Stepped Support Ring for Thinned Semiconductor Wafer TSVs
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Solution Overview
Problem
Conventional wafer thinning methods face challenges in producing semiconductor wafers with through substrate vias (TSVs) of 300 μm or less without causing cracking or subsurface damage, due to limitations in high temperature processing and damage from grinding into metallic fillers, which restricts the thinning of semiconductor wafers to 150 μm or less.
Innovation Solution
A method involving a two-pass grinding process using a coarse and fine grinding wheel to form a stepped support ring, which terminates before reaching TSVs to minimize damage, and an automatic feedback system to stop grinding when reaching TSVs, avoiding further polishing actions and maintaining structural integrity, allowing for TSVs to be formed with minimal surface and subsurface damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional wafer thinning approach is used with bonding material and high temperature processing, then wafer can be thinned, but bonding material outgases at 200-300°C limiting high temperature processing and causing contamination
Solution Approach 1:
The patent removes the bonding material step entirely from the process. Instead of bonding the wafer to a handle wafer and then debonding, the method directly grinds the back side of the wafer to the desired thickness, extracting the harmful bonding material outgassing problem from the process sequence.
Solution Approach 2:
The patent performs preliminary protective actions by applying a protective coating to the front side of the wafer before grinding begins. This preliminary protection allows the wafer to withstand subsequent high temperature processing without the bonding material constraint.
2Length of stationary object
If grinding is performed into metallic filler material in TSVs, then wafer thickness is reduced, but grinding wheel is destroyed and subsurface damage or destruction of wafer occurs
Solution Approach 1:
The patent employs a two-pass grinding approach where the first pass removes the majority of the material (excessive action) to get close to the target thickness, and the second pass performs precise finishing (partial action) to achieve the exact thickness without grinding into the TSV metallic fillers, thereby preventing wheel destruction and wafer damage.
Solution Approach 2:
The patent implements an automatic feedback system using sensors to detect when the grinding wheel approaches the TSVs. When the sensor detects the metallic filler material, it automatically stops the grinding process, preventing subsurface damage and wheel destruction.
3Manufacturing precision
If final polish action such as CMP, wet etch or plasma etch is applied to thinned wafer, then surface residues are removed, but additional stress is applied causing cracking and rendering dies unsuitable for further processing
Solution Approach 1:
The patent removes the final polish actions (CMP, wet etch, plasma etch) from the process sequence. Instead of performing these additional stress-inducing steps, the method relies on the protective coating and controlled grinding to achieve a surface quality sufficient for further processing, thereby extracting the harmful stress-inducing steps from the process.
4Length of stationary object
If wafer is thinned to 150 μm or less using conventional methods, then TSV depth is reduced, but cracking and subsurface damage occur preventing further processing
Solution Approach 1:
The patent applies a protective coating to the front side of the wafer before the grinding process begins. This preliminary protective action allows the wafer to be thinned to 150 μm or less without cracking or subsurface damage, as the coating reinforces the wafer structure during the critical thinning operation.
Solution Approach 2:
The two-pass grinding method removes material in controlled stages, with the first pass performing excessive removal to get close to the target thickness and the second pass performing precise partial removal to achieve the final thin dimensions without causing damage.
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
Enables the production of thinned semiconductor wafers with TSVs in the 50-150 μm thickness range without cracking, reducing manufacturing costs and time, and allowing for higher temperature processing without additional stress or contamination.
Implementation Method 1
grinding the back side using wafer thinning, polish or grinding equipment
Implementation Method 2
an automatic feedback system to stop grinding when reaching TSVs
Data Source
AI summary
A semiconductor wafer having a plurality of through substrate vias (TSVs) is disclosed. The semiconductor wafer includes a stepped support ring on an outer edge of the semiconductor wafer, a usable back side region of the semiconductor wafer substantially enclosed by the stepped support ring, and the plurality of TSVs extending from a front side of the semiconductor wafer to the usable back side region of the semiconductor wafer. The stepped support ring includes a step between an outer ring and an inner ring of the stepped support ring. The semiconductor wafer further includes a back side metal on the usable back side region of the semiconductor wafer, a plurality of semiconductor devices on the front side of the semiconductor wafer, where at least one of the plurality of semiconductor devices is coupled to the back side metal through at least one of the plurality of TSVs.