Patent ID: 6348808
Filing Date: 2002-02-19
Classification: G01R

Abstract:
A test structure in a semiconductor substrate, the test structure for measuring a level of mobile ionic contamination, the test structure comprising:a substrate contact pad for making electrical contact with the semiconductor substrate, a source region formed in the semiconductor substrate, the source region having source region fingers, a source region contact pad for making electrical contact to the source region, a drain region formed in the semiconductor substrate, the drain region having drain region fingers, with the drain region fingers of the drain region interdigitated with the source region fingers of the source region, a drain region contact pad for making electrical contact to the drain region, the source region contact pad and the drain region contact pad adapted for selectively applying a first voltage between the source region and the drain region, a channel region formed in the semiconductor substrate, the channel region disposed in a serpentine configuration between the interdigitated source region fingers and the drain region fingers, an insulation layer formed over the channel region between the source region and the drain region, a gate electrode formed over the insulation layer, the gate electrode having a length sufficient to permit accurate resistance measurements of the gate electrode so as to determine a temperature of the gate electrode, the gate electrode having a serpentine shape so as to fit the length of the gate electrode within a compact area of the semiconductor substrate, and the gate electrode formed of a metal so as to heat across the entire length and width of the gate electrode when a current is applied through the gate electrode, a first gate contact pad disposed at a first end of the gate electrode, and a second gate contact pad disposed at a second end of the gate electrode, at least one of the first gate contact pad and the second gate contact pad for selectively applying an increasing second voltage to the gate electrode and for measuring a threshold voltage when current starts to flow between the source region and the drain region, the first gate contact pad and the second gate contact pad for selectively applying the current through the gate electrode and thereby heating the gate electrode, the insulation layer, and the channel region with a joule effect, with a thermal gradient between the gate electrode, the insulation layer, and the channel region, thereby drawing mobile ion contamination toward an interface between the channel region and the insulation layer, the substrate contact pad for selectively applying a third voltage to the semiconductor substrate, where the thermal gradient and the third voltage reduce the threshold voltage, and the reduction in threshold voltage is proportional to the level of mobile ion contamination.