Activated reactive evaporation

In direction evaporation, the evaporant is the refractory compound itself, whereas in reactive or activated reactive evaporation (ARE), a metal or a low valency metal compound is evaporated in the presence of a partial pressure of a reactive gas to form a compound deposit, eg, Ti is evaporated in the presence of N2 to form TiN, or Si or SiO is evaporated in the presence of O2 to form Si02. 

In some cases, the deposition rate can be increased by the action of a plasma in a process known as activated reactive evaporation (ARE). PI The plasma enhances the reactions and modifies the growth kinetics of the deposit. 

O. Marcovitch, Z. Klein, and I. Lubezky, Transparent conductive indium oxide films deposited on low temperature substrates by activated reactive evaporation, Appl. Opt., 28 2792-2795 (1989). 

This supplemental activation of the gas mixture is established by placing a positive electrode in the gas volume. This technique is called Activated Reactive Evaporation (ARE) and is illustrated in figure 13.7. 

Figure 13.7 Activated reactive evaporation (G= gas supply S= substrate V= source TE= positive electrode P= pumps).

Other compound films especially nitrides or carbides can be fabricated with high rates by a special activated reactive evaporation technique, ARE, developed by Bun-shah, see [391], in which the evaporant vapour species and the reaction gas are ionized or activated by impact of secondary electrons. 

Activated reactive evaporation with different starting materials, the ion current density is approximately 0,3 mA.cm 2 [396]. 

A technique which has received increasing interest in the last few years is the preparation of cubic nitride films by activated reactive evaporation with a gas activation nozzle [111 to 115]. While the boron is evaporated by an electron beam, nitrogen (with admixed argon) is activated in the nozzle supplied with a positive bias. Electrons thus attracted to the nozzle from the plasma zone enhance the discharge in the vicinity of the gas outlet. Acceleration of the ionized species towards the substrate is achieved by connecting it to a negative radiofrequency bias [111]. 

Cubic boron nitride films have also been prepared by activated reactive evaporation of boric acid in an NH3 plasma formed between a hot filament and an anode [119 to 121]. Other reports on ionized deposition of BN layers [122,123] and on p-BN deposited by sputtering in an NH3 or N2/Ar atmosphere [124, 125] show that the formation of the different BN phases in the resultant coatings depends critically on the conditions of the process. About the effects of the total gas pressure and the type of sputtering gas on the stresses of thin p-BN films, see [138]. 

Cubic boron nitride (cBN) is a very promising material that, after diamond, displays the highest hardness, excellent thermal conductivity, and important characteristic properties such as high electrical insulation and chemical and thermal stability. The cBN film can be deposited on a cemented carbide insert using activated reactive evaporation with a gas activation nozzle. Figure 20 shows the relation between the micro Vickers hardness (10 g load) of a BN film and its... 

Figure 20 Micro Vickers hardness of BN film deposited using activated reactive evaporation with a gas activation nozzle. Load 10 g. (Reprinted from Ref. 12 with permission from Elsevier Science.)...

Inagawa K, Watanabe K, Saitoh K, Yuchi Y, Itoh A. Structure and properties of c-BN film deposited by activated reactive evaporation with a gas activation nozzle. Surf Coat Technol 39/40 253, 1989. 

Activated reactive evaporation (PVD technology) Evaporation through a plasma of reactive gas in order to deposit a film of a compound material. The plasma activation increases the reaction probability and decreases the pressure of reactive gas needed to form the compound material. 

Bayard-Alpert gauge Bias active reactive evaporation Broad band antireflection Body-centered cubic (crystallography)... 

Since the reactive gas in the RE process is in a molecular state and thus less likely to react with the vapor species, the formation of a well crystallized stoichiometric film requires high thermal activation at the substrate. This problem becomes acute in situations where the reactive gas consists of more than one element. The typical examples are S1H and CH CgHg for the formation of silicides and carbides respectively. The concept of electron impact ionization and excitation of the reactive gas in the substrate-source space, as introduced by Bunshah and Raghuram solved this problem. The ionization and excitation of the gas activates the compound forming reactions and the compound films can be synthesl2 d at a much lower substrate temperature. This process is known as Activated Reactive Evaporation (ARE). 

Figure 3 Schematic of the Activated Reactive Evaporation Process (72).

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