REPAIR OF SOFT-X-RAY OPTICAL-ELEMENTS BY STRIPPING AND REDEPOSITION OF MO SI REFLECTIVE COATINGS/

Experiments aimed at recovering soft-x-ray projection lithography mirr ors that have defective reflective coatings by stripping and redeposit ion of Mo/Si multilayers are being reported. Two wet etchants were fou nd that would remove the multilayers from composite glass substrates. One etchant is a solution of potassium ferricyanide and sodium hydroxi de in water; the other is nitric acid with a minute quantity of hydrof luoric acid. Although each of these solutions offers preferential etch selection of the multilayers over the substrate glass, the selectivit ies are insufficient. The result is a surface roughening that lowers t he reflectance from subsequently deposited multilayer coatings to an u nacceptable level. With the addition of a carbon barrier layer between the substrate and the multilayer coating, either etchant can be used to strip the multilayers without damage to the underlying substrate su rface.