Wafer Laser Cutting with Underfill Debris Management
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Solution Overview
Problem
The deposition of debris on the wafer surface and projected electrodes during laser beam cutting of semiconductor wafers is a challenge, especially due to the brittleness of low-k insulation layers and the difficulty in forming protective films over bumps, leading to short-circuits and reduced productivity.
Innovation Solution
A method involving the application of an underfill material, such as epoxy or polyimide resin, to cover the wafer surface, followed by laser beam irradiation along planned cutting lines to remove the underfill material and debris, preventing their deposition on the electrodes and surface, and subsequent cutting to expose the electrodes flush in height, thereby ensuring smooth cutting and preventing debris accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If laser beam irradiation is used to cut the wafer, then cutting precision is improved, but debris is deposited on the wafer surface and electrodes
Solution Approach 1:
The underfill material is applied to cover the wafer surface and electrodes before laser beam irradiation. This preliminary covering action prevents debris from depositing on the electrodes during the subsequent laser cutting process, while still allowing the laser to achieve precise cutting through the underfill material and insulation layer.
Solution Approach 2:
The underfill material serves as an intermediary substance between the laser beam and the electrodes. It absorbs the harmful debris generated during laser cutting and protects the electrodes from contamination, while being removable afterward to expose the cleaned electrode surfaces.
2Object-generated harmful factors
If a protective film is formed on the wafer surface to prevent debris deposition, then debris prevention is improved, but the film cannot be properly formed over projected electrodes
Solution Approach 1:
The underfill material functions as a temporary, disposable protective layer that is applied, serves its debris-prevention purpose during laser cutting, and then is removed. This approach avoids the need for complex permanent protective film structures that would need to accommodate the three-dimensional electrode surfaces.
3Productivity
If the insulation layer is cut by dicing, then productivity is improved, but the brittle insulation layer is exfoliated or crushed
Solution Approach 1:
The patent replaces the mechanical dicing process with laser beam irradiation for cutting the insulation layer. This substitution eliminates the mechanical stresses that cause exfoliation and crushing of the brittle low-k insulation layer, while maintaining high cutting efficiency through the use of laser energy.
4Object-generated harmful factors
If the underfill material is removed by laser beam irradiation, then debris deposition is prevented, but the underfill material must be selectively removed
Solution Approach 1:
The laser beam irradiation parameters are optimized to achieve selective removal of the underfill material along the cutting lines while leaving the electrodes and other areas intact. This local differentiation in material removal enables debris prevention without requiring complex additional processing steps.
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 debris deposition on the wafer surface and electrodes, ensuring smooth cutting and enhanced productivity by using an underfill material to manage debris during laser beam cutting, while maintaining the integrity of the insulation layer and projected electrodes.
Implementation Method 1
a laser beam irradiation step for irradiating the wafer with a laser beam from the surface and along the planned cutting lines so as to remove at least the underfill material present over the planned cutting lines
Data Source
AI summary
An underfill material is provided on the surface of a wafer in such a manner as to cover bumps, then the wafer is irradiated with a laser beam from the surface thereof and along planned cutting lines so as to remove an insulation layer and the underfill material present over the planned cutting lines, and the debris generated in this instance are deposited on the underfill material and are thereby prevented from being deposited on the wafer surface and/or on the bumps. Subsequently, a surface layer of the underfill material is cut so as to make the bumps flush in height and to expose the tips of the bumps.