Silicon Dry Etching for Sub-30 μm Die-to-Wafer Thinning
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Solution Overview
Problem
Current chip-to-wafer bonding is limited to dies thicker than 30 μm due to handling limitations and equipment constraints, leading to issues like die breakage and warpage, and existing thinning processes like CMP and grinding are inefficient for thin dies thinner than 30 μm, which fail to achieve 30 μm, which cause chipping, cracking, and yield loss.
Innovation Solution
A dry etching process using a plasma comprising fluorine is employed to selectively thin the die surface relative to the substrate surface, utilizing SF6, CF4, or C4F8 gases, with a protective layer to prevent substrate damage, achieving a removal rate of greater than 1 μm/min.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional thinning processes (grinding or CMP) are used on dies, then material removal is achieved, but die damage (chipping, cracking, delamination) occurs and yield is lost
Solution Approach 1:
The patent replaces mechanical thinning processes (grinding, CMP) with a plasma-based chemical etching process using fluorine-containing gases. This substitution eliminates mechanical contact and associated damage while achieving precise thickness control through selective etching of the die material versus the substrate material.
Solution Approach 2:
The patent utilizes selective etching by changing the chemical parameters of the plasma process. By selecting appropriate fluorine-containing gases and controlling plasma conditions, the process achieves differential removal rates between the die and substrate materials, enabling precise thickness control without mechanical damage.
2Length of moving object
If die thickness is reduced below 30 μm, then electrical and thermal properties improve and form factor is reduced, but handling becomes difficult and die breakage occurs
Solution Approach 1:
The patent performs thinning of the die to below 30 μm before the bonding process, rather than attempting to handle and bond thicker dies and then thin them afterward. This preliminary thinning action enables subsequent handling and bonding operations to proceed without the mechanical strength issues that would arise from handling ultra-thin dies after bonding.
Solution Approach 2:
By using plasma etching instead of mechanical thinning methods, the patent achieves the required sub-30 μm thickness without the mechanical stresses and damages associated with traditional methods, thereby maintaining die integrity even at ultra-thin dimensions.
3Manufacturing precision
If CMP is used for thinning, then surface smoothness is achieved, but removal rate is low (<1 μm/min) and cost is high
Solution Approach 1:
The patent replaces the mechanical CMP process with a plasma-based chemical etching process. This substitution dramatically increases the removal rate to greater than 1 μm/min while maintaining surface quality through controlled chemical removal and subsequent planarization steps.
Solution Approach 2:
By changing from mechanical removal to chemical plasma etching, the patent achieves both high removal rates and surface smoothness through control of plasma parameters, gas composition, and process timing, eliminating the trade-off present in mechanical CMP processes.
4Productivity
If grinding is used for thinning, then material removal is achieved, but high mechanical shear forces cause chipping and cracking
Solution Approach 1:
The patent replaces mechanical grinding with plasma-based chemical etching, eliminating all mechanical contact and shear forces. This substitution maintains high productivity through rapid chemical removal while completely preventing chipping and cracking that result from mechanical stresses.
Solution Approach 2:
By changing the fundamental mechanism from mechanical to chemical removal, the patent achieves rapid material removal through plasma chemistry while eliminating the mechanical shear forces that cause die damage, thereby simultaneously improving productivity and reliability.
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 effectively thins dies to less than 30 μm while maintaining the substrate integrity, avoiding mechanical stress and achieving high removal rates without damaging underlying structures.
Implementation Method 1
dry etching a top surface of the die with a plasma comprising fluorine to selectively remove the top surface of the die relative to a top surface of the substrate
Implementation Method 2
utilizing a plasma comprising fluorine formed from SF6, CF4, C4F8 or a combination thereof to selectively remove the top surface of the chip
Data Source
AI summary
A method of thinning a die engaged with a substrate is disclosed, utilizing dry etching of a top surface of the die with a plasma comprising fluorine to selectively remove the top surface of the die relative to a top surface of the substrate.