Ludwig Kotz

Application of capillary zone electrophoresis with an isotachophoretic initial state to determine anionic impurities on as-polished silicon wafer surfaces

Abstract Mobile inorganic anions such as chloride, sulfate and nitrate were determined up to an analyte-to-matrix-ratio (ATMR) of 1:104 using capillary zone electrophoresis. On adjusting the mobility and the concentration of the co-ion of the electrolyte to an isotachophoretic initial state, the detection limit of the analytes was improved by a factor of 2 by increasing the plate numbers through the isotachophoretic state. The ATMR could be increased to 1:6 · 104. These optimized conditions were applied to the determination of anionogenic impurities on experimental silicon wafer surfaces (d = 150 mm) after dissolution of the native oxide of silicon in isothermally distilled hydrofluoric acid vapour down to the range of 109 anions/cm2. The mobile organic anion oxalate was identified on silicon wafer surfaces for the first time.

Trace-analytical methods for monitoring contaminations in semiconductor-grade Si manufacturing

Generating systematic data on incoming materials, processes, production environments and products by contamination monitoring and analyis is the key element of quality assurance in semiconductor fabrication. To be able to match the analytical capabilities to the requirements of improving materials and processes, the level of sophistication of contamination monitoring and analysis systems must be higher than the expected demands in the fabrication line. The accuracy of each analytical method has to be cross-checked by different independent techniques. Accuracy, precision, power of detection, analysis time and expenses should always be tailored to the particular case. All monitoring methods must run under statistical process control. The methods described meet the analytical requirements of the near future in semiconductor grade silicon manufacturing.

Capillary preconditioning for analysis of anions using indirect UV detection in capillary zone electrophoresis: Systematic investigation of alkaline and acid prerinsing techniques by designed experiments

It is widely accepted in capillary zone electrophoresis, that the use of alkaline prerinse procedures can improve the reproducibility of migration times and of corrected peak areas. In this study we present a systematic investigation of alkaline and acid preconditioning procedures for anion analysis using indirect UV detection by designed experiments according to the methodology of Taguchi. Four frequently used electroosmotic flow modifiers (diethylenetriamine, hexamethonium hydroxide, tetradecyltrimethylammonium hydroxide, and hexadimethrine hydroxide) were examined. The optimized procedures were evaluated with regard to the necessary preconditioning time compared to the analysis time. Furthermore, it was demonstrated that the optimized preconditioning technique could be applied to other indirect detection based CE systems. For all examined electrolyte systems, relative standard deviations below 0.5% for migration times and below 5% for corrected peak areas (n=20) were achieved using automated peak integration without further manual reprocessing.

Diagnostic and monitoring tools of large scale Si-manufacturing: trace-analytical tools and techniques in Si-wafer manufacturing

In order to facilitate fast corrective actions, all process media, crucial process steps and intermediate product stages of wafering must be monitored by suitable analytical tools. The analyzes have to provide reliable, relevant and real-time results at justifiable economy. Preferably, they should be serviceable in on-line configuration under strict SPC conditions. The following chapters outline the performance of the few analytical techniques, that optimally satisfy these requirements.

Modification and validation of the pyromellitic acid electrolyte for the capillary electrophoretic determination of anions.

For the determination of inorganic and organic anions, the pyromellitic acid (PMA) electrolyte is widely used. The pH adjustment of the self-prepared electrolyte was very challenging to satisfy the pH of specification of pH 7.8 +/- 0.1. A modification was proposed to provide a more simple electrolyte by buffering the PMA electrolyte with triethanolamine (TEA) only instead of adjusting the pH by NaOH and TEA. Thus, the proposed electrolyte consisted of 2.25 mmol l(-1) PMA, 0.75 mmol 1(-1) hexamethonium hydroxide and 12 mmol 1(-1) TEA. The performance of the PMA electrolyte buffered by TEA only was compared to a commercial available PMA and statistically validated in accordance with the methodology of Taguchi. No statistically significant difference could be found for both electrolytes assessing the performance and detection limits of hydrodynamic, stacking and electrokinetic injection with transient isotachophoretic preconcentration as well as repeatability of migration times, peak resolutions and peak symmetries.