Pulsed Laser Shield Tunnels for Off-Angle Wafer Division
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Solution Overview
Problem
Wafers with off-angle single crystal substrates, such as LiN or LiTaO3, cannot be reliably divided into individual devices due to the formation of altered layers and cracks following the c-plane when using existing laser processing methods.
Innovation Solution
A method involving setting the numerical aperture of a focusing lens for a pulsed laser beam within a specific range (0.05 to 0.2) and applying the beam from the back side of the wafer to form shield tunnels from the back surface to the front, allowing for secure division of the wafer along the division lines, while also splitting films coating the surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a pulsed laser beam is applied with the focal point positioned inside the wafer to form altered layers along division lines, then the wafer substrate can be divided, but the film coating the surfaces of the division lines cannot be divided
Solution Approach 1:
The division process is segmented into two distinct stages: first, a laser beam divides the film coating along the division lines; second, another laser beam divides the substrate along the same division lines. This segmentation ensures that both the film and substrate are completely divided, resolving the contradiction between achieving narrow division lines and ensuring complete division of all layers.
2Productivity
If altered layers are formed inside an off-angle single crystal substrate by existing laser methods, then processing can proceed, but altered layers and cracks form following the c-plane preventing proper division
Solution Approach 1:
The invention changes the parameter of focal point positioning from inside the substrate to precisely on the front surface of the substrate. This parameter change, combined with setting a specific numerical aperture range (0.05 to 0.2), prevents the formation of altered layers that follow the c-plane in off-angle substrates, thereby enabling accurate division along the division lines while maintaining processing capability.
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 approach avoids the formation of altered layers and cracks, enabling reliable division of wafers with off-angle single crystal substrates into individual device chips with high productivity.
Implementation Method 1
applying the pulsed laser beam along the division lines from a back side of the single crystal substrate, with a focal point of the pulsed laser beam positioned at a desired position from a back surface of the single crystal substrate, so as to form shield tunnels each composed of a pore and a pore-shielding amorphous portion along the division lines from the focal point positioned inside the single crystal substrate
Data Source
AI summary
A wafer is formed with a plurality of division lines on a front surface of a single crystal substrate having an off angle and formed with devices in a plurality of regions partitioned by the division lines. The wafer is processed by setting a numerical aperture (NA) of a focusing lens for focusing a pulsed laser beam so that a value obtained by dividing the numerical aperture (NA) by a refractive index (N) of the single crystal substrate falls within the range from 0.05 to 0.2. The pulsed laser beam is applied along the division lines, with a focal point of the pulsed laser beam positioned at a desired position from a back surface of the single crystal substrate, so as to form shield tunnels each composed of a pore and a pore-shielding amorphous portion along the division lines from the focal point positioned inside the single crystal substrate.