Wafer Laser Division via Phase Shift Mask
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Solution Overview
Problem
The existing wafer processing methods using a laser beam to form modified layers for dividing wafers can result in random cracks, leading to destruction of devices on the front surface due to reflected and dispersed laser beams.
Innovation Solution
A wafer processing method employing a laser processing apparatus with a phase shift mask that creates a 180-degree phase difference in the laser beam intensity distribution, ensuring two peaks separated in the X-axis direction, which reduces random crack formation and minimizes damage to devices by controlling the direction of laser beam reflection and dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a laser beam of a wavelength transmissible through the wafer is used to form modified layers, then the wafer can be divided along planned dividing lines with the modified layers as a starting point, but a part of the laser beam reaches the front surface side without being absorbed and may destroy devices when reflected and dispersed by cracks
Solution Approach 1:
The invention converts the harmful reflected laser beam into a beneficial tool by using the phase shift mask to create two peaks in intensity distribution. The reflected beam from cracks is redirected toward the planned dividing lines rather than toward devices, transforming a potential harm into a feature that enhances division precision while protecting devices.
Solution Approach 2:
The phase shift mask creates non-uniform intensity distribution with two distinct peaks separated in the X-axis direction. This local variation in laser intensity allows different regions to serve different functions: one peak creates modified layers for division while the other directs reflected energy away from devices, providing spatially differentiated protection.
2Reliability
If the laser beam intensity distribution has two peaks separated in the X-axis direction, then random crack formation is reduced and device destruction is prevented, but the device complexity of the laser processing apparatus increases due to the phase shift mask
Solution Approach 1:
The phase shift mask serves as an intermediary optical element placed between the laser oscillator and condenser. It modifies the laser beam's phase distribution to create the desired two-peak intensity pattern, acting as a mediator that transforms the laser output without requiring fundamental changes to the laser source itself, thus balancing reliability improvement with acceptable complexity increase.
3Manufacturing precision
If the phase shift mask is reversed to reverse phase distribution of the laser beam, then processing precision is maintained under changed relative movement conditions, but the processing time increases due to additional mask reversing steps
Solution Approach 1:
The phase shift mask is made reversible to adapt to changing processing conditions. By dynamically reversing the mask orientation, the system maintains optimal phase distribution and processing precision regardless of relative movement directions between the chuck table and laser beam irradiating unit, enabling flexible adaptation without sacrificing precision.
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 device destruction by controlling the direction of cracks and ensuring precise processing conditions, even when the relative movement between the chuck table and laser beam irradiating unit is changed, thereby maintaining high precision and preventing damage from random crack reflections.
Implementation Method 1
a phase shift mask disposed between the laser oscillator and the condenser, the phase shift mask forming a phase difference of 180 degrees between a part of the laser beam guided to the condenser and a remaining part of the laser beam guided to the condenser such that intensity distribution of the laser beam applied to the wafer has two peaks separated from each other in the X-axis direction
Implementation Method 2
a condenser configured to condense the laser beam oscillated by the laser oscillator and irradiate the wafer with the laser beam
Implementation Method 3
a method is known which modifies the inside of the wafer by applying a laser beam (a transmissible laser beam) of a wavelength transmissible through the wafer from the back surface side of the wafer and condensing the laser beam within the wafer, and thus forms modified layers (modified regions) that are fragile as compared with other regions
Implementation Method 4
in a case where minute cracks randomly extend from the modified layers, for example, the laser beam reflected and dispersed by the cracks may reach the devices on the front surface side, and destroy the devices
Data Source
AI summary
A wafer processing method includes a modified layer forming step of forming a modified layer along a planned dividing line within a wafer and a dividing step of dividing the wafer along the planned dividing line with the modified layer as a starting point by applying a force to the wafer. The modified layer forming step includes a forward path modified layer forming step, a backward path modified layer forming step, and a phase shift mask reversing step of reversing a phase shift mask so as to reverse phase distribution of a laser beam applied to the wafer in an X-axis direction after the forward path modified layer forming step and before the backward path modified layer forming step, or after the backward path modified layer forming step and before the forward path modified layer forming step.