Stacked Wafer Kerf Formation and Back Grinding
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Solution Overview
Problem
The challenge in manufacturing stacked semiconductor devices is the difficulty in reducing wafer thickness without causing chipping of the side surfaces, which affects the quality and integrity of the stacked device.
Innovation Solution
A method involving kerf or modified layer formation on semiconductor wafers, followed by sequential stacking and back grinding steps, allows for precise thickness reduction without the need for cutting blades, thereby preventing surface chipping. This method includes forming kerfs or modified layers on the wafers, stacking them with electrodes for bonding, and grinding to expose these features on the backside, allowing for easy lamination and minimization of device thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the thickness of each semiconductor wafer is reduced to 50 μm or less by grinding, then the size of each stacked device is reduced, but each semiconductor wafer becomes easily broken making lamination difficult
Solution Approach 1:
The patent applies preliminary action by forming kerfs (grooves) on the front surface of each wafer before the stacking process. These kerfs are filled with adhesive in advance, creating reinforced structures that prevent wafer breakage during subsequent handling and lamination steps. This preliminary reinforcement allows the wafer to be ground to the desired thin thickness while maintaining sufficient strength for the stacking process.
2Ease of manufacture
If the stacked wafer is cut along each street by using a cutting blade, then the stacked device is divided into individual devices, but the side surface of each stacked device becomes chipped causing quality degradation
Solution Approach 1:
The patent replaces the mechanical cutting blade system with a chemical separation system. Instead of using a cutting blade to physically divide the stacked wafer, the invention uses adhesive-filled kerfs that are selectively removed or separated. This substitution eliminates the mechanical contact that causes chipping, thereby maintaining side surface quality while achieving device division.
3Ease of operation
If conventional stacking methods are used with thick wafers, then lamination is easier, but the final stacked device size cannot be reduced
Solution Approach 1:
The patent applies parameter changes by modifying the wafer structure through kerf formation and adhesive filling. The kerfs create localized reinforcement zones that change the mechanical parameters of the wafer, allowing it to maintain high strength despite being ground to thin thickness. This structural parameter change enables both easy lamination and reduced final device size.
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 enables the successful reduction of wafer thickness while preventing side surface chipping, facilitating easier lamination and minimizing the thickness of stacked devices, thus enhancing their quality and manufacturing efficiency.
Implementation Method 1
a kerf forming step of forming a kerf on the front side of each wafer along each street prior to grinding the back side of each wafer
Implementation Method 2
grinding the back side of each wafer to reduce the thickness of each wafer to a predetermined finished thickness
Implementation Method 3
the front side of the second wafer stacked on the front side of the first wafer is bonded thereto through an adhesive
Data Source
AI summary
A stacked device manufacturing method including a kerf forming step of forming a kerf on the front side of each of plural wafers along each street, the kerf having a depth corresponding to a predetermined finished thickness of each wafer, a first stacking step of stacking a first one of the wafers and a second one of the wafers in such a manner that the front side of the second wafer is opposed to the front side of the first wafer and that the electrodes of the second wafer are respectively bonded to the electrodes of the first wafer, a first back grinding step of grinding the back side of the second wafer to expose each kerf of the second wafer to the back side of the second wafer, a second stacking step of stacking a third one of the wafers to the second wafer in such a manner that the front side of the third wafer is opposed to the back side of the second wafer and that the electrodes of the third wafer are respectively bonded to the electrodes of the second wafer, and a second back grinding step of grinding the back side of the third wafer to expose each kerf of the third wafer to the back side of the third wafer.