Molecular Layer Deposition of Nanoscale Organic Films for Nanoelectronics Applications

The trend toward nanoelectronics motivates the development of new materials and processes. Novel organic materials are of interest for various applications, and this talk will focus on the development of nanoscale organic films for lithography and patterning.  Current photoresist materials are facing many challenges introduced by advanced lithography, particularly the need for excellent compositional homogeneity and ultrathin film thickness.  Traditional spin-on polymeric resists have inherent limitations in achieving a high level of control over the chemical composition, leading to interest in alternative methods for making photoresists.  In this work, we demonstrate that molecular layer deposition (MLD) is a promising method for synthesizing photoresists because it allows for precise control over organic film thickness and composition.  As an analogue to atomic layer deposition (ALD), MLD utilizes sequential, self-limiting reactions of organic precursors to build a thin film directly on a substrate surface.  An advantage of MLD is that it grows organic films by depositing only one molecular layer at each precursor dose, which in turn allows for fine tuning of the position and concentration of various functionalities in the deposited film.  In our study, we use bifunctional precursors, diamine and diisocyanate, to build polyurea resist films via urea coupling reaction.  Acid-labile groups are embedded in the backbone of the diamine precursor and incorporated into the resist film with a highly uniform distribution.  Two methods of incorporating photo acid generator (PAG) are employed.  The first method is to soak a PAG into the resist film after deposition and the second approach is to form in-situ polymer-bound PAG.  By this novel synthetic approach, both aromatic and aliphatic polyurea films were successfully deposited by MLD and characterized for both materials properties and resist response. Electron-beam lithographic tests are carried on the MLD photoresists. Among the various MLD films studied, the aliphatic film performed best as a photoresist material, with a good sensitivity of 30 µC/cm² with 100kV e-beam exposure, and a patterned line resolution of sub-100 nm.  Other uses of MLD for advanced patterning methods, as well as fundamental studies into the mechanism of MLD, will also be described.