Martine Claes

Comparison of grazing emission XRF with total reflection XRF and other X-ray emission techniques

A preliminary comparison of a new x-ray fluorescence (XRF) technique, grazing emission x-ray fluorescence (GEXRF), with several other XRF techniques is described, based on previous experiments and literature. These techniques are total reflection XRF, conventional energy-dispersive XRF, wavelength-dispersive XRF and particle-induced x-ray emission. The comparison is done from a number of viewpoints, including preferred sample type and size, multi-element determination, interferences, accuracy, detection limits and cost of instruments. Different analytical procedures for aqueous solutions between these techniques are indicated. Particular emphasis is placed on the position of the GEXRF technique, and it is indicated for what sample types and/or analytical problems GEXRF will offer significant advantages over the other techniques.

Bulk Properties of MOCVD-Deposited HfO2 Layers for High k Dielectric Applications

The physical bulk properties of metalorganic chemical vapor deposited (MOCVD) deposited HfO 2 layers were characterized as a function of deposition temperature. thickness, and starting surface. It is shown that depositing HfO 2 layers at 300°C results in a lower density film compared to films deposited at higher temperature (e.g., 485 and 600°C). In addition, it is shown that layers deposited at 300°C contain significant amounts of carbon originating from the organic precursor (tetrakis-diethylamidohafnium). As a result of the low density and/or carbon contamination, the dielectric properties of these layers are very poor. It is observed that the density of the film is heavily dependent on the thickness, where very thin layers have a density that is only a fraction of the bulk density regardless of the deposition temperature. For thicker layers, a higher deposition temperature is seen to result in a higher density, although still lower than bulk density, as observed by ellipsometric porosimetry. Finally, the crystalline state of the material is found to be dependent on the deposition temperature, thickness, and post-deposition anneal. Based on our results, MOCVD deposited HfO 2 layers are expected to be polycrystalline and present in its cubic and/or monoclinic phase.

Optimization of sample preparation for grazing emission X-ray fluorescence in micro- and trace analysis applications

Abstract Grazing emission X-ray fluorescence (GEXRF) is a new development in X-ray fluorescence analysis related to total-reflection XRF. An optical flat carrying the sample is irradiated at an angle of approximately 90° with an uncollimated polychromatic X-ray beam. The emitted fluorescent radiation of the sample elements is measured at very small angles using wavelength dispersive detection. For the application of GEXRF in micro- and trace analysis, a sample preparation procedure for analysis of liquid samples has been developed. Polycarbonate was investigated as a possible material for the sample carrier. Homogeneous distribution of the sample on the support was achieved by special pre-treatment of the carrier. This pre-treatment includes siliconizing the polycarbonate disks with Serva silicone solution, after which the siliconized carriers are placed in an oxygen plasma asher. Finally, to obtain a spot of the same size as the X-ray beam (≈30 mm diameter), a thin silicone layer is placed as a ring on the carriers with an ear pick. Electron microprobe analyses were performed to check the distribution of the liquid sample deposit, and GEXRF measurements were used to check the reproducibility of sample preparation.

Alternative Photoresist Removal Process to Minimize Damage of Low-k Material Induced by Ash Plasma

Dry ashing of photoresist (PR) using oxygen-containing plasma applied subsequently to an etch plasma leads to degradation of porous low-k material. The surface region is substantially depleted in carbon. The low-k film becomes more hydrophilic after being subjected to plasma etch and especially ash process as evidenced by water absorption results. The amount of absorbed water into a 30% porosity film at moisture saturation is estimated to be about 15% of the film volume, which corresponds to 50% of the total pores in the low-k film. A wet, alternative means for PR removal based on dissolution of PR in organic solvents combined with physical forces is presented. Under certain conditions, megasonic cleaning resulted in complete removal of the PR layer without damaging of the dielectric lines. These results suggest that the PR crust is permeable to these solvents and that out-diffusion of dissolved bulk PR also occurred through the crust. Dissolution of bulk PR in organic solvents first makes the PR structure more fragile, then the physical energy helps to remove the remaining crust mechanically without dissolving it. Compared to plasma ashing, solvent strip shows no carbon depletion and no significant increase in k-value.

