Finding the impurities
13 Jun 2003
Agilent Technologies has announced a sensitive method for determining inorganic impurities in semiconductor-grade sulphuric acid using inductively coupled plasma mass spectrometry (ICP-MS).
Sulphuric acid is an important material used in the manufacture of semiconductor devices and the new ICP-MS method can identify impurities at the 5 parts-per-trillion level.
Trace metal impurities in semiconductor components are a major cause of device failures. Reagents used in the production process are a significant source of contamination, so reagent vendors are continually working to develop products with lower levels of impurities.
Sulphuric acid (H2SO4) is commonly used to clean wafer surfaces and is available with very low levels of impurities (<1 ug/L). The determination of impurities at these levels is challenging because the high viscosity and high boiling point of sulphuric acid make analysis, directly on the material, difficult.
Older methods involve removal of the sample matrix by evaporation before analysis, an approach that is both time consuming and increases the chance of contamination. Another difficulty is the presence of plasma- and matrix-based polyatomic compounds in the H2SO4 that interfere with ultratrace analysis using conventional quadrupole ICP-MS.
The new method uses the Agilent 7500cs ICP-MS, featuring a highly sensitive version of Agilent's Octopole Reaction System (ORS). The ORS eliminates all plasma- and matrix-based interferences for elements such as K, Ca, Ti, Cr, Fe, Co, Ni, Cu and Zn and provides excellent ion transmission and sensitivity.
Sample preparation consists of a simple dilution with water followed by direct analysis. This method shortens analysis time and reduces the potential for sample contamination frequently encountered with evaporative matrix elimination techniques.
The system can measure all analytes at high plasma power to promote complete decomposition of the s sulphuric acid in the plasma, creating high signal stability and reducing the frequency of routine maintenance. All analytes are measured on mass, in a single analytical run, with typical total analysis time of four minutes.
