1 Introduction

1.1 Sputtering process

Sputtering technique is a physical vapor deposition technique that is considered a successful technique as a result of its features like a high film deposition rate and low-temperature structures [1]. It is a simple and economical method for producing thin films of alloys, metals, carbides, nitrides, and oxides [2]. The most common approach to this technique is the magnetron sputtering technique that uses a magnetic field to assist the process of depositing thin films onto a substrate. The particles (atoms and ions) are ejected through the transfer of momentum from the Ar ions. In a magnetron sputtering, electrons are confined along the magnetic field lines. A gaseous plasma that confines electrons is generated, and then accelerated to bombardment the target, which will lead to erode the material and eject them in the form of neutral particles and a minor component of ions. Inert gas is typically used as sputter gas like argon or even an active gas like nitrogen. Then, these ejected particles will place onto the substrate and coat a thin film of the target.

The magnetron sputtering technique offers great advantages compared with other techniques like uniform, homogeneity, and great adhesion deposition over the comparatively large area, facility to choose the substrate material and target material with very high melting points, high deposition rate, and also easy of the control of thickness [3]. However, several disadvantages of reactive sputtering for instance target poisoning, poor deposition rates, and arcing causing defects in the thin film [4]. From the other hand, there are main factors used to tune the thickness of the synthesized films in sputtering technique. These factors are the integrated pulse energy, deposition time, [5] chamber pressure, plasma gas, the angle of target and the substrate, and substrate temperature which is important to reduce the dopant redistribution and defect formation related to high-temperature processing [6].

However, different energy sources are required to maintain the plasma state in magnetron sputtering technique while it is losing power inside the chamber such as direct current (DC) for conductive targets for instance aluminum and copper, radio frequency (RF) for nonconductive targets like silicon and manganese dioxide, ion-beam sputtering which can depend only on an ion source without using any magnetic field, ion-assisted deposition reactive sputtering, and high-power impulse magnetron sputtering (HIPIMS) that produce higher energy flux of sputtered comparing with DC magnetron sputtering and ionized atoms are delivered to the growing surface in pulses repeated at certain frequency [5, 7]. Some materials deposited by magnetron sputtering have found applications in energy such as in gas turbine blade coating and solar panels, electronics/microelectronics application in flip-chip backside metallization and sensors, and many other applications in various fields.

1.2 History of boron carbon nitride (BCN) thin film technology

In the recent years, thin film technology was applied in the field of semiconductors science. More interestingly, BCN films represented a potential material as protective and hard coatings for cutting tools and for other wear-resistance uses [8,9,10,11,12,13,14]. Drude in 1889 discussed the earliest fabrication of thin films under vacuum with unique characteristics on the glass of discharge tubes [15]. The principal properties of the materials could be improved by the formation of thin films instead of other structural arrangements. For instance, few numbers of microns of gold material coated onto glass surface make the glass conductive. Furthermore, thin film technology was used to prepare metastable phases at low temperature especially with applying plasma techniques such as sputter deposition and plasma assisted chemical vapor deposition (PACVD) techniques. For example, cubic boron nitride could be prepared easily at lower pressure and temperature than bulk fabrication processes. Moreover, PACVD techniques were employed to prepare polycrystalline diamond at 20 mbar pressure and lower than 1000 K temperature [16]. Thin film technology has been applied to semiconductor and photovoltaic cell technologies [17, 18]. It is well known that elemental solids of group IVA and compounds between IIIA and VA groups were applied in the aforesaid technologies because of their excellent physical and electrical properties. Within the next sections, the unique behaviors of BN and B4C materials will be discussed as well as the promising properties resulting from combining these materials to synthesize BCN thin films.

1.2.1 Boron nitride (BN) thin films

Diamond, c-BN, and boron carbide (B4C) are among the hardest known materials apart from nanocomposites or nano-multilayer materials. The structures of diamond and c-BN are very close to each other. Graphite and h-BN exhibit layered structures with weak van der Waals forces. More interestingly, graphite is a semi-metal while h-BN is an insulator.

Boron nitride material is a dry lubricant with excellent properties, which can be altered with respect to the crystal morphology. BN layers were applied in electron-field emitters, high-temperature dielectrics, tribological devices, and optoelectronic systems [19,20,115]. To investigate the physical and the chemical characteristics of deposited films, graphite, and B4C targets were applied in RF sputtering by Essafti et al. to deposit amorphous CN, amorphous BC, and amorphous BCN thin films on silicon substrates. It was found that carbon atoms bound to nitrogen atoms majorly as sp2 C=N rather than sp3 C–N and exist as C–C bonds in the deposited BCN films. In addition, C=N and B–N bonds were also formed. The films were deposited with varying proportions and diverse bonding forms. The great variation in the shape and the binding energies of the C1s core level XPS spectra indicated the difference in the morphology of the synthesized films [116].

3.8 Corrosion studies

Composites are applied in a wide range of applications because of their promising properties [117,118,119,120,121,122,123,124,125]. To illustrate, the corrosion behavior of BCN films has been attracted a growing attention of researchers to allow their application in different environments. The electrochemical polarization and dissolution rate of a deposited BCN thin film in acidic, neutral, and alkaline mediums were studied by Byon et al. The dissolution rate of B1.0C2.4N1.0 thin film was declined in NaOH < NaCl < HCl solutions (Fig. 5a). In 1 M NaOH medium, it was revealed that as the C ratio increases as the dissolution rate of the BCN film decreases (Fig. 5b). In addition, a B1.0C(3.2–4.4)N1.2 thin film was noticed to exhibit a superior corrosion-resistant performance [126].

