Organoiodine Functionality Bearing Resists for Electron-Beam and Helium Ion Beam Lithography: Complex and Sub-16 nm Patterning

Abstract

Given the current need for resist materials for patterning transistors with ultralow nodes, there has been a quest for developing resists with improved performance for nanoscale patterning with good contrast. The present work demonstrates polymeric resists (MAPDST-TIPMA) developed through the integration of a radiation-sensitive monomer (MAPDST) with an organoiodine functionality (TIPMA) for sub-16 nm patterning using electron-beam and helium ion beam lithography. The structural integrity was established by several spectroscopic techniques particularly NMR, FTIR, XPS, and GPC. These polymeric resists possess weight-average molecular weight (Mw) in the range of 10000–12000 with low PDI. While the resists 3a and 3b were synthesized with feed ratios of 80:20 and 70:30 of the monomers MAPDST and TIPMA, respectively, the actual microstructure compositions were calculated, using XPS and GPC data, to be ∼94:6 and 91:9, respectively. The present resists have the potential for patterning 16 nm line/space features when exposed to e-beam. Also, 15 nm features were successfully patterned using MAPDST-TIPMA resists. The line edge roughness (LER) and line width roughness (LWR) of the 20 nm L/3S features were calculated to be 2.48 and 3.6 nm, respectively. Moreover, complex nanofeatures of different shapes were successfully patterned using 3b. A critical analysis of nanofeatures using AFM revealed that the patterns are very well developed with a sharp wall profile. The normalized resist thickness (NRT) curve was established to evaluate the sensitivity of the present resist which was calculated to be 341 μC/cm2 at 20 keV. The nature and slope of the NRT curve indicated that MAPDST-TIPMA is a negative tone resist with good contrast. Finally, the resist was found to be highly sensitive to He+ beam (sensitivity ∼6.21 μC/cm2) resulting in 20 nm L/S as well as 15 nm features with a good wall profile.