Maskless Direct Write Grayscale Lithography for MEMS Applications

Grayscale lithography is one area of lithography that has been relatively underutilized. There are several reasons for this, but one of the most prominent is the difficulty of modern techniques of grayscale exposure. However, this paper discusses a relatively novel approach to grayscale exposure using mask writing technology. Traditional lithography is characterized by the binary exposure of photoresist: meaning that some areas are exposed while other areas remain completely unexposed. The goal of grayscale lithography is to expose a gradient of intensities to photoresist. The result of this is a topography of photoresist that is potentially much more complicated than its binary counterpart. This paper will discuss direct write grayscale lithography using the Heidelberg DWL 66FS Laser Pattern Generator. Traditionally the Heidelberg DWL 66FS is used for binary exposure, but it also has the ability to vary laser intensity during an exposure. By varying the intensity of the focused laser beam, the user is able to expose photoresist differently in various regions of the substrate, generating the grayscale structure.