Fig. 5
figure 5

Dissolution rate (−Δd/Δt) of a B1.0C2.4N1.0 films in 1 M HCl, 1 M NaCl, and 1 M NaOH mediums, b B1.0C(0.5–4.4)N(0.9–1.2) films in 1 M NaOH medium [126]

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3.9 Raman spectroscopy studies

Raman spectroscopy is a technique applied to measure the wavelength and intensities of inelastically scattered light by measuring the change in rotational, electronic or vibrational energy of a molecule. The properties and microstructures of the films can be investigated by Raman spectroscopy [127]. The long-range ordered crystalline structure can be predicted from Raman results. To illustrate, Tsai et al. used pulsed-DC magnetron sputtering technique to deposit BCN films using B4C target under Ar/N2 gas flow. Numerous processing factors were discovered to grow BCN films with high c-BN content [128]. To characterize the composition and phases, Raman spectroscopy with other techniques was used. By changing temperature and substrate bias, the deposited BCN films displayed h-BN, c-BN, wurtzite-BN (w-BN) phases and their mixed phases. By controlling the substrate bias and stage deposition technique, 90% c-BN film was obtained with clear facets and grains [128].

4 Metal-insulator-metal (MIM) devices based on BCN thin films

Prakash A. and Sundaram K. synthesized BCN thin films by RF magnetron sputtering using B4C target at various flow ratios of N2 and Ar gasses and deposition temperatures to study the electrical properties of metal-insulator-metal (MIM) devices. They found that increasing the N2 gas in the BCN film and the substrate temperatures leads to drop the dielectric constant but increasing the dielectric breakdown strength and the resistivity. Moreover, the highest dielectric breakdown strength of 3.4 MV/cm of BCN films achieved with a dielectric constant of 2.13 and resistivity of 3 × 1012 Ω.cm [129]. Another paper conducted by Prakash et al. for MIM devices tested for their potential UV photodetection capability by using BCN films applied in harsh environment applications. They used dual target RF magnetron sputtering, BN target as DC sputtering and B4C as RF magnetron sputtering with N2 and Ar as processing gas to form BCN films. Glass substrate used to produce MIM structure, deposited by aluminum strips as a bottom electrode using a mechanical mask in a thermal evaporation technique and loaded in the sputtering system to deposit a thin film of BCN of a thickness of 100 to 120 nm. The last step ended by creating the top electrode through depositing a number of gold strips over the BCN film, a thin layer of gold fabricated by using thermal evaporation process to form a transparent top electrode for the photo-detector window. Using UV photocurrent measurements, the optoelectronic performance of the BCN MIM device was examined using UV photocurrent measurements. The device achieved a UV photocurrent response of two orders higher with respect to dark current in the range − 3 to 3 V [130].

Table 1 represents different processing parameters used to prepare thin BCN films. This table summarizes the targets used in both of RF and DC powers, deposition gasses, and the various temperatures used during the deposition and the main results.

Table 1 Summary for different processing parameters used to prepare BCN thin films
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5 Conclusion

Sputtering technique is considered as an excellent method to synthesize thin films with availability to use various types of substrates and deposit uniform films over a relatively large area. Many studies conducted the synthesis of BCN by RF magnetron sputtering and investigated different properties of the films and the effect of varying deposition parameters. The increase of N2 flow resulted in a significant decrease in the elastic modulus, hardness, and wear resistance and led to reducing the amount of boron and carbon in BCN films. From the other hand, varying the temperature and annealing affected the refractive index and the optical bandgap. Furthermore, even at high annealing temperature at 1000 °C, it has been found that BCN films possess an unlimited vacuum thermal stability. Sputtering power also played a primary role in enhancing the elastic coefficients, hardness and elastic modulus of the synthesized films. Changing the bias voltage and substrate temperature allowed to control the bond contents in the deposited films. The hardness of BCN films can be improved by increasing the substrate temperature. The incorporation of about 20% of N2 leads to producing BCN films with either electrically insulating behavior with a low dielectric constant or high mechanical characteristics. When the nitrogen content in the BCN film was surged, the optical transmission was increased dramatically while increasing the substrate temperature modified the transmission slightly. Furthermore, deposition BCN films at 400 °C offered the highest PL intensity, reducing the deposition temperature reduced the PL intensity. Cu diffusion could be increased by increasing the boron loading of BCN thin films whereas, changing the annealing temperature revealed very small Cu diffusion enhancement. Increasing the N2 content and substrate temperature diminished the dielectric constant of the deposited BCN films. In addition, increasing the substrate temperature increased the breakdown voltage initially then followed by a slight decrease. The resistivity was found to be constant and can be slightly modified with increasing the substrate temperature. Corrosion studies revealed that B1.0C(3.2–4.4)N1.2 thin films provided superior corrosion-resistant properties. BCN MIM devices achieved a UV photocurrent response of two orders higher with respect to dark current in the range − 3 to 3 V.