Confined etchant layer technique for two-dimensional lithography at high resolution using electrochemical scanning tunnelling microscopy
In order to realize two-dimensional lithography at high resolution (several tens of nanometres), a new approach to the lithography of a fine pattern using a confined etchant layer technique (CELT) in an electrochemical system is presented. A mould plate of conductive material with a high-resolution line pattern (which can be prepared with the aid of e.g. electron beams) is used instead of the tip in scanning tunnelling microscopy (STM). The etchant species is generated at the surface of the mould plate by electrochemical photochemical or photoelectrochemical methods, then diffuses away from the surface of the mould plate. The key feature of CELT is the design of a chemical reaction which rapidly destroys the etchant (e.g. within microseconds on average) following its generation. Therefore, the gradient of the concentration of etchant can be greatly enhanced and the thickness of the diffusion layer can be greatly decreased to several tens of nanometres. Thus, the etchant layer is confined and its outer boundary can essentially retain the fine structure of the pattern of the mould plate. Then the substrate to be corroded is adjusted by ECSTM to approach the mould plate within several tens of nanometres and the corroded pattern can retain the fine structure giving a resolution of several tens of nanometres.