Scanning capacitance microscopy for electrical characterization of semiconductors and dielectrics

Abstract

A scanning capacitance microscope (SCM) combines an atomic force microscope (AFM) with a 1-GHz tuned inductance-capacitance-resistance (LCR) circuit to measure the capacitance between a conducting tip and sample. When applied to a semiconductor sample, an ac voltage at around 10 kHz is used to induce a depletion region within the semiconductor. The resulting differential capacitance is measured with a lock-in amplifier. The SCM contrast is proportional to this differential capacitance, which in turn is proportional to the inverse square root of the dopant concentration in the semiconductor beneath the tip. In this way dopant gradients in semiconductors, either natural or process induced, can be imaged. The differential capacitance measured by the SCM is also dependent on the properties of any native oxide or deposited dielectric film on the semiconductor surface, and the carrier mobility, which may be degraded near defects. This chapter will first review the history, principles, and modes of operation of the SCM. The remainder of the chapter will discuss major applications of scanning capacitance microscopy (SCM) for the electrical characterization of semiconductors and dielectric films, including qualitative characterization for integrated circuit failure analysis, quantitative dopant profiling and models for interpreting SCM images as dopant profiles, applications to semiconductors other than silicon, characterization of dielectric films, and optical pumping for carrier mobility measurements. © 2007 Springer Science+Business Media, LLC.