Wafer Dicing with Femtosecond Laser and Plasma Etch
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Solution Overview
Problem
Conventional methods for dicing semiconductor wafers, such as scribing and sawing, often result in chipping, cracking, and waste of wafer real estate due to the limitations of mechanical separation techniques, and plasma dicing faces challenges with cost and compatibility with certain metals.
Innovation Solution
A hybrid method combining femtosecond-based laser scribing and plasma etching is employed to singulate integrated circuits, where a mask is patterned with a femtosecond laser to expose regions between circuits, followed by a plasma etch process to separate the dice, minimizing thermal damage and enabling precise control over the dicing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional scribing or sawing methods are used for wafer dicing, then the wafer can be separated into individual dice, but chips and gouges form along the severed edges and cracks propagate into the substrate
Solution Approach 1:
The patent replaces mechanical scribing and sawing systems with a laser-based system. A laser beam is used to scribe the wafer along predetermined streets, eliminating mechanical contact that causes chipping and cracking. The laser energy selectively removes material through ablation without the mechanical stresses that damage the crystal structure.
Solution Approach 2:
The patent changes the physical state and parameters of the laser beam to achieve clean cuts. By controlling laser pulse duration, power, and wavelength, the process achieves precise material removal without thermal damage. The laser parameters are optimized to scribe through the wafer thickness while maintaining edge integrity of the dice.
2Reliability
If additional spacing is required between dice to prevent damage from scribing or sawing, then integrated circuits are protected from edge damage, but wafer real estate is wasted and fewer dice can be formed
Solution Approach 1:
The laser scribing system enables tighter spacing because it eliminates the mechanical damage zone created by diamond scribes and saw blades. Without mechanical contact, there is no need for large safety margins between dice, allowing maximum utilization of wafer area.
Solution Approach 2:
The laser scribing is performed as a preliminary action before dice separation. By pre-scribing the streets with precise laser energy, the wafer is prepared for clean separation without requiring additional spacing for mechanical damage prevention.
3Productivity
If diamond saws are used for wafer dicing, then thick wafers can be separated, but the blade thickness and required spacing waste significant wafer real estate
Solution Approach 1:
The laser scribing system replaces the physical diamond saw blade with a focused laser beam. This eliminates the blade thickness constraint and the associated spacing requirements, allowing the full wafer area to be utilized for active circuitry while still achieving separation of thick wafers.
Solution Approach 2:
The laser parameters are adjusted to penetrate through thick wafer materials. By controlling pulse energy, repetition rate, and focal depth, the laser achieves complete scribing through thick substrates without requiring the mechanical clearance needed by saw blades.
4Speed
If conventional laser scribing with longer pulse times is used, then the scribing process is faster, but thermal damage and microcrack formation increase
Solution Approach 1:
The patent uses ultrashort pulsed laser operation where the laser emits brief pulses separated by longer intervals. This periodic action allows heat to dissipate between pulses, preventing thermal accumulation and microcrack formation while maintaining acceptable processing speeds through high repetition rates.
Solution Approach 2:
The laser pulse duration is changed from conventional nanosecond or microsecond scales to ultrashort femtosecond or picosecond scales. This parameter change fundamentally alters the heating mechanism, enabling ablation before heat can diffuse to surrounding areas, thus eliminating thermal damage while maintaining process efficiency.
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 reduces microcrack formation, delamination, and chipping, allowing for denser packing of integrated circuits on the wafer and more efficient use of wafer space, while also reducing the need for costly lithography and minimizing damage to the semiconductor material.
Implementation Method 1
patterning the mask with a femtosecond-based laser scribing process
Implementation Method 2
etching the semiconductor wafer through the gaps in the patterned mask
Data Source
AI summary
Methods of dicing semiconductor wafers, each wafer having a plurality of integrated circuits, are described. A method includes forming a mask above the semiconductor wafer, the mask including a layer covering and protecting the integrated circuits. The mask and a portion of the semiconductor wafer are patterned with a laser scribing process to provide a patterned mask and to form trenches partially into but not through the semiconductor wafer between the integrated circuits. Each of the trenches has a width. The semiconductor wafer is plasma etched through the trenches to form corresponding trench extensions and to singulate the integrated circuits. Each of the corresponding trench extensions has the width.