- SEMI MF81 - Test Method for Measuring Radial Resistivity Variation on Silicon Wafers
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 March 2016; originally published by ASTM International as ASTM F81-67T; previously published June 2011.
NOTICE: This Document was reapproved with minor editorial changes.
The radial resistivity variation of bulk semiconductor material is an important materials acceptance requirement for semiconductor device fabrication and is also used for quality control purposes.
The four-point probe method provides a test that requires little specimen preparation and that is nondestructive in that the wafer is left intact. The method can be applied to wafers using the resistivity-measuring apparatus and procedures of SEMI MF84 if provisions are made for making measurements at several sites on the wafer (see ¶ 7.1). Appropriate correction factors must be applied to compensate for effects of the wafer geometry (see ¶ 12.1).
Radial resistivity variations are a function of the crystal growth process and dopant, in both characteristic shape and magnitude. Because no single sampling plan is adequate to characterize the resistivity variations of all crystal types or for all applications, four sampling plans are included in this test method.
This Test Method provides procedures for the determination of relative radial variation of resistivity of semiconductor wafers cut from silicon single crystals grown either by the Czochralski or floating-zone technique.
This Test Method provides procedures for using SEMI MF84 for the four-point probe measurement of radial resistivity variation.
This Test Method yields a measure of the variation in resistivity between the center and selected outer regions of the specimen. The amount of information obtained regarding the magnitude and form of the variation in the intervening regions when using the four-point probe array depends on the sampling plan chosen (see ¶ 8.2). The interpretation of the variations measured as radial variations may be in error if azimuthal variations on the wafer or axial variations along the crystal length are not negligible.
This Test Method can be applied to single crystals of silicon in circular wafer form, the thickness of which is less than one-half of the average probe spacing, and the diameter of which is at least 15 mm (0.6 in.). Measurements can be made on any specimen for which reliable resistivity measurements can be obtained. The resistivity measurement procedure of SEMI MF84 has been tested on specimens having resistivities between 0.0008 and 2000 Ω·cm for p-type silicon and between 0.0008 and 6000 Ω·cm for n-type silicon. Geometrical correction factors required for these measurements are included for the case of standard wafer diameters, and are available in tabulated form for other cases.
Several sampling plans are given that specify sets of measurement sites on the wafers being tested. The sampling plans allow differing levels of detail of resistivity variation to be obtained. One of these sampling plans is selected and agreed upon by the parties to the measurement (see ¶ 8.1).
Referenced SEMI Standards
SEMI M1 — Specification for Polished Single Crystal Silicon Wafers
SEMI M59 — Terminology for Silicon Technology
SEMI MF84 — Test Method for Measuring Resistivity of Silicon Slices with a Collinear Four-Probe Array
SEMI MF2074 — Guide for Measuring Diameter of Silicon and Other Semiconductor Wafers