Method and apparatus for measuring film thickness

A method for measuring thickness of a film comprising:

• engaging a probe assembly including a plurality of probes with a surface of a film;
• applying a first arbitrary voltage from a variable voltage source at a first time to said probe assembly to create a first arbitrary current through a portion of said film;
• measuring said first current through said portion of said film at said first time;
• measuring a first voltage between two of said probes at said first time;
• applying a second arbitrary voltage from said voltage source at a second time to said probe assembly to create a second arbitrary current through said portion of said film, wherein said second arbitrary voltage is different from said first arbitrary voltage and said second arbitrary current is different from said first arbitrary current;
• measuring said second current through said portion of said film at said second time;
• measuring a second voltage between two of said probes at said second time;
• calculating a sheet resistance from the ratio of said first voltage to said first current and said second voltage to said second current;
• and
• calculating film thickness from the ratio of a known resistivity of said film to said sheet resistance.

An apparatus for measuring film thickness comprising:

• a probe assembly including four probes;
• a current sensor;
• a variable voltage source coupled to said probe assembly by said current sensor to create a variable voltage, thereby creating a variable current in a film when said probe assembly is engaged with a surface of said film;
• a voltage sensor coupled to said probe assembly to sense a voltage between two probes of said probe assembly;
• and
• a device for determining film thickness from said measured current and said measured voltage.