Spreading Resistance Measurements on Silicon with Non-blocking Aluminum-Silicon Contacts

Abstract

The paper concerns the measurement of resistivity fluctuations in n-type silicon starting material in the resistivity range from 1 to 1000 Ω cm. The microscopic resistivity fluctuations that are associated with the well-known striations require a measurement technique of high accuracy and high local resolution. We chose the spreading resistance method. However, in contrast to the conventional method, in which the metal probe is pressed directly onto the silicon surface, we supply the silicon slice with non-blocking aluminum-silicon contacts. The radius of the contact area is exactly defined. Any contact radius can be realized according to the resolution desired in lateral direction and in depth. When the metal probe is applied to the aluminum-silicon contact, the contact is not destroyed. Thus it is possible to perform spreading resistance measurements and four-point probe measurements along one and the same measuring track and in this manner at the same time to vary the local resolution. A comparison of both measurement results will in particular yield information on the conditions of the resistivity in axial direction of the slice. Essential prerequisites for an absolute measurement are fulfilled with the aluminum-silicon contact. However, the investigations made up to now show that the resistivity calculated from the spreading resistance is smaller than the one obtained with the four-point probe measurement by approximately a factor of 0.8.