Ta Seed Layer for Au Bump Surface Uniformity
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Solution Overview
Problem
Conventional thin-film magnetic heads face challenges in achieving excellent surface properties for Au plated films due to the inheritance of crystal structures from Cu plated films, leading to poor bonding strength and surface roughness issues during wire bonding.
Innovation Solution
A thin-film device with a bump structure using a Ta film as the first conductor film, which has a finer crystal structure than Ti, prevents the Au plated film from reflecting the crystal shape of the Cu film, resulting in improved surface properties and bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Ti film is used as a seed film for Au plated film growth, then the Au plated film can be formed, but the surface becomes uneven due to inheritance of Cu plated film crystal structure, resulting in poor bonding strength
Solution Approach 1:
The patent introduces an intermediate layer (Ta film or Mo film) between the Cu plated film and the Au plated film. This intermediary layer has a fine crystal structure that prevents the Au plated film from inheriting the uneven crystal structure of the Cu plated film, thereby mediating the interface between the two layers and achieving both formability and surface uniformity.
Solution Approach 2:
The patent changes the material parameter of the seed film from Ti to Ta or Mo, which have different crystal structures with finer grain sizes. This parameter change in the seed film material prevents the transmission of large crystal structures to the Au plated film, resulting in improved surface uniformity and bonding strength.
2Reliability
If the Au plated film is made thick enough to ensure coverage, then surface coverage is improved, but surface roughness increases due to crystal structure inheritance, interfering with wire bonding
Solution Approach 1:
The Ta or Mo film serves as an intermediary layer that decouples the crystal structure relationship between Cu and Au layers. This allows the Au plated film to achieve adequate thickness for coverage while maintaining a fine, uniform surface topology that does not interfere with wire bonding operations.
3Reliability
If a three-dimensional wiring structure with projecting portion is used, then electrical contact capability is improved, but the Au plated film surface becomes uneven, decreasing bonding strength
Solution Approach 1:
The patent applies local quality by making the crystal structure refinement local to the bump surface area. The Ta or Mo film is specifically positioned at the bump location where wire bonding occurs, providing fine crystal structure locally to ensure good bonding strength, while the rest of the three-dimensional wiring structure maintains its electrical contact capability.
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
The use of a Ta film as a seed layer for the Au plated film significantly enhances the surface roughness and bonding strength, improving the overall performance of the thin-film magnetic head and magnetic recording/reproducing apparatus.
Implementation Method 1
the Au plated film grows to inherit the crystal structure of the Cu plated film (or epitaxially grows)
Data Source
AI summary
The present invention relates to a thin-film device whose bump has an improved surface property. A thin-film element of the thin-film device includes at least one of an electromagnetic conversion element, a passive element and an active element. A lead conductor film containing Cu as a main component is connected to the thin-film element. The lead conductor is provided with a bump. The bump includes a first conductor film and a second conductor film. The first conductor film is adhered onto the lead conductor film and is a Ta film or made of a material having a comparably fine crystal structure. The second conductor film is a plated film which is directly or indirectly formed on the first conductor film and contains Au as a main component.