Etchant Segmentation for Flip-Chip Bump Uniformity
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Solution Overview
Problem
The conventional flip-chip packaging process for forming bumps often results in solder corrosion and an undercut phenomenon due to etching selectivity issues, leading to uneven bumps and reduced yield and stability.
Innovation Solution
A method involving a first etchant composed of sulfuric acid, phosphoric acid, ferric chloride, and ammonium persulfate or sulfuric acid, phosphoric acid, ferric chloride, and potassium monopersulfate is used to etch the wetting and barrier layers, followed by a second etchant of sulfuric acid and deionized water to remove the adhesive layer, preventing undercut issues and ensuring even etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional etchant (nitric acid, acetic acid, hydrogen peroxide, hydrochloric acid, and sulfuric acid) is used to etch the under bump metallurgy layer, then the etching process can remove portions of the metallurgy layer, but it causes solder corrosion and undercut phenomenon leading to uneven bumps
Solution Approach 1:
The patent segments the etching process into three distinct sequential steps using different etchants: first etchant for the wetting layer, second etchant for the barrier layer, and third etchant for the adhesive layer. This segmentation allows each etchant to be optimized for its specific target layer, preventing the solder corrosion and undercut issues caused by using a single conventional etchant for all layers.
Solution Approach 2:
The patent changes the chemical composition parameters of the etchant at different stages of the process. Specifically, it uses different chemical formulations for etching the wetting layer, barrier layer, and adhesive layer respectively. This parameter change ensures that each etching step has optimal selectivity for its target layer while protecting the solder from corrosion and preventing undercut phenomenon.
2Productivity
If the etching selectivity is high enough to etch the under bump metallurgy layer effectively, then the etching process can remove the metallurgy layer portions, but it damages the adhesive layer and creates undercut holes
Solution Approach 1:
The patent divides the etching process into three segmented steps, each with a specific etchant optimized for a particular layer. This segmentation maintains high etching efficiency for each layer while preventing damage to other layers, thereby improving process stability and eliminating the undercut phenomenon that reduces reliability.
Solution Approach 2:
The patent applies different etching characteristics (local quality) to different layers of the under bump metallurgy layer. Each layer (wetting layer, barrier layer, adhesive layer) is etched with a specifically formulated etchant that provides the appropriate etching rate and selectivity for that layer, ensuring both high productivity and reliability.
3Device complexity
If a single etchant composition is used for etching the under bump metallurgy layer, then the process is simple, but it causes composition shift in bumps and affects yield
Solution Approach 1:
The patent segments the etching process into three steps with different etchants, which increases process complexity but is necessary to achieve precise control over bump composition uniformity. Each segmented step targets a specific layer, preventing composition shift in the bumps and improving manufacturing precision despite the increased complexity.
Solution Approach 2:
The patent changes the chemical parameters of the etchant between steps to achieve precise control over the etching of each layer. This parameter change ensures that each layer is etched to the correct depth without affecting the solder composition, thereby maintaining bump composition uniformity even though the process complexity increases.
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 prevents solder corrosion and undercut phenomena, resulting in more stable and uniform bump formation, enhancing the overall yield and stability of the fabrication process.
Implementation Method 1
a first etching process is performed by utilizing a first etchant composed of sulfuric acid, phosphoric acid, ferric chloride, and ammonium persulfate, or sulfuric acid, phosphoric acid, ferric chloride, and potassium monopersulfate
Implementation Method 2
a second etching process is performed by utilizing a second etchant composed of sulfuric acid and deionized water
Implementation Method 3
by utilizing the solder 24 as a mask, the etching process removes a portion of the under bump metallurgy layer 18
Data Source
AI summary
A method for forming bumps is disclosed. First, a substrate having an adhesive, a barrier, and a wetting layer thereon is provided. Next, a patterned photoresist is formed on the wetting layer, in which the patterned photoresist includes at least one opening for exposing a portion of the wetting layer. Next, a solder is deposited in the opening, and a stripping process is performed to remove the patterned photoresist. Next, a first etchant is utilized to perform a first etching process for etching a portion of the wetting and barrier layers by utilizing the solder as a mask, in which the first etchant is selected from the group consisting of: sulfuric acid, phosphoric acid, ferric chloride, ammonium persulfate, and potassium monopersulfate. Next, a second etchant is utilized to perform a second etching process removing a portion of the adhesive layer, and a reflow process is performed to form a bump.