Isolation on Si wafers by MeV proton bombardment for RF integrated circuits

Abstract

This paper studies issues related with using high energy protons to create local semi-insulating silicon regions on IC wafers for device isolation and realization of high-Q IC inductors, Topics on two approaches, i.e., one using Al as the radiation mask and the other using proton direct-write on wafers were studied, It was shown that Al can effectively mask the proton bombardment of 15 MeV up to the fluence of 10(17) cm(-2). For the unmasking direct write of the proton bombardment, isolation in the silicon wafer can be achieved without damaging active devices if the proton fluence is kept below 1 x 10(14) cm-2 with the substrate resistivity level chosen at 140 Omega -cm, or kept at 1 x 10(15) cm(-2) with the substrate resistivity level chosen at 15 Omega -cm. Under the above approaches, the 1 h-200 degreesC thermal treatment, which is necessary for device final packaging, still gives enough high resistivity for the semi-insulating regions while recovers somewhat the active device characteristics, For the integrated passive inductor fabricated on the surface of the silicon wafer, the proton radiation improves its Q value.