Wafer Division via Offset Laser Modified Layers
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Solution Overview
Problem
The existing laser processing method for dividing semiconductor wafers along crossing division lines results in meandering breaking lines due to random crack growth from stacked modified layers, leading to reduced quality of device chips.
Innovation Solution
A wafer processing method that forms a first modified layer inside the wafer using a laser beam applied from the back side with the focal point set near the front side, followed by a second modified layer formed with the focal point slightly offset in the Y direction, to control the direction of crack growth and suppress meandering, and then reduces the wafer thickness through back grinding to divide it into individual device chips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple modified layers are formed in a stacked manner inside the wafer along each division line to enable reliable division, then the wafer can be divided into individual device chips, but cracks grow in random directions from the first modified layer causing meandering breaking lines that reduce device quality
Solution Approach 1:
The patent introduces a spatial offset in the Y-direction between the first and second modified layers, transforming a one-dimensional stacked structure into a two-dimensional offset structure. This dimensional change directs crack propagation along a controlled path from the second modified layer through the first modified layer to the front surface, preventing random meandering while maintaining division reliability.
Solution Approach 2:
The patent applies different spatial positions to different modified layers along the same division line. The first modified layer is positioned at a specific depth, while the second modified layer is offset in the Y-direction, creating local structural variations that guide crack propagation direction and prevent random cracking, thereby improving breaking line quality.
2Measurement precision
If the focal point of the laser beam is set directly above the first modified layer to form the second modified layer, then the modified layers are perfectly aligned, but cracks grow in random directions causing meandering breaking lines
Solution Approach 1:
The patent deliberately introduces asymmetry by offsetting the focal point position for forming the second modified layer in the Y-direction relative to the first modified layer. This asymmetric positioning prevents direct vertical alignment that would allow random crack growth, instead creating a controlled angular path for crack propagation that results in straighter breaking lines.
3Manufacturing precision
If the focal point of the laser beam is offset in the Y direction to define crack growth direction, then meandering of the breaking line is suppressed, but the modified layers are no longer perfectly aligned
Solution Approach 1:
The patent performs preliminary positioning of the focal point at an offset position before forming the second modified layer. This preliminary action establishes a predetermined crack growth path that prioritizes breaking line quality over perfect alignment, as the offset position is calculated in advance to achieve the desired crack direction from the second modified layer through the first modified layer to the front surface.
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 defines the direction of crack growth, preventing meandering and enhancing the quality of the breaking line, thereby improving the accuracy and reliability of wafer division into individual device chips.
Implementation Method 1
applying a laser beam having a transmission wavelength to the wafer from the back side along each division line in a state where a focal point of the laser beam is set inside the wafer
Implementation Method 2
forming a first modified layer inside the wafer along each division line
Implementation Method 3
the focal point of the laser beam in the second modified layer forming step is set at a position slightly displaced by a predetermined offset amount from a position directly above the first modified layer in a Y direction, thereby defining a direction of extension of a crack
Implementation Method 4
grinding the back side of the wafer to reduce the thickness of the wafer to a predetermined thickness
Data Source
AI summary
Disclosed herein is a wafer processing method including a first modified layer forming step of applying a laser beam having a transmission wavelength to a wafer from the back side thereof along each division line in the condition where the focal point of the laser beam is set inside the wafer near the front side thereof, thereby forming a first modified layer inside the wafer along each division line. The wafer processing method further includes a second modified layer forming step of applying the laser beam to the wafer from the back side thereof along each division line in the condition where the focal point of the laser beam is set adjacent to the first modified layer thereabove toward the back side of the wafer, thereby forming a second modified layer for growing a crack from the first modified layer toward the front side of the wafer.