Paper AS-TuM4
Advances in Organic Depth Profiling for Polymer Devices

Tuesday, November 1, 2011, 9:00 am, Room 102

Knowledge of the distribution of organics within an organic matrix is important to the innovation and manufacture of many advanced technologies including polymer electronics and photovoltaics, medical devices, ink-jet printing technologies and drug delivery systems. Organic depth profiling using sputtering with cluster ions and imaging by SIMS or XPS have revolutionised the analytical capability for these important systems, providing uniquely detailed 3D chemical information. However, despite recent progress, organic depth profiling is not yet routinely applied to industry problems. The principal reason for this is that organic sputtering only works for a limited set of materials [1] and unfortunately it fails completely for many industrially important materials, such as conjugated polymers in the organics electronics industry. Consequently, an important recent development is the use of nitric oxide (NO) flooding [2] as a radical scavenger to reduce ion induced cross-linking during depth profiling.

In this study, we use model polymer layers, including polystyrene and industrially relevant conjugated polymers, to demonstrate the benefits of using NO flooding for polymers that do not sputter under normal conditions and evaluate the basic metrology. Understanding the mechanisms for damage, cross-linking, radical generation and radical reaction is vital in developing this technique to work with industrial materials. Using C₆₀²⁺ as a sputtering ion beam, it is found that NO flooding combined with sample cooling [3] significantly reduce the disappearance cross-section for characteristic fragments. For polystyrene model systems, the steady state intensity of C₇H₇⁺ can be increased from typically < 0.1% of the initial intensity at normal experimental conditions to 50% when NO flooding is used in conjunction with cooling. We also demonstrate successful depth profiles on 1 μm thick polymer material, showing high and constant sputtering yields with ~ 30 nm depth resolution to the interface. Our results show a dramatic improvement for the depth profiling of difficult type II polymers. NO flooding may be used along with other developments e.g. large argon cluster ions [4], sample cooling and sample rotation [3], and has the potential to provide a step change in analytical capability for industrial samples.

_{[1] C. M. Mahoney. Mass Spectrom. Rev., 2010, 29, 247}

_{[2] N. Tuccitto, I. Delfanti, V. Spampinato and A. Licciardello, presented at SIMS XVII, Toronto, 2009.}

_{[3] P. Sjovall, D. Rading, S. Ray, L. Yang and A. G. Shard, J. Phys. Chem. B, 2010, 114, 769.}

_{[4] J. L. S. Lee, S. Ninomiya, J. Matsuo, I. S. Gilmore, M. P. Seah and A. G. Shard, Anal. Chem. 2010, 82, 98.}