Wafer Dicing via Reverse-Side Laser Cutting and Pre-Sawing
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Solution Overview
Problem
The existing methods for processing wafers with low-k films, such as those described in Japanese Patent Laid-open No. 2005-064231, face issues like reduced productivity, blade displacement, debris scattering, thermal stress, and reduced device density due to the need for multiple laser grooves and protective coatings, which compromise the quality of the resulting device chips.
Innovation Solution
A method involving the placement of a protective member on the wafer, grinding the reverse side, forming cut grooves from the reverse side, and applying a laser beam along these grooves to sever the wafer into individual device chips, eliminating the need for multiple laser grooves and reducing thermal stress, while using an adhesive tape for support and pick-up to enhance productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a laser grooving process is carried out to remove the low-k film along streets, then the quality of device chips is improved, but productivity is reduced due to the need to form at least two laser-processed grooves along each street
Solution Approach 1:
The patent applies laser beams from the reverse side of the wafer instead of from the face side. This inversion allows the laser to remove the low-k film and sever the wafer along dicing lines without requiring multiple grooves, as the laser energy is applied directly to the low-k film from the opposite direction, achieving complete removal and separation in a single pass while maintaining productivity
Solution Approach 2:
The patent changes the dimension of laser beam application by switching from top-down (face side) to bottom-up (reverse side) processing. This dimensional change allows the laser to access and remove the low-k film more effectively, eliminating the need for multiple grooves and enabling complete wafer severance along the dicing lines in one operation
2Productivity
If the low-k film is not removed sufficiently by laser grooving, then productivity is maintained, but the dicing blade becomes displaced or slanted and unevenly worn
Solution Approach 1:
By applying the laser from the reverse side, the patent ensures complete removal of the low-k film without leaving residual material that could cause blade displacement. The inverted approach allows the laser to cleanly sever the wafer along the dicing lines, providing a precise guide for the dicing blade while maintaining productivity through single-pass processing
3Manufacturing precision
If a laser grooving process is performed on the face side of the wafer, then the low-k film can be processed, but debris is scattered around from the wafer, tending to lower the quality of resultant devices
Solution Approach 1:
The patent eliminates debris scattering by applying the laser from the reverse side of the wafer. This inversion causes the laser processing and material removal to occur away from the device surfaces on the face side, preventing debris from landing on and contaminating the devices. The severing process generates minimal debris that does not affect device quality
4Manufacturing precision
If multiple laser beams are applied to form wide streets for low-k film removal, then the low-k film is completely removed, but thermal stresses are developed and remain in the wafer, possibly reducing the flexural strength of resultant devices
Solution Approach 1:
By applying the laser from the reverse side, the patent achieves complete low-k film removal with a single beam pass along each dicing line, eliminating the need for multiple beams and wide streets. This reduces the total thermal energy input into the wafer, minimizing thermal stress accumulation and preserving the flexural strength of the resulting devices
5Manufacturing precision
If wide streets are required on the wafer for laser processing, then the low-k film can be removed along dicing lines, but areas on the wafer where devices are to be formed are reduced, resulting in a reduction in the number of devices that can be produced from the wafer
Solution Approach 1:
The patent applies the laser from the reverse side to remove the low-k film and sever the wafer along narrow dicing lines. This approach requires minimal street width, maximizing the active device area on each wafer and increasing the number of devices that can be produced per wafer while maintaining complete low-k film removal and clean separation
6Reliability
If a passivation film is deposited on the upper surface of the low-k film, then the inside of the wafer is protected from ambient moisture and metal ions, but heat generated by the low-k film is trapped, causing lateral processing or undercut that tends to cause the low-k film to flake off
Solution Approach 1:
By applying the laser from the reverse side of the wafer, the patent processes the low-k film from the opposite direction of the passivation film. This allows heat to escape laterally through the passivation film rather than being trapped, preventing lateral processing and undercut that would cause the low-k film to flake off. The passivation film remains intact and continues to provide protection from moisture and metal ions
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 increases productivity by avoiding blade displacement and debris, reduces thermal stress, and maintains device quality by eliminating the need for wide dicing lines, allowing for efficient separation and bonding of device chips without compromising their integrity.
Implementation Method 1
applying a laser beam to the wafer from the reverse side thereof along the cut grooves to completely sever the wafer
Data Source
AI summary
A wafer processing method includes a protective member laying step of placing a protective member on a face side of a wafer, a reverse side grinding step of grinding a reverse side of the wafer to thin the wafer, a cut groove forming step of positioning a cutting blade in alignment with projected dicing lines one at a time on the reverse side of the wafer, cutting the wafer with the cutting blade to form cut grooves in the wafer which terminate short of the face side thereof, and a cutting step of applying a laser beam to the wafer from the reverse side thereof along the cut grooves to completely sever the wafer along the projected dicing lines into individual device chips.