Ar Implantation, a Passivation Technique for High-Resistivity Silicon within the MCM-D Technology

High-resistivity silicon (HRSi) has excellent properties as substrate material to integrate microwave passive components and system in a package (SiP) modules. However, the existence of a layer of free surface charges under the silicon-silicon dioxide interface generated by impurities in the SiO₂ and in the interface itself undermines the RF properties of the bulk HRSi. This paper demonstrates that the surface charges increase the RF loss of CPW lines processed on HRSi and make their loss DC dependent. It also presents how Ar implantation can successfully restore the excellent RF properties of the bulk HRSi in terms of loss and DC dependency. An Ar implant dose 10 times lower than previously reported is demonstrated to be sufficient, lowering the cost of the passivation step. The substrate loss of passivated HRSi is shown to be comparable to that of AF45 glass regarding inductors and a better Q for CPW lines has been measured in the case of HRSi. This approach withstands the most critical processing step of imec´s MCM-D technology and therefore it is a suitable technique to passivate the surface of HRSi within this technology