AVS 45th International Symposium
    Applied Surface Science Division Thursday Sessions
       Session AS-ThA

Invited Paper AS-ThA3
TOF-SIMS Depth Profiling of Novel Si Devices

Thursday, November 5, 1998, 2:40 pm, Room 307

Session: SIMS - Depth Profiling and Molecular Surface Analysis
Presenter: J.G.M. van Berkum, Philips CFT - Materials Analysis, The Netherlands
Authors: J.G.M. van Berkum, Philips CFT - Materials Analysis, The Netherlands
P.C. Zalm, Philips CFT - Materials Analysis, The Netherlands
Correspondent: Click to Email
Since about two years, concentration depth profiles of dopants in e.g. Si are not only measured with magnetic-sector SIMS or quadrupole SIMS, but also with time-of-flight (TOF) SIMS. In this technique, two ion sources are operated alternatingly: (i) a short-pulsed high-energy ‘analysis’ beam (typically 800 ps 11 keV Ar@super +@) produces secondary ion mass spectra and (ii) in between the pulses a low-energy ‘sputter’ beam (typically <1 keV O@sub 2@@super +@ or Cs@super +@) erodes the surface. The ion beam mixing is (almost) completely determined by the energy of the sputter beam. Therefore, a very good depth resolution can be obtained without concessions to the analysis beam. High mass resolution (up to M/@DELTA@M=10.000) can be maintained due to the short pulse length and imaging during the depth profile with a lateral resolution down to 100 nm is possible. Thanks to the simultaneous mass detection, TOF-SIMS is particularly useful for devices with ultra-steep dopant profiles in the presence of other dopants or in devices with oxide layers or SiGe hetero-epitaxial layers. For example, for understanding the electrical behaviour of Schottky diodes or tunnel diodes with a high concentration of one or two dopants in an ultra-thin SiGe layer, it is essential to measure the dopant and the Ge concentrations at exactly the same depth. The same holds for CMOS devices with SiGe channel (typically a few nm’s of SiGe at a few nm’s distance from the gate oxide) or bipolar transistors with hetero-epitaxial base. The optimum condition for such measurements may differ from the optimum conditions for the elements separately. For B, P, As and Ge in Si, we often use O@sub 2@@super +@ primary ions, positive secondary ions and oxygen flooding to enhance the ion yields and suppress the pre-equilibrium effects. The segregation of Ge due to oxygen flooding is quantified by comparative measurements using different measurement conditions.