The decision of dispersion uniformity problem the target provides films reception with uniform thickness. With this purpose magnetron systems use in a combination with standard planetary intrachamber devices that allows besieging a film which non-uniformity of thickness does not exceed 2 %.
The Important question by development of vacuum installations with magnetron systems of dispersion is the choice of exhaust means of chambers and the design of vacuum system. It is dictated by features of dispersion process:
1) It is necessary to provide a low level of polluting impurity for what it is used high-vacuum spill;
2) Process is necessary to spend at enough high pressure of working gas (0,5-1) P, not peculiar to the majority of high-vacuum pumps, and big gas streams.
Use of not warmed up working chambers, which walls provide intensive gas evolution, forces to spend constant "washing" of working volume by inert gas for removal of polluting impurity. At target dispersion the part of particles gets on walls of the chamber and equipment of the chamber that leads to their heating, and, hence, and to increase of gas evolution from walls and equipments of the chamber. To avoid undesirable gas evolution the chamber supply with system of cooling. For protection of vacuum system elements against of sprayed material sedimentation filters are installed.
Magnetron atomizing system (MAS) is one of versions of diode dispersions schemes. Operation of magnetron atomizer is based on target-cathode material dispersion at its bombardment by ions of the working gas formed in plasma of the abnormal glow discharge. Secondary electron emission arising at it keeps up the discharge and causes dispersion of a target-cathode material. High dispersion speed, characteristic for these systems, is achieved by increase in density of an ionic current due to localization of plasma at a sprayed surface of target by means of crossed electric and magnetic fields [14].
Basic elements of the magnetron atomizing system: the cathode, the anode and the magnetic system intended for localization of plasma at a target-cathode surface.
Figure 3.1. The scheme of planar magnetron atomizing system
1 - the basis; 2 - the case; 3 - constant magnets; 4 - the anode; 5 - the cathode-target; a - erosion zone.
Most widely apply planar magnetrons (figure 3.1). On the cathode the direct voltage (300 … 800) from the power supply applies; under the cathode the magnetic system consisting from central and the peripheral constant magnets 3, located on the basis 1 of m-metal is located. All elements of MAS are mounted on the case 2.
At applying of a direct voltage between target (negative potential) and the anode (positive or zero potential) there is a non-uniform electric field and the abnormal decaying discharge is raised. Presence of the closed magnetic field at a sprayed surface of a target allows localizing plasma of the discharge directly at a target. Emitted from the cathode under action of ionic bombardment electrons are grasped by magnetic field, imparts complex cycloid movement to them on the closed trajectories at a target surface. Electrons appear as though in a trap created on the one hand by a magnetic field, returning electrons on the cathode, and on the other hand - a target surface which is pushing electrons away. Electrons cycling in this trap until there will be some ionizing collisions with atoms of working gas as a result of which electron will lose the energy received from electric field. Thus, the most part of electrons energy before it will get on the anode, is used on ionization and excitation that considerably increases efficiency of ionization process and leads to increase of positive ions concentration at a target surface. It in turn causes increase in intensity of ionic bombardment of a target and significant growth of dispersion speed, and consequently, deposition rate of the film [14].
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