Non-Flat UBM Layer for Semiconductor Bump Adhesion
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Solution Overview
Problem
Conventional under bump metallurgy (UBM) layers in semiconductor devices are prone to delamination due to thermal and mechanical stress, leading to package failure in flip chip technology, as they are flat and lack sufficient adhesion to the contact pad.
Innovation Solution
A novel UBM layer is formed by depositing a passivation layer, patterning it to expose contact pad areas, and then depositing a non-flat UBM layer with adhesion, wetting, and protection layers, followed by the deposition of an electrically conductive material which is reflowed to create a solder bump, providing structural support and improved adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat UBM layer is used, then the manufacturing process is simple, but the adhesion strength between solder bump and contact pad is insufficient leading to delamination
Solution Approach 1:
The UBM layer is transformed from a flat planar structure to a three-dimensional protruding structure that extends upward from the contact pad surface. This curvature and vertical extension increases the surface area for bonding and creates a mechanical interlock with the solder bump, significantly improving adhesion strength while maintaining manufacturing feasibility through standard deposition and patterning processes.
2Productivity
If chip size increases to increase device density, then more devices can be integrated, but thermal and mechanical stress buildup increases causing package failure
Solution Approach 1:
The UBM layer geometry is changed from flat to protruding, creating a three-dimensional structure with increased height and surface area. This parameter change in the UBM layer morphology enhances its ability to withstand thermal and mechanical stresses by distributing stress more effectively and providing a stronger bonding interface with the solder bump, thereby improving package reliability in high-density applications.
3Device complexity
If conventional flat UBM layers are used, then the process is straightforward, but delamination occurs during thermal and mechanical stress cycles
Solution Approach 1:
The UBM layer is designed with a protruding three-dimensional structure that curves upward from the contact pad surface. This curved geometry provides better stress distribution and mechanical interlocking with the solder bump, preventing delamination during thermal and mechanical stress cycles while maintaining a relatively simple fabrication process.
4Ease of manufacture
If solder bumps are formed on flat UBM layers, then the bonding process is simple, but the bond is not strong enough to withstand thermal expansion mismatches
Solution Approach 1:
The protruding UBM layer creates a curved bonding surface that extends vertically from the contact pad. This three-dimensional curved structure increases the bonding surface area and creates a mechanical interlock with the solder bump, significantly enhancing bond strength to withstand thermal expansion mismatches while keeping the bonding process relatively simple.
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 non-flat UBM layer design enhances the adhesion of solder bumps to the contact pad, improving the reliability and performance of semiconductor devices by preventing delamination during thermal and mechanical stress cycles.
Implementation Method 1
the electrically conductive material is reflowed to provide a bump on the semiconductor substrate
Data Source
AI summary
Methods for forming a bump on a semiconductor substrate, the substrate having a contact pad thereon, is provided. In one embodiment, the method comprises depositing a passivation layer over the substrate and the contact pad. The passivation layer is patterned and etched to form a plurality of openings in the passivation layer exposing portions of the contact pad. An under bump metallurgy (UBM) layer is deposited over the etched passivation layer and in the plurality of openings thereof to contact the contact pad. A photoresist layer is formed on the UBM layer and then patterned and etched to form at least one opening substantially overlying the contact pad. An electrically conductive material is deposited into the opening formed in the photoresist layer and overlying the UBM layer and aligned with the contact pad. A portion of the remaining photoresist layer is removed. The UBM layer is etched using the electrically conductive material as a mask. Thereafter, the electrically conductive material is reflowed to provide a bump on the semiconductor substrate.