All-Wet Strip Approaches for Post-Etch Photoresist Layers After Low-K Patterning

Plasma chemistries, applied during low-k patterning processes in back-end of line (BEOL) applications, modify the photoresist (PR) layer present on top of the etched structures. The remaining resist layer after plasma etch is resilient towards most organic solvents and aqueous solutions. Conventionally, the layer is removed before copper deposition using an oxidizing plasma process. This approach is not acceptable anymore due to damage of the dielectric, i.e. k-value degradation and chemical modifications [1,2]. In order to obtain less damaging photoresist removal processes for post low-k etch, the use of wet-only methods is under investigation.

Determination of silicon in organic matrices with grazing-emission X-ray fluorescence spectrometry☆

Abstract The potential of a prototype grazing-emission X-ray fluorescence spectrometer for reliable analysis of sample solutions, obtained by pressurized microwave oven digestion of Si-spiked organic and biological materials, was investigated as part of an inter-laboratory study. The fact that this grazing-emission technique is based on the total reflection phenomenon and wavelength-dispersive detection, gives it the benefit to determine light elements in a sensitive way. Results of the determination of silicon in pork liver, cellulose, urine, serum, spinach, beer, mineral water and horsetail (dry plant extract) samples are presented. Some of the results are compared with those obtained with other analytical techniques. The study proved that determination of silicon traces in biological matrices represents an extremely difficult task, however, measurements of silicon are achieved with acceptable precision. The most important problems still arise when sample pre-treatment is needed prior to analysis.

Quantification in grazing-emission X-ray fluorescence spectrometry☆

Abstract In grazing-emission X-ray fluorescence (GEXRF) spectrometry wavelength-dispersive detection can be applied. Much softer radiation and hence lighter elements than in total-reflection X-ray (TXRF) spectrometry can thus be detected. We used simulations to investigate methods of quantification of GEXRF results involving soft characteristic radiation. From these studies, it is concluded that for ultra-thin layers, e.g. the sub-monolayer amounts encountered in semiconductor contamination analysis, calibration plots are linear. For thicker layers, quantification should be performed very carefully because of deviations from linearity due to absorption of radiation and to oscillations in the calibration curve. These oscillations are caused by interference of fluorescence radiation emitted directly towards the detector and radiation reflected at the sample–substrate interface. Suggestions for a judicious choice of measurement conditions are made and the benefits of internal standardisation are discussed.

Progress in laboratory grazing emission x‐ray fluorescence spectrometry

Recently, grazing emission x-ray fluorescence (GEXRF) spectrometry, also referred to as grazing exit spectrometry, attained a special position in the field of XRF. The technique exploits the advantages of the total-reflection phenomenon as is done in the related total-reflection XRF technique. The prospects of grazing emission techniques stimulated researchers to explore this field more in detail. This paper describes recent developments in laboratory GEXRF spectrometry together with the applications already performed. The focus is on the progress of a GEXRF spectrometer at normal incidence for the analysis of light elements by using a wavelength-dispersive detector. With a prototype GEXRF instrument, it is demonstrated that good limits of detection, at the high 10 10 at cm -2 for level wafer analysis and sub-nanogram level for trace analysis of environmental samples, can be achieved.

Inventory of regulations and analysis techniques for trace elements in some water supply companies in Eastern and Western Europe

With the ultimate objective in contributing to the improvement of the quality control of drinking water and to facilitate the checking of its compliance with the respective regulations, an inventory of analytical techniques used in water supply companies in Eastern and Western European countries is presented. The existing regulations for drinking water and bottled mineral water quality with respect to trace elements in these countries are compared to regulations of the World Health Organisation. The data obtained can be useful for further harmonisation of the respective regulations in Europe.

Dielectric Reliability of 50 nm Half Pitch Structures in Aurora® LK

The dielectric reliability of Aurora® LK (k = 3.0) material has been evaluated on a 50 nm half pitch test structure. These were fabricated using a double patterning scheme and TiN metal hard mask. The introduction of a suitable post-etch residue removal step and close-coupled processing between Cu electroplating and chemical mechanical polishing were found to be key for achieving high yield. Median time-dependent dielectric lifetime of 10 years is reached at an electrical field of 1.4 MV/cm, comparable to earlier reported results with SiO2 as dielectric. The reliability performance is found to be significantly layout dependent with corners being weak points due to local field enhancement.