Copper Bond Pads With Micro-Protrusions for Low-Pressure Bonding
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Solution Overview
Problem
Direct copper-copper bonding in semiconductor devices faces challenges due to the difficulty in achieving adequate inter-diffusion and surface planarity, as well as the risk of damage from high bonding forces, which are exacerbated by copper's softness and susceptibility to 'dishing' and oxide erosion during chemical-mechanical planarization (CMP) processes.
Innovation Solution
The use of metallic elements projecting from the bond pads, which deform under pressure to facilitate direct metal-to-metal bonding, reducing the required bonding force and eliminating the need for stringent surface quality and planarity, allowing for bonding pressures similar to those used in solder-based processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct copper-copper bonding is performed to achieve good mechanical, thermal, and electrical performance, then bonding strength and electrical performance are improved, but surface planarity and quality deteriorate due to copper's softness and susceptibility to dishing and oxide erosion during CMP processing
Solution Approach 1:
The bond pad surface is segmented into multiple discrete micro-protrusions rather than a continuous flat surface. Each protrusion acts as an independent bonding site, allowing the overall bond pad to achieve adequate inter-diffusion and bonding while individual protrusions maintain sufficient height and surface quality despite copper's susceptibility to CMP-induced dishing and erosion.
2Strength
If high bonding force is applied to achieve adequate inter-diffusion at the copper-copper interface, then bonding strength is improved, but damage to bond pads and underlying TSVs or circuits increases
Solution Approach 1:
The bonding interface is divided into multiple discrete micro-protrusions. This segmentation allows the total bonding force to be distributed across many individual contact points, reducing the peak stress and force concentration on any single location. Consequently, adequate inter-diffusion and bonding strength are achieved without exceeding the damage threshold of the soft copper bond pads or underlying sensitive structures.
Solution Approach 2:
The bond pad structure transitions from a uniformly flat surface to a non-uniform surface with localized micro-protrusions. These protrusions concentrate the bonding action at specific locations with sufficient height and surface quality, while the surrounding areas experience reduced stress. This local quality variation enables effective bonding at protrusion tips while protecting the broader bond pad area and underlying circuits from excessive force damage.
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 effective direct metal-to-metal bonding with reduced pressure, minimizing damage to underlying circuitry and TSVs, while maintaining good mechanical and electrical coupling, thus overcoming the limitations of traditional direct copper-copper bonding methods.
Implementation Method 1
metallic elements projecting from the bond pads, which deform under pressure to facilitate direct metal-to-metal bonding
Data Source
AI summary
A bond pad with micro-protrusions for direct metallic bonding. In one embodiment, a semiconductor device comprises a semiconductor substrate, a through-silicon via (TSV) extending through the semiconductor substrate, and a copper pad electrically connected to the TSV and having a coupling side. The semiconductor device further includes a copper element that projects away from the coupling side of the copper pad. In another embodiment, a bonded semiconductor assembly comprises a first semiconductor substrate with a first TSV and a first copper pad electrically coupled to the first TSV, wherein the first copper pad has a first coupling side. The bonded semiconductor assembly further comprises a second semiconductor substrate, opposite to the first semiconductor substrate, the second semiconductor substrate comprising a second copper pad having a second coupling side. A plurality of copper connecting elements extend between the first and second coupling sides of the first and second copper pads.