Systematic Temperature Effects in the Argon Cluster Ion Sputter Depth Profiling of Organic Materials Using Secondary Ion Mass Spectrometry

Abstract

Abstract. A study is presented of the effects of sample temperature on the sputter depth profiling of two organic materials, NPB (N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine) and Irganox 1010, using a 5 keV Ar 2000 + cluster ion beam and analysis by secondary ion mass spectrometry. It is shown that at low temperatures, the yields increase slowly with temperature in accordance with the Universal Sputtering Yield equation where the energy term is now modified by Trouton's rule. This occurs up to a transition temperature, T T , which is, in turn, approximately 0.8T M , where T M is the sample melting temperature in Kelvin. For NPB and Irganox 1010, these transition temperatures are close to 15°C and 0°C, respectively. Above this temperature, the rate of increase of the sputtering yield rises by an order of magnitude. During sputtering, the depth resolution also changes with temperature with a very small change occurring below T T . At higher temperatures, the depth resolution improves but then rapidly degrades, possibly as a result first of local crater surface diffusion and then of bulk inter-diffusion. The secondary ion spectra also change with temperature with the intensities of the molecular entities increasing least. This agrees with a model in which the molecular entities arise near the crater rim. It is recommended that for consistent results, measurements for organic materials are always made at temperatures significantly below T T or 0.8 T M , and this is generally below room temperature.

New horizons in sputter depth profiling inorganics with giant gas cluster sources: Niobium oxide thin films

“…Similar results have been observed for the cluster ion beam C 60 + for the depth profiling of poly(methylmethacrylate) . Recent experiments by Seah and coworkers using Ar GCIB sputtering of molecular layers have shown that both the depth resolution and the SIMS spectra are very dependent on the sample temperature. The depth resolution decreased and then increased with sample temperature as the diffusion regime changed from surface diffusion to bulk diffusion.…”

“…This was attributed to an increase in sputter rate with temperature. Increases in sputter rates with increasing sample temperatures are observed for a wide variety of materials, including metals, using both atomic and cluster beams …”

“…Argon giant gas cluster ion beams (GCIBs), which contain between hundreds and thousands of Ar atoms, were developed in the early 1990s for surface smoothing, shallow doping, and low‐damage etching during semiconductor processing . More recently, Ar GCIBs have been developed for use in secondary ion mass spectrometry (SIMS) and X‐ray photoelectron spectroscopy (XPS) . Gas cluster ion beams have two important properties: high particle numbers and low particle velocities compared to atomic, molecular, or small cluster ion beams.…”

“…To date, most studies have focused on organic materials, including polymers, amino acids, DNA, proteins, cells, organic semiconductors, and molecular layers, such as Irganox 1010 . There have been far fewer studies on inorganic materials .…”

SIMS of Organic Materials—Interface Location in Argon Gas Cluster Depth Profiles Using Negative Secondary Ions

“…They showed that the peak was more affected by the beam energy than the centroid and attributed this to the changes in sputtering rate during the initial transient effect at the surface. At depths beyond the initial transient, the centroid of delta functions can mark positions extremely accurately and Seah et al [ 8 ] show data for organic materials in this way with very low scatters of 0.4 nm in depth over 250 nm. An example of the rate change in the outermost 5 nm of organic material is given by Seah et al [ 9 ] who point out the need to consider whether the interface is blurred locally (so that the composition changes slowly) or if it is sharp locally and blurred by the summing of separate events over the wavy surface.…”