High-throughput jet and flash imprint lithography for advanced semiconductor memory

Abstract

Imprint lithography has been shown to be an effective technique for replication of nano-scale features. Jet and Flash Imprint Lithography (J-FIL) involves the field-by-field deposition and exposure of a low viscosity resist deposited by jetting technology onto the substrate. The patterned mask is lowered into the fluid which then quickly flows into the relief patterns in the mask by capillary action. Following this filling step, the resist is crosslinked under UV radiation, and then the mask is removed, leaving a patterned resist on the substrate. Non-fill defectivity must always be considered within the context of process throughput. Processing steps such as resist exposure time and mask/wafer separation are well understood, and typical times for the steps are on the order of 0.10 to 0.20 seconds. To achieve a total process throughput of 20 wafers per hour (wph), it is necessary to complete the fluid fill step in 1.0 seconds, making it the key limiting step in an imprint process. Recently, defect densities of less than 1.0/cm2 have been achieved at a fill time of 1.2 seconds by reducing resist drop size and optimizing the drop pattern. There are several parameters that can impact resist filling. Key parameters include resist drop volume (smaller is better), system controls (which address drop spreading after jetting), Design for Imprint or DFI (to accelerate drop spreading) and material engineering (to promote wetting between the resist and underlying adhesion layer). In addition, it is mandatory to maintain fast filling, even for edge field imprinting. This paper addresses the improvements made with reduced drop volume and enhanced surface wetting to demonstrate that fast filling can be achieved for both full fields and edge fields. By incorporating the changes to the process noted above, we are now attaining fill times of 1 second with non-fill defectivity of ~ 0.1 defects/cm2.