Bonded Wafer Rim Separation for Thin Grinding Without Chipping
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Solution Overview
Problem
Existing wafer processing methods for three-dimensionally stacked semiconductor wafers face issues with edge chipping and contamination during grinding, as well as the risk of device damage from cutting debris and residual edge material.
Innovation Solution
A method involving bonding two wafers, forming modified layers inside the first wafer using a laser beam, removing the outer peripheral region with a cutting blade, and then grinding the wafer to a finish thickness, while ensuring the cutting blade does not reach the second wafer to prevent device damage and minimize debris.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the wafer is ground extremely thin to achieve low-profile device chips, then the desired thin profile is achieved, but the outer peripheral edge forms a knife edge that is prone to chipping during grinding
Solution Approach 1:
The patent applies preliminary action by forming modified layers and cracks in the outer peripheral region before the grinding process. The laser irradiation creates predetermined structural changes that prepare the material to resist chipping during subsequent grinding operations, preventing the formation of knife edges even when the wafer is ground extremely thin.
Solution Approach 2:
The patent changes the physical and chemical parameters of the wafer's outer peripheral region through laser irradiation. The modified layers alter the material structure, density, and mechanical properties in the affected region, creating a gradient that prevents stress concentration and chipping while allowing the bulk of the wafer to be ground to the desired thin profile.
2Reliability
If edge trimming is performed by cutting the outer peripheral edge to prevent knife edge formation, then edge chipping is suppressed, but cutting debris is produced that can contaminate devices
Solution Approach 1:
The patent replaces the mechanical cutting process with a non-contact laser irradiation process. Instead of using a cutting blade that generates mechanical debris, the laser modifies the material structure through energy input, creating modified layers and cracks without producing contaminating debris. This substitution eliminates the harmful byproducts of mechanical cutting while achieving the same edge protection effect.
Solution Approach 2:
The patent uses laser irradiation to change the physical and chemical parameters of the outer peripheral region, creating modified layers that suppress chipping. This thermal/optical process avoids the mechanical contact and debris generation associated with traditional cutting methods, thereby preventing device contamination while maintaining edge integrity.
3Reliability
If modified layers are formed by laser irradiation to suppress edge chipping, then chipping is prevented, but the outer peripheral surplus region may remain without separation or be caught between the grinding wheel and wafer
Solution Approach 1:
The patent applies preliminary action by forming cracks that extend from the modified layers created through laser irradiation. These pre-formed cracks create natural separation planes that guide the removal of the outer peripheral surplus region during grinding, ensuring complete separation without leaving residual material that could interfere with the grinding process or device integrity.
Solution Approach 2:
The patent segments the wafer structure by creating modified layers and cracks in the outer peripheral region. This segmentation divides the surplus material into distinct zones with different structural properties, facilitating controlled removal during grinding while preserving the integrity of the device regions. The cracks act as separation boundaries that prevent the surplus region from being caught between the grinding wheel and wafer.
4Manufacturing precision
If a cutting blade is used to remove the outer peripheral region, then surplus material can be separated, but the cutting process may produce debris that damages devices
Solution Approach 1:
The patent replaces the mechanical cutting blade process with a combination of laser irradiation and controlled grinding. The laser creates modified layers and cracks that define the removal boundary, and the subsequent grinding process removes the surplus material through abrasion rather than mechanical cutting. This substitution eliminates the generation of cutting debris while achieving precise removal of the outer peripheral region.
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 removes the outer peripheral surplus region without damaging the devices, reducing the risk of edge chipping and contamination, and ensures precise thinning of the wafer while minimizing debris production.
Implementation Method 1
forming modified layers in an annular pattern and cracks, which spread from the modified layers, inside the first wafer by irradiating an annular region on an inner side by a predetermined distance from an outer peripheral edge in the first wafer with a laser beam of a wavelength having transmissivity for the first wafer
Data Source
AI summary
A wafer processing method includes a step of forming a bonded wafer by provisionally bonding a first wafer and a second wafer, a step of forming, with a laser beam, modified layers in an annular pattern and cracks, which spread from the modified layers, inside the first wafer, a step of increasing bonded strength of the bonded wafer by anneal processing, a step of removing an outer peripheral region on a side of the outer peripheral edge relative to the modified layers and the cracks, by positioning a cutting blade at the annular region of the first wafer, and causing the cutting blade to cut in from a side of the other side of the first wafer to a depth not reaching the second wafer, and a step of thinning the first wafer to a finish thickness by grinding the first wafer from the side of the other side.