Trench Separation Diffusion for High Voltage Semiconductor Edge Termination
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Solution Overview
Problem
Existing edge termination techniques for high voltage semiconductor devices are impractical for reverse blocking voltage ratings beyond 3000 volts due to lengthy diffusion times and large lateral dimensions of separation diffusion structures, making them commercially unviable for higher voltage applications.
Innovation Solution
A P-type peripheral aluminum diffusion region and deep peripheral trench structure is implemented, where the P-type dopants are diffused into the sidewalls of the trench, forming a single P-type separation edge diffusion structure that extends from the top to the bottom of the die, surrounding the active area and avoiding bevel edge terminations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional separation edge diffusion is used for high voltage devices, then breakdown protection is achieved, but diffusion time becomes excessively long (10,000 hours for 600 micron wafer)
Solution Approach 1:
The separation diffusion process is divided into two independent stages: first forming a P-type region at the bottom surface, then forming a P-type region at the top surface. These two segmented diffusion processes meet in the middle to create the complete separation diffusion structure, reducing total diffusion time from 10,000 hours to a practical duration.
Solution Approach 2:
The invention transitions from a single-direction (top-down) diffusion approach to a dual-direction (bottom-up and top-down) diffusion strategy. By utilizing both surfaces of the wafer as diffusion sources, the process effectively adds a spatial dimension to the diffusion operation, halving the required diffusion time while maintaining adequate separation depth.
2Reliability
If wafer thickness is increased to withstand higher reverse voltages, then breakdown voltage increases, but diffusion time increases with the square of thickness
Solution Approach 1:
The diffusion task is segmented into two simultaneous operations starting from opposite surfaces. For a 600 micron wafer requiring 10,000 hours of single-source diffusion, the segmented approach uses two sources each diffusing for approximately half the time, achieving the same separation depth much faster.
Solution Approach 2:
The solution adds a spatial dimension by utilizing both top and bottom surfaces as diffusion sources. This bidirectional approach transforms a one-dimensional diffusion problem into a two-directional process, reducing the time required proportionally to the square of the thickness reduction in each direction.
3Reliability
If deep separation diffusion is formed to prevent breakdown, then vertical separation is achieved, but lateral diffusion consumes excessive die area
Solution Approach 1:
The invention applies different doping characteristics to different regions: the separation diffusion regions are formed with controlled lateral spread to provide adequate vertical separation, while the active device regions maintain their original doping profiles for optimal device performance. This local differentiation allows deep separation where needed without unnecessarily consuming die area in active regions.
Solution Approach 2:
The separation diffusion is performed partially from each surface, extending just enough to meet in the middle and provide adequate separation. Rather than forming excessive lateral diffusion from single deep sources, the partial action from both surfaces achieves the required separation with minimal lateral spread, preserving die area for active devices.
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 allows semiconductor devices to withstand very high reverse blocking voltages (e.g., 8500 volts) without breakdown, reducing diffusion time to less than 200 hours and avoiding the complexities and expenses of bevel edge terminations, while maintaining adequate die thickness to retain depletion regions under high reverse blocking voltage.
Implementation Method 1
P type dopants are diffused into the sidewalls of the trench, so that a P type sidewall doped region extends laterally inward from the inner sidewall of the trench
Data Source
AI summary
A manufacturable and economically viable edge termination structure allows a semiconductor device to withstand a very high reverse blocking voltage (for example, 8500 volts) without suffering breakdown. A P type peripheral aluminum diffusion region extends around the bottom periphery of a thick die. The peripheral aluminum diffusion region extends upward from the bottom surface of the die, extending into N- type bulk silicon. A deep peripheral trench extends around the upper periphery of the die. The deep trench extends from the topside of the die down toward the peripheral aluminum diffusion region. A P type sidewall doped region extends laterally inward from the inner sidewall of the trench, and extends laterally outward from the outer sidewall of the trench. The P type sidewall doped region joins with the P type peripheral aluminum diffusion region, thereby forming a separation edge diffusion structure that surrounds the active area of the die.