This paper reviews techniques for determining B concentration and isotopic ratio and their application to soil and plant samples. Boron concentration has been determined utilising spectrophotometry, potentiometry, chromatography, flame atomic emission and absorption spectrometry, inductively coupled plasma (ICP) optical emission (OES) and mass spectrometry (MS), and neutron activation analysis using neutron radiography and prompt-γ activation analysis. Isotopic ratios of B have been measured by ICP–MS, thermal ionisation mass spectrometry (TIMS) and secondary ion mass spectrometry (SIMS). For isotopic measurements, TIMS and SIMS are more sensitive and provide higher degrees of accuracy and resolution than ICP–MS, however, extensive sample preparation and purification, and time-consuming measurements limit their usefulness for routine analyses.

Techniques for boron determination and their application to the analysis of plant and soil samples

Determination of ultra trace contaminants on silicon wafer surfaces using total-reflection X-ray fluorescence TXRF ‘state-of-the-art’

We report on instrumentation-related challenges of applying graphite furnace atomic absorption spectroscopy (GF-AAS) and inductively coupled plasma mass spectrometry (ICP-MS). We show that a significant amount of polyatomic species derived from silicon sample solution in the plasma, such as SiO, SiOH, SiOH 2 ·SiOH 3 , SiO 2 , SiO 2 H, SiO 2 H 2 and SiO 2 H 3 , can hamper the detection limits of many elements of interest. This paper describes a method for eliminating these polyatomic ions. We discuss the advantages and disadvantages of vapor phase decomposition method (VPD), drop etching method (DE) and drop sandwich-etching method (DSE) for the recovery of metal impurities from a silicon wafer surface. We report the application of the DSE method for the evaluation of near-surface metal impurities, used for gettering studies. We describe the direct acid bulk decomposition (DABD) and the room temperature acid vapor phase decomposition method (RT-AVPD) for the determination of metal impurities in bulk silicon. Finally, we report concentration of trace metal contamination in several chemical reagent solutions.

Recent advanced applications of AAS and ICP-MS in the semiconductor industry

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.

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

The vapor phase decomposition (VPD) technique is used to dissolve the silicon oxide layer on a Si wafer surface by exposing the wafer to HF vapor. After VPD, the hydrophobic Si wafer surface is scanned with an acidic droplet of solution to extract the surface trace metals. ICP-MS is applied for the determination of metals in the droplet of solution. Matrix effects resulting from the formation of polyatomic species are investigated. The molecular interferences from the presence of different levels of Si concentration left after VPD are investigated. The interference of F on 59Co is found to be negligible and controllable. They are also insignificant for the isotopes of Ga, Cu, Ge and Ni. However, for 47Ti, 68Zn and 44Ca, pronounced matrix effects are observed. A procedure for reducing Si concentration resulting from thick oxide films is carried out and optimum ICP-MS parameters are chosen for the measurement of these samples. Instrumental and method detection limits for 35 elements of interest are determined and provided in this study. Spike recovery for these 35 elements is also performed and the accuracy of the method is confirmed for 34 elements. Silver recovery is poor due to the reduction of this element on the silicon surface. An alternative extraction solution containing HNO3 and HCl is used to collect Ag from the Si wafer surface.

Advances in trace element analysis of silicon wafer surfaces by vapor phase decomposition (VPD) and inductively coupled plasma mass spectrometry (ICP-MS)

A highly sensitive multielement analytical method known as vapor phase decomposition flow injection inductively coupled plasma-mass spectrometry (ICP-MS) was developed and used to measure the concentration of trace metals on silicon wafer surfaces. The method uses hydrogen fluoride vapor to decompose and release metal contaminants from a surface oxide. These trace metals are then collected by scanning a small drop of dilute acid solution throughout the wafer surface. Trace metals in the solution are measured by ICP-MS using flow injection (FI) sample introduction. Potentially, 60 8 11 2 elements can be measured with detection limits ranging from 10 to 10 atom/cm. Typical surface concentrations of trace metals on silicon wafers with native oxides and dielectric oxides were measured and presented.

Measurement of Trace Metallic Contaminants on Silicon Wafer Surfaces in Native and Dielectric Silicon Oxides by Vapor Phase Decomposition Flow Injection Inductively Coupled Plasma‐Mass Spectrometry

Boron determination in borophosphosilicate glass films by the ICP-AES or ICP-MS technique can be performed after dissolution of the sample in HF solution. However, addition of HF to boric acid standard solution can cause a drift in the slope of the calibration curve. The signal change was correlated with the kinetics of the borontetrafluoride complex formation reaction. The mechanism was explained by the selectively increased boron transport into the plasma, which was caused by the more efficient diffusion of borontrifluoride gas through the aerosol particles into the nebulizer gas. With the kinetics of borontetrafluoride complex formation taken into consideration, an accurate and precise method was developed for the determination of boron in BPSG films.

János Fucskó

Papers

Measurement of Trace Metallic Contaminants on Silicon Wafer Surfaces in Native and Dielectric Silicon Oxides by Vapor Phase Decomposition Flow Injection Inductively Coupled Plasma‐Mass Spectrometry

Fluoride Interference in the Determination of Boron by Inductively Coupled Plasma Emission Spectroscopy