DS0303 -

Development of a new microplasma process for hexagonal boron nitride synthesis – DESYNIB

Development of a microplasma process for hexagonal boron nitride deposition

The DESYNIB project has allowed a new chemical vapor deposition process assisted by microplasmas of hexagonal boron nitride on large surfaces to be developed. The experimental and theoretical researchs carried out in the frame of this project have allowed the fundamental mechanisms governing the deposition process to be identified.

Development of a deposition process assisted by microplasma of hexagonal boron nitride – identification of the mechanisms governing the process.

The principal objectives of the DESYNIB project are : (i) to develop an efficient plasma reactor for the deposition of high potential materials on large surfaces and (ii) to optimize the quality of the deposited layers by understanding the mechanisms involved in growth processes using reactive plasmas. The targeted material is hexagonal boron nitride (h-BN), a strategic material highly demanded for electronic and optoelectronic applications, but the development of applications based on this material is still held back by the poor availability of high-quality epitaxial films on large areas. In this context, the project has four main scientific objectives: (i) to understand the fundamental physics of a MHCD in reactive gas (N2), (ii) to build a multi-holes MHCD array reactor, so-called “matrix reactor”, that allows high atomic nitrogen density to be reached, a key parameter for the deposition and growth of nitride films, (iii) to study and optimize the deposition of epitaxial h-BN films on large surfaces (up to 5 cm in diameter) by injecting boron-containing precursor in the matrix reactor and (iv) to evaluate the possibility to implement the plasma source into a commercial reactor.

The fundamental study of a Micro Hollow Cathode Discharge (MHCD) in reactive gas (argon/nitrogen mixture) has been carried out thanks to experimental diagnostics which allow the electrical parameters of the discharge (voltage, current, resistance) and the key species densities for the deposition process (i.e. electrons, atomic nitrogen and metastable argon atoms) to be determined. A volume-averaged model (0D) has been developed and compared to the measurements. The model allows the mechanisms related to the optimisation of the atomic nitrogen production to be highlighted. A comparative study between two high-voltage pulsed power supplies allows the development of the power supply used to ignite the plasma source in the deposition reactor. A large part of the time dedicated to the development and the construction of the deposition reactor was related to the development of the boron precursor injector in the low pressure chamber where the heating and polarizable substrate holder is located. The precursor being liquid at room temperature, we use a cylinder bubbler to inject it in the chamber controlling precisely the injected quantity.

The new process developed in the frame of this project allows for the first time the deposition of hexagonal boron nitride films on 2-in. substrates at lower temperatures than the conventional deposition processes. The fundamental study carried out in parallel has allowed the existence of an optimal nitrogen fraction in the argon/nitrogen mixture for the production of atomic nitrogen , key species for nitride deposition, to be highlighted. The JCJC project will continue through a new funded PRC project (call 2020), in partnership with two other french laboratories, which will allow the optimisation of the deposition process as well as its expansion with the deposition of other materials.

The possibility opened up by microplasmas to deposit hexagonal boron nitride at temperatures lower than conventional processes allows the energetic cost to be reduced and the use of heat sensitive substrates. The versatile character of this new process opens very interesting perspectives for the deposition of other materials by microplasmas, in particular graphene whose unique properties are optimized when it is associated to hexagonal boron nitride.

The work done in the frame of this project has been published in two papers and two others are being prepared. The results have been presented in 13 international conferences (1 invited) and 3 national conferences (1 invited).


The DESYNIB project aims to develop and optimize an innovative Micro Hollow Cathode Discharge (MHCD) deposition reactor on large surfaces of hexagonal boron nitride (h-BN), in nitrogen atmosphere. This innovative project, driven by a consortium of young researchers having a solid and complementary expertise in plasma processes and material sciences, will open a new exploratory research axis in the Laboratory of Material Sciences and Processes (CNRS LSPM, UPR 3407).
h-BN is a strategic material for strong added value applications, such as photonics and electronics. The scientific community still lacks an efficient growth method to deposit homogeneous thin epitaxial h-BN films on large surfaces (we aim to deposit on 5 cm substrates in this project). MHCDs allow high electron densities and therefore high dissociation degree of the precursors to be reached which is particularly suited for nitride deposition given the high bond energy of molecular nitrogen (9.5 eV). Since these micro discharges are not in thermodynamic equilibrium, it is also possible to considerably reduce the deposition temperature compared to conventional processes.
This project will be organized in three work packages: (i) fundamental study of the MHCD in reactive gases, (ii) construction and study of a matrix reactor and (iii) h-BN deposition with a matrix reactor. It will involve theoretical and experimental research to understand the fundamental mechanisms governing the deposition process and to optimize the reactor. This latter will be composed of two chambers. A “plasma source stage” will provide an effective source of atoms thanks to the MHCD array while the created discharge will expand into a “deposition stage” where the boron precursor will be injected and the substrate located. The reactor construction involves thoughtful engineering work including manufacturing of the MHCD array and designing the generator used to supply the discharge.
The plasma source will be characterized to determine the relevant parameters of the process, such as densities, fluxes and temperatures of reactive species under different operating conditions. State-of-the art diagnostics will be used, based on optical (absorption and emission spectroscopy, fluorescence) and electrical measurements. A volume-averaged model (0D) that allows scaling laws to be obtained and the exploration of a large parameter space, will be developed to study the physics involved in one-hole MHCD. This will allow the reactive species concentrations to be calculated as a function of the external parameters (pressure, power, flow rate). This 0D model will be usefully completed by a hybrid model which will allow the 2D modelling of the plasma expansion in the deposition chamber. This expansion will be studied both in the case of one hole and multi-holes, to take into account possible interactions between adjacent holes. Thorough comparison of experiments and model results will be made in order to improve the sizing of the plasma reactor.
The deposition of h-BN will be optimized by varying the key process parameters such as pressure, plasma source-substrate distance, surface temperature, and boron concentration, and through a detailed study of the boron-precursor injection system. The h-BN films will be characterized in the LSPM laboratory by X-ray Diffraction and Raman Spectroscopy to evaluate the phase purity and quality, and also by scanning electron microscopy for the surface morphology observation. Collaborations with experts, already contacted, in Transmission Electron Microscopy (University Paris 7 and University of Zaragoza in Spain) and in confocal microscopy (University Montpellier 2) will allow the quality of the films to be benchmarked.
In terms of valorisation, a French industrial company (ANNEALSYS) has already manifested its will to implement such a plasma source into its existing Chemical Vapor Deposition reactors, after the consortium has obtained a proof of concept.

Project coordination

Claudia Lazzaroni (Laboratoire des Sciences des Procédés et des Matériaux)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LSPM UPR3407 Laboratoire des Sciences des Procédés et des Matériaux
LSPM (CNRS DR PV) Laboratoire des Sciences des Procédés et des Matériaux

Help of the ANR 213,300 euros
Beginning and duration of the scientific project: - 48 Months

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