Qualification of BitClean technology in photomask production

Makers and users of advanced technology photomasks have seen increased difficulties with the removal of persistent, or stubborn, nano-particle contamination. Shrinking pattern geometries, and new mask clean technologies to minimize haze, have both increased the number of problems and loss of mask yield due to these non-removable nano-particles. A novel technique (BitCleanTM) has been developed using the MerlinTM platform, a scanning probe microscope system originally designed for nanomachining photomask defect repair. Progress in the technical development of this approach into a manufacture-able solution is reviewed and its effectiveness is shown in selectively removing adherent particles without touching surrounding sensitive structures. Results will also be reviewed that were generated in the qualification and acceptance of this new technology in a photomask production environment. These results will be discussed in their relation to the minimum particle size allowed on a given design, particle removal efficiency per pass of the NanoBitTM (PREPP), and the resultant average removal throughput of particles unaffected by any other available mask clean process.