Sputter Coater
Sputter coaters are devices which deposit a substance (target) onto a substrate by means of ion etching.
Types
There are many variantions on the design of Sputtering devices. Many with advantages and disadvantages.
Diode
The Diode sputtering setup is the most simple of all the sputtering setups. It consists, in essence a plate capacitor within a vacuum chamber. The Cathode plate is made of the material that is to be deposited and the Anode is the object to be coated. These are then placed into a vacuum chamber filled, usually, with an Inert Gas Atmosphere. Typically Argon is used, though other gases, including air, can be used with various effects. See the section on working gasses for more details.
Diode type sputtering setups have various downsides, among these are ones inherrit to all DC type sputtering setups, in that only conductive targets may be used. Another major downside is that the Substrate (object to be coated) is strongly heated by Electron bombardment from the Cathode. This can cause structural changes in the object which can be unacceptable in electron microscopy. Another downside to the Diode sputtering setup is that the sputtering rate is rather low compared to other setups.
This effect of Diode sputtering is observed in any plasma device opperated at DC. Thus if sputtering is to be minimized, a metal with very low sputtering yield is to be used. Examples include, among others, Tantalum and Tungsten.
Cold Diode / Magnetron
This advancement of the Diode setup is what is now commonly used in electron microscope preperation, as it elimminated, or at least minimizses the effect of electron bombardment heating of the substrate.
The Cold Diode consists, again much like the pure Diode of a plate capacitor. However, unlike the pure Diode the Cathode is fitted with a magnet structure creating a field which traps electrons and ion in the vecinity of the cathode plate. This has several effects, these include the reduction of electron bombardment heating of the substrate, though this can still occoure depending on the magnetic field and geometry of the setup. The second effect is that, due to concentrating the electron and ion flux on the cathode, the rate at which it is etched away is increased. Thus shorter sputtering times can be achieved. The cathode and magnet structure is typically surrounded by a shielding can with an opening exposing the target, but shielding the rest of the structure. Thus preventing the supttering of superstructure materials together with the target.
Due to trapping the electrons and ions around the cathode, this is much more strongly heated then in the pure diode. This usually nesessitates the use of water cooling to keep the cathode cold enough not to demagnetize the magnetic structure due to heating it past the Curie temperature as well as preventing damage to the target.
Triode
The Triode sputtering setup