Power Semiconductor Device Shadow-Mask Free Ion Implantation
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Solution Overview
Problem
Existing power semiconductor devices face challenges in achieving precise alignment during ion implantation for lifetime control regions, leading to potential misalignment and negative effects on safe operating area and blocking capability, particularly due to the complexity and inaccuracies in using shadow masks for protecting the termination region.
Innovation Solution
A power semiconductor device with a protecting layer that serves as both an irradiation mask and a protective layer, featuring a thin and thick portion to precisely control ion implantation, allowing for accurate placement of the lifetime control region within the active and termination regions without the need for a shadow mask, thereby enhancing alignment precision and reducing the risk of mechanical damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a shadow mask is used to protect the termination region during ion implantation, then the lifetime control region can be formed in the active region, but misalignment occurs leading to ion implantation into the termination region which negatively influences safe operating area and blocking capability
Solution Approach 1:
The patent combines the protective function and mask function into a single structure. The termination region is provided with a protective layer that simultaneously serves as an ion implantation mask, eliminating the need for separate shadow masks and their associated alignment problems.
Solution Approach 2:
The protective layer on the termination region performs multiple functions: it protects the termination region structure, serves as an ion implantation mask to prevent ion penetration into the termination region, and enables precise formation of the lifetime control region in the active region without requiring separate alignment procedures.
2Reliability
If a shadow mask is positioned to protect the termination region, then ion implantation into the termination region is prevented, but the shadow mask positioning is difficult and aligning accuracy is low leading to misalignment
Solution Approach 1:
The protective layer and mask function are merged into a single integrated structure formed directly on the termination region, eliminating the separate shadow mask component and its complex positioning requirements.
Solution Approach 2:
The protective layer on the termination region automatically serves as the ion implantation mask for that region. The mask pattern is defined by the device geometry itself rather than requiring a separate masking step, making the process self-aligning and eliminating positioning complexity.
3Productivity
If the entire anode side surface is irradiated with lifetime control region forming ions, then the lifetime control region is formed in the active region, but ions also implant into the termination region which negatively influences electrical characteristics
Solution Approach 1:
The protective layer provides local protection to the termination region while allowing ion implantation in the active region. This creates spatially selective ion penetration: ions pass through areas without protective layer (active region) but are blocked by the protective layer in the termination region, enabling localized lifetime control without affecting termination region electrical characteristics.
4Reliability
If a shadow mask is used to protect the circumferential portion of the termination region, then ion implantation is prevented in that region, but the shadow mask may mechanically damage the underlying surface during positioning or removal
Solution Approach 1:
The protective layer and mask are merged into a single structure that is already present on the device. This eliminates the need to handle, position, and remove separate shadow masks, thereby eliminating the mechanical damage risk associated with shadow mask operations.
Solution Approach 2:
The protective layer on the termination region inherently serves as the ion implantation mask. Since the protective layer is already part of the device structure, there are no external masks to handle or remove, eliminating the risk of mechanical damage from mask manipulation.
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 solution enables improved electrical characteristics by ensuring precise control of the lifetime control region, reducing the size of the termination region, and minimizing the risk of mechanical damage and pollution, resulting in optimized electrical performance and simplified production processes.
Implementation Method 1
forming a lifetime control region in the semiconductor wafer by irradiating the semiconductor wafer with ions using the protecting layer as an irradiation mask
Implementation Method 2
The thick portion has an inner end and an outer end laterally surrounding the inner end. The plurality of floating field rings is formed below the thick portion of the protecting layer
Data Source
AI summary
A power semiconductor device comprises a wafer (2) having an active region (AR) and a termination region (TR) laterally surrounding the active region; floating field rings in the termination region; a lifetime control region comprising defects reducing a carrier lifetime; and a protecting layer (6) on the wafer. The protecting layer covers the termination region and comprises a thin portion (61) and a thick portion (62) laterally surrounding the thin portion. The thick portion covers the floating field rings. The lifetime control region (5) extends in a lateral direction throughout the active region and in the termination region throughout a portion which is covered by the thin portion and not in a portion which is covered by the thick portion. According to a fabrication method the lifetime control region is formed by irradiating the wafer (2) with ions using the protecting layer (6) as an irradiation mask.