Analysis of organic multilayers and 3D structures using Ar cluster ions

Abstract

Ar cluster sputtering of organic multilayers such as organic light-emitting diode model structures and Irganox delta layers is studied with time-of-flight secondary ion mass spectroscopy in the dual beam mode. Results for sputtering yield volumes and depth resolution are presented for Ar clusters with sizes from 500 to 5000 atoms in the energy range from 2.5 to 20 keV. The sputtering yield volume shows a linear dependence on the energy per atom for all materials in this study with a material-dependent threshold below 1 eV/atom. The sputtering yield volume at a given energy per atom increases with the cluster size. At constant beam energies, the sputtering yield volume decreases slightly with increasing cluster size. The depth resolution is investigated for the two model systems as a function of energy and cluster size, and it will be shown that the depth resolution depends mainly on the sample roughening. The depth resolution is approximately proportional to the depth of the impact crater at a given cluster size and energy. The optimum depth resolution achieved is in the range of 4-5 nm and is fairly constant with depth. At very low energies per atom close to the threshold energy, ripple formation is observed that leads to a fast degradation of the depth resolution with depth. This can be completely eliminated by fast sample rotation. Finally, the perspective of 3D analysis of organic devices with high depth resolution in the dual beam mode will be discussed. Figure 1. a) Sputtering yield volume of HTM-1 versus energy/atom for sputtering with Ar cluster sizes from 500 to 5000. b) Sputtering yield volume of HTM-1 for Ar cluster energies from 2.5 keV to 20 keV as a function of the cluster size.

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

“…The behaviors of all component parts are consistent with these. Note that the measure of depth resolution, 16% to 84%, given by Niehuis et al [3] will lead to slightly smaller values than the FWHMs here. In both NPB and Irganox 1010 there is a significant reduction in FWHM once the temperature rises above T T .…”

“…Since the introduction of cluster sputter ion sources, this has become increasingly important for the analysis of organic materials, including organic electronic devices and biological specimens where the distribution of materials such as lipids and pharmaceutical molecules can be imaged with sub-micrometer resolution using secondary ion mass spectrometry (SIMS) [1][2][3][4][5][6][7]. For the sputter depth profiling of organic materials, the sputtering ion of choice today is the argon cluster ion [8].…”

“…These improvements are clearly seen in the comparison between data using C 60 + primary ions [9] and argon clusters [10] in the depth profiles of Irganox 3114 delta layers in Irganox 1010. Careful studies of such samples show that sample rotation is beneficial [3], achieving depth resolutions measured by the full width at half maximum (FWHM) as low as 4 nm at depths up to 300 nm.…”

Improved mass resolution and mass accuracy in TOF-SIMS spectra and images using argon gas cluster ion beams

“…According to computer simulations 1 and experimental [2][3][4][5][6] reports, the ejection of high mass secondary ions is enhanced with the nonlinear effects of multiple collisions when large-sized cluster ion beams bombard the organic surfaces. There are some reports that a cluster ion beam as the sputtering ion source can successfully accomplish depth profiling of organic [7][8][9][10] and amino acid films 11 without ion damage.…”

In-Situ TOF-SIMS and SFM Measurements Providing True 3D Chemical Characterization of Inorganic and Organic Nanostructures

“…Although this beam energy is rather low, the sputtering of organic materials would lead to strong radiation damage and a rapid loss of the molecular ion signals. This is avoided by the use of large gas clusters with energies per atom in the range from 1 -10 eV [2] allowing high quality molecular depth profiles of organic multilayers with a depth resolution of 5 nm [3] as well as 3D analysis of organic nanostructures [4]. The SFM unit with a beam deflection design is mounted on a 3-axis high precision flexure stage scanner.…”