Laser Wafer Thinning with Ultrasonic-Assisted Peeling
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Solution Overview
Problem
The existing methods for thinning lithium tantalate wafers, such as grinding, result in severe wear of grindstones and low productivity due to the high thermal expansion coefficient of lithium tantalate, and previous attempts to enhance peel-off properties using ultrasonic waves have been insufficient when applied after support substrate bonding or before complete peeling.
Innovation Solution
A wafer thinning method involving the sequential bonding of support substrates, laser-induced separation start point formation, and staged ultrasonic wave application to create modified layers and cracks, followed by ultrasonic-assisted peeling to reduce grindstone wear and enhance peel-off efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If a laser beam is applied inside a wafer to form a peel-off layer, then grindstone wear is reduced, but the peel-off property is lowered due to crack exposure
Solution Approach 1:
The patent applies ultrasonic waves before the peeling process to pre-treat the wafer and enhance crack development at the peel-off layer. This preliminary action prepares the wafer structure to facilitate better peeling performance while maintaining the benefits of laser-induced peel-off layer formation
Solution Approach 2:
The patent utilizes ultrasonic vibration to apply mechanical energy to the wafer, causing internal stress and crack propagation that enhances the peel-off property. The ultrasonic waves create micro-vibrations that propagate cracks through the modified layer, improving the separation efficiency
2Ease of operation
If ultrasonic waves are applied after support substrate bonding, then handling is easier, but the peel-off property is not enhanced sufficiently
Solution Approach 1:
The patent applies ultrasonic waves at multiple stages: first before support substrate bonding to enhance initial peel-off properties, and then after bonding to further improve peel-off while maintaining handling ease. This multi-stage preliminary action ensures optimal peel-off enhancement at each process stage
3Length of moving object
If grinding is used to thin the wafer, then thickness is reduced, but productivity is lowered and grindstone wear increases
Solution Approach 1:
The patent replaces the traditional mechanical grinding system with a combination of laser beam processing and ultrasonic wave application. The laser creates a modified layer that serves as a peel-off layer, and ultrasonic waves enhance crack propagation, eliminating the need for extensive mechanical grinding and significantly improving productivity while reducing grindstone wear
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 reduces grindstone wear and enhances productivity by improving the peel-off property of lithium tantalate wafers, allowing for efficient thinning while minimizing the risk of cracking and breakage during the peeling process.
Implementation Method 1
positioning a focused spot of a laser beam with a wavelength transmittable through the wafer from the second surface side of the wafer inside the wafer, and applying the laser beam while moving the focused spot and the wafer relative to each other
Implementation Method 2
forming separation start points each including a modified layer parallel to the second surface and cracks extending from the modified layer
Implementation Method 3
applying an ultrasonic wave to the wafer from the second surface side of the wafer
Implementation Method 4
applying an ultrasonic wave to a wafer is available. With this method, however, even if an ultrasonic wave is applied to the wafer after a support substrate is bonded to the wafer, the peel-off property is not enhanced sufficiently
Data Source
AI summary
A wafer thinning method for a wafer includes bonding a first support substrate to a first surface of the wafer, positioning a focused spot of a laser beam with a wavelength transmittable through the wafer from a second surface side of the wafer inside the wafer, and applying the laser beam while moving the focused spot and the wafer relative to each other in a direction parallel to the second surface, thereby forming separation start points each including a modified layer parallel to the second surface and cracks extending from the modified layer, applying an ultrasonic wave to the wafer from the second surface side of the wafer, bonding a second support substrate to the second surface of the wafer, and separating the wafer at the separation start points into a first wafer having the first surface and a second wafer having the second surface, thereby thinning the wafer.