Determination of sub-parts per billion boron contamination in N⁺ Czochralski silicon substrates by SIMS

Microelectronic devices fabricated in silicon epitaxial layers on heavily doped substrates are less prone to latch-up and alpha-particle-induced soft errors. Unfortunately, trace amounts of boron in N⁺ antimony-doped silicon substrates can cause deleterious effects. Attempts to measure this boron contamination by conventional electrical methods have failed because of the high Sb concentration. Secondary ion mass spectrometry (SIMS) is an extremely sensitive method capable of detecting sub-parts-per-billion boron contamination and the results are not affected by high Sb doping concentrations. A well-designed SIMS experimental protocol has been developed to yield routine detection limits below 10¹³ atom/cm³. Based on the statistics obtained from a control sample, the analytical precision is ±8% at a boron concentration of 1.7×10¹⁴ atom/cm³. SIMS thus provides the required sensitivity and reliability for this important measurement.