We have investigated the effects of gate-first and gate-last process on oxide/InGaAs interface quality using In0.53Ga0.47As metal-oxide-semiconductor capacitors (MOSCAPs) with atomic-layer-deposited (ALD) oxides. Sequence of source/drain activation anneal in the process results in remarkable electrical and physical difference. Applying gate-last process provides significant frequency dispersion reduction and interface trap density reduction for InGaAs MOSCAPs compared to gate-first process. A large amount of In–O, Ga–O, and As–As bonds was observed on InGaAs surface after gate-first process while no detectable interface reaction after gate-last process. Electrical and physical results also show that ALD Al2O3 exhibits better interface quality on InGaAs than HfO2.
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Zhao et al. (2009) studied this question.