Ten years of two-color photolithography [Invited]

Two-color approaches in photolithography involve the use of photoresists that are activated with one color of visible or near-ultraviolet light and are deactivated with a second color. Such approaches have enabled resolution beyond the diffraction limit and hold great promise for improving the resolution down to the 20 nm level. This review presents and contrasts the different two-color lithographic (2CL) approaches that have emerged over the last decade in linear and multiphoton lithography. The basic advantages and limitations of each method are discussed, as well as the challenges that must be addressed in the near feature to push the limits of 2CL techniques. With further advances, multicolor techniques are anticipated to become a leading tabletop tool for performing 3D lithography with resolution that rivals that of more expensive solutions, such as electron-beam lithography.