Face-to-Back Wafer Bonding Without TSVs for Low-Temperature Assembly
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Solution Overview
Problem
Current methods of assembly, particularly through silicon vias (TSVs) and hybrid bonding, face challenges such as bulk and inefficiencies in bonding the front side of one structure with the back side of another in a 'Face To Back' configuration, necessitating improved techniques for electrical connection and handling of heat-sensitive elements.
Innovation Solution
A method involving the formation of semiconductor wafers with metal contacts, activation of these contacts under vacuum, and bonding them without breaking vacuum, using a handle that can be inactive or active, with steps including forming amorphous silicon layers and using surface-activated bonding or adhesive layers for assembly, allowing for efficient electrical connection and handling of heat-sensitive components at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If through silicon vias (TSVs) are used for assembly, then electrical connection between structures is achieved, but the bulk and complexity of the assembly process increases
Solution Approach 1:
The patent extracts and removes the second semiconductor layer to expose the second metal contacts, eliminating the need for through silicon vias. This extraction approach simplifies the assembly process by directly exposing the bonding surfaces without requiring complex via formation and filling steps, thereby reducing device complexity while maintaining reliable electrical connection.
Solution Approach 2:
The patent performs preliminary activation of metal contact surfaces before bonding to ensure optimal bonding conditions. By pre-treating the surfaces with activation in the same vacuum chamber, the method prepares the bonding interfaces in advance, which simplifies the overall assembly process and eliminates the need for additional processing steps outside the vacuum environment.
2Reliability
If hybrid bonding is used to bond front side with back side in Face To Back configuration, then electrical connection is achieved, but the process becomes inefficient and complex
Solution Approach 1:
The patent performs preliminary activation of both first and second metal contact surfaces within the same vacuum chamber before bonding. This pre-activation preparation ensures that surfaces are optimally conditioned for bonding, which streamlines the overall process and improves bonding efficiency by eliminating the need for additional activation steps after vacuum establishment.
Solution Approach 2:
The patent merges multiple operations (activation of first metal contacts, activation of second metal contacts, and bonding) into a single continuous vacuum process. By combining these steps without breaking vacuum, the method improves productivity by reducing process time and eliminating the need for multiple chamber transitions, while still achieving reliable electrical connection.
3Ease of manufacture
If conventional bonding methods are used, then assembly is achieved, but thermal stress damages heat-sensitive elements
Solution Approach 1:
The patent changes the temperature parameter by performing bonding at low temperatures within the vacuum chamber. This parameter modification allows the assembly process to proceed without subjecting heat-sensitive elements to damaging thermal stress, while still achieving effective bonding through the activated metal contact surfaces and controlled vacuum environment.
Solution Approach 2:
The patent uses a vacuum environment as an inert atmosphere throughout the bonding process. This inert environment protects heat-sensitive elements from oxidation and other thermal damage that would occur in atmospheric conditions, enabling low-temperature bonding while maintaining assembly capability.
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 method enables high-quality silicon-on-silicon assembly with reduced thermal stress, compatible with heat-sensitive elements, and eliminates the need for through silicon vias, enhancing the assembly process by maintaining vacuum conditions and using low-temperature bonding steps.
Implementation Method 1
activating the surface of the first metal contacts opposite to the first semiconductor layer and, between steps d) and e), activating a surface of the second metal contacts exposed during step d)
Implementation Method 2
The two activating steps are carried out during a same step, under vacuum in a same activation chamber
Implementation Method 3
bonding the first and second wafers to electrically connect the first metal contacts to the second metal contacts
Data Source
AI summary
A first wafer includes a first semiconductor layer and first metal contacts on a side of a first surface of the first semiconductor layer. A second wafer includes a second semiconductor layer and second metal contacts on a side of a first surface of the second semiconductor layer. A handle is bonded onto a surface of the second wafer opposite to the second semiconductor layer. The second semiconductor layer is then removed to expose the second metal contacts. A bonding is then performed between the first and second wafers to electrically connect the first metal contacts to the second metal contacts.