Triratna Muneshwar

Low temperature plasma enhanced atomic layer deposition of conducting zirconium nitride films using tetrakis (dimethylamido) zirconium and forming gas (5% H2 + 95% N2) plasma

Zirconium nitride (ZrN) has the lowest bulk electrical resistivity and high thermal stability among group IV and V transition metal nitrides, which makes it a promising material for ULSI applications such as a diffusion barrier for Cu interconnects, contact metal in III-V semiconductor devices, and in high density memory structures. Plasma enhanced atomic layer deposition (PEALD) of conducting ZrN thin films using Zr[N(CH3)2]4 and forming gas (5% H2 + 95% N2) plasma is reported in this article. The growth per cycle (GPC) for every deposition was determined from analysis of dynamic in-situ spectroscopic ellipsometry (d-iSE) measurements. An experimental design is proposed for faster determination of ALD growth saturation curves. At substrate temperature of 150 °C, a GPC of 0.10 nm/cycle was observed for self-limiting ZrN PEALD growth. The electrical resistivity of ZrN films deposited on SiO2 substrate was found to be 559.5 ± 18.5 μΩ cm with negligible change in resistivity even after ∼1000 h exposure to ai...

Sustained hole inversion layer in a wide-bandgap metal-oxide semiconductor with enhanced tunnel current

Wide-bandgap, metal-oxide thin-film transistors have been limited to low-power, n-type electronic applications because of the unipolar nature of these devices. Variations from the n-type field-effect transistor architecture have not been widely investigated as a result of the lack of available p-type wide-bandgap inorganic semiconductors. Here, we present a wide-bandgap metal-oxide n-type semiconductor that is able to sustain a strong p-type inversion layer using a high-dielectric-constant barrier dielectric when sourced with a heterogeneous p-type material. A demonstration of the utility of the inversion layer was also investigated and utilized as the controlling element in a unique tunnelling junction transistor. The resulting electrical performance of this prototype device exhibited among the highest reported current, power and transconductance densities. Further utilization of the p-type inversion layer is critical to unlocking the previously unexplored capability of metal-oxide thin-film transistors, such applications with next-generation display switches, sensors, radio frequency circuits and power converters.

Influence of atomic layer deposition valve temperature on ZrN plasma enhanced atomic layer deposition growth

Atomic layer deposition (ALD) relies on a sequence of self-limiting surface reactions for thin film growth. The effect of non-ALD side reactions, from insufficient purging between pulses and from precursor self-decomposition, on film growth is well known. In this article, precursor condensation within an ALD valve is described, and the effect of the continuous precursor source from condensate evaporation on ALD growth is discussed. The influence of the ALD valve temperature on growth and electrical resistivity of ZrN plasma enhanced ALD (PEALD) films is reported. Increasing ALD valve temperature from 75 to 95 °C, with other process parameters being identical, decreased both the growth per cycle and electrical resistivity (ρ) of ZrN PEALD films from 0.10 to 0.07 nm/cycle and from 560 to 350 μΩ cm, respectively. Our results show that the non-ALD growth resulting from condensate accumulation is eliminated at valve temperatures close to the pressure corrected boiling point of precursor.

Plasma enhanced atomic layer deposition of ZnO with diethyl zinc and oxygen plasma: Effect of precursor decomposition

Although atomic layer deposition (ALD) of ZnO using diethyl zinc (DEZ) precursor has been extensively reported, variation in growth-per-cycle (GPC) values and the range of substrate temperature (Tsub) for ALD growth between related studies remain unexplained. For identical processes, GPC for the characteristic self-limiting ALD growth is expected to be comparable. Hence, a significant variation in GPC among published ZnO ALD studies strongly suggests a concealed non-ALD growth component. To investigate this, the authors report plasma-enhanced ALD growth of ZnO using DEZ precursor and O2 inductively coupled plasma. The effect of Tsub on ZnO GPC was studied with deposition cycles (1) 0.02 s–15 s–6 s–15 s, (2) 0.10 s–15 s–15 s–15 s, and (3) 0.20 s–15 s–30 s–15 s, where the cycle parameters t1–t2–t3–t4 denote duration of DEZ pulse, post-DEZ purge, plasma exposure, and postplasma purge, respectively. The non-ALD growth characteristics observed at Tsub  ≥ 60 °C are discussed and attributed to DEZ precursor decomposition. The authors demonstrate ZnO growth at Tsub  = 50 °C to be self-limiting with respect to both t1 and t3 giving GPC of 0.101 ± 0.001 nm/cycle. The effect of precursor decomposition related (non-ALD) growth at Tsub  ≥ 60 °C is illustrated from comparison of optical dielectric function, electrical resistivity, and surface roughness of ZnO films deposited at Tsub  = 50, 125, and 200 °C.

