Growth Of Boron Nitride Films Research Articles

Electron-Enhanced Atomic Layer Deposition of Boron Nitride Thin Films at Room Temperature and 100 °C

Electron-enhanced atomic layer deposition (EE-ALD) was used to deposit boron nitride (BN) thin films at room temperature and 100 °C using sequential exposures of borazine (B3N3H6) and electrons. Electron-stimulated desorption (ESD) of hydrogen surface species and the corresponding creation of reactive dangling bonds are believed to facilitate borazine adsorption and reduce the temperature required for BN film deposition. In situ ellipsometry measurements showed that the BN film thickness increased linearly versus the number of EE-ALD cycles at room temperature. Maximum growth rates of ~3.2 Å/cycle were measured at electron energies of 80-160 eV. BN film growth was self-limiting versus borazine and electron exposures, as expected for an ALD process. The calculated average hydrogen ESD cross section was σ = 4.2 × 10-17 cm2. Ex situ spectroscopic ellipsometry measurements across the ~1 cm2 area of the BN film defined by the electron beam displayed good uniformity in thickness. Ex situ X-ray photoelectron spectroscopy and in situ Auger spectroscopy revealed high purity, slightly boron-rich BN films with C and O impurity levels <3 at. %. High-resolution transmission electron microscopy (HR-TEM) imaging revealed polycrystalline hexagonal and turbostratic BN with the basal planes approximately parallel to the substrate surface. Ex situ grazing incidence X-ray diffraction measurements observed peaks consistent with hexagonal BN with domain sizes of 1-2 nm. The BN EE-ALD growth rate of ~3.2 Å/cycle is close to the distance of 3.3 Å between BN planes in hexagonal BN. The growth rate and HR-TEM images suggest that approximately one monolayer of BN is deposited for every BN EE-ALD cycle. TEM and scanning TEM/electron energy loss spectroscopy measurements of BN EE-ALD on trenched wafers also showed preferential BN EE-ALD on the horizontal surfaces. This selective deposition on the horizontal surfaces suggests that EE-ALD may enable bottom-up filling of vias and trenches.

Growth of boron nitride films on w‐AlN (0001), 4° off‐cut 4H‐SiC (0001), W (110) and Cr (110) substrates by Chemical Vapor Deposition

Boron Nitride is a promising group 13–group 15 compound material that exhibits various interesting properties like wide band gap, chemical stability, attractive mechanical properties and other. The growth behavior of this material has not been investigated in sufficient details to tailor properties of the resulting films. In this work we present the results on the growth of turbostratic boron nitride (t‐BN) thin films at a relatively high growth rate of 3 μm/h with the aim to investigate the potential use of boron trichloride in combination with ammonia as precursors for growth. Deposition experiments were conducted in a vertical cold wall high temperature chemical vapor deposition reactor in the temperature range 1000°C–1700°C depending on the substrate used. Templates of w‐AlN (0001), 4° off‐cut 4H‐SiC (0001), Cr (110) and W (110) were employed as substrates for the BN growth. As‐grown BN layers were characterized by Scanning Electron Microscopy, X‐Ray Diffraction, Electron Diffraction and Raman Spectroscopy. The results indicate that temperature and N/B ratio have a great influence on the crystallinity of the deposited films. For AlN and SiC substrates, a temperature of 1600°C and N/B ratio in range between 3 and 7.5 were identified as the best parameters for the growth of a 2 μm thick t‐BN layer with a spacing between basal planes of about 3.36 Å compare to the 3.33 Å spacing between basal planes of hexagonal or rhombohedral BN (h‐BN or r‐BN). For Cr and W substrates which have a lower mismatch with h‐BN (1 and 8.8 %), layers of t‐BN were deposited at much lower temperature (1000°C–1150°C) with a spacing between basal planes of 3.5 Å and morphology similar to that observed on SiC substrates. We obtained t‐BN layers with in plane strong disorder but out of plane orientation (c‐axis normal to the surface).

