Hybrid Bonding Interface Structure for Low-Temperature Copper Joining
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Solution Overview
Problem
Conventional direct hybrid bonding processes require high annealing temperatures, which impose thermal stress on semiconductor components and are difficult to control in high volume manufacturing, limiting the ability to achieve ultra-high density electrical interconnects.
Innovation Solution
Layer structures with precise metal recess distances and thermal expansion features allow direct metal-to-metal bonding at low annealing temperatures (150°C or below) by converting horizontal thermal expansion into vertical expansion, using dielectric confinement and optimized copper crystal planes to facilitate bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional direct hybrid bonding processes use high annealing temperatures to achieve direct metal-to-metal bonding, then bonding reliability is improved, but thermal stress on semiconductor components increases and manufacturing control becomes difficult
Solution Approach 1:
The patent changes the temperature parameter from conventional high annealing temperatures (typically 250-400°C) to low annealing temperatures (150°C or below). This parameter change enables direct metal-to-metal bonding while avoiding thermal stress damage to semiconductor components. The low temperature is achieved through precise control of metal recess distance and utilization of thermal expansion effects.
Solution Approach 2:
The patent utilizes thermal expansion of metal pads during the annealing process to achieve bonding. The metal pads are designed with specific recess distances that allow them to expand thermally at low temperatures (150°C or below) to bridge the gap and form direct metal-to-metal bonds, eliminating the need for high temperature annealing that causes thermal stress.
2Strength
If high annealing temperatures are used for direct metal-to-metal bonding, then bonding strength is improved, but manufacturing precision control becomes difficult in high volume production
Solution Approach 1:
The patent changes the annealing temperature parameter from high (250-400°C) to low (150°C or below), which improves manufacturing precision control. Low temperature annealing is easier to control precisely in high volume manufacturing, eliminating the difficulties associated with high temperature control while maintaining bonding strength through optimized metal recess distances and thermal expansion effects.
Solution Approach 2:
The patent performs preliminary actions by precisely controlling the metal recess distance during fabrication and creating optimized layer structures with specific thermal expansion properties. This preliminary preparation enables the metal pads to achieve proper bonding strength through thermal expansion at low, easily controllable annealing temperatures, avoiding the need for high temperature control precision.
3Reliability
If conventional annealing temperatures are used for direct hybrid bonding, then direct metal-to-metal bonding is achieved, but energy consumption increases and processing cost rises
Solution Approach 1:
The patent changes the annealing temperature parameter from high to low (150°C or below), which directly reduces the energy consumption and processing cost while maintaining the reliability of direct metal-to-metal bonding. The low temperature requirement is achieved through precise metal recess distance control and optimized layer structures that utilize thermal expansion effects.
Solution Approach 2:
The patent utilizes thermal expansion of metal pads at low temperatures to achieve direct metal-to-metal bonding. By designing the metal recess distance and layer structures to work with thermal expansion at 150°C or below, the patent eliminates the need for high energy consumption associated with conventional high temperature annealing processes.
4Reliability
If high annealing temperatures are used for direct hybrid bonding, then bonding completeness is improved, but processing time and thermal budget increase
Solution Approach 1:
The patent changes the annealing temperature parameter to low (150°C or below) and optimizes the annealing duration. The low temperature process achieves bonding completeness through precisely controlled metal recess distances and optimized layer structures, reducing the overall thermal budget and processing time compared to conventional high temperature long-duration annealing.
Solution Approach 2:
The patent utilizes thermal expansion effects at low temperatures to achieve rapid bonding. The optimized layer structures and metal recess distances are designed to work with thermal expansion at 150°C or below, enabling complete bonding in shorter durations and reducing the overall annealing time and thermal budget.
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
Enables hundreds of thousands to over one million electrical interconnects per square millimeter to be formed at lower temperatures and energy budgets, ensuring reliable bonding without solder or adhesive use, suitable for high volume manufacturing.
Implementation Method 1
the metal pads or vias expand vertically more than the surrounding dielectric material, due to the difference in coefficients of thermal expansion (CTEs) between metals and dielectrics
Implementation Method 2
The dielectric portions of the bonding surfaces (for example, silicon oxide) forms oxide-to-oxide bonding spontaneously when the prepared surfaces are bought together
Implementation Method 3
Bonding between metal pads initiates when copper atoms (for example, for copper pads) at each surface begin to make mutual metallic bonds with other copper atoms on the other side of the interface
Data Source
AI summary
Layer structures for making direct metal-to-metal bonds at low temperatures and shorter annealing durations in microelectronics are provided. Example bonding interface structures enable direct metal-to-metal bonding of interconnects at low annealing temperatures of 150° C. or below, and at a lower energy budget. The example structures provide a precise metal recess distance for conductive pads and vias being bonded that can be achieved in high volume manufacturing. The example structures provide a vertical stack of conductive layers under the bonding interface, with geometries and thermal expansion features designed to vertically expand the stack at lower temperatures over the precise recess distance to make the direct metal-to-metal bonds. Further enhancements, such as surface nanotexture and copper crystal plane selection, can further actuate the direct metal-to-metal bonding at lowered annealing temperatures and shorter annealing durations.