Semiconductor Wafer Back Metal Removal via Pressurized Fluid
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Solution Overview
Problem
Current methods for singulating semiconductor wafers, such as sawing and laser scribing, result in significant material loss and damage to cut edges, while plasma etching methods struggle with effectively removing back metal layers due to their non-reactivity with metal layers.
Innovation Solution
A method involving a semiconductor wafer with etched scribe streets is used, where a deformable plastic sheet is pressed with a pressurized fluid to break the metal layer at the scribe streets, allowing for efficient separation of back metal layers without damaging the semiconductor material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If sawing or laser scribing is used to singulate semiconductor wafers, then the wafer can be divided into individual devices, but significant material is lost and cut edges are damaged
Solution Approach 1:
The patent replaces mechanical sawing and thermal laser scribing with a chemical plasma etching process to create scribe streets. This substitution eliminates the need for physical contact and high heat input, thereby minimizing material loss and preventing edge damage while achieving precise wafer singulation.
Solution Approach 2:
The patent changes the etching parameters by using a dual-frequency RF plasma source with specific power settings (e.g., 13.56 MHz and 27.12 MHz frequencies) to achieve high etch rates with minimal lateral etching. This parameter optimization allows narrow scribe streets to be formed quickly without damaging adjacent device edges, increasing devices per wafer.
2Loss of substance
If plasma etching is used to create narrow scribe streets, then material loss is reduced, but back metal layers cannot be effectively removed
Solution Approach 1:
The patent performs preliminary plasma etching to create narrow scribe streets that expose the back metal layers. This preliminary action prepares the structure for subsequent metal removal by defining precise pathways while minimizing material loss, allowing the metal removal step to be more effective and targeted.
Solution Approach 2:
The patent introduces a deformable plastic sheet as an intermediary medium during the metal removal process. The sheet is pressed against the wafer back surface, and its deformation under pressure helps to mechanically fracture and remove the exposed back metal layers from the narrow scribe streets without damaging the semiconductor devices.
3Productivity
If the scribe street width is reduced to increase devices per wafer, then more devices can be made per wafer, but the risk of edge damage increases
Solution Approach 1:
The patent replaces mechanical sawing with plasma etching to create narrow scribe streets. This substitution eliminates mechanical contact and associated edge damage, allowing scribe streets to be made as narrow as possible without compromising device integrity, thereby maximizing devices per wafer while maintaining reliability.
Solution Approach 2:
The patent uses periodic pulsed plasma etching with controlled duty cycles to etch narrow scribe streets. The pulsed nature of the plasma allows for precise control of etch depth and width, preventing lateral etching that could damage device edges while ensuring complete penetration through the wafer thickness, thus enabling narrow scribe streets without edge damage.
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 minimizes material loss and edge damage, enabling more devices per wafer and reducing the cost of fabrication by effectively removing back metal layers using high-pressure fluid application.
Implementation Method 1
employing a pressurized fluid to deform the plastic sheet and break the metal layer at the scribe streets
Implementation Method 2
deform the plastic sheet and break the metal layer
Data Source
AI summary
A method of dividing a semiconductor wafer in which a sheet of deformable material engaging the metal layer side of the wafer has pressurized fluid applied thereto to cause the metal layer to break at the locations of wafer scribe streets.