- SEMI MF1188 - Test Method for Interstitial Oxygen Content of Silicon by Infrared Absorption With Short Baseline
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 F1188; previously published September 2012.
The presence of oxygen can be beneficial to certain manufacturing operations by preventing the formation of process-induced defects. Oxygen is introduced into silicon wafers during the crystal growing process. Hence, it is important to control the oxygen content of silicon crystals.
Measurement of the intensity of the 1107 cm-1 oxygen-in-silicon band with an infrared spectrophotometer enables the determination of the value of the absorption coefficient and, hence, by the use of a calibration factor or linear regression curve, the content of interstitial oxygen.
This Test Method can be used as a referee method for determining the interstitial oxygen content of silicon slices. Knowledge of the interstitial oxygen content of silicon wafers is necessary for materials acceptance and control of fabrication processes, as well as for research and development.
This Test Method covers the determination of the interstitial oxygen content of single crystal silicon by measurement of an infrared absorption band at room temperature, using a short baseline drawn between 1040 and 1160 cm- 1 to reduce the uncertainties due to perturbations in the IR absorption at the end-point regions of longer baselines that arise from effects other than absorption by interstitial oxygen. Use of the short baseline results in improved precision of the method.
For historical reasons, the long baseline method is being retained in Appendix 1 in the form published in the 1993a edition of this Test Method. This baseline was also used in ASTM F121, the predecessor to this Test Method, and in the analysis of infrared data from the grand round robin (GRR) experiment.
This Test Method requires the use of a computerized spectrophotometer, preferably a Fourier transform infrared (FT-IR) spectrophotometer. This method is incorporated into many modern FT-IR instruments.
This Test Method requires the use of an oxygen-free reference specimen.
It is recommended that a reference material set, such as NIST SRM 2551, another certified reference material set for oxygen content of silicon, or reference materials traceable to the certified reference materials (CRMs), be used to calibrate the spectrophotometer in order to reduce bias.
The useful range of oxygen concentration measurable by this Test Method is from 1 × 1016 atoms/cm3 to the maximum amount of interstitial oxygen soluble in silicon.
If the spectrophotometer is calibrated using 2 mm thick double side polished CRMs, this Test Method is suitable for use only with 2 mm thick, double side polished test specimens. It can be extended to the measurement of test specimens polished on one or both sides with thickness in the range 0.4 to 4 mm with the use of working reference materials traceable to the double side polished CRMs.
The oxygen concentration obtained using this Test Method assumes a linear relationship between the interstitial oxygen concentration and the absorption coefficient of the 1107 cm-1 band associated with interstitial oxygen in silicon.
The recommended calibration factor to convert absorption at 1107 cm- 1 to oxygen content is IOC-88, which is based on the analysis of the international GRR experiment.
Referenced SEMI Standards
SEMI C29 — Specification and Guide for 4.9% Hydrofluoric Acid 10:1 v/v
SEMI M44 — Guide to Conversion Factors for Interstitial Oxygen in Silicon
SEMI M59 — Terminology for Silicon Technology