IMPURITY DETERMINATION IN ELECTRONIC MATERIALS BY ACCELERATOR MASS-SPECTROMETRY

An Accelerator Mass Spectrometry (AMS) facility has been developed in the Ion Beam Modification and Analysis Laboratory (IBMAL) at the University of North Texas (UNT) through a collaboration between UNT, Texas Instruments, Inc., the National Science Foundation, and the Office of Naval Research. The computer-controlled AMS instrument. which allows automated mass scans of stable isotopes in solid materials, removes molecular interferences which are present in Secondary Ion Mass Spectrometry (SIMS) allowing higher sensitivities for some elements than SIMS. A new low sample-contamination, raster-scanning, depth-profiling ion source has been constructed for this AMS facility. This source coupled to the AMS system should provide sensitivities of ppt (1 part in 10(12) or 10(10) atoms/cm3) for many elements in the periodic table. The AMS system design is discussed including ion generation with the new ion source, ion analysis with the tandem accelerator and spectrometer, and ion detection hardware and software. Each of these functions may be viewed as a sub-assembly with a dedicated IBM computer controlling the appropriate functions. Results using the AMS facility to characterize trace element impurities in Si and CdZnTe electronic materials are discussed.