Deposition of Cubic Boron Nitride Thin Films using Electron-Beam
Evaporation
S. P. Vemuri, S. Nasrazadani
Engineering Technology Department, University of North Texas, Denton, TX-76203
Abstract
Boron nitride thin films have been prepared at room temperature using an electron beam
evaporator on Silicon Substrates in an ultra high vacuum environment. The structure and
composition of the thin films have been measured using Fourier transformer infrared
spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM) and
X-ray photoelectron spectroscopy (XPS). The FTIR transmittance spectrum shows
absorption peaks at 1042 cm-1 and 788.89 cm
–1
corresponding to cubic boron nitride
(cBN) and hexagonal boron nitride (hBN) respectively. XRD pattern shows peak near 2
of 390 corresponding to orthorhombic boron nitride.
Keywords: Boron nitride, Electron beam evaporation, Characterization techniques
1. Introduction
Boron nitride films exist in various structural forms such as cubic, hexagonal, tetragonal,
orthorhombic etc., Out of all these cubic phase of boron nitride is known to be the most
attractive material because of its extreme hardness, wear resistance, thermal stability and
chemical inertness. cBN also has wide band gap thus it can be doped with both p-type
and n-type impurities. It is the second hardest material next to diamond. These properties
of cBN motivated to prepare cBN in the form of thin films for protective, wear-resistance
cutting applications and as semiconductors for electronic device applications [1-3].
Even though cubic boron nitride is thermally more stable form of boron nitride it is
proven that it is extremely difficult to grow thin films of it. Various chemical vapor
deposition and physical vapor deposition processes have been employed to progress the
synthesis of cBN significantly [4]. Most of these techniques use ion beam enhanced
deposition in which thin film is grown by bombarding the energized ions. This intense
energetic ion bombardment tends to produce high compressive stress thus making the
film peel off the substrate [5].
In this paper we prepared cBN thin films employing a novel technique that involves
electron beam evaporation of bulk boron nitride pellets onto silicon substrates maintained
at room temperature. A large sample area has been deposited with boron nitride. FTIR
spectrum shows the peak corresponding to cubic phase of boron nitride.
2. Experimental Setup
Film Deposition
In this work, Silicon (100) substrates were used to deposit thin films of cubic boron
nitride. Before being loaded into the vacuum chamber the silicon wafers were cleaned
with HF acid, rinsed with deionized water and blown dry by the nitrogen gas. The clean
substrate is then loaded into the chamber, which is maintained at a pressure of 2 X 10-8
torr. The apparatus of electron beam evaporation used in this study is shown in Fig. 1.
The vacuum chamber used for experiments was-------- in diameter and ------- in height.
The evaporator gun is placed at the bottom of the chamber vertically and the substrate
holder is mounted on the top. Boron nitride pellets were placed in the crucible that can be
held at a high potential of 2 KeV. At the emission current of 40 mA the evaporation
begins. The deposition parameters used in this experiments are shown in Table. 1. The
thickness of the films deposited by this process is -------------.
1
2
3
Fig. 1. Schematic diagram of E-beam evaporator. (1) Vacuum Chamber; (2) Substrate
Holder; (3) Evaporator Gun
Table.1. Table of Deposition Parameters for E-beam evaporation
Parameter
Condition
Chamber pressure
2 X 10-8 torr
Substrate temperature
25oC
Filament temperature
2000oC
Electron beam energy
2 KeV
Source to substrate distance
Target material
Bulk boron nitride
Film Characterization
The films were first characterized by Fourier transform infrared spectroscopy in
transmittance mode. Two peaks at around 788 and 1042 cm-1 were observed after
deducting the background spectra of the uncoated substrate. The band at 788 cm -1 is
corresponding to hBN and one at 1042 cm-1 is corresponding to the cBN. The crystal
structure was determined by X-ray diffraction spectra of the films. The binding energy
and film composition were determined using X-ray photoelectron spectroscopy with Al
K radiation and a Scanning electron microscope was used to examine the surface
morphology of the thin films.
3. Results and discussion
The FTIR spectra of the boron nitride films in Fig. 2 show sharp bands at 788 and 1042
cm-1. The peak at 788 cm-1 is attributed to the presence of hBN and the absorption peak at
1042 cm-1 is due to the presence of cBN. The absorption peaks corresponding to hBN are
weak than that for cBN, thus it can be estimated that the fraction of cBN is high.
The X-ray diffraction pattern of the boron nitride film deposited on a substrate at room
temperature is shown in Fig. 3. An intense peak at 2 approximately equal to 14.091 and
39.169 was observed and an intense hump centered at 2 equal to 20.88o was also found.
There was no distinct peak corresponding to cubic boron nitride (2 = 43.297). The peaks
at 2 equal to 14.091 and 39.169 correspond to orthorhombic boron nitride (001) with d
spacing of 6.28 Ao and (131) with d spacing of 2.298 Ao respectively. As discussed by J.
Ullmann et al. [6] boron nitride films with high cubic content does not yield good results
in XRD experiment. The intense hump at 2 of 20.88 is also due to the orthorhombic
111) phase of the boron nitride with d spacing of 4.25 Ao.
The elemental composition of the thin film deposited is determined using X-ray
photoelectron spectroscopy. Fig. 4 is the XPS spectrum of film deposited. This spectrum
shows the presence of carbon, oxygen, Silicon and Boron. Though there was boron in the
spectrum it was bonded with oxygen to form B2O3. The value of 189 eV is attributed to
the free boron whereas boron combined with nitrogen is expected to be at binding energy
of 190.4 eV. Since the film is very thin the XPS used haven’t provided the desired
results.
The thickness of the film deposited was measured using ---------- . Fig. 5 shows the XRD
pattern of the thin film to determine the thickness. The thickness of the film is measured
using the formula:
2t(sinn+1 - sinn) = 
Where t is the thickness of the film deposited, n+1 is the  value for the sample, and n is
the value of  for the substrate.
By using this formula the thickness of the film was determined to be 103.1  12 Ao
Conclusions
The boron nitride thin films deposited by electron beam evaporation of solid boron
nitride pellets have different structural forms like hexagonal, orthorhombic and also
cubic. It can also be said that thin films can be deposited even if the substrate is at room
temperature. Characterizing the film deposited with different techniques such as FTIR,
XRD, XPS and SEM confirmed the presence of cBN along with other structural forms.
Since the film is very thin the exact stoichiometry of the film was not determined. The
future work in this direction can yield formation of boron nitride thin films with less
expense and within short span of time.
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