One-dimensional structure of boron nitride on chromium (1 1 0) – a study of the growth of boron nitride by chemical vapour deposition of borazine

The nucleation and growth of boron nitride films on a chromium (1 1 0) surface by thermal decomposition of borazine (HBNH) 3 was investigated by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and X-ray photoelectron diffraction (XPD). The boron nitride film forms a chemically non-uniform one-dimensional superstructure with short range order along the [ 1 1 ¯ 0 ] direction and long range order along [0 0 1]. Moreover, the thermal stability of the resulting BN film was investigated and a chemical reaction with the substrate was observed leading to the formation of Cr–B– and Cr–N– bonds at the interface and indicating the onset of the formation of hard boride and nitride phases in the system Cr–B–N.

Theoretical rate constants for the reaction BF 2 + NF = BF 3 + N of importance in boron nitride chemistry

A kinetic mechanism was developed for the growth of boron nitride films, including up to 35 species and 1012 gas-phase reactions. For 117 elementary reactions, rate constants are available from published experimental/theoretical data and a code was written to estimate the others using transition state theory. As an example of our approach, we report here results for one of these reactions, BF 2 + NF = BF 3 + N of presumable importance for the mechanism, using geometries and electronic energies (including their first and second derivatives), calculated ab initio along the minimum energy path. The reaction proceeds in two steps and rate constants were calculated for the temperature range 200–4000 K.

Atomic Force Microscopy study of hexagonal boron nitride film growth on 6H‐SiC (0001)

AbstractBoron nitride thin films with their unique mechanical and electrical properties are of interest for various applications and have been grown on a number of different substrates. The cover picture from this issue's Editor's Choice [1] shows an Atomic Force Microscopy topography of a hexagonal BN film grown on 6H‐SiC substrate by Plasma Enhanced Chemical Vapor Deposition at 600 °C. Interesting stress‐relief features developed on the non‐reactive substrate. The corresponding author Kian Ping Loh is Assistant Professor at the National University of Singapore. His research is devoted to the growth of diamond and boron nitride thin films and the fabrication of nanocrystalline diamond and boron nitride nanotubes.As a follow‐up to the recent special issue on ‘Physics of Organic Semiconductors’ [2], Detlef Berner gives insights into organic light emitting diode functioning by coordinated experiment and simulation in his Review Article [3].The present issue also sees the start of our rapid research letters, the fastest peer‐reviewed publication medium in solid state physics. For more information see www.pss‐rapid.com and the Editorial by the Editor‐in‐Chief Martin Stutzmann on page 7 [4].

Atomic force microscopy study of hexagonal boron nitride film growth on 6H‐SiC (0001)

AbstractThe growth of hexagonal Boron Nitride films (h‐BN) on 6H‐SiC (0001) using plasma‐excited borazine has been studied. On 6H‐SiC (0001), the growth of pin‐hole free, compact h‐BN film is difficult due to poor wetting properties between h‐BN and 6H‐SiC. The strained BN layer releases its elastic energy by a morphological instability at the interface. This strain relief mechanism gives rise to a buckling of the film into longitudinal islands and round trenches between 500–700 °C. At 300 and 900 °C however, the strained islands can attain their minimum‐energy size to form homogeneously‐sized spherical islands with diameter of ∼500 nm. Compositional analysis of the BN films grown at 900 °C using XPS shows that these are actually BCxN film with x ∼ 0.15, whereas the films grown at 300 °C have less carbon incorporation but higher O content. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

On the mechanisms of cubic boron nitride film growth

Cubic boron nitride (c-BN) is the most attractive BN allotrope due to its outstanding physical and chemical properties. Deposition of c-BN films is typically accomplished using ion-assisted physical vapor deposition methods. Recently, low-stress and thick c-BN films were successfully grown by chemical vapor deposition approaches. It was also shown that c-BN growth is possible by ion implantation with ion energies above 10 keV. Independent of the deposition method, there exist pronounced similarities regarding the nucleation and growth conditions as well as the film structure. Despite these similarities, the different c-BN growth methods are most probably based on different underlying physical processes. This is reflected in characteristic differences in the c-BN growth conditions, such as different ion energy and growth temperature regimes, and different chemical precursors. In this contribution the growth conditions for several c-BN growth methods are compared and an attempt will be made to extract the relevant physical processes for c-BN growth. We propose three different major processes leading to c-BN growth: (i) the subplantation process taking place in ion-assisted PVD and ion beam deposition; (ii) a process involving gas phase and surface chemistry taking place in fluorine-assisted plasma-CVD at high temperatures; and (iii) internal growth during B and N ion implantation into c-BN bulk material.

