The possible ways in which nitrogen may be present in and interact with metal silicides are outlined. It is shown that, although contaminant nitrogen can be easily eliminated in deposition systems and processing ambients, understanding the role of nitrogen in metals and metal silicides may be important for various nitridation processes used for VLSI fabrication.
Nitrogen isotope 15N is controllably introduced into either the metal or silicon in a metal-silicon binary couple. Silicide formation is induced by vacuum annealing. After various thermal treatments, 15N is profiled by the 15N(p,α)12C nuclear reaction. A detailed description of this technique is given.
The metals investigated are Pd, Ni, Co, Pt, Ta, Mo and Ti. Metal silicides are grouped into three categories according to the moving species during silicide formation: metal, silicon or both. The interpretation of nitrogen evolution during silicide formation is based on the identity of the moving species. A wide variety of nitrogen redistribution patterns (segregation, incorporation, accumulation, dilution and fast diffusion) are observed in different samples, depending on parameters such as nitrogen diffusivity and solubility in its host matrix, and nitrogen bond strength to the silicide forming species.
The presence of nitrogen sometimes will slow down the silicide growth rate. The degree of slowing down generally depends on the amount of nitrogen incorporated. In case of refractory metal, a large concentration up to 25 at% of oxygen is found to be incorporated during metal film deposition. The redistribution of oxygen during annealing is investigated using the 16O(d,α)14N nuclear reaction.
Two additional studies on different subjects are reported. The first one investigates the dry and wet oxidation behavior of Ti and Hf nitrides. A parabolic oxidation rate is found in all cases except the wet oxidation of HfN. The other study extends the work on dopant enhanced epitaxial regrowth of Si to three substrate orientations. It is found that the enhancement factor is the same, independent of the substrate orientation. An improved crystalline quality is observed for epitaxial Si regrown on an <111> substrate.
