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SEMI M33 Document Information:
Title
TEST METHOD FOR THE DETERMINATION OF RESIDUAL SURFACE CONTAMINATION ON SILICON WAFERS BY MEANS OF TOTAL REFLECTION X-RAY FLUORESCENCE SPECTROSCOPY (TXRF)
Semiconductor Equipment and Materials International
Publication Date:
Sep 1, 1998
Scope:
This document specifies a VPD-TXRF (Vapor Phase Decomposition
Total Reflection X-Ray Fluorescence Spectroscopy) method to analyze
the elemental composition and areal density of impurities, that
include cations and anions with atomic numbers between 16 (S) and
92 (U) independent of their chemical state, with the exception of
the X-ray source material, on polished or epitaxial silicon wafer
surfaces in native or thermally grown oxide or in residues of
microdroplets of process chemicals or media as analyzed with TXRF
on silicon wafer surfaces.
This test is especially useful for analyzing metallic elements
such as K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, (Mo), Pd, Ag, Sn,
Sb, Ta, (W), Pt, (Au), Hg, and Pb and non-metallic elements such as
S, Cl, As, Br, and I through their characteristic K and L lines.
(Elements in brackets are usual X-ray sources.) For limitations in
the nature of analytes refer to the note in ¶ 14.7.
This test method can be used to analyze areal surface
contamination that can be collected in a microdroplet during the
specified VPD preparation and the collection of the digested
surface contamination in the range of 5 x 108
through 5 x 1012 atoms/cm2.
Theoretically, the detection limit (LOD) of each analyte depends
upon its atomic number. As defined by DIN 32645 "Limit of
detection, determination and quantification" the LOD of TXRF is
also depending upon many parameters, such as:
• excitation energy,
• intensity of incident X-ray,
• instrumental background,
• crystallographic interferences, such as Bragg diffraction
conditions,
• impurities in the beam path,
• contamination of the blank scanning solution (see ¶ 4.5),
• contamination level in the analytical ambient,
• surface microroughness of wafer at the microdroplet (see ¶
6.7),
• and integration time.
Concerning the surface conditions to be analyzed, the VPD-TXRF
method is invasive. Nevertheless, the TXRF analysis of the
microdroplet residue can be repeated many times provided that the
prepared specimen is stored in a clean environment. The substrate
and/or surrogate wafers can be recycled for monitoring
purposes.
The user of this test method must assure that the metrology
equipment is under control by the procedures commonly utilized in
the performing laboratory. In the absence of established control
procedures the use of 4.11.2 EN-ISO 9001 is recommended.
NOTICE SAFETY PRECAUTIONS — This standard does not purport to
address the safety concerns, associated with its use. It is the
responsibility of the user of this standard to establish and
maintain appropriate safety and health practices and comply with
the local regulatory ordinance. X-ray irradiation and handling of
HNO3, HF and H2O2 are dangerous. Operators must comply with X-ray
safety regulations and be trained to wear protective garments and
glasses when handling HNO3, HF and H2O2. These chemicals should be
handled in a ventilated area (under exhaust.)
Purpose
The test provides the analytical procedure to determine the
trace level of contaminating elements of an atomic number higher
than 15 on polished or epitaxial silicon wafer surfaces in native
or thermally grown or tetraethylorthosilicate (TEOS) oxide or in
residues of microdroplets of process chemicals or media as analyzed
with TXRF on silicon wafer surfaces as described in ¶ 15.1 and ¶
15.2.
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