Bonded Wafer Chamfer Removal Using Stair-Step Laser Modified Layers
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Solution Overview
Problem
Existing methods for removing chamfered parts on bonded wafers using cutting blades or grinding abrasive stones are time-consuming, leading to low productivity and potential damage to the other wafer.
Innovation Solution
A method involving a laser beam that branches into multiple focal points to form modified layers in a descending stair pattern, followed by grinding to remove the chamfered part, using a processing apparatus with a chuck table, laser beam irradiation unit, and feed mechanisms to control the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cutting blades or grinding abrasive stones are directly positioned to the outer circumference of the wafer to remove the chamfered part, then the knife-edge is suppressed, but it takes a considerable length of time and productivity is low
Solution Approach 1:
The patent replaces the mechanical cutting blade or grinding abrasive stone system with a laser beam system. The laser beam irradiates the chamfered part from the back surface of the first wafer, forming modified layers that cause cracks to develop and remove the chamfered part. This substitution eliminates direct mechanical contact, significantly reducing processing time while maintaining effective chamfered part removal and preventing knife-edge formation.
Solution Approach 2:
The patent introduces modified layers as an intermediary mechanism between the laser beam and the chamfered part. The laser beam forms modified layers within the wafer substrate, which then induce cracks that propagate to remove the chamfered part. This intermediary approach allows indirect removal of the chamfered part without direct mechanical contact, improving productivity while achieving the desired shape modification.
2Reliability
If cutting blades or grinding abrasive stones are directly positioned to the outer circumference of the wafer to remove the chamfered part, then the knife-edge is suppressed, but the other wafer in the bonded wafer is scratched
Solution Approach 1:
The patent replaces the mechanical cutting blade or grinding abrasive stone system with a laser beam system. The laser beam irradiates the chamfered part from the back surface of the first wafer, forming modified layers that cause cracks to develop and remove the chamfered part. This substitution eliminates direct mechanical contact, significantly reducing processing time while maintaining effective chamfered part removal and preventing knife-edge formation.
Solution Approach 2:
The patent introduces modified layers as an intermediary mechanism between the laser beam and the chamfered part. The laser beam forms modified layers within the wafer substrate, which then induce cracks that propagate to remove the chamfered part. This intermediary approach allows indirect removal of the chamfered part without direct mechanical contact, improving productivity while achieving the desired shape modification.
3Manufacturing precision
If the back surface of the one wafer is ground to execute thinning, then the wafer is thinned, but the chamfered part becomes a sharp shape like a knife-edge and cracks develop from the knife-edge to the inside of the wafer
Solution Approach 1:
The patent applies preliminary action by removing the chamfered part before the wafer thinning process. The laser beam irradiates the chamfered part first, forming modified layers and inducing cracks that remove the chamfered part. Only after this preliminary removal is the wafer thinned by grinding the back surface. This sequence prevents the formation of knife-edge shapes and subsequent crack development during thinning.
Solution Approach 2:
The patent replaces the mechanical cutting blade or grinding abrasive stone system with a laser beam system. The laser beam irradiates the chamfered part from the back surface of the first wafer, forming modified layers that cause cracks to develop and remove the chamfered part. This substitution eliminates direct mechanical contact, significantly reducing processing time while maintaining effective chamfered part removal and preventing knife-edge formation.
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 significantly reduces processing time and improves productivity while preventing damage to the other wafer.
Implementation Method 1
a laser beam with a wavelength having transmissibility with respect to the first wafer is branched into a plurality of branch laser beams, and focal points of the respective branch laser beams are set at different positions
Implementation Method 2
executing irradiation with the branch laser beams
Implementation Method 3
grinding the back surface of the first wafer to thin the first wafer
Implementation Method 4
cracks develop from the plurality of modified layers toward the joining layer
Data Source
AI summary
A processing method of a bonded wafer includes forming a plurality of modified layers in a form of rings through positioning focal points of laser beams with a wavelength having transmissibility with respect to a first wafer inside the first wafer, from which a chamfered part is to be removed, from a back surface of the first wafer and executing irradiation, holding a second wafer side on a chuck table, and grinding the back surface of the first wafer to thin the first wafer. In the forming the modified layers, the focal points of the laser beams are set in such a manner as to gradually get closer to a joining layer in a direction from an inner side of the first wafer toward an outer side thereof, so that the plurality of ring-shaped modified layers are formed in a form of descending stairs.