Stress relaxation of EB resist for X-ray mask fabrication

We have investigated the ZEP resist characteristics of stress relaxation and reduction by applying some additives to the ZEP resist. The stress of the resist film was significantly reduced in ZEP resist with beta-Carotene. Without an additive, the stress of the ZEP resist film reduced from 30 MPa to 25 MPa as a result of the delay time after resist coating. On the other hand, with the addition of 5 wt% beta-Carotene, the stress of the resist film just after coated was almost same to that of the resist film without an additive. The stress, however, decreased to 15 MPa for one month. The stress change caused by deep UV exposure in the beta-carotene additive system became one-third of that in the non-additive system. This system had a similar pattern replication quality to the original ZEP resist. It is considered that this system is useful for improving the image placement accuracy in EB writing on the membrane such as an x-ray mask.