Microstructural Characterization of LPCVD (Low Pressure Chemical Vapor Deposition) Tungsten Interfaces

Three important interfacial morphologies are observed in LPCVD tungsten on silicon lateral encroachment, interface roughness, and wormhole structures. They have been shown to be, in part at least, a result of defect condition. Defects which have been positively identified using XTEM include residual native oxide and dislocations from ion implantation. A third phase, possibly tungsten silicide, has been observed but not uniquely identified. Extensive lateral encroachment has been shown to be related to the presence of residual implant damage. Specifically, dislocation loops under oxide grown over arsenic implanted silicon were implicated. Interface roughness appears to result from both residual native oxide patches on the silicon surface as well as to the formation of small protrusions of a third, probably silicide phase. The electron microscopy techniques of microdiffraction and Moire analysis were used in an attempt to identify the third phase. The presence of a third phase has lead to the proposal of a mechanism for the formation of the wormhole structure. Additional work, currently underway, will establish the identity of both the interfacial phase and the wormhole particles.