- SEMI MF95 - Test Method for Thickness of Lightly Doped Silicon Epitaxial Layers on Heavily Doped Silicon Substrates Using an Infrared Dispersive Spectrophotometer
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 F95; previously published October 2012.
The thickness of the epitaxial layer is an important process control and materials acceptance requirement for silicon epitaxial wafers.
This Test Method provides a technique for the measurement of the thickness of epitaxial layers of silicon deposited on silicon substrates.
This Test Method is suitable for reference measurements.
This Test Method is a manual technique that requires the use of a dispersive infrared spectrophotometer. For this measurement, the resistivity of the substrate must be less than 0.02 Ω·cm at 23°C and the resistivity of the layer must be greater than 0.1 Ω·cm at 23°C. A brief description of the theory of this Test Method is given in Related Information 1.
This technique is capable of measuring the thickness of both n- and p-type layers greater than 2 µm thick. With reduced precision, the technique may also be applied to both n- and p-type layers from 0.5 to 2 µm thick.
Automated test systems, utilizing Fourier-transform infrared spectrophotometry (FT-IR), are now widely used for epitaxial layer thickness measurements. Because such instruments are normally supplied with proprietary software for measurement analysis, detailed procedures for the use of such instruments are not included in this Test Method. However, for information purposes, estimates of single instrument repeatability and multi-instrument reproducibility, based on a 1986/1987 multilaboratory comparison of FT-IR instrument measurements are given in Note 6 and Related Information 2.
Procedures for preparing the specimen, for measuring its size, and for determining the temperature of the specimen during the measurements are also given.
Referenced SEMI Standards
SEMI M59 — Terminology for Silicon Technology
SEMI MF84 — Test Method for Measuring Resistivity of Silicon Wafers with an In-Line Four-Point Probe