Low dielectric constant (low-kappa) hybrid organosiloxane polymer (HOSP) displayed larger instability with Al compared to Cu capacitors when investigated using the bias temperature stressing (BTS) and triangular voltage sweep (TVS) techniques. We attributed this instability to ion penetration from the gate metal. As SiO2 is a well-known barrier against Al penetration, an attempt was made to create a SiO2-like surface on HOSP using different plasma treatments. The plasma conditions were selected to minimize bulk damage to the polymer. While N2O and O-2 plasmas caused bulk electrical damage, N-2 and Ar plasma treatments dramatically reduced ion penetration from the Al gate into HOSP. this was seen from the decrease in the BTS C- V shift as well as the TVS ion peak area. A short (1 min) low-power (30 W) N-2 plasma treatment was effective as an aluminum ion penetration barrier, without significantly increasing the refractive index or dielectric constant value of HOSP. Formation of a SiO2-like surface was confirmed from x-ray photoelectron spectroscopy investigations. The above plasma-treatment approach reveals one possible route to attain the "zero barrier thickness" requirement for interconnect systems.