Wafer Chamfer Removal Using Laser-Formed Modified Layers
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Solution Overview
Problem
The existing methods for processing wafers with chamfered portions at their outer periphery fail to completely remove these portions, leading to remnants that act as contaminants or cause chipping during the division of device chips, thereby compromising the quality of individual chips.
Innovation Solution
A processing method involving a modified layer forming step using a laser beam with a focal point positioned between the effective area and the chamfered portion, followed by an external force application to bend and remove the chamfered portion from the wafer's back surface, ensuring complete removal without damaging the front surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the wafer is thinned by being ground at its back surface, then the desired thickness is achieved, but the chamfered portion is sharpened like a knife edge causing injury risk and crack extension
Solution Approach 1:
A modified layer is formed in advance within the chamfered portion using laser irradiation before the grinding process. This preliminary modification creates a controlled structure that prevents the chamfered portion from becoming sharply pointed during subsequent thinning, thereby eliminating the injury and cracking risks while maintaining precise thickness control.
Solution Approach 2:
A modified layer is introduced as an intermediary structure within the chamfered portion. This modified layer acts as a buffer that absorbs and distributes stress during grinding, preventing the formation of sharp edges and reducing the risk of cracks extending into the effective area, thus mediating between the grinding process and the chamfered portion integrity.
2Object-affected harmful factors
If the chamfered portion is removed by external force during grinding processing, then the sharp edge problem is solved, but the chamfered portion may not be completely removed and remains as a contaminant source
Solution Approach 1:
The modified layer is formed in advance within the chamfered portion, creating a predetermined weak structure. During subsequent processing, this pre-modified layer is easily and completely removed along with the chamfered portion, ensuring no remnants remain that could become contaminants, while the external force required for removal is significantly reduced.
Solution Approach 2:
The physical and chemical parameters of the chamfered portion are changed through laser modification, creating a modified layer with different properties than the original material. This parameter change makes the chamfered portion more susceptible to complete removal by external forces during processing, ensuring thorough elimination without leaving contaminant remnants.
3Object-affected harmful factors
If the chamfered portion is removed by external force, then the knife edge problem is solved, but individual device chips may experience chipping during division
Solution Approach 1:
The modified layer is formed in advance within the chamfered portion, creating a controlled weak structure that removes the sharp edge hazard. This preliminary modification also prevents stress concentration at the chamfered portion boundaries, thereby preventing chipping of individual device chips during the subsequent division process and ensuring chip integrity.
Solution Approach 2:
The modified layer serves as an intermediary that absorbs and distributes mechanical stress during the division process. By preventing stress concentration at the chamfered portion edges, this intermediary layer protects the integrity of individual device chips during cutting, eliminating both the sharp edge hazard and the chipping risk.
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 chamfered portion from the wafer's periphery, preventing contamination and chipping of device chips, thereby enhancing the quality and integrity of the processed chips.
Implementation Method 1
irradiating the wafer, from a back surface thereof, with a laser beam of a wavelength having transmissivity for the wafer with a focal point of the laser beam positioned inside a boundary portion between the effective area and the chamfered portion, whereby a modified layer is formed along the chamfered portion
Implementation Method 2
applying an external force to the outer periphery of the wafer to remove the chamfered portion
Implementation Method 3
grinding the back surface of the wafer to process the wafer to a desired thickness
Data Source
AI summary
A processing method of a wafer includes a modified layer forming step of irradiating the wafer, from its back surface, with a laser beam of a wavelength having transmissivity for the wafer with its focal point positioned inside a boundary portion between an effective area and a chamfered portion, whereby a modified layer is formed along the chamfered portion, a chamfered portion removing step of applying an external force to an outer periphery of the wafer, and grinding the back surface of the wafer to a desired wafer thickness. The modified layer forming step includes a first step of forming a first modified layer relatively deep with cracks formed extending to the front surface, and a second step of forming a second modified layer relatively shallow, adjacent and on an outer or inner side of the first modified layer, with cracks formed not extending to the front surface.