Effect of Specimen Temperature on C60+-Ar+ Co-Sputtering of Polymers

It is known that owing to high sputtering yield, cluster ions like C60+ produce more high-mass secondary ions and yield less damaged in the remaining surface than atomic ion sputtering. However, in some polymer, damage still accumulates with C60+ sputtering, so that subsequently acquired chemical information during depth profile can be different from its initial state. Beside of using different type of primary ion and mixed ion co-sputtering of different fluence, the effect of specimen temperature to the depth profile of organic materials is examined in this work. The ion beam induced change in the chemical structure of polymethylmethacrylate (PMMA) at different temperatures was examined by X-ray Photoelectron Spectroscopy (XPS) and Dynamic-Secondary Ion Mass Spectrometry (D-SIMS). At lower temperature (-120 °C), because the energy of primary was dissipated more quickly than that at room temperature, less damage to the chemical structure and higher secondary ion intensities are observed. Similar to that observed with SF5+ ion sputtering, the sputtering rate increases with increasing temperature. This behavior is attributed to that the cluster ion beam tends to scissor the polymer chains and delay the cross-linking, the higher mobility of molecules at higher temperature promoted the sputtering materials. On the other hand, it is found that the sputter rate decreased with increasing temperature when low-energy Ar+ is used concurrently. This opposite behavior is attributed to that the Ar+ induced radicals and the high mobility at higher temperature allows cross-linking hence the sputtering rate decreased with increasing temperature. Furthermore, in co-sputtering, it was expected that higher sputter energy would yield higher sputter rate. However, because of the interaction between ion beams leads to the breakage the C60 ion, the use of high energy Ar+ yields lower sputter rate.