pn -junction delineation in Si devices using scanning capacitance spectroscopy

Abstract

The scanning capacitance microscope ͑SCM͒ is a carrier-sensitive imaging tool based upon the well-known scanning-probe microscope ͑SPM͒. As reported in Edwards et al. ͓Appl. Phys. Lett. 72, 698 ͑1998͔͒, scanning capacitance spectroscopy ͑SCS͒ is a new data-taking method employing an SCM. SCS produces a two-dimensional map of the electrical pn junctions in a Si device and also provides an estimate of the depletion width. In this article, we report a series of microelectronics applications of SCS in which we image submicron transistors, Si bipolar transistors, and shallow-trench isolation structures. We describe two failure-analysis applications involving submicron transistors and shallow-trench isolation. We show a process-development application in which SCS provides microscopic evidence of the physical origins of the narrow-emitter effect in Si bipolar transistors. We image the depletion width in a Si bipolar transistor to explain an electric field-induced hot-carrier reliability failure. We show two sample geometries that can be used to examine different device properties.

Influence of Interface Traps and Surface Mobility Degradation on Scanning Capacitance Microscopy Measurement

“…While SCM has been successfully demonstrated for the dopant profile extraction of uniformly doped substrates, it is known that dopant profile extraction across a p-n junction from SCM data presents significant difficulties [5]- [8]. The use of the inverse modeling technique based on MOS capacitor physics to extract the dopant profile [9], [10] has not been successful to date due to the fact that many physical effects influencing the experimental SCM data are not accounted for in the associated forward modeling.…”

“…Within the space charge region (approximately m m), shows both negative and positive peaks similar to what is observed in a low-frequency MOS C-V curve but measured at 915-MHz, indicating both are accumulation-to-depletion transitions. This arises from the fact that holes and electrons are supplied as majority carriers from the p-side at negative dc bias and from the n-side at a positive dc bias respectively [8].…”

Modeling mobility degradation in scanning capacitance microscopy for semiconductor dopant profile measurement

“…In the space charge region, both negative and positive peaks of dC / dV are shown, similar to low frequency C-V curve. This is because majority carriers of both types are available for accumulation from either side of the space charge region [14].…”

“…However quantitative dopant profile extraction by SCM is still facing difficulties: The selection of appropriate dc bias to acquire SCM image has been an interest to researchers [4]; wear in probe tip causes signals to distort and the influence of probe tip geometry has also been studied [5]. While the calibration curve method [6,7], in which theoretical C-V curves are calculated and normalized based on the known substrate dopant concentration, has been proven successful for dopant profile extraction of uniformly doped substrates or modest dopant gradient, dopant profile extraction across a p-n junction still remains a challenging task [8,9,10,11]. This is due to the fact that the influence of built-in field of a p-n junction induced space charge region and lateral supply of carriers are not considered when using the calibration curve method, and a better understanding of the interaction between p-n junction and SCM probe is needed to correctly interpret SCM data.…”

Nanoscale Characterization Of Ultra-Thin Dielectrics Using Scanning Capacitance Microscopy

“…SCM relies on the presence of an oxide on the surface, necessary to form the Metal-Oxide-Semiconductor (MOS) stack which is at the basis of the SCM operation. In order to test the quality of this top oxide (Si02 [3] or Zr02 [4]), detect the p-n junctions [5] or find out the best experimental conditions for dopant mapping (e.g. best signal to noise ratio), Scanning Capacitance Spectroscopy (SCS) has been developed in order to record the SCM signal (AC/AV) as a function of the applied continuous voltage VDC [6].…”