Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 04 processing: Difference between revisions

Aligner: Maskless 04 is both a direct writer and not a direct laser writer. In Raster mode, it works like MLA 1, 2, and 3, where an image is projected onto the substrate surface, and stepped/scanned across the substrate in order to produce the entire pattern. In Vector mode, it is a direct laser writer, where a focused laser beam is moved across the substrate surface in order to trace out the pattern.

The light source in Raster mode is a 6W 365nm LED. The exposure light is passed through a spatial light modulator in the form of a digital micro-mirror device. The individual mirrors of the DMD are switched in order to represent an area of the design, and are timed in order to yield the desired exposure dose, while taking into account illumination uniformity, soft-stitching, and possibly also sub-pixel interpolation. This image is projected onto the substrate through a lens(system). The projected image yields a pixel size of 0.5µm X 0.5µm at wafer scale. This writing field is stepped across the substrate, in order to expose the entire design, each field overlapping slightly in order to minimize stitching errors.  

The light source in Vector mode is a 120mW 405nm diode laser. The laser beam is focused onto the substrate through a lens(system). The size of the focused spot is controlled using a set of pinholes (1, 2, 5, 10, or 25µm). By moving the stage at a constant velocity while switching the laser on and off, the pattern represented in the design is exposed in the resist. The dose the resist will receive is a function of the output power of the laser, the size of the pinhole, and the velocity of the stage.