Plasma enhanced atomic layer deposition and laser plasma deposition of ultra-thin ZnO films for Schottky barrier devices

Zinc oxide (ZnO) based materials have attracted much attentions in the past decades for potential utilizations in transparent conducting oxides (TCOs), thin film transistors (TFTs) and light emitting diodes (LEDs) due to its superior properties such as large bandgap (3.37eV), large exciton binding energy (60 meV), high transparency and capability of synthesis under low to intermedium temperature. ZnO thin films are capable to grow on various substrates such as glasses, polymer, and sapphire under low deposition temperature, which makes it attractive in flexible electronics. Schottky contacts for ZnO thin film is an essential study for further applications of this material in photodetector and TFTs. Transparent ZnO based TFTs has become one of the most advance topics for device application currently as one of the most promising technologies leading in the next generation of display. The display market forecast has predicted that transparent display is expected to overtake Flat Panel Display in the next decade1.

Atomic Layer Deposition

Abstract Atomic layer deposition (ALD) for thin film deposition is one of the most important techniques that is enabling the continuous miniaturization of semiconductor devices. ALD film growth is obtained by repeating a sequence of two or more self-limiting surface reactions wherein the respective reactants are periodically introduced onto the substrate with intermediate reactor purging. The self-limiting nature of ALD reactions provides a precise sub-nanometer control over deposition thickness. Uniform distribution of surface active sites ensures that the introduced reactants uniformly react on the entire substrate surface including any non-planar features, hence ALD provides excellent thickness uniformity and step coverage. In ALD process development, the selection of reactants and deposition cycle parameters are made based on the thermodynamics and kinetics of the involved surface reactions. This chapter provides a brief survey on the present status of ALD in semiconductor device fabrication, and outlines few of the major challenges in the application of ALD in large-volume fabrication.

Surface reaction kinetics in atomic layer deposition: An analytical model and experiments

Atomic layer deposition (ALD) surface reactions are comprised of several elementary surface interactions (such as physisorption, desorption, and chemisorption) occurring at the substrate. Since ALD processes are often far from thermodynamic equilibrium, the surface saturation behavior is controlled by the kinetics of these involved interactions. In this article, we present a first-order kinetic model for ALD reaction, to simulate the cumulative effect of precursor exposure (tA), post-precursor purge (tP1), reactant exposure (tB), post-reactant purge (tP2), and substrate temperature (Tsub) on the resulting growth per cycle (GPC) in an ABAB… pulsed ALD process. Furthermore, to simulate the effect of inadequate reactor purges (tP1, and/or tP2) and undesired non-ALD side reactions, reaction pathways to account excess GPC are also taken into consideration. From our model calculations, we simulate GPC vs Tsub trends observed in ALD growth experiments and demonstrate that the process temperature window (ΔTALD) for a constant GPC depends upon the deposition cycle parameters tA, tP1, tB, and tP2. The modeled GPC vs Tsub trends are discussed and compared with SiNx, ZrN, and ZnO PEALD growth experiments.Atomic layer deposition (ALD) surface reactions are comprised of several elementary surface interactions (such as physisorption, desorption, and chemisorption) occurring at the substrate. Since ALD processes are often far from thermodynamic equilibrium, the surface saturation behavior is controlled by the kinetics of these involved interactions. In this article, we present a first-order kinetic model for ALD reaction, to simulate the cumulative effect of precursor exposure (tA), post-precursor purge (tP1), reactant exposure (tB), post-reactant purge (tP2), and substrate temperature (Tsub) on the resulting growth per cycle (GPC) in an ABAB… pulsed ALD process. Furthermore, to simulate the effect of inadequate reactor purges (tP1, and/or tP2) and undesired non-ALD side reactions, reaction pathways to account excess GPC are also taken into consideration. From our model calculations, we simulate GPC vs Tsub trends observed in ALD growth experiments and demonstrate that the process temperature window (ΔTALD) f...