Oxidation-enhanced diffusion nitridation

For example, during oxidation, enhanced diffusion of phosphorus, boron, and arsenic are observed, as well as retarded diffusion of antimony. However, if direct nitridization of the silicon surface occurs, then the inverse effects are observed, that is, enhanced antimony diffusion and retarded phosphorus diffusion. Also, oxidation-enhanced diffusion is significantly affected by doping. As either p- or n-type doping concentration increases above nh oxidation-enhanced diffusion diminishes. If chlorine is introduced into the oxidizing ambient, oxidation-enhanced diffusion is likewise diminished. 

Diffusion in the Presence of Excess Point Defects. Oxidation-Enhanced Diffusion. Oxidation generally enhances the diffusion of group III and group V elements except for antimony (Figure 13). Oxidation-enhanced diffusion is generally observed by depositing a silicon nitride mask on the silicon surface that will prohibit oxidation in the regions that it covers. 

Thus a connection to regions of higher oxygen partial pressure is obtained and instead of nitrides titanium oxide is formed at the metal/oxide interface. As a consequence local temporary regions of high oxidation rate are formed within the scale which may lead to nodules observed on the surface of the oxide scale. At higher temperatures such cracks arc not found possibly because of an increased plasticity of the aluminium depleted subsurface zone or because of a rapid healing rate due to enhanced diffusion... 

All experiments were performed on 200mm wafers using Semitool s plating tool. Trenches with various geometries and aspect-ratios were patterned in silicon oxide coated wafers. Titanium Nitride (TiN) or Tantalum (Ta) diffusion barriers with nominal thickness of 300 A were deposited on the trenches by vacuum techniques such as PVD or CVD. Unless specified differently, a PVD copper adhesion layer with a nominal thickness of 200A was deposited on top of the barrier by PVD techniques. This thin PVD copper adhesion layer was electrochemically enhanced in Semitool s proprietary ECD seed plating solution prior to the full deposition from an acid copper sulfate bath. 

The nitride formation is enhanced by the presence of Nb as alloying element (Figge etal., 1993 Sunderkotter etal., 1999). When a nitride layer covers the substrate surface completely, the oxidation resistance is significantly improved owing to the layer that works as an effective diffusion barrier. 

---