Wafer Laser Cutting via Thermal Contraction
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Solution Overview
Problem
Conventional methods for cutting semiconductor wafers, such as blade-saw cutting and existing laser cutting techniques, face challenges like mechanical stress, debris contamination, and high operating costs, particularly when cutting thin wafers with advanced materials, which affect the quality and efficiency of wafer dicing.
Innovation Solution
A method and system utilizing a laser beam to generate a crack within the wafer by converging the beam to form a focal point, causing differential contraction and solidification rates within the focal volume, thereby cutting the wafer without mechanical stress and debris, using a fiber laser with controlled power density and pulse duration to induce melting or thermal heating below the vaporization threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If blade-saw cutting is used to cut semiconductor wafers, then cutting can be achieved, but mechanical stress is introduced into the wafer causing fracture risk especially in thin wafers
Solution Approach 1:
The patent replaces the mechanical blade-saw cutting system with a laser-based system. The laser beam focuses energy to create a crack within the wafer through thermal effects, eliminating direct mechanical contact and the associated mechanical stress that causes fracture in thin wafers.
Solution Approach 2:
The patent changes the cutting mechanism from mechanical force to thermal energy concentration. By controlling laser parameters (power, pulse duration, focus position), the process transitions from surface heating to internal crack generation, fundamentally changing how the cutting action is transmitted to the wafer material.
2Productivity
If conventional laser cutting is used with high power density above vaporization threshold, then cutting speed is improved, but debris comprising silicon deposits is produced on the wafer surface
Solution Approach 1:
The patent changes the laser power density parameter from above vaporization threshold to below vaporization threshold. This parameter change shifts the material removal mechanism from vaporization (which creates debris) to crack propagation through differential thermal contraction, eliminating silicon deposit formation while maintaining cutting effectiveness.
Solution Approach 2:
The patent utilizes controlled phase transitions of silicon during laser irradiation. By maintaining power density below the vaporization threshold, the process induces melting and rapid solidification cycles that create thermal stress cracks, avoiding the vaporization phase transition that generates debris.
3Object-generated harmful factors
If assist gas is used to remove silicon deposits during laser cutting, then wafer surface quality is improved, but operating costs increase
Solution Approach 1:
The patent extracts or eliminates the source of the problem (silicon deposits) by changing the laser processing parameters to prevent deposit formation in the first place. This removes the need for assist gas systems and their associated operating costs, addressing the contradiction at its root cause rather than treating the symptom.
4Object-generated harmful factors
If water jet-guided laser beam is used to remove debris, then debris removal is achieved, but water presence is undesirable for wafers with integrated circuits
Solution Approach 1:
The patent eliminates the need for water jet debris removal by changing the fundamental cutting mechanism to one that doesn't produce vaporization debris. This extracts the water removal system from the process entirely, avoiding water contamination risks while maintaining clean cut surfaces.
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 allows for precise cutting of semiconductor wafers with minimal mechanical stress and debris, reducing operational costs and improving the quality of the cutting process, enabling the use of thinner wafers and advanced materials while minimizing the need for assist gases or external forces.
Implementation Method 1
irradiating a laser beam towards a surface of the wafer and converging the laser beam to form a focal point so that a focal volume defined by the focal point and a boundary of the laser beam within the wafer is formed
Implementation Method 2
Energy encompassed within the focal volume causes the wafer located at the periphery of the focal volume to contract faster than the wafer located within the focal volume, thereby generating a crack within the wafer
Implementation Method 3
Chemical bonds in the target material are broken by the photochemical action of the laser beam and cutting may be achieved by moving the scanning laser beam or the working platform to produce the desired shape
Implementation Method 4
Due to the photochemical action of the laser beam to break the bonds in the silicon wafer, debris comprising deposits of silicon are produced on the surface of the wafer
Implementation Method 5
a laser power density lower than the vapourisation threshold of the wafer ablation
Data Source
AI summary
A method for cutting a semiconductor wafer by generating a crack within the wafer, and a system thereof, are provided. The method comprises irradiating a laser beam towards a surface of the wafer and converging the laser beam to form a focal point so that a focal volume defined by the focal point and a boundary of the laser beam within the wafer is formed. Energy encompassed within the focal volume causes the wafer located at the periphery of the focal volume to contract faster than the wafer located within the focal volume, thereby generating a crack within the wafer.