Aqueous ammonium sulfide to modify the surface of low κ dielectric thin films

The modification of polymeric surfaces can lead to the improvements in metallic and dielectric adhesion. Since most of the polymer surfaces are hydrophobic and relatively inert, it is often the goal to functionalize their surface without damaging the underlying sub-surface material. This study focuses on the use of ammonium sulfide to modify the surface of low κ thin-film materials utilized as interlayer dielectrics for ultra-large-scale integrated (ULSI) devices. Results show that Trikon™ (κ=2.8), a hybrid material, can easily become hydrophilic with 50 wt.% (NH4)2S(aq) exposure, whereas, SiLK™ (κ=2.65), a poly(arylene ether), is only slightly modified with exposure to (NH4)2S(aq). X-ray photoelectron spectroscopy and contact angle goniometry confirm the nature of the surface chemistry of both low κ thin films. Further, ultrathin films (∼32 Å) of unannealed poly(p-xylylene) (parylene N) behave much differently with exposure to (NH4)2S(aq) compared to relatively thick (∼2500 Å) films exhibiting a precipitous drop in contact with the short exposure times. However, the same ultrathin films, when annealed at 350 °C for 1 h in high vacuum, behave much like the thick unannealed films. A proposed mechanism is presented to explain this interesting behavior with the parylene thin films.