Wafer Edge Thinning Using Laser-Formed Annular Modified Layers
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Solution Overview
Problem
Existing wafer processing methods face issues with high abrasive stone consumption, costly edge trimming, uneven wear, and residual adhesive layers leading to potential device breakage during polishing.
Innovation Solution
A processing method involving trimming, bonding, annular modified layer formation, auxiliary modified layer formation, and surplus region removal using laser irradiation and grinding to minimize edge chipping and abrasive wear, while ensuring precise thinning and reducing the risk of wafer breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the outer circumferential edge is chamfered and the wafer is ground very thinly, then the wafer can be thinned to a small thickness, but the outer circumferential edge becomes a knife-edge and chipping at the edge is liable to occur
Solution Approach 1:
The patent applies preliminary action by forming an annular modified layer at the outer circumferential edge before the thinning process. This modified layer, created through laser irradiation, pre-strengthens the edge region that will otherwise become a vulnerable knife-edge during thin grinding, thereby preventing chipping while enabling precise thickness control.
2Reliability
If a generally-called edge trimming technique is used to cut the outer circumferential edge, then chipping is prevented, but the amount of consumption of an abrasive stone is large and the cost is high
Solution Approach 1:
The patent replaces the mechanical edge trimming system with a laser-based modified layer formation system. Instead of using abrasive stones to mechanically cut and remove material from the edge, the invention uses laser irradiation to create a modified layer that prevents chipping, thereby eliminating the need for extensive abrasive stone consumption associated with traditional mechanical trimming.
3Reliability
If irradiation with a laser beam is executed to form an annular modified layer, then edge strength is enhanced, but a region on the side of the outer circumferential part relative to the modified layer remains adhering and it is impossible to remove this region well
Solution Approach 1:
The patent applies segmentation by dividing the outer circumferential region into two distinct zones: an inner region with the annular modified layer formed by laser irradiation for strength enhancement, and an outer region that is intentionally left with residual adhesive for controlled removal. This segmentation allows the modified layer to provide edge strength while the segmented outer region can be selectively removed without compromising the strengthened inner edge.
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 reduces the risk of wafer breakage, minimizes abrasive stone consumption, and prevents device contamination by forming controlled modified layers for precise edge removal, enhancing the efficiency and cost-effectiveness of the wafer thinning process.
Implementation Method 1
forming an annular modified layer along the boundary between the outer circumferential surplus region that has not been removed in the trimming step in the first wafer and the device region by positioning the focal point of a laser beam with a wavelength having transmissibility with respect to the first wafer to the inside of the first wafer and executing irradiation with the laser beam
Implementation Method 2
a grinding step of grinding the back surface side of the first wafer to execute thinning to a predetermined finished thickness
Data Source
AI summary
A wafer is processed by causing a cutting blade to cut into an outer circumferential surplus region of a first wafer from the front surface side by a predetermined thickness and executing cutting along the outer circumferential edge to form an annular step part in the outer circumferential surplus region, bonding the front surface side of the first wafer and the front surface side of a second wafer to form a bonded wafer, forming an annular modified layer by positioning the focal point of a laser beam with a wavelength having transmissibility with respect to the first wafer to the inside of the first wafer and executing irradiation with the laser beam along the boundary between a device region and the outer circumferential surplus region from the back surface side, and grinding the back surface side of the first wafer to execute thinning to a predetermined finished thickness.