Excimer laser lithography is promising as next-generation semiconductor lithography because of its shorter wavelength of exposure light. However, due to the restriction of available optical materials, the projection lens which is specifically designed for narrow band excimer laser beam has much greater chromatic aberration against visible light. So, a TTL (Through The Lens) alignment system using visible light had a difficulty in applying to this type of projection lens. At this time, by means of introducing a compactly designed chromatic aberration correction lens, and optical heterodyne method, above-mentioned difficulty was removed. High accurate overlay accuracy of 3742nm ( x+3σ) was obtained on the developed excimer laser lithography system. Also this paper shows some discussions on the non-linearity feature of heterodyne interferometers.
