A Scanning Capacitance Microscope (SCM) combines an Atomic Force Microscope (AFM) with a 1-GHz tuned-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 a semiconductor and a corresponding differential capacitance, which is measured with a lock-in amplifier. The contrast obtained by an SCM is proportional to the 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 an 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 paper will first review the history, and principals and modes of operation of an SCM. The remainder of the paper will discuss major applications of scanning capacitance microscopy for the electrical characterization of semiconductors and dielectric films, including qualitative characterization for integrated circuit failure analysis, quantitative dopant profiling and models for interpreting scanning capacitance microscopy images as dopant profiles, applications to semiconductors other than silicon, characterization of dielectric films, and optical pumping for carrier mobility measurements.
Citation: Electrical and Electromechanical Characterization by Scanning Probe Microscopy
Publisher Info: Springer Science + Business Media, Inc., New York, NY
Pub Type: Books
Capacitance-Voltage Characterization, Dielectrics, Dopant Profiling, MOS, Scanning Capacitance Microscope, SCM