(Color online) Schematic of the custom-built, hot-wall ALD reactor. The main part is a cylindrical tube, heated externally. The tube is fitted with inlets for N2 carrier gas and precursors close to its upstream end. A sample stage with in-situ temperature monitoring is positioned near the center of the tube. A separately pumped mass spectrometer is used to analyze gas sampled downstream of the stage by means of a needle valve. The calculated carrier gas flow and diffusion through the tube indicate even distribution of the gas. The flow profile in the mid section of the tube is shown.
SnOx growth rate determined by VASE, as a function of (a) and (c) TDMASn pulse length t1 for timing sequences of t1:30:2:30 s and (b) and (d) H2O pulse length t3 for timing sequences of 1:30:t3:30 s. The substrate was Si(100) at 150 °C for (a) and (b) and at 30 °C for (c) and (d).
SnOx film thickness as a function of number of ALD cycles yielding a growth rate of 0.70 Å/cycle. Thicknesses were obtained using VASE for films deposited on Si(100) at 150 °C with a time sequence of 1:30:2:30.
SnOx ALD growth rate as a function of temperature determined using VASE for films deposited on Si(100) for 200 cycles with timing sequence 1:30:2:30 s.
SnOx growth rate at 30 °C determined by VASE as a function of nitrogen purge time following (a) TDMASn pulse length and (b) H2O pulse length for timing sequences of 1:t2:2:t4 s. The substrate was Si(100).
X-ray photoelectron spectroscopy survey scan of 46 nm SnOx film deposited on Si(100) at 150 °C after Ar+ sputtering.
(Color online) XRD patterns for a 130 nm film of SnOx deposited on Si(100) at 150 °C as function of annealing temperature under flow of N2, as-deposited (featureless black curve) and after 600 °C anneal (upper curve, with diffraction peaks).
SEM images of a 46 nm SnOx film deposited on Si(100) at 150 °C (a)as-deposited; (b) post-500 °C anneal; (c) post-600 °C anneal; (d) cross-section of film post-600 °C anneal. The scale bars are 300 nm.
(Color online) (a) SnOx film refractive index and (b) extinction coefficient extracted from spectroscopic ellipsometry, as a function of the substrate temperature for films deposited using 200 ALD cycles. The inset in (b) illustrates plots of (α hν)1/2 with linear fits (dashed lines) to the approximately linear portion of the curve. Bandgaps are estimated from the intersection of the linear fits with (α hν)1/2 = 0. (c) Estimated bandgaps as a function of temperature, after 200 cycles of ALD. (d) Bandgaps as a function of film thickness for varying number of ALD cycles and a substrate temperature fixed to 150 °C. The dashed lines in (c) and (d) represent quadratic fits to the data.
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