Use of photocurrent-voltage characteristics of MOS structures to determine insulator bulk trapped charge densities and centroids

Abstract

A new technique is described for determining the density and centroid of trapped space charge in the oxide layer of metal-oxide-semiconductor (MOS) structures. Photo-current-voltage (photo I-V) characteristics for both the metal-oxide and Si-oxide interfaces are used to determine the internal fields due to bulk trapped charge, and hence its density and centroid. Experimental examples for locating both positive and negative charge are presented. For negative charge, an Al-Si0₂-W-SiO₂-Si structure (MOWOS) with a layer of approximately 10¹⁴ W atoms/cm² deposited 80 Å from the Si-SiO₂ interface and charged by electronic internal photoemission is investigated. For positive charge, the location of trapped holes generated by 16.85 eV photons or x-rays in the SiO₂ layer of an MOS structure under a voltage bias is discussed. The photo I-V technique is compared to others in terms of its direct, rapid, minimally perturbing, low current, and low field characteristics.