Application of high resolution-ICP-MS (sector field-ICP-MS) to the fast and sensitive quality control of process chemicals in semiconductor manufacturing

For fast routine analysis of process chemicals used in semiconductor technology such as tetramethylammonium hydroxide (TMAH), ammonium fluoride/hydrofluoric acid mixtures, phosphoric, sulphuric or peroxodisulphuric acid (PDSA) low blanks are the paramount requirement for reliable sector field ICP-MS ultratrace analysis. When solutions containing a high amount of dissolved solids e.g. seawater samples have been analysed before, a thorough cleaning procedure and an adapted element menu is essential to lower the instrument blanks where possible or to achieve sufficient limits of detection (LoD) even at high blank levels. Due to its improved transmission and its ability to resolve spectral interferences inductively coupled plasma-sector field mass spectrometry is capable of detecting 1 ng/g of all metal impurities even K, Ca, and Fe in every matrix used for semiconductor production. LoDs range from < 1 to 30 pg/mL in diluted chemicals corresponding to 5 to 800 pg/mL in the original. This work describes the experiences with instrument cleaning and maintenance, sample preparation and introduction. The interface region between torch and lenses was seen to be the main source of blanks for elements such as Na. All sample manipulation has to be carried out under clean room conditions. The use of an inert sample introduction system (ISIS), platinum cones and at least medium resolution for elements between 24 and 80 amu creates a very robust method. High efficiency sample introduction systems such as USN and MCN have been studied alternatively.     

Application of SIMS in semiconductor research

Summary Nowadays SIMS is a well-established analytical technique in semiconductor research. Materials research and process development are the main fields of application in silicon technology, whereas for III–V compound semiconductors much attention has been paid to assessment of multilayer structures grown by advanced growth methods. Recent applications of SIMS in these fields are the subject of the present paper. Emphasis will be placed upon optimizing the SIMS results with respect to accuracy and depth resolution.

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Anwendungen von SIMS in der Halbleiterforschung

     

Architectural control of magnetic semiconductor nanocrystals.

Shape- and dopant-controlled magnetic semiconductor nanocrystals have been achieved by the thermolysis of nonpyrophoric and less reactive single molecular precursors under a monosurfactant system. Reaction parameters governing both the intrinsic crystalline phase and the growth regime (kinetic vs thermodynamic) are found to be important for the synthesis of various shapes of MnS nanocrystals that include cubes, spheres, 1-dimensional (1-D) monowires, and branched wires (bipods, tripods, and tetrapods). Obtained nanowires exhibit enhanced optical and magnetic properties compared to those of 0-D nanospheres. Proper choice of molecular precursors and kinetically driven low-temperature growth afford dopant controlled 1-D Cd1-xMn(x)S nanorods at high levels (up to approximately 12%) of Mn, which is supported by repeated surface exchange experiments and X-ray diffraction (XRD) and electron paramagnetic resonance (EPR) analyses.     

Application of neutron activation in the control of an ore disintegration process

The disintegration of realgar ore has been followed by neutron activation method in order to determine the amount of arsenic sulfide dissolved from As₂S₃. Interest in exploring realgar ore comes from the fact that its constituents (As₂S₃-72%, Sb₂S₃-0.4%, FeS₂, Fe₂O₃-19.6%, SiO₂-5%, Ca, Mg carbonates-3%) make it almost perfect for neutron activation analysis, because the activity is largely due to⁷⁶As. It is possible to follow the effects of different chemical procedures in the disintegration by means of -spectrometry of the samples before and after chemical treatment.     

Application of FT-Raman spectroscopy to quality control in brick clays firing process

This paper reports the study of the mineralogical evolution during the firing process (800-1150 degrees C) of the main types of raw materials used for the brick industry in Santa Cruz de Mudela (Ciudad Real, Spain). The mineralogical diversity observed in these materials leads to different behaviour during the shaping, drying and firing stages. Traditional use of similar working conditions in local industries, despite the mineralogical differences in the starting material, promotes the presence of defects in the drying and/or firing stages. This study attempt to implement some analytical guideline for the raw materials in order to improve the final product. Three types of raw materials obtained in different quarries have been characterised by means of chemical analysis with electron microprobe, powder X-ray diffraction and FT-Raman spectroscopy. The main difference between the clays studied is the carbonate content: one of the analysed samples is deficient in this component, while it is present as calcite (8%) or as calcite (14%) plus dolomite (10%) in the rest. The observed compositional differences seem to be relevant in the firing process. FT-Raman spectra reveal the onset of early vitrification (at about 900 degrees C) in the sample without carbonate. The importance of calcium and magnesium oxides, obtained from the corresponding carbonates, for the synthesis of new mineral phases that could slow down the vitrification process is discussed.     

Application of wet chemistry techniques to process analysis and control

The availability of reliable and rugged automatic titrators, flow-injection analysers and ion chromatographs provides opportunities for their application in industrial process analysis. The control of industrial processes such as the removal of sulphur during gas treatment presents a challenge as accurate on-line and in-line analysers are required. The application of automatic titrators and ion chromatographs to the compositional analysis of caustic and alkanolamine gas sweetening solutions is described. Comparisons with other techniques such as flow-injection analysis and ultraviolet and near-infrared spectrometry are made and the pertinent features and benefits of each are discussed.     

