Deuteron activation analysis of ultra-trace carbon in boron-doped Si single crystals

The charged particle activation analysis of ultra-trace carbon in boron-doped silicon with the¹²C(d,n)¹³N reaction has been developed. In order to apply¹³N substoichiometric separation to determine carbon in silicon, we studied the rapid dissolution of silicon using nitric acid as the¹³N carrier. Its amounts were as small and definite as possible and the nitrogen oxide gas produced during the dissolution was collected. Silicon was dissolved for 6 min in a mixture of hydrofluoric acid, acetic acid and phosphoric acid, which contained potassium nitrate as the¹³N carrier and nitrogen oxide was collected in the sodium hydroxide solution. In order to combine the dissolution method with¹³N substoichiometric separation, the conditions for steam distillation as pre-separation were also refined in relation to increases in the amount of carrier. Nitrogen-13 was separated substoichiometrically after silicon dissolution and steam distillation. This analytical procedure was used to determine carbon in boron-doped CZ–Si. Carbon at 0.7–12.7·10¹⁵ atoms/cm³ was determined with good reproducibility. It took less than 30 min to start the radioactivity measurement after the end of iradiation. The detection limit was 2·10¹³ atoms/cm³ (0.2 ppb).