Hybrid Bonding Interface With Ti Oxide for Fine-Pitch Reliability
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Solution Overview
Problem
Current hybrid bonding techniques face challenges in achieving robust bond strength and reliability at reduced bonding pitches due to issues like electromigration, uneven bonding surfaces, and high-temperature annealing, which lead to voids, delamination, and conductivity decay.
Innovation Solution
A hybrid bonding method involving ultra-high vacuum deposition of a thin metal layer, followed by in-situ atomic diffusion bonding and low-temperature annealing, forms a strong interfacial metal oxide layer to enhance bond strength and reliability, using metals like Ti with oxide dielectrics to prevent electromigration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pitch size is reduced to increase density, then productivity is improved, but bond integrity deteriorates due to electromigration and reliability issues
Solution Approach 1:
A titanium (Ti) intermediate layer is deposited between the copper (Cu) pads of opposing wafers. This Ti layer acts as a diffusion barrier that prevents Cu atoms from migrating across the bonding interface, thereby maintaining bond integrity at reduced pitch sizes. The Ti layer forms a strong metallurgical bond with Cu while blocking electromigration, enabling high-density interconnects without reliability penalties.
Solution Approach 2:
The bonding process utilizes atomic diffusion bonding at elevated temperatures (e.g., 400-450°C) to achieve strong metallurgical bonds. By controlling the temperature parameter during bonding, the process enables Cu-Cu direct bonding with high bond strength while the subsequent Ti layer prevents electromigration at reduced pitches, resolving the contradiction between density and reliability.
2Productivity
If pitch size is reduced to scale technology, then productivity is improved, but manufacturing precision deteriorates due to uneven bonding surfaces and potential shorts
Solution Approach 1:
The titanium intermediate layer serves as a buffer that compensates for surface topography variations. The Ti atoms diffuse into the Cu surface irregularities, creating a more uniform bonding interface. This intermediary layer prevents direct Cu-Cu contact at asperity points that would cause shorts, while still enabling strong overall bonding across the entire interface.
Solution Approach 2:
The Ti layer is deposited onto the Cu pads before the bonding process. This preliminary action of depositing Ti creates a controlled, uniform layer that pre-prevents electromigration pathways and provides a consistent bonding surface. The Ti deposition occurs under ultra-high vacuum conditions to ensure uniform thickness and composition across the entire wafer surface.
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 bond strengths exceeding 1.5 J/m² and reduces manufacturing costs by eliminating the need for high-temperature annealing and expensive plasma treatments, while ensuring reliable bond integrity and manufacturability.
Implementation Method 1
heating the microelectronic assembly to a temperature sufficient to bond the metal layer to the bonding surface of the first microelectronic structure and to the bonding surface of the second microelectronic structure
Implementation Method 2
cause oxidation of the deposited metal, resulting in a desirable and strong bond strength
Data Source
AI summary
A microelectronic assembly and a method of forming same. The assembly includes: first and second microelectronic structures; and an interface layer between the two microelectronic structures including dielectric portions in registration with dielectric layers of each of the microelectronic structures, and electrically conductive portions in registration with electrically conductive structures of each of the microelectronic structures, wherein the dielectric portions include an oxide of a metal, and the electrically conductive portions include the metal.