Long term reproducibility of secondary ion mass spectroscopy measurements in silicon

Abstract

The long term reproducibility of quantitative secondary ion mass spectroscopy (SIMS) analysis is assessed using three independent analytical procedures important to the microelectronics industry: the determination of oxygen, boron, and surface impurities in silicon. Thousands of measurements acquired from carefully selected statistical process control samples provide an excellent data base. The oxygen measurement yields a repeatability of +2% at a concentration of 28 ppma (instrumental background around 1.4 ppma). A relative standard deviation of 8.3% is achieved for the boron measurement. The boron concentration in the control sample is 5.8 ppba. Many different control samples have been monitored for surface SIMS contamination measurements, and the RSD ranges from 5% to over 100% depending on the element and magnitude of the areal densities. Our results indicate that SIMS is an excellent technique for long-term process control when rigorous analytical protocols are adopted. The oxygen and boron measurements as well as the measurement of surface sodium, aluminum, and potassium on silicon have been accepted by ASTM as standard procedures. Our analytical protocols have been extended to depth profiling analysis, such as ion implanter dose matching which is an important measurement for the semiconductor industry.