Electroless porous silicon formation applied to fabrication of boron–silica–glass cantilevers

• Published in: Journal of micromechanics and microengineering Vol. 20; no. 1; pp. 015034 - 015034 (11)
• Main Authors: Teva, J, Davis, Z J, Hansen, O
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.01.2010; Institute of Physics
• Subjects: Anisotropy; Applied sciences; Electronics; Etching; Ethyl alcohol; Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Materials handling; Mechanical engineering. Machine design; Mechanical instruments, equipment and techniques; Microelectronic fabrication (materials and surfaces technology); Micromachining; Micromechanical devices and systems; Optimization; Physics; Porous silicon; Precision engineering, watch making; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Wafers; Bulk micromachining; Glass; Etching rate; Chemical etching; Chemical sensor; Porous material; Silica; Optimization; Cantilever beam; Reproducibility; Hydrofluoric acid; Silicon; Production process
• ISSN: 0960-1317; 1361-6439
• DOI: 10.1088/0960-1317/20/1/015034

This work describes the characterization and optimization of anisotropic formation of porous silicon in large volumes (0.5-1 mm3) of silicon by an electroless wet etching technique. The main goal is to use porous silicon as a sacrificial volume for bulk micromachining processes, especially in cases where etching of the full wafer thickness is needed. The porous silicon volume is formed by a metal-assisted etching in a wet chemical solution composed of hydrogen peroxide (30%), hydrofluoric acid (40%) and ethanol. This paper focuses on optimizing the etching conditions in terms of maximizing the etching rate and reproducibility of the etching. In addition to that, a study of the morphology of the pore that is obtained by this technique is presented. The results from the characterization of the process are applied to the fabrication of boron-silica-glass cantilevers that serve as a platform for bio-chemical sensors. The porous silicon volume is formed in an early step of the fabrication process, allowing easy handling of the wafer during all of the micromachining processes in the process flow. In the final process step, the porous silicon is quickly etched by immersing the wafer in a KOH solution.