Magnetron Sputtering

Magnetron Sputtering In PVD Thin Film Coating

Sputtering as a phenomenon was first observed back in the 1850s but remained a scientific curiosity until the 1940s, when diode sputtering was firstly used to some significant extent as a commercial coating process.

Sputtering is the process whereby atoms or molecules of a material are ejected from a target by the bombardment of high-energy particles. However, main disadvantages of diode sputtering were related to the very low deposition rates and large cost. Then, in the mid-1970s, a magnetically enhanced variant of the diode sputtering known as magnetron sputtering emerged.

Magnetron sputtering is a high-rate vacuum coating technique for depositing metals, alloys, and compounds onto a wide range of materials with thicknesses up to millimeter. It exhibits several important advantages over other vacuum coating techniques, a property that led to the development of a large number of commercial applications from microelectronic fabrication to simple decorative coatings. There are various advantages of magnetron sputtering as below:

1. High deposition rates;

2. Ease of sputtering any metal, alloy, or compound;

3. High-purity films;

4. Extremely high adhesion of films;

5. Excellent coverage of steps and small features;

6. Ability to coat heat-sensitive substrates;

7. Ease of automation;

8. Excellent uniformity on large-area substrates, for example, architectural glass.

As working principle, when power is supplied to a magnetron, a negative voltage of typically − 300 V or more is applied to the target. This negative voltage attracts positive ions to the target surface inducing at the same time large kinetic energy. It is well known that an energy transfer occurs when a positive ion collides with atoms at the surface of a solid. If the energy transferred to a lattice site is greater than the binding energy, primary recoil atoms can be created, which can further collide with other atoms and distribute their energy via collision cascades. Sputtering occurs if the energy transferred on a direction normal to the surface is larger than about three times the surface binding energy (approximately equal to the heat of sublimation).

Sputtering of a target atom is just one of the possible results of ion bombardment of a surface. Aside from sputtering, the second important process is the emission of secondary electrons from the target surface. These secondary electrons enable the glow discharge to be sustained. The sputter process has almost no restrictions in the type of the target materials, ranging from pure metals where a DC power can be used to semiconductors and isolators that require either RF power or pulsed DC. Deposition can be carried out in either nonreactive (inert gas only) or reactive (inert and reactive gas) discharges with single or multielemental targets.