Heavy‐Ion Backscattering Spectrometry

Abstract

AbstractHeavy‐ion backscattering spectrometry (HIBS) is a new technique for nondestructively analyzing ultratrace levels of impurities on the surface of very pure substrates. Although any high‐Zcontaminant (Z≥ 18) on a pure low‐Zsubstrate can be measured, recent practical applications for HIBS have focused on measuring contaminants found on silicon wafers used in semiconductor manufacturing. Therefore, discussions of HIBS focus in this area. The technique is based on the same principles described for high‐energy Rutherford backscattering spectrometry (RBS) and medium‐energy ion backscattering spectrometry.The motivation for HIBS is to detect metallic contamination at levels significantly below those that can be detected by RBS or medium‐energy ion backscattering, both of which have a limit of ∼1 × 1013atoms/cm2for near‐surface impurities. It had been reported that contamination control in the microelectronics industry will require tools that can measure ∼1 × 1010atoms/cm2for transition metals in starting material. The detection limit for well‐separated elements on a clean Si surface ranges from ∼6 × 109atoms/cm2for Fe to ∼3 × 108atoms/cm2for Au, without the use of vapor phase decomposition (VPD) to preconcentrate the impurities. Using VPD would improve the sensitivity by at least an order of magnitude.The HIBS technique is illustrated Other surface analysis techniques for detection of trace element contamination are briefly discussed, with the strengths and weaknesses of each compared to those of HIBS. A detailed discussion of the basic theoretical and practical aspects of HIBS is provided.