Wafer Thinning via Grinding and Planarization to Prevent Lateral Undercutting
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Solution Overview
Problem
The existing wafer thinning methods for 3D-IC technology involve expensive epitaxial wafers and acid etching, which cause lateral undercutting and reduce the effective chip area due to the need for trimming.
Innovation Solution
A method involving grinding followed by chemical-mechanical planarization processes to thin wafers, eliminating the need for epitaxial layers and reducing lateral undercutting, thereby increasing the effective chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If an epitaxial layer is grown on the silicon substrate to serve as an acid-etching stop layer, then a flat silicon surface can be obtained after thinning, but the cost increases significantly
Solution Approach 1:
The patent extracts and removes the epitaxial layer from the thinning process, replacing it with direct grinding of the silicon substrate followed by chemical-mechanical planarization. This eliminates the need for expensive epitaxial growth while achieving the required surface flatness through alternative mechanical and chemical processes.
Solution Approach 2:
The patent replaces the chemical etching process (which requires an epitaxial stop layer) with a mechanical grinding process followed by chemical-mechanical planarization. This substitution eliminates the need for the epitaxial layer while achieving comparable or superior surface flatness.
2Manufacturing precision
If acid etching is used to thin the wafer, then the epitaxial layer can serve as a stop layer, but lateral undercutting occurs which reduces the effective chip area
Solution Approach 1:
The patent replaces chemical etching with mechanical grinding followed by chemical-mechanical planarization. The mechanical grinding process removes material vertically without the lateral undercutting that occurs in chemical etching, thereby preserving the full chip area while still achieving the required surface flatness.
Solution Approach 2:
The patent changes the fundamental parameter of the thinning process from chemical etching to mechanical grinding combined with chemical-mechanical planarization. This parameter change eliminates the lateral undercutting mechanism inherent in chemical etching while maintaining the ability to achieve flat surfaces through controlled material removal.
3Manufacturing precision
If multiple trimming processes are performed to remove lateral undercutting, then the wafer flatness is improved, but the effective chip area is reduced
Solution Approach 1:
The patent extracts and eliminates the need for multiple trimming processes by using mechanical grinding followed by chemical-mechanical planarization from the beginning. This prevents lateral undercutting before it occurs, removing the need for subsequent trimming operations and preserving maximum chip area.
Solution Approach 2:
The patent performs preliminary mechanical grinding and chemical-mechanical planarization to establish the correct geometry and flatness before any bonding or subsequent processing occurs. This preliminary action prevents the formation of lateral undercutting that would otherwise require later trimming to correct.
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 method reduces the number of trimming processes, decreases costs, and enhances the flatness of the wafer surface without lateral undercutting, resulting in a larger effective chip area.
Implementation Method 1
grinding the to-be-thinned wafer on a rear surface of the to-be-thinned wafer
Implementation Method 2
performing a first planarization process on a rear surface of the grinded wafer to restore surface flatness of the grinded wafer
Data Source
AI summary
A wafer thinning method and a wafer structure are provided. In the wafer thinning method, a to-be-thinned wafer is provided, and the to-be-thinned wafer is grinded on a rear surface of the to-be-thinned wafer. Then, a first planarization process is performed on a rear surface of the grinded wafer to restore surface flatness of the grinded wafer, and a second planarization process is performed on a rear surface of the wafer obtained after the first planarization process is performed until a target thinned thickness is reached.