Performance studies on inversion channels of nMOSFETs under extreme mechanical load

Test chips containing nMOSFET with different gate orientations were processed on a (100) silicon wafer using a 0.65 μm CMOS technology. The wafer was diced into strips. The strips were thinned down to a thickness t of 65 μm and bent parallel to the [110]-direction through a four-point bending fixture. For the first time uniaxial mechanical stress up to 350 MPa was applied externally to the strips. In order to get reference values thick strips of 300 μm thickness were also investigated. The drain current I_D was measured for different bending stress values. The relative current change ΔI_D/I_D shows a linear behavior with respect to the applied stress. No other effect than piezoresistance plays a major role in changing the current in stressed thin chips.