Application of total reflection X-ray fluorescence in semiconductor surface analysis

doi:10.1016/0584-8547(89)80054-0

Spectrochimica Acta Part B: Atomic Spectroscopy

Volume 44, Issue 5, 1989, Pages 483-490

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Abstract

Total reflection X-ray fluorescence (TXRF) is introduced as a novel and versatile method for the determination of metal trace impurities on semiconductor surfaces. Apparatus and measurement techniques are conceptually simple, nevertheless allowing for accurate quantification of surface coverages down to 10¹¹ atoms/cm². The examples given demonstrate the usefulness of TXRF for contamination control in silicon wafer processing. These examples include measurements on as-received wafers from different vendors and the characterization of deposition and cleaning procedures. The method is compared with other surface sensitive techniques. Low detection limits, simultaneous multi-element analysis, exemption from sample preparation and absence of sample charging problems as well as availability of standards for quantification are the main advantages of TXRF. Finally, some possibilities for future applications are discussed.

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The angular dependence of soft X-ray emission spectra from a sandwich structured sample has been studied. Greatly enhanced surface sensitivity is observed at grazing emission. Soft X-ray emission allows chemical state information to be obtained owing to high spectral resolution and small lifetime broadening. Well-established theory from grazing incidence X-ray fluorescence spectroscopy has been used to evaluate and interpret the experimental data.
Trends in applications and strategies in the analysis of thin films, interfaces and surfaces
1994, Analytica Chimica Acta
Prominent aims and general aspects of the analysis of thin films, interfaces and surfaces are reviewed. The terminology is presented, and a limited sketch displays the major techniques important in this field. Some topical subjects in thin film analysis are identified, starting from its application for support of technology. This leads to reflections upon some trends concerning both optimization and application.
The role of total-reflection X-ray fluorescence in atomic spectroscopy
1993, Spectrochimica Acta Part B: Atomic Spectroscopy
Total-reflection X-ray fluorescence (TXRF) is a universal and economic method for the simultaneous determination of elements with atomic numbers > 11 down to the lower pg-level. It is a microanalytical tool for the analysis of small sample amounts placed on flat carriers and for contaminations on flat sample surfaces. Analyses of stratified near-surface layers are made possible by varying the incident angle of the primary beam in the region of total-reflection. This non-destructive method is especially suitable for thin layers of a few nanometres, deposited on wafer material although not usable as a microprobe method with a high lateral resolution. Furthermore, depth profiles of biological samples can be recorded by means of microtome sectioning of only a few micrometres, as, for example in the gradient analysis of human organs. In addition to micro- and surface-layer analysis, TXRF is effectively applied to element trace analysis. Homogeneous solutions, for example aqueous solutions, high-purity adds or body fluids, are pipetted onto carriers and, after evaporation, the dry residues are analysed directly down to the $pg ml$ region. Particularly advantageous is the absence of matrix effects, so that an easy calibration can be carried out by adding a single internal standard element. A digestion or separation step preceding the actual determination becomes necessary if a more complex matrix is to be analysed or especially low detection limits have to be reached. A critical evaluation of the recent developments in atomic spectroscopy places TXRF in a leading position. Its outstanding features compete with those of e.g. electrothermal atomic absorption spectrometry (ETAAS), microwave induced plasma optical emission spectroscopy (MIP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) in the field of micro- and trace analysis and with Rutherford backscattering (RBS) and secondary ion mass spectrometry (SIMS) in the surface-layer analysis.
Basic features of total-reflection X-ray fluorescence analysis on silicon wafers
1993, Spectrochimica Acta Part B: Atomic Spectroscopy
The effect observed in total-reflection X-ray fluorescence (TXRF) where the penetration depth of the exciting X-rays on flat and polished silicon samples is reduced to a few nanometres makes TXRF a valuable tool for wafer analysis. Some basic principles and parameters that describe the phenomena of total reflection are discussed in this paper. The important influence of the proper setting of the glancing angle on the correct and reproducible quantification of surface contaminations is demonstrated. Furthermore, an overview is given dealing with the basic features of direct measurements on wafers.
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Total reflection X-ray fluorescence of single and multiple thin-layer samples
1991, Spectrochimica Acta Part B: Atomic Spectroscopy
In Total-reflection X-Ray Fluorescence (TXRF) the penetration depth of the exciting X-rays can be varied between a few nanometers and a few micrometers. In this paper the extension of the application of this technique to thin-film analysis is studied.
First a theory is described with which the angular dependence of TXRF intensities can be calculated. Next calculated data are shown for various thin-film samples. The theoretical results compare favourably with preliminary experiments performed with a modified diffractrometer equipped with an energy-dispersive X-ray detector.
The conclusion is that TXRF, especially when combined with X-ray reflectivity measurements, is a promising technique to obtain information about quantity and distribution of material over the various layers. The expected detection limits for this case are of the order of 10¹³ atoms cm⁻².

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ReviewApplication of total reflection X-ray fluorescence in semiconductor surface analysis

Abstract

Nucl. Instr. Meth.

Spectrochim. Acta

Nucl. Instr. Meth

Spectrochim. Acta

Appl. Surf. Sci.

CMOS-Technologie

J. Appl. Phys.

Review
Application of total reflection X-ray fluorescence in semiconductor surface analysis