Characterization of double diffused MOS structures

An investigation of boron distribution close to SiO2-Si interface has been made using both SIMS and differential sheet resistance techniques. It has been observed that for SIMS profiles, there is no dip at the SiO2-Si interface while the differential sheet resistance profiles show a dip at SiO2-SI and the magnitude of the dip varies with ambient. From annealing experiments it is concluded that some boron near SiO2-Si interface becomes electrically inactive and can therefore not be detected by differential sheet resistance technique. These results enable determination of electrically active boron on the surface for double diffused devices. A technique has been developed to measure lateral junctions for both single and double diffused junctions. After careful measurements of these junctions, a model has been developed to predict lateral junctions. This model also predicts lateral impurity profiles. Based on this, a more accurate model has been developed for predicting threshold voltage of double diffused MOS devices. Based on electrically active impurity distribution in the channel and lateral junction measurements, it has been possible to develop a DMOS T process schedule incorporating HCl gate oxide which controls oxide charges. From the devices made in this work, it has been possible to measure accurately and predict both channel length and threshold voltage of the devices. The device I-V characteristics have also been modelled by taking into account peak impurity concentration in the channel, mobility reduction, velocity saturation and drift region resistance which is modulated by the gate voltage. The I-V models strongly depend upon accurate modelling of impurity distribution in the channel.