Deep multilevel wet etching of fused silica glass microstructures in BOE solution
Citation
Konstantinova, T. G., Andronic, M. M., Baklykov, D. A., Stukalova, V. E., Ezenkova, D. A., Zikiy, E. V., Bashinova, M. V., Solovev, A. A., Lotkov, E. S., Ryzhikov, I. A., & Rodionov, I. A. (2023). Deep multilevel wet etching of fused silica glass microstructures in BOE solution. Scientific Reports, 13(1), article 5542. https://doi.org/10.1038/s41598-023-32503-w
Keywords
- Fused silica glass
- Deep wet etching
- Buffered oxide etch (BOE)
- Multilevel microstructures
- Stepped mask
- Photoresist
- Metal mask
- Molybdenum
- Etch rate
- Etch isotropy
- Mask resistance
- Microdevices
- Microfabrication
Brief
This article presents a novel method for fabricating multilevel microstructures in fused silica glass using a deep wet etching technique with a buffered oxide etch (BOE) solution and a stepped photoresist/metal mask.
Summary
The article, published in Scientific Reports in 2023, focuses on a method for fabricating multilevel microstructures in fused silica glass using deep wet etching with a buffered oxide etch (BOE) solution. The authors, Konstantinova et al., highlight the importance of fused silica glass in microdevices due to its chemical resistance and desirable optical, electrical, and mechanical properties. They note that while wet etching is a key method for fabricating such devices, maintaining the integrity of the protective mask in the aggressive etching solution presents a challenge.
The authors propose a fabrication process for multilevel microstructures in fused silica glass, achieved through deep etching using a stepped mask. This process involves multiple steps:
- Calculating the concentration of fluoride components in the BOE solution: This calculation considers factors like pH and the ratio of ammonium fluoride (NH4F) to hydrofluoric acid (HF) to determine the ideal etching conditions.
- Experimentally investigating the influence of BOE concentration on etching parameters: The study examines the impact of different BOE concentrations (ranging from 1:1 to 14:1 NH4F:HF) on the resistance of the mask, the etch rate, and the isotropy of the etching profile. The authors use a metal/photoresist mask for this purpose.
- Identifying the optimal BOE concentration for etching: Through calculations and experiments, the authors determine that a BOE concentration of 3:1 (NH4F:HF) yields the best results. This concentration corresponds to the maximum concentration of HF−2, which is a key reactive species in the BOE solution.
- Demonstrating a multilevel etching process: This process utilizes the optimized BOE concentration (3:1) and a stepped protective photoresist/metal mask created through a two-step photolithography process. This method enables the fabrication of microstructures with depths exceeding 200 μm and etch rates of up to 3 μm/min.
The authors conclude that their proposed fabrication route, employing a stepped mask and optimized BOE concentration, offers a reliable method for creating high-quality multilevel microstructures in fused silica glass. The process, which requires only a single initial photolithography step, allows for the integration of complex multilevel elements in microdevices.