RESUMO
In this work, we developed a drop-type chemiluminescence (CL) system with a partial least squares (PLS) calibration in which the coaxial optical fiber sensing head was developed for sampling and detection to determine Cu(2+) and Co(2+) on a silicon wafer directly. The use of time-resolved signal generation and PLS calibration in addition to CL allowed us to determine the metal ions simultaneously and selectively, based on the kinetic difference of Cu and Co ions in the luminol-H(2)O(2) system. Two component mixtures with a set of 15 wafer fragments were orthogonally calibrated. After prediction test, the method was applied to an intentionally contaminated silicon wafer and validated by inductively coupled plasma-mass spectrometer (ICP-MS) measurement with a HF-HNO(3) scanning solution. The average concentrations of Cu(2+) and Co(2+) of 3.45 (±0.95) × 10(13) and 2.30 (±1.18) × 10(11) atoms per cm(2), respectively, were obtained, which were very close to the ICP-MS results of 3.70 × 10(13) for Cu(2+) and 2.46 × 10(11) atoms per cm(2) for Co(2+). In conclusion, this drop mode CL showed almost more than 10 times better reproducibility than the typical batch mode for the profile measurement. Moreover, the adoption of PLS calibration added the function of selectivity for the simultaneous determination to this CL system, in addition to the direct mapping capability for the solid surface analysis.
RESUMO
A highly sensitive chemiluminescence (CL) system which consumed low sample and reagent volumes in the microlitre range was developed for direct determination and mapping of ultra-trace metal contaminants on solid surfaces, such as silicon wafers or flat display panels. The analytical result of the system was confirmed with ICP-MS. The system was composed of a scanner, sensor and a wafer moving stage. The scanner, with a scanning tip made of 0.03'' i.d. PTFE tubing, was used to collect metal impurities on the wafer surface with 5 µL of scanning solution. A coaxial sensing head of about 13 mm o.d. and 110 mm height was designed both to inject a luminescent reagent of luminol-H(2)O(2) mixture and to collect the luminescence light resulting from the reaction with metal ions of Co(2+), Fe(2+), Cu(2+), and Ni(2+). Due to the almost zero background, an extremely low limit of detection of 20.8 pg/mL for Co(2+) in 1% hydrofluoric acid (HF) was obtained from the calibration curve. In order to map the spatial distribution of the impurities, 11 cross sections of a Co-contaminated wafer were selected and scanned individually with a diluted HF solution. A contaminant level of 1.45-7.11 × 10(11) atoms cm(-2) was obtained for each section with an average of 4.21 × 10(11) atoms cm(-2), which was similar to the analytical result of 5.48 × 10(11) atoms cm(-2) obtained from vapor phase deposition-inductively coupled plasma-mass spectrometry (VPD-ICP-MS). Although this CL system does not have selectivity for each specific metal ion, its high sensitivity facilitates the monitoring and mapping of metal impurities of Co, Fe, Cu, etc. on the wafer directly and it can be used as an on-line inspection sensor for the first time in the semiconductor industry.
