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Wafering Process - Coggle Diagram

- - - - to determine whether a wafer is N or P type
      - Two probes make ohmic contact with the wafer surface. One is heated 25-100˚C hotter than the other. A voltmeter placed across the probes will measure a potential difference whose polarity indicates whether the material is N or P type.
      - For N-type sample: The majority carriers are electrons. At the hot probe, the thermal energy of the electrons is higher than the cold probe so the electrons will tend to diffuse away from the hot probe, driven by the temperature gradient. As the electrons diffuse away from the hot probe, they leave behind the positively charged, immobile donor atoms that provided the electrons. The negatively charged mobile electrons tend to build up near the cold probe, which results in the hot probe becoming positive with respect to the cold probe.
      - For P-type sample: The majority carriers are holes. The polarity of the induced voltage would be reversed.
  - - - allow to force the current through the two outer probes and measure the voltage drop with the two inner probes using a high-impedance voltmeter.
      - most common method of measuring the wafer resistivity
      - Problem with probe contacts: eliminated in the voltage measurement since no current flows through these contacts.
      - Measurement principle (Resistivity):
    - - uses shapes on wafer