Optimization of the refractory x-ray mask fabrication sequence

This article discusses the effects different process flows have on the material and control requirements for refractory (subtractive) x-ray masks. Our investigation of x-ray masks shows that a film's stress uniformity is more critical (for distortion) than the magnitude of the stress. In particular, we find for the wafer sequence the requirement on the membrane him's stress uniformity is the most critical specification. For the membrane sequence, the requirement is for stress uniformity for films that are removed from the membrane (after pattern formation). We find that SiC reduces the distortions from the film stress gradient, however, the frame structure determines the distortions from a film's mean stress. Finally, we conclude the best choice of an x-ray mask how should be decided on our ability to modify wafer equipment and processes, to control the stress uniformity of the membrane film, to control the stress and uniformity of the resist, hardmask, and absorber films, and finally to handle the lithography required to create predistorted mask patterns. (C) 1996 American Vacuum Society.