Nitrogen Atmosphere for Annealing for Semiconductors
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Figure 1724 shows several chemical reactions occurring during annealing of a transistor structure coated with Ti to form a low resistive TiSi2 layer at the source, gate, and drain. When silicon and titanium are reacted, Ti and Si can diffuse laterally over the isolation regions and form thin filaments of TiSix that can electronically connect a gate electrode and source/drain regions and can cause failure of the device. This phenomenon is called "bridging". On the other hand, those by-products (TiSix, TiOx, and TiN) form over the isolation regions and cannot easily be etched in conventional salicide etching solutions. The use of a nitrogen atmosphere during thermal annealing is essential in preventing this failure mechanism [1] because nitrogen quickly diffuses into the grain boundaries and significantly suppresses any long-range silicon diffusion in the titanium layer. Furthermore, to avoid the by-product formation, the annealing temperature cannot be too high.

several chemical reactions occurring during annealing of a transistor structure coated with Ti to form a low resistive SiTi2 layer

Figure 1724. Several chemical reactions occurring during annealing of a transistor structure coated with Ti to form a low resistive SiTi2 layer.

 

 

 

[1] C. K. Lau, “Method of Forming Titanium Disilicide,” U.S. Patent 4,545,116, 1985.

 

 

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