Low Resistance Isolation Diffusion Structure in High Voltage Power Devices
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Solution Overview
Problem
Conventional high voltage power devices, such as thyristors and diodes, have vertical separation diffusion structures with high resistance due to low dopant concentration at the center, making them unsuitable for applications requiring low resistance current paths, like flip chip applications.
Innovation Solution
A two-step aluminum diffusion process followed by a compensation diffusion step is used to form an isolation diffusion structure with a low resistance current path, where aluminum is diffused into the substrate from both sides, and boron is introduced to compensate for out-diffusion, resulting in a p-type structure extending from the upper to the lower surface of the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional single-step aluminum diffusion process is used to form isolation diffusion structures, then the manufacturing process is simple, but the resulting structure has high resistance due to low dopant concentration at the center
Solution Approach 1:
The diffusion process is divided into three distinct stages: first diffusion step, second diffusion step, and compensation diffusion step. Each stage serves a specific purpose in building up the dopant concentration profile, transforming a single complex diffusion into multiple manageable steps that collectively achieve low resistance.
Solution Approach 2:
The first diffusion step establishes the initial aluminum dopant distribution from both front and back surfaces. This preliminary action creates the foundation for subsequent diffusion steps, allowing the dopant concentration to be progressively enhanced and homogenized in the center region.
Solution Approach 3:
The diffusion process parameters (time, temperature, dopant sources) are changed between steps. The first step uses aluminum sources at specific conditions, the second step extends diffusion time or adjusts conditions to homogenize concentration, and the compensation step adjusts dopant levels to achieve the target low resistance while maintaining high breakdown voltage.
2Object-affected harmful factors
If aluminum sources are removed after the first diffusion step, then surface defects are reduced, but dopant concentration homogeneity deteriorates
Solution Approach 1:
Aluminum sources are removed after the first diffusion step as a preliminary action to prevent surface defects and contamination. This removal is intentional and followed by a second diffusion step that continues dopant diffusion without additional surface sources, achieving both defect reduction and concentration homogenization.
Solution Approach 2:
The diffusion conditions are changed in the second step after source removal. By adjusting diffusion parameters (time, temperature, atmosphere) in the absence of surface sources, the process homogenizes dopant concentration throughout the substrate thickness while maintaining clean surfaces free from aluminum-related defects.
3Power
If the isolation diffusion structure is designed to carry high current, then the device handles higher power, but the resistance must be reduced below conventional levels
Solution Approach 1:
The dopant concentration profile is segmented into different regions through multi-step diffusion: higher concentration near surfaces from the first step, and enhanced central concentration from the second step. This segmentation of the diffusion process creates an optimized profile that minimizes resistance while maintaining structural integrity for high current handling.
Solution Approach 2:
The compensation diffusion step changes the dopant parameters by introducing additional dopants or adjusting diffusion conditions to specifically target and reduce the resistance of the isolation diffusion structure. This parameter adjustment enables the structure to carry high currents (10-200 amperes) while maintaining low resistance values.
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 achieves a significantly lower resistance in the isolation diffusion structure, enabling it to handle higher currents and voltages, specifically 10 A and 1600 V, while reducing surface defects and enhancing the structure's suitability for flip chip applications.
Implementation Method 1
The substrate is annealed for a first given time to drive the dopants from the first and second dopants sources into the substrate
Implementation Method 2
The substrate is annealed for a second given time to homogenize dopant concentration within the substrate after the first and second dopant sources have been removed
Implementation Method 3
annealing the substrate for the second given time results in out-diffusion of dopants proximate the upper and lower surfaces of the substrate
Data Source
AI summary
A method for forming a high voltage semiconductor power device comprises providing a first dopant source of first conductivity on an upper surface of a substrate of second conductivity. A second dopant source of first conductivity is provided on a lower surface of the substrate. The substrate is annealed for a first given time to drive the dopants from the first and second dopants sources into the substrate. The first and second dopant sources are removed from the upper and lower surfaces of the substrate. The substrate is annealed for a second given time to homogenize dopant concentration within the substrate after the first and second dopant sources have been removed, where the annealing the substrate for the second given time results in out-diffusion of dopants proximate the upper and lower surfaces of the substrate. Compensation dopants are provided into the substrate after annealing the substrate for the second given time to compensate the out-diffusion of the dopants proximate the upper and lower surfaces. The dopants driven into the substrate define an isolation diffusion structure that extends from the upper surface to the lower surface.