Silicon Nanomembrane Transfer via Polymer Support and DRIE
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Solution Overview
Problem
Conventional methods for transferring silicon nanomembranes (SiNMs) are limited by sample size compatibility with CMOS technology, mechanical handling-induced stress, and inability to handle large area transfers, especially when integrating crystalline silicon layers on multiple substrates.
Innovation Solution
A novel transfer process involving a polymer structural support, such as SU-8, and Deep Reactive Ion Etch (DRIE) to remove the SOI handle, allowing for the transfer of large area SiNMs to multiple substrates, including contoured surfaces, by using a sacrificial polymer layer and selective etching techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If conventional transfer methods are used, then small sample transfers are achievable, but large area transfers cannot be performed
Solution Approach 1:
The transfer process segments the handling of large area SiNMs by using a rigid SOI platform that can be divided into multiple substrates. The SOI handle wafer acts as a segmentation tool, allowing the large area membrane to be transferred in manageable sections while maintaining overall integrity and alignment across multiple target substrates.
Solution Approach 2:
The patent introduces a polymer support layer as an intermediary between the SiNM and the target substrate. This polymer layer provides mechanical support during transfer, enabling large area membranes to be handled without direct mechanical contact that would cause stress or damage. The polymer acts as a mediator that can be selectively removed after transfer.
2Ease of manufacture
If mechanical handling is used during transfer, then transfer process is simple, but stress and damage are induced to the membrane
Solution Approach 1:
The polymer support layer serves as an intermediary that eliminates the need for direct mechanical handling of the fragile SiNM. Instead of mechanically manipulating the membrane itself, the process handles the robust polymer-supported structure, thereby avoiding stress and damage to the membrane while maintaining process simplicity.
Solution Approach 2:
The patent replaces mechanical handling methods with a chemical/electrochemical approach using DRIE etching to release the SiNM from the SOI handle. This substitution eliminates mechanical stress entirely by using selective etching to detach the membrane, which then adheres to the target substrate through van der Waals forces or other non-mechanical mechanisms.
3Ease of operation
If SOI handle removal is performed, then SiNM transfer is enabled, but substrate alignment precision must be maintained
Solution Approach 1:
The patent performs preliminary alignment of the SOI substrate with the target substrate before the DRIE etching process removes the handle. Alignment marks are established in advance, and the rigid SOI platform maintains this alignment throughout the etching process. The polymer support layer is also prepared in advance with appropriate thickness and adhesion properties to ensure proper positioning after handle removal.
Solution Approach 2:
The polymer support layer provides beforehand cushioning that maintains substrate positioning during the handle removal process. This layer prevents sudden shifts or misalignments that could occur during etching, and ensures that the SiNM remains properly positioned as it transfers to the target substrate. The polymer's mechanical properties are selected to provide adequate cushioning while maintaining alignment precision.
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
Enables the scalable, stress-free transfer of large area SiNMs with precise alignment and uniformity, compatible with CMOS technology, and capable of handling multiple arrays and contoured surfaces, overcoming limitations of existing transfer methods.
Implementation Method 1
the substrates may be heated to a temperature >60° C. to reflow the polymer. This may permit air to escape from between the polymer layer and SOI substrate
Implementation Method 2
the two substrates may then go through a Deep Reactive Ion Etch (DRIE), e.g., with SF6 chemistry, to remove the handle of the SOI substrate
Implementation Method 3
A sacrificial polymer layer, such as cyclohexyl methacrylate (CHMA), which may be decomposed by thermal treatment, may be used to function as the polymer support layer and may be selectively removed after transfer
Implementation Method 4
the oxide may be selectively removed, e.g., with a buffered oxide wet etch, leaving the transferred SiNM on the recipient substrate
Data Source
AI summary
A transfer process for silicon nanomembranes (SiNM) may involve treating a recipient substrate with a polymer structural support. After treating the recipient substrate, a substrate containing the intended transferable devices may be brought in direct contact with the aforementioned polymer layer. The two substrates may then go through a Deep Reactive Ion Etch (DRIE) to remove at least a portion of the substrate containing the devices. Oxide may be selectively removed with a buffered oxide wet etch, leaving the transferred SiNM on the recipient substrate with the Underlying polymer layer.