Chris Vinckier

Saturation effects in TXRF on micro-droplet residue samples

Total reflection X-ray fluorescence spectrometry (TXRF) is a well-accepted technique for ultra-trace analysis of ultra-pure reagents and silicon wafers. Nevertheless, the technique’s linear range is not well characterized. In this paper, the upper limits of the linear range of TXRF on micro-droplet residues are identified and the origin of the non-linear effect is investigated. It is observed experimentally that a systematic decrease in the accuracy occurs as a function of the metallic content, starting from amounts above 3–10 ng, depending on the sample composition. A mass-absorption model for thin films is re-formulated for the micro-droplet residue samples and the model parameters are tested on the experimental observations. The calculations are in good agreement with the experimental data. Finally, solutions to deal with these saturation effects are discussed and a method to extend the dynamic range of TXRF is proposed.

Identification of the oxidation products of the reaction between α-pinene and hydroxyl radicals by gas and high-performance liquid chromatography with mass spectrometric detection

In this paper an identification method is described for determining the degradation products of the reaction of alpha-pinene with hydroxyl radicals. The study is carried out in a fast-flow reactor equipped with a specially designed microwave cavity (type Surfatron) allowing to operate at pressures up to 100 Torr (1 Torr=133.322 Pa). The semivolatile products are collected on a liquid nitrogen trap (LN2 trap) and the batch samples are subsequently analysed by GC-MS and HPLC-MS. Some samples were also collected directly on a LpDNPH-cartridge, followed by HPLC-MS analysis. When experiments were carried out at 50 Torr both GC-MS and HPLC-MS measurements showed that campholenealdehyde and pinonaldehyde were identified as condensable oxidation products for the alpha-pinene/OH reaction, with pinonaldehyde being the main product. Furthermore, the LN2 trap collection method based on the in situ conversion of aldehydes and ketones to their 2,4-dinitrophenylhydrazone derivatives allowed the determination of formaldehyde, acetaldehyde and acetone. Although formaldehyde and acetone are present in small amounts in blank samples it could be established that formaldehyde and acetone are also formed in the alpha-pinene/OH reaction.

On the Application of a Thin Ozone Based Wet Chemical Oxide as an Interface for ALD High-k Deposition

Introduction In order to keep pace with CMOS scaling trends, alternative gate oxide materials, with a high dielectric constant, were proposed. To have a low interface trap density, good mobility [1], and good Atomic Layer Deposition (ALD) growth characteristics [2], the presence of an interfacial oxide layer is still prerequisite. Hydroxyl groups are the key players for the initiation of the ALD reaction [3]. In this work the application of downscaled ozone based wet chemical oxide as a surface pretreatment for ALD high-k deposition is examined.

The fabrication of a novel composite gaas/sio2 nucleation layer on silicon for heteroepitaxial overgrowth by molecular-beam epitaxy

We report on the fabrication of a composite GaAsSiO2 nucleation layer. The layer is formed by a deposition of a GaAs island layer by molecular beam epitaxy (MBE), followed by an oxidation step of the silicon regions surrounding the islands. In this way, small GaAs islands, for which the critical thickness for misfit dislocation generation is increased, are surrounded by a stable amorphous phase. Lateral overgrowth seeded by the individual GaAs islands might enhance the overall epilayer quality. We describe the fabrication and cleaning of such a composite GaAsSiOx nucleation layer that is compatible with the epitaxy process. Preliminary regrowth on a non-optimized composite surface resulted in GaAs-on-silicon quality equal to standard GaAs-on-silicon. Compared with GaAs epitaxy on porous silicon, another seeded growth technique, the composite surface technique has greater technological potential for the monolithic integration of GaAs and silicon electronics.

Another look at the electron attachment to nitrous oxide

Ab initio molecular orbital calculations up to the coupled-cluster level with the aug-cc-pVQZ basis set allowed us to have a new look at the electron affinity of nitrous oxide (N2O) resulting in a detection of a new N2O− entity, and thereby a novel mechanism for the dissociative electron attachment process, N2O+e−→N2+O−. Addition of an electron to the linear N2O ground state (X 1Σ+) leads first to an open-chain bound anion which lies 25 kJ/mol above the neutral. Upon a cyclization of the open anion with an additional energy barrier of 25 kJ/mol, a cyclic anionic species is formed which is more stable than the open isomer and lies now, at most, 3 kJ/mol above the neutral ground state (the transition structure for cyclization being 50 kJ/mol above neutral N2O). The cyclic anionic species constitutes a weak complex between N2 and O− characterized by a binding energy of only 16 kJ/mol. The electronic structure of the anion complex is analyzed, a number of earlier experimental results are clarified and a resol...

