In excimer laser micromachining, imaging systems are used to control the power and spatial distribution of UV light on-target. In an imaging system, the power distribution of the light at the object (mask) plane is relayed to the image (work) plane. As a result, edge quality and power distribution on-target are independent of beam coherence, divergence and for the most part, diffraction effects. The ultimate imaging resolution of excimer laser light is on the order of its wavelength (i.e. 0.2 to 0.4 µm). However, optical imperfections as well as spherical and chromatic aberrations make it difficult to achieve the theoretical resolution. Simple lens systems can achieve resolutions down to 5m, while more complex systems can achieve submicron resolutions with higher-cost optics.
The simplest laser imaging system consists of a mask and an imaging lens. More complex systems can include beam conditioning optics and automatic mask aligners. The following illustration shows a conceptual diagram of a near-field imaging system.
Theoretical near-field imaging system