Wafer Dividing Method Using Laser Modified Layers and Back Grinding
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Solution Overview
Problem
The existing methods for dividing semiconductor wafers into individual devices using a die attach film (DAF) face challenges in efficiently dividing the DAF along the boundaries of the devices without reducing the die strength, particularly when using techniques like stealth dicing and dicing before grinding.
Innovation Solution
A wafer dividing method that involves forming modified layers inside the wafer using a laser beam, followed by grinding to remove these layers, and then using an annular frame with dicing tape to expand and divide the DAF along the device boundaries, ensuring the die strength is maintained.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If stealth dicing is used to form modified layers inside the wafer and expand the dicing tape to divide the DAF, then the DAF can be easily divided along device boundaries, but the die strength of each device is reduced by modified layers remaining on the outer circumference
Solution Approach 1:
The patent applies preliminary action by performing the back grinding step to remove modified layers BEFORE attaching the DAF and dicing tape. This sequence ensures that when the dicing tape is later expanded to divide the DAF, no modified layers remain on the device outer circumferences to compromise die strength, while still achieving easy DAF division along device boundaries.
2Length of moving object
If dicing before grinding is used to reduce wafer thickness to 50 μm or less, then thinner devices are achieved, but it is relatively difficult to divide the DAF along device boundaries
Solution Approach 1:
The patent applies preliminary action by performing back grinding to remove modified layers BEFORE DAF attachment. This creates a clean surface that enables easy DAF division along device boundaries when the dicing tape is expanded, while still achieving the thin device thickness target of 50 μm or less through the dicing before grinding approach.
3Manufacturing precision
If modified layers are formed inside the wafer along division lines, then the wafer can be divided into individual devices with small spacing, but the modified layers remain on the outer circumference and reduce die strength
Solution Approach 1:
The patent applies preliminary action by performing back grinding to remove modified layers from the wafer back surface BEFORE attaching the DAF and dicing tape. This timing ensures that modified layers are completely removed from device outer circumferences, eliminating the die strength reduction problem while preserving the manufacturing precision benefit of small spacing between divided devices.
Solution Approach 2:
The patent applies the extraction principle by removing the harmful modified layers from the wafer structure before subsequent processing steps. The back grinding step extracts these modified layers from the device outer circumferences, separating the useful function (precise device division with small spacing) from the harmful effect (die strength reduction).
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 allows for easy division of the DAF along the device boundaries without reducing the die strength, enabling the production of thinner devices with improved productivity.
Implementation Method 1
applying a laser beam having a transmission wavelength to the wafer from the back side of the wafer along the division lines in the condition where the focal point of the laser beam is set inside the wafer
Implementation Method 2
grinding the back side of the wafer to reduce the thickness of the wafer to a predetermined thickness
Data Source
AI summary
A wafer is divided into individual devices along division lines formed on the front side of the wafer. The devices are respectively formed in a plurality of regions partitioned by the division lines. A protective member is provided on the front of the wafer, and the back of the wafer is ground to a predetermined thickness. A laser beam is applied to the wafer from the back side of the wafer along the division lines with the focal point of the laser beam set inside the wafer at a position corresponding to each division line, thereby forming a plurality of modified layers inside the wafer along the division lines. The wafer is divided along the modified layers into the individual devices, and the back side of the wafer is ground to remove the modified layers and reduce the thickness of each device to the finished thickness.