Application of lead electroplating for X-ray absorber patterning

Synchrotron radiation X-ray lithography provides high structural resolution down to 0.2 mym, where the pattern transfer capability is mainly limited by the feature size of the absorber patterns of the X-ray mask. Up to now, only gold has been set very successfully in our mask making process, but the disadvantage of gold is the low acceptance in IC production lines because it might contaminate the wafers and degrade the electrical parameters of chips. Therefore, the properties of electroplated lead as an alternative have been studied, because the acceptance of lead is by far higher in production lines. This paper shows that electroplated lead fulfills the demands on an absorber material for X-ray masks concerning resolution and contrast. Structures down to 0.2 mym can be achieved, and 1.5 mym of lead provides a sufficient contrast for pattern transfer even with a 4-fold exposure dose. The mechanical stress of electroplated load is negligible and no significant mask distortion occurs due to absorber stress, even after annealing at 100 degrees C. (IMT)