Wafer Dicing Retrograde Cavity for Backside Metallization
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Solution Overview
Problem
The existing semiconductor wafer dicing processes are incompatible with thick metal layers, leading to chipped die and metal stringers due to scrap metal fly-off during dicing, especially when using lasers, and result in damage to the semiconductor die.
Innovation Solution
A retrograde cavity is created between the die on the semiconductor wafer before backside metallization, using techniques like laser dicing or a rotating saw blade, to form a gap that prevents the formation of a continuous thick metal layer, allowing for a less resistive separation process with negative slope sidewalls to prevent metal deposition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser dicing is used to cut thick metal layers, then separation can be achieved, but chipped die and metal stringers occur due to scrap metal fly-off
Solution Approach 1:
A retrograde cavity is formed in the substrate before depositing the thick metal layer. This preliminary action creates a geometric structure with negative slope sidewalls that prevent metal deposition in the cavity region, thereby eliminating scrap metal fly-off during subsequent dicing operations and preventing damage to the semiconductor die.
2Productivity
If a saw is used to singulate a wafer with a thick metal layer, then the thick metal layer can be cut, but chipped die and metal stringers still occur due to scrap metal fly-off
Solution Approach 1:
The retrograde cavity is created before metal deposition, establishing a physical geometry that prevents metal accumulation in the separation zone. This preliminary structural preparation ensures that subsequent sawing or dicing operations do not generate scrap metal fly-off, thereby eliminating chipped die and metal stringers.
3Ease of manufacture
If a thick metal layer is deposited on the back side of the wafer, then backside metallization is achieved, but the dicing process becomes incompatible and causes damage
Solution Approach 1:
The retrograde cavity creates a localized region with different geometry (negative slope sidewalls) compared to the rest of the substrate. This local geometric modification specifically prevents metal deposition in the cavity area while allowing thick metal layers to be deposited elsewhere on the back side, thus enabling backside metallization without compromising dicing quality.
4Manufacturing precision
If laser dicing is used for thin substrates, then precise cutting is achieved, but it is incompatible with thick metal layers
Solution Approach 1:
By forming the retrograde cavity before metal deposition, the patent creates a pre-engineered separation zone that is geometrically optimized to prevent metal accumulation. This allows subsequent dicing processes to operate on thin substrates with high precision while the thick metal layers deposited elsewhere do not interfere with the cutting process.
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 reduces damage to semiconductor die by preventing metal formation on sidewalls and facilitating a more efficient final separation process, minimizing chipping and metal stringers, and enabling the use of saws instead of lasers for thicker substrates.
Implementation Method 1
The retrograde cavity forms a gap width between the die to prevent the formation of the thick metal layer between the die, which results in a less resistive final separation process since the full thick metal layer does not need to be cut between the die. The sidewalls of the retrograde cavity also have sufficient negative slope to prevent metal formation on the sidewalls.
Implementation Method 2
The retrograde cavity can be formed using laser dicing or a rotating saw blade, or similar separation technique.
Implementation Method 3
The retrograde cavity can be formed using laser dicing or a rotating saw blade, or similar separation technique.
Data Source
AI summary
Method embodiments of wafer dicing for backside metallization are provided. One method includes: applying dicing tape to a front side of a semiconductor wafer, wherein the front side of the semiconductor wafer includes active circuitry; cutting a back side of the semiconductor wafer, the back side opposite the front side, wherein the cutting forms a retrograde cavity in a street of the semiconductor wafer, the retrograde cavity has a gap width at the back side of the semiconductor wafer, and the retrograde cavity has sidewalls with negative slope; depositing a metal layer on the back side of the semiconductor wafer, wherein the gap width is large enough to prevent formation of the metal layer over the retrograde cavity; and cutting through the street of the semiconductor wafer subsequent to the depositing the metal layer.