Scanning probe microscopy for 2-D semiconductor dopant profiling and device failure analysis

We have extended the capabilities of an atomic force microscope (AFM) with double heterodyne force detection, to include both electrostatic force microscopy (EFM) and scanning differential capacitance microscopy (SdCM). Samples measured with this tool are imaged simultaneously in each of these three modes. Inhomogeneities in surface topography (AFM), surface work function (EFM) and sub-surface charge (SdCM) are thus detected at once. We work in non-contact mode in order to interact non-destructively with our samples, with resultant lateral spatial resolution of 25–50 nm. Variations in surface topography of less than 1 nm, and surface potential variations as small as 1 mV, are imaged easily. We have applied the techniques based on this tool to microfabricated materials and device structures. In particular, we have studied the metal-oxide-silicon field-effect transistor (MOSFET) structure, of importance to microelectronic science and engineering. Following a brief description of our detection system, this work will describe our measurements of dopant profiles related to this structure. It will also demonstrate our ground-breaking application of scanned probe techniques to the analysis of other materials defects, and of device failure, in these structures. The work will conclude with a quantitative discussion of the three most limiting factors for our techniques: parasitic capacitance; convolved signals; and large-signal behavior of the cantilever.