Low-Temperature Bonding for Ultra-Thin UTBOX Structures
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Solution Overview
Problem
Current methods for producing ultra-thin buried oxide (UTBOX) and direct silicon bonding (DSB) structures face challenges such as the formation of defects like blisters or film free zones due to high-temperature heat treatments, which are costly and limit the production of structures with thicknesses below 50 nm, especially when using the Smart Cut layer transfer method.
Innovation Solution
A method involving a heat treatment at temperatures below 400°C for fracture and bonding, combined with a rapid thermal annealing step above 900°C to stabilize the bonding interface, and optional mechanical or chemical thinning, to produce high-quality UTBOX or DSB structures without the need for thick oxide layers or insulating layers between substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature heat treatments (900°C to 1300°C) are applied to resorb bonding defects, then bonding defects may be eliminated, but the process becomes costly and limits the production of ultra-thin structures
Solution Approach 1:
The patent applies preliminary surface preparation treatments (hydrophilic or hydrophobic characterization) and controlled low-temperature heat treatments (below 400°C) before bonding to prevent defect formation. By performing preparatory actions that strengthen molecular bonding and control degassing, the need for costly high-temperature resorption treatments is eliminated.
Solution Approach 2:
The patent changes the temperature parameter from conventional high-temperature (900°C-1300°C) resorption treatments to low-temperature treatments (below 400°C) combined with optimized surface preparation parameters. This parameter change enables defect prevention without requiring expensive high-temperature equipment while maintaining bonding interface quality.
2Strength
If heat treatments between 600°C and 800°C are applied to thin semi-conductor layers, then bonding may be reinforced, but defects in the form of blisters or film free zones form
Solution Approach 1:
The patent applies preliminary surface treatments to confer hydrophilic or hydrophobic character to substrate surfaces before bonding. This preliminary action strengthens molecular bonding at the interface, enabling reinforcement of bonding strength without requiring subsequent high-temperature heat treatments that would cause blister formation in thin layers.
Solution Approach 2:
The patent skips the intermediate temperature range (600°C-800°C) that causes blister formation by directly transitioning from low-temperature surface preparation to either room temperature bonding or controlled low-temperature reinforcement (below 400°C). This avoids the harmful thermal regime while achieving bonding reinforcement.
3Reliability
If thick oxide layers are used on substrate surfaces before bonding, then molecular bonding may be achieved, but the final oxide thickness cannot be reduced below a certain limit
Solution Approach 1:
The patent applies preliminary surface preparation treatments that enable molecular bonding to occur with much thinner oxide layers than conventional methods. By conferring hydrophilic or hydrophobic character to surfaces and controlling the bonding process at low temperatures, the patent achieves stable molecular bonding with oxide layers that can be reduced to ultra-thin dimensions (below 50 nm) without compromising bonding reliability.
4Length of moving object
If the thickness of the semi-conductor layer is reduced below 50 nm to produce ultra-thin structures, then advanced device performance is achieved, but defect formation increases
Solution Approach 1:
The patent applies preliminary surface preparation and low-temperature bonding processes that are specifically optimized for ultra-thin layers. By controlling surface characteristics and performing bonding below 400°C, the patent prevents defect formation in ultra-thin semi-conductor layers (below 50 nm), enabling production of high-quality UTBOX and DSB structures that would otherwise be prone to blister and film free zone defects.
Solution Approach 2:
The patent changes the temperature parameter from conventional high-temperature processing to low-temperature processing (below 400°C) throughout the bonding and heat treatment steps. This parameter change is critical for maintaining the integrity of ultra-thin layers while achieving reliable molecular bonding, thereby enabling production of advanced ultra-thin structures with high reliability.
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 reduces defectivity and allows for the production of ultra-thin UTBOX and DSB structures with minimal heat exposure, maintaining the quality of the bonding interface and enabling the transfer of semiconductor layers with reduced thermal budget, thus overcoming the limitations of existing high-temperature processes.
Implementation Method 1
A method is proposed which consists in applying a heat treatment, at temperatures below 400°C. for fracture and bonding
Implementation Method 2
a rapid thermal annealing step above 900°C to stabilize the bonding interface
Implementation Method 3
the assembly by molecular bonding of a donor substrate with a receiver substrate
Data Source
Figure 1A~1D
Figure 1E~2C
Figure 2D~3B
AI summary
The invention relates to a method for producing UTBOX type structures comprising: a) the assembly of a substrate, known as "donor" substrate (1), with a substrate, known as "receiver" substrate (2), at least one of the two substrates comprising an insulating layer (3) of thickness less than 50 nm, b) a first heat treatment for reinforcing the assembly between the two substrates, at temperature below 400°C, carried out during the assembly and/or after assembly, to reinforce said assembly, c) a second heat treatment at temperature above 900°C, the exposure time between 400°C and 900°C being less than 1 minute or 30 seconds.