Nickel Thermocompression Bonding for Low-Temperature 3D Interconnects
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Solution Overview
Problem
Conventional 3D interconnect bonding techniques using solder reflow face challenges when adding subsequent chips, leading to loss of alignment, parallelism, and contact due to re-melting of original solder connections, which also causes thermal stress and degradation of heat-sensitive components.
Innovation Solution
The method involves cold temperature bonding below the melting point of the conductive material, using oxide reduction and passivation steps to improve adhesion and conductance, and controlling the bond height through applied force, allowing for scalable 3D assembly without solder reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder reflow techniques are used to bond chips, then electrical and mechanical connections are formed, but subsequent chip additions cause re-melting of original connections leading to loss of alignment and parallelism
Solution Approach 1:
The patent changes the bonding temperature parameter from above-melting-point reflow to below-melting-point thermocompression bonding. This allows subsequent chips to be bonded without re-melting previous connections, thereby maintaining alignment accuracy and parallelism while still achieving reliable electrical and mechanical connections through controlled compression and oxide reduction
Solution Approach 2:
The patent applies oxide reduction and passivation treatments to the contacting metal surfaces before bonding. This preliminary action prevents oxide formation during the below-melting-point bonding process, ensuring good adhesion and conductance without requiring high-temperature reflow that would disrupt previous bonds
2Reliability
If multiple chips are bonded using solder reflow, then interconnects are formed, but thermal cycling causes built-in stress and fatigue in components
Solution Approach 1:
The patent changes the bonding temperature parameter to remain below the melting point of the conductive material throughout the bonding process. This eliminates the thermal cycling that causes expansion/contraction stress in CTE-mismatched materials, preventing built-in stress and fatigue while still achieving strong interconnects through thermocompression and oxide reduction
Solution Approach 2:
The patent converts the typically harmful effect of oxides on metal surfaces into a benefit by applying controlled oxide reduction and passivation. This creates a stable, low-stress bonding interface that actually improves reliability without requiring the harmful thermal cycling of conventional reflow processes
3Reliability
If solder reflow is used for chip bonding, then connections are established, but energy consumption increases and heat-sensitive components degrade
Solution Approach 1:
The patent changes the bonding temperature parameter from high-temperature reflow to low-temperature thermocompression bonding below the melting point. This dramatically reduces energy consumption while maintaining bonding strength through the combination of oxide reduction, passivation, and controlled compression forces that create reliable electrical and mechanical connections without excessive heat
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 achieves high reliability, alignment accuracy, and design flexibility while reducing energy consumption, minimizing thermal cycling, and avoiding residual stress in the final product, thereby enhancing the overall reliability and performance of the chip stacks.
Implementation Method 1
directing plasma-activated radical-enriched gas flow at substantially atmospheric pressure both to first contacting metallizations on a first element and also to second contacting metallizations on a second element, both to reduce native oxides from said contacting metallizations
Implementation Method 2
passivate said contacting metallizations against re-oxidation
Implementation Method 3
compressing said first and second contacting metallizations together, without any conductive liquid phase material, to thereby bond said second element to said first element
Implementation Method 4
improve the adhesion and specific conductance of each interconnect
Data Source
AI summary
Methods and systems for low-force, low-temperature thermocompression bonding. The present application teaches new methods and structures for three-dimensional integrated circuits, in which cold thermocompression bonding is used to provide reliable bonding. To achieve this, reduction and passivation steps are preferably both used to reduce native oxide on the contact metals and to prevent reformation of native oxide, preferably using atmospheric plasma treatments. Preferably the physical compression height of the elements is set to be only enough to reliably achieve at least some compression of each bonding element pair, compensating for any lack of flatness. Preferably the thermocompression bonding is performed well below the melting point. This not only avoids the deformation of lower levels which is induced by reflow techniques, but also provides a steep relation of force versus z-axis travel, so that a drastically-increasing resistance to compression helps to regulate the degree of thermocompression.