Page 192 - Semiconductor Manufacturing Handbook

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PHYSICAL VAPOR DEPOSITION

PHYSICAL VAPOR DEPOSITION 13.15

200 Cu
Au
Sn Ag

Pt
150 Ni
Relative sputter rate 100 Cr Vacuum
Al
molten
target
V2A
Hot pressed
Cr
Ti
Ta target
50 W

0
500 1000 1500
Power/W
FIGURE 13.18 Relative sputtering rate as function of sputter
power. 10

• Layer density
• Layer hardness
• Pinhole density and
• Layer composition

13.7.6 Reactive Sputtering

In reactive sputtering a chemical reaction between target atoms and a reactive gas occurs. The result-
ing layer is a compound of the target and the reactive gas material (e.g., Ti + O → TiO ). The reac-
2 2
tion (Fig. 13.19) can take place (a) at the target, (b) in the gas-phase, or (c) on the substrate. Reactive
sputtering is frequently used for oxides, carbides, and nitrides.

13.7.7 Magnetron Sputtering
In conventional sputtering, only a few secondary atoms contribute to further ionization of Ar atoms.
Most electrons are collected at the anode leading to heating of the substrate. Magnetron sputtering
increases the number of electrons contributing to ionization of Ar atoms by using an electromag-
netic field. The E and B fields cause a cycloid motion of the charge carriers in the plasma. The
deflection radii of the electrons are much smaller than that of the ions. Therefore, the electrons con-
centrate close to the target leading to a larger probability of ionization and thus, a higher sputter rate.
r
r
The (EB× ) drift causes electrons to flow to a special anode rather than to the substrate, therefore
reducing heating of the substrate. Magnetron sputtering, naturally, has a larger impact in dc sputter-
ing, but is used in HF/RF sputtering as well. The drawback of magnetron sputtering is the inhomo-
geneous use and ablation of the target (Fig. 13.20) leading to early need for replacement. New
methods with more complex electromagnetic field geometries allow for a more efficient use of the
target material. Normally, a target supplier will reclaim the remaining material on the base plate and

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