Atomic Layer Deposition of InN Using Trimethylindium and Ammonia Plasma

Abstract

<div>InN is a low band gap, high electron mobility semiconductor material of interest to optoelectronics and telecommunication. Such applications require the deposition of uniform crystalline InN thin films on large area substrates, with deposition temperatures compatible with this temperature-sensitive material. As conventional chemical vapor deposition (CVD) struggles with the low temperature tolerated by the InN crystal, we hypothesize that a time-resolved, surface-controlled CVD route could offer a way</div><div>forward for InN thin film deposition. In this work, we report atomic layer deposition of crystalline, wurtzite InN thin films using trimethylindium and ammonia plasma on Si (100). We found a narrow ALD window of 240–260 °C with a deposition rate of 0.36 Å/cycle and that the flow of ammonia into the plasma is an important parameter for the crystalline quality of the film. X-ray photoelectron spectroscopy measurements shows nearly stoichiometric InN with low carbon level (< 1 atomic %) and oxygen level (< 5 atomic %) in the film bulk. The low carbon level is attributed to a favorable surface chemistry enabled by the NH<sub>3</sub> plasma. The film bulk oxygen content is attributed to oxidation upon exposure to air via grain boundary diffusion and possibly by formation of oxygen containing species in the plasma discharge.</div>

Surface chemistry in atomic layer deposition of AlN thin films from Al(CH3)3 and NH3 studied by mass spectrometry

“…The plasma emission lines from OES included NH at 336.1 nm, N2 at 357.1 nm, and N2 + at 391.4 nm and 427.6 nm. 13 ' 14 Additionally, the emission peaks at around 336-337 nm indicated the presence of excited NH and N2 radicals, 14 corresponding to specific transitions, supporting the existence of NHx and N2 species.…”

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

“…To circumvent the low vapor pressures of 1 and 2, a fill-empty approach was employed. This approach has been previously reported 9 , in brief it uses several pulses of In-precursor with first a high, then low flow of carrier gas into the bubbler. This creates a larger pressure gradient between the bubbler and the reaction chamber, which facilitates the movement of the precursor into the reaction chamber.…”

“…The NH3 plasma has previously been studied by optical emission spectroscopy and no optically active oxygen containing species where found. 9 The significantly higher standard enthalpy of formation for In2O3 (-926 kJ/mol) compared to that of InN (-138 kJ/mol) means that oxidation of InN upon air exposure is favoured. 31 As the films are polycrystalline (Figure 4), oxygen diffusion into the grain boundaries is a likely process 32 and thus air exposure post deposition is a possible cause for the oxygen levels in the InN films.…”

“…If self-limiting surface chemistry is achieved, such an approach would be an atomic layer deposition (ALD) process. ALD of InN has been demonstrated using In(CH3)3 and N2 plasma 7,8 or NH3 plasma 9 , affording InN of high crystalline quality, albeit with significant levels of carbon impurities emanating from the In-C bonds in the In(CH3)3 precursor. Low temperature ALD processes based on precursors with metal-carbon bonds are known to render carbon impurities in the few atomic percent range.…”