The base current and related 1/f noise for SiGeHBTs realized by SEG/NSEG technology on SOI and bulk substrates

摘要

It is shown that the high base current and associated low-frequency noise typical for the SiGe HBTs prepared by the selective epitaxial growth of the collector and non-selective epitaxial growth of the base and emitter (SEG/NSEG technology), can be related to the mechanical stress between the collector and the field oxide surrounding the collector in these devices. The reason is that such stress provokes the viscous flow of the surface oxide producing an "action-at-distance" effect which results in the creation of additional fast and slow surface centers at the single crystal emitter and passivating oxide interface and in the oxide, respectively. The increase of fast center density increases the recombination base current component while the increase of slow center density increases the intensity of the 1/f noise source. As a result, any factor that promotes the reduction of the stress or the decrease of the intensity of the surface oxide viscous flow serves to decrease the base current and its 1/f noise. Thus we have found that we can mitigate the undesirable effects by the following solutions: increasing the temperature of the SEG of the collector T-SEG, decreasing the temperature of the rapid thermal activation T-RTA, implantation of BF2 into the field oxide before the collector and base layers are grown, replacement of the bulk substrate by SOI. It is shown that the maximal decreases of the base current I-B and of the spectral density of the 1/f noise S-IB are as high as factors of 30 and 8000, respectively. Therefore, the technology conditions have been identified to guarantee a sufficiently low level of both excess base current noise and base current. (C) 2006 Elsevier Ltd. All rights reserved.