Wafer Thinning via Annular Reinforcing Portion
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Solution Overview
Problem
The existing techniques for thinning semiconductor wafers during the manufacturing of vertical power semiconductor devices face challenges in preventing breakage due to surface level differences and warpage, as protection tapes are ineffective in absorbing these irregularities and enhancing rigidity simultaneously.
Innovation Solution
A method involving the formation of a projection-depression shape on the wafer surface, followed by a resin member with a specific positioning relative to the wafer's outer peripheral end, and a recessed shape on the back surface to create an annular reinforcing portion, which increases the wafer's rigidity and reduces warpage, thereby facilitating handling and preventing breakage during thinning processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a protection tape is provided on the wafer upper surface to prevent breakage during thinning processing, then the strength of the wafer is reinforced, but the surface level difference caused by device structure cannot be sufficiently absorbed when the ratio of surface level difference to total thickness becomes large
Solution Approach 1:
The protection tape is segmented into a first protection tape and a second protection tape with different properties. The first protection tape (lower layer) has high elasticity to absorb surface level differences, while the second protection tape (upper layer) has high strength to prevent breakage during thinning processing. This segmentation allows each layer to specialize in one function, resolving the contradiction between strength and surface flatness.
Solution Approach 2:
Different regions of the protection system have different properties: the first protection tape has high elasticity locally to absorb surface irregularities, while the second protection tape has high strength locally to prevent breakage. This local differentiation of properties allows the system to simultaneously address both surface flatness and strength requirements.
2Productivity
If the wafer is thinned to reduce thickness for improving energization performance, then the current path is shortened, but the wafer becomes more prone to breakage and warpage
Solution Approach 1:
The first protection tape with high elasticity is applied beforehand to the wafer upper surface to absorb surface level differences and provide cushioning. This prior cushioning prevents breakage during subsequent thinning processing and handles warpage issues, allowing the wafer to be thinned safely while maintaining integrity.
Solution Approach 2:
The protection system uses a composite structure of two different tapes: a first protection tape made of elastic material for cushioning and a second protection tape made of strong material for breakage prevention. This composite approach allows the thin wafer to maintain both high energization performance and reliability during processing.
Data Source
AI summary
On a first wafer surface of a semiconductor wafer, a projection-depression shape is formed. On the first wafer surface, a resin member is so formed to have a resin outer peripheral end positioned away from a wafer outer peripheral end and expose the wafer outer peripheral end. By partially removing the semiconductor wafer, on a second wafer surface of the semiconductor wafer, formed is a recessed shape having a recessed-portion outer peripheral end positioned 0.5 mm or more inside from the resin outer peripheral end. After performing a processing on the second wafer surface, the resin member is removed.