Fundamental role of ion bombardment for the synthesis of cubic boron nitride films

Boron nitride film growth from B and N ion deposition is studied. We observe growth of the cubic phase $(c\ensuremath{-}\mathrm{BN})$ between 75 eV and 5 keV and a transition to ${\mathrm{sp}}^{2}$-bonded BN growth between 5 and 10 keV, as predicted by the cylindrical spike model. Atomic rearrangements in thermal spikes are identified as the mechanism responsible for $c\ensuremath{-}\mathrm{BN}$ formation and suppression of defect accumulation. The onset of defect accumulation eventually enhances the growth of ${\mathrm{sp}}^{2}$-bonded BN. The results highlight the fundamental role of the balance between thermal spikes and defect accumulation in ion deposition processes.

Kinetic and Surface Mechanisms to Growth of Hexagonal Boron Nitride

ABSTRACTA mechanism is presented for the gas-phase chemistry and surface reactions describing the growth of boron nitride films. The gas phase mechanism includes 33 species and 216 elementary reactions. Rate parameters for 117 elementary reactions were obtained from published experimental/theoretical data and those for the other 99 were determined using transition state theory. The mechanism examined here is an extension and update of a previous mechanism that contained 26 species and 67 elementary reactions. Standard reaction flux/pathway and gradient sensitivity analysis techniques are used to identify important reaction pathways. The calculations were handled through the use of the ChemKin software package. The model was applied to the growth of hexagonal boron nitride in an arcjet plasma source operating on mixture of BF3, H2 and N2. From the growth rate and experimental conditions for such reactors, this work demonstrates that species with mole fractions in the range of 1 × 10-10 − 2 × 10-4 (easily generated by gas-phase conditions) can account for the measured growth rate. A comparison of the predicted mole fractions of the gas-phase species present for the experimental residence times with those required to account for the measured film growth rates allows us to identify possible growth precursors. At the experimental settings, it is found that the residence time of the reacting species does not allow the flow to reach the chemical equilibrium, and that many radicals other than the source gases can account for the measured BN growth rate. The gas-phase is shown to be removed from thermodynamic equilibrium. For comparison, the equilibrium mole fractions were also calculated using an available equilibrium chemistry solver, STANJAN. Growth rates of 10-9 to 10-6 kg m-1 s-1 were measured for a wide range of H2, BF3 and NF3 flux. Both the finite-rate kinetics and equilibrium calculations confirm the importance of added hydrogen to facilitate boron nitride condensation from the gas phase. A simple surface mechanism with 7 steps is proposed with rate constants chosen to best fit the experimental growth kinetics. The results of the model, with surface rate coefficients determined from analogous gas-phase reactions, tuned slightly to agree with the experimental growth rates for BFx, x = 1, 2 or 3, as the rate-limiting growth precursor. It is also shown that the hydrogen atom has a great influence in the growth rate and that fluorine atom etches the hBN films.

Spectroscopic in situ diagnostics of boron nitride film growth in plasma-enhanced deposition

The development of in situ diagnostics of the most important species and reactions in the plasma and/or on the surface during thin-film growth is one of the current topics in plasma-enhanced vapor deposition. In situ thin film diagnostic methods which could be used in plasma processing are restricted due to the presence of electrons and ions. The advantages and disadvantages of different applicable methods will be discussed. The spectroscopic in situ control of boron nitride film growth is presented as an example of surface modification in low-temperature, low-pressure plasma processing. The growth of cubic and hexagonal boron nitride is observed by polarized infrared reflection spectroscopy in absorption and ellipsometric configurations as well as by single-wavelength ellipsometry in the visible spectral range. Modeling of the experimental results gives detailed information on growth conditions and internal stress of the films.

