Patterning a cellulose based dual-tone photoresist via deep X-ray lithography

The desire to combine properties such as ready availability, low price and biodegradability makes cellulose derivatives such as Trimethylsilyl cellulose (TMSC) an ideal precursor suited to study different applications on the abundant material, cellulose. Here we introduce a lithographic approach to pattern the cellulose derivative, TMSC, via photoinduced X-ray conversion. Thin films of this biopolymer were irradiated by means of proximity deep X-ray lithography. With increasing energy dose, we found distinct structural and chemical changes resulting in two polarity transitions and related thereto material solubility alterations. Based on this, we demonstrate that positive and negative tone structures can be obtained in one single exposure at the same energy dose. Notably, the positive tone pattern is produced when applying Isopropyl alcohol (IPA) or purified water to dissolve the exposed surface. In contrast, the negative tone structure is produced with toluene. These findings suggest TMSC as a potential dual-tone photoresist applicable in microelectronics or surface chemistry where it can be applied as a dielectric layer, a pattern template, used in microfluidics or functionalized for bioassays.