Compounds comprising the element boron have many applications, in various fields. These compounds are used, for example, in the electronics industry, in the glass industry, in detergents, in enamels and ceramic glazes, in agriculture, in the iron and steel industry, in metallurgy, in cements and concretes, in paints, in nuclear power stations, and in the pharmaceutical field. These compounds can also be used for coating combustion chambers, turbine blades, tools, etc.
More particularly, some of these compounds are used for giving materials other properties, such as optical and electrical properties. For example, boron (a column III element) is widely used in the semiconductor industry where it serves as a dopant, especially in silicon or in transparent conducting oxides (TCOs) such as zinc oxide (ZnO).
The most commonly used techniques for applying a layer of boron and/or doping materials with boron are the CVD and PVD deposition techniques.
It is known to use, via the CVD technique, diborane (B2H6), trimethylborane (B(CH3)3 or TMB), triethylborane (B(C2H5)3 or TEB) or boron trifluoride (BF3) as precursors of the element boron to “p-type” dope thin films of silicon in order to produce, for example, solar cells.
Reference can also be made to documents U.S. Pat. No. 6,100,202 and U.S. Pat. No. 5,646,075 which mention the use of trimethylborate or triisopropylborate.
It is also known, via the CVD technique, how to dope transparent conducting oxides, such as zinc oxide, with boron by using diborane as a boron precursor. This doping allows these oxides to become conducting while retaining their transparency. TCOs are widely used materials since numerous applications seek the combination of optical transparency and electrical conductivity. Mention may in particular be made, as applications, of flat screens, de-icing windows, heat-reflective windows, electrochromic mirrors and windows, touch screens, electromagnetic shielding, electrostatic charge dissipation and solar cells.
Furthermore, it has been proposed to use boron tri-isopropoxide (B(OiPr)3) as an agent for doping zinc oxide via the sol-gel technique.
However, these compounds have the major disadvantage of being dangerous to handle. For example, diborane and trimethylborane are highly flammable and very toxic. Specifically, a dose of 30 to 90 mg/m3 of diborane is lethal after 4 hours of exposure to this product. As regards trimethylborane, it is a pyrophoric gas.
Furthermore, the cost of these compounds is very high.
A person skilled in the art seeks to use compounds that are less dangerous to handle while minimizing the costs, in order to increase the competitiveness of the end product.
Therefore, there remains the need to propose novel CVD and PVD deposition processes for which the costs are reduced, while optimizing safety during product handling.