Direct Imprinting of Porous Silicon via Metal-Assisted Chemical Etching

• Published in: Advanced functional materials 2016-05, Vol.26 (17), p.2929-2939
• Main Authors: Azeredo, Bruno P., Lin, Yu-Wei, Avagyan, Arik, Sivaguru, Mayandi, Hsu, Keng, Ferreira, Placid
• Format: Article
• Language: English
• Subjects: Channels; Chemical etching; electrochemistry; metal-assisted chemical etching; nanoimprint; nanomanufacturing; Patterning; Plastic deformation; Polystyrene resins; Porous silicon; Semiconductors; Three dimensional
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201505153

Conventional lithographical techniques used for bulk semiconductors produce dramatically poor results when used for micro and mesoporous materials such as porous silicon (PS). In this work, for the first time, a high‐throughput, single‐step, direct imprinting process for PS not involving plastic deformation or high‐temperature processing is reported. Based on the underlying mechanism of metal‐assisted chemical etching (MACE), this process uses a pre‐patterned polymer stamp coated with a noble metal catalyst to etch PS immersed in an HF‐oxidizer mixture. The process not only overcomes the difficulties in patterning PS but it does so with a stamp that may be reused multiple times depending on its chemical and mechanical degradation. The process is shown to be capable of centimeter‐scale parallel 3D patterning with sub‐20 nm resolution. It is found that PS facilitates mass transport of reactants and products, and the overall etch rate is limited by local depletion of reactants. The versatility of this direct imprinting technique is demonstrated by its ability to produce curvilinear and planar 3D features (e.g., paraboloids, parabolic cylinders, sinusoidal waves, and straight sidewall channels). Miniaturized optical elements such as diffraction gratings and microconcentrators are built and characterized highlighting potential use of PS in silicon photonics. A high‐throughput, single‐step, highly parallelizable, direct imprinting process for porous silicon that does not involve plastic deformation or high‐temperature processing is presented. Exploiting the underlying mechanism of metal‐assisted chemical etching, this process not only overcomes the difficulties in patterning porous silicon, but it does so with a reusable stamp producing 3D patterns with sub‐20 nm resolution.