Simple and Versatile High Aspect Ratio Nanostructuring via Zinc Oxide Masking

This article reports a new universal masking technique based on ZnO. This technique combines two main properties of the material. ZnO has an extremely low pulverization rate making the material well adapted for dry etching, and second, it can be easily chemically dissolved in solution making the material well suited for masking. Using ZnO as a mask on silicon, one can achieve selectivity as high as 60. This allows one to etch holes through a 30 mu m thick wafer. Sub-100 nm features are obtained using interferential lithography as a masking technique. There is no intrinsic limitation in this technique excepting the texture of the initial ZnO thin film. To demonstrate the versatility of this technique, it has been successively applied to other materials such as Si3N4, TiO2, and an organic resist (SU-8) with a selectivity of up to 15:1, 5:1, and 35:1, respectively. The technique reported in this article opens the way to universal masking which is extremely important for the development of multifunctional nanostructured surfaces in any kind of materials with direct applications in antireflection coating, hydrophobicity, and hydrophilicity to only name a few.