Total-reflection X-ray fluorescence analysis for semiconductor process characterization

Semiconductor process characterization techniques based on total-reflection X-ray fluorescence (TXRF) analysis are reviewed and discussed. One of the most critical factors in obtaining reliable determinations by TXRF is the reliability of the standard samples that are used. Conventional physisorption standard samples such as spin coat wafers have two potential drawbacks: reproducibility of depth profile and stability. A method of chemisorption called ‘immersion in alkaline hydrogen peroxide solution (IAP)’ was proposed that provides answers to these two problems. IAP standard samples were used to experimentally examine three methods of TXRF application: Straight-TXRF, VPD-TXRF, and Sweeping-TXRF. In the application of Straight-TXRF, the linearity of Cu at a level of 10⁹ atoms cm⁻² is examined. In the application of VPD-TXRF, test results of VPD-TXRF for both transition metals and light elements are shown. Finally, a new measurement protocol called Sweeping-TXRF is proposed to conduct whole-surface analysis without chemical preconcentration.     

Application of ion chromatography in the semiconductor industry

This review discusses ion-chromatographic advances in the semiconductor industry during the past 5 years. Through the development of more selective and sensitive instruments and columns, plus better attention to contamination control, the detection limits for many analyses are now in the low-ppt (w/w) range. The primary area of interest continues to be anion analysis, since spectroscopy remains the industry's preferred technique for quantifying cationic species. Noteworthy ion-chromatographic methods for analyzing semiconductor chemicals, gases, and solid samples are discussed and evaluated critically. Thirty-eight references are included.     

Time-series analysis in analytical process control

Analysis of time series tries to extract tendencies from measured values dependent on time. For this purpose the cusum technique has proved to be a very sensitive tool for the evaluation of both current and completed time series. Even very weak tendencies can be detected at a high level of noise. Time-series analysis further tries to predict values to come from hitherto performed measurements. As a very flexible model exponential smoothing could be successfully used. Even for processes with a high extent of non-stationarity this model allowed a good prediction owing to the dynamics of the process. Three types of time-series analysis, i.e., evaluation of current measurements, retrospective evaluation and prediction of data (also known as “in vivo”, “post mortem” and “in futurum” time-series analysis) are demonstrated for problems stemming from analytical process control.     

Application of LIBS to the in-line process control of liquid high-alloy steel under pressure

A process optimization and control system called VAI-CON Chem has been developed that uses laser-induced breakdown spectroscopy (LIBS) to quasi-continuously chemically analyze liquid high-alloy steel under pressure. The beam from a Nd:YAG laser, located on safe ground and operating at its fundamental wavelength, is guided by a mirror system to a process tuyere below bath level. Passing through the ∼1.5 m long tuyere, the beam is then focused onto the steel bath. Light emitted from the induced plasma passes back through the tuyere, which is coupled to a fiber optic cable that carries the information over a distance of approximately 10 m back to an Echelle spectrometer located beside the laser. Calibrations were performed using the complete system, located in a laboratory, during system testing. An induction furnace was used to simulate the AOD converter, wherein the samples were molten and superheated to a temperature of ∼1600 °C and kept at a pressure of ∼1.7 bar under an argon atmosphere. Twelve different high alloyed reference samples taken from normal AOD production with Fe concentrations of >48 wt.% and non-Fe element concentrations of up to 25 wt.% were available for calibration. The mean residual deviations (defined as the square root of the variance of the concentration ratios determined by LIBS and the reference element concentration ratios) obtained were close to those reported for other comparable high-alloy samples that were investigated at room temperature under normal atmospheric pressure.     

Synthetic control over polymorph formation in the d-band semiconductor system FeS2

Pyrite, also known as fool''s gold is the thermodynamic stable polymorph of FeS₂. It is widely considered as a promising d-band semiconductor for various applications due to its intriguing physical properties. Marcasite is the other naturally occurring polymorph of FeS₂. Measurements on natural crystals have shown that it has similarly promising electronic, mechanical, and optical properties as pyrite. However, it has been only scarcely investigated so far, because the laboratory-based synthesis of phase-pure samples or high quality marcasite single crystal has been a challenge until now. Here, we report the targeted phase formation via hydrothermal synthesis of marcasite and pyrite. The formation condition and phase purity of the FeS₂ polymorphs are systematically studied in the form of a comprehensive synthesis map. We, furthermore, report on a detailed analysis of marcasite single crystal growth by a space-separated hydrothermal synthesis. We observe that single phase product of marcasite forms only on the surface under the involvement of H₂S and sulphur vapor. The availability of high-quality crystals of marcasite allows us to measure the fundamental physical properties, including an allowed direct optical bandgap of 0.76 eV, temperature independent diamagnetism, an electronic transport gap of 0.11 eV, and a room-temperature carrier concentration of 4.14 × 10¹⁸ cm⁻³. X-ray absorption/emission spectroscopy are employed to measure the band gap of the two FeS₂ phases. We find marcasite has a band gap of 0.73 eV, while pyrite has a band gap of 0.87 eV. Our results indicate that marcasite – that is now synthetically available in a straightforward fashion – is as equally promising as pyrite as candidate for various semiconductor applications based on earth abundant elements.

