- SEMI MF673 - Test Method for Measuring Resistivity of Semiconductor Wafers or Sheet Resistance of Semiconductor Films with a Noncontact Eddy-Current Gauge
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 2, 2017. Available at www.semiviews.org and www.semi.org in March 2017; originally published by ASTM International as ASTM F673-80; previously published October 2014.
Resistivity is a primary quantity for characterization and specification of material used for semiconductor electronic devices. Sheet resistance is a primary quantity for characterization, specification, and monitoring of thin film fabrication processes.
This Test Method outlines the principles of eddy-current measurements as they relate to semiconductor substrates and certain thin films fabricated on such substrates as well as requirements for setting up and calibrating such instruments for use particularly at a buyer-seller interface.
An eddy-current instrument directly measures conductance of a specimen. Values of sheet resistance and resistivity are calculated from the measured conductance, with the resistivity values also requiring a measurement of specimen thickness.
This Test Method covers the nondestructive measurement of bulk resistivity of silicon and certain gallium-arsenide wafers and of the sheet resistance of thin films of silicon or gallium-arsenide fabricated on a limited range of substrates at the wafer center point using a noncontact eddy-current gauge.
This Test Method is presently limited to single-crystal and polycrystalline silicon and extrinsically conducting gallium-arsenide bulk specimens or to thin films of silicon or gallium-arsenide fabricated on relatively high resistivity substrates but in principle can be extended to cover other semiconductor materials.
The bulk silicon or gallium-arsenide specimens may be single crystal or polycrystalline and of either conductivity type (p or n) in the form of wafers (round or other shape) that are free of diffusions or other conducting layers that are fabricated thereon, that are free of cracks, voids or other structural discontinuities, and that have (1) an edge-to-edge dimension, measured through the center point of the wafer, not less than 25 mm; (2) thickness in the range 0.1 mm to 1.0 mm, inclusive, and (3) resistivity in the range 0.001 Ω·cm to 200 Ω·cm, inclusive. Not all combinations of thickness and resistivity may be measurable. The instrument is fundamentally limited to a fixed sheet resistance range, such as that given in ¶ 2.2.2.
The thin films of silicon or gallium-arsenide may be fabricated by diffusion, epitaxial or ion implant processes. The sheet resistance of the layer shall be in the nominal range from 2 Ω to 3000 Ω per square. The substrate on which the thin film is fabricated shall have a minimum edge to edge dimension of 25 mm, measured through the center point and an effective sheet resistance at least 1000 times that of the thin film.
This Test Method requires no specimen preparation. Measurements are not affected by specimen surface finish.
This Test Method requires the use of resistivity standards to calibrate the apparatus (see ¶ 7.1), and a set of reference specimens for qualifying the apparatus (see ¶ 7.1.1).
Two test methods are covered by this Standard.
Method I ascertains the conformance of the apparatus to linearity and slope limits (±1 digit) over a broad range (2 decades) of calibration standard values. It qualifies apparatus for use over a wide range of sample values.
Method II assumes instrument linearity between calibration standards whose values are narrowly separated (typically ±25% of the anticipated sample range median point). Method II is particularly well suited to computer-based systems where all measurements can be quickly and automatically corrected for value offset and for temperature coefficient of resistivity.
Referenced SEMI Standards
SEMI M59 — Terminology for Silicon Technology
SEMI MF81 — Test Method for Measuring Radial Resistivity Variation on Silicon Wafers
SEMI MF84 — Test Method for Measuring Resistivity of Silicon Wafers with an In-Line Four-Point Probe
SEMI MF374 — Test Method for Sheet Resistance of Silicon Epitaxial, Diffused, Polysilicon, and Ion-Implanted Layers Using an In-Line Four-Point Probe with the Single-Configuration Procedure
SEMI MF533 — Test Method for Thickness and Thickness Variation of Silicon Wafers
SEMI MF1527 — Guide for Application of Certified Reference Materials and Reference Wafers for Calibration and Control of Instruments for Measuring Resistivity of Silicon