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 combination of vapor-phase decomposition (VPD) and total reflection x-ray fluorescence (TXRF) was used for the trace analysis of light elements (Na and Al) and transition metals (Fe, Ni, Cu, and Zn). TXRF measurement using the W Mα line was conducted for the high-sensitivity analysis of Na and Al. Through the use of VPD/TXRF, the lower limits of detection (LLDs) were improved by two orders of magnitude compared with those of TXRF without use of the VPD technique. For 150 mm Si wafers, the LLD was 3 × 1010 atoms cm−2 for Na and 2 × 109 atoms cm−2 for Al. The LLDs for Fe, Ni, Cu, and Zn were 4 × 107, 5 × 107, 6 × 107 and 9 × 107 atoms cm−2, respectively. The analytical results obtained by VPD/TXRF were cross-checked with results obtained by atomic absorption spectrometry. The two sets of values were in good agreement. The glancing angle dependence of TXRF intensity was investigated on samples before and after undergoing VPD treatment. The angle dependence proved that the sample after VPD treatment became a particle type on the wafer. Copyright © 1999 John Wiley & Sons, Ltd.

VPD/TXRF analysis of trace elements on a silicon wafer

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

Samantha S. Tan

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