Radio frequency glow discharge optical emission spectroscopy: a new weapon in the depth profiling arsenal

Abstract

While the array of analytical methods routinely applied for depth profile analysis was fairly static over the decades of the 1980s and 1990s, there appears to be an emerging technique that has a number of very positive and complementary attributes, and warrants serious consideration by the thin film community. Radio frequency glow discharge optical emission spectroscopy (rf-GD-OES) is a technique that provides depth-resolved elemental composition information on a wide variety of sample types. In a manner very much like most depth profiling methods, the rf-GD plasma utilizes an ion sputtering step to ablate sample material in a layer-by-layer fashion. Different from the more commonly applied methods, the device operates at elevated pressures [2-10 Torr Ar (266-1,330 Pa)] and has the inherent capability of sputtering electrically insulating materials directly, without any auxiliary means of charge compensation. In addition, sputtering rates on the order of 1 micro m/min provide rapid analysis, with depth resolving powers that are comparable to high-vacuum sputtering methods. Three examples of the use of the rf-GD-OES method are presented as examples of its analytical potential: (1) boron-implanted silicon wafer, (2) a barrier-type alumina film, and (3) a porous-type alumina film. It is believed that the method holds a great deal of promise as part of the arsenal of weapons in the thin films laboratory.

Depth elemental characterization of 1D self-aligned TiO2 nanotubes using calibrated radio frequency glow discharge optical emission spectroscopy (GDOES)

“…Nevertheless, various depth profiling analytical methods have been used to evaluate the elemental distribution in these layers, mainly by sputtering using ion beam-based methods [10], in comparison with X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) or time of flight secondary ion mass spectrometry (TOF-SIMS). However, when used for the analysis of TiO2 nanotubular layers, with lengths of tubes of several micrometers or even several tens of micrometres, all these techniques encounter practical difficulties due to time consuming.…”

“…It is worth to mention that, GDOES has no lateral resolution -the sputtered area is several mm 2but it is known to be extremely fast compared to SIMS or XPS and it can measure all elements of interest including C, O, H etc. [10,14]. A particular advantage for our work of the Glow discharge (GD) plasma when operated with a pulsed RF source is the possibility to adjust the sputtering rate in order to achieve a "gentle" sectioning of the tubes.…”

Radiofrequency glow-discharge devices for direct solid analysis

“…In addition, the nature of the rf sputtering process is such that charge compensation is not required for analysis of insulating materials. Plasma sensitivity factors are also far more uniform and universal between sample matrix types than are found in SIMS [61]. Other advantages include the high sample throughput and the low cost of the analysis.…”

“…They described some limitations of the rf-GD-OES technique compared with the dominant high vacuum analytical methods, particularly the impossibility of performing surface imaging and severely limited direct determination of the chemical form of a given element [61]. However, in comparison with high-vacuum ion-beam sputtering methods such as dynamic SIMS, the rf-GD provides a several orders of magnitude higher current beam of much lower-energy ions.…”

“…Although depth resolution degrades with sputtered depth, it is still quite satisfactory. Comparison of the capabilities of the rf-GD-OES technique for depth profile analysis and with other conventional thin-film analysis techniques was carried out by Hodoroaba and co-workers [60] and by Marcus and co-workers [61]. Hodoroaba and co-workers compared two depth-profiling techniques, rf-GD-OES and the radiofrequency mode of plasma secondary neutral mass spectrometry (HFM-SNMS), for analysis of electrically non-conductive samples.…”