Synthesis of Anodic Oxide Thin Films on Si{100} Wafers and Their Characterization in TMAH for MEMS

Abstract

Silicon dioxide thin films are most widely used for different applications in microelectromechanical system (MEMS) fabrication such as etch mask, structural and sacrificial layers. Anodic oxidation method offers several advantages over other techniques, such as room temperature deposition, low cost, simple experiment setup, etc. In the present work, anodic oxidation of silicon is employed to grow oxide thin films at wafer-scale at room temperature. As-grown oxide films are characterized using ellipsometry, scanning electron microscope (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, optical microscope and 3D measuring laser microscope. Thickness uniformity and refractive index are measured using ellipsometry. FTIR spectra are used to conform the absence of hydroxyl and water absorption in the films. In order to exploit the application of anodic oxide in MEMS, the etch rates and the corner undercutting are studied in different concentration TMAH solutions at various temperatures. The as-grown oxide thin films with a thickness of about 155 nm are successfully demonstrated for the realization of various shapes freestanding MEMS structures such as rectangular cantilever beams, diaphragms, etc. using TMAH solution. Furthermore, as-grown oxide is used as mask to fabricate cavities with different shape and sizes in silicon substrate using wet anisotropic etching.

Effect of NH2OH on Etching Characteristics of Si{100} in KOH Solution

“…In silicon wet anisotropic etching, silicon dioxide is a preferred etch mask due to its easy synthesis and patterning by photolithography followed by oxide etching in buffered hydrofluoric (BHF) solution. 42 that NH 2 OH-added 20 wt% KOH not only exhibits high speed silicon etching characteristics but also shows improved etch selectivity between Si and SiO 2 over pure KOH.…”

A novel ZnO piezoelectric microcantilever energy scavenger: Fabrication and characterization

“…Tetramethyl ammonium hydroxide (TMAH) is a popular anisotropic silicon (Si) etchant, it contains no alkali metal ions and hence compatible for Micromachining processes [33].…”

“…The Piezoelectric ZnO microcantilevers were fabricated by micromachining process and patterned by standard optical lithography steps and followed by etching/liftoff of successive layers stack. Tetramethyl ammonium hydroxide (TMAH) is a popular anisotropic silicon (Si) etchant, it contains no alkali metal ions and hence compatible for Micromachining processes [33]. The side walls of the etched Si were defined by the (111) planes.…”