Thinned Wafer Recess for Low On-State Resistance
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Solution Overview
Problem
Conventional methods for manufacturing vertical power devices on thinned wafers face challenges in reducing on-state power loss due to high resistance through the bulk of the device, limiting the minimum thickness of the wafer to about 200 microns to maintain yield and prevent breakage.
Innovation Solution
A method involving the formation of a thinned wafer with a recessed central portion and a thicker peripheral edge support portion, allowing for further thinning of the central portion while maintaining mechanical stability, and the use of a glassivation layer and specific diffusion and metallization steps to reduce on-state resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the wafer thickness is reduced to reduce on-state resistance and power loss, then the on-state power loss decreases, but the mechanical strength and yield deteriorate due to increased likelihood of wafer breakage
Solution Approach 1:
The wafer is segmented into two distinct thickness zones: a thinned central portion (about 50-150 microns) for low resistance and a thicker peripheral edge support portion (about 200-500 microns) for mechanical strength. This segmentation allows each zone to fulfill its specific function optimally without compromising the other.
Solution Approach 2:
Different regions of the wafer are given different local properties: the central region is thinned to reduce resistance for power device operation, while the peripheral region is kept thick to provide mechanical support and prevent breakage during handling and processing.
2Loss of energy
If the wafer thickness is reduced to about 200 microns or less, then the on-state resistance decreases, but the mechanical stability and handling capability worsen
Solution Approach 1:
The wafer structure is divided into a thinned central portion and a thicker peripheral support portion, allowing the central area to be sufficiently thin for low resistance while the peripheral area maintains sufficient thickness for mechanical stability.
Solution Approach 2:
The wafer exhibits non-uniform thickness with locally optimized properties: the central region is thinned to minimize resistance, while the peripheral region retains original thickness to provide mechanical strength and handling stability.
3Device complexity
If the peripheral edge support portion is removed to reduce device complexity, then the manufacturing process simplifies, but the wafer becomes prone to warpage and breakage
Solution Approach 1:
The peripheral edge support portion is retained throughout the manufacturing process to provide preliminary mechanical support during critical operations such as diffusion, metallization, and dicing, preventing warpage and breakage before the final product is completed.
Solution Approach 2:
The thicker peripheral edge support portion acts as a mechanical cushion or support structure that protects the thinned central portion from stress and damage during handling and processing, preventing warpage and breakage in advance.
Data Source
AI summary
A recess is formed into a first side of a wafer such that a thinned center portion of the wafer is formed, and such that the central portion is surrounded by a thicker peripheral edge support portion. The second side of the wafer remains substantially entirely planar. After formation of the thinned wafer, vertical power devices are formed into the first side of the central portion of the wafer. Formation of the devices involves forming a plurality of diffusion regions into the first side of the thinned central portion. Metal electrodes are formed on the first and second sides, the peripheral portion is cut from the wafer, and the thin central portion is diced to form separate power devices. In one example, a first commercial entity manufactures the thinned wafers, and a second commercial entity obtains the thinned wafers and performs subsequent processing to form the vertical power devices.