Determination of Trace Amounts of Boron in Silicon and Germanium by Curcumin Spectrophotometry after Methyl Borate Distillation

A high-sensitivity, high-precision analytical method was developed to determine trace amounts of boron in silicon or germanium semiconductor materials. Silicon was dissolved with a mixture of hydrofluoric acid and nitric acid, while germanium was dissolved with aqua regia. In order to prevent boron from being vaporized by heating in hydrofluoric acid, phosphoric acid and sulfuric acid were added to the solution. After the sample solution was thoroughly dehydrated by heating, silicon was vaporized as SiF₄; however, germanium remained as a white precipitate (GeO₂). By the addition of methyl alcohol to the dehydrated sample solution and subsequently heating it, boron could be separated as methyl borate from the sample solution. The resulting methyl borate was absorbed in a sodium hydroxide solution, and then boron was determined by a curcumin spectrophotometric method. The recoveries of boron after distillation were almost 100% in both silicon and germanium. The detection limit of boron was 0.1 ppm in silicon and germanium.