| For the design of deep sub-micron MOS devices, in which short channel effects are significant, the 2D doping and carrier profiles in the well and in the source/drain extension regions must be well characterized. To profile these regions, we propose a tunneling based approach, Scanning Tunneling Microscopy and Spectroscopy (STM/STS). This technique shows sensitivity to the carrier concentration, and its lateral resolution is not compromised by the tip radius.; Measurements are taken on Si(100)-2x1:H surfaces containing lateral variations in the dopant profile. We outline sample fabrication and subsequent cleaning and passivation steps to create a well reconstructed and passivated surface. To ensure that tips are similar in shape, we propose in situ methods to monitor and restore the tip condition. Measurements at an atomic length scale underscore the importance of taking into account the fine electronic structure of the surface. We demonstrate that STM/STS is capable of profiling a pn junction with sub-nanometer spatial resolution and in a repeatable manner, as long as measurement points are confined to well passivated regions away from defects and dangling bonds. Profiles obtained from STS measurements show close agreement with simulated and dI/dV profiles.; Our proposed method can be extended to measurements along a cross-section. We argue in favor of creating cross-sections along the {lcub}111{rcub} plane, because it has a well defined reconstruction and can be easily passivated by hydrogen. Measurements are taken on uniformly doped Si(111) samples passivated by a NH4F solution. Even in the presence of an organic monolayer of contaminants, our STS measurements show clear distinction between n- and p-doped regions. To improve measurements, contaminants can be selectively removed through thermal desorption. The combination of ex situ passivation and in situ selective desorption offers an attractive low temperature solution for cross-sectional work. |