Extension of Multichannel Spectroscopic Ellipsometry into the Ultraviolet for Real Time Characterization of the Growth of Wide Bandgap Materials from 1.5 to 6.5 eV

ABSTRACTIn this article, we report the results of a successful effort to extend rotating-polarizer multichannel ellipsometry into the ultraviolet (uv) spectral region above 5 eV. Key modifications over previous system designs include (i) incorporation of a see-through deuterium (D2) lamp that allows a tandem Xe/D2 source configuration for a usable spectral output from 1.5 to 6.5 eV, (ii) MgF 2 Rochon polarizers for high transmission in the uv without the need for optical activity corrections, and (iii) a spectrograph with a concave grating blazed at 2500 A and internally mounted order-sorting filters. With these modifications, we can collect 132-point ellipsometric spectra over the range from 1.5 to 6.5 eV with a minimum acquisition time of 24.5 ms (one optical cycle). For averages over two and eighty optical cycles (requiring 49 ms and 1.96 s, respectively), the standard deviations in (Ψ, Δ) are (0.04°, 0.08°) and (0.008°, 0.015°), respectively, measured on a thermally-oxidized silicon wafer at a photon energy of 6 eV. In this first report, we briefly describe problems faced in the development of the new instrument. As an example of the applications of the instrument, we present the results of a real time study of the growth of a hexagonal boron nitride (BN) thin film by rf magnetron sputtering on a Si wafer substrate at a temperature of 250°C. The instrument is expected to be useful in BN film growth studies since the additional data in the uv assist in discriminating the wide band gap (Eg) hexagonal (4 &lt; Eg &lt; 5.8 eV) and cubic (Eg &gt; 6 eV) phases of this material.

In situ characterization of cubic boron nitride film growth in the IR spectral region

Cubic boron nitride (c-BN) layers were deposited by a plasma activated process in a hollow cathode arc deposition device. The deposition process is analyzed by in situ polarized infrared reflection spectroscopy. The s-polarized infrared reflectance spectra of a growing BN film show the structure of the in-plane vibration of sp 2 bonded BN at 1370 cm −1 for film thicknesses greater than 20 nm. At thicknesses greater than 50 nm, the out of plane vibration at 780 cm −1 can be observed also. The signature of the cubic phase can be detected at a thickness of 95 nm. By simulation of the spectra, the damping constant of the c-BN oscillator was estimated to be 170 cm −1, nearly independent of the thickness. The transverse optical mode frequency of the c-BN phonon starts at 1090 cm −1, decreases to a minimum of 1070 cm −1 at a film thickness of 300 nm and increases at higher thicknesses. Up to a film thickness of 300 nm the oscillator strength increases from 5×10 5 cm −2 to 22×10 5 cm −2 and remains constant during further growth. The c-BN layer growth was investigated in situ during the variation of the DC bias voltage. At a bias voltage of −275 V a reflectance feature can be observed at 1360 cm −1 corresponding to the in-plane vibration of sp 2 bonded material.

Formation of BN nanoarches: Possibly the key to cubic boron nitride film growth

The formation of epitaxial nanotubes (nanoarches) on the surface of hexagonal BN (h-BN) during electron irradiation is reported. In addition to implications in terms of understanding fullerene based structures, we suggest that these act as the nucleation sites for cubic BN (c-BN) growth and may lead to improved film growth. We also report a strong dependence upon the microscope vacuum, which may be critical in understanding irreproducibility in film growth.

