The Endocyclic Carbon Substituent of Guanidinate and Amidinate Precursors Controlling ALD of InN Films

Indium nitride (InN) is an interesting material for future high frequency electronics, due to its high electron mobility. The problematic deposition of InN films currently prevents full exploration of InN based electronics. We present studies of atomic layer deposition (ALD) of InN using In precursors with bidentate ligands forming In–N bonds; tris(N,N-dimethyl-N’,N’’-diisoproprylguanidinato)indium(III), tris(N,N’-diisopropylamidinato)indium(III) and tris(N,N’-diisopropylformamidinato)indium(III). These compounds form a series were the size of the substituent in the endocyclic position decreases from –NMe₂, to –Me and to –H, respectively. We show that when the size of the substituent decreases, InN films with higher crystalline- and optical quality, lower roughness and an In/N ratio closer to unity is achieved. From quantum chemical calculations we show that the smaller substituents lead to less steric repulsion and weaker bonds between the ligand and In centre. We propose that these effects render a more favoured surface chemistry for the nitidisation step in the ALD cycle which explains the improved film properties.