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Sputtering target

Sputtering target

There are several forms of Thin Film Deposition which is a vacuum technology for applying coatings of pure materials to the surface of various objects. The coatings are usually in the thickness range of angstroms to microns and can be a single material or multiple materials in a layered structure.

The object to be coated is referred to as the substrate, and can be any of a wide variety of things such as: semiconductor wafers, solar cells, optical components, or many other possibilities. The materials to be applied can be pure atomic elements including both metals and non metals, or can be molecules such as oxides and nitrides.

Coating methods include Physical Vapor Deposition (PVD) and one technique is called Sputtering. Sputtering involves introducing a controlled gas, usually chemically inert argon, into a vacuum chamber, and electrically energizing a cathode to establish a self sustaining plasma. The exposed surface of the cathode, called the target, is a slab of the material to be coated onto the substrates.

The gas atoms lose electrons inside the plasma to become positively charged ions, which are then accelerated into the target and strike with sufficient kinetic energy to dislodge atoms or molecules of the target material. It can be thought of as a sort of atomic scale bead blasting. This sputtered material now constitutes a vapor stream, which traverses the chamber and hits the substrate, sticking to it as a coating or "film".

In order to get good film adhesion, it is, of course, necessary for the substrate surface to be clean. Appropriate cleaning and handling steps must be employed prior to placing substrates into the vacuum chamber. In addition, it is not uncommon to also have optional in situ cleaning features such as sputter etch incorporated into the sputter system.

Steps may have to be taken to control various film properties as desired. Fortunately, sputter system design can allow adjustability of a number of parameters in order to give process engineers the ability to achieve desired results for such variables as thickness, uniformity, adhesion strength, stress, grain structure, optical or electrical properties, etc.

There are also considerations such as what type of power to use on the cathodes. DC power is suitable for conductive materials, but RF power can also sputter non conductive materials. Pulsed DC has advantages for some processes such as reactive sputtering.

Another process option is Reactive Sputtering, which utilizes a non inert gas, such as oxygen, in combination with an elemental target material, such as silicon. This gas creates a chemical reaction with the sputtered atoms inside the chamber forming a new compound (silicon oxide in this example) which becomes the coating instead of the original pure target material.

Thin Film Deposition Sputter systems can also be configured with various hardware or software options. These can include sputter etch or ion source capability for in situ cleaning of substrate surfaces, or substrate pre heat stations. Other options can include multiple cathodes, confocal arrangements of cathodes, load lock stations and/or substrate handlers, as well as substrate bias capability.

Accessories such as residual gas analyzers (RGA's), and other custom features and custom automation are also available. Magnetron cathodes are the most popular type, and are available in various sizes and shapes. Cryogenic pumps are the most popular type of high vacuum pump, but other options are available if desired.

In its various forms, Thin Film Deposition Sputtering offers the advantages of film adhesion strength and good step or via coverage. With appropriate mechanical configuration, it is also possible to perform simultaneous double sided coating, and load lock chamber entry and exit are commonly available.