Direct, low frequency capacitance measurement for scanning capacitance microscopy
AssigneeThe Ohio State University
InventorsJonathan P. Pelz, David T. Lee, Bharat Bhushan
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Abstract
A system and method for measuring capacitance between a probe and a semiconductor sample, which may be useful in the field of scanning capacitance microscopy (SCM). The present invention also includes a method for analyzing measured capacitance data by subtracting any changes in capacitance that are due to changes in long-range stray capacitance that occur when the probe assembly is scanned.
Claims22
A system for measuring capacitance, said system comprising:
- a power supply adapted to provide an AC voltage;
- a sample in electrical communication with said power supply, said sample comprising a dielectric layer and a substrate layer;
- a probe substantially adjacent to said dielectric layer of said sample;
- a phase shifter in electrical communication with said power supply;
- a coupling capacitor adapted to receive an output of said phase shifter;
- a current amplifier adapted to receive a net current from said probe and said coupling capacitor;
- and
- a lock-in amplifier adapted to determine a displacement component and a dissipative component of said net current.
A method for measuring capacitance, said method comprising:
- providing a sample comprising a dielectric layer and a substrate layer;
- positioning a probe substantially adjacent to said dielectric layer of said sample;
- supplying an AC voltage to said sample such that a probe-sample current flows through a probe-sample junction;
- shifting said AC voltage;
- driving a bucking current through a capacitance Ccc;
- adding said probe-sample current and said bucking current to produce a net current;
- determining a displacement component of said net current;
- and
- determining a capacitance change from said displacement component of said net current.
A method for determining capacitance, said method comprising:
- providing a sample comprising a dielectric layer and a substrate layer;
- positioning a tip of a probe substantially adjacent to said dielectric layer of said sample;
- supplying an AC voltage to said sample while scanning said tip across said sample;
- determining capacitance data as a function of probe height relative to said sample and as a function of lateral probe position;
- and
- accounting for capacitance changes due to the lateral position and height of said probe relative to said sample.
A method for measuring nm-scale tip-sample capacitance, said method comprising:
- measuring a cantilever deflection and a change in probe-sample capacitance relative to a reference level as a function of a probe assembly height;
- fitting out-of-contact data to a function;
- subtracting said function from capacitance data to get a residual capacitance as a function of said probe assembly height;
- and
- determining said residual capacitance at a z-position where said cantilever deflection is zero.
Dependencies are inferred from the claim text.