Wafer Division via Backside Laser Ablation
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Solution Overview
Problem
The challenge in dividing semiconductor wafers with low-k films is that the brittle low-k film can delaminate during cutting, causing damage to the devices, and existing methods using laser processing can result in debris damaging image sensors.
Innovation Solution
A wafer processing method involving a protective member on the front side, cutting a division groove on the back side of the substrate, and applying a laser beam from the back side to cut the substrate and functional layer along the division lines, preventing debris from reaching the image sensors and reducing the width of division lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a cutting blade is used to cut the semiconductor wafer along the division lines, then the wafer can be divided into individual devices, but the low-k film may delaminate and cause damage to the devices
Solution Approach 1:
The cutting process is segmented into two distinct stages: first, a cutting blade creates grooves along the division lines to a controlled depth that stops before reaching the low-k film; second, a laser beam completes the cutting through the low-k film and functional layer. This segmentation allows mechanical cutting to handle the robust substrate while laser processing handles the delicate low-k film, preventing delamination
Solution Approach 2:
The patent introduces an intermediary stopping point where the mechanical cutting blade creates grooves that terminate before contacting the low-k film. This intermediary step prepares the substrate by creating guiding grooves without directly interacting with the brittle low-k film, thereby serving as a mediator between the mechanical cutting process and the laser processing step
2Manufacturing precision
If laser beam is applied to the front side of the wafer to form laser processed grooves, then the functional layer can be divided, but debris may scatter and damage the devices
Solution Approach 1:
The patent inverts the conventional laser processing approach by applying the laser beam from the back side of the substrate rather than the front side. This inversion allows the laser to process the functional layer and low-k film through the substrate from the opposite direction, preventing debris from scattering onto the device surfaces and causing damage
Solution Approach 2:
The patent extracts the harmful debris generation and scattering problem by changing the laser processing direction. By removing the front-side laser processing step entirely and replacing it with back-side processing, the source of debris damage is eliminated, as debris is generated away from the sensitive device surfaces
3Productivity
If the division lines are made wider to ensure complete separation, then all devices can be divided, but the number of image sensors per wafer is reduced
Solution Approach 1:
The patent changes the processing parameters by combining mechanical cutting depth control with laser processing power and duration parameters. The mechanical blade cuts to a precise depth that stops before the low-k film, and the laser parameters are optimized to complete the cut through the remaining material, allowing narrower division lines while ensuring complete separation
Solution Approach 2:
The patent employs a composite processing approach combining mechanical cutting and laser processing. The mechanical blade provides precise groove formation in the substrate, while the laser provides precise material removal through the low-k film and functional layer. This composite method allows for narrower, more precise division lines that ensure complete separation without sacrificing sensor density
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 effectively prevents damage to image sensors by containing debris and allows for precise cutting of the wafer, increasing the number of image sensors per wafer and improving productivity by reducing the width of division lines.
Implementation Method 1
applying a laser beam from the back side to cut the substrate and functional layer along the division lines
Data Source
AI summary
A wafer processing method for dividing a wafer (including a substrate and a functional layer formed on the front side of the substrate) along a plurality of division lines. The functional layer is partitioned by the division lines to define a plurality of regions. The method includes the following steps: attaching a protective member to the front side of the wafer; cutting the back side of the substrate of the wafer in an area corresponding to each division line with a cutting blade, thereby forming a division groove having a depth not reaching the functional layer so that a part of the substrate is left in this area; applying a laser beam to the wafer from the back side of the substrate along the bottom of each division groove extending along each division line to thereby cut the part of the substrate and the functional layer along each division line.