Under-Bump Metallurgy Surface Profiling for Bump Coplanarity
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Solution Overview
Problem
The semiconductor industry faces challenges in achieving coplanarity of conductive bumps with different widths, leading to issues like cold joints and solder bridges, which result in device defects and increased production costs due to the varying heights of top surfaces caused by reflowing conductive materials over under-bump metallizations (UBMs) of different widths.
Innovation Solution
The method involves forming first UBMs with concave upper surfaces and second UBMs with flat or convex surfaces by controlling the concentration of a leveling agent in the plating solution and current density during the plating process, allowing for simultaneous formation of UBMs and conductive connectors, which corrects the height difference and improves coplanarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If UBMs with different widths are formed using conventional plating processes, then various types of connections can be provided, but the top surfaces of conductive bumps are disposed at different levels resulting in poor coplanarity
Solution Approach 1:
The patent applies local quality by forming wide UBMs with concave top surfaces and narrow UBMs with flat or convex top surfaces. This localized differentiation in surface geometry allows each UBM type to accommodate its specific conductive connector width while achieving uniform coplanarity across all bump tops, resolving the contradiction between connection versatility and manufacturing precision
Solution Approach 2:
The patent implements preliminary action by pre-forming the UBM surface geometry (concave or convex) before depositing the conductive material. This advance preparation ensures that when conductive material is deposited and reflowed, the top surfaces naturally align to the same level, eliminating coplanarity issues that would otherwise require additional corrective steps
2Productivity
If conventional plating processes are used for forming UBMs, then production can proceed, but yield loss occurs due to cold joints and solder bridges
Solution Approach 1:
The patent improves joint quality by tailoring the UBM surface geometry to the specific connector type: concave surfaces for wide connectors prevent solder bridges, while flat or convex surfaces for narrow connectors ensure proper wetting and eliminate cold joints. This localized optimization maintains high production throughput while reducing defect rates
Solution Approach 2:
The patent converts the potential harm of varying UBM widths into a benefit by intentionally creating corresponding variations in surface geometry (concave vs. flat/convex). This transformation turns what would be a source of defects into a mechanism that actively prevents cold joints and solder bridges, improving reliability without sacrificing productivity
3Manufacturing precision
If multiple masks are used to form UBMs with different surface profiles, then coplanarity can be achieved, but production time and costs increase
Solution Approach 1:
The patent achieves coplanarity by changing the plating process parameters - specifically the concentration of leveling agent and current density - rather than using multiple masks. This single-step process variation allows simultaneous formation of different UBM surface profiles, eliminating the time and cost associated with multiple photolithography and etching steps while maintaining precise coplanarity
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 reduces yield loss, device defects, and production time by ensuring the top surfaces of conductive connectors are closer to coplanar, thereby minimizing cold joints and solder bridges, while also reducing the number of masks required and associated costs.
Implementation Method 1
controlling the concentration of a leveling agent in the plating solution and current density during the plating process
Data Source
AI summary
Methods for forming under-bump metallurgy (UBM) structures having different surface profiles and semiconductor devices formed by the same are disclosed. In an embodiment, a semiconductor device includes a first redistribution line and a second redistribution line over a semiconductor substrate; a first passivation layer over the first redistribution line and the second redistribution line; a first under-bump metallurgy (UBM) structure over and electrically coupled to the first redistribution line, the first UBM structure extending through the first passivation layer, a top surface of the first UBM structure being concave; and a second UBM structure over and electrically coupled to the second redistribution line, the second UBM structure extending through the first passivation layer, a top surface of the second UBM structure being flat or convex.