| Soft Lithography is a group of non-photolithographic techniques currently being explored in our group. Four such techniques--microcontact printing ({dollar}mu{dollar}CP), replica molding (REM), micromolding in capillaries (MIMIC), and microtransfer molding ({dollar}mu{dollar}TM)--have been demonstrated for fabricating micro- and nanostructures of a variety of materials with dimension {dollar}ge{dollar}30 nm.; Part I (Chapters 1-5) reviews several aspects of the three molding techniques REM, MIMIC, and {dollar}mu{dollar}TM.; Chapters 1-3 describe {dollar}mu{dollar}TM and MIMIC, and the use of these techniques in the fabrication of functional devices. {dollar}mu{dollar}TM is capable of generating {dollar}mu{dollar}m-scale structures over large areas, on both planar and contoured surfaces, and is able to make 3-dimensional structures layer by layer. The capability of {dollar}mu{dollar}TM and MIMIC has been demonstrated in the fabrication of single-mode waveguides, waveguide couplers and interferometers. The coupling between waveguides can be tailored by waveguide spacing or the differential in curing time between the waveguides and the cladding.; Chapters 4-5 demonstrate the combination of REM and shrinkable polystyrene (PS) films to reduce the feature size of microstructures and to generate microstructures with high aspect ratios on both planar and curved surfaces. A shrinkable PS film is patterned with relief structures, and then heated and shrinks. Thermal shrinkage results in a 100-fold increase in the aspect ratio of the patterned microstructures in the PS film. The microstructures in the shrunken PS films can be transferred to many other materials by REM.; Part II (Chapters 6-7) focuses on two issues in the microfabrication using self-assembled monolayers (SAMs) as ultrathin resists.; Chapter 6 describes a selective etching solution for transferring patterns of SAMs of alkanethiolates into the underlying layers (e.g., gold, silver, and copper). This etching solution uses thiosulfate as the ligand that coordinates to the metal ions, and ferricyanide as the oxidant. It has been demonstrated to be less toxic, more efficient, and provide fewer defects in the SAM-protected metallic regions upon etching.; Chapter 7 describes a technique to measure the surface density of defects in SAMs of hexadecanethiolates on gold and in the structures prepared by using the SAMs as resists and the aqueous ferricyanide solution as the etchant, under conditions that may be encountered in lithographic processing. This technique uses two steps of amplification through chemical reaction to convert pinhole defects in SAMs into easily imaged, micron-scale pits in an underlying Si support. |
