Quantitative secondary ion mass spectrometry (SIMS) of III-V materials

Abstract

Secondary ion mass spectrometry (SIMS) provides direct methods to characterize the chemical composition of III-V materials at major, minor and trace level concentrations as a function of layer depth. SIMS employs keV primary ions to sputter the surface and sensitive mass spectrometry techniques to mass analyze and detect sputtered secondary ions which are characteristic of the sample composition. In-depth compositional analysis of these materials by SIMS relies on a number of its unique features including: (1) keV primary ion sputtering yielding nanometer depth resolutions, (2) the use of MCs + detection techniques for quantifying major and minor constituents, and (3) ion implant standards for quantifying trace constituents like dopants and impurities. Nanometer depth resolution in SIMS sputtering provides accurate detection of diffusion of dopants, impurities and major constituents. MCs + refers to the detection of molecular ions of an element (M) and the Cs + primary beam. MCs + minimizes SIMS matrix effects in analysis for major and minor constituents, thus providing good quantification. This paper presents a SIMS study of Al x Ga (1-x )As structures with three different x values. MCs + (M=Al or Ga) data are presented for the accurate determination of major and minor components. Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD) data were cross-correlated with the MCs + results. Three specimens with different x values were ion implanted with H, C, O, Mg, Si, Zn and Se to study quantification of trace levels. SIMS data acquired on a double focusing instrument (CAMECA IMS-4f) and a quadrupole instrument (PHI ADEPT 1010) are also compared. Lastly, we discuss our efforts to improve the analysis precision for p- and n-type dopants in AlGaAs which currently is +/- 3% (1 sigma).