Angled Sidewall Conductive Pillar for Bump Structure
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Solution Overview
Problem
As semiconductor devices miniaturize, existing bond pads become inadequate in ensuring reliable electrical connections due to increased formation of inter-metal compounds and solder material loss during reflowing processes, affecting the performance and density of integrated circuits.
Innovation Solution
The formation of a conductive pillar with an angled sidewall, which reduces the amount of solder material flowing onto its sides during reflowing, thereby minimizing inter-metal compound formation and maintaining sufficient solder on the pillar for reliable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bond pads are used for electrical connections in miniaturized semiconductor devices, then device integration and density are improved, but inter-metal compound formation increases and solder material is lost during reflowing
Solution Approach 1:
The conductive pillar is designed with an asymmetric angled sidewall profile instead of a symmetric vertical sidewall. The angled sidewall slopes away from the solder material flow direction, creating an asymmetric geometry that passively redirects solder flow and prevents accumulation on the pillar sidewalls during reflowing, thereby reducing inter-metal compound formation while maintaining connection reliability
Solution Approach 2:
The angled sidewall of the conductive pillar introduces a curved or sloped surface geometry instead of a straight vertical sidewall. This curvature design facilitates controlled solder material flow along the angled surface, preventing solder from adhering to and flowing down the pillar sidewalls, thus minimizing solder loss and inter-metal compound formation
2Reliability
If solder material is applied generously to ensure sufficient bonding, then connection reliability is improved, but solder material loss during reflowing increases
Solution Approach 1:
The angled sidewall creates an asymmetric surface that passively controls solder material distribution during reflowing. The slope directs excess solder material away from the pillar, allowing sufficient bonding material to be applied without resulting in proportional increases in solder loss, as the geometry inherently manages material flow and prevents unwanted accumulation
Solution Approach 2:
The angled sidewall design converts the potentially harmful effect of solder material flow during reflowing into a beneficial self-cleaning effect. The flowing solder is redirected by the angled surface away from the pillar, transforming what would be material loss into a controlled process that actually protects the pillar from excessive solder accumulation and inter-metal compound formation
3Ease of manufacture
If vertical sidewall conductive pillars are used, then manufacturing simplicity is maintained, but inter-metal compound formation increases on the pillar sides
Solution Approach 1:
The manufacturing process is modified to create an asymmetric angled sidewall profile during conductive pillar formation. This geometric modification is integrated into the existing fabrication workflow, maintaining ease of manufacture while the resulting asymmetric geometry passively prevents inter-metal compound formation by redirecting solder flow away from the pillar sidewalls during subsequent reflowing processes
Data Source
AI summary
Methods for forming semiconductor structures are provided. The method for forming a semiconductor structure includes forming a metal pad over a first substrate and forming a resist layer having an opening over the metal layer. The method for forming a semiconductor structure further includes forming a conductive pillar and a solder layer over the conductive pillar in the opening of the resist layer and removing the resist layer. The method for forming a semiconductor structure further includes removing a portion of the conductive pillar so that the conductive pillar has an angled sidewall.