The Endocyclic Carbon Substituent of Guanidinate and Amidinate Precursors Controlling Atomic Layer Deposition of InN Films

Abstract

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 crystallinity 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 nitridation step in the ALD cycle which explains the improved film properties.

Elucidating the role of nitrogen plasma composition in the low-temperature self-limiting growth of indium nitride thin films

“…35,38 The lower BE peak at 396.5 eV is assigned to nitrogen in the form of InN. 23,31,32,[35][36][37][38][39][40][41][43][44][45][46][47][48][49][50][51][52][53] For Ar/N 2 -plasma samples, the additional components are at 397.2 and 398.3 eV. The upper component is preserved aer sputtering into the bulk of the lm and can be assigned to an In-N-O bonding environment, which leaves the middle component unassigned.…”

“…33,34 To date, there have been multiple efforts towards low-temperature InN growth via PE-ALD. 17,[30][31][32][35][36][37][38][39][40][41] Initial epitaxial growth of InN at sub-300 C was achieved by plasma-enhanced atomic layer epitaxy (PE-ALE) where the lms exhibited substrate-dependent varying crystallographic orientations. 17,36 In a relatively recent study, PE-ALD of monocrystalline InN lms has also been reported at 250 C using N 2 -plasma on lower-lattice-mismatched ZnO/Al 2 O 3 substrates, where the lms were fully relaxed with no voids or interlayers at the interfaces.…”

“…17,36 In a relatively recent study, PE-ALD of monocrystalline InN lms has also been reported at 250 C using N 2 -plasma on lower-lattice-mismatched ZnO/Al 2 O 3 substrates, where the lms were fully relaxed with no voids or interlayers at the interfaces. 31 Moreover, Pedersen et al have recently employed NH 3 -plasma to grow crystalline InN lms 38,39 via PE-ALD, despite its adverse environmental impacts and corrosivity. Majority of the studies around PE-ALD deposition of InN report on single-phase h-InN lms when using hydrogen-free nitrogen plasmas, whereas addition of H 2 to the plasma gas has resulted in degraded lm quality with elevated impurity content and even lm porosity.…”

“…[30][31][32]35,37 Although there have been a number of studies on the plasma-assisted ALD of InN employing N 2 /H 2 and/or N 2 -only plasma compositions, an in-depth investigation of the surface reactions taking place during individual PE-ALD cycles is still signicantly missing. [30][31][32][33][34][35][36][37][38][39][40][41] In this work, we particularly investigate the role of hydrogen radicals in the surface reactions of TMI with Ar/N 2 plasma in a custom-designed compact hollowcathode plasma-ALD reactor. Unlike all previous efforts on PE-ALD of InN utilizing N 2 -plasma, we have observed a major phase transformation from crystalline nitride phase (h-InN) to oxide phase (c-In 2 O 3 ) with the addition of H 2 to Ar/N 2 plasma gas.…”

On the dynamics in chemical vapor deposition of InN

“…20 ALD of InN has been demonstrated using trimethyl indium (TMI) and either nitrogen plasma 21,22 or NH3 plasma 23 , rendering crystalline InN films. ALD of InN has also been demonstrated using precursors with chelating ligands with In-N bonds, demonstrating polycrystalline 24 or epitaxial InN 25 with NH3 plasma. Recently, we demonstrated that epitaxial and homogeneous wurtzite InN film on 4H-SiC substrate with a thickness down to 5 nm can be grown by using plasma ALD at 320°C, 26 which has never been reported by other growth techniques.…”