Das Atomgewicht des Nebuliums

Ohne Zusammenfassung     

Novel methods of TXRF analysis for silicon wafer surface inspection

TXRF became a standard, on-line inspection tool for controlling the cleanliness of polished Si wafers for semiconductor use. Wafer makers strive for an all-over metallic cleanliness of < 10¹⁰ atoms · cm^–2. The all-over cleanliness can be analyzed using VPD/TXRF. For VPD preparation and scanning we have developed an automatic system coupled with TXRF. With synchrotron radiation TXRF we were able to detect 13 fg of Ni in a residual microdroplet, i.e.10⁵ atoms · cm^–2. Received: 8 January 1998 / Revised: 13 July 1998 / Accepted: 30 July 1998     

Trace analysis of microcontaminations in compliance with ISO 9001: monitoring and diagnostics in large-scale silicon manufacturing

 Severing principles are reported concerning the certification of and quality assurance in a trace-analysis laboratory that handles a large number of real samples, about 60 000 analyses/year with 50 validated methods. ISO 9001 emphasizes monitoring rather than diagnostics. For monitoring purposes the trace-analysis methods must be highly selective and of high precision, with high throughput and uptime within a justifiable economic framework in the analytical range of interest. All trace-analysis methods must be cross-checked using independent analytical tools. The analytical laboratory must be fully integrated in the total quality management of the plant. The analyst must know not only the performance of the trace-analysis tools but also the materials and processes involved in manufacturing. Received: 19 October 1995 Accepted: 15 November 1995     

Periodic solutions of nonlinear differential equations with double resonance

Summary We prove the existence of periodic solutions of a second order nonlinear ordinary differential equation whose nonlinearity is at resonance with two successive eigenvalues of the associated linear operator and satisfies some Landesman-Laser type conditions at both of them.     

Optimization of the electrokinetic sample introduction in capillary electrophoresis for the ultra trace determination of anions on silicon wafer surfaces

Summary A capillary electrophoretic method for the ultra trace determination of anions on silicon wafer surfaces is presented. In several sets of experiments designed according to the methodology of Taguchi, electrokinetic sample introduction with transient isotachophoretic preconcentration was simultaneously optimized for peak height, peak area, peak asymmetry, efficiency, peak resolution, and reproducibility of migration time and peak area. The blank reading of the method showed no cross contamination. Thus, a detection limit of 10 nmol L⁻¹ and a linear range from 50 to 500 nmol L⁻¹ were obtained and verified by two independent instruments. Furthermore, the method was applied to the determination of anions on wafers from a regular production line wetting the whole wafer surface with ultrapure water. The capillary electrophoretic results agree with those obtained by ion chromatography. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996.     

Characterization of silicon wafers through deposition of self-assembled monolayers

AFM imaging of the adsorption of self-assembled octadecylsiloxane (ODS) monolayers has been utilized for probing surface properties of silicon wafers. It has been found that both growth rate of the organic films and island size of sub-monolayer films are influenced by the doping level of the wafers as well as by the surface finishing step during wafer production. Generally, higher doping levels led to lower adsorption rates and smaller islands. Variation of the sample pretreatment used for surface finishing of similarly doped wafers led only to significant changes of the island size, but not of the surface coverage. The results presented open up a valuable perspective for characterizing the surface homogeneity of silicon wafers which is an important parameter for monitoring-wafers in semiconductor industry. Received: 26 June 2000 / Revised: 26 July 2000 / Accepted: 1 August 2000     

Comparison of different gettering techniques for Cu–p+ versus polysilicon and oxygen precipitates

We performed measurements of gettering efficiencies for Cu in silicon wafers with competing gettering sites. Epitaxial wafers (p/p+) boron-doped with a polysilicon back side allowed us to compare p+ gettering with polysilicon gettering. We further measured metal distributions in p+/p- epitaxial test wafers, with the p- substrate wafers pretreated for oxygen precipitation to compare p+ gettering with oxygen precipitate gettering. Our test started with a reproducible spin-on contamination in the 10¹² atoms/cm² range, followed by thermal treatment in order to redistribute the metallic impurity. Wafers were then analyzed by a novel wet chemical layer-by-layer etching technique in combination with inductively coupled plasma mass spectrometry. This led to “stratigraphical” concentration profiles of the impurity, with typical detection limits of 5–10×10¹² atoms/cm³. Twenty-five percent of the total Cu contamination in the p/p+/poly wafer was found in the p+ layer, whilst 75% was gettered by the polysilicon. Obviously, polysilicon exhibits a stronger gettering than p+ silicon, but due to the large distance from the front surface, polysilicon was less effective in reducing impurities from the front side of a wafer compared with p+ gettering. An epitaxial layer p+ on top of p- substrates with oxygen precipitates gettered 50% of the total Cu; while the other 50% of the Cu was measured in the p- substrate wafer with oxygen precipitates. Without oxygen precipitates, 100% of the spiked Cu contamination was detected inside the p+ layer. Gettering by oxygen precipitates thus occurs in the same temperature range as that where p+ silicon begins to getter Cu. Received: 3 September 2001 / Accepted: 17 October 2001 / Published online: 27 March 2002