Kalha, Curran; (2024) X-ray Photoelectron Spectroscopy of TixW1-x Diffusion Barriers. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Copper is now the material of choice for metallisation schemes in silicon-based power semiconductor devices. However, its integration into these devices is challenging as Cu readily reacts with Si at relatively low temperatures. To circumvent this reaction, a thin metal layer known as a diffusion barrier is required to isolate Cu from Si. The binary alloy of titanium and tungsten (TiW) is shown to be an effective barrier, however, at high temperatures (400°C), the alloy degrades through the out-diffusion of Ti, compromising the device's integrity. Given the importance of the barrier, there is a large drive to conduct an advanced characterisation of the barriers' response to annealing. Soft X-ray photoelectron spectroscopy (SXPS) is a powerful surface-sensitive characterisation technique used to explore the chemical states and electronic structure of a material. Within the last two decades, hard X-ray photoelectron spectroscopy (HAXPES) has gained popularity as its use of hard X-rays extends the probing depth of the conventional technique, allowing for the bulk of a material and/or buried interfaces to be probed. Here, SXPS and HAXPES are combined to investigate the thermal stability of the TiW barrier, the buried TiW/Cu interface and this detrimental degradation mechanism.

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