Diffusion barriers in semiconductor contact metallization: Dissertation

New inspirations respecting the idea to stabilize semiconductor contact metallization by incorporating a diffusion barrier layer are overviewed.The recent progress is surveyed on the basis of another, more general review dealing with the subject in fundamental concepts.Diffusion barriers are classified in terms of their structure or their relative stability at elevated temperatures.It is pointed out that elemental metallic films are not the most favorable choices for diffusion barriers, but that certain compounds or alloys show better performance than simple metals.It is also noted that not only the elemental composition but the film structure, too, determines the value of the barrier.Multilayer configurations to optimize the overall contact performance are considered.Experimental investigations concentrate on properties of tungsten--nitrogen alloys and titanium nitride for the application as diffusion barriers in silicon and gallium arsenide metallization schemes.Nitrogen is shown to stabilize tungsten barriers unless metallurgical contact to highly reactive metals such as titanium is made: at high temperatures titanium is able to reduce tungsten--nitrogen alloys.In ohmic contacts to gallium arsenide, titanium nitride is shown to enhance thermal stability.Properties of sputter deposited titanium nitride films are, however, greatly affected by deposition parameters, such as pressure or bias voltage.