Abstract
We report on Si nanopatterning through an on-chip self-assembled porous anodic alumina (PAA) masking layer using reactive ion etching based on fluorine chemistry. Three different gases/gas mixtures were investigated: pure SF6, SF6/O2, and SF6/CHF3. For the first time, a systematic investigation of the etch rate and process anisotropy was performed. It was found that in all cases, the etch rate through the PAA mask was 2 to 3 times lower than that on non-masked areas. With SF6, the etching process is, as expected, isotropic. By the addition of O2, the etch rate does not significantly change, while anisotropy is slightly improved. The lowest etch rate and the best anisotropy were obtained with the SF6/CHF3 gas mixture. The pattern of the hexagonally arranged pores of the alumina film is, in this case, perfectly transferred to the Si surface. This is possible both on large areas and on restricted pre-defined areas on the Si wafer.PACS78.67.Rb, 81.07.-b, 61.46.-w
Highlights
Si nanopatterning finds important applications in nanoelectronics, photonics, and sensors
Porous anodic alumina (PAA) films can be fabricated on the Si wafer by electrochemical oxidation of a thin Al film deposited on the Si surface by physical vapor deposition
We applied optimized PAA thin films on Si with regular long range pore arrangement and we investigated the pattern transfer to the Si wafer using reactive ion etching (RIE) with three different fluorine gas mixtures: pure SF6, SF6/O2, and SF6/CHF3
Summary
Si nanopatterning finds important applications in nanoelectronics, photonics, and sensors. Advanced techniques as electron beam lithography or focused ion beam milling can be used in this respect; they are both expensive and time consuming when large areas have to be patterned. The use of a masking layer either on the whole wafer or locally on pre-defined areas on the Si substrate can provide a good and cost-effective alternative to the above techniques. Porous anodic alumina (PAA) thin films on Si offer important possibilities in this respect. The so-formed aluminum oxide (alumina) shows highly ordered vertical pores that can reach the Si substrate and can be used either as a masking layer for Si nanopatterning [1,2,3,4] or as a template for nanowire and nanocrystal growth within the pores. PAA films can be used as the dielectric material in metal-oxide-metal (MIM) capacitors [5,6,7]
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