire bonding. At least one of the depth and doping level of the body region (30) is locally increased within the transistor cells (14') located within one or more first areas (122) of the first major surface (12) of the semiconductor substrate (11). One or more of the first areas (120) are located underneath the first contact pad (33).