Two-Stage Silicon Hole Etching for High-Aspect-Ratio Microneedles
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Solution Overview
Problem
Existing methods for manufacturing microneedles with high aspect ratios face challenges such as pain during insertion due to insufficient thinness, limitations in wall shape leading to poor analyte detection, and residue formation during etching processes.
Innovation Solution
A method involving anisotropic ion etching with a compensation pattern followed by anisotropic wet etching is used to create a microneedle with a controlled wall shape and high aspect ratio, utilizing a monocrystalline silicon substrate and specific etching compounds like KOH and TMAH to achieve smooth, flat walls suitable for analyte detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If deep reactive ion etching process is used to manufacture microneedles with high aspect ratio, then the microneedles can be thin enough to avoid user pain, but the walls become rounded which is not favorable for deposition of detection coating
Solution Approach 1:
The etching process is segmented into two distinct stages: first anisotropic ion etching to create the high aspect ratio structure, then anisotropic wet etching to reshape the walls. This segmentation allows each process to optimize for its specific function - the first for thickness control and the second for wall shape formation.
Solution Approach 2:
An intermediary compensation pattern is introduced in the etching mask that temporarily modifies the etching profile. This pattern acts as a mediator that guides the ion etching process to create an intermediate shape that will transform into the desired final shape after wet etching, enabling control over the final wall geometry.
2Length of moving object
If deep reactive ion etching process is used to manufacture microneedles with high aspect ratio, then the microneedles can reach the interstitial fluid of the dermis, but residues remain attached to the entrance of the hole which disrupts fabrication
Solution Approach 1:
The harmful residues are selectively removed through the anisotropic wet etching step that follows the ion etching. The wet etching process specifically targets and extracts the residues from the hole entrance while preserving the microneedle structure, thereby eliminating the harmful byproduct of the first etching process.
3Object-affected harmful factors
If microneedles are made thinner to avoid user pain, then user comfort improves, but the aspect ratio must be increased which complicates the manufacturing process
Solution Approach 1:
The manufacturing approach changes the etching parameters by transitioning from a single deep reactive ion etching process to a two-step process involving anisotropic ion etching followed by anisotropic wet etching. This parameter change enables better control over the microneedle geometry, allowing thinner dimensions while managing the increased process complexity through systematic process design.
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 method enables the production of microneedles with high aspect ratios and controlled wall shapes, minimizing pain and enhancing analyte detection efficiency while reducing residue formation.
Implementation Method 1
etching a hole in the substrate by anisotropic ion etching of the substrate from the etching zone, through the opening, to a first depth
Implementation Method 2
etching the hole subsequent to the etching of step c), by anisotropic wet etching dependent on an orientation of a crystal plane of the substrate, from a wall of the substrate formed by the anisotropic ion etching during step c)
Data Source
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AI summary
The present invention relates to a method for etching a deep hole in a high aspect ratio monocrystalline silicon substrate, the substrate comprising a first face, the hole extending in a principal direction from the first face, the hole being formed by a first part of the substrate wall extending between the first face of the substrate and a first slope break over a first depth in the principal direction, and by a second part of the substrate wall extending between the first slope break and a bottom of the hole over a second depth in the principal direction, the first slope break forming a concavity of the hole.