a method for microfabrication of a microfluidic device having sub - millimeter three dimensional relief structures is disclosed . in this method , homogeneous surfaces , which do not exhibit apparent pixel geometry , emerge from the interaction of the overlapping of diffracted light under opaque pixels and the nonlinear polymerization properties of the photoresist material . the method requires a single photolithographic step and allows for the fabrication of microstructures over large areas with topographic modulation of features smaller than 100 micrometers . the method generates topography that is useful in a broad range of microfluidic applications .