Alloy Bump Composition Control via Segmented Electroplating
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Solution Overview
Problem
Existing methods for forming alloy bumps with high aspect ratios face challenges in maintaining stable metal composition, particularly during the miniaturization of electronic circuits, as one metal may fail to deposit at the bottom of openings while another deposits excessively, leading to unstable plating composition.
Innovation Solution
A method involving the lamination of multiple plating films by electroplating, followed by heat treatment to alloy them, allowing for convenient control of composition and achieving a homogenous alloy bump with balanced metal content without the need for continuous acid concentration monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the thickness of resist is increased to form high aspect ratio alloy bumps, then the height of metal bump can be controlled, but one metal may fail to deposit on the bottom of openings while another metal deposits in large quantity, leading to unstable plating composition
Solution Approach 1:
The alloy bump formation process is segmented into two independent stages: first, separate metal plating films are deposited individually through electroplating; second, these films are alloyed together through heat treatment. This segmentation allows each metal layer to be deposited with controlled thickness and composition, avoiding the compositional instability that occurs when attempting to deposit multiple metals simultaneously in high aspect ratio openings.
Solution Approach 2:
The metal plating films are formed in advance as separate layers before the alloying step. By preliminarily depositing each metal layer with controlled thickness, the composition can be stabilized before the final alloying process, ensuring uniform distribution of metals in the high aspect ratio bump structure.
2Stability of the object's composition
If continuous monitoring of acid concentration is performed to stabilize metal composition, then the metal composition of alloy bump can be maintained constant, but the process complexity increases and delicate adjustment becomes difficult
Solution Approach 1:
The plating process is segmented into separate steps for depositing different metal layers, eliminating the need for continuous acid concentration monitoring. Each layer can be deposited with predetermined thickness, and the overall composition is controlled by the relative thicknesses of the individual layers rather than by real-time chemical composition adjustments.
Solution Approach 2:
The chemical control method (continuous monitoring and adjustment of acid concentration) is replaced with a physical control method (controlling the thickness of individual plating layers). This substitution simplifies the process by using measurable physical parameters (film thickness) instead of complex chemical parameters (acid concentration).
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 enables the formation of alloy bumps with desired and stable composition, reducing the complexity of the process and allowing for adjustments in film thicknesses to achieve a smooth surface and homogenous composition, even at lower temperatures than the melting points of the individual metals.
Implementation Method 1
a step of forming a first plating film on the under-bump metal by electroplating; a step of forming a second plating film on the first plating film by electroplating
Implementation Method 2
a step of forming the alloy bump by heat treating the substrate to thereby alloy the first plating film and the second plating film
Data Source
AI summary
In order to manufacture an alloy bump, a resist pattern having openings which expose a substrate is formed on the substrate, an under-bump metal is formed on the substrate inside the openings, a first plating film is formed on the under-bump metal by electroplating, a second plating film containing no metal components which are contained in the first plating film is formed on the first plating film by electroplating, the resist pattern is removed, and the alloy bump is formed by heat treating the substrate to thereby alloy the first plating film and the second plating film.