TABLE OF CONTENTS Lithography is similar to photography. Like photography makes use of a film coated with photosensitive chemicals to capture an image, lithography makes use of a substrate coated with photoresist material for etching of a specific pattern. Creation of nano- and microfluidic chips makes use of various lithographic techniques. For creation of micro- or nano-fluidic chips, this pattern is in the form of micro- or nano-sized channels and chambers.
This appendix provides an overview of the lithographic techniques.
Light from a source is thrown on the substrate coated with photoresist material of the required thickness. However, a mask that is in the shape of the pattern to be etched on the coated substrate (CS), blocks part of the light. Both electromagnetic radiation and electrically charged particles can be used to irradiate the coated substrate. Electromagnetic radiation may be in the form of visible, ultraviolet, or X-rays depending on the energy required to cast an impression on CS and sensitivity of the photoresist material. For irradiating with electrically charged particles, electron, proton, or ion beam is used.
Photoresist material consists of polymeric or metallic material. Among polymers poly(dimethylsiloxane) (PDMS) is preferred for creating biochips. In the case of metallic coatings, their halides or oxides are used. Irradiation modifies solubility of the exposed area of the coating. If solubility of the irradiated area is enhanced, the coating material is called positive photoresist. If solubility of the irradiated area is diminished, the coating material is called negative photoresist. After exposure, area on...