Thresholds for the phase formation of cubic boron nitride thin films

We introduce a phase diagram for boron nitride film growth. It is based on studies of the influence of the ion energy and substrate temperature on the phase formation using mass-selected ion-beam deposition of ${\mathrm{B}}^{+}$ and ${\mathrm{N}}^{+}$ ions. For the formation of the cubic phase we find threshold values of 125 eV for the ion energy and 150 \ifmmode^\circ\else\textdegree\fi{}C for the substrate temperature. Furthermore, we find a characteristic ion energy and substrate temperature dependence of the compressive stress, yielding low stress values for high energies and/or temperatures. c-BN nucleation and growth is attributed to a subsurface process qualitatively described by the subplantation model.

Initial stage of cubic boron nitride film growth from vapor phase

Low pressure inductively coupled plasma enhanced chemical vapor deposition (ICP–CVD) made it possible to deposit stoichiometric boron nitride (BN) films with thickness gradients in lateral direction, which clearly demonstrate the progresses of the cubic BN (c-BN) growth. Under optimal deposition conditions, single-phase c-BN grows on the initially deposited sp2-bonded BN layer, which had a critical sp2-BN-thickness of around 30–100 nm, depending on the substrate potential. It was also found that there exists a very close correlation between the c-BN formation and Ar incorporation, which was lower than the detection limit in the sp2-bonded BN layer, while approximately 0.4 at. % Ar was detected in the c-BN layer. Furthermore, drastic change of the strained state in the film and the surface morphology upon the transition of the growth phase from sp2-bonded BN to c-BN was confirmed. As a whole, the comprehensive characterization of the initial progress of the c-BN formation suggested that a highly compressed state in the atomistic local scale, not in the macro scale, should be essential for the c-BN formation.

Growth and characterization of epitaxial cubic boron nitride films on silicon.

We report the growth of boron nitride films on (001) faces of silicon using the method of pulsed-excimer-laser ablation. The structure of the deposited films is cubic zinc blende with a lattice constant of 3.619 \AA{}. The films were found to be heteroepitaxial with the cubic BN〈100〉 axes parallel to Si〈100〉, as characterized by x-ray diffraction and high-resolution transmission electron microscopy. We find evidence for an unusual 3:2 commensurate lattice matching.

7287. Growth of boron nitride films by gas molecular-beam epitaxy: M J Paisley et al,J Vac Sci Technol, B8, 1990, 323–326

7287. Growth of boron nitride films by gas molecular-beam epitaxy: M J Paisley et al,J Vac Sci Technol, B8, 1990, 323–326

Growth of boron nitride films by gas molecular-beam epitaxy

Boron nitride is a thermally stable and chemically inert material with a wide bandgap. As such, it has potential optoelectronic applications as windows, deep ultraviolet (UV) detectors, or UV light-emitting devices. Since it has a very high surface energy and a lattice parameter which is very similar to diamond, it may also prove to be an excellent substrate material for heteroepitaxial thin film growth of this material. This paper reports the preliminary results of the growth of BN thin films using gas source molecular beam epitaxy. The B source evaporated elemental B produced in a new high temperature effusion cell. The nitrogen source consisted of N ions as well as activated N atoms and molecules obtained from the decomposition of purified N2 by passing it through an electron cyclotron resonance plasma unit designed specifically for molecular-beam epitaxy (MBE) systems. A graded GaN–BN layer deposited on a monocrystalline β-SiC (100) film was used as the substrate for growth of each BN film. Transmission electron microscopy of the latter films showed them to be amorphous; however reflection high-energy electron diffraction (RHEED) patterns obtained during deposition indicated the presence of some microcrystallinity.

X-Ray Diffraction Study of Cubic Boron Nitride Grown Epitaxially on Silicon

ABSTRACTWe report the growth of boron nitride films on (001), (110), and (111) faces of silicon using the method of pulsed excimer laser ablation. The structure of the Alms grown on the (001) and (110) orientations of Si is cubic zincblende with a lattice constant of 3.619 Å. The films were found to be heteroepitaxial on silicon (001) with the cubic BN (100) axes parallel to Si (100), as characterized by x-ray diffraction and high-resolution transmission electron microscopy. In that system, we find evidence for an unusual 3:2 commensurate lattice matching. The films appear to cubic but randomly oriented on the Si (110), and no evidence for crystallinity is found for films grown on Si (111).