- SEMI MF1617 - Test Method for Measuring Surface Sodium, Aluminum, Potassium, and Iron on Silicon and EPI Substrates by Secondary Ion Mass Spectrometry
This Standard was technically approved by the Silicon Wafer Global Technical Committee. This edition was approved for publication by the global Audits and Reviews Subcommittee on February 1, 2016. Available at www.semiviews.org and www.semi.org in April 2016; originally published by ASTM International as ASTM F1617-95; previously published July 2010.
NOTICE: This Document was reapproved with minor editorial changes.
Secondary ion mass spectrometry (SIMS) can measure on polished silicon wafer product the following:
- the sodium and potassium areal densities that can affect voltage flatband shifts in integrated circuits, and,
- the aluminum areal density that can affect the thermal oxide growth rate.
- the iron areal density that can affect gate oxide integrity, minority carrier lifetime, and current leakage.
The SIMS measurement facilitates the production of silicon wafers with upper control limits on sodium, potassium, aluminum, and iron areal densities.
This Test Method can be used for monitoring a mirror-polished wafer cleaning process, for research and development, and for materials acceptance purposes.
This Test Method can provide spatial information for these metal contaminants, including near-edge substrate contamination levels.
This Test Method is especially useful for determining the surface metal areal densities in the native oxide or chemically grown oxide of polished silicon substrates after cleaning.
This Test Method covers the determination of total sodium, aluminum, potassium, and iron on the surface of mirror-polished single crystal silicon and silicon epi substrates using SIMS. This Test Method measures the total amount of each metal, because this test method is independent of the metal's chemistry or electrical activity.
This Test Method can be used for silicon with all dopant species and dopant concentrations.
This Test Method is especially designed to be used for surface metal contamination that is located within approximately 5 nm of the surface of the wafer.
This Test Method is useful for sodium, aluminum, potassium, and iron areal densities between 109 and 1014 atoms/cm2. The limit of detection is determined by either the BLANK value or by count rate limitations, and may vary with instrumentation.
This Test Method is complementary to:
Total reflection X-ray fluorescence (TXRF), that can detect higher atomic number Z, surface metals such as iron, but does not have useful (<1011 atoms/cm2) detection limits for sodium, potassium, and aluminum on silicon.
Vapor phase decomposition (VPD) of surface metals followed by atomic absorption spectroscopy (AAS) or inductively coupled plasma mass spectrometry (ICP-MS) of the VPD residue, where the metal detection limits are 108 to 1010 atoms/cm2. There is no spatial information available and the VPD pre-concentration of metals is dependent upon the chemistry of each metal.
Referenced SEMI Standards