Atomic Echo


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 100 nm 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.

Ideal Uses of DHEM

  • To measure the depth profile of active dopants, sheet resistance and carrier mobility in an electrically isolated semiconductor layer
  • To evaluate dopant activation or variation of mobility through the film and at interfaces


  • Carrier concentration (active dopants) is measured, in contrast to SIMS, which measures total dopant concentration
  • Dynamic thickness reduction and measurement of mobility, sheet resistance and carrier concentration


  • Destructive
  • A p-n junction must be isolating the film to be measured from the substrate, or the film to be measured must be on an insulating layer

DHEM Technical Specifications

  • Typical substrates include Si, Ge, SiGe
  • Other substrates such as III-V thin-film materials can be analyzed with extra processing steps
  • Active dopant and mobility depth profiles for near-surface and up to 100 nm are achievable, with monolayer resolution
  • Minimum sample size 1.5×1.5 cm

Atomic Echo