- 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
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, 2018. Available at www.semiviews.org and www.semi.org in July 2018; originally published by ASTM International as ASTM F374-74T; previously published March 2012.
NOTICE: This Document was reapproved with minor editorial changes.
The sheet resistance of silicon epitaxial, diffused, and implanted layers is an important materials acceptance and process control parameter. The sheet resistance measurement may be used by itself or may be combined with a value of layer thickness, obtained separately, to obtain an estimate of the resistivity of an epitaxial or polysilicon layer or of the surface concentration of dopant for diffused layers.
This Test Method is suitable for use in materials acceptance, manufacturing control, research, and development.
This Test Method covers the direct measurement of the average sheet resistance of thin layers of silicon formed by epitaxy, diffusion, or implantation onto or below the surface of a circular silicon wafer having the opposite conductivity type from the thin layer to be measured or by the deposition of polysilicon over an insulating layer. Measurements are made at the center of the wafer using a single-configuration of the four-point probe. In this configuration, the current is passed through the outer pins and the resulting potential difference is measured with the inner pins.
This Test Method applies to circular samples with diameter greater than 15.9 mm (0.625 in.).
This Test Method is known to be applicable on films having thickness at least 0.2 µm. It can be used to measure sheet resistance in the range 10 to 5,000 Ω, inclusive.
The principle of this Test Method can be extended to cover lower or higher values of sheet resistance; however, the precision of the method has not been evaluated for sheet resistance ranges other than those given in ¶ 2.3.
Procedures for preparing the specimen, for measuring its size, and for determining the temperature of the specimen during the measurement are also given. Abbreviated tables of correction factors appropriate to circular geometry are included with the method so that appropriate calculations can be made conveniently.
This Test Method includes procedures for checking both the probe head and the electrical measuring apparatus.
The spacing between the four probe tips is determined from measurements of indentations made by the probe tips in a polished silicon surface. This test also is used to determine the condition of the probe tips.
The accuracy of the electrical measuring equipment is tested by means of an analog circuit containing a known standard resistor together with other resistors that simulate the resistance at the contacts between the probe tips and the semiconductor surface.
The values stated in SI units are to be regarded as the standard. Any values given in parentheses are for information only.
Referenced SEMI Standards
SEMI C19 — Specification for Acetone
SEMI C28 — Specification and Guide for Hydrofluoric Acid
SEMI C31 — Specification for Methanol
SEMI C59 — Specification for Nitrogen
SEMI M59 — Terminology for Silicon Technology
SEMI MF42 — Test Method for Conductivity Type of Extrinsic Semiconducting Materials
SEMI MF1529 — Test Method for Sheet Resistance Uniformity Evaluation by In-Line Four-Point Probe with the Dual-Configuration Procedure
SEMI MF2074 — Guide for Measuring Diameter of Silicon and Other Semiconductor Wafers