RF Sputtering of Molybdenum Target

With the development of modern electronic technology, the requirements for film-forming quality of semiconductor devices are getting higher and higher, thus promoting the progress of vacuum deposition technology, of which RF sputtering is a better film-forming method. RF sputtering can use some refractory metal materials or dielectric materials as thin films at lower temperatures. The contamination during sputtering is much smaller than that of evaporation, the film quality is relatively pure, the adhesion between the film and the substrate is strong, and the layer thickness is also uniform. In addition, the exchange frequency of the sputtering target is very small, a target can be used continuously for a long time before it needs to be replaced, and the sputtering rate has nothing to do with the vapor pressure of various components, and it has almost no fractionation effect. The portions are more even.

Generally sputtering can only sputter conductive metal materials, and it is not suitable for non-conductive non-metal materials (especially those with good isolation performance). At this time, RF sputtering can solve this contradiction. The sputtering target and its assembly schematic diagram are shown in Figure 1. When argon ion Ar + impinges on the dielectric target, positive charges accumulate on the surface of the target, due to the same repulsion Therefore, the Ar + that continues to bombard the target surface is repelled, so that sputtering cannot be performed. However, if a metal electrode is added on the back of the dielectric target, a high-frequency voltage is applied to this electrode to induce displacement current in the medium, so that the positive charge registered on the surface of the medium during the negative half cycle will be within the positive half cycle Neutralized by the displacement current, the sputtering process can be carried out, so RF sputtering can be applied to metallic materials or non-metallic materials.

The sputtering of molybdenum metal is carried out in two steps:

1) Pre-sputtering: Before the sample has been transferred under the target, "splash" in advance for 5 minutes, the purpose is to remove the adsorbate on the surface of the metal molybdenum target.

2) Positive sputtering: Transfer the sample directly under the target, and formally sputter for 5 minutes, the film thickness is about 2900 Angstroms (the distance between the target and the substrate is about 4 cm). After the sputtering is completed, the argon flushing valve must be closed, the surface of the molybdenum film is oxidized for too long, and the resistance increases.