Ultra-shallow junction depth profile analysis using TOF-SIMS and TXRF

The drive to fabricate ever shallower source/drain and channel junctions in DRAM and microprocessor production constitutes a great challenge for their analytical characterization. Ultra-shallow SIMS profiling requires high depth resolution and a small surface transient region. It also has to account for the interface between the native oxide and the Si bulk. We have investigated the shallow depth profiling capabilities of TOF-SIMS and TXRF. TOF-SIMS is well established for high sensitivity microarea surface analysis. The technique features high mass resolution, high transmission and a parallel mass registration. Depth profiles are performed in the dual beam mode allowing an independent optimization of the analyzing and sputtering ion beam. The application of a low energy SF5+ sputtering ion beam provides depth resolution in the 0.5 nm range and minimizes the width of the near surface transient region. When depth profiling silicon, the oxidation state of the receding surface can be derived from the intensities of the positive secondary ion intensities Si2On+ (n=0....4). This allows the correction of changes in erosion rate and relative sensitivity factors which are caused by a varying surface oxidation state. For instance, such a variation of the surface oxidation state always occurs in the near surface region. The detection of the interface between the native oxide and the Si bulk and constant sputter and ion yields at this interface are accomplished by the incorporation of O-18. TXRF has proved to be a powerful technique for the analysis of metallic contaminations on wafer surfaces. One of the advanced applications of this technique is the characterization of ultra-shallow implant profiles. In contrast to the SIMS technique, TXRF provides only an integral value of implants for a near surface layer of some nm thickness. But TXRF is non-destructive, and, therefore, it can be used as a rapid in-fab characterization technique.