Laser shockwave cleaning of EUV reticles

Particles on the surface of the EUV reticle can cause serious imaging errors during exposure. Laser shockwave cleaning is a novel cleaning method, that shows great potential to remove these particles, without destroying the delicate surface of the reticle. In an effort to assess the cleaning performance of this method, a number of cleaning experiments were performed on wafers contaminated with glass spheres. These experiments showed that with the current setup, it was possible to remove particles as small as 500 nm from the surface of the wafer, at gap distances of 0.5 and 1.0 mm. Furthermore, the transient behaviour of the shockwave was studied with laser flash shadowgraphy. This showed that the shockwave is initially elliptical in shape, and that it can be described by the Taylor & Sedov solution for a point explosion.