The problem of magnetron sputtering ferromagnetic target

- Mar 28, 2019-

The problem of magnetron sputtering ferromagnetic target

 

The rapid development of electronic information technology has created a huge demand for magnetic film and magnetic components. The preparation of magnetic film and magnetic components is inseparable from the ferromagnetic metals and alloys such as Fe, Co and Ni. Magnetron sputtering is a widely used method for manufacturing magnetic components by depositing high quality magnetic films because of its high purity and precise structure control. However, magnetron sputtering deposition of magnetic films has some problems such as difficulty in normal sputtering of ferromagnetic target materials, which hinders the production and application of high-performance magnetic films and devices.

 

The problem of magnetron sputtering ferromagnetic target

 

For Fe, Co, Ni, Fe2O3, permalloy and other ferromagnetic materials, to achieve low temperature, high speed sputtering deposition, the use of ordinary magnetron sputtering will be greatly limited. This is due to the above several target magnetoresistance materials is very low, most of the magnetic field is shown in figure 1 as almost entirely through from inside the ferromagnetic material, make the upper part of the target material surface residual magnetic field is too small, unable to form the electron area effectively, parallel to the target can't be formed on the surface of the secondary electron circular cycloid movement of the strong magnetic field, the magnetron sputtering not be performed. At this time, magnetron sputtering becomes a very inefficient diode sputtering, which greatly reduces the deposition rate of the film and heats up the substrate.

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FIG. 1 schematic diagram of magnetic field line passing through ferromagnetic target (C is the center axis of magnetic field line channel)

 

In addition to the magnetic shielding effect, the phenomenon of plasma magnetic polymerization becomes more serious when sputtered ferromagnetic materials are compared with ordinary target materials. As shown in FIG. 2, points 1 and 3 in FIG. 2 (a) are points on both sides of axis C in the magnetic field line channel. During sputtering, due to the co-existence of electric field and magnetic field, the electrons at points 1 and 3 are affected by coulomb force and lorentz force and move towards axis C in the magnetic field channel, while the electrons at point 2 are not affected by transverse force.

 

Therefore, the plasma at the spool is the most, the sputtering at the corresponding position of the target is the most intense, and the sputtering rate is the largest. This condition is present in all target sputtering. However, when sputtering ferromagnetic target, the phenomenon of plasma magnetic polymerization is more serious.

 

From figure 2 (d) can be seen, due to the plasma magnetic phenomenon, first appeared in the lines of magnetic force channel mid-line sputtering channel, the original through the lines of magnetic force from inside the ferromagnetic material will leak out from the channel, the deeper the sputtering of the channel, the leakage magnetic field lines, the lines of magnetic force of the magnetic field intensity, the greater the axis so that more of the electronic in magnetic field lines axial magnetic poly, the axial joints more plasma in the magnetic field lines, hence the greater the channel of the sputtering rate, eventually lead to the channel of the target material was splashing wear faster. Because the internal passage of the ferromagnetic target is far more than that of the ordinary target, its magnetic field lines flow out more, the magnetic field intensity at the axis of the magnetic line is larger, and the sputtering etching rate at the channel is faster.

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FIG. 2 plasma magnetic polymerization phenomenon during sputtering of ferromagnetic target f-one of numerous magnetic field lines on the surface of target

(a) magnetic field line channels on the target surface; (b) target magnetic field at the beginning of sputtering; (c) target magnetic field after sputtering for some time; (d) target magnetic fields to be etched through


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