For a planar magnetron sputtering target, the magnetic steel is placed behind the target, and magnetic lines passing through the surface of the target to form a magnetic field on the surface of the target. The magnetic field B parallel to the target surface and the electric field E perpendicular to the target surface, they forms a drift field E×B that is parallel to the target surface. The drift field E×B has the function of trapping for electrons, which increases the electron density of the target surface, increases the collision probability of electrons with neutral gas molecules, and strengthens the ionization rate of the sputtering gas, thereby increasing the sputtering rate. For a typical planar rectangular magnetron sputtering target, the magnetic steel arrangement is shown in Fig.1 (the adjacent magnetic steels have opposite polarities, ie NSN or SNS).
Fig.1 Diagram of magnetic steel layout and magnetic field distribution
The magnetic field line distribution in Fig.1 is calculated by numerical simulation. It can be seen that the area where magnetic field line on the target surface is approximately parallel to the target surface is narrow. Since in the magnetron sputtering system, the sputtering area of the target surface is mainly concentrated in this area where magnetic field line on the target surface is approximately parallel to the target surface. The width of the etched trench becomes narrower as the etch depth increases during the sputtering process. The resulting etch profile is shown in Fig.2.
Fig.2 The etching caused by the usual magnetic steel arrangement
According to the area calculation, the target utilization ratio of the above-mentioned magnetic steel arrangement method is only about 20%. It can be seen that the usual arrangement of magnetic steels makes it difficult to obtain high target utilization rates and deposition rates.