SOI Substrate Finishing Method for Flake Reduction
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Solution Overview
Problem
The existing finishing methods for silicon-on-insulator (SOI) substrates, particularly those involving rapid thermal annealing (RTA) and sacrificial oxidation, fail to effectively reduce particle contamination known as 'flaking', which degrades the quality of the final substrate and is exacerbated by cold wall oven processes.
Innovation Solution
A finishing method comprising two successive cycles of RTA and sacrificial oxidation, where the second sacrificial oxidation step removes a thinner oxide thickness than the first, with specific thickness ranges (e.g., first removed oxide thickness > 150 nm and second < 130 nm) to minimize flake contamination, while maintaining smoothing and thinning properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional RTA and sacrificial oxidation finishing methods are used, then the roughness of the active silicon layer is improved and the bonding interface is stabilized, but particle contamination known as 'flaking' increases and degrades substrate quality
Solution Approach 1:
The finishing process is divided into multiple sequential stages: initial sacrificial oxidation, first RTA treatment, intermediate cleaning, second sacrificial oxidation, and final RTA treatment. Each stage performs a specific function to progressively improve surface quality while controlling flake generation. The segmentation allows optimization of each step's parameters to balance smoothing benefits against flake contamination risks.
Solution Approach 2:
The invention employs periodic alternation between oxidation and thermal annealing cycles. Each cycle consists of sacrificial oxidation followed by RTA treatment, with intermediate cleaning steps. This periodic action allows the surface to be repeatedly smoothed and cleaned, progressively reducing both roughness and particle contamination through multiple iterations rather than a single prolonged treatment.
2Manufacturing precision
If sacrificial oxidation steps are performed to remove oxide layers, then the active silicon layer thickness is controlled, but flake contamination is generated and deposited on the substrate surface
Solution Approach 1:
The invention converts the harmful flake contamination generated during sacrificial oxidation into a beneficial cleaning opportunity. By performing RTA treatment immediately after each oxidation step, the flakes are thermally activated and removed during subsequent cleaning stages. The harmful flakes become a diagnostic indicator that triggers the next cleaning cycle, ultimately improving rather than degrading surface quality.
Solution Approach 2:
The RTA treatment acts as an intermediary process between sacrificial oxidation and cleaning steps. It serves as a bridge that prepares the surface for effective cleaning by activating and loosening flake contaminants, making them more susceptible to removal in subsequent cleaning stages. This intermediary treatment transforms the direct harmful effect of oxidation into a controllable process step.
3Loss of energy
If cold wall oven processes are used for RTA treatment, then energy efficiency is improved, but flake contamination is exacerbated
Solution Approach 1:
The invention implements preparatory cleaning steps before final substrate processing and protective measures during oxidation. By performing intermediate cleaning after the first RTA treatment and before subsequent processing steps, flakes generated during oxidation are removed before they can contaminate the final product. This beforehand cushioning prevents energy-efficient cold wall oven processes from exacerbating contamination issues.
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 significantly reduces flake contamination by a factor of up to 5, as demonstrated by defect measurements, improving the quality of the SOI substrate and meeting low-defect requirements for electronics applications.
Implementation Method 1
RTA is conducted at high temperature for a short time, in a neutral or reducing atmosphere, for example hydrogen and/or argon. As an example, for a SOI substrate it may be conducted at a temperature in the order of 1200° C, for a time of less than three minutes.
Implementation Method 2
The oxidation step is generally performed using thermal treatment, by wet or dry process. The result is the formation of an oxide layer on the free surface of the active silicon layer of the SOI substrate.
Implementation Method 3
The de-oxidation step is generally performed by immersing the oxidized SOI substrate into an acid bath, to remove the previously formed surface oxide and thereby to bring the active silicon layer to the desired final thickness, by reducing its thickness.
Data Source
Figure 1A~1G
Figure 2
Figure 3A~3C
AI summary
The invention concerns a finishing method for a substrate (1) of silicon-on-insulator SOI type, comprising an oxide layer (3) buried between an active silicon layer (4) and a support layer(2) in silicon, this method comprising the application of finishing steps whose successive steps are:a)rapid thermal annealing RTA of said substrate (1) b)sacrificial oxidation step of its active layer (4), c)rapid thermal annealing RTA of said substrate obtained after step (b), d)sacrificial oxidation step of said active layer of the substrate (1') which underwent step c), this method being characterized in that sacrificial oxidation step b) is conducted so as to remove a first oxide thickness (5) and in that sacrificial oxidation step d) is conducted so as to remove a second oxide thickness thinner than the first.