Evaluation of Die Stress Using van der Pauw Sensors

Piezoresistive sensors fabricated on (100) and (111) silicon surfaces are capable of measuring from four to all six stress components on the surface of a die. Such resistor based sensors have been successfully designed and fabricated on these wafer planes, and are being used for measurement of die stresses in electronic packaging. However, the use of resistor sensors has several drawbacks including their large size, low sensitivity, and limited functional temperature range. Van der Pauw (VDP) structures have been identified as one potential sensor candidate for overcoming the limitations of large resistor sensors. In this paper, the feasibility of using van der Pauw structures as stress sensors has been demonstrated. The sensitivity of VDP structures fabricated on both (100) and (111) silicon surfaces to uniaxial stress has been measured using four-point-bending tests, and typical results are presented. The observed VDP stress sensitivities are much higher than those of their analogous resistor sensor counterparts. Preliminary finite difference based anisotropic conduction simulation results are in general agreement with the observed measurements.