Determination of the oxidation products of the reaction between α-pinene and hydroxyl radicals by high-performance liquid chromatography

In this paper a method is described for determining and quantifying the degradation products of the reaction of alpha-pinene with hydroxyl radicals. The study is carried out in a fast-flow reactor equipped with a specially designed microwave cavity (type Surfatron) allowing to operate at pressures up to 100 Torr (1 Torr=133.322 Pa). The semi-volatile products are collected on a liquid nitrogen trap (LN2 trap) coated with a 2,4-dinitrophenylhydrazine (2,4-DNPH) solution and the batch samples are subsequently analyzed by HPLC. In order to perform quantitative measurements the batch samples contained two internal standards: benzaldehyde-2,4-DNPH and tolualdehyde-2,4-DNPH. In the experiments carried out at 50 Torr and 100 Torr, HPLC measurements showed that the semi-volatile products formaldehyde, acetaldehyde, acetone, campholenealdehyde and pinonaldehyde could be quantified as oxidation products for the alpha-pinene/OH reaction, with pinonaldehyde being the main product. Assuming that all these five oxidation products have the same collection efficiency on the LN2 trap, one arrives at the following relative product yields (expressed in mol %) at 50 and 100 Torr, respectively: 9.7+/-0.7 and 6+/-5 for formaldehyde; 1.1+/-0.1 and 0.9+/-0.5 for acetaldehyde; 16+/-1 and 6+/-2 for acetone; 11+/-2 and 5.5+/-0.7 for campholenealdehyde; 63+/-3 and 82+/-7 for pinonaldehyde.

Aging phenomena in the removal of nano-particles from Si wafers

With the continuous shrinkage of critical sizes in semiconductor manufacturing, nano-particles smaller than 100-nm are becoming a potential threat to devices in chips. Storage of wafers contaminated during process steps often results in a decrease of particle removal efficiency in subsequent clean, a phenomenon referred to as aging. In this work, the influence of aging on the removal of silica and silicon nitride nano-particles from hydrophilic Si wafers was studied for different storage conditions. Trends observed for aging as a function of particle size and for different tools indicated that aging will become an issue for critical cleans where substrate etching must be kept very low and the physical component of the clean must be decreased to prevent damage to fine structures. Controlling the relative humidity during storage helped in lowering the effect of aging.

Materials compatibility and organic build-up during ozone-based cleaning of semiconductor devices

As integrated circuits keep on shrinking, micro-contamination needs further to be controlled, such as particles, metallic and organic species left on the wafer surface. Nowadays the use of ozonated chemistries in cleaning processes is gaining interest since the cleaning processes are urging towards more environmentally friendly processes . However the generation and transport of ozone may lead to contamination into the cleaning solutions. This work looks at some organic and inorganic species introduced in deionized water (DIW) when processing with ozone.

Photoresist Stripping by Ozone/Water Processes: Effect of Additives

Introduction In the last decade, numerous papers have been published showing the high potential of ozone/water processes in the removal of photoresist (PR) layers [1,2]. However, reaction and transport mechanisms are far from being completely understood due to a number of reasons. At first, one has the complexity of the overall heterogeneous process with three phases: a solid photoresist layer, a (essential) water film and an ozone-rich gas ambient. In this system different transport mechanisms are involved, like the ozone mass transfer from the gas phase into the water and transport of ozone through the water film towards the photoresist surface. Secondly, the complexity is due to the chemistry of ozone in water. When dissolved in water, ozone is not stable but decomposes according to a radical chain mechanism [3]. The intermediates formed in this decomposition are highly reactive radicals that are also able to degrade the resist material (indirect oxidation). Besides the water temperature and pH, the rate of ozone decomposition is also determined by the presence of certain compounds in the process water [4]. Depending on their chemical action, they can either enhance the direct oxidation of the resist material by ozone itself or the indirect oxidation by the radical intermediates. This may ultimately lead to higher strip rates and thus a lower processing time. In this work it was investigated experimentally whether higher strip rates can be obtained by spiking the process water with of a number of selected additives. The observations will be compared with our previous experimental findings and the results will generate valuable information concerning the reaction mechanisms occurring.

A quantum chemical study on the potential energy surface of Mg(1S) + N2O reaction

The singlet (1A′) potential energy surface (PES) of the Mg+N2O reaction has been studied at both MP2/6-311+G∗ and CCSD(T)/6-311+G∗ levels. Two kinds of reaction channels have been identified: the first one is when the Mg atom approaches N2O in a perpendicular fashion (⌊Mg–O–N≈90.0°) and the second is when Mg approaches from the end-on (oxygen side) of N2O (⌊Mg–O–N≈148.0°). The CCSD(T) activation barrier for the perpendicular approach is 48.8 kJ/mol and compares well with the experimentally determined value (44.3±1.3kJ/mol). The transition structure for the end-on approach has higher energy barrier, 95.7 kJ/mol. Charges analysis and electron density calculations by atoms-in-molecule theory showed that the reaction mechanism is controlled by covalent interactions between the Mg atom and the O end of N2O rather than by an electron transfer from the Mg atom to the N2O molecule.