Deep, High Aspect Ratio Etches in Alumina Films for MEMS and Advanced Packages

We have explored the use of a highly anisotropic thick film, anodic aluminum oxide (AAO), for use in producing high aspect ratio structures that can be used in MEMS and packaging applications. We have found that under certain conditions, this material can be etched with extremely high anisotropic etch ratios, resulting in highly vertical structures. If prepared properly, the AAO film contains a high density of vertical nanopores that enhance the etch rate in the vertical direction when etching in a sodium hydroxide solution. The AAO films can be prepared at various thicknesses, ranging from a few microns to several hundred microns thick. Thus, deep vertical structures can be formed in AAO by a simple low cost wet etching process. AAO is an excellent structural material and dielectric, making this a candidate replacement material for many applications requiring vertical microstructures.