Pyrite, also known as fool''s gold is the thermodynamic stable polymorph of FeS₂.     

Minority carrier lifetime control in power semiconductor devices by fast neutron irradiation

A new technology for controlling reduction of minority carrier lifetime of power semiconductor devices was given in this paper, using fast neutron irradiation in nuclear reactor. The effects of high frequency thyristor by fast neutron irradiation is mainly discussed. Furthermore, a comparison is made with electron irradiated, ⁶⁰Co-gamma irradiated and gold diffused devices. The conclusion shows, the trade-off of forward voltage drop and turn-off time of fast neutron irradiated devices is alike with gold diffused devices, while the leakage current is less than that of gold diffused devices, and not different from the electron or Gamma irradiated devices. Moreover, the deep energy levels of fast neutron irradiation in silicon was shown in this paper, and a single dominant level of Ec-0.44eV is identified for controlling minority carrier lifetime.     

Chemical control of charge transfer and recombination at semiconductor photoelectrode surfaces

Semiconductor/liquid contacts provide very efficient systems for converting sunlight into electrical and/or chemical energy. Until recently, relatively little was understood about the factors that control the rates of interfacial charge transfer in such systems. This Forum Article summarizes recent results that have elucidated the key factors that control such charge-transfer rates, including verification of the Marcus inverted region, identification of the maximum charge-transfer rate constant for outer-sphere, nonadsorbing redox couples at optimal exoergicity, the role of nuclear reorganization on the value of the interfacial charge-transfer rate constant at semiconductor electrodes, and the effects of pH-induced changes in the driving force on the rates of such systems. In addition, we discuss methods for using main group inorganic chemistry to control the electrical properties of surfaces of important semiconductors for solar energy conversion, with specific emphasis on alkylation of the (111)-oriented surface of Si. Control of the rates at which carriers cross such interfaces, along with control of the rates at which carriers recombine at such interfaces, forms the basis for exerting chemical control over the key solar energy conversion properties of semiconductor photoelectrode-based devices.     

Fluorinated gases for semiconductor manufacture: process advances in chemical vapor deposition chamber cleaning

In the past several years, the semiconductor industry has been presented with various options for cleaning of plasma enhanced chemical vapor deposition (PECVD) tool chambers. In this paper, we assess the relative merits of the latest chamber cleaning processes. These processes will be compared on the overall cleaning performance (process throughput, efficiency of clean) the economic performance (gas usage, costs) and the environmental performance (perfluorocarbon (PFC) emissions). Direct comparisons between chemistries will be made whenever relevant process factors (e.g. tool type, film, analysis methods) are held constant.We have previously reported both laboratory and commercial CVD tool results comparing different chamber cleaning gases. These studies using both Novellus Concept-1 and AMAT P-5000 tools, indicated that a “drop-in” alternative such as octafluorocyclobutane (c-C₄F₈) would significantly lower PFC emissions (up to 85%) as well as decrease process costs through reductions in gas consumption. In this paper, we further extend this work to include qualification and implementation at chipmakers on a variety of tools, wafer sizes, and films. Key process data on film properties such as uniformity, number of particles, and thickness is also presented.The overall results support and extend the basic conclusions reached earlier: c-C₄F₈ has the lowest process cost of any cleaning gas, without any penalty in cleaning performance (process throughput) but most importantly, it also offers the lowest PFC emissions of any fluorocarbon-based process. It is a true drop-in alternative offering the unique win-win combination of improved environmental performance while also reducing processing costs.     

On-line process analysis and control in biotechnology

Measuring techniques can be developed and adapted for the characterization of bioreactors, for on-line process analysis and for the determination of biological parameters of cells during fermentation. Mathematical models can be formulated for bioreactors and cell regulation and a combined model for these can be reduced for use in process control. Microprocessors and minicomputers give further scope for data acquisition, model implementation and process control.     

Flow injection analysis in on-line process control

Flow injection systems are serious candidates for a new generation of chemical on-line analyzers because there is a growing interest in instruments that combine versatility with the possibility of attaining high sampling frequencies. For real on-line applications the instrument and its component parts have to meet the highest standards with respect to reliability and maintenance. These aspects are considered in some detail, and some industrial applications are briefly discussed.     

Intelligent control of a pH process

A new strategy, to augment the pH process control is offered in this paper. The intelligent controller proposed herein is based on an inverse neural plant model. An integration term is introduced to improve the pure inverse neural controller performance. This element, adjusted by a fuzzy system with respect to the control error, operates in parallel with the neural controller to ensure offset-free performance, in case of system uncertainties or modelling mismatch. Four fuzzy rules were applied to generate the integrator parameters. Experimental results, carried out under pH control on a laboratory scale set-up, demonstrate the feasibility of the proposed control system. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.