NDT profiling of dopants and photoconductivity in si with high spatial resolution using evanescent microwave probes

摘要

According to the semiconductor industry road-map, nondestructive metrology tools are very desirable and crucial to the continued growth of the industry in the next 5 years. A variety of local probe based tools based on scanning tunneling microscope, such as micro-Kelvin probe and scanning tunneling microscope are being developed to address some of the issues in ultralarge scale integrated circuits (ULSI). In ULSI the gate length is less than 0.25 mum that necessitates very shallow junction depths (500A) with very large doping concentrations (10~(19) cm~(-3)) with lateral extensiosn of = 0.1-1 mum. Measuring the doping concentration in these ultra shallow junctions is quite chalenging since the number of doping atoms (10~(19)x500x10~(-8)x10~(-4) x 10~(-4)) is around 5x10~5 inside the junction under the best of the circumstances. Thus, the measuring probe should be able to detect 5x10~5 impurity atoms in the background of 10~9 background silcon atoms (concentration approx approx 10~(23) cm~(-3)). This requires a detection capability of 1 in 2000 over a very small volume. There are other problems as well. The total number of impurity atoms may considerably vary from one junction to another junction due to random fluctuations.