Within the context of Metrology, “Traceability” indicates that the results of a measurement -- or a series of measurements -- are in a known, valid, and authenticated relationship to internationally recognized standards and, that a thoroughly documented, unbroken chain of reference is established to a specific measurement authority.

The following methods relate to PSI Traceability -- Mainly to the United States National Standardization Authority -- The NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY (NIST).

1. Calibration of metrology tools and measurement instruments, using NIST Standard Reference Material (SRM).

2. Measurements and certification using NIST methods and same apparatus.

3. Measurement and analysis using well-established, scientific FIRST PRINCIPLES, and CONSTANTS OF NATURE.

4. Artifacts submitted to NIST for calibration and certification by their laboratories.

5. Calibration in accordance with INDUSTRY STANDARDS, implying a rigorous adherence to industry standard methods, practices, procedures and definitions, such as ASTM or ANSI/NCSL Z540.1 methods.

This method provides what is defined as a “consensus traceability” through the rigorous application of test and measurement methods. These protocols and methodology have been developed by expert groups, and subjected to inter-laboratory comparisons and statistical analysis.

Most often, new SRM are developed in this way, such as ultra thin film thickness standards and nitride standards.

By far, the most understood method is Method 1, in which a laboratory acquires SRM from NIST or another internationally recognized authority, and uses these as primary standards for the calibration of instruments.

PSI Film thickness standards are most frequently rendered traceable via a combination of at least 4 of the above methods. PSI uses NIST SRM material to calibrate and monitor internal metrology equipment, which in turn is used in measuring and establishing “secondary standards”. In addition PSI Standards is ISO/IEC 17025 Accredited by NVLAP/NIST, and is a nationally recognized calibration laboratory. Lab code: 200669-0.

Ellipsometry is by far the most reliable and accurate measurement technique for producing secondary standards for various reasons:

1. It is the technique used by NIST to create and develop a film thickness SRM. A research grade ellipsometer can be easily configured to reproduce the exact measurement conditions of NIST (AOI -- or Angle of Incidence -- and wavelength), with comparable accuracy and precision.

2. The measurement of the changes in polarization state-of-light (Delta and Psi) are straight forward, and directly comparable to those of NIST.

3. The calibration of the instrument and measurements are based on Scientific First Principle – the fundamental properties of light.

4. The calculations of the derived values are based upon the same mathematical model that is used by NIST.

5. The nominal values of the standards manufactured by PSI are selected to ensure that the Delta and Psi values are as close to identical as those of the SRMs manufactured by NIST. This ensures that the nominal thickness and index values are the same as –or multiples of – the primary standards issued by NIST.

6. The conceptual and mathematical models used to convert the measured values to useful, physical data are the same as the ones mandated by NIST.

The physical standards made by PSI Standards are manufactured from identical or superior materials, in identical or superior conditions, as are the ones produced by NIST - thermally grown Silicon Dioxide or LPCVD Silicon Nitride on Prime grade P type <100> Silicon wafers, in a sub “Class 10” Semiconductor Fab.




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