When the semiconductor industry first started on EUV lithography, almost everyone believed that the optics would be the hardest things to do. Wavefront error—deviations of a light wave from its ideal—comes from imperfections in mirrors and lenses. A good lens aims for lambda/10 error; EUV optics must hit lambda/50. With EUV’s 13.5 nm wavelength, that’s 260 picometers. For context, a water molecule is 275 pm wide. That’s the total error budget—for the entire six-mirror system. Because errors add in quadrature, each mirror gets 106 pm rms. But mirrors double light deviation on reflection, so surface accuracy must be halved: 53 pm rms. That’s the radius of a hydrogen atom. It is 20 times harder for an EUV system with six mirrors to achieve the same wavefront performance of a DUV system with 60 surfaces. In this video, we go back to the machine you guys all know and love (again) and the finest multilayer mirrors ever made in history.