Multi-segment Focusing Lens for Laser Wafer Dicing
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Solution Overview
Problem
Current methods for dicing semiconductor wafers, such as diamond disk saws and laser ablation, face limitations including low processing speed, poor edge quality, debris generation, and thermal damage, especially when processing thicker wafers or materials with surface features, which degrade device yield and performance.
Innovation Solution
A multi-segment focusing lens is used to concentrate a pulsed laser beam into multiple focal points within the wafer, creating deep and narrow damage structures along the intended cleaving line, allowing for efficient separation with minimal surface disruption and reduced thermal impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If diamond disk saw is used for dicing, then cutting capability is achieved, but processing speed is low and edge quality is poor
Solution Approach 1:
The patent replaces the mechanical diamond disk saw system with a laser-based processing system. The laser beam creates damage structures within the wafer material through optical breakdown, enabling separation without mechanical contact. This substitution eliminates the inherent limitations of mechanical sawing including low speed, wide kerf, and poor edge quality while achieving high-speed processing with precise, clean edges.
Solution Approach 2:
The laser processing utilizes phase transitions of material through optical breakdown and ablation. The high-intensity laser pulse causes instantaneous vaporization and plasma formation, creating narrow damage structures that guide crack propagation. This phase transition mechanism enables precise material removal with minimal heat-affected zone, resolving the contradiction between processing speed and edge quality.
2Productivity
If laser ablation is used for dicing, then processing speed improves, but kerf width increases and thermal damage occurs
Solution Approach 1:
The patent employs focused laser beams that concentrate energy into extremely small focal volumes within the wafer, creating highly localized damage structures. The energy deposition is confined to specific regions along the intended cleavage line, leaving surrounding areas unaffected. This local quality approach maintains high processing speed while eliminating the wide heat-affected zone and excessive kerf width associated with conventional laser ablation.
Solution Approach 2:
The system uses pulsed laser radiation with controlled repetition rates to create periodic damage structures along the cleavage line. By delivering energy in discrete pulses rather than continuous wave, the material has time to cool between pulses, preventing cumulative thermal damage while maintaining efficient processing speed through high repetition rate operation.
3Measurement precision
If high NA lens is used for stealth dicing, then focusing precision improves, but depth of focus decreases and multiple cracks occur
Solution Approach 1:
The patent transitions from two-dimensional surface focusing to three-dimensional volumetric focusing by creating an extended focal region or focal stack within the wafer thickness. This is achieved through cylindrical lens combinations or astigmatic focusing that elongate the focal point into a line or volume, maintaining high intensity over an extended depth range. This dimensional change enables single-pass processing of thick wafers with precise crack control, eliminating the need for multiple passes and associated surface cracking.
Solution Approach 2:
The optical system is designed to perform multiple functions: it provides tight focusing for precise damage structure creation, maintains extended depth of focus for thick wafer processing, and controls crack propagation direction. The universal optical configuration handles varying wafer thicknesses and materials while maintaining consistent processing quality, resolving the contradiction between focusing precision and crack control.
4Manufacturing precision
If multiple passes are used for thick wafers, then complete separation is achieved, but processing time increases and yield decreases
Solution Approach 1:
The system performs preliminary damage structure creation throughout the entire wafer thickness in a single pass using extended focal region techniques. By pre-establishing damage zones along the complete cleavage path before separation, the material is prepared for clean fracture without requiring multiple processing passes. This preliminary action maintains high separation quality while eliminating the time loss associated with repeated processing.
Solution Approach 2:
The patent implements continuous single-pass processing where the laser beam continuously creates damage structures along the entire cleavage line in one traversal of the wafer. This continuous action eliminates the interruptions and repositioning time associated with multiple passes, maintaining both separation quality and processing speed. The useful action of material modification continues uninterrupted from entry to exit of the wafer.
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 enables high-quality dicing with reduced thermal damage and debris, improved processing speed, and increased throughput for both thin and thick wafers, including those with surface features, by maintaining high intensity over a longer depth and narrower width, thus enhancing semiconductor device performance and yield.
Implementation Method 1
The surface of the work-piece is irradiated with a pulsed laser beam according to the predetermined cutting line under conditions sufficient to cause multi-photon absorption, where the beam is aligned to produce a focal spot (or condensed point: a high energy/photon density zone) inside the bulk of the work-piece
Implementation Method 2
A multi-segment focusing lens is used to concentrate a pulsed laser beam into multiple focal points within the wafer
Implementation Method 3
consequently forming modified area along the predetermined cleaving line by moving the focal spot in the cleaving plain
Data Source
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AI summary
The invention provides an effective laser processing method that allows to cut/scribe/cleave/dice or, generally speaking, separate, hard, brittle, and solid wafers or glass sheets, which are either bare or have microelectronic or MEMS devices formed on them. The laser processing method comprises a step of modifying a pulsed laser beam by a shaping and focusing unit, including a multi-segment lens (1 ). Said multi-segment lens creates multiple beam convergence zones, more particularly, multiple focal points, said and interference spike shape intensity distribution exceeding the optical damage threshold of the workpiece material. Said interference spike shape intensity distribution is situated in the bulk of the workpiece. During the aforementioned step a modified area is created. The laser processing method further comprises a step of creating a number of such damage structures in a predetermined breaking line or curved trajectory by relative translation of the workpiece in relation to the focal point of the laser beam.