Photoelectron effects in x‐ray mask replication

In this paper some experimental observations of the interference of photoelectrons in an x‐ray mask replicating process are reported on. High resolution low contrast (i.e., producing absorbed dose ratios of less than 2) x‐ray masks have been used to produce lines smaller than 0.1 μm in poly(methlmethacrylate) (PMMA) on a silicon substrate with an aspect ratio of about 2. When the experiment was repeated on a gold plated substrate, anomalous adhesion problems were encountered. Lines smaller than 0.2 μm, for example, had poor adhesion, and those smaller than 0.1 μm had entirely lifted off. A higher contrast mask, with a dose contrast of about 6, and with smaller features was tried on the same two substrates. Using this mask, 800 A lines in PMMA in 0.5 μm thick resist have been demonstrated, with good adhesion. These effects are consistent with the assumption that the x rays that penetrate the mask’s absorber, and the resist, but are absorbed in the plating base, generating photoelectrons, which then propaga...