Semiconductor UBM Recess Design for Void Reduction
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Solution Overview
Problem
The formation of voids in the under bump metallization (UBM) layer degrades the reliability of bumps in semiconductor structures, affecting the performance and density of integrated circuits.
Innovation Solution
A semiconductor structure with an under bump metallization layer is fabricated by forming a substrate with a metal pad, an insulating layer, and a recess adjacent to the metal pad, where the under bump metallization layer contacts the metal pad and extends into the recess, increasing contact area and preventing voids by altering the path of gold atoms during plating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a plating step is performed to plate metal layers on the exposed portion of a metal pad, then the UBM layer is formed, but the bottom of the plated layers becomes rough with voids formed therein, degrading reliability
Solution Approach 1:
The patent introduces a preliminary action by forming a protrusion on the metal pad surface before the plating step. This protrusion serves as a pre-prepared structure that guides the plating process, ensuring that the plated layers form a smooth, continuous structure from the beginning rather than developing defects during plating. The protrusion is created through a selective etching process that removes insulating material to expose the metal pad in a controlled manner, establishing a favorable foundation for subsequent plating operations.
Solution Approach 2:
The protrusion acts as an intermediary structure between the metal pad and the plated layers. It provides a transition zone that facilitates uniform metal deposition during plating, preventing direct contact issues between the plating solution and the metal pad surface that would otherwise cause voids and roughness. The protrusion mediates the interaction between the plating process and the substrate, ensuring reliable UBM layer formation.
2Ease of manufacture
If the UBM layer is plated directly on the metal pad, then the plating process is simple, but voids form at the bottom of the plated layers
Solution Approach 1:
The protrusion is formed in advance through a selective etching process that removes insulating material. This preliminary structuring of the substrate surface creates optimal conditions for the subsequent plating process, ensuring that metal layers deposit uniformly without forming voids. The extra etching step is straightforward and integrates well with existing fabrication processes.
3Reliability
If the recess is formed deeper to increase contact area, then attachment to insulating layer improves, but the path for gold atoms becomes too long, affecting plating efficiency
Solution Approach 1:
The patent optimizes the geometric parameters of the protrusion, specifically controlling its height and width ratios. By maintaining the height within 0.5-2.0 times the width, the design achieves optimal balance between providing sufficient attachment area and limiting the diffusion path length for gold atoms. This parameter optimization ensures both reliable attachment and efficient plating without requiring excessive process time or material.
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 enhances the attachment of the under bump metallization layer to the insulating layer, reducing the formation of voids and maintaining electrical performance by elongating the path for gold atoms, thus preventing voids from damaging the solder bumps.
Implementation Method 1
enhances the attachment of the under bump metallization layer to the insulating layer
Implementation Method 2
The UBM layer formation includes performing a plating step to plate metal layers on the exposed portion of a metal pad
Data Source
AI summary
A semiconductor structure with an under bump metallization (UBM) layer is provided. The semiconductor structure at least includes a substrate, a metal pad disposed on the substrate, an insulating layer covering the substrate and an edge of the metal pad, wherein at least one recess is disposed within the insulating layer and a first UBM layer contacts the metal pad. The recess is adjacent to the metal pad and the recess is in the shape of a ring. The first UBM layer contacts part of the recess.