What Is a Sputtering Machine?

Ray Hawk

A sputtering machine is usually a small, sealed chamber where energetic particles such as electrons bombard a source material that ejects atoms off of the surface. These atoms then bounce off of the chamber walls, coating a sample object inside the chamber. Scanning electron microscopes (SEMs), which rely on the electrical conductivity of samples to view features at a nanometer scale, often rely on this machine to coat biological samples with a thin layer of platinum first for viewing. Other uses for sputtering machine technology includes coating thin films in the deposition process for the semiconductor industry and to etch a surface layer away from a material to determine its chemical composition.

Gold cutlery can undergo a sputter deposition.
Gold cutlery can undergo a sputter deposition.

Though the machines for which a sputtering machine prepares a sample can be very complex and expensive, sputtering equipment doesn't have to be. These machines can be relatively simple devices operating on established physical principles, and often lack moving parts or the need for complex maintenance. They range in size from small table top devices to large floor models.

Expensive jewelry may undergo a sputter deposition.
Expensive jewelry may undergo a sputter deposition.

Physical vapor deposition is one routine method used in sputtering machine design. The deposition material is converted into a vapor in a sputter chamber under low pressure, usually a partial vacuum. The vapor condenses onto the substrate material in the chamber to form a thin film. This film can be only several layers of atoms or molecules thick, and will thicken in direct proportion to how long the sputtering process is continued. Other factors in thin-film thickness include the mass of each material involved and the energy level of the coating particles, which can charged from tens of electron volts on up to the thousands.

Charged atoms known as ions are also used by a sputtering machine in a process known as potential sputtering. The sputter material is given an ionic charge which it then loses when it impacts with the target surface. Related to this process is reactive ion etching (RIE), which utilizes naturally ionic materials in secondary ion mass spectrometery (SIMS) research, to analyze the presence of trace elements in materials. Static SIMS processing will sputter to such a fine rate that only a tenth of an atomic monolayer will be removed from the target surface. It is, therefore, another useful tool in nanotechnology research as is the sputtering machine for the SEM.

Other uses include coating flat glass, acrylics, and other plastics, as well as ceramics and crystals other than silicon. They can also be used as a very fine method of cleaning and polishing delicate components. Expensive jewelry and tableware such as gold cutlery can also undergo a sputter deposition, as can specialized gold and aluminum films.

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