Stacked Wafer Manufacturing via Reinforcing Substrate Bonding
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Solution Overview
Problem
The challenge in manufacturing stacked wafers is the difficulty in reliably bonding electrodes of second semiconductor devices to those of a mother wafer due to the bending of the stacking wafer after grinding, which results in faulty electrical continuity and low productivity, especially when removing a reinforcing substrate that requires high temperatures.
Innovation Solution
A method involving the use of a protective member during grinding, followed by bonding a reinforcing wafer to the back side of the stacking wafer, allowing for precise thickness reduction and division of the wafer without applying load or heat, enabling reliable electrode bonding and improved productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the stacking wafer is ground to reduce thickness to tens of micrometers, then the size reduction and higher functionality are achieved, but the wafer loses rigidity and bends making proper stacking difficult
Solution Approach 1:
A reinforcing substrate is bonded to the back surface of the stacking wafer before the wafer is ground to reduce thickness. This preliminary reinforcement prevents the wafer from bending during subsequent handling and stacking operations, allowing the wafer to be thinned to tens of micrometers while maintaining sufficient rigidity for proper electrode alignment and stacking.
2Strength
If a substrate is bonded through wax to prevent bending during grinding, then wafer rigidity is maintained, but high temperature heating is required for substrate removal reducing productivity
Solution Approach 1:
The bonding method is changed from wax bonding (requiring high temperature heating above 250°C for removal) to adhesive bonding using a solvent-based adhesive. This parameter change in the bonding mechanism allows the reinforcing substrate to be removed simply by applying a solvent, eliminating the need for high-temperature heating and significantly improving productivity.
Solution Approach 2:
The thermal removal process (heating to high temperature) is replaced with a chemical dissolution process using a solvent. Instead of using heat to break the wax bond, a solvent is applied to dissolve the adhesive bonding the reinforcing substrate, enabling simple and quick substrate removal without thermal processing.
3Ease of manufacture
If the stacking wafer is ground without reinforcement, then the process is simpler, but the wafer bends and electrode bonding reliability deteriorates
Solution Approach 1:
The reinforcing substrate is bonded to the wafer back surface before grinding, ensuring the wafer maintains its flatness and rigidity throughout the thickness reduction process. This preliminary reinforcement enables reliable electrode bonding after stacking, as the wafer will not bend during handling and positioning.
Solution Approach 2:
The reinforcing substrate serves as a temporary support structure that is introduced during manufacturing, performs its function of preventing bending during grinding and initial handling, and is then completely removed after the wafer is stacked and bonded. This extraction of the reinforcement after use maintains electrode bonding reliability while allowing simple processing.
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 ensures reliable bonding of electrodes and enhances productivity by preventing wafer bending and eliminating the need for high-temperature processing during substrate removal, allowing for precise handling and efficient assembly of stacked wafers.
Implementation Method 1
a bonding layer for bonding the substrate to the front side of the stacking wafer
Implementation Method 2
via holes for embedding the electrodes are formed in each second semiconductor device by laser processing
Data Source
AI summary
A manufacturing method for a stacked wafer configured by bonding a mother wafer having a plurality of first semiconductor device and a stacking wafer having a plurality of second semiconductor devices. The manufacturing method includes the steps of attaching a protective member to the front side of the stacking wafer to protect the second semiconductor devices, next grinding the back side of the stacking wafer, next bonding the front side of a reinforcing wafer through a bonding layer to the back side of the stacking wafer, next dividing the stacking wafer together with the reinforcing wafer into the plural second semiconductor devices, next bonding the front side of each second semiconductor device to the front side of the mother wafer to thereby connect the electrodes of each second semiconductor device to the electrodes of the corresponding first semiconductor device of the mother wafer, and finally grinding the reinforcing wafer bonded to the back side of each second semiconductor device to thereby remove the reinforcing wafer.