Wafer Division Using Adhesive-Free Polyester Sheet
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Solution Overview
Problem
The existing wafer processing methods using adhesive tapes for dividing wafers into device chips often result in the adhesive layer adhering to the back side of the chips, leading to quality degradation due to the melting and fixation of the adhesive layer during laser ablation.
Innovation Solution
A wafer processing method utilizing a polyester sheet without an adhesive layer for thermocompression bonding with the wafer and ring frame, allowing laser ablation to create division grooves and facilitating easy chip separation by cooling and expanding the polyester sheet to reduce the load on the chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adhesive tape is used to hold the wafer during laser processing, then the wafer can be securely fixed and processed, but the adhesive layer melts and adheres to the back side of the device chips, degrading their quality
Solution Approach 1:
The adhesive layer is completely removed from the holding structure. Instead of using adhesive tape, the patent employs a double-sided adhesive sheet where the adhesive is applied only to the back side of the wafer, not to the device chips themselves. This extraction of the adhesive from the chip-contact surface eliminates the harmful adhesion effect while maintaining secure wafer fixation during laser processing.
Solution Approach 2:
A double-sided adhesive sheet serves as an intermediary between the wafer and the holding structure. The adhesive sheet has adhesive properties on both sides: one side bonds to the wafer back surface, and the other side bonds to the holding structure. This intermediary approach allows secure fixation without direct adhesive contact with the device chips, preventing adhesive contamination.
2Manufacturing precision
If laser beam is applied with sufficient energy to form deep division grooves, then reliable wafer division is achieved, but the heat melts the adhesive layer and causes it to fix to the chip back side
Solution Approach 1:
The adhesive layer is extracted from the path of heat transfer to the device chips. By positioning the adhesive on the wafer back surface rather than on the chip contact surface, the high-temperature laser processing zone is separated from the adhesive, preventing thermal melting and subsequent adhesion to chips while maintaining sufficient laser energy for deep groove formation.
Solution Approach 2:
The holding structure is segmented into distinct functional zones: the adhesive sheet is positioned only in regions corresponding to wafer back surface contact, while the device chip front surfaces remain completely free of adhesive. This spatial segmentation allows high-energy laser processing without compromising chip quality.
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 prevents the adhesive layer from adhering to the device chips, thereby maintaining chip quality by eliminating the issue of adhesive layer adherence and enhancing the separation process.
Implementation Method 1
the laser beam is applied from the laser processing unit to the wafer. When the laser beam is applied to the wafer, laser ablation occurs to form a division groove in the wafer along each division line
Implementation Method 2
a uniting step of heating the polyester sheet as applying a pressure to the polyester sheet after performing the polyester sheet providing step, thereby uniting the wafer and the ring frame through the polyester sheet by thermocompression bonding
Implementation Method 3
a pickup step of cooling the polyester sheet in each region of the polyester sheet corresponding to each device chip, pushing up each device chip from the polyester sheet side to pick up each device chip from the polyester sheet
Data Source
AI summary
A wafer processing method includes a polyester sheet providing step of positioning a wafer in an inside opening of a ring frame and providing a polyester sheet on a back side of the wafer and on a back side of the ring frame, a uniting step of heating the polyester sheet as applying a pressure to the polyester sheet to thereby unite the wafer and the ring frame through the polyester sheet by thermocompression bonding, a dividing step of applying a laser beam to the wafer to form division grooves in the wafer, thereby dividing the wafer into individual device chips, and a pickup step of cooling the polyester sheet in each region of the polyester sheet corresponding to each device chip, pushing up each device chip from the polyester sheet side to pick up each device chip from the polyester sheet.