Semiconductor Die Bonding with Solder-First Metal Interconnects
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Solution Overview
Problem
Current 3D stacking methods for integrated circuit dies and wafers face low throughput due to slow direct metal-to-metal bonding processes, especially in die-to-wafer applications, and solder bonding methods suffer from reliability issues and scalability limitations.
Innovation Solution
A method involving the use of solder bumps and contact areas for initial fast bonding, followed by a single heating step to establish direct metal-metal bonds, allowing for simultaneous bonding of multiple dies to a wafer without the need for separate heating processes for each die, utilizing capillary forces for alignment and a dielectric underfill to enhance the bonding process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct metal-to-metal bonding is used for 3D stacking, then lower electrical resistance and higher reliability are achieved, but bonding time increases to tens of minutes reducing throughput
Solution Approach 1:
The bonding process is segmented into two distinct stages: first, rapid solder bonding establishes initial mechanical and electrical connection in seconds; second, a subsequent heating step completes the metal-to-metal bonding for optimal reliability. This segmentation allows each stage to be optimized independently, achieving both high throughput and high reliability.
Solution Approach 2:
Solder bumps are used to establish preliminary bonding between components before the final metal-to-metal bonding is achieved. The solder provides initial mechanical support and electrical connection, allowing components to be held in position while the metal bonding process completes in a subsequent heating step.
2Productivity
If solder bonding is used for fast bonding in 3D stacking, then bonding time is reduced to a few seconds increasing throughput, but intermetallic compound formation raises reliability issues and contact resistance increases
Solution Approach 1:
The bonding process uses parameter changes by first employing solder material with lower melting point for rapid bonding at相对较低 temperatures, then applying higher temperatures in a subsequent step to transform the connection into a metal-to-metal bond. This parameter transformation eliminates intermetallic compound formation while maintaining the speed advantage of solder bonding.
3Reliability
If separate heating steps are performed for each die in die-to-wafer bonding, then complete metal-to-metal bonding is achieved, but processing time increases significantly
Solution Approach 1:
Multiple separate heating steps for individual dies are merged into a single collective heating step. The wafer with multiple attached dies is heated simultaneously in one process, achieving complete metal-to-metal bonding for all dies at once. This merging reduces total processing time while ensuring thorough bonding across all components.
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 significantly increases the throughput of the bonding process by allowing a single heating step for multiple dies and wafers, reducing mechanical pressure requirements and minimizing contamination risks, while maintaining low contact resistance and scalability.
Implementation Method 1
the solder bumps and contact areas are configured so that the protruding metal contact structures of one of the components are in physical contact with the corresponding protruding metal contact structures or the metal pads of the other component while not forming a metal bond
Implementation Method 2
subjecting the assembly to a heat treatment for bonding the protruding metal contact structures to the corresponding metal structures or pads
Data Source
AI summary
A method of bonding semiconductor components is described. In one aspect a first component, for example a semiconductor die, is bonded to a second component, for example a semiconductor wafer or another die, by direct metal-metal bonds between metal bumps on one component and corresponding bumps or contact pads on the other component. In addition, a number of solder bumps are provided on one of the components, and corresponding contact areas on the other component, and fast solidified solder connections are established between the solder bumps and the corresponding contact areas, without realizing the metal-metal bonds. The latter metal-metal bonds are established in a heating step performed after the soldering step. This enables a fast bonding process applied to multiple dies bonded on different areas of the wafer and/or stacked one on top of the other, followed by a single heating step for realizing metal-metal bonds between the respective dies and the wafer or between multiple stacked dies. The method allows to improve the throughput of the bonding process, as the heating step takes place only once for a plurality of dies and/or wafers.