Differential Hall Effect Metrology (DHEM) is an electrical characterization technique used for obtaining depth profiles of active dopants (carrier concentration), sheet resistance and carrier mobility through an electrically isolated semiconductor film. Typically, Si, SiGe, Ge samples are analyzed up to 100nm depth. Non-typical samples such as thicker III-V or Si samples have also been analyzed with extra processing steps.
Films to be characterized are patterned to form a test pattern mesa which electrically isolates a portion of the semiconductor film from the rest of the surrounding bulk material. The test pattern mesa has four regions for probe contacts. The contacts need to be reasonably ohmic and inject stable currents at levels that produces high signal-to-noise ratios. A process nozzle sealed in the middle of the test pattern continuously oxidizes or etches a test region in contact with electrolytes by means of electrochemical processing.
To obtain DHEM data, the electrically active thickness (electrical path) of the semiconductor layer at the test region is reduced in controlled steps by electrochemical processing (etching or oxidation), and the sheet resistance and mobility of the remaining film is determined by Hall effect measurements after each thickness reduction step. This procedure is repeated until the desired crater depth is reached or until the sheet resistance of the film exceeds about 1 M ohm/square (may be lower for some materials such as Ge). The resulting data is then interpreted using differential equations which yield sheet resistance, resistivity, carrier concentration, and mobility profiles as a function of depth.
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