Depth profiling of ultratrace chromium, iron, nickel, and copper in silicon wafers by electrothermal vaporization/ICP-MS

• Published in: BUNSEKI KAGAKU Vol. 43; no. 2; pp. 173 - 176
• Main Authors: TOMITA, Mitsuhiro, TAKENAKA, Miyuki, MATSUNAGA, Hideki, TSUCHIYA, Norihiko, KUBOTA, Atsuko
• Format: Journal Article
• Language: English; Japanese
• Published: Tokyo The Japan Society for Analytical Chemistry 01.02.1994; Nippon Bunseki Kagakkai; Japan Science and Technology Agency
• Subjects: chromium; depth profiling; electrothermal vaporization/ICP-MS; iron; nickel; silicon wafer
• ISSN: 0525-1931
• DOI: 10.2116/bunsekikagaku.43.173

A method of etching micro thin layers for silicon wafers by a wet chemical technique has been developed. Ultratrace concentrations of Cr, Fe, Ni, and Cu in the etching solution were determined by electrothermal vaporization ICP-MS (ETV/ICP-MS). Silicon wafers 0.01 to 10μm thick could be dissolved by controlling the acidities of HF and HNO3 in the etching solution. The thickness was calculated from the Si concentration of the etching solution by ordinary spectrophotometry using the Molybdenum Blue method. Silicon wafers were etched by 10 ml of acid solutions containing appropriate concentrations of HF and HNO3. After the etching process, an aliquot of the solution was used for Si measurement. The rest was dried, dissolved in water and then subjected to elemental analysis by ETV/ICP-MS. The micro depth profiling of Cr, Fe, Ni, and Cu of a reference sample was done using the proposed method and showed good agreement with that obtained by SIMS. When a few practical silicon wafer samples were also analyzed by this method, it was found that different types of silicon wafer had clearly different depth profiles of elements. The detection limits were 0.005 ng/g for Cu and Ni, and 0.01 ng/g for Cr and Fe.