Bonded Wafer Edge Removal Using Two-Step Opposed Cutting
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Solution Overview
Problem
Existing methods for edge trimming bonded wafers face challenges in completely removing the first wafer while leaving the joining layer intact, leading to defects and exposure of the second wafer's peripheral portion, which can break devices and complicate reuse of the second wafer.
Innovation Solution
A method involving a two-step cutting process using a first cutting blade to form a step portion on the first wafer and a second cutting blade to remove the outer peripheral portion with up-cutting, ensuring the joining layer remains intact by positioning the second cutting blade closer to the second wafer and opposite the velocity vector of the bonded wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lower end of the cutting blade is positioned at the boundary between the first wafer and the joining layer to cut only the first wafer, then the second wafer is not cut, but the first wafer is not completely cut and removed in the annular region
Solution Approach 1:
The cutting process is divided into two distinct stages: first cutting to form a step portion with depth not reaching the second wafer, and second cutting to remove the outer peripheral portion with the blade positioned closer to the second wafer. This segmentation allows each cutting stage to have optimized depth control, ensuring complete removal of the first wafer while preventing exposure of the second wafer.
Solution Approach 2:
The first cutting step creates a step portion that serves as a preliminary structure, establishing a depth reference that prevents the second cutting blade from exposing the second wafer. This preliminary action ensures that even with cutting depth variations, the second wafer remains protected.
2Reliability
If the lower end of the cutting blade is lowered to the position of the second wafer to completely remove the first wafer, then the first wafer is completely cut, but the outer peripheral portion of the second wafer is exposed and etched in subsequent steps
Solution Approach 1:
The cutting depth is locally optimized for different regions: in the first cutting step, the blade depth is controlled to create a step portion, and in the second cutting step, the blade is positioned closer to the second wafer but the velocity vector opposition ensures the joining layer remains intact, protecting the second wafer's outer peripheral portion from etching damage.
Solution Approach 2:
Instead of positioning the cutting blade to cut through the joining layer (which would expose the second wafer), the invention positions the blade closer to the second wafer but rotates the blade and wafer in opposite directions. This inverted approach uses the velocity vector opposition to prevent the blade from cutting the joining layer, thereby protecting the second wafer while still removing the first wafer.
3Object-affected harmful factors
If conventional edge trimming is applied to ensure the joining layer remains over the outer peripheral portion of the second wafer, then the second wafer is protected, but complete removal of the first wafer cannot be ensured due to cutting depth variation
Solution Approach 1:
The cutting process is segmented into two steps with different blade positions and rotation directions. The first step creates a step portion, and the second step removes the remaining first wafer material. This segmentation ensures that even with cutting depth variations, the first wafer is completely removed while the second wafer remains protected by the joining layer.
Solution Approach 2:
In the second cutting step, the blade and wafer are rotated in opposite directions, creating velocity vector opposition. This inverted rotation prevents the blade from cutting the joining layer despite the blade being positioned closer to the second wafer, thereby ensuring both complete first wafer removal and second wafer protection.
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 effectively removes the first wafer without exposing the second wafer's peripheral portion, preserving the joining layer and preventing device damage, allowing for the reuse of the second wafer as a support substrate.
Implementation Method 1
forming, in an outer peripheral portion of the first wafer, a first step portion having a depth that does not reach the second wafer and by which the first wafer remains, by rotating the holding table about the rotational shaft in a state in which a first cutting blade mounted to a distal end portion of a first spindle is caused to cut into the outer peripheral portion of the first wafer
Implementation Method 2
removing the outer peripheral portion of the first wafer by rotating the holding table about the rotational shaft in a state in which a second cutting blade mounted to a distal end portion of a second spindle is rotated about the second spindle while a lower end of the second cutting blade is positioned to a position that is closer to the second wafer than to a bottom surface of the first step portion... such that a direction of a velocity vector of the lower end of the second cutting blade becomes opposite a direction of a velocity vector of the bonded wafer
Data Source
AI summary
A processing method for a bonded wafer includes forming, in an outer peripheral portion of a first wafer, a first step portion having a depth that does not reach a second wafer and by which the first wafer remains, and removing the outer peripheral portion of the first wafer by rotating the holding table about a rotational shaft in a state in which a lower end of a second cutting blade is positioned to a position where a joining layer is present, in which, in the removing the outer peripheral portion of the first wafer, the second cutting blade and the holding table are rotated such that the direction of the velocity vector of the lower end of the second cutting blade becomes opposite the direction of the velocity vector of the bonded at a position corresponding to the lower end of the second cutting blade.