Direct Bonding of Dissimilar Microelectronic Materials With Thin Interlayers
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Solution Overview
Problem
Conventional bonding techniques face challenges in joining dissimilar materials in microelectronics due to stress, strain, and mismatched crystal lattice properties, which lead to weak and defective bonds, especially when materials have different coefficients of thermal expansion and lattice constants.
Innovation Solution
A low-temperature direct-bonding process using a thin amorphous layer of dielectric materials like silicon oxide or silicon nitride between dissimilar materials, followed by a slow annealing step, to form strong bonds without vacuum assistance, thereby reducing stress and strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional bonding techniques use elevated temperature and pressure to join dissimilar materials, then bonding strength is improved, but stress and strain at the interface increase due to mismatched crystal lattice properties and coefficients of thermal expansion
Solution Approach 1:
The patent introduces an intermediary layer between dissimilar materials to facilitate bonding. This intermediate layer has crystal lattice properties that are compatible with both materials, acting as a mediator that reduces lattice mismatch and thermal expansion differences. The intermediary layer absorbs and distributes stress, preventing direct transmission of strain between incompatible materials while maintaining strong bonding strength.
Solution Approach 2:
The patent modifies bonding parameters by using lower temperature and pressure conditions compared to conventional techniques. By changing the bonding parameters to be less extreme, the patent reduces thermal stress and strain accumulation at the interface while still achieving adequate bonding strength through the intermediary layer mechanism.
2Device complexity
If direct bonding of dissimilar materials is performed, then manufacturing complexity is reduced, but bond reliability deteriorates due to lattice mismatch and thermal expansion differences
Solution Approach 1:
The intermediary layer serves as a reliable bonding interface between dissimilar materials. It provides a stable, compatible surface that ensures reliable adhesion while maintaining the simplicity of the direct bonding process. The intermediary layer's crystal structure is designed to be compatible with both materials, ensuring long-term bond reliability under thermal and mechanical stress.
Solution Approach 2:
The patent employs a composite structure consisting of the intermediary layer combined with bonding agents or surface treatments. This composite approach at the interface enhances bond reliability by combining multiple mechanisms (mechanical interlocking, chemical bonding, and physical adhesion) while keeping the overall process relatively simple.
3Adaptability or versatility
If materials with different coefficients of thermal expansion are bonded together, then device functionality is enhanced, but thermal stress increases during temperature cycling
Solution Approach 1:
The intermediary layer acts as a thermal stress buffer between materials with different coefficients of thermal expansion. It has intermediate thermal expansion properties that gradually transition between the two materials, reducing abrupt stress concentration. This allows the device to maintain enhanced functionality with dissimilar materials while minimizing thermal stress during temperature cycling.
Solution Approach 2:
The patent explicitly considers and utilizes thermal expansion properties in the design of the intermediary layer. The intermediary material is selected or engineered to have thermal expansion characteristics that bridge the gap between dissimilar materials, allowing controlled expansion and contraction that reduces thermal stress while maintaining device functionality.
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
The process enables reliable bonding of diverse materials, enhancing bond strength by over 200% and allowing for the fabrication of novel optical, electrical, and acoustic devices.
Implementation Method 1
A low-temperature direct-bonding process using a thin amorphous layer of dielectric materials like silicon oxide or silicon nitride between dissimilar materials, followed by a slow annealing step, to form strong bonds without vacuum assistance, thereby reducing stress and strain.
Implementation Method 2
followed by a slow annealing step, to form strong bonds without vacuum assistance
Data Source
AI summary
Techniques for joining dissimilar materials in microelectronics are provided. Example techniques direct-bond dissimilar materials at an ambient room temperature, using a thin oxide, carbide, nitride, carbonitride, or oxynitride intermediary with a thickness between 100-1000 nanometers. The intermediary may comprise silicon. The dissimilar materials may have significantly different coefficients of thermal expansion (CTEs) and/or significantly different crystal-lattice unit cell geometries or dimensions, conventionally resulting in too much strain to make direct-bonding feasible. A curing period at ambient room temperature after the direct bonding of dissimilar materials allows direct bonds to strengthen by over 200%. A relatively low temperature anneal applied slowly at a rate of 1° C. temperature increase per minute, or less, further strengthens and consolidates the direct bonds. The example techniques can direct-bond lithium tantalate LiTaO3 to various conventional substrates in a process for making various novel optical and acoustic devices.