OTS (July 2006) -- FSI’s ANTARES^® CryoKinetic cleaning system uses a high-velocity argon/nitrogen cryogenic aerosol to remove surface particles and other residue. Customers have reported using the technique at many points throughout both FEOL and BEOL processes.

A recent study demonstrated the value of CryoKinetic cleaning in removing particulates left by the via etch and ash process. Chemical treatments used at this point are known to cause defects as they attack underlying copper structures through pinholes in the protective etch stop layer. Water treatments cause similar corrosion problems and introduce moisture into porous low k dielectrics. The ANTARES CryoKinetic process is completely dry, non-reactive and non-contact. It provides high particle removal efficiency (PRE) without damaging copper or adding water to the dielectric.

Avoiding Copper Pitting

In advanced damascene processes vias are formed using reactive ion etching through a previously deposited dielectric layer (see figure 1). An etch stop layer between metal levels terminates the etch process and protects the underlying copper line. Etch stop layers are deposited using chemical vapor deposition processes that may leave small pinhole defects. The etch process, and the subsequent ash process used to remove photoresist, can stress and enlarge these defects, providing access to the underlying copper to any subsequently applied chemical agent. Both etching and ashing create particulate contaminants that must be removed before further processing, usually through chemical- or water-based cleaning processes. Chemical treatments can attack the underlying copper through the pinhole defects in the etch stop layer causing pits and corrosion that interfere with good electrical continuity between the via and the underlying copper line. Water-based treatments can also corrode the copper and are known to change the properties of porous dielectric materials through the absorption of water.

Figure 1: Vias are etched through the dielectric to contact underlying copper lines. Pinhole defects in the protective etch stop layer can allow water and chemicals to attack underlying copper and be absorbed by adjacent dielectric materials.

The ANTARES CryoKinetic process is a desirable alternative to water and chemical processes for particle removal after via etch. The nitrogen and argon used in the process are completely inert and will not attack copper or dielectric materials. It is completely water free, avoiding any opportunity for water absorption by the dielectric material adjacent to the via and has proven to raise yield in this application and others. ANTARES CryoKinetic cleaning system will become increasingly important as porous low-k dielectrics come into widespread use at the 45nm technology node and below. Contact FSI International to see first hand how the ANTARES CryoKinetic cleaning system can solve your damascene interconnect issues.